Protective effect of melatonin on naphthalene-induced oxidative stress and DNA damage in cultured macrophage J774A.1 cells.

Naphthalene is a bicyclic aromatic compound that is widely used in various domestic and commercial applications. Previous studies in our laboratory have demonstrated enhanced production of reactive oxygen species, lipid peroxidation and DNA fragmentation in both in vitro and in vivo models following treatment with naphthalene. Melatonin (N-acetyl-5-methoxytryptamine), an indole hormone, is the chief secretory product of the pineal gland and is an efficient free radical scavenger and antioxidant, both in vitro and in vivo. In this study, we have investigated the ability of 1 mM melatonin to protect against naphthalene-induced oxidative stress and DNA damage in cultured macrophage J774A.1 cells. No significant changes were observed when these macrophage cells were treated with 100 microM naphthalene. Approximately 2.0-, 4.2- and 4.4-fold increases in cytochrome c reduction were observed at 200, 400 and 500 mM concentrations of naphthalene, demonstrating the increased production of superoxide anion. At 24 h, lipid peroxidation increased by approximately 1.4-, 2.1- and 2.2-fold following treatment of these cells with 200, 400 and 500 mM concentrations of naphthalene, respectively, while 1.6-, 2.8- and 2.8-fold increases in DNA fragmentation were observed at these same concentrations. Two hour pretreatment of these cultured cells with 1 mM melatonin provided approximately 26-44% decreases in lipid peroxidation, superoxide anion production and DNA fragmentation in cells treated with 400 and 500 microM naphthalene. Cellular viability decreased significantly when cells were incubated with concentrations of naphthalene greater than 100 microM, while preincubation with melatonin significantly increased the cellular viability. These results demonstrate that naphthalene may induce toxic manifestations by enhanced production of reactive oxygen free radicals, resulting in lipid peroxidation and DNA damage, while preincubation with melatonin significantly suppressed cytoxicity in J774A.1 macrophage cells.

Ca(2+)-calmodulin antagonist chlorpromazine and poly(ADP-ribose) polymerase modulators 4-aminobenzamide and nicotinamide influence hepatic expression of BCL-XL and P53 and protect against acetaminophen-induced programmed and unprogrammed cell death in mice.

Acetaminophen (AAP), the analgesic hepatotoxicant, is a powerful inducer of oxidative stress, DNA fragmentation, and apoptosis. The anti-apoptotic oncogene bcl-XL, and the pro-apoptotic oncogene p53 are two key regulators of cell cycle progression and/or apoptosis subsequent to DNA damage in vitro and in vivo. This study investigated the effect of AAP on the expression of these oncogenes and whether agents that modulate DNA fragmentation (chlorpromazine, CPZ) and DNA repair through poly(ADP-Ribose) polymerase (PARP) activity (4-AB: 4-aminobenzamide) can protect against AAP-induced hepatotoxicity by inhibiting oxidative stress, DNA fragmentation, and/or by altering the expression of bcl-XL and p53. In addition, the protective effect of supplemental nicotinamide (NICO), known to be depleted in cells with high PARP activity during DNA repair, is similarly evaluated. Male ICR mice (3 months old) were administered vehicle alone; nontoxic doses of 4-AB (400 mg/kg, ip), NICO (250 mg/kg, ip) or CPZ (25 mg/kg, ip), hepatotoxic dose of AAP alone (500 mg/kg, ip), or AAP plus one of the protective agents 1 h later. All animals were sacrificed 24 h following AAP administration. Serum alanine aminotransferase activity (ALT), hepatic histopathology and lipid peroxidation, DNA damage, and expression of bcl-XL and p53 (western blot analysis) were compared in various groups. All of the three agents significantly prevented AAP-induced liver injury, lipid peroxidation, DNA damage, and associated apoptotic and necrotic cell deaths, 4-AB being the most effective and NICO the least. Compared to control, there was a considerable decrease in bcl-XL expression, and an increase in p53 expression in AAP-exposed livers. The effect of AAP on bcl-XL was antagonized and that on p53 was synergized by the PARP-modulator 4-AB as well as NICO, whereas the endonuclease inhibitor CPZ was without effect on either bcl-XL or p53 expression. These results suggest that the hepatotoxic effect of AAP involves multiple mechanisms including oxidative stress, upregulation of endonuclease (or caspase-activated DNAse) and alteration of pro- and anti-apoptotic oncogenes. The observed antagonism of AAP-induced hepatocellular apoptosis and/or necrosis by modulators of multiple processes including DNA repair suggests the likelihood that a more effective therapy against AAP intoxication should involve a combination of antidotes.

Protection against drug- and chemical-induced multiorgan toxicity by a novel IH636 grape seed proanthocyanidin extract.

Grape seed proanthocyanidins have been demonstrated to exhibit a broad spectrum of pharmacological, therapeutic and chemoprotective properties. In our previous studies, IH636 grape seed proanthocyanidin extract (GSPE, commercially known as ActiVin) demonstrated excellent concentration- and dose-dependent free radical scavenging abilities in both in vitro and in vivo models and provided significantly better protection than vitamins C, E and beta-carotene. GSPE demonstrated significant cytotoxicity towards human breast, lung and gastric adenocarcinoma cells, while enhancing the growth and viability of normal human gastric mucosal cells and macrophage J774A.1 cells. In this study, the bioavailability and protective ability of GSPE were examined against acetaminophen-induced hepatoxicity, amiodarone-induced pulmonary toxicity, doxorubicin-induced cardiotoxicity, cadmium chloride-induced nephrotoxicity, dimethylnitrosamine-induced spleenotoxicity and O-ethyl-S,S-dipropyl phosphorodithioate (MOCAP)-induced neurotoxicity in mice. In each experiment, half of the test animals were orally fed GSPE for 7-10 days prior to drug/chemical exposure, while the other half received no GSPE. Parameters of analysis included changes in serum chemistry [alanine amino-transferase (ALT), blood urea nitrogen and creatine kinase], histopathology and integrity of genomic DNA. The results indicated that GSPE preexposure prior to the drugs/chemicals such as acetaminophen, amiodarone, doxorubicin, cadmium chloride or dimethylnitrosamine treatment, provided near complete protection in terms of serum chemistry changes (ALT, blood urea nitrogen and creatine kinase) and inhibition of both forms of cell death, e.g., apoptosis and necrosis. DNA damage in various tissues triggered by these agents was significantly reduced. Histopathological examination of the organs evaluated reflected similar patterns to those of the serum chemistry and DNA results. MOCAP exposure showed symptoms of severe neurotoxicity coupled with serum chemistry changes in the absence of any significant genomic change or brain pathology. GSPE afforded only partial protection in the brain tissue. These results suggest that GSPE exposure is bioavailable and provides significant multiorgan protection against drug- and chemical-induced toxic assaults.

Free radicals and grape seed proanthocyanidin extract: importance in human health and disease prevention.

Free radicals have been implicated in over a hundred disease conditions in humans, including arthritis, hemorrhagic shock, atherosclerosis, advancing age, ischemia and reperfusion injury of many organs, Alzheimer and Parkinson's disease, gastrointestinal dysfunctions, tumor promotion and carcinogenesis, and AIDS. Antioxidants are potent scavengers of free radicals and serve as inhibitors of neoplastic processes. A large number of synthetic and natural antioxidants have been demonstrated to induce beneficial effects on human health and disease prevention. However, the structure-activity relationship, bioavailability and therapeutic efficacy of the antioxidants differ extensively. Oligomeric proanthocyanidins, naturally occurring antioxidants widely available in fruits, vegetables, nuts, seeds, flowers and bark, have been reported to possess a broad spectrum of biological, pharmacological and therapeutic activities against free radicals and oxidative stress. We have assessed the concentration- or dose-dependent free radical scavenging ability of a novel IH636 grape seed proanthocyanidin extract (GSPE) both in vitro and in vivo models, and compared the free radical scavenging ability of GSPE with vitamins C, E and beta-carotene. These experiments demonstrated that GSPE is highly bioavailable and provides significantly greater protection against free radicals and free radical-induced lipid peroxidation and DNA damage than vitamins C, E and beta-carotene. GSPE was also shown to demonstrate cytotoxicity towards human breast, lung and gastric adenocarcinoma cells, while enhancing the growth and viability of normal human gastric mucosal cells. The comparative protective effects of GSPE, vitamins C and E were examined on tobacco-induced oxidative stress and apoptotic cell death in human oral keratinocytes. Oxidative tissue damage was determined by lipid peroxidation and DNA fragmentation, while apoptotic cell death was assessed by flow cytometry. GSPE provided significantly better protection as compared to vitamins C and E, singly and in combination. GSPE also demonstrated excellent protection against acetaminophen overdose-induced liver and kidney damage by regulating bcl-X(L) gene, DNA damage and presumably by reducing oxidative stress. GSPE demonstrated excellent protection against myocardial ischemia-reperfusion injury and myocardial infarction in rats. GSPE was also shown to upregulate bcl(2) gene and downregulate the oncogene c-myc. Topical application of GSPE enhances sun protection factor in human volunteers, as well as supplementation of GSPE ameliorates chronic pancreatitis in humans. These results demonstrate that GSPE provides excellent protection against oxidative stress and free radical-mediated tissue injury.

A hepatotoxic dose of acetaminophen modulates expression of BCL-2, BCL-X(L), and BCL-X(S) during apoptotic and necrotic death of mouse liver cells in vivo.

The protein BCL-X(L) and protein product of proto-oncogene bcl-2 act as apoptosis antagonists, and BCL-X(S) serve as a dominant death promoter, including apoptosis following exposure to chemotherapeutic drugs. This investigation examined whether some aspects of the highly integrated process of acetaminophen (AAP)-induced hepatotoxicity involve down-regulation or upregulation of expression of BCL-2, BCL-X(L) and BCL-X(S) in mouse liver in vivo. Male ICR mice (CD-1; 35-45 g) were treated ip with a hepatotoxic dose of AAP (500 mg/kg) and sacrificed 0, 6, and 18 h later. Blood was collected upon sacrifice for determination of serum alanine aminotransferase (ALT) activity and the liver was sectioned for histopathological diagnosis of necrosis/apoptosis. Portions of liver tissues were also used for DNA extraction (for gel electrophoresis) and Western blot analysis. This study demonstrates that administration of a hepatotoxic dose of AAP to ICR mice results in severe liver injury (ALT leakage >200-fold at 6 h and >600-fold at 18 h) leading to massive cell death by apoptosis (diagnosed by nuclear ultrastructure, histopathology, and DNA ladder), in addition to necrosis coupled with spectacular changes in the BCL-X(L) expression (6 and 18 h after AAP administration). Western blot analysis of the liver proteins revealed that mouse liver expresses two proteins, BCL-X(L) and BCL-X(S), and does not express BCL-2. As the toxicity progressed, during 6 and 18 h post-AAP administration, the BCL-X(L) protein band shifted to a slower mobility band which might represent a phosphorylated form of BCL-X(L). Appearance of this higher molecular weight BCL-X(L) protein band correlated with massive apoptotic death of liver cells along with ladder-like DNA fragmentation. In the same time period, death inhibitory gene bcl-2 remained unexpressed, and the level of expression of BCL-X(S) remained unaltered. Whether the consistent level of expression of BCL-X(S) reflected inability of AAP to influence its expression remains unknown. Unaltered expression of BCL-X(S) in the near total absence of BCL-2 expression raises questions regarding the death promoting role of BCL-X(S) in vivo. The precise role of modified form of BCL-X(L) remains elusive. However, this study may have demonstrated for the first time drug-induced changes in the expression of anti-apoptotic gene BCL-X(L), and a positive link between AAP-induced apoptotic death and modification of BCL-X(L) protein in vivo.

Unique organoprotective properties of a novel IH636 grape seed proanthocyanidin extract on cadmium chloride-induced nephrotoxicity, dimethylnitrosamine (DMN)-induced splenotoxicity and mocap-induced neurotoxicity in mice.

Several observations, both in humans and laboratory animals, have suggested that proanthocyanidins exhibit a broad spectrum of pharmacological, therapeutic and chemoprotective properties. Specifically, some of our earlier studies have shown that IH636 grape seed proanthocyanidin extract (GSPE, commercially known as ActiVin) provides excellent concentration- and dose-dependent protection against toxicities induced by diverse agents, such as acetaminophen, hydrogen peroxide, 12-O-tetradecanoylphorbol-13-acetate (TPA), smokeless-tobacco extract, idarubicin and 4-hydroxyperoxycyclophosphamide in both in vitro and in vivo models. In some models, GSPE proved to be a better cytoprotectant than vitamins C, E and beta-carotene. The purpose of this investigation was three fold: (i) to indirectly assess the bioavailability of GSPE in multiple target organs, (ii) quantify GSPE's capacity to avert cadmium chloride (CdCl2)-induced nephrotoxicity, dimethylnitrosamine (DMN)-induced splenotoxicity and O-ethyl-S,S-dipropyl phosphorodithioate (MOCAP)-induced neurotoxicity, and lastly (iii) to evaluate possible mechanisms of protection in mice. In order to determine all these, three separate experiments were designed and each experiment consisted of four groups, such as vehicle control, GSPE alone, toxicant alone and GSPE + toxicant. GSPE was administered orally (100 mg/Kg) for 7-8 days prior to the toxicant exposure. Parameters of the analyses included evaluation of serum chemistry changes (ALT, BUN and CK), histopathology and integrity of genomic DNA, both quantitatively and qualitatively. Results indicate that GSPE preexposure prior to cadmium chloride and DMN provided near complete protection in terms of serum chemistry changes (ALT, BUN and CK) and inhibition of both forms of cell death. e.g., apoptosis and necrosis. DNA damage, a common denominator usually associated with both apoptosis and necrosis was significantly reduced by GSPE treatment. Histopathological examination of organs correlated strongly with the changes in serum chemistry and the DNA modification data. Surprisingly, MOCAP exposure showed symptoms of neurotoxicity coupled with serum chemistry changes in the absence of any significant genomic DNA damage or brain pathology. Although, GSPE appeared to partially protect the neural tissue, it powerfully antagonized MOCAP-induced mortality. Taken together, this study suggests that in vivo GSPE-preexposure may protect multiple target organs from a variety of toxic assaults induced by diverse chemical entities.

In vivo protection of dna damage associated apoptotic and necrotic cell deaths during acetaminophen-induced nephrotoxicity, amiodarone-induced lung toxicity and doxorubicin-induced cardiotoxicity by a novel IH636 grape seed proanthocyanidin extract.

Grape seed extract, primarily a mixture of proanthocyanidins, has been shown to modulate a wide-range of biological, pharmacological and toxicological effects which are mainly cytoprotective. This study assessed the ability of IH636 grape seed proanthocyanidin extract (GSPE) to prevent acetaminophen (AAP)-induced nephrotoxicity, amiodarone (AMI)-induced lung toxicity, and doxorubicin (DOX)-induced cardiotoxicity in mice. Experimental design consisted of four groups: control (vehicle alone), GSPE alone, drug alone and GSPE+drug. For the cytoprotection study, animals were orally gavaged 100 mg/Kg GSPE for 7-10 days followed by i.p. injections of organ specific three drugs (AAP: 500 mg/Kg for 24 h; AMI: 50 mg/Kg/day for four days; DOX: 20 mg/Kg for 48 h). Parameters of study included analysis of serum chemistry (ALT, BUN and CPK), and orderly fragmentation of genomic DNA (both endonuclease-dependent and independent) in addition to microscopic evaluation of damage and/or protection in corresponding PAS stained tissues. Results indicate that GSPE preexposure prior to AAP, AMI and DOX, provided near complete protection in terms of serum chemistry changes (ALT, BUN and CPK), and significantly reduced DNA fragmentation. Histopathological examination of kidney, heart and lung sections revealed moderate to massive tissue damage with a variety of morphological aberrations by all the three drugs in the absence of GSPE preexposure than in its presence. GSPE+drug exposed tissues exhibited minor residual damage or near total recovery. Additionally, histopathological alterations mirrored both serum chemistry changes and the pattern of DNA fragmentation. Interestingly, all the drugs, such as, AAP, AMI and DOX induced apoptotic death in addition to necrosis in the respective organs which was very effectively blocked by GSPE. Since AAP, AMI and DOX undergo biotransformation and are known to produce damaging radicals in vivo, the protection by GSPE may be linked to both inhibition of metabolism and/or detoxification of cytotoxic radicals. In addition, its' presumed contribution to DNA repair may be another important attribute, which played a role in the chemoprevention process. Additionally, this may have been the first report on AMI-induced apoptotic death in the lung tissue. Taken together, these events undoubtedly establish GSPE's abundant bioavailability, and the power to defend multiple target organs from toxic assaults induced by structurally diverse and functionally different entities in vivo.

A novel proanthocyanidin IH636 grape seed extract increases in vivo Bcl-XL expression and prevents acetaminophen-induced programmed and unprogrammed cell death in mouse liver.

Several molecular events in the apoptotic or necrotic death of hepatocytes induced by acetaminophen (AAP) now appear to be well defined. Recent studies also indicate that select expression of bcl-Xl is possibly modified during AAP-induced liver injury. The purpose of this study was several-fold: (i) to examine the hepatoprotective ability of short-term (3-day) and long-term (7-day) exposures of a grape seed proanthocyanidin extract (GSPE) on AAP-induced liver injury and animal lethality; (ii) to monitor effects of GSPE on one of the prime targets of AAP, i.e., hepatocellular genomic DNA and associated apoptotic and necrotic death; and (iii) to unravel changes in the pattern of expression of an antiapoptotic gene, bcl-Xl in the liver. In order to investigate these events, male ICR mice (30-40 g) were administered nontoxic doses of GSPE (3 or 7 days, 100 mg/kg, po), followed by hepatotoxic doses of AAP (400 and 500 mg/kg, ip), and sacrificed 24 h later. Serum was analyzed for alanine aminotransferase activity (ALT) and the liver for histopathological diagnosis of apoptosis/necrosis. The ability of AAP to promote apoptotic DNA fragmentation and its counteraction by GSPE in the liver was also evaluated quantitatively (by a sedimentation assay) and qualitatively (by agarose gel electrophoresis). Portions of livers were also subjected to Western blot analysis (27,000g fraction of liver homogenates) to examine the pattern of expression of cell death inhibitory gene bcl-Xl. Results indicate that 7-day GSPE preexposure induced dramatic protection and markedly decreased liver injury and animal lethality culminated by AAP, when compared to a short-term 3-day exposure. Abrogation of toxicity was also mirrored in DNA fragmentation. Histopathological evaluation of liver sections showed remarkable counteraction of AAP-toxicity by this novel GSPE and substantial inhibition of both apoptotic and necrotic liver cell death. Agarose gel electrophoresis revealed that 7-day GSPE preexposure prior to AAP administration completely blocked Ca(2+)/Mg(2+)-Ca(2+)/Mg(2+)-dependent-endonuclease-mediated ladder-like fragmentation of genomic DNA and significantly altered the bcl-Xl expression. The most dramatic changes observed in this study were: (i) substantial increase in the expression of bcl-Xl in the liver by 7-day GSPE exposure alone; (ii) significant modification bcl-Xl expression by AAP alone; and (iii) dramatic inhibition of AAP-induced modification of bcl-Xl (phosphorylation?) expression by GSPE. In summary, these observations demonstrate that GSPE preexposure may significantly attenuate AAP-induced hepatic DNA damage, apoptotic and necrotic cell death of liver cells, and, most remarkably, antagonize the influence of AAP-induced changes in bcl-Xl expression in vivo.

Smokeless tobacco, oxidative stress, apoptosis, and antioxidants in human oral keratinocytes.

We have investigated the effects of a smokeless tobacco extract (STE) on lipid peroxidation, cytochrome c reduction, DNA fragmentation and apoptotic cell death in normal human oral keratinocyte cells, and assessed the protective abilities of selected antioxidants. The cells, isolated and cultured from human oral tissues, were treated with STE (0-300 microl;g/ml) for 24 h. Superoxide anion production was determined by cytochrome c reductase. Oxidative tissue damage was determined by lipid peroxidation and DNA fragmentation, whereas apoptotic cell death was assessed by flow cytometry. STE-induced fragmentation of genomic DNA was also determined by gel electrophoresis. The comparative protective abilities of vitamin C (75 microM), vitamin E (75 microM), a combination of vitamins C & E (75 microM each), and a novel grape seed proanthocyanidin (IH636) extract (GSPE) (100 microg/ml) against STE induced oxidative stress and tissue damage were also determined. Following treatment of the cells with 300 microg STE/ml 1.5-7.6-fold increases in lipid peroxidation, cytochrome c reduction and DNA fragmentation were observed. The addition of the antioxidants to cells treated with STE provided 10-54% decreases in these parameters. Approximately 9, 29, and 35% increases in apoptotic cell death were observed following treatment with 100, 200, and 300 microg STE/ml, respectively, and 51-85% decreases in apoptotic cell death were observed with the antioxidants. The results demonstrate that STE produces oxidative tissue damage and apoptosis, which can be attenuated by antioxidants including vitamin C, vitamin E, a combination of vitamins C plus E and GSPE. GSPE exhibited better protection against STE than vitamins C and E, singly and in combination.

Protective effects of zinc salts on TPA-induced hepatic and brain lipid peroxidation, glutathione depletion, DNA damage and peritoneal macrophage activation in mice.

1. The comparative protective abilities of zinc L-methionine, zinc DL-methionine, zinc sulfate, zinc gluconate, L-methionine, DL-methionine, and vitamin E succinate (VES) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced lipid peroxidation, DNA fragmentation, and glutathione depletion in the hepatic and brain tissues, and production of reactive oxygen species by peritoneal macrophages were assessed. In addition, mice were fed a zinc-deficient diet for 5 weeks, and treated with TPA and/or zinc L-methionine or zinc DL-methionine, and similar studies were conducted. 2. The zinc-deficient diet induced oxidative stress in the hepatic and brain tissues as well as in the peritoneal macrophages as evidenced by significantly enhanced lipid peroxidation. DNA fragmentation, glutathione depletion, and production of reactive oxygen species. 3. Treatment of mice with zinc L-methionine, zinc DL-methionine, and VES decreased TPA-induced reactive oxygen species production as evidenced by significant decreases in chemiluminescence in peritoneal macrophages by approximately 45%, 31%, and 47%, respectively, and cytochrome c reduction by approximately 54%, 35%, and 41%, respectively, as compared with control values. Similar results were observed with liver and brain lipid peroxidation, DNA fragmentation, and glutathione depletion. 4. Zinc salts and antioxidants provided significant protection against TPA-induced oxidative damage. Zinc L-methionine provided the best protection.

DMBA induces programmed cell death (apoptosis) in the A20.1 murine B cell lymphoma.

The mechanism by which 7,12-dimethylbenz[a]anthracene (DMBA) produces cytotoxicity in lymphocytes was investigated in these studies using the murine A20.1 B cell lymphoma. Results show that in vitro exposure of these cells to 10-30 microM DMBA for 4 hr produced an increase in intracellular Ca2+, DNA fragmentation, and subsequent cell death. Elevation of Ca2+ and DNA fragmentation induced by DMBA were greatly pronounced when the A20.1 cells were exposed at high cell density (10(7) cells/ml). DMBA-induced DNA fragmentation and cell death were inhibited by coexposure of A20.1 cells to a calcium chelator (EDTA), a general nuclease and polymerase inhibitor (aurintricarboxylic acid), and a protein synthesis inhibitor (cycloheximide). These agents have been previously shown to inhibit apoptosis in lymphocytes and other cells exposed to chemical agents. We also found that cyclosporin A, an inhibitor of Ca(2+)-dependent pathways of T and B cell activation, prevented apoptosis in the A20.1 cell line. These results demonstrate that DMBA induces programmed cell death (apoptosis) in the A20.1 murine B cell lymphoma by Ca(2+)-dependent pathways. The increased sensitivity of A20.1 at high cell density to Ca2+ elevation and DNA fragmentation suggests that cell to cell interactions may also be important in this process.

Induction of P4502E1 by acetone in isolated rabbit hepatocytes. Role of increased protein and mRNA synthesis.

The molecular mechanism(s) underlying induction of the hepatic microsomal cytochrome P4502E1 (2E1) by xenobiotics (e.g. ethanol and acetone) is controversial. Proposed mechanisms include increased rates of enzyme synthesis due to elevated 2E1 mRNA levels, enhanced translation of pre-existing mRNA, or stabilization of 2E1 protein. To further assess which, if any, of these events predominates during the initial stages of 2E1 protein induction, we investigated the effects of acetone treatment on 2E1 content in cultured rabbit hepatocytes, an in vitro system that allows for precise control of the cellular mileau. Hepatocytes harvested from female rabbits and plated on plastic dishes with serum-supplemented medium were 90-100% viable for at least 48 hr in culture. Analysis of immunoreactive 2E1 content and aniline hydroxylase activity in microsomes isolated from hepatocytes cultured for up to 24 hr revealed that 2E1 expression was equal to that of microsomes from unplated cells and by 48 hr of culture, 2E1 levels decreased by only 35%. Moreover, microsomes isolated from cells exposed to 17 mM acetone for 24 hr exhibited a 53 and 62% increase in aniline hydroxylase activity and 2E1 content, respectively, compared to untreated cells. To explain these increases, the rate of 2E1 protein synthesis was determined in untreated cells or in cells treated with 17 mM acetone by first exposing hepatocytes to medium supplemented with 35S-labeled methionine and cysteine ([35S]Met/Cys) and subsequently assessing radiolabel incorporation into 2E1 protein. While no difference was found between untreated and acetone-treated cells in the incorporation of [35S]Met/Cys into trichloracetic acid-precipitable microsomal proteins, immunoaffinity purification of 2E1 revealed that incorporation of 35S-labeled amino acids specifically into 2E1 was elevated by acetone to 200% of control values. Treatment of hepatocytes with the transcriptional inhibitor, alpha-amanitin, markedly inhibited this acetone-mediated increase in [35S]Met/Cys incorporation into 2E1. Analysis of hepatocyte RNA revealed that acetone increased 2E1 mRNA to 130 and 160% of control levels at 6 and 24 hr, respectively, and that these increases were prevented by pretreatment with alpha-amanitin. Our results indicate that acetone increases 2E1 protein levels in cultured rabbit hepatocytes by stimulating its rate of de novo synthesis. Since this increase in 2E1 synthesis stems, at least in part, from the acetone-mediated enhancement of hepatocyte 2E1 mRNA content and is inhibitable by alpha-amanitin, transcriptional activation of the rabbit CYP2E1 gene is apparently involved in the induction of 2E1 protein by acetone.

Acetaminophen-induced cytotoxicity in cultured mouse hepatocytes: effects of Ca(2+)-endonuclease, DNA repair, and glutathione depletion inhibitors on DNA fragmentation and cell death.

Hepatotoxic alkylation of mouse liver cells by acetaminophen is characterized by an early loss of ion regulation, accumulation of Ca2+ in the nucleus, and fragmentation of DNA in vitro and in vivo. Acetaminophen-induced DNA cleavage is accompanied by the formation of a "ladder" of DNA fragments characteristic of Ca(2+)-mediated endonuclease activation. These events unfold well in advance of cytotoxicity and the development of necrosis. The present study utilized cultured mouse hepatocytes and mechanistic probes to test whether DNA fragmentation and cell death might be related in a "cause-and-effect" manner. Cells were isolated by collagenase perfusion, cultured in Williams' E medium for 22-26 hr, and exposed to acetaminophen. Aurintricarboxylic acid, a general Ca(2+)-endonuclease inhibitor, and EGTA, a chelator of Ca2+ required for endonuclease activation, significantly decreased DNA fragmentation at 6 and 12 hr and virtually abolished cytotoxicity. N-Acetylcysteine also eliminated DNA fragmentation and cytotoxicity. 3-Aminobenzamide, an inhibitor of poly(ADP-ribose) polymerase-stimulated DNA repair, failed to alter the amount of DNA fragmentation at 6 hr but substantially increased acetaminophen cytotoxicity in hepatocytes at 12 hr. With the exception of when DNA repair was inhibited by 3-aminobenzamide, Ca2+ accumulation in the nucleus, DNA fragmentation, and hepatocyte death varied consistently and predictably with one another. Collectively, these findings suggest that unrepaired damage to DNA contributes to acetaminophen-induced cell death in vivo and may play a role in necrosis in vivo.

Inhibition of cell division in hepatoma cell cultures by chlordecone and carbon tetrachloride combination.

The propensity of chlordecone (CD) to potentiate the hepatotoxic and lethal effects of CCl(4) is well established. Mirex (M), a close structural analogue of CD, or phenobarbital (PB), both powerful inducers of hepatic microsomal drug metabolizing enzymes, are much weaker potentiators of CCl(4) toxicity. Considerable evidence has accumulated to suggest that this increase in CCl(4) toxicity caused by CD is due to the failure of the hepatocellular regeneration, tissue repair and hepatolobular restoration mechanisms. This interaction occurs at concentrations of CD and CCl(4) that are individually non-toxic and do not interfere with hepatocellular division. To test this unique interaction at cellular level, we employed a rapidly dividing Reuber hepatoma cell line in vitro. Cells were pretreated with a non-toxic dose of either CD, M or PB and exposed to a single addition of CCl(4) in the concentration range 5 to 40 mm 16 days later. The results indicate that CD + CCl(4) combination specifically arrested hepatocellular division. The inhibition of cell division occurred at individually non-toxic concentrations of CD and CCl(4). M + CCl(4) or PB + CCl(4) failed to manifest similar effects. At higher concentrations, these combinations caused cellular toxicity, resulting in cell death. Suppression of cell division might play an important role in the progression of chemical-induced toxicities in the liver. This unique observation opens up new avenues to investigate biochemical molecular mechanisms underlying the interference with hepatocellular division.