A study by micropuncture and microdissection of acute renal damage in rats

Novel Mechanistic PBPK Model to Predict Renal Clearance in Varying Stages of CKD by Incorporating Tubular Adaptation and Dynamic Passive Reabsorption

Chronic kidney disease (CKD) has significant effects on renal clearance (CLr ) of drugs. Physiologically-based pharmacokinetic (PBPK) models have been used to predict CKD effects on transporter-mediated renal active secretion and CLr for hydrophilic nonpermeable compounds. However, no studies have shown systematic PBPK modeling of renal passive reabsorption or CLr for hydrophobic permeable drugs in CKD. The goal of this study was to expand our previously developed and verified mechanistic kidney model to develop a universal model to predict changes in CLr in CKD for permeable and nonpermeable drugs that accounts for the dramatic nonlinear effect of CKD on renal passive reabsorption of permeable drugs. The developed model incorporates physiologically-based tubular changes of reduced water reabsorption/increased tubular flow rate per remaining functional nephron in CKD. The final adaptive kidney model successfully (absolute fold error (AFE) all < 2) predicted renal passive reabsorption and CLr for 20 permeable and nonpermeable test compounds across the stages of CKD. In contrast, use of proportional glomerular filtration rate reduction approach without addressing tubular adaptation processes in CKD to predict CLr generated unacceptable CLr predictions (AFE = 2.61-7.35) for permeable compounds in severe CKD. Finally, the adaptive kidney model accurately predicted CLr of para-amino-hippuric acid and memantine, two secreted compounds, in CKD, suggesting successful integration of active secretion into the model, along with passive reabsorption. In conclusion, the developed adaptive kidney model enables mechanistic predictions of in vivo CLr through CKD progression without any empirical scaling factors and can be used for CLr predictions prior to assessment of drug disposition in renal impairment.

A general empirical model for renal drug handling in pharmacokinetic analyses

Dose adjustment in renal insufficiency is generally based on the assumption that renal drug clearance is related linearly to glomerular filtration rate. The theory underpinning this model is the intact nephron hypothesis, which says that impaired renal function is caused by a reduction in the number of complete (intact) nephrons. The purpose of the present commentary is to propose a general empirical model for renal drug handling. We will explore models for renal function under two scenarios: one that aligns with the intact nephron hypothesis, and one that relaxes the assumptions of this hypothesis. We propose that a nonlinear, non-intact nephron model will allow for differences in renal drug handling, while incorporating the intact nephron hypothesis model as a special case.

Effect of potassium dichromate on renal brush border membrane enzymes and phosphate transport in rats

Chromium is widely used in industry but exposure to chromium compounds in the workplace can result in nephrotoxicity. Various nephrotoxicants affect the brush border membrane (BBM) lining the epithelial cells of the proximal tubule, but there have been no studies regarding the effect of potassium dichromate (K2Cr2O7), a hexava-lent chromium compound, on renal BBM. In the present work, the effect of administering a single intraperitoneal dose (15 mg/kg body weight) of K2Cr2O7 on rat renal BBM enzymes and inorganic phosphate (Pi) transport was studied. The animals were administered normal saline (control) or K2Cr2O7 and sacrificed 1, 2, 4 and 8 days after treatment. K2Cr2O7 induced reversible damage to the rat kidney function as indicated by serum creatinine (Scr) and urea nitrogen levels. The activities of BBM marker enzymes were significantly decreased in isolated BBM vesicles (BBMV) and homogenates of cortex and medulla on 1, 2 and 4 days after administration of K2Cr2O7with complete recovery to control values after 8 days. The decrease in the activities of the enzymes was mainly due to changes in maximum velocity (Vmax) values, while the Michaelis constant (Km) remained unchanged. The sodium dependent Pi transport across BBMV was reduced by 50% after treatment with K2Cr2O7. Thus, the administration of a single dose of K2Cr2O7 leads to impairment in the functions of renal BBM. These results suggest that the nephrotoxicity of K2Cr2O7 may be mediated, at least in part, by its effect on renal BBM.

Evaluation of protective action of α-tocopherol in chromium-induced oxidative stress in female reproductive system of rats

The present study was aimed to investigate whether α-tocopherol could protect the chromium (Cr) VI-induced oxidative stress in female reproductive system of rats and to explore the underlying mechanisms of the same. A total of 24 Wistar adult female rats were equally divided into four groups. Group 1 served as control, while groups 2 and 3 were administered K2Cr2O7 (10 mg/kg b.wt. s.c. single dose). In addition to Cr, group 3 also received α-tocopherol @ 125 mg/kg daily by oral gavage for 14 days. Group 4 was maintained as α-tocopherol control (dose as above). Body weights were recorded at the beginning and at the end of experiment. Further, the rats were observed for occurrence of estrus cycle. At the end of 14 days, blood samples were drawn for sero-biochemical analysis. Subsequently, all the rats were sacrificed to collect uterus along with ovaries for assay of tissue peroxidation, anti-oxidant and functional markers, and histopathology. Administration of chromium (Cr) VI to rats revealed a significant (P < 0.05) accumulation of cholesterol and a prolonged diestrus phase leading to impaired fertility in rats. Administration of chromium (Cr) VI significantly (P < 0.05) reduced the antioxidant markers such as superoxide dismutase (SOD) and reduced glutathione (GSH), along with significant (P < 0.05) increase in peroxidation markers such as malondialdehyde and protein carbonyls in ovaries. The functional marker in serum such as total protein was decreased, whereas other functional markers viz alanine transaminase (ALT), blood urea nitrogen (BUN) and creatinine were increased. Prominent pathological changes were observed in the uterus and ovaries of Cr-treated group. Co-treatment with α-tocopherol significantly (P < 0.05) reversed the (Cr) VI induced changes.

Kidney injury molecule-1 expression in rat proximal tubule after treatment with segment-specific nephrotoxicants: a tool for early screening of potential kidney toxicity

Dose-response expression of kidney injury molecule-1 (KIM-1) gene in kidney cortex and its correlation with morphology and traditional biomarkers of nephrotoxicity (plasma creatinine and blood urea nitrogen, BUN) or segment-specific marker of proximal tubule injury (kidney glutamine synthetase, GSK) were studied in male rats treated with proximal tubule segment-specific nephrotoxicants. These included hexachloro-1:3-butadiene (HCBD, S(3) segment-specific), potassium dichromate (chromate, S(1)-S(2) segment-specific), and cephaloridine (Cph, S(2) segment-specific). Rats were treated with a single intraperitoneal (ip) injection of HCBD 25, 50, and 100 mg/kg, subcutaneous (sc) injection of chromate 8, 12.5, and 25 mg/kg; or ip injection of Cph 250, 500, and 1,000 mg/kg. KIM-1 gene showed a dose-dependent up-regulation induced by all segment-specific nephrotoxicants. Interestingly, magnitude of the up-regulation reflected the severity of microscopic tubular changes (degeneration, necrosis, and regeneration). Even low-severity microscopic observations were evidenced by significant gene expression changes. Furthermore, KIM-1 showed significant up-regulation even in the absence of morphological changes. In contrast, traditional and specific markers demonstrated low sensitivity or specificity. In conclusion, this study suggested KIM-1 as a sensitive molecular marker of different levels of tubular injury, and it is likely to represent a potential tool for early screening of nephrotoxicants.

Chromium poisoning in rats feeding on tannery residues

The Brazilian tannery industry produces annually an enormous amount of scraps and leather shavings impregnated with chromium due to the tanning process. Technologies have been developed to remove chromium from this material. The resultant residue from the chromium removal process is high in protein with a high digestibility, suggesting that this residue may be used to feed monogastric animals. However, due to the nature of this residue, there is a risk of chromium poisoning and the introduction of botulism. The aim of this work was to establish the risks of adding tannery residues to animal feeds, using rats as an experimental model. Forty-eight Wistar rats were placed under eight treatments in a 2 by 4 factorial arrangement. The rats were fed over 60 days with a standard AIN-93 diet and the treatments consisted of replacing part of the diet with 0, 25, 37.5 or 50% of the chromium-tanned leather residue, in natura, known as ‘wet blue’, or the same percentages of this residue after chromium extraction. Industrial processing was able to remove 70–80% of the chromium from the residue. This high chromium level had a negative effect on the weight gain of the animals and caused lesions in the kidneys especially due to the chromium extraction material, suggesting that the removal process increases the biological activity of chromium, making it nefrotoxic. The gravity of this effect was directly proportional to the inclusion level. The results of this study indicate that until industrial processing is refined so that more of the chromium residue is removed, the use of the tannery residues in animal feeds is not safe.

Evaluation of aging influence on renal toxicity caused by segment-specific nephrotoxicants of the proximal tubule in rat

Little is known concerning the sensitivity of aged rats to xenobiotics inducing kidney damage. To increase this knowledge, the age-dependent response of the kidney to hexachloro-1 : 3-butadiene (HCBD) or potassium dichromate (chromate) was investigated. Rats were treated at different ages with a single dose of segment-specific nephrotoxicants of the proximal tubule, chosen on the basis of their specificity for S(3) and for S(1)-S(2) segments, respectively. The toxicological impact of these xenobiotics has been evaluated through biochemical and genomic markers, and histopathological investigation of kidney samples. HCBD treatment induced tubular necrosis of the S(3) segment of the proximal tubule associated with changes of toxicological markers unrelated to the age. In contrast, chromate treatment induced an increased kidney damage related to the rat age. In fact, histopathological investigation revealed that at 1 month of age tubular vacuolar degeneration was seen affecting S(1)-S(2) segments of the proximal tubule, whereas at 3 months of age tubular necrosis occurred in the same segments associated with tubular dilation of the distal portions. Consistently, biochemical analysis confirmed a direct correlation among genomic and biochemical marker variability and animal age. Altogether, the results show that during aging there is an increased sensitivity of kidney to chromate but not to HCBD-induced damage and evidence differential age-related selectivity of rats for nephrotoxic compounds. Significance for human risk assessment is discussed.

Acute renal failure enhances the antidotal activity of pralidoxime towards paraoxon-induced respiratory toxicity

We recently showed in a rat model of dichromate-induced acute renal failure (ARF) that the elimination but not the distribution of pralidoxime was altered resulting in sustained plasma pralidoxime concentrations. The aim of this study was to compare the efficiency of pralidoxime in normal and acute renal failure rats against paraoxon-induced respiratory toxicity. Ventilation at rest was assessed using whole-body plethysmography after subcutaneous administration of either saline or paraoxon (50% of the LD(50)), in the control and ARF rats. Thirty minutes after administration of paraoxon, either saline or 50mg/kg of pralidoxime was administered intramuscularly. ARF had no significant effects on the ventilation at rest. The effects of paraoxon on respiration were not significantly different in the control and ARF group. Paraoxon increased the total time (T(TOT)), expiratory time (T(E)) and tidal volume (V(T)), and decreased the respiratory frequency (f). In paraoxon-poisoned rats with normal renal function, pralidoxime had a significant but transient effect regarding the T(TOT) and V(T) (p<0.05). In the ARF group, the same dose of pralidoxime significantly decreased the T(TOT), T(E), and V(T) and increased f during 90 min (p<0.01). In conclusion, pralidoxime had partial and transient effects towards paraoxon-induced respiratory toxicity in control rats; and a complete and sustained correction in ARF rats.

Comparison of kidney injury molecule-1 and other nephrotoxicity biomarkers in urine and kidney following acute exposure to gentamicin, mercury, and chromium

Sensitive biomarkers are needed to detect kidney injury at the earliest stages. The objective of this study was to determine whether the appearance of kidney injury molecule-1 (Kim-1) protein ectodomain in urine and kidney injury molecule-1/hepatitis A viral cellular receptor-1 (Kim-1/Havcr1) gene expression in kidney tissue may be more predictive of renal injury after exposure to nephrotoxicants when compared to traditionally used biomarkers. Male Sprague-Dawley rats were injected with a range of doses of gentamicin, mercury (Hg; HgCl2), or chromium (Cr; K2Cr2O7). The results showed that increases in urinary Kim-1 and kidney Kim-1/Havcr1 gene expression paralleled the degree of severity of renal histopathology and were detected at lower doses of nephrotoxicants when compared to blood urea nitrogen (BUN), serum creatinine, and urinary N-acetyl-beta-D-glucosaminidase (NAG). In a time course study, urinary Kim-1 was elevated within 24 h after exposure to gentamicin (100 mg/kg), Hg (0.25 mg/kg), or Cr (5 mg/kg) and remained elevated through 72 h. NAG responses were nephrotoxicant dependent with elevations occurring early (gentamicin), late (Cr), or no change (Hg). At 72 h, after treatment with any of the three nephrotoxicants, there was increased Kim-1 immunoreactivity and necrosis involving approximately 50% of the proximal tubules; however, only urinary Kim-1 was significantly increased, while BUN, serum creatinine, and NAG were not different from controls. In rats treated with the hepatotoxicant galactosamine (1.1 mg/kg), serum alanine aminotransferase was increased, but no increase in urinary Kim-1 was observed. Urinary Kim-1 and kidney Kim-1/Havcr1 expression appear to be sensitive and tissue-specific biomarkers that will improve detection of early acute kidney injury following exposure to nephrotoxic chemicals and drugs.

Renal proximal tubule segment-specific nephrotoxicity: an overview on biomarkers and histopathology

The correspondence between histopathological findings and segment-specific biomarkers was investigated in rats treated with segment-specific nephrotoxicants. Male Wistar rats were treated with a single injection of K2Cr2O7 (25 mg/kg s.c. in saline), cis-Pt (10 mg/kg i.p. in buffered MSO) or HCBD (100 mg/kg i.p. in corn oil). Twenty-four and 48 hours after treatment, the rats were sacrificed and the kidneys were drawn for histopathological and biochemical evaluation, i.e., GS activity in renal cortex and PAH uptake in renal cortical slices. Histopathological findings show that cis-Pt and HCBD cause diffuse necrosis of S3 segment of proximal tubules in the outer stripe of outer medulla, respectively. On the contrary, K2Cr2O7 damages exclusively S1-S2 segments, inducing vacuolization at 24 hr and diffuse necrosis at 48 hr after treatment. GS activity in renal tissue is significantly decreased after HCBD and cis-Pt, but not K2Cr2O7 treatment. In contrast, PAH uptake is significantly reduced by K2Cr2O7, but not by cis-Pt or HCBD treatment (even if HCBD causes a slight decrease 48 hr after treatment). The evidence of this study confirms the high specificity of GS activity as marker of S3 segment injury, that PAH uptake is prevalently active in the S1-S2 segments, and that there is complete correspondence among segment-specific nephrotoxicants, biomarkers of segment-specific damage, and histopathological findings.

Beneficial effect of retinoic acid on the outcome of experimental acute renal failure

BACKGROUND

Retinoic acid (RA) exerts beneficial effects on vascular remodelling and experimental nephritis, and plays a role in kidney development. Pathological changes caused by acute renal failure (ARF) result in high mortality. We determined whether RA ameliorates ARF-induced pathology caused by potassium dichromate (PD).

METHODS

Adult Wistar female rats (210-250 g) were randomly allocated to four groups: (i) an ARF group that received PD [15 mg/kg body weight (bw), single dose subcutaneously]; (ii) a group that received PD plus RA (1 mg/kg bw) beginning at 5 days before PD and that continued for 14 additional days; (iii) a group that received PD plus thyroxine (T(4); 8 micro g/100 g bw) with RA; and (iv) a group that received only the vehicle for PD (saline solution). We evaluated functional, biochemical and morphological characteristics of the kidneys.

RESULTS

PD-induced alterations in serum creatinine, creatinine clearance (C(cr)) and fractional excretion of sodium (FeNa) were less severe when rats received RA. PD increased lipoperoxidation and this alteration was partially blocked by RA. Animals undergoing ARF showed severe histological injury (brush border loss, acidophilia, oedema, pyknosis, karyorhexis, cell detachment and disruption of the basement membrane). These alterations were less severe in RA-treated rats, indicating a protective effect on functional and morphological alterations. Alterations in urinary sediment were reduced by RA. The simultaneous administration of T(4) with RA did not produce additional protection.

CONCLUSION

RA exerted beneficial effects on the duration and severity of renal damage induced by PD in a model of renal failure resembling ARF in humans. The protective effect of RA may be mediated by diminished lipoperoxidative damage.

Tubular segment-specific biomarkers of nephrotoxicity in the rat

Segment-specific localization of p-aminohippuric acid accumulation and glutamine synthetase activity along the proximal tubule was investigated in kidneys of rats treated with segment-specific nephrotoxicants such as potassium dichromate (pars convoluta) and hexachloro-1:3-butadiene (pars recta). Potassium dichromate and the highest dose (200 mg/kg b.w.) of hexachloro-1:3-butadiene caused a significant, dose-dependent decrease of p-aminohippuric acid uptake in the renal cortical slices 24 and 48 h after the treatment. In contrast, hexachloro-1:3-butadiene and only the highest dose (40 mg/kg b.w.) of potassium dichromate, caused a significant dose-dependent decrease of glutamine synthetase activity in the kidney beginning 24 h after treatment. Finally, potassium dichromate and the highest dose (200 mg/kg b.w.) of hexachloro-1:3-butadiene (48 h after the treatment) caused a significant dose-dependent loss of kidney protein content. The results suggest that p-aminohippuric acid accumulation is localized in the pars convoluta and confirm that glutamine synthetase is in the pars recta of the rat proximal tubule. p-Aminohippuric acid uptake impairment and glutamine synthetase activity loss caused by the highest doses of hexachloro-1:3-butadiene and potassium dichromate, respectively, suggests that high doses of segment-specific chemicals may involve other portions of the proximal tubule; in addition, the decrease of glutamine synthetase activity caused by potassium dichromate may be related to the protein content loss.

Effects of perindopril and hydrochlorothiazide on the long-term progression of lithium-induced chronic renal failure in rats

Administration of lithium in the diet to new-born rats induces chronic renal failure associated with hypertension, proteinuria and irreversible tubulo-interstitial morphological changes. In the present study we induced chronic renal failure by administration of lithium for 16 weeks to new-born rats, and examined the spontaneous course of this nephropathy and the effects of antihypertensive treatment with either perindopril (12 mg/kg diet) or hydrochlorothiazide (500-1000 mg/kg diet) during a 24 weeks follow up period without lithium. In the placebo group, progression to terminal uraemia occurred in all rats with severe renal failure (initial Purea > 15 mM) (10 of 18). Rats with mild-moderate renal failure (Purea 9-15 mM) showed no deterioration in renal function despite persistent systolic hypertension and irreversible structural renal changes. Perindopril normalized the blood pressure in all rats but did not prevent the progression to terminal uraemia (8 to 18). Hydrochlorothiazide partially controlled the hypertension and accellerated the progression of uraemia without increasing the mortality (7 of 17). Irrespective of treatments, the predominant quantitative structural changes (e.g. decreased volume of proximal tubular cells) showed significant correlations with the degree of renal dysfunction, but not with systolic blood pressure in the surviving rats. It is concluded that progression of lithium-induced nephropathy to terminal uraemia occurs when the nephrotoxic insult results in a more than 50% reduction of the glomerular filtration rate, judged from Purea levels. The failure of effective antihypertensive treatment with an angiotension-converting enzyme inhibitor to modify the progression suggests that in this model, systemic or glomerular hypertension may not be an important pathophysiological factor. The structural and functional deterioration observed in Li-uraemic rats during treatment with hydrochlorothiazide remains unexplained.

Atubular glomeruli in chronic renal disease

The pathological changes in chronic renal failure are heterogeneous and may depend on the primary disease process. Renal function is better correlated with tubular and interstitial changes than with glomerular changes detectable in simple two-dimensional sections. Atubular glomeruli have been demonstrated in many tubulointerstitial disorders. They constitute a significant portion of the glomerular population in some chronic renal diseases. The atubular glomeruli are generally small, but they have open capillaries and minor ultrastructural changes. The number of capillaries is decreased. Glomeruli connected to normal proximal tubules have volumes at the normal level or above. They have not been shown to be eliminated. The presence of atubular glomeruli may explain the correlation between the volume of proximal tubules and the volume of interstitium, on the one hand, and altered renal function on the other. The presence of atubular glomeruli could explain the irreversibility of chronic renal diseases. It is likely that interstitial fibrosis and tubular atrophy in themselves contribute to the decrease in renal function of both glomerular and nonglomerular renal diseases. In glomerular diseases, the glomerular lesion and hyperfiltration may play the major part in the pathogenesis of the deterioration of renal function. The available evidence points toward glomerulo-tubular disconnection as an important and common cause of progression and irreversibility of chronic renal diseases. It provides a simple explanation for the common observation of severely reduced kidney function and mostly normal-looking glomeruli--at least in two dimensions.

Acute renal failure in a case of fatal chromic acid poisoning

Despite its frequent use in industry, acute poisoning by chromic acid has very rarely been reported. We report a patient who developed massive gastrointestinal hemorrhage, acute renal failure, and hepatic injury following chromic acid ingestion, and subsequently died. Postmortem liver and kidney biopsies revealed centrilobular necrosis and severe acute tubular necrosis, respectively.

Induction of type 2 cystatin in rat submandibular glands by systemically administered agents

An inducible type 2 cystatin has earlier been characterized in submandibular glands and kidneys of rats treated with isoproterenol, as well as in kidneys of rats with experimental renal disease. The purpose now was to determine whether giving agents that have systemic toxicity could also be associated with induction of cystatin in rat salivary glands. Female Wistar rats (200-250 g) were given isoproterenol, cyclocytidine, potassium dichromate or turpentine oil. After autopsy, the organs were sectioned, fixed in 10% formalin, and processed routinely. Paraffin sections were processed for both the peroxidase-antiperoxidase and the avidin-biotin-alkaline phosphatase immunocytochemical methods. The submandibular glands of rats given cyclocytidine had generalized, strong staining of acinar cells, as well as occasional weak staining within granular convoluted tubules. Animals given either potassium dichromate or turpentine oil exhibited moderate staining for cystatin in submandibular acini. Rats given isoproterenol as a positive control exhibited strong acinar staining throughout the submandibular gland, while the glands of untreated rats were unreactive. Inducible type 2 cystatin could not be detected in the parotid or sublingual glands, or in trachea, lung, stomach, small intestine, large intestine, spleen, liver and pancreas, after treatment with any of the systemic agents evaluated. The results indicate that elaboration of type 2 cystatin can be induced by a variety of systemically administered agents other than isoproterenol, and suggest that elaboration of type 2 cystatin may represent a more generalized response to tissue injury.

Induction of type 2 salivary cystatin in immunological and chemical kidney injury

We have previously reported that isoproterenol induces type 2 salivary cystatin in both submandibular glands and kidney tubule cells of rats but not in any other organs examined. In the present study, we investigated whether this salivary protein is induced in other conditions that show kidney tubule injury. Immunocytochemistry, using a monospecific antiserum to this cystatin, revealed specific staining within the proximal tubule epithelium of the cortex as well as in the inner and outer stripe of the medulla of immunologically and chemically injured rats. Cystatin could not be detected in kidneys from healthy rats by means of immunocytochemistry. Weak staining was found in 3/3 kidneys of rats treated with turpentine and in 5/5 animals treated with potassium dichromate. In rats treated with puromycin, cystatin could not be demonstrated in 5/5 animals having proteinuria of less than 100 mg/24 h; however, moderate staining was observed in 4/5 puromycin-treated rats having proteinuria greater than 100 mg/24 h. In Heymann nephritis, cystatin was present in 7/31 kidneys with proteinuria lasting 6 to 15 weeks and in none (0/7) with proteinuria of shorter duration. Strong staining was also observed in 10/10 kidneys from rats with moderate-to-severe chronic serum sickness. This study shows that elaboration of type 2 cystatin in rats is not limited to salivary glands and, with our previous study, suggests that induction of this cysteine inhibitor may represent a local response to generalized tissue injury in both submandibular and renal tissues. These findings further demonstrate that induction of cystatin in salivary glands is not unique to these glands and suggest that induction of this cysteine proteinase inhibitor may represent a local response to tissue injury caused by diverse mechanisms.

The role of glutathione in the acute nephrotoxicity of sodium dichromate

Ascorbate treatment 30 min prior to sodium dichromate (20 or 30 mg/kg, s.c.) shows higher potency than that of glutathione (GSH) in protecting against both the metabolic disturbance and nephrotoxicity induced by dichromate. However, ascorbate treatment after 2 h of dichromate intoxication had no effect on dichromate-induced blood urea nitrogen (BUN) elevation 3 days after intoxication. In contrast, dichromate-induced glucosuria, which reached maximum levels at 3 days after treatment, was significantly decreased by GSH or N-acetyl cysteine (NAC) treatment, even if its administration was after 24 h of dichromate intoxication. Pretreatment with GSH depletors such as diethyl maleate (DEM) and buthionine sulfoximine (BSO) had no effect on dichromate-induced nephrotoxicity. GSH levels in the liver and kidney were not affected at 3 h after dichromate treatment. However, dichromate significantly increased tissue GSH levels with a marked increase in liver per kidney GSH ratio at 24 h after treatment, if food was withheld subsequent to dichromate treatment, indicating that GSH biosynthesis resulted from the accelerated protein breakdown. These results suggest that GSH-mediated dichromate reduction is not a kinetically favorable pathway in vivo; however, GSH plays an important role in protection against dichromate-induced nephrotoxicity. In addition, the cellular metabolism of dichromate in the early period after treatment is important in the pathogenesis of its nephrotoxicity.

Development of renal toxicity in F344 rats gavaged with mercuric chloride for 2 weeks, or 2, 4, 6, 15, and 24 months

Both sexes of F344 rats were gavaged with maximal tolerated doses of mercuric chloride for periods from 2 wk to up to 2 yr to investigate chronic nephrotoxicity and potential carcinogenicity. The toxicity of mercuric chloride was excessive after 2 wk of exposure to doses ranging from 1.25 to 20 mg/kg, compromising renal function by selectively destroying cells of the proximal tubules, and eliciting marked elevations in urinary biomarker enzymes diagnostic for acute renal tubule necrosis. In the 2-wk studies, urinary alkaline phosphatase and aspartate amino-transferase were most sensitive to renal mercury toxicity among a panel of six enzymes, exhibiting twofold increases above controls at the 5.0 mg/kg dose, before changes in the other enzymes occurred. Urinary lactate dehydrogenase was the most responsive enzyme, with up to 11-fold increases in activity above controls. In response to mercuric chloride exposure of 5.0 mg/kg for 2-6 mo, the greatest and most persistent increases in elevation of urinary enzyme activities were exhibited by alkaline phosphatase and gamma-glutamyl transferase, which increased two-to threefold above controls. At this interval, the maximal severity of the renal lesions in both sexes of rats was graded as minimal to mild. Beyond 6 mo none of the urinary enzymes measured in this study was adequate as biomarkers of nephrotoxicity, although the severity of the renal lesions had progressed. Mercury accumulated in a dose-related fashion primarily in the kidney, and to a lesser extent in the liver. The severity of the renal lesions was increased by continued exposure to mercuric chloride, as tissue concentrations of mercury rose in proportion to dose. Mercuric chloride treatment for 2 yr clearly exacerbated the severity of the spontaneous nephrotoxicity prevalent in aging F344 rats. The excessive mortality that occurred in the male rats was probably due to a combination of these factors. No renal tumors were detected in rats, possibly because the potential for their development was reduced; however, direct tissue contact with mercury induced squamous-cell papillomas of the forestomach in both sexes.

Fetal nephrotoxicity

Investigation of fetal nephrotoxicity by maternally administered nephrotoxins is hampered by many constraints, including the maternal effects of the nephrotoxin, the ability of the nephrotoxin to cross the placenta and the difficulties associated with direct fetal intervention. In the pouch young of the North American opossum, Didelphis virginiana, we describe the toxic effects of a heavy metal on the immature metanephric kidneys. Varying doses of uranyl nitrate, a heavy metal salt, were administered to opossum pups in the pouch approximately 20 days after birth and the kidneys were harvested 3 to 12 days later for histological analysis. Group 1 consisted of 4 untreated and 5 saline treated pups. Group 2 (9 pups) received 10 to 15 mg./kg. intraperitoneal uranyl nitrate. Group 3 (6 pups) were given a uranyl nitrate dose of 25 mg./kg. Group 4, the high dose group, received either 58 mg./kg. (3 pups) or 87 mg./kg. (3 pups) of intraperitoneal uranyl nitrate. Group 1 kidneys demonstrated no pathological changes except for some mild renal tubular vacuolization seen in the saline treated animals. In group 2 tubular dilatation and necrosis were present 3 days after treatment; tubular regeneration could be seen by day 7. In group 3 glomerular cystic changes, interstitial fibrosis and tubular regeneration were present by day 7. Some restoration of normal architecture occurred by day 12 with fibrosis apparent. Group 4 animals demonstrated much more pronounced cystic changes of glomeruli and tubules as early as day 5 with marked interstitial fibrosis and prominent tubular regeneration. By day 12 group 4 pups continued to demonstrate significant and severe glomerular and tubular cystic changes with marked interstitial fibrosis. Inflammation, although present in all groups (except control), was never prominent. This first description of the effect of heavy metal toxicity on the immature metanephric kidney could provide an insight into the mechanisms of disordered kidney growth.

Nephrotoxicity of sodium dichromate depending on the route of administration

A comparison of the effects of intraperitoneal and subcutaneous routes of administration of sodium dichromate on nephrotoxicity in rats was studied. Dichromate when injected subcutaneously (SC group) produced a higher degree of nephrotoxicity than when administered intraperitoneally (IP group). It caused severe progressive proteinuria followed by polyuria and glucosuria, reaching maximum levels at 3 days after treatment in the SC group, whereas it produced mild proteinuria without glucosuria in the IP group. The dose-dependent increases in blood urea nitrogen (BUN) and creatinine concentrations, shown in the SC group, were not observed in the IP group. However, between the two groups, there were no great differences in either the urinary excretion rate of chromium or the electrophoretic patterns of urinary protein in the day 1 urine specimens. Pretreatment of phenobarbital (PB) had no remarkable effect on the dichromate-induced nephrotoxicity. In contrast, it potentiated dichromate-induced hepatotoxicity, the indices of which were the elevation in serum alanine aminotransferase (ALT) activity and hepatic lipid peroxide formation. These results suggest that the dependence of dichromate-induced nephrotoxicity on the route of administration is related to the chemical forms of chromium reaching the kidney, and the necrotizing property of dichromate results from its metabolic fate in vivo.

Effect of sodium dichromate on carbohydrate metabolism

Subcutaneous injection of sodium dichromate into male Sprague-Dawley rats immediately produced a variety of metabolic changes in a dose-dependent manner. Serum lactate and glucose were significantly increased after dichromate treatment, reaching maximum levels at 15 and 30 min, respectively. Then, the toxicity progressively diminished. In contrast, a steady increase in blood urea nitrogen (BUN) concentration was caused by dichromate, reaching maximum levels at 60 min after the administration; elevated BUN levels were sustained for several hours thereafter. Unlike KCN (5 mg/kg, ip) and As2O3 (5 mg/kg, ip), dichromate rapidly decreased serum insulin within 15 min after intoxication in doses of 20 and 40 mg/kg; hypoinsulinemia lasted 60 min. However, insulin levels returned to the normal range at 120 min after treatment. Dichromate-induced metabolic disturbance was also observed in the 24 hr-fasted rats, the response of which was similar to normal rats except for later hyperglycemia. In both cases, the duration time was short (30 to 60 min). Adrenalectomy and insulin pretreatment had no effect on dichromate-induced hyperglycemia. These results suggest that dichromate-induced metabolic disturbance results from the concomitant effects of a sudden decrease in serum insulin level and its direct inhibitory effect on carbohydrate metabolism. In addition, the characteristic biphasic pattern of metabolic disturbance might be related to metabolic fate of dichromate in vivo.

Chromium-induced kidney disease

Kidney disease is often cited as one of the adverse effects of chromium, yet chronic renal disease due to occupational or environmental exposure to chromium has not yet been reported. Occasional cases of acute tubular necrosis (ATN) following massive absorption of chromate have been described. Chromate-induced ATN has been extensively studied in experimental animals following parenteral administration of large doses of potassium chromate (hexavalent) (15 mg/kg body weight). The chromate is selectively accumulated in the convoluted proximal tubule where necrosis occurs. An adverse long-term effect of low-dose chromium exposure on the kidneys is suggested by reports of low molecular weight (LMW) proteinuria in chromium workers. Excessive urinary excretion of beta 2-microglobulin, a specific proximal tubule brush border protein, and retinol-binding protein has been reported among chrome platers and welders. However, LMW proteinuria occurs after a variety of physiologic stresses, is usually reversible, and cannot by itself be considered evidence of chronic renal disease. Chromate-induced ATN and LMW proteinuria in chromium workers, nevertheless, raise the possibility that low-level, long-term exposure may produce persistent renal injury. The absence of evidence of chromate-induced exposure may produce persistent renal injury. The absence of evidence of chromate-induced chronic renal disease cannot be interpreted as evidence of the absence of such injury. Rather, it must be recognized that no prospective cohort or case-control study of the delayed renal effects of low-level, long-term exposure to chromium has been published.

Prediction of the renal clearance of cimetidine using endogenous N-1-methylnicotinamide

We investigated the influence of the type rather than the degree of renal insufficiency on the renal clearance of drugs. Different models of site specific experimental renal failure (ERF) have been developed in the rat; proximal tubular necrosis, induced by cisplatin; papillary necrosis, induced by 2-bromoethylamine, and glomerulonephritis, induced by sodium aurothiomalate or by antiglomerular basement membrane antibody. Several parameters of kidney function were assessed: the clearance of inulin, PAH, and endogenous N-1-methylnicotinamide (NMN). Plasma BUN and creatinine concentrations, and the presence of proteinuria and glucosuria were also measured. Our results showed a nonparallel decrease in glomerular filtration rate (GFR) and tubular secretion as measured by the secretory clearance of endogenous NMN or by the secretory clearance of p-aminohippuric acid (PAH), that is incompatible with the "intact nephron hypothesis." As a result, the renal clearance of cimetidine, a drug eliminated mainly by renal secretion, correlated better with the renal clearance of endogenous NMN than with the GFR. We conclude that (i) our models of ERF demonstrated the existence of glomerulo-tubular imbalance that is contrary to expectations based on the intact nephron hypothesis; (ii) the type of the renal disease has a direct influence on the renal clearance of cimetidine; (iii) the clearance of endogenous NMN may be a valuable noninvasive test for assessing renal tubular secretion which could be useful in predicting the clearance of drugs eliminated predominantly by tubular secretion.

Acute toxic effect of sodium dichromate on metabolism

The effect of sodium dichromate on cellular metabolism was investigated. Intraperitoneal injection of sodium dichromate into the rat (20 or 40 mg/kg) caused significant increases in serum lactate, pyruvate, and creatinine concentrations within 15 min after intoxication. Severe hyperglycemia occurred thereafter, as a result of increased hepatic glycogenolysis, which was seen in the first 2 h after dichromate. However, liver glycogen was resynthesized in 24 h-fasted rats after glucose refeeding. Dichromate decreased serum total amino acids, with a consequent increase in blood urea nitrogen (BUN) concentration. Unlike HgCl2 (2 mg/kg, i.p.), As2O3 (5 mg/kg, i.p.), and KCN (5 mg/kg, i.p.), dichromate showed the largest metabolic disturbance only in the early period after treatment. In addition, dichromate produced cyanosis, which appeared during the period of the accelerated glycolysis and breakdown of creatinine phosphate. Regardless of chemical species, only the hexavalent chromium compounds had an effect on the cellular metabolism. Trivalent chromium compounds had no effect at all. These results suggest that dichromate possesses a characteristic dual action on cellular metabolism, which might be related to its metabolic fate.

Renal epithelial amino acid concentrations in mercury-induced and postischemic acute renal failure

The concentration of 18 alpha-amino acids (AAs) in plasma and renal cortical cell water were measured 3 or 24 hr after 1 hr of unilateral renal artery clamping or 24 or 48 hr after 15 mg/kg body weight HgCl2 injection sc as a test of epithelial integrity. Cellular glycine (Gly), hydroxyproline (Hpr), ornithine (Orn), phenylalanine (Phe), serine (Ser), and tryptophan (Trp) concentrations were depressed 24 hr after HgCl2 (p less than 0.05), but the remaining 12 AAs were not distinguishable from control despite the presence of severe renal failure. ARginine (Arg), glutamic acid (Glu), and valine (Val) also were decreased (P less than 0.05) 24 hr later, but concentrations of half of all measured AAs were still normal. Cellular alanine (Ala), Arg, Glu, Gly, Phe, and Ser concentrations were decreased 3 hr after ischemia, p less than 0.05, but 12 AAs were unchanged and only Arg, Phe, Ser, and threonine (Thr) were reduced 24 hr after ischemia was reversed. Concentrations of even the most affected AAs remained notably higher than in plasma in both forms of acute renal failure (ARF). Total loss of AAs from a small proportion of tubular cells would be hidden by essentially normal concentrations in the rest, and such losses may well have occurred. Unless cellular AAs in ARF are almost completely bound, however, the well-maintained cell:plasma AA concentration ratios indicate that cellular energetics were adequate for AA uptake and that epithelial permeability to AAs in the vast majority of cells was not greatly disturbed. Such findings suggest that most of the epithelium, although seriously damaged, had remained viable.

Glomerular hemodynamics in established glycerol-induced acute renal failure in the rat

The glomerular dynamic correlates of failed filtration were studied in volume replete rats with established glycerol-induced acute renal failure (ARF). Over one-half of all nephrons formed virtually no filtrate, while the single nephron glomerular filtration rate (SNGFR) of fluid-filled nephrons, measured at the glomerulotubular junction to preclude the possibility of covert tubular leakage, averaged one-sixth of control (P less than 0.001). Even that low mean value was elevated by a few nephrons with a near normal SNGFR. Renal failure thus reflected both total filtration failure in the majority of nephrons and massively reduced filtration in most of the remainder. Glomerular capillary pressure (Pg) averaged some 14 mmHg below control (P less than 0.001), whereas the arterial colloid osmotic and Bowman's space pressures were not significantly altered. Renocortical and whole kidney blood flow were also unchanged. Marked internephron functional heterogeneity precluded estimates of the ultrafiltration coefficient. However, the fall in SNGFR correlated well with the markedly depressed Pg and afferent net filtration pressure (delta PnetA, P less than 0.001), which in turn were caused by increased preglomerular resistance and a reciprocal fall in efferent arteriolar resistance. This complex change in intrarenal resistances was largely, if not entirely, responsible for failed filtration in this ARF model.

Dose-response and time-response biochemical and histological study of potassium dichromate-induced nephrotoxicity in the rat

This study provides quantitative toxicological data on potassium dichromate-induced renal damage and considers the possible difficulties arising from the non-invasive in vivo assessment of renal damage, with particular attention to enzymuria. Renal damage induced in male Wistar rats by single sc injections of potassium dichromate was assessed 52 to 72 hr after doses ranging from 3 to 20 mg potassium dichromate/kg body weight and throughout a 9-day period following a dose of 20 mg potassium dichromate/kg. The earliest and most sensitive non-invasive functional change in the dose-response and time-response studies was an elevation in the rate of urinary excretion of protein. Evidence of tissue damage was observed with elevations in the urinary excretion rates of the brush border enzymes, gamma-glutamyltransferase, alkaline phosphatase and leucine aminopeptidase, the cytosolic enzymes, aspartate aminotransferase and lactate dehydrogenase and the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Such changes occurred as early as the abnormal urinary protein excretion, but returned to control or sub-control values sooner. Urinary brush border enzyme excretion returned to control values within 48 hr following potassium dichromate injection, despite histological and histochemical evidence of extensive renal damage and renal dysfunction. Elevations in plasma aspartate aminotransferase and lactate dehydrogenase levels were observed, but histochemical and isoenzyme studies would be needed to determine the source of these increases. The simplest and most persistent indicators of renal damage were the urinary excretion of protein and N-acetyl-beta-D-glucosaminidase.

Anatomic and physiologic age changes in the kidney

Cross-sectional studies of renal function in man indicate there is a progressive decline with age after the age of 40 years. The blood vessels, glomeruli, tubules and interstitium are all potential sites of primary involvement in the aging process as well as for renal disease. Regardless of the anatomic structure initially affected, most chronic renal conditions evolve with destruction of the entire nephron. Whether the observed decrease in renal function associated with aging is the result of intervening pathologic processes, e.g. ischemia (vascular obliteration) or infection, or is the result of a more insidious involutional process, it has generated much discussion but few answers. The purpose of this report is to review the descriptive studies documenting the changes in renal morphology and physiology with age and to focus on what is known about the mechanisms involved in these losses of renal substances and function.

Normal and abnormal aspects of proteinuria. Part I: Mechanisms, characteristics and analyses of urinary protein. Part II: Clinical considerations

Part I highlights the mechanisms of glomerular filtration and tubular reabsorption of plasma proteins, selected characteristics of urinary proteins based upon electrophoretic properties and recent advances in clinical laboratory analysis of proteinuria. Both structural characteristic of the glomerular capillary wall and molecular properties of plasma proteins are important determinants of glomerular filtration. Proteins filtered by the glomerulus subsequently appear in urine only after escaping the efficient mechanisms of tubular reabsorption. Albumin is one such protein and constitutes the major protein in normal urine although trace amounts of alpha, beta, and gamma globulins are also detectable. Several techniques of protein analysis have thus been developed to specifically measure albumin as well as other plasma proteins. Other methods have been adapted to measure total urinary protein content enabling the clinician to readily monitor renal function in health and disease. The second part of this review will consider conditions associated with proteinuria in both asymptomatic individuals and patients with renal disease. Asymptomatic proteinuria encompasses states of excess protein excretion during conditions of orthostasis, exercise, travel to high altitude of fever. Proteinuria during renal disease has received considerable interest as a means to monitor kidney function. It is therefore classified according to the type of damage incurred: (1) glomerular-type where large molecular weight proteins are excreted (2) tubular-type where small molecular weight proteins are excreted and (3) mixed-type characterized by both large and small molecular weight proteinuria.

The effect of potassium dichromate and mercuric chloride on urinary excretion and organ and subcellular distribution of [203Hg]mercuric chloride in rats

The mechanism by which subthreshold/non-effective doses or concentrations of potassium dichromate (K2Cr2O7) potentiate the effect of moderately effective dose/concentrations of mercuric chloride (HgCl2) on renal organic ion transport is not understood. To investigate this effect, the rate of excretion of mercury from the intact animal and the renal and hepatic accumulation and subcellular distribution of mercury within kidney cortex following pretreatment or in vitro exposure to K2Cr2O7 were undertaken. Coincidental administration of K2Cr2O7 had no significant effect in altering the rate of excretion of labeled mercury. Organ distribution showed time dependence; however, the presence of K2Cr2O7 did not increase renal mercury concentrations. In fact, significantly less mercury was found at 4 h in the kidneys of rats receiving both metal salts. Subcellular distribution of labeled mercury (203Hg) was also not significantly altered by the presence of K2Cr2O7, although the distribution patterns for in vitro exposure and pretreated tissues were different. These studies show that K2Cr2O7 does not produce alterations in urinary elimination, organ distribution or subcellular distribution of mercury.

Cortical and papillary absorptive defects in gentamicin nephrotoxicity

Renal function was examined in rats given daily injections of gentamicin (100 to 150 mg/kg) for 10 to 14 days. Whole kidney inulin clearance fell and urine volume increased. Single nephron GFR of surface nephrons varied. Some nephrons had no filtration, some had low rates, and some had high rates. Abnormal renal tubular epithelial inulin permeability was demonstrated by microinjection. Micropuncture of individual nephrons early and later in their course demonstrated reduced fluid reabsorption along the proximal convoluted tubule of superficial nephrons. Rates of fluid delivery to the late proximal and distal tubule were elevated. The rate of fluid reabsorption in the superficial loop of Henle was increased. Maximal urine osmolality and papillary tissue content of urea was reduced. The polyuria, therefore, results from decreased fluid reabsorption by proximal tubules and, probably, by papillary collecting ducts. The decrease in proximal fluid reabsorption is probably secondary to impaired solute reabsorption. A decrease in collecting duct fluid absorption can be attributed to the observed decrease in papillary solute concentration.

Theoretical analysis of pathogenetic mechanisms in experimental acute renal failure

A network thermodynamic model of glomerular dynamics has been employed to determine the degree of change in individual glomerular vascular resistances, hydraulic conductivity and proximal tubule pressure that, singly or in concert, could lower GFR to the degree expected in experimental acute renal failure (ARF). In both the rat and dog, the analysis shows that filtration failure is not achieved until preglomerular resistance (RA) is increased at least twofold or postglomerular resistance (RE) is decreased by 74% or more with all other determinants held at control values. Tubular obstruction alone will not provide failed filtration until tubule pressure is increased to 30 to 40 mm Hg in the rat and 44 mm Hg in the dog. A much smaller change in tubular pressure can contribute greatly to the development of filtration failure, however, when occurring in association with major change in individual vascular resistances. Glomerular capillary resistance must be increased to a value more than twice the normal sum of RA and RE (greater than fivefold in the dog), and glomerular capillary hydraulic conductivity lowered to below 5% of control, as isolated changes, before full filtration failure is approached. There is no reason to believe that most forms of ARF relate to only a single abnormality, however, and the effect of concomitant changes in individual resistances, hydraulic conductivity and proximal tubule pressure on glomerular filtration and blood flow is presented in the text and figures. A possible mechanism by which altered blood viscosity at the efferent arteriole may contribute to ARF is discussed and quantified. The degree of change in any determinant required to exert a given effect on filtration is independent of etiology, thus rendering the results of this analysis equally valid for any other pathological event which causes a significantly reduced GFR in the rat or dog.