S-adenosylmethionine synthesis: molecular mechanisms and clinical implications

Protection of S-adenosyl methionine against the toxicity of clivorine on hepatocytes

In this study, we investigated the protective effects of S-adenosyl-l-methionine (SAM), which is a precursor of cellular reduced glutathione (GSH), against the hepatotoxicity of pyrrolizidine alkaloid clivorine. MTT assay showed that SAM (5μM) prevented the cytotoxicity of clivorine on human normal liver L-02 cells. DNA fragmentation assay showed that SAM (5μM) improved clivorine-induced L-02 cell apoptosis, and the results of Western blot showed that SAM (5μM) decreased clivorine-induced caspase-3 activation. Cellular GSH analysis showed that when L-02 cells were exposed to different concentrations (0, 3, 10, 30, 50 and 100μM) of clivorine for 48h, cellular GSH was decreased in a concentration-dependent manner, while SAM (5μM) enhanced 50μM clivorine decreased cellular GSH. Further MTT assay showed that 5mM GSH and 5mM N-acetyl-l-cysteine (NAC) both had protective effects against clivorine-induced hepatotoxicity. Our results suggest that SAM has protective effects against the hepatotoxicity of clivorine possibly by enhancing cellular GSH level and increasing cellular defensive ability against clivorine-induced cytotoxicity.

Targeting the methionine cycle for melanoma therapy with 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin

The higher expression of methionine cycle genes in melanoma cells than in normal melanocytes may be related with increased protein synthesis and transmethylation reactions and the subsequent need for high levels of methionine. 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG), a trimethoxy derivative of epicatechin-3-gallate (ECG), effectively suppressed proliferation of melanoma cells in cultures by inducing apoptosis. TMECG modulates the expression of genes involved in methionine metabolism, cellular methylation and glutathione synthesis in melanoma cells. TMECG treatment of melanoma cells resulted in the downregulation of antiapoptotic Bcl-2, the upregulation of proapoptotic Bax and the activation of caspase-3; however, it did not induce the expression of the apoptosis protease-activating factor-1 (Apaf-1). Having elucidated the effects of TMECG on the melanoma methionine cycle, we designed therapeuthical strategies to increase its effectiveness. Combinations of TMECG with S-adenosylmethionine or compounds that modulate the intracellular concentration of adenosine strongly increase the antiproliferative effects of TMECG. The ability of TMECG to target multiple aspects related with melanoma survival, with a high degree of potency, points to its clinical value in melanoma therapy.

The transition from fatty liver to NASH associates with SAMe depletion in db/db mice fed a methionine choline-deficient diet

Nonalcoholic fatty liver disease (NAFLD) is highly prevalent in the Western population. By mechanisms that are not completely understood, this disease may progress to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). db/db mice spontaneously develop hepatic steatosis, which progresses to NASH when these mice are fed a methionine choline-deficient (MCD) diet. The goal of our studies was to identify lipid and methionine metabolism pathways affected by MCD feeding to determine potential causal events leading to the development of NASH from benign steatosis. db/db mice fed the MCD diet for 2 weeks exhibited signs of incipient NASH development such as upregulated cytokines and chemokines. At this time point, MCD diet feeding caused S-adenosylmethionine (SAMe) depletion in db/db mice, while wild-type mice on the same diet retained hepatic SAMe levels. SAMe depletion exerts pleiotropic effects upon liver homeostasis and is commonly associated with a variety of liver insults such as thioacetamide, CCL4, and alcohol treatment; thus, SAMe depletion may serve as the second hit in NASH development. It is possible that differences in hepatic lipid and/or methionine metabolism between wild-type and db/db mice underlay the differential maintenance of SAMe levels during methionine and choline restriction. Indeed, db/db mice exhibited inhibited lipid oxidation pathways, which may be a priming factor for NASH development, and db/db mice fed the MCD diet had differential methionine adenosyltransferase (MAT) expression. The occurrence of SAMe depletion at this early, benign stage of NASH development in db/db mice with fatty liver suggests that SAMe supplementation may be (A) targeted to individuals susceptible to NASH (i.e., NAFLD patients) and (B) preventative of NASH before substantial liver injury has occurred.

S-adenosyl-L-methionine attenuates oxidative stress and hepatic stellate cell activation in an ethanol-LPS-induced fibrotic rat model

Previous studies report S-adenosyl-L-methionine (SAMe) can exert hepatoprotective effects. At present, the role of SAMe in affecting the activation and/or proliferation of hepatic stellate cells (HSCs) during alcohol-induced fibrotic disease progression is poorly understood. In the human disease state, chronic ethanol intake increases hepatic exposure to LPS and magnifies the hepatic insult leading to fibrosis and cirrhosis. In this study, we developed a "2-hit" ethanol-LPS fibrotic liver rat model with which to investigate the effects of SAMe as a hepatic antifibrotic treatment. Male rats were maintained on liquid diets containing either ethanol or isocalorically matched controls for 8 weeks. Animals received ethanol alone (E), ethanol concomitant with twice weekly LPS injections (EL), or ethanol, LPS, and daily SAMe injections. When using this model, SAMe-treated animals demonstrated significantly decreased fibrosis, oxidative stress, steatosis, and improved liver function versus the EL group. In addition, the EL group showed increased HSC activation, an effect that was abrogated by the addition of SAMe. Analysis of the transforming growth factor-beta (TGF-beta) signaling pathways demonstrated increased hepatic TGF-beta and Smad3 messenger RNA expression in the E and EL groups, which was inhibited in the presence of SAMe. Conversely, SAMe led to increased Smad7 (an inhibitor of TGF-beta signaling) messenger RNA expression. These data demonstrate chronic ethanol feeding combined with LPS induces liver fibrosis, and the addition of SAMe significantly reduces hepatic injury and fibrosis through inhibition of oxidative stress and HSC activation.

Beneficial drugs for liver diseases

Liver diseases are a major problem of worldwide proportions. However, the number of drugs actually used successfully in humans is very small. In this review some of the most promising/studied drugs utilized for liver diseases were chosen and analysed critically from the basic to the clinical point of view. Antiviral agents are not discussed because excellent reviews have appeared on this topic. The compounds/preparations described herein are, alphabetically: colchicine, corticosteroids, curcumin, glycyrrhizin, interferons (for their antifibrotic properties), Liv 52, nitric oxide, resveratrol, silymarin, sulfoadenosylmethionine, and thalidomide. Colchicine and corticosteroids have been studied extensively in animals and humans; most clinical studies suggest that these compounds are not useful in the treatment of liver diseases. Glycyrrhizin is an herbal medicine with several components that has interesting hepatoprotective properties in patients with subacute liver failure but deserves more prospective controlled trials. Interferon has shown interesting antifibrotic properties in animals and humans; prospective studies on their antifibrotic/fibrolytic activity are required. Curcumin, resveratrol and thalidomide are very attractive newly discovered protective and curative compounds on experimental hepatic diseases. Their mechanism of action is associated with the ability to down-regulate NF-kappaB and to decrease pronecrotic and profibrotic cytokines. Unfortunately, clinical studies are lacking. Sulfoadenosylmethionine and silymarin are also promising drugs utilized mainly in cholestasis but the benefits can be expanded if more controlled trials are performed. The future is to carry out controlled prospective double-blind multicenter studies with the newly discovered drugs with proven beneficial effects on animals. Fundamental hepatobiology should also be encouraged.

S-adenosyl-L-methionine decreases the elevated hepatotoxicity induced by Fas agonistic antibody plus acute ethanol pretreatment in mice

The current study was designed to investigate the effect and potential mechanism of exogenous administration of S-adenosyl-l-methionine (SAM) on the enhanced hepatotoxicity induced by the Fas agonistic Jo2 antibody plus acute ethanol pretreatment in C57BL/6 mice. Acute ethanol plus Jo2 treatment produces liver toxicity under conditions in which ethanol alone or Jo2 alone do not. SAM significantly attenuated this elevated hepatotoxicity in mice as manifested by a decrease of serum aminotransferases and morphological amelioration. Levels of SAM and activity of methionine adenosyltransferase were lowered by the ethanol plus Jo2 treatment but restored by administration of SAM. The ethanol plus Jo2 treatment increased activity and content of CYP2E1, iNOS content and TNF-alpha levels; these increases were blunted by SAM. SAM also protected against the elevated oxidative and nitrosative stress found after ethanol plus Jo2, likely due to the decreases in CYP2E1, iNOS and TNF-alpha. Calcium-induced swelling of mitochondria was enhanced by the ethanol plus Jo2 treatment and this was prevented by SAM. JNK and P38 MAPK were activated by the ethanol plus Jo2 treatment; JNK activation was partially prevented by SAM. It is suggested that SAM protects against the ethanol plus Jo2 toxicity by restoring hepatic SAM levels, preventing the increase in iNOS, CYP2E1 and TNF-alpha and there by lowering the elevated oxidative/nitrosative stress and activation of the JNK signal pathway, ultimately preventing mitochondrial damage.

A decrease in S-adenosyl-L-methionine potentiates arachidonic acid cytotoxicity in primary rat hepatocytes enriched in CYP2E1

Previous studies show that treatment with a polyunsaturated fatty acid, arachidonic acid (AA), or high concentrations of cycloleucine, an inhibitor of methionine adenosyltransferase (MAT), which lowers levels of S-adenosyl-L-methionine (SAM), increased toxicity in hepatocytes from pyrazole-treated rats which expressed high levels of cytochrome P450 2E1 (CYP2E1). In this study, I used concentrations of cycloleucine or AA, which by themselves do not produce any toxicity, to evaluate whether a decrease in SAM sensitizes hepatocytes to AA toxicity, especially in hepatocytes enriched in CYP2E1. Levels of SAM were lower by 50% in hepatocytes from pyrazole- compared to saline-treated rats. Cycloleucine treatment caused a 50% decline in SAM levels with both hepatocyte preparations and SAM levels were lowest in the pyrazole-treated hepatocytes. The combination of cycloleucine plus AA produced some toxicity and apoptosis in hepatocytes from saline-treated rats but increased toxicity and apoptosis was found in the hepatocytes from pyrazole-treated rats. Cytotoxicity could be prevented by incubation with SAM, the antioxidant trolox, and the mitochondrial permeability transition inhibitor trifluoperazine. The enhanced cytotoxicity could also be protected by treating rats with chlormethiazole, a specific inhibitor of CYP2E1, thus validating the role of CYP2E1. Cycloleucine plus AA treatment elevated production of reactive oxygen species (ROS) and lipid peroxidation to greater extents with the hepatocytes from pyrazole-treated rats than that from the saline-treated rats. I hypothesize that increased production of ROS by hepatocytes enriched in CYP2E1 potentiates AA-induced lipid peroxidation and toxicity when hepatoprotective levels of SAM are lowered. Such interactions, e.g. induction of CYP2E1, decline in SAM and polyunsaturated fatty acid-induced lipid peroxidation, may contribute to alcohol-induced liver injury.

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

Fatty liver disease associated with chronic alcohol consumption or obesity/type 2 diabetes has emerged as a serious public health problem. Steatosis, accumulation of triglyceride in hepatocytes, is now recognized as a critical "first-hit" in the pathogenesis of liver disease. It is proposed that steatosis "primes" the liver to progress to more severe liver pathologies when individuals are exposed to subsequent metabolic and/or environmental stressors or "second-hits." Genetic risk factors can also influence the susceptibility to and severity of fatty liver disease. Furthermore, oxidative stress, disrupted nitric oxide (NO) signaling, and mitochondrial dysfunction are proposed to be key molecular events that accelerate or worsen steatosis and initiate progression to steatohepatitis and fibrosis. This review article will discuss the following topics regarding the pathobiology and molecular mechanisms responsible for fatty liver disease: (1) the "two-hit" or "multi-hit" hypothesis, (2) the role of mitochondrial bioenergetic defects and oxidant stress, (3) the interplay between NO and mitochondria in fatty liver disease, (4) genetic risk factors and oxidative stress-responsive genes, and (5) the feasibility of antioxidants for treatment.

S-Adenosylmethionine in cell growth, apoptosis and liver cancer

S-Adenosylmethionine (SAMe), the principal biological methyl donor, is synthesized from methionine and ATP in a reaction catalyzed by methionine adenosyltransferase (MAT). In mammals, two genes (MAT1A and MAT2A), encode for two homologous MAT catalytic subunits, while a third gene MAT2beta, encodes for the beta-subunit that regulates MAT2A-encoded isoenzyme. Normal liver expresses MAT1A, whereas extrahepatic tissues express MAT2A. MAT2A and MAT2 beta are induced in human hepatocellular carcinoma (HCC), which facilitate cancer cell growth. Patients with cirrhosis of various etiologies, including alcohol, have decreased hepatic MAT activity and SAMe biosynthesis. Consequences of hepatic SAMe deficiency as illustrated by the Mat1a knock-out mouse model include increased susceptibility to steatosis and oxidative liver injury, spontaneous development of steatohepatitis and HCC. Predisposition to HCC can be partly explained by the effect of SAMe on growth. Thus, SAMe inhibits the mitogenic effect of growth factors such as hepatocyte growth factor and, following partial hepatectomy, a fall in SAMe level is required for the liver to regenerate. During liver regeneration, the fall in hepatic SAMe is transient. If the fall were to persist, it would favor a proliferative phenotype and, ultimately, development of HCC. Not only does SAMe control liver growth, it also regulates apoptosis. Interestingly, SAMe is anti-apoptotic in normal hepatocytes but pro-apoptotic in liver cancer cells. In liver cancer cells but not in normal human hepatocytes, SAMe can selectively induce Bcl-x(S), an alternatively spliced isoform of Bcl-x(L) that promotes apoptosis. This should make SAMe an attractive agent for both chemoprevention and treatment of HCC.

Application of prodrugs to inflammatory diseases of the gut

Oral delivery is the most common and preferred route of drug administration although the digestive tract exhibits several obstacles to drug delivery including motility and intraluminal pH profiles. The gut milieu represents the largest mucosal surface exposed to microorganisms with 10^10-12 colony forming bacteria/g of colonic content. Approximately, one third of fecal dry matter is made of bacteria/ bacterial components. Indeed, the normal gut microbiota is responsible for healthy digestion of dietary fibers (polysaccharides) and fermentation of short chain fatty acids such as acetate and butyrate that provide carbon sources (fuel) for these bacteria. Inflammatory bowel disease (IBD) results in breakage of the mucosal barrier, an altered microbiota and dysregulated gut immunity. Prodrugs that are chemically constructed to target colonic release or are degraded specifically by colonic bacteria, can be useful in the treatment of IBD. This review describes the progress in digestive tract prodrug design and delivery in light of gut metabolic activities.

Heme oxygenase-1 is a novel target and antioxidant mediator of S-adenosylmethionine

The sulfur compound and dietary supplement S-adenosylmethionine (SAM) has been reported to have cytoprotective and antioxidant properties. However, the underlying mechanisms remain unresolved. The present study investigates the effect of SAM on the expression of the antioxidant stress proteins heme oxygenase-1 (HO-1) and ferritin in endothelial cells. Induction of the HO-1/ferritin-system leads to protection of tissues against several inflammatory stimuli. SAM increased the protein and mRNA levels of HO-1 in cultured endothelial cells. Induction of HO-1 gene expression was associated with elevated ferritin protein levels and regulated at the transcriptional level via increased promoter activity. HO-1 upregulation by SAM was causally related to a decrease in NADPH-mediated production of oxygen radicals. Our results demonstrate that the HO-1/ferritin-system is a novel target of the antioxidant compound SAM.

Alleviation of acute ethanol-induced liver injury and impaired metabolomics of S-containing substances by betaine supplementation

Oxidative stress is suggested to play a key role in the development of alcoholic liver injury. We investigated the induction of oxidative damage in association with changes in hepatic concentrations of sulfur-containing substances in mice challenged with binge-like ethanol administration. Also the protective effect of dietary betaine against ethanol-induced liver injury was determined. Serum alanine aminotransferase activity, TNFalpha level, and hepatic malondialdehyde level were increased significantly by ethanol administration. Hepatic Cyp2e1 was induced to 250% of control. Ethanol administration decreased hepatic S-adenosylmethionine, cysteine, and glutathione, but elevated hypotaurine and taurine levels. Betaine supplied in drinking water for 2 weeks attenuated the induction of alcoholic liver injury and Cyp2e1 significantly. Reduction of hepatic S-adenosylmethionine and glutathione was alleviated, and elevation of hypotaurine and taurine was depressed. The results suggest that betaine may protect the liver against ethanol-induced oxidative injury most probably via its effects on the sulfur-amino acid metabolism.

Ecto-5'-nucleotidase (CD73) -mediated extracellular adenosine production plays a critical role in hepatic fibrosis

Adenosine is a potent endogenous regulator of tissue repair that is released from injured cells and tissues. Hepatic fibrosis results from chronic hepatic injury, and we have previously reported that endogenously generated adenosine, acting at A(2A) receptors, plays a role in toxin-induced hepatic fibrosis. Adenosine may form intracellularly and then be transported to the extracellular space or it may form extracellularly from adenine nucleotides released from injured cells. Because ecto-5'-nucleotidase (CD73) catalyzes the terminal step in extracellular adenosine formation from AMP, we determined whether CD73 plays a role in the development of hepatic fibrosis. Mice were treated overnight with PBS, CCl(4), ethanol, or thioacetamide (TAA); their livers were harvested, and slices were incubated in medium for 20 h before adenosine concentration in the supernatant was measured by HPLC. Hepatic fibrosis was induced by CCl(4) or TAA treatment in CD73 knockout (CD73KO and C57BL/6 background) and C57BL/6 control mice [wild-type (WT)] mice and quantified by digital analysis of picrosirius red stained slides and hydroxyproline content. mRNA expression was quantified by real-time polymerase chain reaction, and protein was quantified by Western blot or enzyme-linked immunosorbent assay. Livers from WT mice treated with CCl(4), ethanol, and TAA released 2- to 3-fold higher levels of adenosine than livers from comparably treated CD73KO mice. CD73KO mice were protected from fibrosis with significantly less collagen content in the livers of CD73KO than WT mice after treatment with either CCl(4) or TAA. There were far fewer alpha-smooth muscle actin positive hepatic stellate cells in CCl(4)-treated KO mice than that in WT mice. After CCl(4) treatment, the mRNA level of A(1), A(2A), A(2B), and A(3) adenosine receptors, tumor necrosis factor-alpha, interleukin (IL) -1beta, IL-13r alpha1, matrix metalloproteinase (MMP)-2, MMP-14, tissue inhibitor of metalloproteinase (TIMP) -1, and TIMP-2, and IL-13 level increased markedly in both CD73KO and WT mice, but Col1 alpha1, Col3 alpha1, and transforming growth factor-beta1 mRNA increased much more in WT mice than that in KO mice. Moreover, IL-13r alpha2, MMP-13 mRNA, and MMP-13 protein were higher in KO mice than that in WT mice. These results indicate that adenosine, formed extracellularly from adenine nucleotides, plays a major role in the pathogenesis of hepatic fibrosis and that inhibition of adenosine production or blockade of adenosine receptors may help prevent hepatic fibrosis.

Cobalamin potentiates vinblastine cytotoxicity through downregulation of mdr-1 gene expression in HepG2 cells

BACKGROUND

P-glycoprotein (Pgp), produced by multidrug resistance-1 gene (mdr-1), is a main mechanism developed by cancer cells to guard against anti-cancer drugs. Alterations of DNA methylation of the mdr-1 gene promoter are known to be linked to mdr-1 gene expression and are probably related to intracellular S-adenosyl-methionine. We here used HepG2 cells to determine the role of the methionine cycle (through the use of the Methionine-Synthase (MS) cofactor, cobalamin) on mdr-1 gene expression.

METHODS

Semiquantitative RT-PCR of mdr-1 gene, cellular retention of rhodamine-123, and vinblastine cytotoxicity were carried out on cells cultivated with and without cobalamin. Methylation status of the mdr-1 gene promoter was determined by methylation-specific PCR.

RESULTS

Addition of cobalamin to the cells led to an increase in MS activity, to a significant decrease in mdr-1 gene expression which is correlated to an increase in retention of the Pgp substrate Rhodamine 123. Furthermore, cobalamin potentiated cell sensitivity to vinblastine to the same range as that of the Pgp blocker verapamil and prevented methotrexate-induced up-regulation of mdr-1 gene expression. However, no modification in methylation of the mdr-1 gene promoter was observed.

CONCLUSION

Cobalamin downregulates mdr-1 gene expression, as well as Pgp expression and function, and significantly increases cytotoxicity of vinblastine. The identification of this novel way of diminishing cellular resistance to the chemotherapeutic agent vinblastine holds promises of leading to better treatments for cancer patients.

Treatment of chronic liver injuries in mice by oral administration of ethanolic extract of the fruit of Hovenia dulcis

The present study examined the effects of an ethanolic extract of the fruit of Hovenia dulcis (EHD) on chronic hepatitis induced by carbon tetrachloride (CCl(4)) in mice. CCl(4) (5%; 0.1 ml/10 g body weight) was given twice a week for 9 weeks, and mice received EHD throughout the entire experimental period. Plasma activities of GPT and GOT, and hepatic levels of malondialdehyde were significantly lowered in mice treated with EHD as compared to mice treated with CCl(4) only. Histological evaluation showed that EHD could attenuate the liver fibrosis and necrosis caused by CCl(4). RT-qPCR analysis also showed that EHD treatment decreased hepatic collagen (alpha1)(I) and collagen (alpha1)(III) mRNA expressions. Chronic CCl(4) treatment caused liver injuries in mice, characterized by an increase in hepatic methionine adenosyltransferase (MAT) 2A gene expression, and decreased MAT1A gene expression. EHD significantly reduced the changes in MAT gene expression due to the chronic CCl(4) treatment. These results clearly demonstrate that the EHD can reduce hepatic injuries in mice induced by CCl(4).

The pathogenesis of ethanol versus methionine and choline deficient diet-induced liver injury

The differences and similarities of the pathogenesis of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH) were examined. Mice (six/group) received one of four Lieber-Decarli liquid diets for 6 weeks: (1) paired-fed control diet; (2) control diet with ethanol (ethanol); (3) paired-fed methionine/choline deficient (MCD) diet; and (4) MCD plus ethanol (combination). Hepatotoxicity, histology, and gene expression changes were examined. Both MCD and ethanol induced macrovesicular steatosis. However, the combination diet produced massive steatosis with minor necrosis and inflammation. MCD and combination diets, but not ethanol, induced serum ALT levels by 1.6- and 10-fold, respectively. MCD diet, but not ethanol, also induced serum alkaline phosphatase levels suggesting bile duct injury. Ethanol increased liver fatty acid binding protein (L-FABP) mRNA and protein levels. In contrast, the combination diet decreased L-FABP mRNA and protein levels and increased hepatic free fatty acid and lipid peroxide levels. Ethanol, but not MCD, reduced hepatic S-adenosylmethionine (SAM) and GSH levels. Hepatic TNFalpha protein levels were increased in all treatment groups, however, IL-6, a hepatoprotective cytokine which promotes liver regeneration was increased in ethanol-fed mice (2-fold), but decreased in the combination diet-treated mice. In addition, the combination diet reduced phosphorylated STAT3 and Bcl-2 levels. While MCD diet might cause bile duct injury and cholestasis, ethanol preferentially interferes with the SAM-GSH oxidative stress pathway. The exacerbated liver injury induced by the combination diet might be explained by reduced L-FABP, increased free fatty acids, oxidative stress, and decreased IL-6 protein levels. The combination diet is an efficient model of steatohepatitis.

Enhancing yield of S-adenosylmethionine in Pichia pastoris by controlling NH4 + concentration

Yield of S-adenosylmethionine was improved significantly in recombinant Pichia pastoris by controlling NH(4)(+) concentration. The highest production rate was 0.248 g/L h when NH(4)(+) concentration was 450 mmol/L and no repression of cell growth was observed. Within very short induction time (47 h), 11.63 g/L SAM was obtained in a 3.7 L bioreactor.

S-adenosyl methionine protects ob/ob mice from CYP2E1-mediated liver injury

Pyrazole treatment to induce cytochrome P-450 2E1 (CYP2E1) was recently shown to cause liver injury in ob/ob mice but not in lean mice. The present study investigated the effects of S-adenosyl-l-methionine (SAM) on the CYP2E1-dependent liver injury in ob/ob mice. Pyrazole treatment of ob/ob mice for 2 days caused necrosis, steatosis, and elevated serum transaminase and triglyceride levels compared with saline ob/ob mice. Administration of SAM (50 mg/kg body wt ip every 12 h for 3 days) prevented the observed pathological changes as well as the increase of apoptotic hepatocytes, caspase 3 activity, and serum TNF-alpha levels. SAM administration inhibited CYP2E1 activity but not CYP2E1 content. The pyrazole treatment increased lipid peroxidation, 4-hydroxynonenal and 3-nitrotyrosine protein adducts, and protein carbonyls. These increases in oxidative and nitrosative stress were prevented by SAM. Treatment of ob/ob mice with pyrazole lowered the endogenous SAM levels, and these were elevated after SAM administration. Mitochondrial GSH levels were very low after pyrazole treatment of the ob/ob mice; this was associated with elevated levels of malondialdehyde and 4-hydroxynonenal and 3-nitrotyrosine protein adducts in the mitochondria. All these changes were prevented with SAM administration. SAM protected against pyrazole-induced increase in serum transaminases, necrosis, triglyceride levels, caspase-3 activity, and lipid peroxidation even when administered 1 day after pyrazole treatment. In the absence of pyrazole, SAM lowered the slightly elevated serum transaminases, triglyceride levels, caspase-3 activity, and lipid peroxidation in obese mice. In conclusion, SAM protects against and can also reverse or correct CYP2E1-induced liver damage in ob/ob mice.

[Steatosis, chronic hepatitis virus C infection and homocysteine]

Homocysteine, a sulfuric amino acid involved in methionine metabolism, belongs to the group of intracellular thiols. Hyperhomocysteinemia is frequent in the Caucasian population (more than 15%) and its role in vascular pathology has been clearly established. In hepatology, experimental data in transgenic mice deficient in homocysteine metabolism enzymes have shown the presence of severe liver steatosis with occasional steatohepatitis. In human beings, many studies have found a correlation between homocysteine and steatosis or even NASH. Some authors have suggested a discriminating threshold to differentiate simple steatosis from NASH. In chronic hepatitis C, preliminary data have shown that hyperhomocysteinemia is an independent risk factor for steatosis or even fibrosis. The physiopathological mechanism has now begun to be better understood. On one hand, there is a strong correlation between homocysteine and insulin resistance whatever its etiology. On the other hand, homocysteine has a direct effect on the liver, resulting in over expression of SREBP-1 and favouring steatosis. It stimulates proinflammatory cytokine secretion such as NF kappa B increasing the risk of NASH. Finally, homocysteine could increase the risk of fibrosis by stimulating TIMP 1. Moreover hepatitis C virus induces hypomethylation of STAT 1 and could decrease the antiviral activity of interferon. Results from in vitro studies have shown that the normalisation of STAT 1 methylation by bringing betaine and S Adenosyl Methionine (which belongs to homocysteine cycle) restores the antiviral activity of interferon. These data should be confirmed to evaluate the importance of homocysteine dosage in the diagnosis of NASH. Finally, treatment of hyperhomocysteinemia could have favourable consequences in steatopathies and HCV infection.

Depletion of S-adenosyl-l-methionine with cycloleucine potentiates cytochrome P450 2E1 toxicity in primary rat hepatocytes

S-Adenosyl-l-methionine (SAM) is the principal biological methyl donor. Methionine adenosyltransferase (MAT) catalyzes the only reaction that generates SAM. Hepatocytes were treated with cycloleucine, an inhibitor of MAT, to evaluate whether hepatocytes enriched in cytochrome P450 2E1 (CYP2E1) were more sensitive to a decline in SAM. Cycloleucine decreased SAM and glutathione (GSH) levels and induced cytotoxicity in hepatocytes from pyrazole-treated rats (with an increased content of CYP2E1) to a greater extent as compared to hepatocytes from saline-treated rats. Apoptosis caused by cycloleucine in pyrazole hepatocytes appeared earlier and was more pronounced than control hepatocytes and could be prevented by incubation with SAM, glutathione reduced ethyl ester and antioxidants. The cytotoxicity was prevented by treating rats with chlormethiazole, a specific inhibitor of CYP2E1. Cycloleucine induced greater production of reactive oxygen species (ROS) in pyrazole hepatocytes than in control hepatocytes, and treatment with SAM, Trolox, and chlormethiazole lowered ROS formation. In conclusion, lowering of hepatic SAM levels produced greater toxicity and apoptosis in hepatocytes enriched in CYP2E1. This is due to elevated ROS production by CYP2E1 coupled to lower levels of hepatoprotective SAM and GSH. We speculate that such interactions e.g. induction of CYP2E1, decline in SAM and GSH may contribute to alcohol liver toxicity.

Role of S-adenosyl-L-methionine in liver health and injury

S-adenosylmethionine (SAMe) has rapidly moved from being a methyl donor to a key metabolite that regulates hepatocyte growth, death, and differentiation. Biosynthesis of SAMe occurs in all mammalian cells as the first step in methionine catabolism in a reaction catalyzed by methionine adenosyltransferase (MAT). Decreased hepatic SAMe biosynthesis is a consequence of all forms of chronic liver injury. In an animal model of chronic liver SAMe deficiency, the liver is predisposed to further injury and develops spontaneous steatohepatitis and hepatocellular carcinoma. However, impaired SAMe metabolism, which occurs in patients with mutations of glycine N-methyltransferase (GNMT), can also lead to liver injury. This suggest that hepatic SAMe level needs to be maintained within a certain range, and deficiency or excess can both lead to abnormality. SAMe treatment in experimental animal models of liver injury shows hepatoprotective properties. Meta-analyses also show it is effective in patients with cholestatic liver diseases. Recent data show that exogenous SAMe can regulate hepatocyte growth and death, independent of its role as a methyl donor. This raises the question of its mechanism of action when used pharmacologically. Indeed, many of its actions can be recapitulated by methylthioadenosine (MTA), a by-product of SAMe that is not a methyl donor. A better understanding of why liver injury occurs when SAMe homeostasis is perturbed and mechanisms of action of pharmacologic doses of SAMe are essential in defining which patients will benefit from its use.

Silencing MAT2A gene by RNA interference inhibited cell growth and induced apoptosis in human hepatoma cells

AIMS

A switch in gene expression from MAT1A to MAT2A was found in liver cancer, suggesting that MAT2A plays an important role in facilitating cancer growth. MAT2A is an interesting target for antineoplastic therapy. The molecular mechanisms of silencing MAT2A by RNA interference inhibited cell growth and induced apoptosis in hepatoma cells was studied.

METHODS

We investigated the effects of MAT2A on S-adenosyl-methionine (SAM) production, cell growth and apoptotic cell death in hepatoma cell lines (Bel-7402, HepG2, and Hep3B) using an RNA interference approach.

RESULTS

The treatment of three hepatoma cell lines with small interfering RNA (siRNA) targeting to the MAT2A gene resulted in reducing the MAT II activity, facilitating SAM production, increasing SAM : SAH ratio, inhibiting cell growth and inducing cell apoptosis in hepatoma cells. In addition, silencing MAT2A gene resulted in the stimulation of MAT1A mRNA production, which was blocked by 3-deazaadenosine and l-ethionine, but not d-ethionine, suggesting that such effect was specific and mediated by upregulation of SAM level and SAM : S-adenosylethionine (SAH) ratio.

CONCLUSION

Silencing MAT2A by sequence-specific small interfering RNA caused a switch of MAT gene expression from MAT2A to MAT1A, which led the content of SAM to change to a higher steady-state level that resulted in the inhibition of cell growth and the induction of apoptotic cell death in human hepatoma cells. These results also suggested that MAT2A may hold potential as a new target for liver cancer gene therapy.

Differential gene expression patterns in cyclooxygenase-1 and cyclooxygenase-2 deficient mouse brain

Microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in cyclooxygenase-1 or cyclooxygenase-2 reveals that the two enzymes differentially modulate brain gene expression.

Background

Cyclooxygenase (COX)-1 and COX-2 produce prostanoids from arachidonic acid and are thought to have important yet distinct roles in normal brain function. Deletion of COX-1 or COX-2 results in profound differences both in brain levels of prostaglandin E₂ and in activation of the transcription factor nuclear factor-κB, suggesting that COX-1 and COX-2 play distinct roles in brain arachidonic acid metabolism and regulation of gene expression. To further elucidate the role of COX isoforms in the regulation of the brain transcriptome, microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in COX-1 (COX-1^-/-) or COX-2 (COX-2^-/-) was performed.

Results

A majority (>93%) of the differentially expressed genes in both the cortex and hippocampus were altered in one COX isoform knockout mouse but not the other. The major gene function affected in all genotype comparisons was 'transcriptional regulation'. Distinct biologic and metabolic pathways that were altered in COX^-/- mice included β oxidation, methionine metabolism, janus kinase signaling, and GABAergic neurotransmission.

Conclusion

Our findings suggest that COX-1 and COX-2 differentially modulate brain gene expression. Because certain anti-inflammatory and analgesic treatments are based on inhibition of COX activity, the specific alterations observed in this study further our understanding of the relationship of COX-1 and COX-2 with signaling pathways in brain and of the therapeutic and toxicologic consequences of COX inhibition.

Intracellular expression of Vitreoscilla hemoglobin improves S-adenosylmethionine production in a recombinant Pichia pastoris

To develop an efficient way to produce S-adenosylmethionine (SAM), methionine adenosyltransferase gene (mat) from Streptomyces spectabilis and Vitreoscilla hemoglobin gene (vgb) were coexpressed intracellularly in Pichia pastoris, both under control of methanol-inducible promoter. Expression of mat in P. pastoris resulted in about 27 times higher specific activity of methionine adenosyltransferase (SMAT) and about 19 times higher SAM production relative to their respective control, suggesting that overexpression of mat could be used as an efficient method for constructing SAM-accumulating strain. Under induction concentration of 0.8 and 2.4% methanol, coexpression of vgb improved, though to different extent, cell growth, SAM production, and respiratory rate. However, the effects of VHb on SAM content (specific yield of SAM production) and SMAT seemed to be methanol concentration-dependent. When cells were induced with 0.8% methanol, no significant effects of VHb expression on SAM content and specific SMAT could be detected. When the cells were induced with 2.4% methanol, vgb expression increased SAM content significantly and depressed SMAT remarkably. We suggested that under our experimental scheme, the presence of VHb might improve ATP synthesis rate and thus improve cell growth and SAM production in the recombinant P. pastoris.

Toward the discovery of new biomarkers of hepatocellular carcinoma by proteomics

Primary liver cancer is the fifth most frequent neoplasm and the third most common cause of cancer-related death, with more than 500,000 new cases diagnosed yearly. The outcome for hepatocellular carcinoma (HCC) patients still remains dismal, partly because of our limited knowledge of its molecular pathogenesis and the difficulty in detecting the disease at its early stages. Therefore, studies aimed at the definition of the mechanisms associated with HCC progression and the identification of new biomarkers leading to early diagnosis and more effective therapeutic interventions are urgently needed. Proteomics is a rapidly expanding discipline that is expected to change the way in which diseases will be diagnosed, treated, and monitored in the near future. In the last few years, HCC has been extensively investigated using different proteomic approaches on HCC cell lines, animal models, and human tumor tissues. In this review, state-of-the-art technology on proteomics is overviewed, and recent advances in liver cancer proteomics and their clinical projections are discussed.

Effect of vitamin B6 deficiency on S-adenosylhomocysteine hydrolase activity as a target point for methionine metabolic regulation

The objective of this study was to clarify the relationship between the accumulation of S-adenosylhomocysteine (SAH) and the change in the SAH hydrolase activity in vitamin B6 (B6). Male Wistar rats were fed a control diet (control and pair-fed groups) or B6-free diet (B6-deficient group) for 5 wk. Although the SAH-synthetic activity of SAH hydrolase significantly increased in the B6-deficient group, SAH-hydrolytic activity of SAH hydrolase showed no significant difference in the liver among the three groups. On the other hand, SAH hydrolase mRNA in the liver did not show any significant change. Thus, the accumulation of SAH would be due to the increased SAH-synthetic activity of SAH hydrolase. The disturbed methionine metabolism by B6-deficiency, such as a significant increase of plasma homocysteine, might induce the activation of SAH hydrolase in the direction of SAH synthesis.

S-adenosyl-L-methionine increases skeletal muscle mitochondrial DNA density and whole body insulin sensitivity in OLETF rats

Both mitochondrial dysfunction and alterations in mitochondrial DNA (mtDNA) are implicated in type 2 diabetes mellitus and insulin resistance. Evidence also suggests that metabolism of S-adenosyl-L-methionine (SAM), the universal methyl donor for biological methylation, is associated with mitochondrial dysfunction and insulin resistance. We investigated the effect of SAM on mtDNA density and insulin sensitivity using the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of type 2 diabetes mellitus and insulin resistance. To determine the short-term effect on mtDNA density, SAM (15 mg.kg-1.d-1) was administered intraperitoneally for 7 d to 6 male, 57-wk-old OLETF rats and 6 Long-Evans Tokushima Otsuka (LETO) rats of the same age as a nondiabetic control. To determine the long-term effect, the same dose of SAM was administered daily to 5 male, 6-wk-old OLETF rats until the age of 25 wk; 7 control OLETF rats received vehicle and 7 LETO rats were untreated. Skeletal muscle mtDNA density was measured by either competitive or multiplex PCR and insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. SAM treatment for 1 wk increased skeletal muscle mtDNA density of both OLETF and LETO rats. The long-term SAM treatment significantly reduced body weight gain as well as increased skeletal muscle mtDNA density and whole body insulin sensitivity in OLETF rats compared with their vehicle-treated controls. Furthermore, in all 3 groups, skeletal muscle mtDNA density correlated with insulin sensitivity (r=0.752, P<0.001). In conclusion, SAM treatment increased mtDNA density in the skeletal muscle, improved whole body insulin sensitivity, and prevented body weight gain in OLETF rats.

New insights into the regulation of methyl group and homocysteine metabolism

Hepatic folate, methyl group, and homocysteine metabolism are interrelated pathways that when disrupted are associated with numerous pathologies. Maintenance of normal methyl group and homocysteine homeostasis is dependent on the balance between: S-adenosylmethionine (SAM)-dependent transmethylation, which utilizes methyl groups and produces homocysteine; remethylation of homocysteine back to methionine by folate-dependent and -independent mechanisms; and homocysteine catabolism via the transsulfuration pathway. Recent studies have demonstrated that hormonal imbalance is a factor in the control of key proteins that regulate these pathways. A diabetic state is characterized by increased expression of specific methyltransferases that utilize SAM-derived methyl groups and produce homocysteine. Although the supply of methyl groups from the folate-dependent 1-carbon pool appears to be diminished under diabetic conditions, the increased production of homocysteine is compensated for by stimulation of folate-independent remethylation and catabolism by transsulfuration, resulting in hypohomocysteinemia. Similar changes have been observed with glucocorticoid administration and in a growth hormone-deficient model, which can be prevented by insulin and growth hormone treatment, respectively. Taken together, these reports clearly indicate that hormonal regulation is a major factor in the metabolic control of folate, methyl groups, and homocysteine, thereby providing a potential link between the pathologies associated with these pathways and hormonal imbalance.

Pathogenesis of non-alcoholic steatohepatitis: human data

Non-alcoholic fatty liver disease (NAFLD) has moved rapidly to the forefront of clinical disease, with a prevalence of 30% in the adult United States population and a definite but yet uncertain rate of progression to cirrhosis and end-stage liver disease. This disease has an impact on all areas of clinical medicine, with increasing prevalence and adversity. It is essential to understand the pathophysiologic mechanisms involved in NAFLD, so that therapeutic strategies can be developed. Although fatty liver may be caused by other factors, this review concentrates on fatty liver associated with insulin resistance, sometimes referred to as the primary form.

Amino acids and the regulation of methyl balance in humans

PURPOSE OF REVIEW

To outline recent advances in our understanding of the metabolic basis for the maintenance of cellular S-adenosylmethionine levels and, thus, for facilitating the many crucial methylation reactions in the body. Amino acids are intimately involved in these processes.

RECENT FINDINGS

The application of stable-isotope methodology has permitted accurate estimation of the total transmethylation flux in humans. Chemical balance studies have identified the quantitatively major transmethylation reactions. New evidence points to a key role for deranged S-adenosylmethionine metabolism in the pathogenesis of liver disease. Mutations in key enzymes point to the importance of methyl metabolism in closure of the neural tube, synthesis of creatine and metabolic clearance of methionine. Dietary interventions designed to affect S-adenosylmethionine availability to pregnant mice have been shown to modulate the epigenetic DNA methylation of specific genes.

SUMMARY

These findings are of relevance to the pathogenesis of neural tube defects as well as the interaction between a genetic polymorphism and nutritional status. They also address the issue of methyl group availability and epigenetic regulation. Finally, they are also relevant to the etiology of cirrhosis and steatohepatitis.

S-adenosylmethionine prevents chronic alcohol-induced mitochondrial dysfunction in the rat liver

An early event that occurs in response to alcohol consumption is mitochondrial dysfunction, which is evident in changes to the mitochondrial proteome, respiration defects, and mitochondrial DNA (mtDNA) damage. S-adenosylmethionine (SAM) has emerged as a potential therapeutic for treating alcoholic liver disease through mechanisms that appear to involve decreases in oxidative stress and proinflammatory cytokine production as well as the alleviation of steatosis. Because mitochondria are a source of reactive oxygen/nitrogen species and a target for oxidative damage, we tested the hypothesis that SAM treatment during alcohol exposure preserves organelle function. Mitochondria were isolated from livers of rats fed control and ethanol diets with and without SAM for 5 wk. Alcohol feeding caused a significant decrease in state 3 respiration and the respiratory control ratio, whereas SAM administration prevented these alcohol-mediated defects and preserved hepatic SAM levels. SAM treatment prevented alcohol-associated increases in mitochondrial superoxide production, mtDNA damage, and inducible nitric oxide synthase induction, without a significant lessening of steatosis. Accompanying these indexes of oxidant damage, SAM prevented alcohol-mediated losses in cytochrome c oxidase subunits as shown using blue native PAGE proteomics and immunoblot analysis, which resulted in partial preservation of complex IV activity. SAM treatment attenuated the upregulation of the mitochondrial stress chaperone prohibitin. Although SAM supplementation did not alleviate steatosis by itself, SAM prevented several key alcohol-mediated defects to the mitochondria genome and proteome that contribute to the bioenergetic defect in the liver after alcohol consumption. These findings reveal new molecular targets through which SAM may work to alleviate one critical component of alcohol-induced liver injury: mitochondria dysfunction.

The use of selected nutrition supplements and complementary and alternative medicine in liver disease

Almost all patients with liver disease, especially advanced liver disease, have some evidence of malnutrition, including mineral/vitamin deficiency. A major health trend in the United States has been the significant growth in the use of complementary and alternative medicine (CAM), including nutrition supplements and herbal agents. In the 1990s, the United States government created the National Center for Complementary and Alternative Medicine (NCCAM), as well as the Office on Dietary Supplements, to extend our knowledge in these areas. CAM users are often highly educated and frequently use CAM therapy for chronic diseases, including chronic liver disease. Indeed, most studies suggest that patients with chronic liver disease frequently use nutrition supplements and CAM agents in addition to their traditional medicines. The purpose of this review is to provide an update on the role of nutrition supplements and herbals in liver disease. This article will focus mainly on 7 selected agents (vitamin E, zinc, magnesium, S-adenosylmethionine, betaine, silymarin, and glycyrrhizin), for which there have been not only in vitro and animal studies but also human clinical trials, and we will review both potential efficacy and safety issues.

Comparison of S-Adenosyl-l-methionine and N-Acetylcysteine Protective Effects on Acetaminophen Hepatic Toxicity

Nutraceuticals are widely used by the general public, but very little information is available regarding the effects of nutritional agents on drug toxicity. Excessive doses of acetaminophen (APAP, 4-hydroxyacetanilide) induce hepatic centrilobular necrosis. The naturally occurring substance S-adenosyl-l-methionine (SAMe) has been reported to reduce the hepatic toxicity of APAP. The present study was designed to investigate the hepatoprotective effects of SAMe in comparison to the clinically used antidote N-acetylcysteine (NAC). Male C57BL/6 mice were injected intraperitoneally (i.p.) with an equimolar dose (1.25 mmol/kg) of either SAMe or NAC just before APAP, and the groups were denoted SAMe+APAP and NAC+APAP, respectively. Mice were immediately injected i.p. with 300 mg/kg APAP, and hepatotoxicity was evaluated after 4 h. SAMe was more hepatoprotective than NAC at a dose of 1.25 mmol/kg as liver weight was unchanged by APAP injection in the SAMe+APAP group, whereas liver weight was increased in the NAC+APAP group. SAMe was more hepatoprotective for APAP toxicity than NAC, because alanine aminotransferase levels were lower in the SAMe+APAP. Pretreatment with SAMe maintained total hepatic glutathione (GSH) levels higher than NAC pretreatment before APAP, although total hepatic GSH levels were lower in the SAMe+APAP and NAC+APAP groups than the vehicle control values. Oxidative stress was less extensive in the SAMe+APAP group compared with the APAP-treated mice as indicated by Western blots for protein carbonyls and 4-hydroxynonenal-adducted proteins. In summary, SAMe reduced APAP toxicity and was more potent than NAC in reducing APAP hepatotoxicity.

Interactions of cytokines, S-Adenosylmethionine, and S-Adenosylhomocysteine in alcohol-induced liver disease and immune suppression

Alcoholic liver disease (ALD) remains a leading cause of death in the USA. Defining mechanisms for liver cell death in ALD in order to develop potential new agents for therapeutic intervention is a major focus of the authors' work. Abnormal cytokine metabolism is a major feature of ALD, and a thorough understanding of both mechanisms and interactions of cytokine overproduction and sensitization are critical to developing a possible treatment for ALD. S-Adenosylmethionine has been used in a variety of animal studies and clinical trials and has been reported to improve biochemical parameters of liver function. Last, immunosuppression associated with chronic alcohol abuse is an important predisposing factor to opportunistic infections and cancer. It is the authors' working hypothesis that alcohol consumption leads to chronic activation of the immune system.

S-adenosyl-L-methionine for alcoholic liver diseases

BACKGROUND

Alcohol is a major cause of liver disease and disrupts methionine and oxidative balances. S-adenosyl-L-methionine (SAMe) acts as a methyl donor for methylation reactions and participates in the synthesis of glutathione, the main cellular antioxidant. Randomised clinical trials have addressed the question whether SAMe may benefit patients with alcoholic liver diseases.

OBJECTIVES

To evaluate the beneficial and harmful effects of SAMe for patients with alcoholic liver diseases.

SEARCH STRATEGY

We searched The Cochrane Hepato-Biliary Group Controlled Trials Register (May 2005), The Cochrane Central Register of Controlled Trials in The Cochrane Library (Issue 2, 2005), MEDLINE (1950 to May 2005), EMBASE (1980 to May 2005), and Science Citation Index Expanded (searched May 2005).

SELECTION CRITERIA

We included randomised clinical trials studying patients with alcoholic liver diseases. Interventions encompassed per oral or parenteral administration of SAMe at any dose versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

We performed all analyses according to the intention-to-treat method using RevMan Analyses provided by the Cochrane Collaboration. We evaluated the methodological quality of the randomised clinical trials by quality components.

MAIN RESULTS

We identified nine randomised clinical trials including a heterogeneous sample of 434 patients with alcoholic liver diseases. The methodological quality regarding randomisation was generally low, but 8 out of 9 trials were placebo controlled. Only one trial including 123 patients with alcoholic cirrhosis used adequate methodology and reported clearly on all-cause mortality and liver transplantation. We found no significant effects of SAMe on all-cause mortality (relative risks (RR) 0.62, 95% confidence interval (CI) 0.30 to 1.26), liver-related mortality (RR 0.68, 95% CI 0.31 to 1.48), all-cause mortality or liver transplantation (RR 0.55; 95% CI 0.27 to 1.09), or complications (RR 1.35, 95% CI 0.84 to 2.16), but the analysis is based mostly on one trial only. SAMe was not significantly associated with non-serious adverse events (RR 4.92; 95% CI 0.59 to 40.89) and no serious adverse events were reported.

AUTHORS' CONCLUSIONS

We could not find evidence supporting or refuting the use of SAMe for patients with alcoholic liver diseases. We need more long-term, high-quality randomised trials on SAMe for these patients before SAMe may be recommended for clinical practice.

Opposite action of S-adenosyl methionine and its metabolites on CYP2E1-mediated toxicity in pyrazole-induced rat hepatocytes and HepG2 E47 cells

S-adenosyl-L-methionine (SAMe) is protective against a variety of hepatotoxins, including ethanol. The ability of SAMe to protect against cytochrome P-450 2E1 (CYP2E1)-dependent toxicity was studied in hepatocytes from pyrazole-treated rats and HepG2 E47 cells, both of which actively express CYP2E1. Toxicity was initiated by the addition of arachidonic acid (AA) or by depletion of glutathione after treatment with L-buthionine sulfoximine (BSO). In pyrazole hepatocytes, SAMe (0.25-1 mM) protected against AA but not BSO toxicity. SAMe elevated GSH levels, thus preventing the decline in GSH caused by AA, and SAMe prevented AA-induced lipid peroxidation. SAMe analogs such as methionine or S-adenosyl homocysteine, which elevate GSH, also protected against AA toxicity. 5'-Methylthioadenosine (MTA), which cannot produce GSH, did not protect. The toxicity of BSO was not prevented by SAMe and the analogs because GSH cannot be synthesized. In contrast, in E47 cells, SAMe and MTA but not methionine or S-adenosyl homocysteine potentiated AA and BSO toxicity. Antioxidants such as trolox or N-acetyl cysteine prevented this synergistic toxicity of SAMe plus AA or SAMe plus BSO, respectively. In pyrazole hepatocytes, SAMe prevented the decline in mitochondrial membrane potential produced by AA, whereas in E47 cells, SAMe potentiated the decline in mitochondrial membrane potential. In E47 cells, but not pyrazole hepatocytes, the combination of SAMe plus BSO lowered levels of the antioxidant transcription factor Nrf2. Because SAMe can be metabolized enzymatically or spontaneously to MTA, MTA may play a role in the potentiation of AA and BSO toxicity by SAMe, but the exact mechanisms require further investigation. In conclusion, contrasting effects of SAMe on CYP2E1 toxicity were observed in pyrazole hepatocytes and E47 cells. In hepatocytes, SAMe protects against CYP2E1 toxicity by a mechanism involving maintaining or elevating GSH levels.

Pathophysiological basis for antioxidant therapy in chronic liver disease

Oxidative stress is a common pathogenetic mechanism contributing to initiation and progression of hepatic damage in a variety of liver disorders. Cell damage occurs when there is an excess of reactive species derived from oxygen and nitrogen, or a defect of antioxidant molecules. Experimental research on the delicately regulated molecular strategies whereby cells control the balance between oxidant and antioxidant molecules has progressed in recent years. On the basis of this evidence, antioxidants represent a logical therapeutic strategy for the treatment of chronic liver disease. Clinical studies with large numbers of patients have not yet been performed. However, results from several pilot trials support this concept and indicate that it may be worth performing multicentre studies, particularly combining antioxidants with anti-inflammatory and/or antiviral therapy. Oxidative stress plays a pathogenetic role in liver diseases such as alcoholic liver disease, chronic viral hepatitis, autoimmune liver diseases and non-alcoholic steatohepatitis. The use of antioxidants (e.g. S-adenosylmethionine [SAMe; ademetionine], tocopherol [vitamin E], polyenylphosphatidylcholine or silymarin) has already shown promising results in some of these pathologies.

Rat liver betaine-homocysteine S-methyltransferase equilibrium unfolding: insights into intermediate structure through tryptophan substitutions

Equilibrium folding of rat liver BHMT (betaine-homocysteine methyltransferase), a TIM (triosephosphate isomerase)-barrel tetrameric protein, has been studied using urea as denaturant. A combination of activity measurements, tryptophan fluorescence, CD and sedimentation-velocity studies suggested a multiphasic process including two intermediates, a tetramer (I4) and a monomer (J). Analysis of denaturation curves for single- and six-tryptophan mutants indicated that the main changes leading to the tetrameric intermediate are related to alterations in the helix alpha4 of the barrel, as well as in the dimerization arm. Further dissociation to intermediate J included changes in the loop connecting the C-terminal alpha-helix of contact between dimers, disruption of helix alpha4, and initial alterations in helix alpha7 of the barrel, as well as in the dimerization arm. Evolution of the monomeric intermediate continued through additional perturbations in helix alpha7 of the barrel and the C-terminal loop. Our data highlight the essential role of the C-terminal helix in dimer-dimer binding through its contribution to the increased stability shown by BHMT as compared with other TIM barrel proteins. The results are discussed in the light of the high sequence conservation shown by betaine-homocysteine methyltransferases and the knowledge available for other TIM-barrel proteins.

Oxidation of specific methionine and tryptophan residues of apolipoprotein A-I in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the fifth most common neoplasm with more than 500 000 new cases diagnosed yearly. Although major risk factors of HCC are currently known, the identification of biological targets leading to an early diagnosis of the disease is considered one of the priorities of clinical hepatology. In this work we have used a proteomic approach to identify markers of hepatocarcinogenesis in the serum of a knockout mice deficient in hepatic AdoMet synthesis (MAT1A(-/-)), as well as in patients with HCC. Three isoforms of apolipoprotein A-I (Apo A-I) with different pI were identified in murine serum. Isoform 1 is up-regulated in the serum of MAT1A(-/-) mice much earlier than any histological manifestation of liver disease. Further characterization of the differential isoform by electrospray MS/MS revealed specific oxidation of methionine 85 and 216 to methionine sulfoxide while the sequence of the analogous peptides on isoforms 2 and 3 showed the nonoxidized methionine residues. Enrichment of an acidic isoform of Apo A-I was also assessed in the serum of hepatitis B virus patients who developed HCC. Specific oxidation of methionine 112 to methionine sulfoxide and tryptophans 50 and 108 to formylkinurenine were identified selectively in the up-regulated isoform. Although it is not clear at present whether the occurrence of these modifications has a causal role or simply reflects secondary epiphenomena, this selectively oxidized Apo A-I isoform may be considered as a pathological hallmark that may help to the understanding of the molecular pathogenesis of HCC.

Dysregulated cytokine metabolism, altered hepatic methionine metabolism and proteasome dysfunction in alcoholic liver disease

Alcoholic liver disease (ALD) remains an important complication and cause of morbidity and mortality from alcohol abuse. Major developments in our understanding of the mechanisms of ALD over the past decade are now being translated into new forms of therapy for this disease process which currently has no FDA approved treatment. Cytokines are low molecular weight mediators of cellular communication, and the pro-inflammatory cytokine tumor necrosis factor (TNF) has been shown to play a pivotal role in the development of experimental ALD. Similarly, TNF levels are elevated in the serum of alcoholic hepatitis patients. Abnormal methionine metabolism is well documented in patients with ALD, with patients having elevated serum methionine levels, but low S-adenosylmethionine levels in the liver. On the other hand, S-adenosylhomocysteine and homocysteine levels are elevated in ALD. Recent studies have documented potential interactions between homocysteine and S-adenosylhomocysteine with TNF in the development of ALD. Altered proteasome function also is now well documented in ALD, and decreased proteasome function can cause hepatocyte apoptosis. Recently it has been shown that decreased proteasome function can also act synergistically to enhance TNF hepatotoxicity. Hepatocytes dying of proteasome dysfunction release pro-inflammatory cytokines such as Interleukin-8 to cause sustained inflammation. This article reviews the interactions of cytokines, altered methionine metabolism, and proteasome dysfunction in the development of ALD.

Ameliorative effect of Ganoderma lucidum on carbon tetrachloride-induced liver fibrosis in rats

AIM: To investigate the effects of Reishi mushroom, Ganoderma lucidum extract (GLE), on liver fibrosis induced by carbon tetrachloride (CCl₄) in rats.

METHODS: Rat hepatic fibrosis was induced by CCl₄. Forty Wistar rats were divided randomly into 4 groups: control, CCl₄, and two GLE groups. Except for rats in control group, all rats were administered orally with CCl₄ (20%, 0.2 mL/100 g body weight) twice a week for 8 weeks. Rats in GLE groups were treated daily with GLE (1 600 or 600 mg/kg) via gastrogavage throughout the whole experimental period. Liver function parameters, such as ALT, AST, albumin, and albumin/globulin (A/G) ratio, spleen weight and hepatic amounts of protein, malondiladehyde (MDA) and hydroxyproline (HP) were determined. Histochemical staining of Sirius red was performed. Expression of transforming growth factor β1 (TGF-β1), methionine adenosyltransferase (MAT1) 1A and MAT2A mRNA were detected by using RT-PCR.

RESULTS: CCl₄ caused liver fibrosis, featuring increase in plasma transaminases, hepatic MDA and HP contents, and spleen weight; and decrease in plasma albumin, A/G ratio and hepatic protein level. Compared with CCl₄ group, GLE (600, 1 600 mg/kg) treatment significantly increased plasma albumin level and A/G ratio (P  < 0.05) and reduced the hepatic HP content (P < 0.01). GLE (1 600 mg/kg) treatment markedly decreased the activities of transaminases (P  < 0.05), spleen weight (P  < 0.05) and hepatic MDA content (P  < 0.05); but increased hepatic protein level (P  < 0.05). Liver histology in the GLE (1 600 mg/kg)-treated rats was also improved (P  < 0.01). RT-PCR analysis showed that GLE treatment decreased the expression of TGF-β1 (P  < 0.05-0.001) and changed the expression of MAT1A (P  < 0.05-0.01) and MAT2A (P  < 0.05-0.001).

CONCLUSION: Oral administration of GLE significantly reduces CCl4-induced hepatic fibrosis in rats, probably by exerting a protective effect against hepatocellular necrosis by its free-radical scavenging ability.

S-adenosylmethionine or 5′-methylthioadenosine are unable to prevent fumonisin B1 hepatotoxicity in mice despite increased oxidation in liver

Fumonisins are mycotoxins produced by the fugus Fusarium verticillioides, a common fungus growing on corn. Fumonisin B(1) (FB(1)) is the most toxic and prevalent fumonisin detected in corn and corn-based foods. It produces species-, gender-specific damage, and is hepatotoxic and nephrotoxic in rodents. Disruption of sphingolipid metabolism resulting from inhibition of ceramide synthase leads to alterations of cell signaling events, particularly tumor necrosis factor (TNF)alpha signal pathways and to the toxic effects of FB(1). It has been reported that FB(1) toxicity involves oxidative stress. S-adenosylmethionine (SAM) and methylthioadenosine (MTA), an intermediate metabolite in SAM metabolism, are hepatoprotective by modulating TNFalpha expression and increasing reduced glutathione (GSH) levels. The current study investigated the effects of SAM and MTA on FB(1) hepatotoxicity in C57BL/6N mice. The animals were given SAM or MTA by intraperitoneal injection of 25 mg kg(-1) body weight every 12 h when they received subcutaneous injection of 2.25 mg FB(1) kg(-1) body weight once daily for 5 days. The results showed that neither SAM nor MTA protected FB(1)-induced liver damage indicated by the increases in activities of plasma alanine aminotransferase and aspartate aminotransferase as well as the number of apoptotic hepatocytes. Both agents prevented an increase of free sphingosine but not sphinganine. Neither SAM nor MTA modified the FB(1)-induced expression of TNFalpha, interleukin (IL)-1alpha or IL-1 receptor antagonist. The decreased GSH in liver following FB(1) treatment was not protected by either agent. The data indicate that SAM and MTA are ineffective in protecting against FB(1) toxic effects.

S-Adenosyl-l-methionine Attenuates Hepatotoxicity Induced by Agonistic Jo2 Fas Antibody following CYP2E1 Induction in Mice

S-Adenosyl-l-methionine (SAM) has been shown to be hepatoprotective against many toxic agents. Its possible effectiveness in protecting against CYP2E1-dependent toxicity is not known. We recently reported that treatment of mice with pyrazole to induce CYP2E1 increased hepatotoxicity produced by Fas agonistic Jo2 antibody. The current study was designed to investigate the effect of exogenous administration of SAM on the synergistic hepatotoxicity produced by Fas agonistic Jo2 antibody plus CYP2E1 following pyrazole pretreatment in C57BL/6 mice. Suboptimal administration of Jo2 Fas antibody combined with pyrazole pretreatment caused severe hepatotoxicity as determined by elevations in serum transaminase levels and histopathology. Exogenous administration of SAM (50 mg i.p./kg body weight every 12 h for 3 days) significantly decreased serum transaminases and ameliorated morphological changes of the liver. Addition of SAM elevated hepatic SAM and total reduced glutathione levels and inhibited CYP2E1 activity. SAM also lowered the elevated oxidative stress (lipid peroxidation, protein carbonyls, and superoxide production) and nitrosative stress (induction of inducible nitric-oxide synthase and 3-nitrotyrosine adducts) and increases in caspase-8 and -3 activation produced by the pyrazole plus Jo2 treatment. SAM did not prevent the increase in serum TNF-alpha levels or the decrease in catalase activity in this model. These results indicate that SAM can have an important hepatoprotective role as an effective reagent against Fas plus CYP2E1-induced hepatotoxicity by lowering oxidative and nitrosative stress.

Effect of S-adenosylmethionine on Age-induced Hepatocyte Damage in Old Wistar Rats

Aging is accompanied by changes in the morphology and physiology of organs and tissues, such as the liver. This process might be due to the accumulation of oxidative damage induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Hepatocytes are very rich in mitochondria and have a high respiratory rate, so they are exposed to large amounts of ROS and permanent oxidative stress. S-Adenosylmethionine (SAMe) is an endogenous metabolite that has shown to exert protective effects on different experimental pathological models in which free radicals are involved. The aim of this study was to investigate the effect of SAMe on age-induced damage in hepatocytes. For this purpose, male and female Wistar rats of 18 and 2 months of age were used. Cells were isolated and, after incubation in the presence or in the absence of SAMe, different parameters were measured. Aging induced a significant increase in nitric oxide, carbon monoxide and cGMP, and a reduction in reduced glutathione, ATP and phosphatidylcholine synthesis, as well as in methionine- adenosyl-transferase and methyl-transferase activities. Incubation of old cells with SAMe prevented all these age-related changes, reaching values in some of the parameters similar to those found in young animals. In conclusion, SAMe seems to have beneficial effects against age-induced damage in hepatocytes.

Prevalence and mechanisms of hyperhomocysteinemia in chronic alcoholics

BACKGROUND

Homocysteine (Hcy) is formed as an intermediary in methionine metabolism. Impairment of Hcy remethylation or transulfuration leads to hyperhomocysteinemia, which is considered as a risk factor for atherosclerotic vascular disease and stroke in chronic alcoholics. The aim of the study was to investigate the prevalence of hyperhomocysteinemia in chronic alcoholics and the influence of alcohol consumption, vitamin deficiencies and liver damage on the plasma levels of Hcy.

METHODS

228 chronic alcoholic patients consecutively admitted for detoxication, classified according to clinical and biochemical data in normal liver (n = 117), and in mild to moderate liver disease (n = 111), and 49 healthy controls were studied. Blood levels of Hcy, vitamin B6, vitamin B12 and folate were measured.

RESULTS

Plasma Hcy was significantly higher in chronic alcoholics than in controls (9.66 +/- 8.1 vs. 6.93 +/- 2.33 mumol/liter, p < 0.025). Furthermore, plasma Hcy levels were significantly higher in chronic alcoholics with liver injury (12.17 +/- 10.14 mumol/liter) than in those with normal liver and in controls (p < 0.001). The prevalence of hyperhomocysteinemia was also significantly higher in alcoholics with liver damage than in those with normal liver and in controls (29.7%, 5.1%, and 2%, respectively, p < 0.001). Serum folate values were lower in chronic alcoholics than in controls (4.7 +/- 2.6 vs. 7.6 +/- 2.4 nmol/liter, p < 0.001). The lowest values of folate were found in alcoholics with liver disease, especially in those with hyperhomocysteinemia, with a negative correlation between the two parameters.

CONCLUSIONS

Moderate hyperhomocysteinemia is common in chronic alcoholics, mainly in those with liver damage, suggesting that, although folate deficiencies may have a contributory role, liver impairment, through changes in methionine metabolism, is the most important mechanism for the elevated plasma Hcy found in these patients.

Rickettsial metK-encoded methionine adenosyltransferase expression in an Escherichia coli metK deletion strain

The obligate intracellular bacterium Rickettsia prowazekii has recently been shown to transport the essential metabolite S-adenosylmethionine (SAM). The existence of such a transporter would suggest that the metK gene, coding for the enzyme that synthesizes SAM, is unnecessary for rickettsial growth. Genome sequencing has revealed that this is the case for the metK genes of the spotted fever group and the Madrid E strain of R. prowazekii, which contain recognizable inactivating mutations. However, several strains of the typhus group rickettsiae possess metK genes lacking obvious mutations. In order to determine if these genes code for a product that retains MAT function, an Escherichia coli metK deletion mutant was constructed in which individual rickettsial metK genes were tested for the ability to complement the methionine adenosyltransferase deficiency. Both the R. prowazekii Breinl and R. typhi Wilmington metK genes complemented at a level comparable to that of an E. coli metK control, demonstrating that the typhus group rickettsiae have the capability of synthesizing as well as transporting SAM. However, the appearance of mutations that affect the function of the metK gene products (a stop codon in the Madrid E strain and a 6-bp deletion in the Breinl strain) provides experimental support for the hypothesis that these typhus group genes, like the more degenerate spotted fever group orthologs, are in the process of gene degradation.

Elevated plasma homocysteine concentrations as a predictor of steatohepatitis in patients with non-alcoholic fatty liver disease

BACKGROUND

Although steatosis is common in patients with severe hyperhomocysteinemia due to deficiency of cystathionine beta-synthase, there are no satisfactory data on homocysteine concentrations in patients with non-alcoholic fatty liver disease. The main aim of the present study was to evaluate the clinical significance of plasma homocysteine concentrations in patients with non-alcoholic fatty liver disease.

METHODS

Seventy-one non-alcoholic fatty liver disease patients, 36 patients with chronic viral hepatitis and 30 healthy persons were enrolled in the study. Homocysteine levels were measured by high-performance liquid chromatography. Insulin, folate, vitamin B(12) and lipoprotein levels were also determined in all groups.

RESULTS

Homocysteine in the non-alcoholic fatty liver disease group was found to be significantly higher than other groups. Homocysteine was found to be significantly higher in the non-alcoholic steatohepatitis group when compared with simple steatosis group. A positive correlation was found between homocysteine and triglyceride, very-low-density-lipoprotein (VLDL) cholesterol, insulin, and index of insulin resistance in the non-alcoholic fatty liver disease group, and a negative correlation was found between homocysteine and folate, or vitamin B(12) in all groups. The homocysteine threshold for the prediction of steatohepatitis was 11.935 ng/mL. Furthermore; plasma homocysteine was a statistically significant predictor for severity of necroinflammatory activity in non-alcoholic steatohepatitis.

CONCLUSIONS

The plasma homocysteine concentrations were significantly higher in patients with non-alcoholic fatty liver disease, while the concentrations were not affected by chronic viral hepatitis. Plasma homocysteine is a parameter for discriminating steatohepatitis from simple steatosis. Determining the plasma homocysteine concentrations may facilitate selection of steatosis patients in whom a liver biopsy should be performed.

Antioxidants as novel therapy in a murine model of colitis

Reactive oxygen species (ROS) are increased in inflammatory bowel disease (IBD) and have been implicated as mediators of intestinal inflammation. We investigated the hypothesis that antioxidants with diverse properties attenuate disease progression in a murine dextran sodium sulfate (DSS)-induced colitis model. These antioxidants were (A) S-adenosylmethionine, a glutathione (GSH) precursor; (B) green tea polyphenols, a well-known antioxidant; and (C) 2(R,S)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA), a cysteine prodrug, involved in GSH biosynthesis. BALB/c mice were divided into four groups and provided with the above mentioned antioxidants or the vehicle incorporated into chow. The animals were further divided into two subgroups and given normal drinking water (control) or water supplemented with DSS (to induce colitis), and the progression of the disease was studied. DSS-treated mice developed severe colitis as shown by bloody diarrhea, weight loss and pathological involvement (P<.001). However, all the antioxidants significantly improved diarrhea and colon lesions (P<.01), and increased body weights (P<.05). Hematocrits were significantly less affected in DSS-treated animals receiving antioxidants (P<.01). Colon lengths were significantly decreased due to mucosal inflammation in DSS-treated animals, but antioxidant therapy normalized this pathological finding (P<.001). The blood level of reduced GSH was decreased in DSS-treated mice (P<.05) and returned to normal when treated with antioxidants. Serum amyloid A (acute phase protein; P=.0015) and tumor necrosis factor-alpha (TNF-alpha; pro-inflammatory cytokine; P<.01) were significantly increased in DSS-treated animals (161+/-40 pg/ml) and improved with antioxidant treatment (P<.01). Finally, actin cytoskeleton was distorted and fragmented in the mucosa of DSS-treated mice and improved with antioxidant therapy. In conclusion, three structurally dissimilar antioxidants provided protection against DSS-induced colitis in this murine model, supporting a possible role for antioxidant therapy in IBD patients.