Renal nicnas-2012 copy

An Introduction to the Toxicology of
the Kidney.
Rhian B. Cope BVSc BSc(Hon 1) PhD DABT ERT

1

Content Outline of the Two Lectures.

1. Section 1: A Revision of the Basic Anatomy,
Physiology and Pathophysiology of the Kidney,
Reasons for the Susceptibility of the Kidney to Toxic
Injury and Reactions of the Kidney to Toxic Injury.

2. Section 2: Clinical Signs of Kidney Disease,
Assessment of Renal Function and the
Pathophysiology and Effects of Classical “Must
Know” Renal Toxins/Toxicants.

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Lecture 1.
A Revision of the Basic Anatomy, Physiology and
Pathophysiology of the Kidney, Reasons for the
Susceptibility of the Kidney to Toxic Injury and
Reactions of the Kidney to Toxic Injury.

3

Learning Tasks.
• Learning task 1: Understand the key physiological
functions of the kidneys and the potential consequences
of malfunction.

• Learning task 2: Understand the basic anatomy and
physiology of the nephron and how this relates to toxic
damage.

• Learning task 3: Understand the factors that make the
kidneys prone to toxic damage.

• Learning task 4: Understand the kidney’s responses to
toxic injury and its compensatory mechanisms.

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Learning Task 1: Understand the key physiological
functions of the kidneys and the potential
consequences of malfunction.
.

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Key Physiological Functions of the Kidney
• Filtration and active secretion of body wastes, particularly ammonia,
urea, and other nitrogenous compounds.
• Water conservation.
• Active re-absorption of essential and useful materials filtered by the
kidney, notably glucose, amino acids and small proteins.
• Regulation of body ion levels, notably: sodium, chloride, potassium,
calcium, phosphorus, magnesium.
• Regulation of total body water and blood volumes and long-term
blood pressure.
• Regulation of TBW and blood osmalality.
• Regulation of acid/base status.
• Conversion of 25-hydroxy Vitamin D to 1, 25-dihydroxy Vitamin D
(most biologically active form) by renal 1-∞-hydroxylase.
• Production of erythropoeitin (stimulated by hypoxia)
• Regulation of the availability of mevalonic acid, a necessary
precursor for hepatic cholesterol synthesis
• Removal of insulin from the circulation. 6

Potential Consequences of Abnormal Kidney Function.

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Key Physiological Features of the Kidney
• ~ 10% of body oxygen consumption occurs in the
kidneys. Prone to hypoxia, particularly the PCT and
the thick ascending limb of the Loop of Henle.
– Re-absorption of NaCl accounts for most of the
energy expenditure by the kidneys

• All renal artery branches are end branches without
significant collateral supply

• The kidneys receive ~ 25% of the cardiac output; blood
flow per gram of tissue is higher in the kidneys than in
any other tissue

• 85% of renal blood flow occurs in the cortex; ~ 14% of
blood flow occurs in the outer medulla and ~ 1% of
blood flow occurs in the renal papilla 8

Learning Task 2: Understand the basic anatomy
and physiology of the nephron and how this relates
to toxic damage.

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The Nephron: The Fundamental Sub-Unit of the Kidney.

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Basic Functional Anatomy of the Kidney.
• The glomerulus: the basic filtering unit
– Filtration membrane is formed by the 3 layers:
• Fenestrated capillary endothelium.
• Glomerular basement membrane constructed of
Type IV collagen and polyanionic proteoglycans
(particularly heparan sulfate). What do you think is
the functional consequence of these polyanionic
sites?
• Visceral epithelial cells of Bowman’s capsule
(podocytes) whose pedicels form the filtration slits
(remember, the parietal layer of Bowman’s capsule
and its basement membrane are continuous with
the proximal convoluted tubule).

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Three cell types make up the glomerulus: endothelial (red), mesangial (blue)
and the visceral epithelial cellular podocyte (yellow). Squamous epithelial cells
of the Bowman capsule are easily seen (green). The macula densa (black) is
part of the distal tubule. A collecting duct is in the upper left. Bar = 50 Microns 15

Basic Functional Anatomy of the Kidney: The Glomerulus.
• The formation of the glomerular ultrafiltrate is the net
result of the balance between the glomerular blood
hydrostatic pressure (GHP), the hydrostatic pressure in
Bowman’s space (HBS), the blood colloid oncotic
pressure (BCOP), and the effective hydraulic
permeability of the filtration membrane (the
ultrafiltration coefficient or Kf)

• The effective net filtration pressure (Pnet) = GHP -
(HBS + BCOP); Pnet is typically 10 mm of Hg

• Single nephron glomerular filtration rate (SNGFR) =
PNET x Kf
– Kf is determined by the total surface area available
for filtration and the hydraulic permeability of the
capillary wall
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An Overview of the Regulation of GFR

17


• Autoregulation of glomerular
filtration: glomerular
hydrostatic pressure, and
thus Pnet and GFR are
regulated by the cells of the
macula densa, the NaCl
concentration at the macula
densa of the distal
convoluted tubule of the
nephron, the
renin/angiotensin system and
the vascular smooth muscle
of the afferent and efferent
arterioles:
• Renin release is a critical
part of the renin-angiotensin-
aldosterone system
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The renin-angiotensin system (RAS) or the renin-angiotensin-
aldosterone system (RAAS) is a hormone system that helps
regulate long-term blood pressure and blood volume in the body.
The system can be activated when there is a loss of blood volume
or a drop in blood pressure (such as in a hemorrhage). If the
perfusion of the juxtaglomerular apparatus in the kidneys
decreases, then the juxtaglomerular cells release the enzyme
renin. Renin cleaves an inactive peptide called angiotensinogen,
converting it into angiotensin I. Angiotensin I is then converted to
angiotensin II by angiotensin-converting enzyme (ACE), which is
found mainly in lung capillaries.

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Renin release from Goormaghtigh’s
cells is triggered by ↓ renal perfusion
due to: (1) ↓ pressure in the afferent
arteriole; and/or (2) activation of β1-
adrenergic receptors in the
juxtaglomerular apparatus. Note the
close anatomical relationship
between the macula densa, the
efferent and afferent arterioles, the
glomerulus and the Goormaghtigh’s
cells. This close anatomical
relationship is critical for normal
glomerular autoregulation.

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• Under normal circumstances, the filtration membrane
provides a significant barrier to macromolecules greater
than ~ 100 Å in size.

• Filtration of cationic molecules tends to be more
restricted compared with neutral molecules ions of the
same size due to the presence of anionic binding sites
on the filtration membrane; the filtration of cationic
molecules is facilitated.

• This filtration size approximately equates to the size of
serum albumin and free hemoglobin; unbound free
hemoglobin enters urine more readily than albumin
because of its shape (serum hemoglobin is not
normally filtered because it binds to a haptoglobin, a
large protein).

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• The Mesangium
– The filtration membrane is supported by the mesangium which
consists of Type IV collagen, proteoglycans and other proteins.
Damage to or alteration of the messangial collagen is an
important mechanism in toxicological damage to the
glomerulus.
– Contains mesangial stellate cell
• Contractile and responds to vasoactive hormones (i.e.
angiotensin II)
• Synthesizes and secretes the mesangial matrix
– Contains phagocytic cells
• Function as antigen clearing and presentation cells
• Antigen uptake and clearance from the mesangium is
relatively slow

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Basic Functional Anatomy of the Kidney: Reasons Why
The Glomerulus is Prone to Toxic Injury.
• High exposure to systemically distributed toxicants: glomeruli are
exposed to ~ 70% of plasma that reaches the kidney.

• Anionic sites of glomerular filtration membrane
 Electrostatic interactions with polycations (e.g.
aminoglycosides, particularly gentamicin) --> decrease GFR

• Damage to endothelial and epithelial cells by puromycin,
adriamycin, mitomycin, cyclosporine (messangiolysis).

• Prone to protein deposition and damage to the filtration
membrane.

• Prone to immune complex deposition.
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Basic Functional Anatomy of the Kidney:
Some Useful Formulae Pertaining to Glomerular Filtration.

• Some important concepts and formulae relating to glomerular
filtration:
– Clearance: volume of plasma completely cleared of a
xenobiotic per unit time. C = clearance; U = urine
concentration; V = urine flow; P = plasma concentration; U*V =
urinary excretion

– Clearance is a key measurement of renal function. It is an
indirect measure of GFR.
– It is most commonly measured clinically using urine and
plasma creatinine levels.
– More accurate measurements are made using inulin, an
oligosaccharaide which is 100% removed from the body by
glomerular filtration and is not re-absorbed by the nephron.
For all practical purposes, inulin clearance = GFR
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• Effective renal plasma flow
– Effective renal plasma flow can be measured by para-
aminohippurate (PAH) clearance (“effective” is applied because it
measures the fraction of the total renal plasma flow that perfuses functional
portions of the nephron where it can be filtered and secreted).
– PAH is not reabsorbed, metabolized or synthesized by the
kidney. PAH undergoes both glomerular filtration and tubular
secretion by a rate limited active transport mechanism. If the
afferent arteriolar PAH concentration (Ax) is low enough that
the peritubular load of PAH is below the PAH transport
maximum, then PAH will be completely cleared from the
plasma in a single pass through the kidney.

Ux * f Ux * f
ERPF = =
Ax − Vx Ax * ER
– Ux = urine concentration; f = urine flow rate; Vx = renal vein
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concentration; ER = extraction ratio=1 – Vx/Ax;

• Effective renal plasma flow:
– Vx is impossible to measure, so it is either assumed to be 0
(which results in a slight underestimation of the RPF) or an ER
can be applied (ER is typically 0.9 – 0.95). The ER is
necessary since some PAH (5-10%) is distributed in blood to
the non-filtration functioning areas of the kidney and appears
in the renal vein.

• Effective renal blood flow is an important measurement of renal
perfusion:
ERPF
ERBF =
1 − Hematocrit
• ERBF is the volume of blood delivered to the kidney per unit time.
In humans, the kidneys together receive roughly 20% of cardiac
output, amounting to 1 L/min in a normal 70-kg adult male. 27

• Filtration fraction:
GFR
FF =
ERPF
• The filtration fraction (FF) is defined as the ratio of the GFR to the
RPF and is calculated as the ratio of inulin clearance to PAH
clearance.
• Under normal conditions approximately 180 l /day of plasma flows
through the kidneys and the average adult produces a urine
volume of 1 to 2 L over the same period. This means that greater
than 99% of the filtrate must be reabsorbed by the tubules.
• The FF is a measure of tubular re-absorptive efficiency,
particularly in the proximal convoluted tubule where the bulk of
the re-absorption occurs.

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The Proximal Convoluted Tubule.

• PCT is THE most common site of toxic damage in the
kidney.

• Absorbs ~ 60 – 80% of solute and water present in the
glomerular filtrate due to numerous transport systems
that operate against the osmotic and concentration
gradient present in the proximal tubule (i.e. the net
effect is concentration of the fluid in the proximal
tubule).

• Cells of the proximal tubule have the highest rate of
oxidative metabolism in the kidney and are thus the
most prone to hypoxic injury, particularly the pars recta.
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Metabolic Features of The Proximal Convoluted Tubule.

• Main site of re-absorption of glucose, amino acids,
lactic acid, uric acid, creatine, citric acid, ascorbic acid,
phosphate, sulfate, calcium, potassium, and sodium
ions by active transport

• Re-absorption of chloride ions and other negatively
charged ions occurs passively due to electrochemical
attraction because of the active uptake of Na+; Na+
uptake is mediated by the Na+/K+ ATPase located on
the basolateral cell membranes of the proximal tubular
epithelium
•
Active secretion of substances such as penicillin,
histamine, creatine, and hydrogen ions occurs in the
proximal tubule
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• Proximal tubule reabsorbs almost 100% of the low
molecular weight proteins and amino acids present in
the glomerular filtrate via specific endocytic protein re-
absorption processes.
– Most of this re-absorption occurs in the first 1 mm of the
proximal tubule (S1).
– Protein uptake is a low affinity, high capacity process.
– Factors affecting the efficiency of protein uptake include size
and charge: cationic proteins are more efficiently reabsorbed
than anionic proteins of the same size.

• Proximal convoluted tubule is the main site of weak
organic acid uptake; weak organic acids are actually
anionic at normal urine pH and are taken up by the
apical OAT-K transporters.
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• Proximal convoluted tubule is the main site of re-
absorption of bicarbonate and thus plays an important
role in body acid-base regulation.

• Biotransformation of xenobiotics
– Inducible CYP mixed function oxidases are present at high
levels in the S2 or S3 segment of the proximal tubule (i.e.
proximal convoluted tubule or pars recta depending upon
species): the proximal tubule is a major site of damage for
xenobiotics that undergo toxication by phase I metabolism (i.e.
formation of reactive electrophiles)
– Cyclooxygenase is present in relatively high amounts in the
renal vascular endothelium and medullary interstitium and co-
oxygenation rather than metabolism by CYP is an important
mechanism of pathological Phase I metabolism in the kidney

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Schematic model of organic anion transporters in renal proximal tubule. Uptake of organic anions (OA) across
the basolateral membrane is mediated by the classic sodium-dependent organic anion transport system, which
includes -ketoglutarate (-KG2)/OA exchange via the organic anion transporter (OAT1) and sodium-ketoglutarate
cotransport via the Na+/dicarboxylate cotransporter (SDCT2). A second sodium-independent uptake system for
bulky OA has recently been identified, but its molecular identity is unknown. Intracellular accumulation occurs for
substrates of both transport systems in mitochondria and vesicles of unknown origin. The apical (brush-border)
membrane contains various transport systems for efflux of OA into the lumen or re-absorption from lumen into the
cell. The multidrug resistance transporter, MRP2, mediates primary active luminal secretion. The organic anion
transporting polypetide, OATP1, and the kidney-specific OAT-K1 and OAT-K2 might mediate facilitated OA efflux
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but could also be involved in re-absorption via an exchange mechanism. PEPT1 and PEPT2 mediate luminal
uptake of peptide drugs, whereas CNT1 and CNT2 are involved in re-absorption of nucleosides.


• Functionally, the PCT is divided into 3 segments: S1,
S2 an S3.

– S1 (or P1) = short segment connecting to the
glomerular space;
– S2 (or P2) = represents the bulk of the proximal
convoluted tubule
– S3 (or P3) = represents the bulk of the pars recta

• Each segment of the PCT is physiologically and
functionally different: this is important toxicologically.

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Basic Functional Anatomy of the Kidney: Toxicological Characteristics of the Segments of the PCT.
PCT Segment Toxicological Features

S1 1. Site of bulk of water, amino acid and protein re-absorption in the PCT.
2. Capable of re-absorption by endocytosis (filtered proteins).
3. High levels of OAT3: important in excretion of uremic toxins.
4. MRP2 is present. Important in the protection of the PCT.
5. OCT1 is present. Prone to damage due to concentration of OCT1 substrates in the cell.
6. MDR1/P-glycoprotein (ATP-binding cassette sub-family B member 1) is present. Prone to
damage due to concentration of substrates in the lumen.
7. High levels of PEPT1. Prone to damage due to re-absorption and concentration of substrates
within the cell.

S2 1. High levels of CYP (particularly CYP2E1): prone to damage by Phase I toxication.
2. High level of OAT1: prone to damage by concentration of OAT1 substrates in the cell and lumen
(e.g. ochratoxin A, β-lactamine antibiotics). Site of active excretion of PAH. OAT1 is important in the
excretion of uremic toxins.
3. Active re-absorption of α-2U globulin: site of α-2U globulin/hyaline droplet nephropathy in ♂ rats.
4. MRP2 is present. Important in the protection of the PCT.
5. OCT1 is present. Prone to damage due to concentration of OCT1 substrates in the cell.

S3 1. Contains high levels of brush border gamma-glutamyl transpeptidase -> converts GSH
conjugates to cysteine-glycine conjugates which can then be re-absorbed by the neutral amino acid
transporter: prone to damage due to re-absorption and toxication of GSH conjugates.
2. High levels of intracellular β-lyase which converts cysteine conjugates to reactive thiols.
2. Highest rate of oxidative metabolism in the kidney; particularly prone to hypoxia and vascular
disturbances.
3. High levels of CYP (particularly CYP2E1): prone to damage by Phase I toxication.
4. High levels of OATP on the brush border. Prone to damage due to concentration of OATP
substrates in the lumen.
5. MRP2 is present. Important in protection of the PCT.
7. High levels of PEPT2. Prone to damage due to re-absorption and concentration of substrates
within the cell.
8. High levels of OAT-K1 and OAT-K2. Active re-absorption of anions from the lumen. Prone to 35
damage due to re-absorption and concentration of substrates within the cell.

The Loop of Henle.

• Divided into 3 parts: thin descending limb, thin
ascending limb and the thick ascending limb

• There is a marked change in tubule diameter between
the pars recta and the thin descending limb; this is
important in both pathology and toxicology: obstruction
due to luminal crystal formation.

• Main function of the loop of Henle is the passive re-
absorption of water which is accomplished by a counter
current multiplier effect.

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The Loop of Henle Counter Current Multiplier.
• Selective permeability is the key feature:
• Water can leave descending limb but not the ascending limb of
the loop of Henle.
• Na+ cannot leave descending limb but can leave the
ascending limb of the loop of Henle.

37

The Loop of Henle Counter Current Multiplier.

• Counter current multiplier of the loop of Henle is
important toxicologically because of the potential for the
concentration of toxicants within the tubular lumen.

• Thick ascending limb of the loop of Henle has high levels
of Na active transport and is heavily dependent on
oxidative metabolism: prone to hypoxic damage.

38

Distal Convoluted Tubule.

• Regulates body pH by absorbing bicarbonate and
secreting protons (H+) into the filtrate.

• Regulates body sodium and potassium levels by
secreting K+ and absorbing Na+ using the Na+/K+ ATPase.

• Sodium absorption by the distal tubule is mediated by the
hormone aldosterone. Aldosterone increases sodium re-
absorption.

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Collecting Ducts.
• Accounts for 4-5% of the kidney's re-absorption of
sodium and 5% of the kidney's re-absorption of water. At
times of extreme dehydration, over 24% of the filtered
water may be reabsorbed in the collecting duct system.

• The collecting ducts, particularly the outer medullary and
cortical collecting ducts, are largely impermeable to
water without the presence of antidiuretic hormone
(ADH, or vasopressin).
• In the absence of ADH, water in the renal filtrate is left alone to
enter the urine, promoting diuresis.
• When ADH is present, aquaporins allow for the re-absorption of
this water, thereby inhibiting diuresis.

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Collecting Ducts.
• Water and sodium re-absorption in the collecting ducts is
also regulated by atrial natriuretic peptide which acts to
decrease water and sodium re-absorption

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Learning Task 3: Understand the factors that make
the kidneys prone to toxic damage.

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Factors Predisposing the Kidney to Toxic Injury.

• High blood flow -> 25% of cardiac output  glomeruli
and PCT have high exposures to toxicants in blood

• Active re-absorption and concentration of toxicants by
the PCT

• Ability of S3 PCT to dissociate, re-absorb and
metabolize glutathione-conjugates to reactive thiols.

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Apical Brush Border Renal Tubular Epithelial Cell
S3 PCT S3 PCT

GSH-X

Brush border GGT

X-S- (reactive thiol)

Cysteine-glycine-X
β-lyase

Aminodipeptidase
NAT* Cysteine-X

“X” = typically halogenated alkenes
such as hexochloro-1,3-butadiene,
trichloroehtylene, tetrafluoroethylene,
*NAT = neutral amino acid transporter bromohydroquinone (metabolite of 47
bromobenzene).


• Change in pH in tubular fluid --> change in ionization
state --> increased re-absorption of non-ionized
(lipophilic) toxicants or ion trapping and concentration
within the lumen (depends on the lipophilicity of the
toxicant, which in turn depends on the ionization state
of the toxicant, which in turn depends on the pKa of
toxicant).
• Remember and be able to use the following
(Henderson-Hasselbach equations):
[unionized ]
• For Acids: pKa − pH = log [ionized ]
[ionized ]
• For bases: pKa − pH = log [unionized ]

• pKa = 14 - pKb 48

• High CYP, particularly in S2 & S3 of PCT and particularly
CYP2E1. Prone to Phase I toxication.

• High rates of oxidative metabolism in PCT and thick ascending
limb of the loop of Henle: prone to hypoxic injury.

• Concentration of toxicants within the PCT, loop of Henle and
collecting ducts.

• Kidney lacks collateral blood supply. The medullar is particularly
prone to ischemia. Vasodilatation in the medulla and renal papilla
is dependent on PgE2 and the presence of functional
cyclooxygenase (inhibited by NSAIDs).

• High levels of prostaglandin hydroperoxidase in the renal papilla
i.e. high levels of co-oxidation.
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Learning Task 4: Understand the kidney’s
responses to toxic injury and its compensatory
mechanisms.

50

Responses of Kidney to Toxic Injury

• Toxic responses include:

– Damage to the glomeruli  glomerulonephritis.

– Acute renal failure, which in toxicology is most
commonly associated with nephrotoxic acute tubular
necrosis (particularly the PCT).

– Damage to the interstitium + the tubules  tubulo-
interstitial nephritis.

– Chronic progressive nephropathy or chronic renal
failure. 51

Responses of Kidney to Toxic Injury:
Glomerulonephritis.

• The glomerular filtration membrane, particularly the basement
membrane, is prone to binding immune complexes (IgM –Ag, IgG-
Ag or polymerized IgA). This activates C’ (particularly C’3) and
triggers an inflammatory response.

• The glomeruli are also the targets in secondary thrombotic
thrombocytopenic purpura (associate with penicillins, platelet
aggregation inhibitors such as ticlopidine and clopidogrel, and
Immunosuppressants cyclosporin, mitomycin, tacrolimus/FK506,
and interferon-α). Disease is due to binding of platelet-fibrin
complexes to the glomerular capillaries. Micro-infarction and
inflammation then ensue.

• The glomeruli are also the targets in hemolytic uremic syndrome
due to the verotoxins produced by E. coli O157:H7.
52

Glomerulonephritis.

• Glomerulonephritis is divided into acute and chronic-progressive.
Chronic-progressive GN represents the end-stage of all forms of
progressive glomerulonephritis.

• The hallmark of chronic-progressive GN is the presence of
permanently destroyed/non-functional glomeruli. Hyalinosclerosis
i.e. the total replacement of glomeruli and Bowman's space with
hyaline, is present.
– The hyaline is an amorphous, pink, homogeneous material ,
resulting from combination of plasma proteins, increased
mesangial matrix and collagen. Obstruction of blood flow
results in secondary tubular atrophy, interstitial fibrosis and
thickening of the arterial wall by hyaline deposits. A
lymphocytic inflammation is typically present in the interstitium.

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End-stage of glomerular hyalinosclerosis. Glomeruli are totally replaced by hyaline
connective tissue. There is atrophy of the tubules, which appear shrunken and are
surrounded by a thickened basement membrane. There is also fibrosis of the interstitium
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with arterio- and arteriolosclerosis.

Responses of Kidney to Toxic Injury: Glomerulonephritis.
• There are 5 types of acute GN based upon the histopathology
– Acute diffuse membranoproliferative GN: classically due to a
Type III hypersensitivity response following Group A
Streptococcus infection or drug treatment. Characterized by
hypercellularity due to proliferation of endothelial and
mesangial cells, inflammatory infiltrate with neutrophils and
with monocytes. Triggered by C’ activation, the formation of
C’3-Ag complexes and the formation of C’3-Ag-Ab complexes
that deposit in the glomeruli. This is a commonly observed
xenobiotic-induced glomerulonephritis (Type III hypersensitivity
reaction).

– Rapidly progressive GN (Crescentic GN): due to increased
permeability of the filtration membrane and leakage of fibrin
into Bowman’s space. Renal failure rapidly develops. A mild
form of this type of glomerulonephritis is commonly associated
with treatment with aminoglycoside antibiotics, particularly
gentamicin, which damage the anionic sites on the filtration
membrane.
55

Glomerulonephritis.

• There are 5 types of acute GN based upon the histopathology

– Microangiopathic GN: observed in TTP and HUS.
Characteristic is the presence of fibrin-thrombi in the
glomerular capillaries. Often progresses to
membranoproliferative GN. TTP can be drug-induced!

– Mesangial proliferative GN: due to deposition of polymerized
IgA1 in the mesangium, with a localized proliferation of tissue.

– Minimal change GN: due to a mutation in the nephrin which
leads to podocyte fusion. This is a genetic rather than a
toxicological reaction.

56

Acute GN. Note the neutrophils. 57

Glomerulus from patient with TTP. Note the fibrin-thrombi in the glomerular capillaries.
60

Drug-induced TTP. Note the purpura i.e. extensive subcutaneous hemorrhages. 61
The
prognosis with advanced TTP is very poor.

Glomerulonephritis.

• Hallmarks of glomerulonephritis

– Hematuria i.e. increased RBCs in urine
– Proteinuria
– Decreased GFR and signs of renal failure (see later)
– ± signs of a systemic immune reaction e.g.
arthralgia, malaise, fever
– Hypoproteinemia
– Peripheral edema due to hypoproteinemia
– Fatigue
– Oliguria or polyuria
– Progression to renal failure and end-stage kidney
62

Acute Renal Failure.
• Acute renal failure (ARF) is defined as an abrupt or rapid decline
in renal function. A rise in serum blood urea nitrogen (BUN) or
serum creatinine concentrations, with or without a decrement in
urine output, is usually evidence of ARF. The condition is often
transient and completely reversible.

• ARF may occur following 3 types of event: (1) as an adaptive
response to severe volume depletion and hypotension, with
structurally and functionally intact nephrons; (2) in response to
cytotoxic, ischemic or hypoxic insults to the kidney, with structural
and functional damage; and (3) with obstruction to the passage of
urine. Therefore, ARF may be classified as pre-renal, intrinsic, and
post-renal.

• In toxicology, we mostly deal with intrinsic ARF which is
usually due to tubular (commonly the PCT) or glomerular
damage.

63

• The intrinsic form of the syndrome may be accompanied by a well-
defined sequence of events. The first is an initiation phase,
characterized by daily increases in serum creatinine and BUN,
and reduced urinary volume; the second is a maintenance phase,
during which the glomerular filtration rate (GFR) is relatively stable
and urine volume may be increased (inability to concentrate urine);
and the third is a recovery phase, in which serum creatinine/BUN
levels fall and tubular function is restored. This sequence of events
is not always apparent, and oliguria may not be present.

• A physiologic hallmark of intrinsic ARF is a failure to maximally
concentrate urine i.e. failure to excrete concentrated urine, even in
the presence of oliguria This defect is not responsive to
vasopressin. The injured kidney fails to generate and maintain a
high medullary solute gradient because the accumulation of solute
in the medulla depends on normal distal nephron function. In
intrinsic ARG, urine osmolality is usually less than 300 mOsm/kg
64
irrespective of the volume of urine produced.

• Classifying ARF as oliguric or nonoliguric based on daily urine
excretion may be useful. Oliguria is defined as a daily urine
volume of less than 500 ml/d. Anuria is defined as a urine output
of less than 50 ml/d and, if abrupt in onset, is suggestive of
obstruction.

• Because of the large functional reserve, a substantial amount
of damage must occur before blatant (i.e. presence of uremia)
ARF occurs. Blatant clinically recognizable renal failure, as
evidenced by uremia, will occur when the GFR has decreased
by ~ 50 – 84%.

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• Intrarenal vasoconstriction is the dominant mechanism for the
reduced GFR in patients with ARF.

• The stressed renal microvasculature is more sensitive to
potentially vasoconstrictive drugs and otherwise-tolerated changes
in systemic blood pressure making the decline in GFR seen in the
early stages of ARF worse.

• Prolonged vasoconstriction may evolve into intrinsic ARF,
especially when concomitant large vessel arterial disease occurs.
Renal failure caused by prolonged vasoconstriction (especially
with concomitant large vessel arterial disease) often is induced by
the use of angiotensin-converting enzyme (ACE) inhibitors and/or
diuretics.

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• Causes of intrarenal ARF can be grouped into vascular, tubular,
interstitial, and glomerular factors.

– Vascular factors- Renal Ischemic Tubulonecrosis: any agent
that damages the renal blood supply (vasculitis, embolism) will
produce RITN. Classical example is toxic thrombotic
thrombocytopenic purpura or hemolytic uremic syndrome
(toxins of E. coli O157:H7) which damages the renal
vasculature.

– Nephrotoxic Acute Tubular Necrosis: a multitude of agent are
capable of damaging the renal tubular epithelial cells,
particularly the PCT. NATN is undoubtedly THE MOST
COMMON FORM OF TOXIC KIDNEY INJURY! Tubules
become obstructed due to cell debris.

67

Classical Acute Nephrotoxic Tubular Necrosis involving the PCT.
68

• Causes of intrarenal ARF can be grouped into vascular, tubular,
interstitial, and glomerular factors.

– Crystaline Acute Tubular Necrosis. Hallmark is the presence
of crystals within the tubules ± tubular epithelial necrosis.
Classical examples are ethylene glycol and oxalate poisoning.

– Interstitial nephritis usually results from a reaction to a specific
drug or a group of drugs. Classically has an allergic
mechanism. Typical drugs causing this reaction include:
NSAIDs, penicillins, diuretics, cimetidine, and allopurinol.

69

• Irrespective of cause, intrarenal ARF results in the
death of the renal tubular epithelial cells, most
commonly those of the PCT. The hallmarks of this are:

– Enzymeuria  brush border enzymes like ALP and γ-GT or
intracellular enzymes like lactate dehydrogenase, α-GST and
N-acetylglucosaminidase are present in the urine.

– Failure of re-absorption of glomerular filtrate  amino aciduria,
glucoseuria, low molecular weight proteins (cystatin C, α1-
microglobulin, β2-microglobulin, retinol binding protein)

– Presence of sloughed tubular epithelial cells and debris in the
urine  tubular epithelial cell casts, cell remnants.

– Proteinuria  Increase in high molecular weight proteins.
70

• Recovery in ARF
– If the nephron basement membrane and
primordial stem cells remain intact, the nephron
has the potential to recover. If the basement
membrane is destroyed, the nephron probably
will not recover.

– If the individual can be supported through the
uremic phase of ARF and survives long enough,
recovery from ARF is likely. The problem is that
if nephrons are lost, then progression from ARF
to chronic progressive nephropathy is inevitable.

71

Tubulo-Interstitial Nephritis.
• Divided into acute and chronic.

• Toxic acute TIN is usually due to drug-induced hypersensitivity
responses. Classically: NSAIDs, rifampicin, penicillins, sulfa
antibiotics. Classically a Type I hypersensitivity reaction is
involved. Typically reversible. Damage may or may not be
sufficient to produce acute renal failure.

• Toxic chronic TIN is a potential outcome of any xenobiotic that
damages the renal tubules. This either produces neo-antigens or
allows exposure to previously protected antigens. Characterized
by chronic inflammation of the interstitium mediated by
hypersensitivity mechanisms, tubular degeneration and
progression to chronic progressive nephropathy. Classic causes
are NSAIDs, thiazide diuretics, furosemide, allopurinol, phenytoin,
rifampicin, interferon-α.

72

• Clinical signs
– Except in patients with TIN induced by rifampicin and NSAIDs:
• Evidence of a systemic immune reaction i.e. fever, rash,
arthralgia.
• Elevated serum and urine IgE levels.
• ± renal failure.
• ± hematuria.
• Evidence of tubular dysfunction i.e. glycosuria, aminoacid
uria, presence of small proteins in urine.
• Elevated eosinophils in urine.
• Gross proteinuria (large proteins) is rare

73

Acute drug-induced TIN. Note the prominent eosinophils present in the interstitial
inflammatory response and the damage to the tubular epithelium.
74

• Clinical signs

– In patients with TIN induced by rifampicin and NSAIDs
• Minimal tubular changes + interstitial inflammation
• Gross proteinuria with reduced serum albumen and
peripheral edema.

75

Acute NSAID tubulo-interstitial nephritis. Note the prominent mononuclear
inflammatory reaction with no changes to the glomerulus and minimal changes to the
renal tubular epithelium. This type of response is also characteristic of rifampicin TIN.
76

Chronic TIN. The interstitium is expanded by fibrosis with distortion of tubules
and periglomerular fibrosis. Glomeruli do not show pathologic changes 77

Chronic Progressive Nephropathy/Chronic Renal Failure.
• Any injury to the kidney has the potential to trigger
chronic progressive nephropathy if it results in the
destruction or reduced function of nephrons. This
includes: glomerular injury, vascular injury or damage
to the tubules.

• IT IS THE COMMON, END-STAGE PROCESS AND
PATHOLOGY FOR ANY PROCESS THAT RESULTS
IN A DECREASD GFR AND LOSS OF FUNCTIONAL
NEPHRONS.

• The kidneys have a substantial capacity to compensate
for the loss of nephrons; however compensatory
responses trigger a slow and progressive loss of renal
function, i.e. CPN, which is defined as a progressive
decrease in GFR.
78

• Classification of CPN:

– Stage 1: Kidney damage with normal or increased GFR (>90
mL/min/1.73 m2); clinically normal.

– Stage 2: Mild reduction in GFR (60-89 mL/min/1.73 m2);
asymptomatic.

– Stage 3: Moderate reduction in GFR (30-59 mL/min/1.73 m2);
asymptomatic.

– Stage 4: Severe reduction in GFR (15-29 mL/min/1.73 m2);
uremia present.

– Stage 5: Kidney failure (GFR <15 mL/min/1.73 m2 or dialysis);
79
end stage renal failure.

• Any injury to the kidney has the potential to trigger chronic
progressive nephropathy if it results in the destruction or reduced
function of nephrons.

• The kidneys have a substantial capacity to compensate for the
loss of nephrons by attempting to increase the single nephron
GFR; however, irrespective of the cause of the original loss of
nephrons, the compensatory responses trigger a slow and
progressive loss of renal function, i.e. CPN, which is defined as a
progressive decrease in GFR.

80

Loss of functional nephrons
Cycle of Nephron Loss in CPN
Decreased GFR

Glomerular autoregulation
system triggered

Glomerular hypertension

↑ GHP

40 – 60% ↑ in SNGFR

Protein overload of the glomerular
filtration barrier , mechanical injury of
capillary structure

Proteinuria, mesangial expansion,
Focal segmental glomerular sclerosis
↑ mesangial matrix and basement
membrane thickening 81

• Common Effects of CPN:
– Hyperkalemia usually develops when GFR falls to less than 20-
25 ml/min because of the decreased ability of the kidneys to
excrete potassium.

– Metabolic acidosis due to: (1)inability to produce enough
ammonia in the proximal tubules to excrete the endogenous
acid into the urine in the form of ammonium; and (2)
accumulation of phosphates, sulfates, and other organic
anions.

– Extracellular volume expansion and total-body volume
overload results from failure of sodium and free water
excretion. This generally becomes clinically manifest when
GFR falls to less than 10-15 mL/min, when compensatory
mechanisms have become exhausted. Patients present with
82
peripheral and, not uncommonly, pulmonary edema and

– Normochromic normocytic anemia principally develops from
decreased renal synthesis of erythropoietin.

– Secondary hyperparathyroidism develops because of
hypocalcemia, decreased renal synthesis of 1,25-
dihydroxycholecalciferol (1,25-dihydroxyvitamin D, or calcitriol),
and hyperphosphatemia.

– Uremic encephalopathy is a marker of the late stages (often
terminal) of CPN. The exact cause of UE is unknown.
Accumulating metabolites of proteins and amino acids affect
the entire neuraxis. Changes in sensorium include loss of
memory, impaired concentration, depression, delusions,
lethargy, irritability, fatigue, insomnia, psychosis, stupor,
catatonia, and coma. Patients may complain of slurred speech,
83
pruritus, muscle twitches, or restless legs.

– GI symptoms – anorexia, nausea, vomiting, diarrhea
– Skin manifestations - dry skin, pruritus, ecchymosis
– Fatigue, increased somnolence, failure to thrive

• Less Common Effects of CPN
– Pericarditis - Can complicate with cardiac tamponade, possibly
resulting in death
– Peripheral neuropathy
– Restless leg syndrome
– Malnutrition
– Erectile dysfunction, decreased libido, amenorrhea
– Platelet dysfunction with tendency to bleeding

84

Lecture 2.
Clinical Signs of Kidney Disease,
Assessment of Renal Function and the
Pathophysiology and Effects of Classical
“Must Know” Renal Toxins/Toxicants.

Learning Tasks.
• Learning task 5: Understand the clinical signs of renal
disease.

• Learning task 6: Understand the techniques used to
assess renal function and disease.

• Learning task 7: Understand the pathophysiology and
effects of the classical “must know” renal toxins/toxicants.

Learning Task 5: Understand the clinical signs of
renal disease.

Clinical Signs of Renal Disease.
• Signs of renal failure:

– Elevated serum creatinine and blood urea
nitrogen (BUN)  azotemia (no clinical signs) 
uremia (clinical signs present).

– Decreased urine production (oliguria)

– Inability to concentrate (i.e. form high specific
gravity urine) urine despite reduced urine volume
(hyposthenuria). Urine specific gravity between
1.007 and 1.010 (plasma SG is 1.020)

• Assessment of severity of acute renal failure:

– At Risk: serum creatinine increased 1.5 times OR urine
production of <0.5 ml/kg body weight for 6 hours.
–
– Renal Injury Present: creatinine 2.0 times OR urine
production <0.5 ml/kg for 12 h.

– Renal Failure: creatinine 3.0 times OR creatinine >355
μmol/l (with a rise of >44) or urine output below 0.3 ml/kg
for 24 h.
–
– Loss of Renal Function: persistent ARF or more than four
weeks complete loss of kidney function

• Clinical effects of uremia:

– Uremia is a clinical syndrome associated with fluid,
electrolyte, and hormone imbalances and metabolic
abnormalities, which develop in parallel with deterioration
of renal function.

– Uremia usually develops only after the creatinine
clearance falls to less than 10 mL/min, although some
patients may be symptomatic at higher clearance levels,
especially if renal failure acutely develops.

– The syndrome may be heralded by the clinical onset of
nausea, vomiting, fatigue, anorexia, weight loss, muscle
cramps, pruritus, change in mental status, uremic
encephalopathy

• Clinical effects of uremia:

– Other effects:
• Acidosis (metabolic)
• Hyperkalemia
• Hypocalcemia, hyperphosphatemia, and increased PTH
levels
• Reduced insulin clearance and increased insulin
secretion can lead to increased episodes of
hypoglycemia
• Cardiovascular abnormalities, including uremic
pericarditis, pericardial effusions, calcium and
phosphate deposition–associated worsening of
underlying valvular disorders, and uremic suppression
of myocardial contractility

Learning Task 6: Understand the techniques used
to assess renal function and disease.

Assessment of Renal Function.
• Blood BUN/Creatinine
– Insensitive measures of renal function
– GFR must decrease by 50 – 80% before changes in blood
BUN/creatinine are seen
– Creatinine clearance is often used as a clinical measure of
GFR

• Assessment of GFR
– Inulin clearance

• Assessment of renal blood flow
– PAH clearance

Urinalysis.
• Presence or absence of protein
– Protein can be from: blood (e.g. albumen), failure of re-
absorption of low molecular weight proteins (e.g. beta-2
microglobulin), or from tubular injury. Excessive protein in
the urine is always abnormal
– Presence of small proteins (e.g. beta-2 microglobulin)
suggest PCT damage (failure of re-absorption).

• Presence or absence of blood/hemoglobin
– Test does not distinguish between blood or hemoglobin
– Neither are normally filtered
– Presence suggests severe hemolytic disease (i.e.
presence of free Hb in circulation) or severe damage to the
nephron or bleeding into the urinary tract.
– Presence in urine is always abnormal.

Urinalysis.
• Presence or absence of protein
– Glucose: except following meals, presence of glucose in
urine suggests either high blood glucose (diabetes
mellitus) or PCT injury (failure of re-absorption).

• Specific gravity
– Tests for the ability to concentrate urine

• pH

• Ketone bodies
– Acetoacetate, acetate and beta-hydroxybutyrate
– Indicators of ketogenesis i.e. consumption of fatty acids for
energy

Urinalysis.

• WBC number: increased suggests interstitial nephritis,
glomerulonephritis or infection within the urinary tract

• Eosinophil count: increased suggests allergic interstitial
nephritis

• Neoplastic cells

• Parasites

Urinalysis.

• Casts
– RBC casts: suggests haemorrhage
– WBC casts: suggests inflammation
– Granular casts: remnants of sloughed tubular epithelium
i.e. suggests tubular injury

• Crystals
– Ca oxalate (ethylene glycol)
– Urate
– Stones

Granular cast: remnants of
sloughed tubular epithelial
cells

THE Gold Standard!.

• Renal biopsy is still THE gold standard for assessment of
kidney disease!

Learning Task 7: Understand the pathophysiology
and effects of the classical “must know” renal
toxins/toxicants.

Classical “Must Know Renal Toxicants.”

• ACE inhibitors • Cyclosporin A
• Acetominophen • Doxorubicin
• α-2U globulin/hyaline • Mercury
droplet nephrosis • Gold
• Aminoglycoside • Methoxyfluorane
antibiotics • Sevofluorane
• Amphoteracin B • Ocratoxin/citrinin
• Bromobenzene and • NSAID nephropathy
halogenated alkenes • Lead
• Carbon tetrachloride • Puromycin
• Chloroform
• Cadmium
• Cephalosporins
• Cis-platin

Angiotensin Converting Enzyme Inhibitors.
• Types of toxicity:

– Hemodynamic
resulting in ↓ GFR

– Immune mediated
glomerulonephritis

Acetominophen Renal Toxicity.
• Classical example of S2 PCT damage in humans and mice due to high
CYP2E1 levels.
• Mechanism differs in rats: primarily a S3 toxicant in rats (metabolite is
para-aminophenol) .

CYP2E1 N-acetyl-p-benzoquinone imine
Acetominophen
(nucleophile)

Conjugation
Sulfonation to GSH
Damage to S2 PCT
(high CYP2E1)
Mercapturic acid

Detoxified if Low Dose
Long-term alcohol abuse has been established as potentiating acetaminophen toxicity
via induction of CYP2E1 and depletion of glutathione. Alcoholic patients may develop
severe liver and kidney damage after ingestion of standard therapeutic doses of
acetaminophen.

α-2u Globulin Nephrosis.
• Unique to the ♂ rat. Does not occur in any other laboratory or domestic
animal or humans.

• Only affects the S2 segment of the PCT of the ♂ rat.

• Important artefact in pre-clinical toxicology screening.

• Predisposes to renal carcinogenesis in the ♂ rat.

• Classical causes are:
– Trimethylpenatne (unleaded gasoline)
– d-Limonene (lemon scent, citrus oils)
– JP-4 jet fuel (shale derived)
– JP-5 jet fuel (shale derived)
– Parafins
– Decalin (decahydronaphthalene)
– Methyl isobutyl ketone
– Pentachloroethane

α-2u Globulin Nephrosis.
CYP Epoxidation
Solvent Epoxide metabolite

α-2u globulin synthesized
in the liver

α-2u globulin-epoxide conjugate

Released into circulation
and filtered by the kidney

Reabsorbed by S2 of PCT

Compensatory cell proliferation
Very slowly degraded in lysosome
acts as a tumor promoter

Cell death

PCT dysfunction

S2 hyaline droplet nephrosis in a ♂ rat subchronically exposed to
JP-4 jet fuel vapor.

Aminoglycoside Antibiotic Nephrosis.

• Gentamicin is the most dangerous of the types currently commonly used.

• Two forms of toxicity:
– Cations and thus bind to the anionic sites of the glomerular filtration
membrane resulting in damage. Typically transient damage in normal
humans.
– Damage to PCT epithelium.

Aminoglycoside Filtered by glomerulus Reabsorbed in PCT

Inhibition of
Bind to –ve charges Accumulate
phospholipases A
of phospholipids in lysosomes
and C

Formation of Lysosomal Apoptosis/necrosis
meyloid bodies rupture

Amphoteracin B Nephrosis.

• Target is the loop of Henle
• Form membrane pores in the loop of Henle and disrupt the counter
current concentrating mechanism
• Cause vasoconstriction in the loop of Henle (direct vasoconstrictor)
• Decreases renal blood flow and GFR (direct vasoconstrictor?)

Bromobenzene and Halogenated Alkenes.
• THE classical example of β-lyase-induced renal damage to the S3 of the
PCT.
• Mechanism:
E1 Liver Circulation Kidney
P2
CY

BB-hydroquinone-
Renal filtration
e
las
ro
hyd
e
oxid
Ep

TCE Metabolism and Renal Damage

Apical Brush Border Renal Tubular Epithelial Cell
S3 PCT S3 PCT

GSH-X

Brush border GGT

X-S- (reactive thiol)

Cysteine-glycine-X
β-lyase

Aminodipeptidase
NAT* Cysteine-X

“X” = typically halogenated alkenes
such as hexochloro-1,3-butadiene,
trichloroehtylene, tetrafluoroethylene,
*NAT = neutral amino acid transporter bromohydroquinone (metabolite of
bromobenzene).

Carbon Tetrachloride.

• Target is the PCT, particularly S3 in rats, due to high CYP2E1 levels

CYP2E1

• Trichloromeithyl radical acts to:
– Reacts with hydrogen to form chloroform which is then metabolized to
a radical
– Reacts with itself to form hexachloroethane
– Reacts with proteins -> SUICIDE SUBSTRATE FOR CYP2E1
– Peroxidizes the polyenoic lipids of the endoplasmic reticulum and
triggers the subsequent generation of secondary free radicals derived
from the lipids in the membrane --> destroys the endoplasmic
reticulum resulting in decreased CYP activity and decreased protein
synthesis

Chloroform.
• Target is the PCT, particularly S3 in rats, due to high CYP2E1 levels
• Similar pathophysiology to CCl4

NU = tissue nuleophile

Phosgene

Organohalides That Do Not Produce Renal Damage.

• Most organohalides produce renal damage, particularly
damage to the PCT, either via CYP metabolism to a radical or
by β-lyase mediated radical formation.

• Renal damage is often NOT the primary effect.

• Important exceptions to this rule:

– Methylene chloride
– Vinyl chloride and vinylidine chloride
– Dichloroethanes

Cadmium.

• T arget is S1/S2 of PCT.

• 50% of total body burden is concentrated in kidnye; long T1/2
(~10 years).

• Damage is progressive and irreversible.

• Damage is due to redox cycling of Cd2+; Cd also produces
immune-mediated glomerulonephritis.

• Soluble Cd salts are more toxic.

Cadmium.

• Decreased renal synthesis of 1,25 dihydroxy vitamin D -->
decreased uptake of Ca from gut  “Itai Itai” disease (“Ouch
Ouch disease).

• Induces metallothioneine in liver and kidney

• Markers of damage
– Urine Cd level (usually Cd-MT) --> indicator of total body
burden.
– Low molecular weight proteins e.g. beta-2 microglobulins,
elevated urinary metallothionein, glucose uria, amino acid
uria (due decrease resorption in PCT due to damage)

Bile Hepatocyte Plasma Kidney PCT Epithelium (S1/S2)

Cd2+
Cd-GSH

Redox cycling
Cd-GSH
Cd-Albumen
Cd2+

Cd2+

Cd-MT Cd-MT
Cd-MT

Lysosome

Severe osteoporitic disease and renal failure
associated with chronic cadmium ingestion in a
population living in an area with acid mine
drainage (Toyama Prefecture, Japan)

Cephalosporins.
Blood PCT Epithelium Tubule Lumen

Cell Death

Disruption of
Cephalosporin OAT-2 Mitochondrial
Respiration

Cephalosporin-
protein adducts

Cephalosporin

Cis-Platin.
•Target is the S3 of the PCT, loop of Henle, DCT.
•Major limitation of cisplatin chemotherapy is dose-
limitations because of nephrotoxicity.
•Mitochondrial toxicant.
•Actively transported into tubular epithelium
•Toxicity is limited by:
•Diuresis with furosemide or manitol
•N-acetylcysteine: suggests that detoxification by GSH
is important

Cyclosporin A.
•Targets
•Interstitium
•Glomerulus
•Vasculature
•Mechanisms:
•Direct damage to the renal vascular endothelium 
glomerular thrombotic microangiopathy  ischemia 
enhanced synthesis of extracellular matrix proteins 
interstitial fibrosis
•Altered eicosanoid metabolism  increased
thromboxane synthesis  renal vasoconstriction 
decreased renal perfusion  ↓ GFR

Increased glomerular cellularity following
cyclosporin endothelial damage

Glomerular focal segmental
glomerulosclerosis following
cyclosporine exposure.

Renal tubular epithelial damage following
cyclosporin exposure. Note the vacuoles.

Cyclosporin interstitial fibrosis (trichrome stain)

Doxorubicin (Adriamycin).
•Target: glomerulus (early onset)  target is vascular
endothelium

Doxorubicin (Adriamycin).
•Target: PCT (late onset) and glomerular (early onset)

Filtered by the Diffuses from the
Doxorubicin
glomerulus lumen into the PCT
epithelium

Pumped back into
the tubular lumen Mitochondrial
via p-glycoprotein accumulation

Redox damage, damage
to mitochondrial DNA

Mercury Toxicokinetics.
•HgO vapor: lipophilic nature allows accumulation in CNS (HgO
 catalase  Hg2+)

•Hg+ (mercurous) salts  Poorly absorbed, very slowly
converted to Hg2+ by catalase; major target is skin
(acrodynia).

•Hg2+ (mercuric) salts
•~ 10% absorbed from GI
• Distributes both in plasma and in RBCs; undergoes
conjugation to GSH
• GSH-Hg2+ accumulates in lysosomes of S3 renal PCT
(major target)

•Pheyl (aryl) mercury --> behaves like Hg2+ salts

Mercury Toxicokinetics.

• Methyl and ethyl Hg (alkyl Hg)
•High lipid solubility
•Forms a cystein complex and actively transported across
the BBB by the neutral amino acid transporter
•Accumulate in CNS particularly in visual cortex
(=calcarine cortex, Brodman area 17)
• Very slowly metabolized to Hg2+ (ultimate toxicant in
CNS)

•Excretion
•Salts --> urine
•Organic --> bile (glutathione conjugate)

Acute Kidney Injury by Mercuric Salts.
•Target is S3 of PCT
•Selectively accumulates in S3 via mechanisms that are
poorly understood
•Luminal uptake:
•Seems to involve GSH-Hg2+ complex and conversion to a
cyst-cyst-Hg2+ compound which is re-absorbed by the
PCT NAT
•The site of formation of GSH-Hg2+ is uncertain:
suggestions include within the blood, within the renal
luminal fluid

•Basolateral uptake
•Via the OAT and dicarboxylate transporters

Acute mercuric salt proximal tubular nephrosis. Note the absence of
epithelium in the PCT tubules (eosinophilic remnants of the cells remain
in the tubules)

Acute Kidney Injury by Mercuric Salts.
•Mechanisms of PCT epithelial damage:

•Hg2+ have an affinity for thiol (SH) groups: disruption of
the functions of a wide range of proteins.
•Damage mitochondria
•Damage membrane proteins
•Damage enzymes

•Changed membrane permeability to Ca ions
•Binds to GSH and metallothionien  induces both these
proteins  protective effect?

Chronic Kidney Injury by Mercuric Salts.
•Target is the glomerulus.
•Produces an immune-mediated glomerulonephropathy.
•Characterized by deposition of IgG-C’ complexes within the
glomerulus.
•Induces autoantibodies to laminin, an important component
of the glomerular basement membrane.

Gold Salts.
•Gold salts are/were used as a treatment for rheumatoid
arthritis.
•Damage the PCT epithelium

Methoxyfluorane.
CYP Fluoride
Methoxyfluorane
Oxidative
dehalogenation

Filtered by glomerulus

Renal tubular damage

Sevofluorane.
•Significance of renal toxicity is controversial; observed in rats
but limited evidence in humans.
Compound A
Sevofluorane + sodalime fluoromethyl-2,2-difluoro-1-
[trifluoromethyl) vinyl ether

Liver: conjugation to GSH Inhaled

Circulation Glomerular S3-brush
filtration border γ-
GGT

β-lyase S3 uptake by NAT Cys-Cys-Compound A

Reactive thiol

Ochratoxin/Citrinin: Porcine Mycotoxin Nephropathy,
Balkan Endemic Nephropathy.

•Produces PCT damage in acute exposure and renal
carcinogenesis on chronic exposure.

•Cinrinin and ochratoxin produce essentially the same clinical
syndromes and are produced by the same fungi: Apsergillus
sp. and Penicillium sp. (particularly A. ochraceus, P.
verrucosum, P. citrinum).

•Classification of ochratoxins.
•Classified A, B and C; A is the most toxic.
•Ochratoxin α is the non-toxic product of ochratoxin
hydrolysis by rumen and large intestine bacterial
metabolism.


•Particular problem in high energy grains, nuts, pepper,
coffee, decaying vegetation, ham.

•Ochratoxin A is relatively stable and a significant fraction
survives autoclaving and similar treatments.

•Concentrates in PCT due to re-absorption via the OAT
system.

•Also competes with PAH for transport into the PCT
epithelium.


•Mechanisms of action:

•Damages the mitotic spindle

•Inhibition of phenylalanine metabolism  results are:
suppression of DNA, RNA and protein synthesis;
suppression of renal gluconeogenesis due to inhibition of
phosphoenolpyruvate carboxykinase (the major rate-
limiting enzyme in this pathway)

•Promotion of lipid peroxidation


•Mechanisms of action:

•Competitive inhibitor of mitochondrial carrier proteins 
suppression of mitochondrial respiration  ATP depletion

•Immunosuppression due to inhibition of lymphocyte
proliferation and NK-cell function

•Teratogen in rodents

•Necrosis of tonsils and lymphoid tissues (particularly
germinal centers) in dogs

NSAID Nephropathy.

•2 basic diseases:
•Damage to the loop of Henle and renal papilla due to
NSAID-induced ischemia

•Immune-mediated interstitial nephritis

•Mechanism of loop of Henle/renal papilla injury (acute
overdose)
•Blood flow in the renal medulla (vasa recta and renal
papilla) is dependent on PgE2-mediated vasodilation.
•NSAIDs inhibit COX resulting in decreased PgE2 
vasoconstriction  ischemia
•Because of high oxygen demand, the thick ascending
limb of the loop of Henle is particularly sesitive

NSAID Nephropathy.

•Mechanism of loop of NSAID interstitial nephritis:

•Immune-mediated hypersensitivity reaction to the NSAID.

•Initial target is the inerstitial tissues although immune
complex deposition in the gomeruli may eventually occur.

•Concurrent treatment with caffeine and acetominophen
seem to promote the problem.

Acute NSAID Interstitial Nephritis

Lead Nephropathy.

•High blood levels results in lead excretion in urine.

•Accumulates as a lead-protein complex in the nuclei of PCT
epithelium  lead inclusions.

•Produces degeneration/necrosis of the PCT.

Lead intranuclear inclusion in the PCT epithelium

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