Histological detection of lipid peroxidation following infusion of tert-butyl hydroperoxide and ADP-iron complex in perfused rat livers

Ethanol Disrupts Hormone-Induced Calcium Signaling in Liver

Receptor-coupled phospholipase C (PLC) is an important target for the actions of ethanol. In the ex vivo perfused rat liver, concentrations of ethanol >100 mM were required to induce a rise in cytosolic calcium (Ca²⁺) suggesting that these responses may only occur after binge ethanol consumption. Conversely, pharmacologically achievable concentrations of ethanol (≤30 mM) decreased the frequency and magnitude of hormone-stimulated cytosolic and nuclear Ca²⁺ oscillations and the parallel translocation of protein kinase C-β to the membrane. Ethanol also inhibited gap junction communication resulting in the loss of coordinated and spatially organized intercellular Ca²⁺ waves in hepatic lobules. Increasing the hormone concentration overcame the effects of ethanol on the frequency of Ca²⁺ oscillations and amplitude of the individual Ca²⁺ transients; however, the Ca²⁺ responses in the intact liver remained disorganized at the intercellular level, suggesting that gap junctions were still inhibited. Pretreating hepatocytes with an alcohol dehydrogenase inhibitor suppressed the effects of ethanol on hormone-induced Ca²⁺ increases, whereas inhibiting aldehyde dehydrogenase potentiated the inhibitory actions of ethanol, suggesting that acetaldehyde is the underlying mediator. Acute ethanol intoxication inhibited the rate of rise and the magnitude of hormone-stimulated production of inositol 1,4,5-trisphosphate (IP₃), but had no effect on the size of Ca²⁺ spikes induced by photolysis of caged IP₃. These findings suggest that ethanol inhibits PLC activity, but does not affect IP₃ receptor function. We propose that by suppressing hormone-stimulated PLC activity, ethanol interferes with the dynamic modulation of [IP₃] that is required to generate large, amplitude Ca²⁺ oscillations.

An overview of the toxic effect of potential human carcinogen Microcystin-LR on testis

The worldwide occurrence of cyanobacterial blooms due to water eutrophication evokes extreme concerns. These blooms produce cyanotoxins which are hazardous to living organisms. So far among these toxins, Microcystin-LR (MC-LR) is the most toxic and the most frequently encountered toxin produced by the cyanobacteria in the contaminated aquatic environment. Microcystin-LR is a potential carcinogen for animals and humans, and the International Agency for Research on Cancer has classified Microcystin-LR as a possible human carcinogen. After liver, testis has been considered as one of the most important target organs of Microcystin-LR toxicity. Microcystin-LR crosses the blood–testis barrier and interferes with DNA damage repair pathway and also increases expression of the proto-oncogenes, genes involved in the response to DNA damage, cell cycle arrest, and apoptosis in testis. Toxicity of MC-LR disrupts the motility and morphology of sperm and also affects the hormone levels of male reproductive system. MC-LR treated mice exhibit oxidative stress in testis through the alteration of antioxidant enzyme activity and also affect the histopathology of male reproductive system. In the present review, an attempt has been made to comprehensively address the impact of MC-LR toxicity on testis.

[Learning toxicology from carbon tetrachloride-induced hepatotoxicity]

The mechanism of carbon tetrachloride (CCl4)-induced hepatotoxicity, especially necrosis and fatty liver, has long been a challenging subject of many researchers from various fields over the past 50 years. Even though the mechanisms of tissue damages are different among chemicals and affected tissues, CCl4 has played a role as a key substance of tissue injury. A number of studies have been conducted and various hypotheses have been raised. As a result, several important basic mechanisms of tissue damages have emerged, involving metabolic activation, reactive free radical metabolites, lipid peroxidation, covalent binding and disturbance of calcium homeostasis. Recent studies also revealed inflammation and regeneration as important modification factors in the tissue injury. The author attempted to summarize the history of CCl4 research with some emphasis on the experiments done by the author and his colleagues. Their studies with isolated perfused rat liver suggest that covalent binding of CCl4 metabolites rather than lipid peroxidation has a significant role in the production of centrilobular necrosis following CCl4 administration. Further studies are necessary to unveil detailed mechanisms of hepatocyte necrosis induced by CCl4.

Histochemical visualization of oxidant stress

Free radicals induce oxidative modification in distinct components of the living matter (lipid, proteins, and DNA). For qualitative and quantitative determination of free radical-induced modifications, different, more or less sensitive biochemical methods are available. Because of the high reactivity and short life of free radicals, ongoing oxidative damage is generally analyzed by measurement of secondary products-such as H(2)O(2), oxidized proteins, peroxidized lipids, and their breakdown products, oxidized DNA-or by fluorographic analysis in combination with fluorescent dyes such as dichlorofluorescin (DCFH). In addition, the determination of free radical-related oxidation products is usually carried out in plasma, urine, or, less frequently, in bioptic material. Consequently, biochemical data seldom reflect the effects of free radical insults in situ. The histochemical visualization of selected molecular markers of oxidative damage can often provide more valuable information concerning the in vivo distribution of oxidative processes. This review summarizes the methods currently available for histochemical detection and indirect visualization of free radical-induced alterations in tissues and isolated cells.

Carbon tetrachloride-induced cell death in perfused livers from phenobarbital-pretreated rats under hypoxic conditions and various ionic milieu. Further evidence for calcium-dependent irreversible changes

The role of Ca2+ in the initiation of carbon tetrachloride (CCl4) hepatotoxicity was studied using perfused livers isolated from phenobarbital-pretreated rats in a single-pass system. Krebs-Henseleit bicarbonate buffer containing 1.3 mM CaCl2 (KHB) was the regular ionic milieu. In the liver perfused with fructose-supplemented regular KHB equilibrated with 95% N2-5% CO2, infusion of 0.5 mM CCl4 caused an early uptake of Ca2+ coupled with K+ leakage and Na+ uptake within the infusion time of 30 min, which was followed by a marked lactic dehydrogenase (LDH) leakage into the effluent perfusate and further Ca2+ uptake by the liver. With Ca(2+)-free medium, the prenecrotic K+ leakage and the successive LDH leakage were suppressed markedly. However, a perfusate exchange from regular to Ca(2+)-free KHB at the end of the prenecrotic stage did not protect against the LDH leakage, and the perfusate exchange conversely did not produce LDH leakage. Perfusion of the liver with high K+(Cl-) medium under 20% O2 markedly suppressed CCl4-induced LDH leakage even in the presence of Ca2+, whereas once CCl4 had acted under regular KHB perfusion, changing the medium to high K+ did not further prevent the LDH leakage. High K(+)-lactobionic acid medium containing Ca2+ and supplemented with fructose also suppressed LDH leakage under 95% N2 without the accompanying prenecrotic Ca2+ uptake. However, a change of the medium after CCl4 infusion to regular KHB containing Ca2+ caused LDH leakage and K+ leakage, with Ca2+ uptake. The prevention of LDH leakage in a different ionic milieu may not be due to suppression of CCl4 bioactivation, since the liver cytochrome P450 content decreased to a similar extent. These findings suggest that entry of extracellular Ca2+ into hepatocytes coupled with K+ leakage and Na+ entry is a prerequisite for CCl4-induced hepatocyte death and that association of Ca2+ with a CCl4-derived radical-mediated process may be necessary for early and irreversible plasma membrane damage.

K(+)-driven sinusoidal efflux of glutathione disulfide under oxidative stress in the perfused rat liver

Tert-butyl hydroperoxide (BHP), hydrogen peroxide and diamide caused a rapid and simultaneous release of glutathione disulfide (GSSG) and K+ in the isolated perfused rat liver. Both BHP-induced effluxes were suppressed by prior depletion of hepatic glutathione, but not by co-infusion of desferrioxamine which prevented lipid peroxidation and cell death. High K+ media decreased the GSSG efflux even though hepatic GSSG levels remained high. The GSSG and K+ effluxes were repeatable if cellular K+ recovered after a short BHP exposure. Ouabain inhibited the K+ re-uptake and decreased the response to repeated BHP challenge. Thus, sinusoidal efflux of GSSG under oxidative stress may be driven by a K+ gradient.

Cardiotoxic effects of nitrofurantoin and tertiary butylhydroperoxide in vitro: are oxygen radicals involved?

Langendorff rat hearts were perfused for 15, 30 or 75 min. with the oxygen radical generators nitrofurantoin (0.25 or 0.5 mmol/l) or tertiary butylhydroperoxide (0.25 mmol/l). Both agents reduced the force of contraction and increased the release of glutathione, oxidized glutathione, lactate dehydrogenase and creatine phosphokinase into the perfusion fluid. The tissue concentration of glutathione was reduced. While there were no signs of an increased production of conjugated dienes, the tissue concentration of malondialdehyde was greater than in control experiments. The variability of the latter effect was large, however, and in most cases the increase was not statistically significant. Addition of catalase (100 mU/ml) or catechin (0.5 mmol/l) to the perfusion medium abolished the nitrofurantoin induced release of oxidized glutathione but did not not prevent or attenuate enzyme leakage from the cells and the development of a negative inotropic effect. These results suggest that the cardiotoxic effects of nitrofurantoin and tertiary butylhydroperoxide cannot be explained by the appearance of oxygen radicals alone and that an increased lipid peroxidation is not the mechanism which is primarily responsible for cell death.