s-adenosylhomocysteine and Chemical-and-Drug-Induced-Liver-Injury

We had previously shown that alcohol consumption can induce cellular isoaspartate protein damage via an impairment of the activity of protein isoaspartyl methyltransferase (PIMT), an enzyme that triggers repair of isoaspartate protein damage. To further investigate the mechanism of isoaspartate accumulation, hepatocytes cultured from control or 4-week ethanol-fed rats were incubated in vitro with tubercidin or adenosine. Both these agents, known to elevate intracellular S-adenosylhomocysteine levels, increased cellular isoaspartate damage over that recorded following ethanol consumption in vivo. Increased isoaspartate damage was attenuated by treatment with betaine. To characterize isoaspartate-damaged proteins that accumulate after ethanol administration, rat liver cytosolic proteins were methylated using exogenous PIMT and (3)H-S-adenosylmethionine and proteins resolved by gel electrophoresis. Three major protein bands of ∼ 75-80 kDa, ∼ 95-100 kDa, and ∼ 155-160 kDa were identified by autoradiography. Column chromatography used to enrich isoaspartate-damaged proteins indicated that damaged proteins from ethanol-fed rats were similar to those that accrued in the livers of PIMT knockout (KO) mice. Carbamoyl phosphate synthase-1 (CPS-1) was partially purified and identified as the ∼ 160 kDa protein target of PIMT in ethanol-fed rats and in PIMT KO mice. Analysis of the liver proteome of 4-week ethanol-fed rats and PIMT KO mice demonstrated elevated cytosolic CPS-1 and betaine homocysteine S-methyltransferase-1 when compared to their respective controls, and a significant reduction of carbonic anhydrase-III (CA-III) evident only in ethanol-fed rats. Ethanol feeding of rats for 8 weeks resulted in a larger (∼ 2.3-fold) increase in CPS-1 levels compared to 4-week ethanol feeding indicating that CPS-1 accumulation correlated with the duration of ethanol consumption. Collectively, our results suggest that elevated isoaspartate and CPS-1, and reduced CA-III levels could serve as biomarkers of hepatocellular injury.

Topics: Animals; Biomarkers; Carbamoyl-Phosphate Synthase (Ammonia); Carbonic Anhydrase III; Cells, Cultured; Chemical and Drug Induced Liver Injury; Ethanol; Isoaspartic Acid; Liver; Male; Mice; Mice, Knockout; Protein D-Aspartate-L-Isoaspartate Methyltransferase; Rats; Rats, Wistar; S-Adenosylhomocysteine

This study aimed to investigate: (i) changes of plasma homocysteine, methionine and S-adenosylhomocysteine levels following high-dose methotrexate (HD-MTX) treatment and (ii) the correlation of these sulfur-containing amino acids with MTX-induced hepatotoxicity. Fifteen pediatric patients with acute lymphoblastic leukemia and one patient with Burkitt lymphoma, with a total of 26 treatment courses of HD-MTX, were enrolled. Homocysteine levels increased at 24 h after HD-MTX treatment, and showed marginal decreases at 48 and 72 h. Methionine levels showed a biphasic pattern, i.e. an initial decrease at 24 h followed by increases at 48 and 72 h. S-adenosylhomocysteine exhibited a marginal decrease at 24 h. Changes of homocysteine exhibited significant correlation only with a maximum increase of alanine aminotransferase or total bilirubin from baseline. This study has demonstrated, for the first time, simultaneous changes of plasma homocysteine, methionine and S-adenosylhomocysteine following HD-MTX. The potential of homocysteine as a marker of hepatotoxicity is also presented.

Topics: Antimetabolites, Antineoplastic; Burkitt Lymphoma; Chemical and Drug Induced Liver Injury; Child; Child, Preschool; Female; Homocysteine; Humans; Liver Function Tests; Male; Methionine; Methotrexate; Precursor Cell Lymphoblastic Leukemia-Lymphoma; S-Adenosylhomocysteine

We previously reported that chronic ethanol intake lowers hepatocellular S-adenosylmethionine to S-adenosylhomocysteine ratio and significantly impairs many liver methylation reactions. One such reaction, catalyzed by guanidinoacetate methyltransferase (GAMT), is a major consumer of methyl groups and utilizes as much as 40% of the SAM-derived groups to convert guanidinoacetate (GAA) to creatine. The exposure to methyl-group consuming compounds has substantially increased over the past decade that puts additional stresses on the cellular methylation potential. The purpose of our study was to investigate whether increased ingestion of a methyl-group consumer (GAA) either alone or combined with ethanol intake, plays a role in the pathogenesis of liver injury. Adult male Wistar rats were pair-fed the Lieber DeCarli control or ethanol diet in the presence or absence of GAA for 2weeks. At the end of the feeding regimen, biochemical and histological analyses were conducted. We observed that 2 weeks of GAA- or ethanol-alone treatment increases hepatic triglyceride accumulation by 4.5 and 7-fold, respectively as compared with the pair-fed controls. However, supplementing GAA in the ethanol diet produced panlobular macro- and micro-vesicular steatosis, a marked decrease in the methylation potential and a 28-fold increased triglyceride accumulation. These GAA-supplemented ethanol diet-fed rats displayed inflammatory changes and significantly increased liver toxicity compared to the other groups. In conclusion, increased methylation demand superimposed on chronic ethanol consumption causes more pronounced liver injury. Thus, alcoholic patients should be cautioned for increased dietary intake of methyl-group consuming compounds even for a short period of time.

Topics: Alcohol Drinking; Amidinotransferases; Animals; Chemical and Drug Induced Liver Injury; Diet; Ethanol; Fatty Liver, Alcoholic; Glycine; Guanidinoacetate N-Methyltransferase; Homocysteine; Liver; Male; Methylation; Rats; Rats, Wistar; S-Adenosylhomocysteine; S-Adenosylmethionine; Triglycerides