l-Methionine Toxicity in Freshly Isolated Mouse Hepatocytes Is Gender-Dependent and Mediated in Part by Transamination

Abstract

L-Methionine (Met) has been implicated in parenteral nutritionassociated cholestasis in infants and, at high levels, it causes liver toxicity by mechanisms that are not clear. In this study, Met toxicity was characterized in freshly isolated male and female mouse hepatocytes incubated with 5 to 30 mM Met for 0 to 5 h. In male hepatocytes, 20 mM Met was cytotoxic at 4 h as indicated by trypan blue exclusion and lactate dehydrogenase leakage assays. Cytotoxicity was preceded by reduced glutathione (GSH) depletion at 3 h without glutathione disulfide formation. Exposure to 30 mM Met resulted in increased cytotoxicity and GSH depletion. It is interesting to note that female hepatocytes were resistant to Met-induced cytotoxicity at these concentrations and showed increased cellular GSH levels compared with hepatocytes exposed to medium alone. The effects of amino-oxyacetic acid (AOAA), an inhibitor of Met transamination, and 3-deazaadenosine (3-DA), an inhibitor of the Met transmethylation pathway enzyme S-adenosylhomocysteine hydrolase, on Met toxicity in male hepatocytes were then examined. Addition of 0.2 mM AOAA partially blocked Met-induced GSH depletion and cytotoxicity, whereas 0.1 mM 3-DA potentiated Met-induced toxicity. Exposure of male hepatocytes to 0.3 mM 3-methylthiopropionic acid (3-MTP), a known Met transamination metabolite, resulted in cytotoxicity and cellular GSH depletion similar to that observed with 30 mM Met, whereas incubations with D-methionine resulted in no toxicity. Female hepatocytes were less sensitive to 3-MTP toxicity than males, which may partially explain their resistance to Met toxicity. Taken together, these results suggest that Met transamination and not transmethylation plays a major role in Met toxicity in male mouse hepatocytes.

Measurement and biological significance of the volatile sulfur compounds hydrogen sulfide, methanethiol and dimethyl sulfide in various biological matrices

“…Some reports relate l-methionine toxicity with elevated transamination, leading to elevated MT levels [74,75]. Toxicity of MT has been ascribed to inhibition of certain enzymes [76,77].…”

The Methionine Transamination Pathway Controls Hepatic Glucose Metabolism through Regulation of the GCN5 Acetyltransferase and the PGC-1α Transcriptional Coactivator

“…KMTB is then oxidatively decarboxylated to 3-methylthiopropionate (MTP) through an irreversible reaction catalyzed by the branched chain 2-oxo acid dehydrogenase complex (BCKDC) (15). MTP is further metabolized to the gaseous methanethiol (16), which has been reported to then be broken down into simpler molecules, including hydrogen sulfide, dimethyl sulfide, and formic acid, with the end products being carbon dioxide and sulfur dioxide (17,18). Although initial reports on methionine transamination suggested that it provides a route for the degradation and clearance of methionine (19), more recently researchers have claimed that transsulfuration serves as the major pathway for the detoxification of excessive methionine (20).…”

Gender differences in biochemical markers and oxidative stress of rats after 28 days oral exposure to a mixture used for weight loss containing p-synephrine, ephedrine, salicin, and caffeine

“…There are many reports of gender being a critical factor in drug-induced liver injury (Hemieda, 2007;McConnachie et al, 2007;Dever, Elfarra, 2008). Moreover, most of those reports demonstrate that males were more susceptible to hepato toxin-induced liver injury than females.…”

“…Moreover, most of those reports demonstrate that males were more susceptible to hepato toxin-induced liver injury than females. Studies have reported that bioactivation and estrogen concentration are mainly responsible for the gender-dependent discrepancy in liver injury (McConnachie et al, 2007;Dever, Elfarra, 2008;Liang et al, 2011). Also, gender differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity.…”