Vitamin B12 and folate decrease inflammation and fibrosis in NASH by preventing syntaxin 17 homocysteinylation

BACKGROUND & AIMS

Several recent clinical studies have shown that serum homocysteine (Hcy) levels are positively correlated, while vitamin B₁₂ (B₁₂) and folate levels are negative correlated, with non-alcoholic steatohepatitis (NASH) severity. However, it is not known whether hyperhomocysteinemia (HHcy) plays a pathogenic role in NASH.

METHODS

We examined the effects of HHcy on NASH progression, metabolism, and autophagy in dietary and genetic mouse models, patients, and primates. We employed vitamin B₁₂ (B₁₂) and folate (Fol) to reverse NASH features in mice and cell culture.

RESULTS

Serum Hcy correlated with hepatic inflammation and fibrosis in NASH. Elevated hepatic Hcy induced and exacerbated NASH. Gene expression of hepatic Hcy-metabolizing enzymes was downregulated in NASH. Surprisingly, we found increased homocysteinylation (Hcy-lation) and ubiquitination of multiple hepatic proteins in NASH including the key autophagosome/lysosome fusion protein, Syntaxin 17 (Stx17). This protein was Hcy-lated and ubiquitinated, and its degradation led to a block in autophagy. Genetic manipulation of Stx17 revealed its critical role in regulating autophagy, inflammation and fibrosis during HHcy. Remarkably, dietary B₁₂/Fol, which promotes enzymatic conversion of Hcy to methionine, decreased HHcy and hepatic Hcy-lated protein levels, restored Stx17 expression and autophagy, stimulated β -oxidation of fatty acids, and improved hepatic histology in mice with pre-established NASH.

CONCLUSIONS

HHcy plays a key role in the pathogenesis of NASH via Stx17 homocysteinylation. B₁₂/folate also may represent a novel first-line therapy for NASH.

LAY SUMMARY

The incidence of non-alcoholic steatohepatitis, for which there are no approved pharmacological therapies, is increasing, posing a significant healthcare challenge. Herein, based on studies in mice, primates and humans, we found that dietary supplementation with vitamin B₁₂ and folate could have therapeutic potential for the prevention or treatment of non-alcoholic steatohepatitis.

A severe case of rat lungworm disease in Hawa'i

A 23-year-old man living on the island of Hawa'i developed a life threatening case of eosinophilic meningitis caused by infection with Angiostrongylus cantonensis (rat lungworm disease: RLWD). He was comatose for 3 months, incurring brain and nerve damage sufficiently extensive that he was not expected to recover. The case was complicated by secondary infections of methicillin-resistant Staphylococcus aureus, Clostridium difficile, and pneumonia, which resulted in an empyema requiring a thoracoscopy and decortication. He was treated with prednisone, mebendozal, and pain medication for RLWD, and antibiotics and antifungal medications for the secondary infections. The administration of herbal supplements was requested by the family and approved, and these were administered through a gastric tube. Less than a month after being declared in a persistent vegetative state the man was able to talk, eat, and had regained some muscle functions. After release from the hospital he continued the use of supplements and received treatments of intravenous vitamin therapy. Four years after onset of the illness he is able to ride a bicycle, is a part time student, plays guitar, and is fluent in two foreign languages. RLWD is an emerging tropical disease of growing importance in Hawa'i.