Critical role of lipid peroxidation in carbon tetrachloride-induced loss of aminopyrine demethylase, cytochrome P-450 and glucose 6-phosphatase

Phytosomes as a Plausible Nano-Delivery System for Enhanced Oral Bioavailability and Improved Hepatoprotective Activity of Silymarin

Silymarin, a phyto-constituent derived from the plant Silybum marianum, has been widely acknowledged for its hepatoprotective activities. Nevertheless, its clinical utility is adversely hampered by its poor water-solubility and its limited oral bioavailability. The aim of this study was to investigate the efficacy of phospholipid-based phytosomes for enhancing the oral bioavailability of silymarin. The phytosomes were prepared using the solvent evaporation technique and were optimized using a full factorial design. The optimized silymarin phytosomal formulation was then characterized for particle size, surface morphology, aqueous solubility, and in vitro drug release. Furthermore, in vivo antioxidant activity, hepatoprotective activity and oral bioavailability of the optimized formula were investigated in a rat model. The prepared silymarin phytosomes were discrete particles with a porous, nearly smooth surface and were 218.4 ± 2.54 nm in diameter. In addition, the optimized silymarin phytosomal formulation showed a significant improvement in aqueous solubility (~360 µg/mL) compared to pure silymarin and manifested a higher rate and extent of silymarin release from the optimized formula in dissolution studies. The in vivo assessment studies revealed that the optimized silymarin phytosomal formulation efficiently exerted a hepatoprotective effect in a CCl₄-induced hepatotoxicity rat model via restoring the normal levels of antioxidant enzymes and ameliorating cellular abnormalities caused by CCl₄-intoxication. Most notably, as compared to pure silymarin, the optimized silymarin phytosomal formulation significantly improved silymarin oral bioavailability, as indicated by a 6-fold increase in the systemic bioavailability. Collectively, phytosomes might represent a plausible phospholipid-based nanocarrier for improving the oral bioavailability of phyto-constituents with poor aqueous solubility.

Phospholipid complex-loaded self-assembled phytosomal soft nanoparticles: evidence of enhanced solubility, dissolution rate, ex vivo permeability, oral bioavailability, and antioxidant potential of mangiferin

In this study, self-assembled phytosomal soft nanoparticles encapsulated with phospholipid complex (MPLC SNPs) using a combination of solvent evaporation and nanoprecipitation method were developed to enhance the biopharmaceutical and antioxidant potential of MGN. The mangiferin-Phospholipon® 90H complex (MPLC) was produced by the solvent evaporation method and optimized using central composite design (CCD). The optimized MPLC was converted into MPLC SNPs using the nanoprecipitation method. The physicochemical and functional characterization of MPLC and MPLC SNPs was carried out by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffractometer (PXRD), proton nuclear magnetic resonance (¹H-NMR), solubility, in vitro dissolution, oral bioavailability, and in vivo antioxidant studies. A CCD formed stable MPLC with the optimal values of 1:1.76, 50.55 °C, and 2.02 h, respectively. Characterization studies supported the formation of a complex. MPLC and MPLC SNPs both enhanced the aqueous solubility (~ 32-fold and ~ 39-fold), dissolution rate around ~ 98% via biphasic release pattern, and permeation rate of ~ 97%, respectively, compared with MGN and MGN SNPs. Liver function tests and in vivo antioxidant studies exhibited that MPLC SNPs significantly preserved the CCl₄-intoxicated liver marker and antioxidant marker enzymes, compared with MGN SNPs. The oral bioavailability of MPLC SNPs was increased appreciably up to ~ 10-fold by increasing the main pharmacokinetic parameters such as C_max, T_max, and AUC. Thus, MPLC SNPs could be engaged as a nanovesicle delivery system for improving the biopharmaceutical and antioxidant potential of MGN. Graphical abstract.

Nano-lipid Complex of Rutin: Development, Characterisation and In Vivo Investigation of Hepatoprotective, Antioxidant Activity and Bioavailability Study in Rats

The current study was aimed to develop an amphiphilic drug-lipid nano-complex of rutin:egg phosphatidylcholine (EPC) to enhance its poor absorption and bioavailability, and investigated the impact of the complex on hepatoprotective and antioxidant activity. Rutin nano-complexes were prepared by solvent evaporation, salting out and lyophilisation methods and compared for the complex formation. For the selected lyophilisation method, principal solvent DMSO, co-solvent (t-butyl alcohol) and rutin:EPC ratios (1:1, 1:2 and 1:3) were selected after optimisation. The properties of the nano-complexes such as complexation, thermal behaviour, surface morphology, molecular crystallinity, particle size, zeta potential, drug content, solubility, in vitro stability study, in vitro drug release, in vitro and in vivo antioxidant study, in vivo hepatoprotective activity and oral bioavailability/pharmacokinetic studies were investigated. Rutin nano-complexes were developed successfully via the lyophilisation method and found to be in nanometric range. Rutin nano-complexes significantly improved the solubility and in vitro drug release, and kinetic studies confirmed the diffusion-controlled release of the drug from the formulation. The nano-complex showed better antioxidant activity in vitro and exhibited well in vitro stability in different pH media. The in vivo study showed better hepatoprotective activity of the formulation compared to pure rutin at the same dose levels with improved oral bioavailability. Carbon tetrachloride (CCl₄)-treated animals (group II) failed to restore the normal levels of serum hepatic marker enzymes and liver antioxidant enzyme compared to the nano-complex-treated animals. The results obtained from solubility, hepatoprotective activity and oral bioavailability studies proved the better efficacy of the nano-complex compared to the pure drug.

Pendimethalin induces oxidative stress, DNA damage, and mitochondrial dysfunction to trigger apoptosis in human lymphocytes and rat bone-marrow cells

Pendimethalin (PM) is a dinitroaniline herbicide extensively applied against the annual grasses and broad-leaved weeds. There is no report available on PM-induced low-dose genotoxicity in human primary cells and in vivo test models. Such data gap has prompted us to evaluate the genotoxic potential of PM in human lymphocytes and rats. PM selectively binds in the minor groove of DNA by forming covalent bonds with G and C nitrogenous bases, as well as with the ribose sugar. PM induces micronucleus formation (MN) in human lymphocytes, indicating its clastogenic potential. Comet assay data showed 35.6-fold greater DNA damage in PM (200 μM)-treated human lymphocytes. Rat bone-marrow cells, at the highest dose of 50 mg/kg b w/day of PM also exhibited 10.5-fold greater DNA damage. PM at 200 μM and 50 mg/kg b w/day induces 193.4 and 229% higher reactive oxygen species generation in human lymphocytes and rat bone-marrow cells. PM-treated human lymphocytes and rat bone-marrow cells both showed dysfunction of mitochondrial membrane potential (ΔΨ _m). PM exposure results in the appearance of 72.2 and 35.2% sub-G₁ apoptotic peaks in human lymphocytes and rat bone-marrow cells when treated with 200 μM and 50 mg/kg b w/day of PM. Rats exposed to PM also showed imbalance in antioxidant enzymes and histological pathology. Overall, our data demonstrated the genotoxic and apoptotic potentials of PM in human and animal test models.

Soya phospholipid complex of mangiferin enhances its hepatoprotectivity by improving its bioavailability and pharmacokinetics

BACKGROUND

Mangiferin is a xanthonoid present in Mangifera indica. It has been reported for a variety of pharmacological activities, including hepatoprotection. However, the major disadvantage of mangiferin is its reduced biological activity due to poor absorption, low bioavailability and rapid elimination from the body after administration. The aim of this study was to prepare a phospholipid complex of mangiferin to overcome these limitations and to investigate the impact of the complex on hepatoprotective activity and bioavailability.

RESULTS

The results showed that the complex has an enhanced hepatoprotective and in vivo antioxidant activity as compared to pure mangiferin at the same dose level (30 and 60 mg kg⁻¹). The complex restored the levels of serum hepatic marker enzymes and liver antioxidant enzymes with respect to carbon tetrachloride-treated animals. The complex also increased the bioavailability of mangiferin in rat serum by 9.75-fold compared to pure mangiferin at the same dose level and enhanced the elimination half-life (t(1/2 el)) from 1.71 ± 0.12 h⁻¹ to 3.52 ± 0.27 h⁻¹.

CONCLUSION

The results suggested that the complexation of mangiferin with soya phospholipid enhanced the hepatoprotection and in vivo antioxidant activity, which may be due to the improved bioavailability and pharmacokinetics of mangiferin in rat serum.

The gallic acid-phospholipid complex improved the antioxidant potential of gallic acid by enhancing its bioavailability

Gallic acid (GA) is well known for its antioxidant and hepatoprotective activity, though its effectiveness is restricted due to rapid metabolism and elimination. To overcome these problems, gallic acid-phospholipid complex was prepared and the effect of phospholipid complexation was investigated on carbon tetrachloride (CCl4)-induced oxidative damage in rat liver. The complex significantly reduced the hepatic marker enzymes in rat serum and restored the antioxidant enzyme levels with respect to CCl4-induced group (P < 0.05 and P < 0.01). Also, the complex improved the pharmacokinetics of GA by increasing the relative bioavailability and elimination half-life. The study therefore suggests that phospholipid complexation has enhanced the therapeutic efficacy of GA which may be due to its improved absorption and increased bioavailability in rat serum.

The gallic acid-phospholipid complex improved the antioxidant potential of gallic acid by enhancing its bioavailability

Gallic acid (GA) is well known for its antioxidant and hepatoprotective activity, though its effectiveness is restricted due to rapid metabolism and elimination. To overcome these problems, gallic acid-phospholipid complex was prepared and the effect of phospholipid complexation was investigated on carbon tetrachloride (CCl4)-induced oxidative damage in rat liver. The complex significantly reduced the hepatic marker enzymes in rat serum and restored the antioxidant enzyme levels with respect to CCl4-induced group (P < 0.05 and P < 0.01). Also, the complex improved the pharmacokinetics of GA by increasing the relative bioavailability and elimination half-life. The study therefore suggests that phospholipid complexation has enhanced the therapeutic efficacy of GA which may be due to its improved absorption and increased bioavailability in rat serum.

Biotransformation of carbon tetrachloride in cultured neurons and astrocytes

The ability of brain neuronal cells to metabolize carbon tetrachloride (CCl(4)) has been studied in an attempt to explain earlier observed toxic effects of CCl(4) on these cells. The expression of cytochrome P-450, the glutathione (GSH) content and the activity of glutathione-S-transferase (GST) were measured in cultured neurons and astrocytes from chick embryo cerebral hemispheres. The metabolism of CCl(4) in the neuron and astrocyte cultures was also assessed by determining the formation of: CCl(2) in membrane preparations of these cells. In the membrane fractions of neurons and astrocytes, no measurable levels of cytochrome P-450 were observed. Nevertheless, neurons as well as astrocytes had a capacity for the metabolism of CCl(4). The metabolic capacity of the neurons was significantly greater than that of the astrocytes. The neuron cultures had a higher initial content of GSH and a higher control activity of GST than had the astrocytes. Neither the GSH level nor GST activity were significantly affected in the neuron cultures after exposure to CCl(4). In astrocyte cultures 2 mm CCl(4) slightly depleted the GSH level and significantly induced GST activity. At 3 mm CCl(4), GSH was depleted by 30% and by more than 50% at 4 mm CCl(4). It can be concluded that the metabolic activation of CCl(4) was higher in neurons than in astrocytes. This can explain the earlier observation of CCl(4)-induced lipid peroxidation in cultured neurons. Moreover, neuron GSH was not able to protect these cells against CCl(4)-induced peroxidative damage. In the astrocytes, on the other hand, GSH and GST appeared to have a role in detoxification of CCl(4).

Enhanced oral bioavailability and antioxidant profile of ellagic acid by phospholipids

Ellagic acid (EA) has been reported as a potent antioxidant from natural resources with several nutritional benefits. The major disadvantage of this phytoconstituent is its rapid elimination from the body after administration. To overcome this limitation, a novel dietary formulation of EA with phospholipid was developed to investigate the effect of this complex on carbon tetrachloride induced liver damage in rats. The antioxidant activity of the complex (equivalent of EA = 25 and 50 mg/kg of body weight) and free EA (25 and 50 mg/kg of body weight) was evaluated by measuring various enzymes in oxidative stress condition. The complex significantly protected the liver by restoring the activity of superoxide dismutase, catalase and liver glutathione, and thiobarbituric acid reactive substances with respect to the carbon tetrachloride treated group (P < 0.05 and < 0.01). The complex provided better protection to rat liver than free EA at the same dose. The serum concentration of EA obtained from the complex (equivalent to 80 mg/kg of EA) was higher (C(max) = 0.54 microg/mL) than that of pure EA (80 mg/kg) (C(max) = 0.21 microg/mL), and the complex maintained effective concentration for a longer period of time in serum. The experimental outcome highlighted better hepatoprotective activity of the EA complex due to its potential antioxidant property compared with the free EA tested at the same dose level.

Therapeutic antioxidant medical gas

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Ex vivo carbon monoxide prevents cytochrome P450 degradation and ischemia/reperfusion injury of kidney grafts

Renal ischemia/reperfusion injury is a major complication of kidney transplantation. We tested if ex vivo delivery of carbon monoxide (CO) to the kidney would ameliorate the renal injury of cold storage that can complicate renal transplantation. Orthotopic syngeneic kidney transplantation was performed in Lewis rats following 24 h of cold preservation in University of Wisconsin solution equilibrated without or with CO (soluble CO levels about 40 microM). Ischemia/reperfusion injury in control grafts resulted in an early upregulation of inflammatory mediator mRNAs and progressive deterioration of graft function. In contrast, the grafts preserved with CO had significantly less oxidative injury and this was associated with improved recipient survival compared to the control group. Renal injury in the control group showed considerable degradation of cytochrome P450 heme proteins, active heme metabolism and increased detrimental intracellular free heme levels. Kidney grafts preserved in CO-equilibrated solution maintained their cytochrome P450 protein levels, had normal intracellular heme levels and had less lipid peroxidation. Our results show that CO-mediated suppression of injurious heme-derived redox reactions offers protection of kidney grafts from cold ischemia/reperfusion injury.

[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.

Curcumin-phospholipid complex: Preparation, therapeutic evaluation and pharmacokinetic study in rats

A novel formulation of curcumin in combination with the phospholipids was developed to overcome the limitation of absorption and to investigate the protective effect of curcumin-phospholipid complex on carbon tetrachloride induced acute liver damage in rats. The antioxidant activity of curcumin-phospholipid complex (equivalent of curcumin 100 and 200 mg/kg body weight) and free curcumin (100 and 200 mg/kg body weight) was evaluated by measuring various enzymes in oxidative stress condition. Curcumin-phospholipid complex significantly protected the liver by restoring the enzyme levels of liver glutathione system and that of superoxide dismutase, catalase and thiobarbituric acid reactive substances with respect to carbon tetrachloride treated group (P < 0.05 and <0.01). The complex provided better protection to rat liver than free curcumin at same doses. Serum concentration of curcumin obtained from the complex (equivalent to 1.0 g/kg of curcumin) was higher (Cmax 1.2 microg/ml) than pure curcumin (1.0 g/kg) (Cmax 0.5 microg/ml) and the complex maintained effective concentration of curcumin for a longer period of time in rat serum. The result proved that curcumin-phospholipid complex has better hepatoprotective activity, owe to its superior antioxidant property, than free curcumin at the same dose level.

Role of CYP2E1 activity in endoplasmic reticulum ubiquitination, proteasome association, and the unfolded protein response

In an experimental model of liver cirrhosis, marked increases in ER proteasome content in rat livers were observed 5 h after acute i.p. injection of the hepatotoxicant CCl4. To confirm the role of CYP2E1 in mediating protein misfolding/damage in the ER via its metabolism of CCl4, 293T cells stably transfected with human CYP2E1 were exposed to CCl4 and cell ER fractions assessed for ubiquitination. Increases in ER ubiquitin conjugates were noted in CYP2E1/293T cells treated with CCl4 and not in controls, suggesting these effects are CYP2E1 specific. Finally, the role of CYP2E1 in ER homeostasis was investigated by examining the unfolded protein response (UPR). When exposed to CCl4, CYP2E1/293T cells but not 293T or CYP1A2/293T cells showed rapid induction of the UPR-inducible ER chaperone BiP. Collectively, the data presented suggest that CYP2E1 is capable of inducing significant ER protein damage and stress via its catalytic activation of pro-oxidants.

Isoprostanes: novel bioactive products of lipid peroxidation

Isoprostanes, are a novel group of prostaglandin-like compounds that are biosynthesised from esterified polyunsaturated fatty acid (PUFA) through a non-enzymatic free radical-catalysed reaction. Several of these compounds possess potent biological activity, as evidenced mainly through their pulmonary and renal vasoconstrictive effects, and have short half-lives. It has been shown that isoprostanes act as full or partial agonists through thromboxane receptors. Both human and experimental studies have indicated associations of isoprostanes and severe inflammatory conditions, ischemia-reperfusion, diabetes and atherosclerosis. Reports have shown that F2-isoprostanes are authentic biomarkers of lipid peroxidation and can be used as potential in vivo indicators of oxidant stress in various clinical conditions, as well as in evaluations of antioxidants or drugs for their free radical-scavenging properties. Higher levels of F2-isoprostanes have been found in the normal human pregnancy compared to non-pregnancy, but their physiological role has not been well studied so far. Since bioactive F2-isoprostanes are continuously formed in various tissues and large amounts of these potent compounds are found unmetabolised in their free acid form in the urine in normal basal conditions with a wide inter-individual variation, their role in the regulation of normal physiological functions could be of further biological interest, but has yet to be disclosed. Their potent biological activity has attracted great attention among scientists, since these compounds are found in humans and animals in both physiological and pathological conditions and can be used as reliable biomarkers of lipid peroxidation.

Hepatotoxicity and mechanism of action of haloalkanes: carbon tetrachloride as a toxicological model

The use of many halogenated alkanes such as carbon tetrachloride (CCl4), chloroform (CHCl3) or iodoform (CHI3), has been banned or severely restricted because of their distinct toxicity. Yet CCl4 continues to provide an important service today as a model substance to elucidate the mechanisms of action of hepatotoxic effects such as fatty degeneration, fibrosis, hepatocellular death, and carcinogenicity. In a matter of dose,exposure time, presence of potentiating agents, or age of the affected organism, regeneration can take place and lead to full recovery from liver damage. CCl4 is activated by cytochrome (CYP)2E1, CYP2B1 or CYP2B2, and possibly CYP3A, to form the trichloromethyl radical, CCl3*. This radical can bind to cellular molecules (nucleic acid, protein, lipid), impairing crucial cellular processes such as lipid metabolism, with the potential outcome of fatty degeneration (steatosis). Adduct formation between CCl3* and DNA is thought to function as initiator of hepatic cancer. This radical can also react with oxygen to form the trichloromethylperoxy radical CCl3OO*, a highly reactive species. CCl3OO* initiates the chain reaction of lipid peroxidation, which attacks and destroys polyunsaturated fatty acids, in particular those associated with phospholipids. This affects the permeabilities of mitochondrial, endoplasmic reticulum, and plasma membranes, resulting in the loss of cellular calcium sequestration and homeostasis, which can contribute heavily to subsequent cell damage. Among the degradation products of fatty acids are reactive aldehydes, especially 4-hydroxynonenal, which bind easily to functional groups of proteins and inhibit important enzyme activities. CCl4 intoxication also leads to hypomethylation of cellular components; in the case of RNA the outcome is thought to be inhibition of protein synthesis, in the case of phospholipids it plays a role in the inhibition of lipoprotein secretion. None of these processes per se is considered the ultimate cause of CCl4-induced cell death; it is by cooperation that they achieve a fatal outcome, provided the toxicant acts in a high single dose, or over longer periods of time at low doses. At the molecular level CCl4 activates tumor necrosis factor (TNF)alpha, nitric oxide (NO), and transforming growth factors (TGF)-alpha and -beta in the cell, processes that appear to direct the cell primarily toward (self-)destruction or fibrosis. TNFalpha pushes toward apoptosis, whereas the TGFs appear to direct toward fibrosis. Interleukin (IL)-6, although induced by TNFalpha, has a clearly antiapoptotic effect, and IL-10 also counteracts TNFalpha action. Thus, both interleukins have the potential to initiate recovery of the CCl4-damaged hepatocyte. Several of the above-mentioned toxication processes can be specifically interrupted with the use of antioxidants and mitogens, respectively, by restoring cellular methylation, or by preserving calcium sequestration. Chemicals that induce cytochromes that metabolize CCl4, or delay tissue regeneration when co-administered with CCl4 will potentiate its toxicity thoroughly, while appropriate CYP450 inhibitors will alleviate much of the toxicity. Oxygen partial pressure can also direct the course of CCl4 hepatotoxicity. Pressures between 5 and 35 mmHg favor lipid peroxidation, whereas absence of oxygen, as well as a partial pressure above 100 mmHg, both prevent lipid peroxidation entirely. Consequently, the location of CCl4-induced damage mirrors the oxygen gradient across the liver lobule. Mixed halogenated methanes and ethanes, found as so-called disinfection byproducts at low concentration in drinking water, elicit symptoms of toxicity very similar to carbon tetrachloride, including carcinogenicity.

Biochemical and histopathological changes in serum creatinine and kidney induced by inhalation of Thimet (Phorate) in male Swiss albino mouse, Mus musculus

This work was conducted to investigate the biochemical and histopathological changes in serum creatinine level and kidney of male Swiss albino mouse, Mus musculus, exposed to the recommended field dose of Thimet (20 kg ha(-1)). The animals were exposed to this dose in a whole-body inhalation chamber for 12 weeks and the biochemical and histopathological changes were studied in the 2nd, 4th, 6th, 8th, 10th, and 12th weeks of exposure. Creatinine level of serum was measured by the Jaffe method, and histopathological lesions were studied by the hematoxylin-eosin staining method. A significant rise in creatinine level was observed from the 4th week of exposure until the end of the experiment. This rise suggests impairment of the glomerular function and tubular damage in the kidneys. These changes were confirmed by histopathological studies in the tubules. Kidney lesions were present throughout the experimental period. These consisted of mild to severe multifocal cloudy and hydropic degeneration with necrosis in the tubules, though the glomerular damage was not seen by light microscopy. After a 30-day recovery period, the histopathological and biochemical changes were absent and normal patterns were restored.

Oxidative preconditioning affords protection against carbon tetrachloride-induced glycogen depletion and oxidative stress in rats

The rectal insufflation of a judicious dose of ozone, selected from that used in clinical practice, is able to promote oxidative preconditioning or oxidative stress tolerance preventing the hepatocellular damage mediated by free radicals. In order to evaluate the effects of ozone oxidative preconditioning on carbon tetrachloride-mediated hepatotoxicity, the following experimental protocol was designed: group 1 (negative control, sunflower oil i.p.); group 2 (CCl(4) in sunflower oil, 1 ml kg(-1) i.p.); group 3 (15 ozone-oxygen pretreatments at a dose of 1 mg kg(-1) via rectal insufflation + CCl(4) as in group 2); group 4 (ozone control group, 15 ozone-oxygen pretreatments + sunflower oil i.p.). Ozone pretreatment prevented glycogen depletion (as demonstrated by biochemical and histopathological findings) and avoided lactate overproduction associated with the hepatotoxic effects of CCl(4). The administration of CCl(4) increased lipid peroxidation (as measured by thiobarbituric acid-reactive substances) and uric acid levels and inhibited superoxide dismutase activity. All these deleterious effects induced by CCl(4) were prevented by ozone pretreatment. The administration of ozone without CCl(4) (ozone control group) did not produce any changes in the evaluated parameters. Our results showed that ozone treatment, in our experimental conditions, was able to prevent anaerobic glycolysis and oxidative stress induced by CCl(4).

Effects of ischemia-reperfusion on individual cytochrome P450 isoforms in the rat kidney

Ischemia-reperfusion of organs such as the kidney produces reactive oxygen and free radical species in tissues and leads to injury of intracellular molecules critical to cell homeostasis. Ischemia-reperfusion affects the NADPH-dependent monooxygenase system including P450 system, which is also a source of reactive oxygen species. In this study, the effects of ischemia-reperfusion on monooxygenase activity and levels of individual P450 isoforms including CYP2C23, 4A2, and 4A8 in the rat kidney were investigated. Ischemia of the rat kidney for 30 min had little effect on lauric acid hydroxylation activity and levels of P450 isoforms but ischemia for 60 min significantly decreased lauric acid omega- and (omega-1)-hydroxylation activities and also decreased the levels of CYP2C23, 4A2, and 4A8. Reperfusion for 60 min after 30-min ischemia decreased the levels of CYP2C23 and 4A2 in the rat kidney although 30-min ischemia did not. Reperfusion for 240 min after 30-min or 60-min ischemia recovered the decreased levels of lauric acid hydroxylation activity and the levels of CYP2C23 and 4A2. Changes in the levels of monooxygenase activity and the levels of P450 isoforms in kidneys by ischemia-reperfusion are faster than those in the liver; it takes several hours for ischemia-reperfusion to affect the levels of monooxygenase activity and the levels of P450 in the rat liver. Our findings suggest that damage of P450 isoforms in the kidney by ischemia-reperfusion occurs by a mechanism different from that in the liver and that active oxygen or free radical species directly attack proteins.

Depression of liver microsomal glucose 6-phosphatase activity in carbon tetrachloride-poisoned rats. Potential synergistic effects of lipid peroxidation and of covalent binding of haloalkane-derived free radicals to cellular components in the process

Depression of liver microsomal glucose-6-phosphatase (G6Pase) activity is a relevant feature of CCl4 poisoning. In vitro studies from several laboratories led to the hypothesis that a CCl4 promoted lipid peroxidation (LP) process is responsible for that effect. In vivo studies from our laboratory with potent antioxidants in dosage regimes inhibiting LP, however, were in contrast with that hypothesis. In this work we studied the potential preventive effects of Pyrazole (Pyr), alpha-tocopherol (alpha T), and 3-amino-1,2,4-triazole (AT) against CCl4-induced depression of G6Pase activity. Pyr decreases the intensity of the covalent binding (CB) of CCl4 reactive metabolites to cellular components but does not inhibit LP in vitro or in vivo. alpha T inhibits LP in vitro and in vivo and AT inhibits both CB and LP. Our present studies give evidence that AT but neither Pyr nor alpha T are able to prevent the CCl4-induced depression of G6Pase activity. Results are compatible with the hypothesis that the cooperation of both factors is critical to explain the observed effects, and suggest that under in vitro experimental conditions used by others the relevance of LP might be artifactually promoted.

Melatonin counteracts lipid peroxidation induced by carbon tetrachloride but does not restore glucose-6 phosphatase activity

Carbon tetrachloride (CCl4) exerts its toxic effects by the generation of free radicals. In this study we investigated whether melatonin, a potent free radical scavenger, could prevent the deleterious effects of CCl4. Liver homogenates and liver microsomes were incubated with CCl4 in the presence of melatonin and lipid peroxidation and glucose-6 phosphatase (G6Pase) activity were determined. All doses of CCl4 (1, 0.5, 0.1 mM) produced significantly high levels of lipid peroxidation, as reflected by increased levels of malonaldehyde and 4-hydroxyalkenals, in both liver homogenates and liver microsomes. These doses of CCl4 concommitantly reduced the activity of microsomal G6Pase. Co-incubation with melatonin dose-dependently (2, 1, 0.5 mM) inhibited the production of lipid peroxidation, but it was unable to restore the activity of G6Pase. In in vivo studies, rats were also treated with melatonin (10 mg/kg, i.p.), given 30 min before and 60 min after the administration of CCl4 (5 ml/kg, i.p.). Significantly elevated levels of lipid peroxidation were measured in the liver and kidney. Melatonin prevented the CCl4-induced lipid peroxidation in the kidney, but not in the liver. These data suggest that melatonin may provide protection against some of the damaging effects of CCl4, possibly due to its ability to scavenge toxic free radicals.

The role of glutathione and protein thiols in CBrCl3-induced cytotoxicity in isolated rat hepatocytes

The role of glutathione (GSH) and protein thiols in the pathobiochemical process of CBrCl3 cytotoxicity was investigated in isolated hepatocytes. Administration of 0.5, 1.0 and 1.5 mmol/l CBrCl3 affected cellular viability as assessed by trypan blue exclusion, release of lactate dehydrogenase and loss of intracellular potassium in a dose-dependent manner. Intracellular glutathione and the capacity to reduce 3-(4,5-dimethylthiazolyl-2-)-2,5-diphenyltetrazolium bromide (MTT, thiazolyl blue) decreased almost independently of the CBrCl3 concentration. Protein thiols were not markedly oxidized in the presence of CBrCl3. However, compromising cellular defence mechanisms by either inhibition of glutathione regeneration or depletion of glutathione enhanced the cytotoxicity of CBrCl3 and induced a loss of protein thiols in the late phase of cellular injury. Under these conditions the thiol-dependent Na+,K+ATPase revealed high sensitivity towards CBrCl3. Thus, glutathione proved to exert effective cytoprotection, and sulfhydryl groups of particular proteins were supposed to be an important target of radical attack.

Ferritin-dependent inactivation of microsomal glucose-6-phosphatase

Glucose-6-phosphatase (G6Pase) is a microsomal enzyme which is very sensitive to inactivation by lipid peroxidation. Experiments were carried out to evaluate whether ferritin, which is the major storage form of iron within cells, could catalyze inactivation of G6Pase and to determine the mechanism responsible for this effect of ferritin. Incubation of microsomes with NADPH in the absence of ferritin led to decreased activity of G6Pase. Ferritin stimulated this inactivation of G6Pase in a time- and concentration-dependent manner. Ferritin did not stimulate G6Pase inactivation when NADH replaced NADPH as the microsomal reductant. Superoxide dismutase but not catalase or DMSO prevented the ferritin-stimulated inactivation of G6Pase suggesting a role for superoxide, but not H2O2 or hydroxyl radical, in the overall mechanism. Trolox, at concentrations which prevent lipid peroxidation, also prevented the ferritin-catalyzed inactivation of G6Pase. Inhibition of G6Pase by ferritin was further enhanced in the presence of ATP but was inhibited in the presence of EDTA or desferrioxamine; ferric-ATP stimulates, whereas ferric-EDTA inhibits microsomal lipid peroxidation. The redox cycling agent paraquat increased the ability of ferritin to inactivate G6Pase by a reaction prevented by superoxide dismutase, trolox, EDTA, and desferrioxamine, but not by catalase or DMSO. Ferritin stimulated microsomal light emission, a reaction reflecting lipid peroxidation, with time and concentration dependence, and sensitivity to scavengers (trolox, superoxide dismutase), iron chelators and paraquat, identical to the inactivation of G6Pase. These results indicate that one possible toxicological consequence of ferritin-catalyzed lipid peroxidation is inhibition of microsomal enzymes such as G6Pase.

Age dependent different influence of carbon tetrachloride on biotransformation of xenobiotics, glutathione content, lipid peroxidation and histopathology of rat liver

15- and 60-day-old male rats were treated with different doses of CCl4 orally. 24 h later cytochrome P-450 (P450) concentration, 7-ethoxyresorufin O-deethylation (EROD) and 7-pentoxy-resorufin O-deethylation (PEROD) activities were determined. Whereas P450 and EROD are lowered to the same extent in both ages, PEROD shows a more pronounced inhibition in the livers of younger rats. The formation of endogenous lipid peroxides (measured as thiobarbituric acid reactive substances) is drastically increased only in the livers of young rats. The hepatic glutathione (GSH) content was unaffected by CCl4 treatment whereas oxidized glutathione is more increased in the livers of adult rats. This can be caused by a higher activity of GSH-peroxidase in the livers of adult rats. The changes in NADPH-induced lipid peroxidation and chemiluminescence correlate partially with the changes in P450 and biotransformation reactions. Histopathologically the liver damage is more extensive in suckling rats. The necrosis is localized predominantly in the perivenous tissue, which has normally the highest activities of toxification and detoxification enzymes.

Effect of phenobarbital treatment on carbon tetrachloride-mediated cytochrome P-450 loss and diene conjugate formation

The effect of phenobarbital treatment on the linkage between carbon tetrachloride-mediated cytochrome P-450 loss and lipid peroxidation in rat liver microsomes was studied. Male Sprague-Dawley rats, pretreated with 3 daily i.p. doses of phenobarbital (50 mg/kg) or saline, were orally dosed with carbon tetrachloride (0.01-2.5 ml/kg), with liver microsomes prepared at 7.5-180 min after carbon tetrachloride treatment. In vivo cytochrome P-450 loss displayed pseudo-first-order kinetics, and the initial rates of diene conjugate formation were saturable with dose. Phenobarbital pretreatment decreased the in vivo t0.5,max from 27.0 to 15.6 min, and increased the Kd,app from 0.78 to 1.30 ml/kg for carbon tetrachloride mediated cytochrome P-450 loss. Phenobarbital had no effect on the in vivo Vmax (1.03 to 1.04 delta OD232 nm/min/mg phospholipid) for carbon tetrachloride mediated diene conjugate formation, but decreased the Km,app from 0.22 to 0.10 ml/kg. These results are consistent with destruction of cytochrome P-450 heme resulting from a metabolite which does not leave the site of generation, and with phenobarbital pretreatment enhancing the initiation of lipid peroxidation.

In vivo NMR, biochemical, and histologic evaluation of alcohol-induced fatty liver in rat and a comparison with CCl4 hepatotoxicity

Magnetic resonance imaging (MRI) and spectroscopy (MRS) were used to follow the time course of ethanol-induced fatty liver in a group of 10 rats fed a diet containing 12% alcohol (ethanol) over a 5-week period. The MR data consisted of T1-weighted images, in vivo 1H spectra, and in vivo T1 relaxation measurements. Changes in short TR images as a result of fatty accumulation were noted only as a slight increase in liver intensity relative to surrounding muscle. A poorly correlated (r = 0.54) increase in water T1 with time was observed. No statistically significant changes in lipid T1 were found. MRS derived lipid content was compared with biochemically derived total lipids and histology. MRS determined liver lipids were found to increase linearly with time (r = 0.91). Biochemically derived lipid content also increased with prolonged exposure to ethanol (r = 0.96). The averages of MRS derived lipid content agreed well with the average changes in biochemically determined total lipid concentration. Histologic examination revealed slight to moderate changes in fatty accumulation with significant variation in the group at the end of the study. On an individual basis the MRS and histologic evaluation were highly correlated (r = 0.94).

Endrin-induced histopathological changes and lipid peroxidation in livers and kidneys of rats, mice, guinea pigs and hamsters

Endrin toxicity may be due to an oxidative stress associated with increased lipid peroxidation, decreased glutathione content, and inhibition of glutathione peroxidase activity. Extensive interspecies variability exists in sensitivity towards endrin. Therefore, histopathological changes and lipid peroxidation in the livers and kidneys of rats, mice, hamsters, and guinea pigs were examined 24 hr after the administration of 4 mg endrin/kg body weight orally in corn oil. Degeneration and necrotic changes with inflammatory cell infiltration were observed in livers and kidneys, and interspecies variability occurred. Fatty changes in the form of hepatic foam cells with cytoplasmic vacuolation were present. Lipofuscin pigments, associated with lipid peroxidation, were observed in hepatocytes and Kupffer cells. These histopathological conditions were prevented in rats which had been pretreated with butylated hydroxyanisole, vitamins E and C, or cysteine, antioxidants and free radical scavengers which have previously been shown to inhibit lipid peroxidation. The extent of endrin-induced lipid peroxidation correlated well with the degree of histopathological changes. Thus, histological changes consistent with the induction of an oxidative stress were observed following the administration of endrin to various animal species.

Lipid peroxidation caused by hyperthermic perfusion of rat liver

The data presented support the premise that hyperthermia-induced hepatocellular injury is the end result of lipid peroxidation. Evidence for lipid peroxidation is the formation of diene conjugates and the decrease in microsomal P450 and glucose-6-phosphatase activity during hyperthermic liver perfusion.

NADPH- and adriamycin-dependent microsomal release of iron and lipid peroxidation

In a previous study (Minotti, G., 1989, Arch. Biochem. Biophys. 268, 398-403) NADPH-supplemented microsomes were found to reduce adriamycin (ADR) to semiquinone free radical (ADR-.), which in turn autoxidized at the expense of oxygen to regenerate ADR and form O2-. Redox cycling of ADR was paralleled by reductive release of membrane-bound nonheme iron, as evidenced by mobilization of bathophenanthroline-chelatable Fe2+. In the present study, iron release was found to increase with concentration of ADR in a superoxide dismutase- and catalase-insensitive manner. This suggested that membrane-bound iron was reduced by ADR-. with negligible contribution by O2-. or interference by its dismutation product H2O2. Following release from microsomes, Fe2+ was reconverted to Fe3+ via two distinct mechanisms: (i) catalase-inhibitable oxidation by H2O2 and (ii) catalase-insensitive autoxidation at the expense of oxygen, which occurred upon chelation by ADR and increased with the ADR:Fe2+ molar ratio. Malondialdehyde formation, indicative of membrane lipid peroxidation, was observed when approximately 50% of Fe2+ was converted to Fe3+. This occurred in presence of catalase and low concentrations of ADR, which prevented Fe2+ oxidation and favored only partial Fe2+ autoxidation, respectively. Lipid peroxidation was inhibited by superoxide dismutase via increased formation of H2O2 from O2-. and excessive Fe2+ oxidation. Lipid peroxidation was also inhibited by high concentrations of ADR, which favored maximum Fe2+ release but also caused excessive Fe2+ autoxidation via formation of very high ADR:Fe2+ molar ratios. These results highlighted multiple and diverging effects of ADR, O2-., and H2O2 on iron release, iron (auto-)oxidation and lipid peroxidation. Stimulation of malondialdehyde formation by catalase suggested that lipid peroxidation was not promoted by reaction of Fe2+ with H2O2 and formation of hydroxyl radical. The requirement for both Fe2+ and Fe3+ was indicative of initiation by some type of Fe2+/Fe3+ complex.

Relationship between hepatic glutathione content and carbon tetrachloride-induced hepatotoxicity in vivo

The relationship between carbon tetrachloride (CCl4)-induced hepatotoxicity and hepatic glutathione (GSH) content was investigated in fed and fasted rats. The elevation of serum glutamic-pyruvic transaminase (GTP) activity by CCl4 treatment was enhanced by fasting. Although the hepatic GSH content fo 12-hour-fasted rats was higher than that of fed rats determined at 6 p.m., the serum GPT activity of the former was higher than that of the latter. Starvation had no effect on the activities of hepatic glutathione peroxidase (GSH-Px) and glutathione reductase (GR). The results suggest that the potentiation of hepatic injury by CCl4 cannot be related to hepatic GSH content.

Three models of free radical-induced cell injury

Three models of free radical-induced cell injury are presented in this review. Each model is described by the mechanism of action of few prototype toxic molecules. Carbon tetrachloride and monobromotrichloromethane were selected as model molecules for alkylating agents that do not induce GSH depletion. Bromobenzene and allyl alcohol were selected as prototypes of GSH depleting agents. Paraquat and menadione were presented as prototypes of redox cycling compounds. All these groups of toxins are converted, during their intracellular metabolism, to active species which can be radical species or electrophilic intermediates. In most cases the activation is catalyzed by the microsomal mixed function oxidase system, while in other cases (e.g. allyl alcohol) cytosolic enzymes are responsible for the activation. Radical species can bind covalently to cellular macromolecules and can promote lipid peroxidation in cellular membranes. Of course both phenomena produce cell damage as in the case of CCl4 or BrCCl3 intoxication. However, the covalent binding is likely to produce damage at the molecular site where it occurs; lipid peroxidation, on the other hand, besides causing loss of membrane structure, also gives rise to toxic products such as 4-hydroxyalkenals and other aldehydes which in principle can move from the site of origin and produce effects at distant sites. Electrophilic intermediates readily reacts with cellular nucleophiles, primarily with GSH. The result is a severe GSH depletion as in the case of bromobenzene or allyl alcohol intoxication. When the depletion reaches some threshold values lipid peroxidation develops abruptly and in an extensive way. This event is accompanied by cellular death. The reason for which lipid peroxidation develops in a cell severely depleted of GSH remains to be clarified. Probably the loss of the defense systems against a constitutive oxidative stress is not compatible with cellular life. Some free radicals generated by one-electron reduction can react with oxygen to give superoxide anions which can be converted to other more dangerous reactive oxygen species. This is the case of paraquat and menadione. Damage to cellular macromolecules is due to the direct action of these oxygen radicals and, at least in the menadione-induced cytotoxicity, lipid peroxidation is not involved. All these initial events affect the protein sulfhydryl groups in the membranes. Since some protein thiols are essential components of the molecular arrangement responsible for the Ca2+ transport across cellular membranes, loss of such thiols can affect the calcium sequestration activity of subcellular compartments, that is the capacity of mitochondria and microsomes to regulate the cytosolic calcium level.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in rat lung microsomal lipids after p-xylene: relationship to inhibition of benzo[a]pyrene metabolism

The relationship between p-xylene's effects on microsomal membranes, cytochrome P-450, and benzo[a]pyrene (BaP) metabolism was studied. p-Xylene (1 g/kg, ip, 1 h) inhibited 3-hydroxy BaP (3-OH) formation and decreased arylhydrocarbon hydroxylase (AHH) activity approximately 40% in rat lung microsomes. BaP dihydrodiol and quinone formation were unchanged by p-xylene administration. Cytochrome P-450 was below the limit of detection in lung microsomes from p-xylene-treated rats. Total phospholipid (PL) and phosphatidylcholine (PC) in microsomal membranes were decreased 28% and 17%, respectively. Cholesterol (CL), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and sphingomyelin (SM) were unchanged. The net activity of enzymes involved in the synthesis of PC, phosphatidylethanolamine-N-methyltransferase I and II (PMT I and PMT II), was slightly elevated by p-xylene. PL/CL and PC/PE ratios, indicators of membrane fluidity, were decreased 34% and 13%, respectively, in microsomes from p-xylene-treated rats. Analysis of fluidity by fluorescence polarization showed that the actual fluidity of treated microsomes was slightly decreased (5%) as compared to controls. The decrease in P-450, PL, and PC is considered to contribute to the inhibition of BaP metabolism.

Reactive intermediates and their toxicological significance

Many chemicals that cause toxicity do so via metabolism to biologically reactive metabolites. However, the nature of the interaction between such reactive metabolites and various cellular components, and the mechanism(s) by which these interactions eventually lead to cell death are poorly understood. The relative importance of macromolecular alkylation (covalent binding), lipid peroxidation, alterations in thiol, calcium and energy homeostasis are discussed with reference to specific toxicants. It is concluded that the cytotoxic effects of reactive metabolites are a consequence of simultaneous and/or sequential alterations in several cellular processes. Further studies are required to determine the relationship between these alterations and cell death.

No effect of modulators of reactive oxygen-induced pathology on microcystin-LR intoxication

Because reactive oxygen species are formed during the metabolism of several toxins that cause similar pathologic changes, we hypothesized that compounds that alter the concentration of reactive oxygen species would alter the toxic effects of the peptide-hepatotoxin produced principally by Microcystis aeruginosa. Pretreatment with alloxan, butylated hydroxyanisole or desferrioxamine did not alter the severity of microcystin-LR intoxication in fed mice. Furthermore, fasting mice for 24 hr before testing, which unmasks lipid peroxidation in paracetamol intoxication, did not alter the effect of butylated hydroxyanisole pretreatment.

The role of lipid peroxidation in liver damage

The consequences of the peroxidative breakdown of membrane lipids have been considered in relation to both the subcellular and tissue aspects of liver injury. Mitochondrial functions can be impaired by lipid peroxidation probably through the oxidation of pyridine nucleotides and the consequent alteration in the uptake of calcium. Several enzymatic functions of the endoplasmic reticulum are also affected as a consequence of peroxidative events and among these are the activities of glucose 6-phosphatase, cytochrome P-450 and the calcium sequestration capacity. Moreover, a release of hydrolytic enzymes from lysosomes and a decrease in the fluidity of plasma membranes can contribute to the liver damage consequent to the stimulation of lipid peroxidation. Extensive studies carried out in vivo and integrated with the use of isolated hepatocytes have shown that lipid peroxidation impairs lipoprotein secretion mainly at the level of the dismission from the Golgi apparatus, rather than during their assembly. However, such an alteration appears to give a late and not essential contribution to the fat accumulation. A more critical role is played by peroxidative reactions in the pathogenesis of acute liver necrosis induced by several pro-oxidant compounds as indicated by the protective effects against hepatocyte damage exerted by antioxidants. In addition, even in the cases where lipid peroxidation has been shown not to be essential in causing cell death there is evidence that it can still act synergistically with other damaging mechanisms in the amplification of liver injury.

Tetrachloromethane metabolism in vivo under normoxia and hypoxia. Biochemical and histopathological effects relative to alkane exhalation

About 250 mumol/kg tetrachloromethane is metabolized by male Sprague-Dawley rats receiving a dose of 500 mumol/kg by inhalation. Determination of enzyme activities and histopathological assessment show that various parameters reflecting cellular injury do not differ for the same amount of tetrachloromethane metabolized under different oxygen partial pressures. On the other hand, the amounts of ethane and pentane exhaled under hypoxic conditions are greater than under normoxia. The previously reported differences in the toxicity of tetrachloromethane upon exposure under normoxia or hypoxia seem to be mainly due to the different amounts of tetrachloromethane metabolized under both conditions.

Changes in rat hepatic microsomal mixed function oxidase activity following exposure to halothane under various oxygen concentrations

This study demonstrates that the exposure of phenobarbitone-treated rats to halothane at an oxygen concentration of either 10% or 14% results in marked decreases in cytochrome P-450 content and aminopyrine demethylase activity in animals sacrificed from 1 to 48 hr post-exposure. The alterations observed in the hepatic mixed function oxidase system were accompanied by increases in serum alanine aminotransferase (ALT), ornithine carbamyl transferase (OCT) and changes in liver pathology. However, the minor changes in cytochrome P-450 content and aminopyrine demethylase activity observed following exposure of enzyme-induced rats to halothane under normoxic conditions (i.e. 21% oxygen) were not of a sufficient magnitude to lead to hepatic cell necrosis. Halothane administration in the absence of phenobarbitone pretreatment (i.e. 21% oxygen) or during hypoxia alone (i.e. either 10% or 14% oxygen) did not result in any systematic changes in the parameters assayed. The results suggest that cytochrome P-450 may catalyse its own inactivation by virtue of greater free radical production under conditions which favour the non-oxygen dependent metabolism of halothane. The impairment in microsomal function as evidenced by decreases in cytochrome P-450 and aminopyrine demethylase activity are considered to occur as a primary consequence of the reductive metabolism of halothane. Data are presented which support the concept of the initiation of hepatic damage occurring during the period of anaesthesia with halothane.

Inhibition of microsomal cytochrome c reductase activity by a series of alpha, beta-unsaturated aldehydes

alpha, beta-Unsaturated aldehydes are reactive and cytotoxic compounds which occur in the environment and are also formed in vivo. Many of these aldehydes have been reported to inhibit hepatic cytochrome P-450. Our laboratory has shown that trans,trans-muconaldehyde (a possible metabolite of benzene) as well as acrolein and crotonaldehyde, when added to hepatic microsomes, decreased cytochrome P-450 (measured spectrophotometrically). Additional studies showed that several alpha, beta-unsaturated aldehydes also inhibited hepatic microsomal NADPH-cytochrome c reductase. Acrolein, crotonaldehyde and trans,trans-muconaldehyde all decreased NADPH-cytochrome c reductase activity in vitro. Concentrations of 0.5, 1.0 and 1.5 mM acrolein decreased activity to 60, 26 and 11% of control respectively. Similar concentrations of trans,trans-muconaldehyde inhibited NADPH-cytochrome c reductase. Crotonaldehyde was a less effective inhibitor of this enzyme. Propionaldehyde, a saturated aldehyde, had no effect on NADPH-cytochrome c reductase activity. Time course experiments with acrolein over a period of 5-45 min suggest that the loss of NADPH-cytochrome c reductase activity is non-linear. The addition of reduced glutathione protected against the inhibition of reductase activity by acrolein. Formation of these aldehydes and their subsequent inhibition of these enzymes may have important consequences in xenobiotic metabolism.

Mechanisms mediating cephaloridine inhibition of renal gluconeogenesis

Incubation of renal cortical slices with cephaloridine (CPH) markedly inhibits pyruvate-supported gluconeogenesis, an effect which is independent of CPH-induced lipid peroxidation. CPH was found to inhibit pyruvate-supported gluconeogenesis in a time-and concentration-dependent manner. Pyruvate-supported gluconeogenesis was inhibited as early as 10 min following incubation of renal cortical slices with 5 mM CPH. Similarly, endogenous gluconeogenesis was impaired following CPH treatment. CPH depressed the renal cortical slice content of ATP by 50%, but only following 90 and 120 min of drug exposure, suggesting that mitochondrial dysfunction does not mediate the inhibition of gluconeogenesis by CPH. To identify the intracellular site(s) of CPH inhibition of gluconeogenesis, the effects of CPH on glucose production were evaluated using substrates catalyzed by rate-limiting reactions. CPH inhibited renal cortical slice gluconeogenesis when the following substrates were used: pyruvate (mitochondrial), oxaloacetate and fructose-1,6-diphosphate (FDP) (postmitochondrial), and glucose-6-phosphate (G6P, endoplasmic reticulum). Inhibition of G6P-supported gluconeogenesis occurred within 5 min of incubation with 5 mM CPH. Direct addition of CPH to microsomal suspensions inhibited G6Pase activity in a concentration-dependent fashion. By contrast, addition of CPH to cytosolic fractions did not affect FDPase activity. CPH increased the Km and decreased the Vmax of G6Pase, indicating mixed competitive and noncompetitive inhibition. These data indicate that the profound inhibition of renal cortical slice gluconeogenesis by CPH is mediated by inhibition of microsomal G6Pase activity.

Effects of carbon tetrachloride on the liver of chickens. Early biochemical and ultrastructural alterations in the absence of detectable lipid peroxidation

Administration of CCl4 i.p. to Leghorn chickens did not promote lipid peroxidation of liver microsomal lipids, as evidenced by either increased diene conjugation or by decreased arachidonic acid content. The hepatotoxin did not produce liver necrosis 24 h after dosing, but decreased the cytochrome P-450 content, and aminopyrine N-demethylase and glucose 6 phosphatase activities at 1, 3, 6 and 24 h. CCl4 administration produced dilation of the rough endoplasmic reticulum and detachment of ribosomes from their membranes. These observations suggest that lipid peroxidation is not the key event in the production of these biochemical and ultrastructural alterations, elicited by CCl4.

Potentiation of carbon tetrachloride hepatotoxicity by chlordecone: dose-response relationships and increased covalent binding in vivo

Chlordecone greatly potentiates carbon tetrachloride (CCl4) hepatotoxicity. In order to quantitate the degree of this potentiation, the effects of a range of doses of CCl4 on two microsomal enzymatic functions and liver enzyme release were examined in chlordecone-treated and control rats. Male Sprague-Dawley rats were pretreated with 15 mg chlordecone per kilogram body weight (BW) intragastrically or with vehicle. After 48 hours, 0 to 250 microliters CCl4 per 100 g body weight were given intraperitoneally (IP), and the rats were killed 24 hours later. Chlordecone treatment produced approximately a 17-fold potentiation of the CCl4-dependent loss of cytochrome P-450 and glucose-6-phosphatase activity, so that a dose of 6 microliters CCl4 per 100 g body weight in the chlordecone-treated animals resulted in a similar amount of damage as observed with 100 microliters CCl4 per 100 g body weight in controls. A similar potentiation by chlordecone was seen with CCl4 induced increases in serum glutamic-oxaloacetic transaminase (SGOT) levels. Chlordecone treatment also increased hepatic cytochrome P-450 levels by 67% and resulted in an increase in the covalent binding of [14-C]-CCl4-derived metabolites to microsomal protein and lipid in vivo.

The role of acrolein in allyl alcohol-induced lipid peroxidation and liver cell damage in mice

Male NMRI mice were fed a sucrose diet for 48 hr in order to reduce the hepatic glutathione content and to level off its diurnal variation. After administration of allyl alcohol (AA: 1.1 mmol/kg), hepatic glutathione (24.3 +/- 7.0 nmol GSH/mg protein) was almost totally lost within the first 15 min (less than 0.5 nmol GSH/mg protein). Subsequently, a massive lipid peroxidation was observed, i.e. the animals exhaled 414 +/- 186 nmol ethane/kg/hr compared to 0.9 +/- 0.8 of controls, and the hepatic TBA-reactive compounds had increased from 55 +/- 16 pmol/mg protein in controls to 317 +/- 163 after 1 hr. Concomitantly, a 40-45% loss of the polyunsaturated fatty acids (arachidonic and docosahexaenoic acid) in the liver lipids was observed. About 80% of the cytosolic alcohol dehydrogenase activity and about 50% of the microsomal P450-content were destroyed. In vivo-inhibition of alcohol dehydrogenase by pyrazole or induction of aldehyde dehydrogenase by phenobarbital abolished AA-induced liver damage as well as glutathione depletion and lipid peroxidation, while inhibition of aldehyde dehydrogenase by cyanamide made a subtoxic dose of AA (0.60 mmol/kg) highly toxic. These results strongly favour the importance of acrylic acid formation as an additional detoxification pathway. Enhanced hepatic levels of glutathione protected in vivo against the damaging effects of AA. Depletion of the liver glutathione content by phorone or diethylmaleate alone caused marginally enhanced lipid peroxidation (phorone) but not liver cell damage. Monooxygenase inhibitors (metyrapone, diethyldithiocarbamate, alpha-naphthoflavone) or an inducer (benz(a)pyrene) did not affect AA-induced toxicity. The ferric iron chelator desferoxaminemethanesulfonate prevented AA-induced lipid peroxidation and liver cell damage in vivo. In vitro, acrolein alone failed to initiate lipid peroxidation in soy bean phospholipid liposomes or in mouse liver microsomes. Thus, acrolein not only impairs the glutathione defense system but also directly destroys cellular proteins and evokes lipid peroxidation by an indirect iron-depending mechanism.

Chlordecone does not interfere with hepatic repair after carbon tetrachloride or partial hepatectomy

The effect of chlordecone (CD) on hepatic repair, measured either as recovery of microsomal enzymatic functions or as the induction of cytosolic thymidine kinase (TK) activity, was evaluated in rats given carbon tetrachloride (CCl4). Carbon tetrachloride was administered to CD-potentiated and control animals using doses of this hepatotoxin which produce similar degrees of damage at 24 hours in both groups of animals (6 and 100 microliters CCl4 per 100 g body weight, respectively). Chlordecone had no significant effect on the time course of recovery of microsomal cytochrome P-450 content or glucose-6-phosphatase activity following CCl4 administration. Hepatic TK activity was measured 48 hours after CCl4 administration as a biochemical index of the hepatic regenerative response. Thymidine kinase activity was increased eightfold in CD-treated rats receiving 6 microliters CCl4 per 100 g body weight, whereas in controls a similar induction of TK activity was produced by 100 microliters CCl4 per 100 g body weight. Therefore, the TK response in CD-treated rats receiving CCl4 is appropriate for the amount of damage produced, suggesting that CD does not inhibit the hepatic regenerative response to CCl4-induced injury. The effect of CD on hepatic repair was also examined in rats receiving a two-thirds partial hepatectomy. Pretreatment of animals with CD had no significant effect on the increase in TK activity produced 24 hours after partial hepatectomy. These results offer no support for the idea that CD impairs hepatic repair after either partial hepatectomy or CCl4 administration.

Role of reactive oxygen intermediates in the hepatotoxicity of endotoxin

Administration of endotoxin (2.5 micrograms/mouse, iv) to Corynebacterium parvum-pretreated (14 days earlier, 1 mg/mouse, i.v.) mice caused a rapid (90 min) decrease in liver cytochrome P450-dependent drug metabolism and an elevation of serum transaminase. The time course of the priming effect of C. parvum suggested that macrophages might be responsible for this sensitization to endotoxin. The antioxidant N-acetylcysteine (500 mg/kg) effectively protected against this depression of liver drug metabolism, thus supporting the hypothesis that liver macrophage-generated free radicals might mediate this hepatotoxic effect of endotoxin.