A novel role for dopamine signaling in the pathogenesis of bone loss from the atypical antipsychotic drug risperidone in female mice.

Atypical antipsychotic (AA) drugs, including risperidone (RIS), are used to treat schizophrenia, bipolar disorder, and autism, and are prescribed off-label for other mental health issues. AA drugs are associated with severe metabolic side effects of obesity and type 2 diabetes. Cross-sectional and longitudinal data also show that risperidone causes bone loss and increases fracture risk in both men and women. There are several potential mechanisms of bone loss from RIS. One is hypogonadism due to hyperprolactinemia from dopamine receptor antagonism. However, many patients have normal prolactin levels; moreover we demonstrated that bone loss from RIS in mice can be blocked by inhibition of β-adrenergic receptor activation with propranolol, suggesting the sympathetic nervous system (SNS) plays a pathological role. Further, when, we treated ovariectomized (OVX) and sham operated mice daily for 8weeks with RIS or vehicle we demonstrated that RIS causes significant trabecular bone loss in both sham operated and OVX mice. RIS directly suppressed osteoblast number in both sham and OVX mice, but increased osteoclast number and surface in OVX mice alone, potentially accounting for the augmented bone loss. Thus, hypogonadism alone cannot explain RIS induced bone loss. In the current study, we show that dopamine and RIS are present in the bone marrow compartment and that RIS can exert its effects directly on bone cells via dopamine receptors. Our findings of both direct and indirect effects of AA drugs on bone are relevant for current and future clinical and translational studies investigating the mechanism of skeletal changes from AA drugs.