Inhibition of S-(1,2-dichlorovinyl)-L-cysteine-induced lipid peroxidation by antioxidants in rabbit renal cortical slices: dissociation of lipid peroxidation and toxicity

Association of XRCC1, XRCC3, and XPD genetic polymorphism with an increased risk of hepatocellular carcinoma because of the hepatitis B and C virus

OBJECTIVE

The south-east Asian and sub-Saharan African populations are the most susceptible to hepatocellular carcinoma (HCC). We aimed to establish whether XRCC1, XRCC3, and XPD are associated with liver cancer in Pakistan and to examine the interaction of hepatitis B virus (HBV) or hepatitis C virus (HCV) with repaired genes in the occurrence of liver cancer.

MATERIALS AND METHODS

We enrolled 74 healthy individuals, 75 had either HBV or HCV, and 50 were HCC patients. The characteristic information of all the study participants were collected through a standard interviewer-administered questionnaire. The PCR-RFLP was used to identify the genotype of the patients.

RESULTS

The results of our study indicated that the patients infected with HBV or HCV had a four or three-fold greater risk of developing liver cancer. Patients older than 55 years of age had a significantly higher risk of developing cancer compared with younger patients. The homozygous wild types Arg/Arg for 280 and Thr/Thr for 241 were more frequent in the controls than in the cases. The allelic frequency of mutant 280His and 399Gln was more pronounced among HCC cases than the controls or the HBV-infected patients.

CONCLUSION

The frequency of the XPD gene in the controls was in Hardy-Weinberg equilibrium, indicating that the gene played a protective role in the Pakistani population. XRCC1 or XRCC3 was associated with liver cancer in the Pakistani population; however, the XPD gene played a vital role in the repair of DNA damage.

Mechanistic analysis of S-(1,2-dichlorovinyl)-L-cysteine-induced cataractogenesis in vitro

Chronic exposure to low concentrations of the nephrotoxic cysteine conjugate S-(1,2-dichlorovinyl)-l-cysteine (DCVC) causes cataracts in mice. This study explored mechanisms of DCVC-induced cataractogenesis using explanted lenses from male Sprague-Dawley rats. Lenses placed in organ culture were exposed to 2.5 microM-1 mM DCVC for 24 hr. DCVC caused concentration and time-dependent changes in biochemical markers of toxicity (lenticular adenosine 5'-triphosphate (ATP) content, mitochondrial reduction of the tetrazolium dye MTT, and glutathione (GSH) content) at concentrations >/=25 microM. Lens clarity was adversely affected at concentrations >/=50 microM. Within 24 hr, 1 mM DCVC altered lens ATP content (-77 +/- 2%), mitochondrial MTT reduction (-40 +/- 3%), and GSH content (-19 +/- 4%) (percent difference from controls, p < 0.05). ATP was the most sensitive index of DCVC exposure in this model, while lens weight was not altered. The role of lenticular DCVC metabolism was investigated using the beta-lyase inhibitor aminooxyacetic acid (AOA) and the flavin monooxygenase (FMO) inhibitor methimazole (MAZ). AOA (1 mM) provided nearly complete protection from changes in biochemical parameters and lens transparency caused by DCVC, while MAZ (1 mM) provided only partial protection. The mitochondrial Ca2+ uniport inhibitor ruthenium red (30 microM) and the poly(ADP ribosyl)transferase inhibitor 3-aminobenzamide (3 mM) were only partially protective, whereas adverse changes in lens transparency and biochemical markers were not prevented by an antioxidant (2 mM dithiothreitol) or nontoxic transport substrates (200 microM probenecid or 10 mm phenylalanine, S-benzyl-L-cysteine or para-aminohippuric acid). Calpain inhibitors E64d (100 microM) and calpain inhibitor II (1 mM) were ineffective in preventing opacity formation caused by DCVC. In a small separate study, DCVC toxicity to explanted lenses from cynomologus monkeys was also ameliorated by coincubation with AOA. These results indicate that opacity formation by DCVC in rodent and primate lenses in vitro is primarily mediated via lenticular beta-lyase metabolism of DCVC to a reactive metabolite. Metabolism of DCVC by FMO and perturbations in mitochondrial calcium (Ca2+) homeostasis and increased poly(ADP-ribosylation) of nuclear proteins may play a limited role in opacity formation in vitro. However, opacity formation does not appear to be the result of oxidative stress or calpain activation. DCVC toxicity to the lens was not blocked with competitive inhibitors of the amino acid and organic anion transporters of DCVC as is found in the kidney.

Prevention of postasphyxia electroretinal dysfunction with a pyridoxal hydrazone

The newborn retina is particularly sensitive and frequently subjected to peroxidative stresses that result in visual sequelae. We compared two iron chelators, deferoxamine and a newer compound, pyridoxal isonicotinoyl hydrazone (PIH), in protecting the retina of newborn pigs (1-3 d old) from asphyxia-reoxygenation insults. Animals were treated IV with either saline, deferoxamine 15.2 mumol/kg (10 mg/kg) or PIH 34.8 mumol/kg (10 mg/kg); n = 10 in each treatment group. Scotopic and photopic electroretinograms (ERG) were recorded before and 40 min after drug treatment as well as 45 min following a 5-min period of asphyxia by interrupting ventilation. In separate animals the indices of peroxidation, malondialdehyde (MDA: TBARS) and hydroperoxides, were measured in retina at the same times. In saline-treated animals, there was a marked increase in MDA and hydroperoxide concentrations in the retina following the asphyxia-reoxygenation period. This was associated with a decrease in the a- (photoreceptor generated) and b-wave (generated by Müller and bipolar cells) amplitudes measured under photopic (cone-mediated response) and scotopic (rod-mediated response) conditions, and an increase in their implicit times. PIH and deferoxamine prevented the postasphyxial increase in MDA and hydroperoxides. However, only PIH prevented the postasphyxial changes in a- and b-wave amplitudes and implicit times, whereas deferoxamine markedly altered the preasphyxial ERG and provided only partial postasphyxial protection simply to the retinal outer segment. Our findings indicate that the iron chelator PIH effectively inhibits peroxidation and retinal electrophysiological alterations secondary to asphyxia-reoxygenation-induced oxidative stresses to newborn animals, whereas deferoxamine adversely affects retinal function; hence, PIH may be a preferred alternative to deferoxamine.

S-(1,2-dichlorovinyl)-L-cysteine-induced nephrotoxicity in the New Zealand white rabbit: characterization of proteinuria and examination of the potential role of oxidative injury

S-(1,2-dichlorovinyl)-L-cysteine (DCVC)-induced nephrotoxicity in vivo was investigated in New Zealand White rabbits. A primary emphasis in these studies was further characterization of DCVC-induced nephrotoxicity using a variety of serum and urinary analytes, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Additionally, the role of oxidative injury was assessed to address the dichotomy between reports indicating that such a mechanism is important in vivo and those indicating that such mechanisms do not contribute substantially to the mechanism of effects observed in vitro. Urine was collected prior to and at 8 and 24 hr after iv administration of DCVC. Serum was collected 15 min prior to and 24 hr after DCVC administration. Rabbits were euthanized 24 hr post-DCVC administration, and kidneys were fixed in formalin and further processed for light microscopic examination. DCVC (10 mg/kg, iv) induced a 45-50-fold increase in total urinary protein excretion, a 10-15-fold increase in urinary N-acetyl-beta-D-glucosaminidase concentration, plus a marked glucosuria by 24 hr postadministration. Additionally, DCVC increased serum creatinine levels by about 2-fold, with a trend toward increased blood urea nitrogen. SDS-PAGE analysis of rabbit urine confirmed the clinical finding of marked proteinuria in DCVC-treated animals, which in contrast to previously reported data was due to the presence of both low and high molecular weight proteins. Antioxidants had no significant effect on DCVC-dependent renal injury, nor was there evidence for DCVC-induced lipid peroxidation, as measured by either thiobarbituric acid-reactive substances or a commercial assay for malondialdehyde and hydroxalkenals.(ABSTRACT TRUNCATED AT 250 WORDS)