Second-generation antipsychotics and metabolism alterations: a systematic review of the role of the gut microbiome

Rationale: Multiple drugs are known to induce metabolic malfunctions, among them second-generation antipsychotics (SGAs). The pathogenesis of such adverse effects is of multifactorial origin. Objectives: We investigated whether SGAs drive dysbiosis, assessed whether gut microbiota alterations affect body weight and metabolic outcomes, and looked for the possible mechanism of metabolic disturbances secondary to SGA treatment in animal and human studies. Methods: A systematic literature search (PubMed/Medline/Embase/ClinicalTrials.gov/PsychInfo) was conducted from database inception until 03 July 2018 for studies that reported the microbiome and weight alterations in SGA-treated subjects. Results: Seven articles reporting studies in mice (experiments = 8) and rats (experiments = 3) were included. Olanzapine was used in five and risperidone in six experiments. Only three articles (experiments = 4) in humans fit our criteria of using risperidone and mixed SGAs. The results confirmed microbiome alterations directly (rodent experiments = 5, human experiments = 4) or indirectly (rodent experiments = 4) with predominantly increased Firmicutes abundance relative to Bacteroidetes, as well as weight gain in rodents (experiments = 8) and humans (experiments = 4). Additionally, olanzapine administration was found to induce both metabolic alterations (adiposity, lipogenesis, plasma free fatty acid, and acetate levels increase) (experiments = 3) and inflammation (experiments = 2) in rodents, whereas risperidone suppressed the resting metabolic rate in rodents (experiments = 5) and elevated fasting blood glucose, triglycerides, LDL, hs-CRP, antioxidant superoxide dismutase, and HOMA-IR in humans (experiment = 1). One rodent study suggested a gender-dependent effect of dysbiosis on body weight. Conclusions: Antipsychotic treatment-related microbiome alterations potentially result in body weight gain and metabolic disturbances. Inflammation and resting metabolic rate suppression seem to play crucial roles in the development of metabolic disorders.