Studies on the role of protein synthesis in cell injury by toxic agents: I. Effect of cycloheximide administration on several factors modulating carbon tetrachloride-induced liver necrosis

Cycloheximide pretreatment (1 mg/kg, ip) slightly attenuated the hepatic necrosis 24 hr after CCl₄ administration and this attenuation was more obvious at 72 hr. A dose of cycloheximide, 2 mg/kg, evoked a marked protective effect even at 24 hr. Cycloheximide administration (1 mg/kg) significantly reduced the body temperature in CCl₄-treated rats but did not change the CCl₄ concentrations in the liver. Prior treatment of the rats with cycloheximide decreased the amount of binding of ¹⁴CCl₄ to liver microsomal lipids and reduced CCl₄-induced lipid peroxidation at 1 hr but not at 6 hr after administration of the hepatotoxin. Cycloheximide did not alter the pentobarbital sleeping time of the rats nor did it interact with microsomes to give spectral changes. Cycloheximide did not alter microsomal cytochrome P-450 reductase activity. Administration of cycloheximide prior to CCl₄ did not prevent the CCl₄-induced decrease in cytochrome P-450 or glucose 6-phosphatase activity caused by the hepatotoxin. However it did prevent the CCl₄-induced polysome breakdown and it did attenuate the severity of the lesions caused by CCl₄ at the ultrastructural level.     

Dose-response effects of various metal ions on rat liver metallothionein,glutathione, heme oxygenase,and cytochrome P-450

Adult male rats received ip injections of the maximum tolerable dose (MTD; μmol/kg/day, in parentheses following metal), or a fraction thereof, of Hg (5), Cd (20), Se (25), Ag (65), Cu (75), Co (100), Ni (120), Zn (200), Mn (250), Fe (300), Pb (400), or Cr (400) 36 and 12 hr before sacrifice. MTDs were estimated from previous studies, and at least three serial dilutions ($\text{1}\text{2}$, $\text{1}\text{4}$, $\text{1}\text{8}$, etc.) of the MTDs were tested for each metal. The effects of metal treatment on hepatic heme oxygenase activity (HO), cytochrome P-450, reduced glutathione (GSH) and metallothionein (MT), and renal MT and GSH were determined. Nine metals increased HO at the MTD, but only Cd, Se, Mn, and Pb increased HO at lower doses. These four metals plus Ag and Cr depressed cytochrome P-450 levels at the MTD, but only Cd, Mn, and Pb depressed cytochrome P-450 at a lower dose. Se increased hepatic GSH at the two highest doses, but all other metals had little or no effect. Kidney GSH was increased by all metals except Cd, Ag, Cu, and Cr, to a maximum level of only 150% of control (Pb). Cd and Zn induced hepatic MT in a dose-related manner to 420 and 580% of control, respectively. On a molar basis, Cd was about eight times more potent than Zn in increasing hepatic MT concentration. Hg, Ni, Mn, Fe, Pb, and Cr also significantly increased hepatic MT, but only to 150–200% of control. Pb had a slight but significant effect on hepatic MT at all doses down to 1/16th the MTD. This effect of PB, as well as other metals having a small effect on MT, may be the result of the effects of stress on MT rather than the metal ion per se. Renal MT was effectively induced by Hg, Cd, Cu, Ni, Zn, and Pb. Relatively small amounts of Hg (0.62 μmol/kg/day) significantly increased renal MT when compared to the minimum effective dose of Cd (10 μmol/kg/day) or Zn (50 μmol/kg/day). In conclusion, metals have a number of effects on potential hepatic and renal biochemical defense mechanisms. Most of the metals lacked specificity, affecting a number but not all of the parameters examined. However, of the 12 metals examined, Zn was the most selective in that it produced marked increases in MT and little or no effect on the other parameters, whereas Cd had the broadest effect, altering all parameters except GSH.     

The effect of alcohols and toluene upon methylene chloride-induced carboxyhemoglobin in the rat and monkey.

Twenty-four hours following administration of CCl₄ (1 ml/kg, ip), plasma activities of aspartate aminotransferase were elevated to the same extent in adult rats and in rats as young as 4 days of age. Similarly, treatment with CCl₄ produced the same degree of triglyceride accumulation in liver of adult rats and rats as young as 4 days of age. The presence of microsomal conjugated dienes, a measure of lipid peroxidation, was observed in adult and developing rats treated with CCl₄. In vitro binding of ¹⁴C derived from ¹⁴CCl₄ to hepatic microsomal protein and lipid was significantly lower in 4- and 14-day-old rats than in adults. These results demonstrate that rats as young as 4 days of age are as susceptible as adults to CCl₄-induced hepatotoxicity, although they have a lower capacity to metabolize CCl₄. Blood concentrations of acetoacetate were three to five times higher in young rats than in adult animals. The mechanism for the high degree of CCl₄-induced liver damage in young rats is not known but may be similar to the mechanisms by which alcohols and diabetes potentiate CCl₄ toxicity.     

Dose-response relationships in 1,3-butanediol-induced potentiation of carbon tetrachloride toxicity

Pretreatment of rats with 1,3-butanediol (BD) (1.0, 5.0, or 10.0% in drinking water) for 7 days enhanced the hepatotoxic, but not the nephrotoxic, effect of a single dose of CCl₄ (0.1 ml/kg, ip) in a dose-related manner. Biochemical tests and light microscopy were employed to assess toxicity. The smallest dosage of BD needed to potentiate CCl₄ hepatotoxicity was estimated to be between 0.1 and 1.0 g/kg/day. The potentiated response appeared to be related to the severity of the metabolic ketosis produced by BD. Pretreatment with BD (10.0%) resulted in increased hepatic microsomal activity and cytochrome P-450 content; the in vitro binding of ¹⁴CCl₄-derived radioactivity to microsomal protein was increased both aerobically and anaerobically, but was greater under aerobic conditions. BD appeared to potentiate CCl₄ liver injury, at least in part, by producing an increase and/or alteration in mixed function activation of CCl₄ to toxic metabolites. Pretreatment with BD (1.0, 10.0%) also resulted in a reduction of hepatic glutathione content. Thus, BD potentiation may arise through several, interrelated pathways.     

Enhanced hepatotoxicity of carbon tetrachloride, thioacetamide, and dimethylnitrosamine by pretreatment of rats with ethanol and some comparisons with potentiation by isopropanol.

Elevated plasma glutamic-pyruvic transaminase (GPT) activity induced by carbon tetrachloride (CCl₄), thioacetamide, or dimethylnitrosamine in male rats was increased by pretreatment with four doses (each 5 ml/kg) of ethanol orally 48, 42, 24, and 18 hr before the hepatotoxic agent. The potentiated hepatotoxicity of CCl₄ was confirmed by histologic evaluation. During the pretreatment, blood ethanol concentrations fluctuated between 0 and 300 mg/100 ml, but were less than 5 mg/100 ml when a hepatotoxic agent was injected ip. Pretreatment with ethanol did not affect the hepatic concentrations of CCl₄ or its metabolite, chloroform (CHCl₃), at 1 hr after administration of CCl₄. The CCl₄-induced diene conjugation tended to increase after ethanol pretreatment and was significantly potentiated by pretreatment with isopropanol or pyrazole and a single dose of ethanol. In rats pretreated with ethanol, covalent binding of ¹⁴CCl₄ to liver protein and lipid in vivo was significantly greater at 6 and 24 hr, but not during the first 3 hr, than in control rats. The in vitro binding of ¹⁴CCl₄, ¹⁴CHCl₃, and ¹⁴CBrCl₃ to hepatic microsomal protein was increased by ethanol pretreatment. Ethanol pretreatment also doubled the in vitro rate of demethylation of dimethyl-nitrosamine by liver microsomes, but did not affect the amount of microsomal protein and cytochrome P-450, NADPH c reductase activity nor the rate of N-demethylation of ethylmorphine. The similarities in microsomal effects of pretreatment with isopropanol and pretreatment with four doses of ethanol suggest that similar mechanisms are involved in their potentiation of CCl₄-induced hepatotoxicity. The potentiation by pretreatment with ethanol, but not with isopropanol, of the hepatotoxicity of thioacetamide and dimethylnitrosamine suggests that ethanol pretreatment also activates some additional mechanisms.     

Antifibrotic effects of ZK14, a novel nitric oxidedonating biphenyldicarboxylate derivative, on rat HSC-T6 cells and CCI4-induced hepatic fibrosis

Aim:

To study the pharmacologic effect of ZK₁₄, a novel nitric oxide-donating biphenyldicarboxylate (DDB) derivative, on HSC-T6 cells and on CCl₄-induced hepatic fibrosis.

Methods:

Inhibition of HSC-T6 cell growth by ZK₁₄ was evaluated by MTT assay. The effect of ZK₁₄ on the percentage of HSC-T6 cells undergoing apoptosis was measured using Annexin-V/PI double-staining and TUNEL assay. Mitochondrial membrane potential (MMP) and caspase activities were tested. Hepatic fibrosis was induced in Sprague-Dawley rats by intraperitoneal injection with 14% CCl₄. Rats with hepatic fibrosis were randomly divided into four groups: model control, ZK₁₄ (20 mg/kg), ZK₁₄ (10 mg/kg) and DDB (5 mg/kg). Levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), hyaluronic acid (HA), type III collagen (PCIII), and nitric oxide (NO) were assessed, and liver samples were stained with hematoxylin-eosin. The NO level in cells treated with ZK₁₄ in vitro was also measured.

Results:

The effect of ZK₁₄ on HSC-T6 cell apoptosis was concentration- and time-dependent, with up to 50% of cells becoming apoptotic when exposed to 100 μmol/L ZK₁₄ for 18 h. ZK₁₄ treatment resulted in mitochondrial membrane depolarization and activation of caspases 3 and 9. At a dose of 20 mg/kg, ZK₁₄ significantly decreased serum transaminase (AST, ALT) activities and fibrotic index (HA, PCIII) levels and significantly inhibited fibrogenesis.

Conclusion:

These data indicate that ZK₁₄, a novel NO-donating DDB derivative, promotes HSC-T6 apoptosis in vitro through a signaling mechanism involving mitochondria and caspase activation and it inhibits CCl₄-induced hepatic fibrosis in vivo. The results suggest that ZK₁₄ has potential therapeutic value in the treatment of hepatic fibrosis.     

Hepatotoxicity and nephrotoxicity in rats induced by carbon tetrachloride and the protective effects of Teucrium polium and vitamin C

This work investigated the protective effects of Teucrium polium (T. polium) and vitamin C (Vit C) against carbon tetrachloride (CCl₄) induced hepatotoxicity and nephrotoxicity in rats. T. polium reduced the Fer reduced antioxidant power (FRAP) (IC₅₀?=?0.89?mg/ml) and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) (IC₅₀?=?0.049 µg/ml) than Vit C, FRAP (IC₅₀?=?0.71?mg/ml) and DPPH (IC₅₀?=?0.029 µg/ml). Male albino Wistar rats were divided into six groups: Group I was used as controls, Group II received CCl₄ in olive oil (0.5?ml/kg) by gavage, Group III received CCl₄ in olive oil (0.5?ml/kg) by gavage after 3 d of receiving T. polium (5?g/l), orally, Group IV received T. polium (5?g/l) alone, by gavage, for 7 d, Group V received CCl₄ in olive oil (0.5?ml/kg) by gavage after 3 d of receiving Vit C (250?mg/kg) by gavage and Group VI received Vit C (250?mg/kg) alone by gavage. CCl₄ showed an increase of serum hepatic and renal markers aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea, and creatinine. Moreover, we noted an increase of lipid peroxidations and a decrease in antioxidants enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) of CCl₄ rats compared to controls. The pretreatment with (200?mg/kg) of T. polium and with Vit C (250?mg/kg) by gavage, for 7 d, displayed their ability to protect against oxidative damage and biochemical changes induced by CCl₄. Our results were in accordance with histopathological observations.     

Effect of tryptophan on hepatic polyribosomes and protein synthesis in rats treated with carbon tetrachloride

This study was concerned with the effect of tryptophan in rats on the disaggregation of hepatic polyribosomes and on the inhibition of hepatic protein synthesis due to the administration of CCl₄. Overnight fasted rats were treated ip with CCl₄ before or after receiving l-tryptophan ip. Rats that received CCl₄ alone showed marked hepatic polyribosomal disaggregation and decreased in vitro hepatic protein synthesis. Rats that received tryptophan before or after CCl₄ showed an improvement in in vitro hepatic protein synthesis, but only the former group revealed an improvement in hepatic polyribosomes. Studies in which rats received [¹⁴C]orotic acid to prelabel hepatic RNA before receiving tryptophan and CCl₄ revealed that tryptophan treatment increased the availability of poly(A)-mRNA in the cytoplasm of livers of CCl₄-treated rats.     

Potentiation of the hepatotoxicity of carbon tetrachloride following preexposure to chlordecone (kepone) in the male rat.

The effect of carbon tetrachloride (CCl₄) challenge on several parameters of hepatic injury was determined in chlordecone (CD)-pretreated male rats. Following a 15-day feeding of 0 or 10 ppm CD, rats received a single intraperitoneal challenge of 0, 25, 50, 100, or 200 μl CCl₄/kg. Twenty-four hours after CCl₄, biliary excretion of phenolphthalein glucuronide (PG), bile secretion, and serum transaminase (SGPT, SGOT) activities were examined as functional indices of hepatic injury. Feeding of 10 ppm CD alone resulted in decreased biliary excretion of PG (59% of control) but had no effect on bile flow or on serum transaminases. Twenty-four hours after CCl₄ alone, the two high doses caused decreased biliary excretion of PG in the absence of any effect on bile flow and doubled serum transaminases at the highest dose (200 μl/kg). A single challenge of CCl₄ to CD-fed rats resulted in a dose-dependent impairment of PG excretion at a dose of 50 μl/kg and higher. Bile secretory function was severely impaired in the CD-fed animals receiving CCl₄ at the doses of 100 and 200 μl/kg. Decreased bile flow was not seen in any other groups. Greatly potentiated hepatotoxicity was reflected in the form of elevated SGPT and SGOT activities which increased in excess of 30- and 10-fold, respectively, in CD-fed rats challenged with CCl₄ at 100 and 200 μl/kg. Parenchymal liposis (cytoplasmic sudanophilic droplets) developed in all CD-fed rats receiving CCl₄, while necrosis occurred after CCl₄ at 50 μl/kg and increased in a dosedependent manner. CCl₄ controls exhibited parenchymal liposis and limited centrilobular necrosis only at the two highest doses of CCl₄. These data indicate a great potential for production of severe liver damage resulting from interactions of CCl₄ and CD exposure at levels which may be independently nontoxic.     

Carbon tetrachloride activation, lipid peroxidation, and the mixed function oxygenase activity of various rat tissues.

In agreement with previous results from other laboratories, cytochrome P-450 (P-450) was found in the microsomal fraction of rat liver, kidney, lung, and testis. Liver microsomal P-450 content was higher in males than in virgin or pregnant females. No P-450 was detected in the microsomal fraction or rat brain, ovaries, placenta, spleen, or adipose tissue. In contrast, microsomal cytochrome c reductase was demonstrated, with different degrees of activity, in all the tissues tested. CCl₄ activation to ·CCl₃, as measured by the irreversible binding of ¹⁴C from ¹⁴CCl₄ to lipids, was observed to some extent in all the organs tested. except adipose tissue. There was a good qualitative correlation between intensity of CCl₄ activation and P-450 content, while no correlation between CCl₄ activation and cytochrome c reductase activity was found. CCl₄-induced lipid peroxidation was only detected in livers from either male or virgin and pregnant female rats. Results suggest that P-450 is involved in CCl₄ activation and that irreversible binding of CCl₄ metabolites to cellular components, rather than lipid peroxidation, is responsible for some biochemical and/or ultrastructural lesions reported in different tissues.     

Effect of cycloheximide and actinomycin D on carbon tetrachloride hepatotoxicity

The effect of the protein synthesis inhibitor, cycloheximide, and the RNA synthesis inhibitor, actinomycin D, on CCl₄ hepatotoxicity was investigated in rats. CCl₄ administration produced elevations in both serum glutamate-oxaloacetate transaminase (SGOT) and hepatic triglyceride concentrations and a decrease in hepatic cytochrome P-450 content at 24 hr. Administration of cycloheximide 30 min prior to CCl₄ prevented the increase in both SGOT and hepatic triglycerides caused by CCl₄: the destruction of cytochrome P-450 was not prevented. Actinomycin D, administered 30 min before CCl₄, reduced the release of GOT but did not prevent either the destruction of cytochrome P-450 or the accumulation of hepatic triglycerides. These observations support the concept that protein synthesis plays an active role in the production of cellular damage produced by CCl₄.     

Biochemical aspects of the protective action of propyl gallate on liver injury in rats poisoned with carbon tetrachloride.

Liver injury in rats intoxicated with a high dose of CCl₄ (2.5 ml/kg, po) is partially prevented by propyl gallate. The accumulation of hepatic triglycerides and the release of liver enzymes into the plasma are more effectively inhibited by this antioxidant in rats given a smaller dose of the hepatotoxin (0.25 ml/kg, po). The antioxidant activity of propyl gallate, administered in vivo, estimated by means of the production of malonyl dialdehyde in liver homogenates in vitro, has been found to decrease progressively after treatment. The concentration of nonesterified fatty acids in the serum is not affected by dosing with propyl gallate. However, propyl gallate releases the block in triglyceride secretion from the liver that occurs after administration of CCl₄. Furthermore, both the uptake of CCl₄ by the liver and the early steps of the free radical reaction (incorporation of labeled metabolites of ¹⁴CCl₄ and double bond shifting in microsomal unsaturated lipids) are unchanged by concomitant dosing with propyl gallate. This free radical scavenger, when administered in discrete doses, more markedly influences both CCl₄ liver damage and the efficiency of the hepatic drug metabolizing enzyme system. This effect in vivo is consistent with the reported in vitro interaction of propyl gallate with microsomal electron transport. These findings indicate that propyl gallate partially interferes with the enzymes bound to the endoplasmic reticulum, but affects the secondary phenomena of lipid peroxidation at the level where lipoproteins are secreted and/or the permeability of plasma membrane is altered.     

Preventive effect of γ-glutamylcysteinylethyl ester on carbon tetrachloride-induced hepatic triglyceride accumulation in mice

The effect of γ-glutamylcysteinylethyl ester (γ-GCE), which is a precursor of reduced glutathione (GSH), on carbon tetrachloride (CCl₄)-induced hepatic triglyceride (TG) accumulation in mice was investigated in comparison with that of GSH. Administration of γ-GCE (160 μmol/kg), but not GSH (160 μmol/kg), to mice at 3 h after CCl₄ injection (1 ml/kg, i.p.) significantly attenuated an increase in hepatic TG concentration at 6, 12, and 24 h after the CCl₄ injection. A decrease in hepatic GSH concentration after the CCl₄ injection was significantly diminished by the γ-GCE administration, but not by the GSH administration. The correlation coefficient between hepatic TG concentration and hepatic GSH concentration was −0.627 (P<0.001) when the results of all mice were grouped together. These results indicate that γ-GCE can attenuate CCl₄-induced hepatic TG accumulation in mice through the maintenance of hepatic GSH level.     

Sugar coated liposomal flavonoid: A unique formulation in combating carbontetrachloride induced hepatic oxidative damage

Rats were administered a single dose of plant origin phenolic antioxidant Quercetin (QC) in free, liposome encapsulated and galactosylated liposome encapsulated forms 2 h prior to hepatotoxic dose of carbontetrachloride (CCl₄, 40% v/v in olive oil, 1 ml/kg b.wt). Among those three different forms of QC tested, only galactosylated liposomal QC provided significant protection against CCl₄ induced hepatic oxidative damage. After 24 h of injection (S.C.) hepatic cells of rats were found susceptible to CCl₄ induced oxidative damage and it was monitored by the increased amount of conjugated diene in hepatic membrane. The two-fold increase in conjugated diene by the induction of CCl₄ was decreased upto normal level by galactosylated liposomal QC pre-treatment.

Carbontetrachloride induced membrane damage in hepatic cells and it was judged by the blood serum pathological and liver tissue histopathological examination. Membrane damage by the induction of CCl₄ was further evaluated by the decreased level of plasma membrane (PM) bound enzyme Na⁺/K⁺ ATPase activity and it was increased only by the pre-treatment of galactosylated liposomal QC.

Carbontetrachloride induced a substantial decrease both in enzymatic and molecular endogenous antioxidant levels in hepatic cells.

The depression in antioxidant system in hepatic cells was completely prevented by a single dose of galactosylated lipsosomal QC prior to CCl₄ treatment.

Liver uptake of QC was estimated after 2 h of the flavonoid injection (8.9 μmol/kg body weight) (free or liposomal forms) and 85% of the injected QC was found in liver in the case of galactosylated liposomal QC. Whereas only 25% of the injected dose was detected in liver when an identical amount of free QC was injected.

Carbontetrachloride also induced an alteration in membrane fluidity and it was evaluated by a decrease in membrane micro-viscosity. Free QC pre-treatment resulted in no protection against CCl₄ induced increase in hepatic membrane fluidity, whereas galactosylated liposomal QC exerted a significant protection against the increase. Results of this study revealed that QC in galactosylated liposome could exert a significant protection against CCl₄ induced hepatocellular injury.     

Irreversible binding of 14C from 14CCl4 to liver microsomal lipids and proteins from rats pretreated with compounds altering microsomal mixed-function oxygenase activity

¹⁴C from ¹⁴CCl₄ irreversibly binds to lipid and protein components of different liver subcellular fractions. Microsomal lipids bind more ¹⁴C than does either mitochondria or 105,000 g supernatant. The proteins from the 105,000 g fraction bind more ¹⁴C than those from the other two fractions. The extent of the irreversible binding of ¹⁴C to microsomal lipids and proteins is decreased by the prior treatment of the rats with cystamine, pyrazole, 3-methylcholanthrene or metopirone while it is increased by pretreatment with phenobarbital. The prior treatment with 2-diethylaminoethyl 2,2-diphenyl valerate hydrochloride (SKF 525A) increased the irreversible binding of ¹⁴C to microsomal lipids, but not to microsomal proteins. The results suggest that the irreversible binding of ¹⁴C to microsomal lipids is a more reliable expression of the CCl₄-activation step than the one to microsomal proteins. The ¹⁴CCl₃ free radicals responsible for the binding of ¹⁴C to lipid would arise during the reduction of the CCl₄/cytochrome P-450 complex mediated by cytochrome P-450 reductase.     

Liver fibrosis in mice induced by carbon tetrachloride and its reversion by luteolin

Hepatic fibrosis is effusive wound healing process in which excessive connective tissue builds up in the liver. Because specific treatments to stop progressive fibrosis of the liver are not available, we have investigated the effects of luteolin on carbon tetrachloride (CCl₄)-induced hepatic fibrosis. Male Balb/C mice were treated with CCl₄ (0.4 ml/kg) intraperitoneally (i.p.), twice a week for 6 weeks. Luteolin was administered i.p. once daily for next 2 weeks, in doses of 10, 25, and 50 mg/kg of body weight. The CCl₄ control group has been observed for spontaneous reversion of fibrosis. CCl₄-intoxication increased serum aminotransferase and alkaline phosphatase levels and disturbed hepatic antioxidative status. Most of these parameters were spontaneously normalized in the CCl₄ control group, although the progression of liver fibrosis was observed histologically. Luteolin treatment has increased hepatic matrix metalloproteinase-9 levels and metallothionein (MT) I/II expression, eliminated fibrinous deposits and restored architecture of the liver in a dose-dependent manner. Concomitantly, the expression of glial fibrillary acidic protein and α-smooth muscle actin indicated deactivation of hepatic stellate cells. Our results suggest the therapeutic effects of luteolin on CCl₄-induced liver fibrosis by promoting extracellular matrix degradation in the fibrotic liver tissue and the strong enhancement of hepatic regenerative capability, with MTs as a critical mediator of liver regeneration.     

The Effect of Nicotine and Its Interaction with Carbon Tetrachloride in the Rat Liver

Abstract: In order to study the effects of nicotine on liver, groups of rats were given nicotine doses that simulated those seen in chronic smoking (54 and 108 μmol/l of nicotine) for 10 days. A subgroup was also given a single subcutaneous injection of 6 g/kg of carbon tetrachloride (CCl₄) shortly before the animals of the group were killed. Histology demonstrated a significant hepatotoxic effect in the group receiving 108 μmol/l of nicotine when compared with the control group in the form of fatty change, focal or confluent necrosis and dark-cell change. The effects in pregnant rats were less severe. Carbon tetrachloride alone induced significant fatty change and focal necrosis in non-pregnant rats but not in pregnant rats. Nicotine also aggravated the CCl₄ induced pathological changes in livers of both non-pregnant and pregnant animals. Thus nicotine alone, when given at a concentration of 108 μmol/l, exerted hepatotoxic effects; the alkaloid also aggravated the hepatotoxicity of CCl₄. Pregnant rats were more resistant to the hepatotoxic effects produced by nicotine and CCl₄.     

TOP1 and 2, polysaccharides from Taraxacum officinale, attenuate CCl4-induced hepatic damage through the modulation of NF-κB and its regulatory mediators

In this work, we estimate the inhibitory effect of two polysaccharides from Taraxacum officinale (TOP) on CCl₄-induced oxidative stress and inflammation in Sprague–Dawley rats. TOP1 and 2 (304, 92 mg/kg bw) were administered for 7 days via a stomach sonde, and hepatitis was induced by a single dose of CCl₄ (50% CCl₄/olive oil; 0.5 mL/kg bw) administration. CCl₄ significantly elevated serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities. Histopathological observation further revealed that CCl₄-induced moderate levels of inflammatory cell infiltration, centrilobular fatty change, apoptosis, and necrosis. However, TOPs pretreatment markedly decreased AST and ALT activities as well as hepatic lesions. TOPs also increased free radical scavenging activity, as exhibited by a lowered TBARS concentration. TOPs pretreatment also reversed other hepatitis-associated symptoms, including GSH depletion, inhibited anti-oxidative enzyme activities, up-regulation of NF-κB and increased expression of its regulatory inflammatory mediators, such as inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. These results suggest that TOPs have a hepatoprotective effect by modulating inflammatory responses and ameliorating oxidative stress.     

Prevention and treatment of carbon tetrachloride hepatotoxicity by cysteine: studies about its mechanism

Cysteine administration to rats (1.9 g/kg po) prevented the development of the necrosis and fatty liver induced by CCl₄. This protective effect was observed when cysteine was given either 30 min before or 1 hr after the administration of CCl₄. Cysteine administration did not prevent the irreversible binding of ¹⁴C from ¹⁴CCl₄ to microsomal lipids, but it partially reduced the binding to microsomal proteins at 6 hr after ¹⁴CCl₄. Cysteine pretreatment did not modify the intensity of the CCl₄-induced lipid peroxidation process or cytochrome P-450 destruction, but it partially prevented depression of glucose-6-phosphatase activity by CCl₄. The results are compatible with the possibility of a protective action of cysteine at a site in the chain of events leading to necrosis, but not the activation step.     

Protective action of the immunomodulator ginsan against carbon tetrachloride-induced liver injury via control of oxidative stress and the inflammatory response

The aim of the present study was to evaluate immunomodulator ginsan, a polysaccharide extracted from Panax ginseng, on carbon tetrachloride (CCl₄)-induced liver injury. BALB/c mice were injected i.p. with ginsan 24 h prior to CCl₄ administration. Serum liver enzyme levels, histology, expression of antioxidant enzymes, and several cytokines/chemokines were subsequently evaluated. Ginsan treatment markedly suppressed the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, and hepatic histological necrosis increased by CCl₄ treatment. Ginsan inhibited CCl₄ induced lipid peroxidation through the cytochrome P450 2E1 (CYP2E1) downregulation. The hepatoprotective effect of ginsan was attributed to induction of anti-oxidant protein contents, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX) as well as restoration of the hepatic glutathione (GSH) concentration. The marked increase of proinflammatory cytokines (IL-1β, IFN-γ) and chemokines (MCP-1, MIP-2β, KC) in CCl₄ treated mice was additionally attenuated by ginsan, thereby preventing leukocyte infiltration and local inflammation. Our results suggest that ginsan effectively prevent liver injury, mainly through downregulation of oxidative stress and inflammatory response.