Gut microbiota-derived trimethylamine N-oxide involved in methamphetamine-induced depression-like behaviors of male mice

Methamphetamine (METH)-provoked psychiatric symptoms are a major health concern, with depression being a prevalent symptom among METH abusers. Recently, gut microbiota-derived metabolites have been involved in various psychosis pathogenesis, but their roles in METH-induced depression remain unclear. This study investigates the implication of gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) in METH-induced depressive-like behaviors (DLBs). We examined the circulating TMAO levels post-METH exposure besides exploring the impacts of TMAO on METH-triggered DLBs. Then, potential causes of TMAO alterations were explored, along with its effects on hippocampal neuronal damage and neuroinflammation. The findings showcased that METH-treated mice displayed DLBs accompanied by increased serum TMAO levels. Similarly, introducing TMAO to the drinking water elevated serum TMAO levels and induced DLBs. Although METH exposure did not notably alter the abundance of the gut microbiota, antibiotic (ABX) therapy suppressed the increased serum TMAO levels and the onset of DLBs. Additionally, choline and L-carnitine levels were elevated following METH exposure, which may be a potential mechanism for TMAO metabolic dysregulation. Elevated TMAO levels resulted in an elevation in Nissl-positive dead cells, the number of microglia, TNF-α, and IL-1β levels, along with TLR-4, NF-κB, and MyD88 expression in the hippocampal CA3 region. Inhibition of TMAO synthesis mitigated METH-provoked neuronal damage and neuroinflammation.