Cytotoxicity of trichloroethylene and S-(1, 2-dichlorovinyl)-L-cysteine in primary cultures of rat renal proximal tubular and distal tubular cells

Mapping Adverse Outcome Pathways for Kidney Injury as a Basis for the Development of Mechanism-Based Animal-Sparing Approaches to Assessment of Nephrotoxicity

In line with recent OECD activities on the use of AOPs in developing Integrated Approaches to Testing and Assessment (IATAs), it is expected that systematic mapping of AOPs leading to systemic toxicity may provide a mechanistic framework for the development and implementation of mechanism-based in vitro endpoints. These may form part of an integrated testing strategy to reduce the need for repeated dose toxicity studies. Focusing on kidney and in particular the proximal tubule epithelium as a key target site of chemical-induced injury, the overall aim of this work is to contribute to building a network of AOPs leading to nephrotoxicity. Current mechanistic understanding of kidney injury initiated by 1) inhibition of mitochondrial DNA polymerase γ (mtDNA Polγ), 2) receptor mediated endocytosis and lysosomal overload, and 3) covalent protein binding, which all present fairly well established, common mechanisms by which certain chemicals or drugs may cause nephrotoxicity, is presented and systematically captured in a formal description of AOPs in line with the OECD AOP development programme and in accordance with the harmonized terminology provided by the Collaborative Adverse Outcome Pathway Wiki. The relative level of confidence in the established AOPs is assessed based on evolved Bradford-Hill weight of evidence considerations of biological plausibility, essentiality and empirical support (temporal and dose-response concordance).

Nephrotoxicity and Renal Pathophysiology: A Contemporary Perspective

The kidney consists of numerous cell types organized into the nephron, which is the basic functional unit of the kidney. Any stimuli that induce loss of these cells can induce kidney damage and renal failure. The cause of renal failure can be intrinsic or extrinsic. Extrinsic causes include cardiovascular disease, obesity, diabetes, sepsis, and lung and liver failure. Intrinsic causes include glomerular nephritis, polycystic kidney disease, renal fibrosis, tubular cell death, and stones. The kidney plays a prominent role in mediating the toxicity of numerous drugs, environmental pollutants and natural substances. Drugs known to be nephrotoxic include several cancer therapeutics, drugs of abuse, antibiotics, and radiocontrast agents. Environmental pollutants known to target the kidney include cadmium, mercury, arsenic, lead, trichloroethylene, bromate, brominated-flame retardants, diglycolic acid, and ethylene glycol. Natural nephrotoxicants include aristolochic acids and mycotoxins such as ochratoxin, fumonisin B1, and citrinin. There are several common characteristics between mechanisms of renal failure induced by nephrotoxicants and extrinsic causes. This common ground exists primarily due to similarities in the molecular mechanisms mediating renal cell death. This review summarizes the current state of the field of nephrotoxicity. It emphasizes integrating our understanding of nephrotoxicity with pathological-induced renal failure. Such approaches are needed to address major questions in the field, which include the diagnosis, prognosis and treatment of both acute and chronic renal failure, and the progression of acute kidney injury to chronic kidney disease.

Glutathione-dependent bioactivation

The classical view of the glutathione (GSH) conjugation pathway involves GSH S-transferase (GST)-dependent formation of thioether conjugates between GSH and an electrophilic substrate, processing to yield the corresponding cysteine S-conjugate, which is then converted to an N-acetylcysteine conjugate (or mercapturate). Mercapturates of most GST substrates are rendered more polar and thus readily excreted in urine. In contrast, there is a growing number of GST substrates that, rather than being detoxified, are bioactivated. These substrates include several halogenated solvents, many of which are nephrotoxic because of the tissue distribution of GSH conjugation pathway enzymes and membrane transporters, and prodrugs of certain chemotherapeutic agents. Although the initiating steps are the same regardless of whether the substrate is detoxified or bioactivated, the cysteine conjugate functions as a branch point. Bioactivated cysteine S-conjugates are metabolized in the kidneys by either cysteine conjugate β-lyase or flavin-containing monooxygenase to produce a reactive intermediate.

The effects of Syzygium aromaticum-derived oleanolic acid on kidney function of male Sprague-Dawley rats and on kidney and liver cell lines

Studies indicate that Syzygium spp-derived oleanolic acid (OA) enhances renal function of streptozotocin (STZ)-induced diabetic rats as evidenced by its reversal of the previously reported inability of the kidney to excrete Na(+) in these animals. We postulated that OA influences Na(+) excretion in the proximal tubule, the site where two-thirds of filtered NaCl is reabsorbed through a process mediated by transport proteins. Therefore, the study investigated the effects of OA on proximal tubular Na(+) handling in male Sprague-Dawley rats using renal lithium clearance (C(Li)). Renal C(Li) has been used widely in animal and clinical studies to assess proximal tubular function. Sub-chronic doses of OA were administered to rats twice every third day for 5 weeks. Rats treated with deionized water served as control animals. Cytotoxicity of OA on kidney and liver cell lines was assessed by the MTT and comet assays. OA increased Na(+) excretion of conscious male Sprague-Dawley rats from week 3 to week 5. By the end of the 5-week experimental period, OA treatment significantly reduced (p < 0.05) plasma creatinine concentration of STZ-induced diabetic rats with a concomitant elevation in glomerular filtration rate (GFR). Acute OA infusion was also associated with increases in fractional excretion of sodium (FE(Na)) and lithium (FE(Li)) in anesthetized rats in the absence of significant changes in GFR. The MTT assay studies demonstrated that OA increased the metabolic activity of kidney and liver cell lines. Taken together with previous observations, this study implicates the proximal tubule in OA-evoked increases in urinary Na(+) output.

Effects of genetic polymorphisms of N-Acetyltransferase on trichloroethylene-induced hypersensitivity dermatitis among exposed workers

The hypersensitivity dermatitis induced by trichloroethylene (TCE) exposure was influenced by individual genetic susceptibility factors. In this paper, a case-control study was conducted to investigate effects of various genotypes and phenotypes of N-Acetyltransferases (NATs) on individual susceptibility to the disease. The study consists of 111 patients with hypersensitivity dermatitis and 154 healthy TCE-exposed workers. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the polymorphic sites of NAT1 at nt 1095 and 1088 and the sites of NAT2 at nt 481, 590, and 857. Logistic regression was used to calculate the odds ratios (ORs) and 95% confidence intervals (95%CI). The results reveal that subjects with intermediate or slow acetylators of NAT2 have a 2.01 fold (95%CI=1.14-3.54) higher risk for the disease than subjects with the fast acetylators. When non-fast NAT2 phenotype (intermediate and slow acetylators) and a slow NAT1 phenotype were combined, the risk for the disease was significantly increased (OR=2.71, 95%CI 1.29-5.70) to the level higher than that observed for NAT2 non-fast acetylators phenotype alone. These findings suggest that slow metabolic phenotype of NAT2 maybe one of risk factor for TCE-induced hypersensitivity dermatitis and combined slow acetylator phenotypes of NAT1 and NAT2 further increase such risk.

Effects ofFicus thonningii(Blume) [Morarceae] Stem-Bark Ethanolic Extract on Blood Glucose, Cardiovascular and Kidney Functions of Rats, and on Kidney Cell Lines of the Proximal (LLC-PK1) and Distal Tubules (MDBK)

Previous observations indicate that Ficus thonningii (Blume) [Moraceae] stem-bark extracts may be useful in the control of diabetes mellitus. Accordingly, we investigated in some experimental animal paradigms the effects of F. thonningii stem-bark ethanolic extract (FTE) on renal and cardiovascular functions as complications of diabetes. Oral glucose tolerance tests were conducted in separate groups of non-diabetic and STZ-treated diabetic rats given glucose load (0.86 g x kg(-1), p.o.) after 18-h fast, followed by various FTE doses (60, 120, and 240 mg x kg(-1)). Rats treated with deionized water (3 mL x kg(-1) p.o.), or metformin (500 mg x kg(-1) p.o.) acted as untreated and treated positive controls, respectively. Blood glucose was monitored at 15-min intervals for the first hour, and hourly thereafter for 3 h. Acute effects of FTE on kidney function and mean arterial blood pressure (MAP) were investigated in anaesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4 h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. FTE was added to the infusate during the treatment period. Chronic effects of FTE were studied in individually caged rats treated daily with FTE (120 mg x kg(-1), p.o.) for five weeks. Cytotoxicity of FTE was assessed by dye-reduction colorimetric (MTT) assay on MDBK and LLCPK1 kidney cell lines exposed for 24 h, 48 h, and 72 h to graded concentrations of the extract. Myocardial contractile performance was evaluated on rat isolated atrial muscle strips. FTE, like metformin, decreased blood glucose levels in non-diabetic and STZ-diabetic rats. Both acute and chronic FTE treatments did not affect renal function. In vitro studies demonstrated that FTE increased MDBK cell metabolic activity by an average of 15% (72 h), and LLCPK1 mirrored the controls. Acute intravenous infusion of FTE reduced the MAP from 119 +/- 1 mmHg to 98 +/- 4 mmHg. The MAP also was reduced throughout the five-week experimental study period. FTE also produced concentration-dependent, negative inotropic and chronotropic effects on rat isolated, electrically driven left-, and spontaneously beating right-, atrial muscle preparations. Our experimental findings suggest that FTE possesses reno- and cardio-protective effects in diabetes mellitus.

Toxicity, biomarkers, genotoxicity, and carcinogenicity of trichloroethylene and its metabolites: a review

Trichloroethylene (TCE) is a prevalent occupational and environmental contaminant that has been reported to cause a variety of toxic effects. This article reviews toxicity, mutagenicity, and carcinogenicity caused by the exposure of TCE and its metabolites in the living system as well as on their (TCE and its metabolites) toxicity biomarkers.

Renal proximal tubules from old Fischer 344 rats grow into epithelial cells in cultures and exhibit increased oxidative stress and reduced D1 receptor function

Earlier we reported defects in D1 receptor function in renal proximal tubules (RPTs) of aged Fischer 344 (F344) and obese Zucker rats. However, the defects in the receptor function in RPTs of obese Zucker rats do not pass onto primary cultures of RPTs from these animals. Here, we determined whether the defects in D1 receptor function in RPTs of aged F344 rats pass onto the primary cultures. RPTs from aged (24-mo) and adult (6-mo) F344 rats were grown into primary cultures. The microscopic studies showed that cells in cultures from adult and old rats were healthy as determined by the shape and size of the cells and nuclei. D1 receptor agonist SKF-38393 produced inhibition of (86)Rb (rubidium) uptake, index of Na-K-ATPase activity, in cells from adult rats, but this was reduced in old rats. Also, SKF-38393 increased the [(35)S]GTPgammaS binding, index of receptor activation, in the membranes of cells from adult rats but to a lesser extent from old rats. Furthermore, there was a downward trend in the levels of D1 receptor numbers and in the receptor proteins in old rats. Interestingly, gp(91phox) subunit of NADPH oxidase and cellular protein carbonyl levels (oxidative stress marker) were higher in cultures from old rats. These results show that RPTs from adult and old F344 rats grow into epithelial cells in cultures. Furthermore, cells in cultures from old rats are at a higher level of oxidative stress, which may be contributing to the reduced D1 receptor function in the cells from old compared with adult rats.

Role of mitochondrial dysfunction in cellular responses to S-(1,2-dichlorovinyl)-L-cysteine in primary cultures of human proximal tubular cells

The nephrotoxic metabolite of the environmental contaminant trichloroethylene, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), is known to elicit cytotoxicity in rat and human proximal tubular (rPT and hPT, respectively) cells that involves inhibition of mitochondrial function. DCVC produces a range of cytotoxic and compensatory responses in hPT cells, depending on dose and exposure time, including necrosis, apoptosis, repair, and enhanced cell proliferation. The present study tested the hypothesis that induction of mitochondrial dysfunction is an obligatory step in the cytotoxicity caused by DCVC in primary cultures of hPT cells. DCVC-induced necrosis was primarily a high concentration (> or =50 microM) and late (> or =24h) response whereas apoptosis and increased proliferation occurred at relatively low concentrations (<50 microM) and early time points (< or =24h). Decreases in cellular DNA content, indicative of cell loss, were observed at DCVC concentrations as low as 1 microM. Involvement of mitochondrial dysfunction in DCVC-induced cytotoxicity was supported by showing that DCVC caused modest depletion of cellular ATP, inhibition of respiration, and activation of caspase-3/7. Cyclosporin A protected cells against DCVC-induced apoptosis and both cyclosporin A and ruthenium red protected cells against DCVC-induced loss of mitochondrial membrane potential. DCVC caused little or no activation of caspase-8 and did not significantly induce expression of Fas receptor, consistent with apoptosis occurring only by the mitochondrial pathway. These results support the conclusion that mitochondrial dysfunction is an early and obligatory step in DCVC-induced cytotoxicity in hPT cells.

L-methionine-dl-sulfoxide metabolism and toxicity in freshly isolated mouse hepatocytes: gender differences and inhibition with aminooxyacetic acid

L-methionine-dl-sulfoxide (MetO) is an L-methionine (Met) metabolite, but its role in Met metabolism and toxicity is not clear. In this study, MetO uptake, metabolism to Met, cytotoxicity, and glutathione (GSH) and glutathione disulfide (GSSG) status were characterized in freshly isolated mouse hepatocytes incubated at 37 degrees C with 0 to 30 mM MetO for 0 to 5 h. In male hepatocytes, dose-dependent cytotoxicity concomitant with GSH depletion without GSSG formation occurred after exposure to 20 or 30 mM MetO but not after exposure to 10 mM MetO. Interestingly, female hepatocytes exposed to 30 mM MetO showed no cytotoxicity and exhibited increased intracellular GSH levels compared with control hepatocytes. Male hepatocytes had approximately 2-fold higher levels of intracellular Met-d-O or Met-l-O after MetO (30 mM) exposure for 0 to 1.5 h compared with female hepatocytes. In hepatocytes of both genders, Met-l-O was detected at nearly 5-fold higher levels than Met-d-O, and no significant increase in cellular Met levels was detected. Addition of aminooxyacetic acid (AOAA), an inhibitor of transamination reactions, to MetO-exposed male hepatocytes resulted in higher cellular Met-d-O and Met-l-O levels and decreased the cytotoxicity of MetO. Interestingly, exposure of control male hepatocytes to AOAA selectively increased cellular Met-d-O levels to levels similar to those observed after exposure to MetO (30 mM). Analysis of MetO transamination activity by glutamine transaminase K in mouse liver cytosol revealed similar rates of MetO transamination in cytosol of both genders. Taken together, these results provide evidence for stereoselective oxidation of Met to Met-d-O under physiological conditions and suggest a major role for MetO transamination in MetO metabolism and toxicity.

L-methionine toxicity in freshly isolated mouse hepatocytes is gender-dependent and mediated in part by transamination

L-methionine (Met) has been implicated in parenteral nutrition-associated cholestasis in infants and, at high levels, it causes liver toxicity by mechanisms that are not clear. In this study, Met toxicity was characterized in freshly isolated male and female mouse hepatocytes incubated with 5 to 30 mM Met for 0 to 5 h. In male hepatocytes, 20 mM Met was cytotoxic at 4 h as indicated by trypan blue exclusion and lactate dehydrogenase leakage assays. Cytotoxicity was preceded by reduced glutathione (GSH) depletion at 3 h without glutathione disulfide formation. Exposure to 30 mM Met resulted in increased cytotoxicity and GSH depletion. It is interesting to note that female hepatocytes were resistant to Met-induced cytotoxicity at these concentrations and showed increased cellular GSH levels compared with hepatocytes exposed to medium alone. The effects of amino-oxyacetic acid (AOAA), an inhibitor of Met transamination, and 3-deazaadenosine (3-DA), an inhibitor of the Met transmethylation pathway enzyme S-adenosylhomocysteine hydrolase, on Met toxicity in male hepatocytes were then examined. Addition of 0.2 mM AOAA partially blocked Met-induced GSH depletion and cytotoxicity, whereas 0.1 mM 3-DA potentiated Met-induced toxicity. Exposure of male hepatocytes to 0.3 mM 3-methylthiopropionic acid (3-MTP), a known Met transamination metabolite, resulted in cytotoxicity and cellular GSH depletion similar to that observed with 30 mM Met, whereas incubations with D-methionine resulted in no toxicity. Female hepatocytes were less sensitive to 3-MTP toxicity than males, which may partially explain their resistance to Met toxicity. Taken together, these results suggest that Met transamination and not transmethylation plays a major role in Met toxicity in male mouse hepatocytes.

CRBP-I in the renal tubulointerstitial compartment of healthy rats and rats with renal fibrosis

BACKGROUND

Cellular retinol-binding protein I (CRBP-I), a member of the intracellular lipid-binding protein (iLBP) superfamily, is a specific marker of quiescent stellate cells in the healthy human liver. In the diseased fibrotic/cirrhotic liver, portal and septal myofibroblasts acquire CRBP-I expression, while activated hepatic stellate cells maintain their CRBP-I expression. Here, we investigate the distribution of CRBP-I in the renal cortex of healthy rats and rats with renal fibrosis.

METHODS

Kidneys of healthy and adriamycin-treated rats were studied by immunohistochemistry, using antibodies against CRBP-I, desmin, vimentin and alpha-smooth muscle actin (alpha-SMA). Double stainings were done with immunofluorescence. Western blotting was performed to semi-quantify the expression levels of vimentin, desmin, alpha-SMA and CRBP-I.

RESULTS

In the normal rat kidney, the convoluted proximal tubular epithelial cells express CRBP-I; no expression is found in the interstitium, nor in the glomeruli. In the adriamycin-induced fibrotic rat kidney, CRBP-I expression diminishes in the convoluted proximal tubular epithelial cells, whereas peritubular myofibroblasts in the interstitium acquire CRBP-I expression.

CONCLUSIONS

In the tubulointerstitial compartment of the adriamycin-induced fibrotic rat kidney, CRBP-I is expressed in a different pattern than in the healthy rat kidney. As the convoluted proximal tubular epithelial cells dedifferentiate during fibrosis, CRBP-I expression decreases. Furthermore, de novo expression of CRBP-I is found in activated myofibroblast-like cells in the interstitium of adriamycin-treated rats. CRBP-I is therefore a useful marker to identify a subpopulation of activated/ myodifferentiated fibroblasts in the rat kidney.

N-acetyltransferase 8, a positional candidate for blood pressure and renal regulation: resequencing, association and in silico study

Background

Kidneys have an important function in blood pressure (BP) regulation and elevated BP may lead to kidney failure. Chr2p12-p13 region linked to BP traits in multiple studies harbours a potential candidate for BP and renal function, N-acetyltransferase 8 (NAT8) expressed in embryonic and adult kidney and associated with nephrotoxicity response.

Methods/Results

We report the first study exploring NAT8 as a potential candidate gene for blood pressure and kidney function. The resequencing (n = 42, random Estonian samples) identified 15 NAT8 polymorphisms, including 6 novel variants. The diversity of NAT8 5' upstream region (π/bp = 0.00320) exceeded up to 10 times the variation in the NAT8 genic region (π/bp = 0.00037) as well as the average variation (π/bp = 0.00040) for the promoters of 29 reference genes associated with hypertension. We suggest that a potential source for such high variation could be an active gene conversion process from NAT8B duplicate gene to NAT8. Similarly to NAT8, several reference genes with the most variable upstream regions have also duplicate copies. The NAT8 promoter SNPs were targeted with pilot quantitative association studies for blood pressure (n = 137, healthy unrelated individuals) and for the index of kidney function – estimated glomerular filtration rate (eGFR; n = 157 hypertensives with and without nephropathy). Minor alleles of these polymorphisms revealed a significant protective effect against elevated systolic BP as well as kidney failure in hypertension patients (p < 0.05; linear regression model, addictive effect).

Conclusion

The full resequencing and pilot association study of a novel positional candidate gene for blood pressure and renal function, human N-acetyltransferase 8, suggested a contribution of highly variable NAT8 promoter polymorphisms in determination of systolic blood pressure and eGFR. Based on in silico analysis, we raise the hypothesis that the alternative SNP alleles of the NAT8 upstream region may have differential effect on gene expression.

Interactive toxicity of inorganic mercury and trichloroethylene in rat and human proximal tubules: effects on apoptosis, necrosis, and glutathione status

Simultaneous or prior exposure to one chemical may alter the concurrent or subsequent response to another chemical, often in unexpected ways. This is particularly true when the two chemicals share common mechanisms of action. The present study uses the paradigm of prior exposure to study the interactive toxicity between inorganic mercury (Hg(2+)) and trichloroethylene (TRI) or its metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in rat and human proximal tubule. Pretreatment of rats with a subtoxic dose of Hg(2+) increased expression of glutathione S-transferase-alpha1 (GSTalpha1) but decreased expression of GSTalpha2, increased activities of several GSH-dependent enzymes, and increased GSH conjugation of TRI. Primary cultures of rat proximal tubular (rPT) cells exhibited both necrosis and apoptosis after incubation with Hg(2+). Pretreatment of human proximal tubular (hPT) cells with Hg(2+) caused little or no changes in GST expression or activities of GSH-dependent enzymes, decreased apoptosis induced by TRI or DCVC, but increased necrosis induced by DCVC. In contrast, pretreatment of hPT cells with TRI or DCVC protected from Hg(2+) by decreasing necrosis and increasing apoptosis. Thus, whereas pretreatment of hPT cells with Hg(2+) exacerbated cellular injury due to TRI or DCVC by shifting the response from apoptosis to necrosis, pretreatment of hPT cells with either TRI or DCVC protected from Hg(2+)-induced cytotoxicity by shifting the response from necrosis to apoptosis. These results demonstrate that by altering processes related to GSH status, susceptibilities of rPT and hPT cells to acute injury from Hg(2+), TRI, or DCVC are markedly altered by prior exposures.

Proteomic Analysis of Alternative Protein Tyrosine Phosphorylation in 1,2-Dichlorovinyl-Cysteine-Induced Cytotoxicity in Primary Cultured Rat Renal Proximal Tubular Cells

Toxicant exposure affects the activity of various protein tyrosine kinases. Using phosphotyrosine proteomics, we identified proteins that were differentially phosphorylated before renal cell detachment and apoptosis. Treatment of primary cultured rat proximal tubular epithelial cells with the model nephrotoxicant S-(1,2-dichlorovinyl)-L-cysteine (DCVC) resulted in early reorganization of F-actin stress fibers and formation of lamellipodia, which was followed by cell detachment from the matrix and apoptosis. This was prevented by genistein-mediated inhibition of protein tyrosine kinases and enhanced by inhibition of protein tyrosine phosphatases using vanadate. Phosphotyrosine proteomics revealed that DCVC-induced renal cell apoptosis was preceded by changes in the tyrosine phosphorylation status of a subset of proteins, as identified by matrix-assisted laser desorption ionization/time of flight-mass spectrometry (MS)/MS including actin-related protein 2 (Arp2), cytokeratin 8, t-complex protein 1 (TCP-1), chaperone containing TCP-1, and gelsolin precursor. The major differentially tyrosine-phosphorylated protein was Arp2, whereas phosphorylation of Arp3 was not affected. Arp2 was located in the lamellipodia that were formed before the onset of apoptosis. Because DCVC-induced cell detachment and apoptosis is regulated by tyrosine kinases, we propose that alterations in tyrosine phosphorylation of a subset of proteins, including Arp2, play a role in the regulation of the F-actin reorganization and lamellipodia formation that precede renal cell apoptosis caused by nephrotoxicants.

Signaling of Mitochondrial Biogenesis following Oxidant Injury

Mitochondrial dysfunction is a common consequence of ischemia-reperfusion and drug injuries. For example, sublethal injury of renal proximal tubular cells (RPTCs) with the model oxidant tert-butylhydroperoxide (TBHP) causes mitochondrial injury that recovers over the course of six days. Although regeneration of mitochondrial function is integral to cell repair and function, the signaling pathway of mitochondrial biogenesis following oxidant injury has not been examined. A 10-fold overexpression of the mitochondrial biogenesis regulator PPAR-gamma cofactor-1alpha (PGC-1alpha) in control RPTCs resulted in a 52% increase in mitochondrial number, a 27% increase in respiratory capacity, and a 30% increase in mitochondrial protein markers, demonstrating that PGC-1alpha mediates mitochondrial biogenesis in RPTCs. RPTCs sublethally injured with TBHP exhibited a 50% decrease in mitochondrial function and increased mitochondrial autophagy. Compared with the controls, PGC-1alpha levels increased 12-fold on days 1, 2, and 3 post-injury and returned to base line on day 4 as mitochondrial function returned. Inhibition p38 MAPK blocked the up-regulation of PGC-1alpha following oxidant injury, whereas inhibition of calcium-calmodulin-dependent protein kinase, calcineurin A, nitric-oxide synthase, and phosphoinositol 3-kinase had no effect. The epidermal growth factor receptor (EGFR) was activated following TBHP exposure, and the EGFR inhibitor AG1478 blocked the up-regulation of PGC-1alpha. Additional inhibitor studies revealed that the sequential activation of Src, p38 MAPK, EGFR, and p38 MAPK regulate the expression of PGC-1alpha following oxidant injury. In contrast, although Akt was activated following oxidant injury, it did not play a role in PGC-1alpha expression. We suggest that mitochondrial biogenesis following oxidant injury is mediated by p38 and EGFR activation of PGC-1alpha.

Key issues in the modes of action and effects of trichloroethylene metabolites for liver and kidney tumorigenesis

Trichloroethylene (TCE) exposure has been associated with increased risk of liver and kidney cancer in both laboratory animal and epidemiologic studies. The U.S. Environmental Protection Agency 2001 draft TCE risk assessment concluded that it is difficult to determine which TCE metabolites may be responsible for these effects, the key events involved in their modes of action (MOAs) , and the relevance of these MOAs to humans. In this article, which is part of a mini-monograph on key issues in the health risk assessment of TCE, we present a review of recently published scientific literature examining the effects of TCE metabolites in the context of the preceding questions. Studies of the TCE metabolites dichloroacetic acid (DCA) , trichloroacetic acid (TCA) , and chloral hydrate suggest that both DCA and TCA are involved in TCE-induced liver tumorigenesis and that many DCA effects are consistent with conditions that increase the risk of liver cancer in humans. Studies of S-(1,2-dichlorovinyl) -l-cysteine have revealed a number of different possible cell signaling effects that may be related to kidney tumorigenesis at lower concentrations than those leading to cytotoxicity. Recent studies of trichloroethanol exploring an alternative hypothesis for kidney tumorigenesis have failed to establish the formation of formate as a key event for TCE-induced kidney tumors. Overall, although MOAs and key events for TCE-induced liver and kidney tumors have yet to be definitively established, these results support the likelihood that toxicity is due to multiple metabolites through several MOAs, none of which appear to be irrelevant to humans.

In vitro viability of human cavernosal endothelial and fibroblastic cells after exposure to papaverine/phentolamine and prostaglandin E1

OBJECTIVE

To investigate the influence of commercially available vasoactive drugs on human cavernosal endothelial and fibroblastic cells in vitro, as although corporal fibrosis is a well known side-effect of intracavernosal injection therapy for erectile dysfunction, the possible detrimental effect of these agents on the endothelium lining the cavernosal vascular spaces is uncertain.

MATERIALS AND METHODS

Cultured primary endothelial (13) and fibroblastic cells (12), obtained from potent patients undergoing penile surgery, were exposed to different physiological dilutions of prostaglandin E1 (PGE1), papaverine/phentolamine or the respective triple-mix of these agents for 30 min. Viable cells were counted and cell metabolic activity measured in these cultures 48 h after drug exposure.

RESULTS

There was a significant dose-dependent decrease in the viable cell count after exposure to papaverine-containing formulations, probably because of the low pH of this substance. This cytotoxic effect was more pronounced in endothelial than in fibroblastic cells, and was not apparent in the PGE1 groups. The relative increase in cell metabolic activity in cultures affected by a moderate cytotoxic effect indicated a regenerative process.

CONCLUSION

These comparative results in endothelial and fibroblastic cell cultures suggest that the endothelium rather than the interstitium of the corpus cavernosum is more sensitive to side-effects produced by intracavernosal injection therapy with papaverine. Thus, unfavourable consequences on the function of the endothelial layer might be as important as the risk of interstitial fibrosis. As these effects were not detected for PGE1 this drug should be preferred to papaverine in clinical practice.

p38 kinase-mediated transactivation of the epidermal growth factor receptor is required for dedifferentiation of renal epithelial cells after oxidant injury

Renal proximal tubular cell (RPTC) dedifferentiation is thought to be a prerequisite for regenerative proliferation and migration after renal injury. However, the specific mediators and the mechanisms that regulate RPTC dedifferentiation have not been elucidated. Because epidermal growth factor (EGF) receptor activity is required for recovery from acute renal failure, we examined the role of the EGF receptor in dedifferentiation and the mechanisms of EGF receptor transactivation in primary cultures of RPTCs after oxidant injury. Exposure of confluent RPTCs to H2O2 resulted in 40% cell death, and surviving RPTCs acquired a dedifferentiated phenotype (e.g. elongated morphology and vimetin expression). The EGF receptor, p38, Src, and MKK3 were activated after oxidant injury and inhibition of the EGF receptor or p38 with specific inhibitors (AG1478 and SB203580, respectively) blocked RPTC dedifferentiation. Treatment with SB203580 or adenoviral overexpression of dominant negative p38alpha or its upstream activator, MKK3, inhibited EGF receptor phosphorylation induced by oxidant injury, whereas AG1478 had no effect on p38 phosphorylation. Inhibition of Src with 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP1) blocked MKK3 and p38 activation, and inhibition of MKK3 blocked p38 activation. In addition, inactivation of Src, MKK3, p38, or the EGF receptor blocked tyrosine phosphorylation of beta-catenin, a key signaling intermediate that is involved in the epithelial-mesenchymal transition and vimentin expression. These results reveal that p38 mediates EGF receptor activation after oxidant injury; that Src activates MMK3, which, in turn, activates p38; and that the EGF receptor signaling pathway plays a critical role in RPTC dedifferentiation.

Cytotoxicity of different intracavernous vasoactive drugs on cultured endothelial cells of human corpus cavernosum penis

OBJECTIVES

To investigate the cytotoxic effect of prostaglandin E(1) (PGE(1)), a standard combination of papaverine/phentolamine, and a triple mixture of these agents on human cavernosal endothelial cells using a cell culture model. The endothelial layer of the corpus cavernosum plays an important role in signal transduction of penile erection and is directly exposed to vasoactive agents after intracavernous injection for erectile dysfunction.

METHODS

Primary endothelial cells were obtained from the corpus cavernosum of 13 potent patients undergoing penile surgery. Cultured cells were exposed for 30 minutes to physiologic dilutions of 20 microg PGE(1), 30 mg papaverine/1 mg phentolamine, or the same dosages of the triple mixture of these agents, each dissolved in 5 to 50 mL sodium chloride. Lactate dehydrogenase release as a cytotoxicity marker was measured 6 hours after drug exposure, and the total cell metabolic activity was quantified after 48 hours with a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS)-based assay. Additionally, the amount of viable cells was identified with a dual fluorescent staining procedure.

RESULTS

The initial release of lactate dehydrogenase was elevated up to 3.2-fold in the concentrated papaverine/phentolamine and triple mixture group compared with PGE(1) and the control. After 48 hours, the papaverine-containing formulations led to a significant dose-dependent decrease in the viable cell count and metabolic activity of the cultures that was not noticed with PGE(1).

CONCLUSIONS

These in vitro data strongly suggest an unfavorable effect of vasoactive agents containing papaverine on cavernosal endothelial cells. Before fibrotic changes of the smooth muscle stroma, the functionally important endothelium of the corpus cavernosum might suffer significantly from intracavernous injection therapy. Therefore, papaverine should no longer be used for this indication.

Cytotoxicity of S-conjugates of the sevoflurane degradation product fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether (Compound A) in a human proximal tubular cell line

Fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE) is a fluorinated alkene formed by degradation of the volatile anesthetic sevoflurane in anesthesia machines. FDVE is nephrotoxic in rats but not humans. Rat FDVE nephrotoxicity is attributed to FDVE glutathione conjugation and bioactivation of subsequent FDVE-cysteine S-conjugates, in part by renal beta-lyase. Although FDVE conjugation and metabolism occur in both rats and humans, the mechanism for selective toxicity in rats and lack of effect in humans is incompletely elucidated. This investigation measured FDVE S-conjugate cytotoxicity in cultured human proximal tubular HK-2 cells, and compared this with known cytotoxic S-conjugates. HK-2 cells were incubated with FDVE and its GSH, cysteine S-mercapturic acid, cysteine S-sulfoxide, and mercapturic acid sulfoxide conjugates (0.1-2.7 mM) for 24 h. Cytotoxicity was determined by lactate dehydrogenase (LDH) release, total LDH, and the ability of viable cells to reduce a tetrazolium-based compound (MTT). FDVE was cytotoxic only at concentrations >/=0.9 mM. No increase in LDH release was observed with either FDVE-GSH conjugate. The FDVE-cysteine conjugates S-(1,1-difluoro-2-fluoromethoxy-2-(trifluoromethyl) ethyl)-L-cysteine (DFEC) and (Z)-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl) vinyl)-L-cysteine ((Z)-FFVC) caused significant differences in LDH release and MTT reduction only at 2.7 mM; (Z)-FFVC was slightly more cytotoxic. Both S-(1,1-difluoro-2-fluoromethoxy-2-(trifluoromethyl) ethyl)-L-cysteine sulfoxide (DFEC-SO) and (Z)-N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl) vinyl)-L-cysteine sulfoxide ((Z)-N-Ac-FFVC-SO) caused slightly greater changes in LDH release or total LDH than the corresponding equimolar DFEC and (Z)-N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl) vinyl)-L-cysteine ((Z)-N-Ac-FFVC) conjugates. In contrast to FDVE S-conjugates, S-(1,2-dichlorovinyl)-L-cysteine was markedly cytotoxic, at concentrations as low as 0.1 mM. These results show that human proximal tubular cells are relatively resistant to FDVE and FDVE S-conjugate cytotoxicity. This may partially explain the lack of FDVE nephrotoxicity in humans.

Roles of necrosis, Apoptosis, and mitochondrial dysfunction in S-(1,2-dichlorovinyl)-L-cysteine sulfoxide-induced cytotoxicity in primary cultures of human renal proximal tubular cells

S-(1,2-Dichlorovinyl)-L-cysteine (DCVC) is the penultimate nephrotoxic metabolite of the environmental contaminant trichloroethylene. Although metabolism of DCVC by the cysteine conjugate beta-lyase is the most studied bioactivation pathway, DCVC may also be metabolized by the flavin-containing monooxygenase (FMO) to yield DCVC sulfoxide (DCVCS). Renal cellular injury induced by DCVCS was investigated in primary cultures of human proximal tubular (hPT) cells by assessment of time- and concentration-dependent effects on cellular morphology, acute cellular necrosis, apoptosis, mitochondrial function, and cellular glutathione (GSH) status. Confluent hPT cells incubated with as little as 10 microM DCVCS for 24 h exhibited morphological changes, although at least 100 microM DCVCS was required to produce marked changes. Acute cellular necrosis did not occur until 48 h with at least 200 microM DCVCS, indicating that this is a high-dose, late response. The extent of necrosis was similar to that with DCVC. In contrast, apoptosis occurred as early as 1 h with as little as 10 microM DCVCS and the extent of apoptosis was much less than that with DCVC. Mitochondrial function was maintained with DCVCS concentrations up to 100 microM, consistent with hPT cells only being competent to undergo apoptosis at early time points and relatively low concentrations. Marked depletion (>50%) of cellular GSH content was only observed with 500 microM DCVCS. These results, combined with previous studies showing protection from DCVC-induced necrosis and apoptosis by the FMO inhibitor methimazole, suggest that formation of DCVCS plays a significant role in trichloroethylene-induced renal cellular injury in hPT cells.

Cellular energetics and glutathione status in NRK-52E cells: toxicological implications

Cellular energetics and redox status were evaluated in NRK-52E cells, a stable cell line derived from rat proximal tubules. To assess toxicological implications of these properties, susceptibility to apoptosis induced by S-(1,2-dichlorovinyl)-L-cysteine (DCVC), a well-known mitochondrial and renal cytotoxicant, was studied. Cells exhibited high activities of several glutathione (GSH)-dependent enzymes, including gamma-glutamylcysteine synthetase, GSH peroxidase, glutathione disulfide reductase, and GSH S-transferase, but very low activities of gamma-glutamyltransferase and alkaline phosphatase, consistent with a low content of brush-border microvilli. Uptake and total cellular accumulation of [14C]alpha-methylglucose was significantly higher when cells were exposed at the basolateral as compared to the brush-border membrane. Similarly, uptake of GSH was nearly 2-fold higher across the basolateral than the brush-border membrane. High activities of (Na(+)+K(+))-ATPase and malic dehydrogenase, but low activities of other mitochondrial enzymes, respiration, and transport of GSH and dicarboxylates into mitochondria were observed. Examination of mitochondrial density by confocal microscopy, using a fluorescent marker (MitoTracker Orange), indicated that NRK-52E cells contain a much lower content of mitochondria than rat renal proximal tubules in vivo. Incubation of cells with DCVC caused time- and concentration-dependent ATP depletion that was largely dependent on transport and bioactivation, as observed in the rat, on induction of apoptosis, and on morphological damage. Comparison with primary cultures of rat and human proximal tubular cells suggests that the NRK-52E cells are modestly less sensitive to DCVC. In most respects, however, NRK-52E cells exhibited functions similar to those of the rat renal proximal tubule in vivo.

Possible involvement of glutathione and p53 in trichloroethylene- and perchloroethylene-induced lipid peroxidation and apoptosis in human lung cancer cells

Trichloroethylene (TCE) and perchloroethylene (PERC) are volatile organic compounds (VOCs) that are primarily inhaled through the respiratory system. The aim of this study was to elucidate the role of glutathione (GSH) and p53 in TCE- and PERC-induced lung toxicity. Human lung adenocarcinoma cells NCI-H460 (p53-wild-type) have constitutively lower levels of GSH than NCI-H1299 (p53-null) cells. The results showed that exposure to vapor TCE and PERC produced a dose-dependent and more pronounced accumulation of H(2)O(2) in p53-WT H460 than p53-null H1299 cells. The accumulation of H(2)O(2) was accompanied by severe cellular damage, as indicated by the significant increase of lipid peroxidation and apoptosis in p53-WT H460 cells, but not p53-null H1299 cells. Cotreatment of p53-WT H460 cells with free radical scavengers, such as D-mannitol, uric acid, and sodium selenite, significantly attenuated the TCE- or PERC-induced lipid peroxidation. In contrast, depletion of GSH in p53-null H1299 cells enhanced TCE- or PERC-induced lipid peroxidation. The levels of p53 and Bax proteins were elevated, while Bcl-2 protein was downregulated in TCE- or PERC-treated p53-WT H460 cells. Activity of caspase 3, the apoptotic executioner, was also significantly enhanced in TCE- or PERC-treated cells. These data suggest that, in human lung cancer cells, GSH plays a vital role in the protection of TCE- and PERC-induced oxidative stress and apoptosis, which may be mediated through a p53-dependent pathway.

Apoptosis, necrosis, and cell proliferation induced by S-(1,2-dichlorovinyl)-L-cysteine in primary cultures of human proximal tubular cells

Apoptosis, necrosis, and cell proliferation induced by S-(1,2-dichlorovinyl)-L-cysteine (DCVC), the cysteine conjugate of the environmental and occupational contaminant trichloroethylene, were studied in primary cultures of human proximal tubular (hPT) cells. Cells from male and female donors were incubated with a range of concentrations of DCVC (10 to 1000 microM) for up to 48 h, and assessments of cellular morphology (phase-contrast microscopy), necrosis (lactate dehydrogenase (LDH) release), apoptosis(cell cycle analysis, annexin V staining, and caspase activation), and proliferation (cell cycle analysis and DNA synthesis) were made. Time- and concentration-dependent changes in cellular morphology, including elongation of cell shape, formation of intracellular vesicles, and formation of apoptotic bodies, were observed. Significant increases in LDH release occurred in hPT cells incubated with < or =100 microM DCVC for at least 24 h. hPT cells from males were modestly more sensitive to DCVC than those from females, with maximal LDH release of 78 and 65% in cells from males and females, respectively. Flow cytometry analysis of propidium iodide-stained and DCVC-treated hPT cells showed that apoptosis occurred at markedly lower concentrations (10 microM) and at much earlier incubation times (2 h) than necrosis. A small increase was also noted in the percentage of cells in S-phase after a 4-h treatment with as little as 10 microM DCVC, suggesting that cell proliferation was stimulated. This was supported further by increased DNA synthesis. These results show that DCVC causes apoptosis and enhances cell proliferation in hPT cells at environmentally relevant doses and at earlier time points and lower concentrations than necrosis.