Metabolism and neurotoxicity of homocysteine thiolactone in mice: protective role of bleomycin hydrolase.
Genetic or nutritional disorders in homocysteine (Hcy) metabolism elevate Hcy-thiolactone and cause heart and brain diseases. Hcy-thiolactone has been implicated in these diseases because it has the ability to modify protein lysine residues and generate toxic N-Hcy-proteins with auto-immunogenic, pro-thrombotic, and amyloidogenic properties. Bleomycin hydrolase (Blmh) has the ability to hydrolyze L-Hcy-thiolactone (but not D-Hcy-thiolactone) to Hcy in vitro, but whether this reflects a physiological function has been unknown. Here, we show that Blmh (-/-) mice excreted in urine 1.8-fold more Hcy-thiolactone than wild-type Blmh (+/+) animals (P = 0.02). Hcy-thiolactone was elevated 2.3-fold in brains (P = 0.004) and 2.0-fold in kidneys (P = 0.047) of Blmh (-/-) mice relative to Blmh (+/+) animals. Plasma N-Hcy-protein was elevated in Blmh (-/-) mice fed a normal (2.3-fold, P < 0.001) or hyperhomocysteinemic diet (1.5-fold, P < 0.001), compared with Blmh (+/+) animals. More intraperitoneally injected L-Hcy-thiolactone was recovered in plasma in Blmh (-/-) mice than in wild-type Blmh (+/+) animals (83.1 vs. 39.3 μM, P < 0.0001). In Blmh (+/+) mice injected intraperitoneally with D-Hcy-thiolactone, D,L-Hcy-thiolactone, or L-Hcy-thiolactone, 88, 47, or 6.3%, respectively, of the injected dose was recovered in plasma. The incidence of seizures induced by L-Hcy-thiolactone injections (3,700 nmol/g body weight) was higher in Blmh (-/-) than in Blmh (+/+) mice (93.8 vs. 29.5%, P < 0.001). Using the Blmh null mice, we provide the first direct evidence that a specific Hcy metabolite, Hcy-thiolactone, rather than Hcy itself, is neurotoxic in vivo. Taken together, our findings indicate that Blmh protects mice against L-Hcy-thiolactone toxicity by metabolizing it to Hcy and suggest a mechanism by which Blmh might protect against neurodegeneration associated with hyperhomocysteinemia and Alzheimer's disease.
Department of Microbiology and Molecular Genetics, International Center for Public Health, UMDNJ-New Jersey Medical School, 225 Warren Street, Newark, NJ 07101, USA.
Kamila
K
Borowczyk
Joanna
J
Tisończyk
Hieronim
H
Jakubowski
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005260:Female; D006207:Half-Life; D006710:Homocysteine / Q000031:analogs & derivatives* / Q000097:blood / Q000502:physiology / Q000652:urine; D020138:Hyperhomocysteinemia / Q000150:complications* / Q000201:enzymology / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019636:Neurodegenerative Diseases / Q000201:enzymology / Q000209:etiology* / Q000378:metabolism; D009928:Organ Specificity; D012640:Seizures / Q000201:enzymology / Q000209:etiology / Q000378:metabolism
D001798:Blood Proteins; D006710:Homocysteine; C007957:homocysteine thiolactone; D003546:Cysteine Endopeptidases; C031262:bleomycin hydrolase