Transcript Structure and Function of the Kidney

Structure and Function of the
Kidney
• The functional unit of the kidney is the nephron
• The major functions of the kidney are to maintain
extracellular fluids, to eliminate wastes resulting
from normal metabolism, and to excrete
xenobiotics and their metabolites
• Mammalian kidneys have 10,000-1,000,000
nephrons per kidney
Renal toxicology
Structure and Function of the
Kidney (cont)
• The glomerulus yields an ultrafiltrate of plasma that
represents 20% of the renal blood flow, ie. 2-3% of cardiac
output
• Endothelial surface is negatively charged and contains
fenestrae
• The glomerular basement membrane is sandwiched
between the epithelial cells and contains anionic
sialoglycoproteins, glycoproteins and collagen IV
• The mesangium provides support
• The outer capsule is Bowman’s capsule
Structure and Function of the
Kidney (cont)
• The tubule resorbs greater than 99% of the glomerular
filtrate
• The proximal tubule has extensive resorption and selective
secretion (convoluted - S1 and S2, straight - S3). S2 is
primary site for low MW protein resorption and S3 is
primary site for P450.
• Thin loop of Henle - resorption of fluids
• Distal tubule - resorption of fluids and acid-base balance
• Collecting duct - resorption of fluids, antidiuretic hormone
and acid-base balance
Medullary
ray
P2
P2
Cortical
labyrinth
P1 / P2
P1
P3
Cortex
Outer
Medulla
P3
DT
Outer
Stripe
Inner
Stripe
TLH
CD
Inner
Medulla
Short et al., Laboratory Investigation,564-577 (1987).
Structure and Function of the
Kidney (cont)
• Produces erythropoietin, which regulates RBC
production
• Hydroxylates 25-OH-cholecalciferol (vitamin D
metabolite), to promote bone resorption and
calcium and phosphorus absorption from the gut
• Releases renin to regulate the peripheral reninangiotensin-aldosterone system (juctaglomerular
apparatus)
Assessment of Kidney Function:
Morphologic Evaluation
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Urinalysis
Gross evaluation of the kidney at necropsy
Histopathology of the kidney
Electron microscopy of the kidney
Assessment of Kidney Function:
Urinalysis
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Proteinuria - indicates glomerular damage
Glycosuria - indicates tubular damage
Urine volume and osmolarity
pH
Enzymes - indicates tubular damage
Microscopic examination - casts, crystals,
bacteria, etc.
Assessment of Kidney Function:
Blood Chemistries
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Blood urea nitrogen (BUN)
Creatinine
Electrolytes - Ca, Mg, K, P
Glomerular filtration rate - determines the
clearance of inulin, creatinine and BUN
• Renal clearance - measures the clearance of
p-aminohippuric acid by filtration and
secretion
Glomerular Disease: Toxicities due
to Alteration of Anionic Charge
• Hexadimethrine - polycationic molecule
reduces anionic charge, which permits
escape of anionic molecules such as
albumin and IgG
• Polynucleoside of puromycin - damages
epithelial foot processes
Glomerular Disease:
Immune Complex Disease
• Anti-GBM mediated glomerulonephritis is
induced by heterologous antibodies
• Antibodies due to exogenous antigens cationized molecules such as lysozyme, IgG
and BSA bind to anionized surfaces;
Concanavalin A binds to sugars in the GBM
Glomerular Disease:
Immune Complex Disease (cont)
Deposition of circulating immune complexes
• Drug or toxin-induced T-cell dependent polyclonal
B-cell activation - mercury in Brown Norway rats
• Unknown mechanism - gold salts, Dpenicillamine, hydralazine
• Antibodies to heterologous proteins - safety
evaluations of recombinant proteins in laboratory
animals
Nephrosis:
Damage to the renal tubule
• Halogenated hydrocarbons - chloroform,
hexachlorobutadiene, trichloroethylene,
dibromochloropropane, & bromobenzene
• Heavy metals - cadmium, mercury & lead
• Antibiotics - cephalosporins &
aminoglycosides
• Mycotoxins - ochratoxin A & citrinin
• Ethylene glycol
• Antineoplastic drugs - cisplatinum
• Alpha2u-globulin nephropathy
Haloalkane Nephrosis
• Chloroform is metabolized by P450 to an
electrophile, phosgene, which is a potent
cytotoxicant.
• Carbon tetrachloride is metabolized to free
radicals and phosgene.
• P450 is localized in the proximal tubule.
• This results in nephrosis with necrosis, enzyme,
glucose and protein excretion in urine, and
increased BUN and creatinine concentrations in
serum.
Haloalkene Nephrotoxicity
• 1,1-Dichloroethylene, trichloroethylene and
tetrachloroethylene are metabolized by
P450 to electrophilic metabolites and or free
radicals.
• These metabolites can be cytotoxic and/or
genotoxic.
• Nephrotoxicity is exacerbated when
glutathione is depleted.
Glutathione-mediated Nephrosis
• Glutathione conjugates of haloalkanes can
form episulfonium ions.
• Primary route for 1,2-dichloroethane, 1,2dibromoethane and 1,2-dibromo-3-chloropropane.
• These can alkylate macromolecules and
cause cytotoxicity and genotoxicity.
Cystine Conjugate -lyase Activation
• Stable cystine conjugates from glutathione
can be formed in the liver from trichloroethylene, tetrafluoroethylene and hexachlorobutadiene and transported to the
kidney.
• They are further metabolized by -lyase in
the kidney to generate reactive thiols.
Biotransformation of Trichloroethylene
H
Cl
Cytochrome
P450
Fe
C C
Cl
Cl
+ GSH
GSH-transferase
H
Cl
C C
H O Cl
C C
Cl
Cl
Cl
H
SG
Cl
-Lyase
H
Cl
C C S
Chlorothioketene
C C
Cl
S CH2
NH3+
CH
COO-
Trichloroethylene-associated
renal cell carcinomas
• Highly exposed workers exhibit nephrosis and an
increased incidence of renal cancer
• TCE and other renal neoplasms have a high incidence of
mutations in the von Hipple-Lindau (VHL) tumor
suppressor gene. This requires mutation of one allele and
deletion of the other
• TCE mutations include a hot spot at nucleotide 454 (CT)
• VHL gene is located at 3p25
• 3p25.5 is a fragile site at the chromosome telomere
• ogg1 mutations are also associated with renal cancer and it
is also located at 3p25
Lead Nephropathy
• Lead induces acute nephrosis of the proximal
tubule and affects blood pressure to the kidney.
• Low molecular weight proteins bind Pb2+, leading
to resorption by endocytosis.
• Cellular and mitochondrial swelling, karyomegaly,
mitosis and intranuclear inculsion bodies are seen.
• Decreased tubular resorption of glucose,
phosphate and amino acids +/- proteinuria
• Chronic exposure causes tubulo-interstitial
disease.
Cadmium Nephrotoxicity
• Metalothionein (Mt) is a low molecular weight
protein that transports cadmium (Cd) to the
kidney.
• Mt is taken up in the lysosomes and Cd is
released. Cd t ½ is 10-30 years in humans.
• Free Cd stimulates synthesis of renal Mt, which
binds Cd. When renal Mt is depleted, toxicity
occurs in S1 and S2.
• Proteinuria, calciuria, aminoaciduria and
glucosuria are seen.
• Chronic exposure leads to tubulo-interstitial
disease. There appears to be a threshold of 200
ppm Cd in the kidney before renal disease occurs.
Mercury Nephropathy
• Hg2+ and methylmercury cause damage to the S3
and S2/S3 segments of the proximal tubule.
• Hg2+ causes damage to the cell membrane and
mitochondria, and loss of cellular control over
intracellular Ca++.
• Chronic exposure results in anti-GBM and
immune-complex disease of the kidney.
• Methylmercury is highly lipid soluble and
concentrates in the proximal tubule, causing
damage to mitochondria and lysosomes.
Chromium Nephropathy
• Cr+6 causes acute nephrosis of S1 and S2.
• It damages the brush border, causing
decreased absorption of proteins, glucose
and amino acids.
• Large membranous myeloid bodies form as
a result of disrupted lysosomal function.
• Decreased glomerular filtration leads to
increased BUN and creatinine.
Ethylene Glycol Nephropathy
• Toxicity first discovered in humans when
ethylene glycol was used as a drug solvent.
• Causes acute renal toxicity in animals after
exposure to anti-freeze.
• Ethylene glycol is metabolized to oxalic
acid.
• Calcium oxylate crystals form in the lumen
of the tubules.
Ethylene Glycol Toxicity
Renal Papillary Necrosis
• Caused by non-steroidal anti-inflammatory
drugs – phenacetin and acetaminophen.
• Highest concentration of drugs are in the
renal papilla.
• Prostaglandin hydroperoxidase is highest in
the medulla and is thought to metabolize
these drugs to reactive quinoneimines.
Urinary Bladder Toxins
• Chemicals that cause bladder stones and
calcium phosphate precipitates frequently
cause bladder cancer in rodents.
• Aromatic amines, tobacco smoke and
parasitic infections cause bladder cancer in
humans.
Saccharin
• Non-genotoxic
• Induces bladder epithelial tumors in male
rats at >1% in the diet
• Must be administered to neonatal animals
• Can act as a promoter for genotoxic agents
• Only the sodium salt of saccharin is
carcinogenic
• Mechanism requires the formation of
calcium phosphate-containing precipitates