Lithium is the most effective mood stabilizer for the treatment of bipolar disorder, but it is toxic at only twice the therapeutic dosage and has many undesirable side effects. It is likely that a small molecule could be found with lithium-like efficacy but without toxicity through target-based drug discovery; however, lithium’s therapeutic target remains equivocal. Inositol monophosphatase is a possible target but no bioavailable inhibitors exist. Here we report that the antioxidant ebselen inhibits inositol monophosphatase and induces lithium-like effects on mouse behaviour, which are reversed with inositol, consistent with a mechanism involving inhibition of inositol recycling. Ebselen is part of the National Institutes of Health Clinical Collection, a chemical library of bioavailable drugs considered clinically safe but without proven use. Therefore, ebselen represents a lithium mimetic with the potential both to validate inositol monophosphatase inhibition as a treatment for bipolar disorder and to serve as a treatment itself.

Inositol monophosphatase (IMPase) catalyses the hydrolysis of inositol monophosphate to inositol and is crucial in the phosphatidylinositol (PI) signalling pathway. Lithium, which is the drug of choice for bipolar disorder, inhibits IMPase at therapeutically relevant plasma concentrations. Both mouse IMPase 1 (MmIMPase 1) and human IMPase 1 (HsIMPase 1) were cloned into pRSET5a, expressed in Escherichia coli, purified and crystallized using the sitting‐drop method. The structures were solved at resolutions of 2.4 and 1.7 Å, respectively. Comparison of MmIMPase 1 and HsIMPase 1 revealed a core r.m.s. deviation of 0.516 Å.

Acetylcholinesterase (AChE), a member of the α/β-hydrolase fold superfamily of proteins, is a serine hydrolase responsible for the hydrolysis of the well studied neurotransmitter acetylcholine (ACh). However, it is becoming clear that AChE has a range of actions other than this 'classical' role. Non-classical AChE functions have been identified in apoptosis, stress-responses, neuritogenesis, and neurodegeneration. Furthermore, these non-classical roles are attributable not only to the native protein, which appears to act as a mediary binding protein under a number of circumstances, but also to peptides cleaved from the parent protein. Peptides cleaved from AChE can act as independent signalling molecules. Here we discuss the implications of non-hydrolytic functions of this multi-tasking protein.

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