Transcriptional mechanisms of lithium action: therapeutic implications

Lithium in the treatment of bipolar disorder: pharmacology and pharmacogenetics

After decades of research, the mechanism of action of lithium in preventing recurrences of bipolar disorder remains only partially understood. Lithium research is complicated by the absence of suitable animal models of bipolar disorder and by having to rely on in vitro studies of peripheral tissues. A number of distinct hypotheses emerged over the years, but none has been conclusively supported or rejected. The common theme emerging from pharmacological and genetic studies is that lithium affects multiple steps in cellular signaling, usually enhancing basal and inhibiting stimulated activities. Some of the key nodes of these regulatory networks include GSK3 (glycogen synthase kinase 3), CREB (cAMP response element-binding protein) and Na(+)-K(+) ATPase. Genetic and pharmacogenetic studies are starting to generate promising findings, but remain limited by small sample sizes. As full responders to lithium seem to represent a unique clinical population, there is inherent value and need for studies of lithium responders. Such studies will be an opportunity to uncover specific effects of lithium in those individuals who clearly benefit from the treatment.

Evaluation of acute antiapoptotic effects of Li+ in neuronal cell cultures

Li(+) exerts protective effect against several neurotoxins in neuronal cell preparations. Here we examined the antiapoptotic effects of GSK3beta in cerebellar granule neurons (CGNs) in the presence of several neurotoxins. Acute treatment with Li(+) protected neurons against nocodazole and serum/potassium (S/K) deprivation, but were ineffective against kainic acid and MPP(+). Li(+) 5 mM also decreased caspase-3 activation induced by nocodazole and S/K deprivation as measured by Ac-DEVD-p-nitroaniline and the breakdown of alpha-spectrin. All the neurotoxins used in the present study activated GSK3beta, evaluated with a specific antibody phospho-GSK-3beta (Ser9) by Western-blot and immunocytochemistry and were always inhibited by Li(+) 5 mM. Our results implicate Li(+) in the regulation of apoptosis mediated by caspase activation (Type I). Furthermore inhibition of GSK3beta by acute treatment with Li(+) 5 mM is not an indicator of neuroprotection. The acute antiapoptotic function of Li(+) is discussed in terms of its inhibition of Type I pathway, the intrinsic (mitochondrial) apoptotic pathway in cerebellar granule cells.

Cytoprotection by lithium and valproate varies between cell types and cellular stresses

Despite much evidence that lithium and valproate, two commonly used mood stabilizers, exhibit neuroprotective properties against an array of insults, the pharmacological relevance of such effects is not clear because most of these studies examined the acute effect of these drugs in supratherapeutic doses against insults which were of limited disease relevance to bipolar disorder. In the present study, we investigated whether lithium and valproate, at clinically relevant doses, protects human neuroblastoma (SH-SY5Y) and glioma (SVG and U87) cells against oxidative stress and endoplasmic reticulum stress in a time-dependent manner. Pretreatment of SH-SY5Y cells for 7 days, but not 1 day, with 1 mM of lithium or 0.6 mM of valproate significantly reduced rotenone and H2O2-induced cytotoxicity, cytochrome c release and caspase-3 activation, and increased Bcl-2 levels. Conversely, neither acute nor chronic treatment of SH-SY5Y cells with lithium or valproate elicited cytoprotective responses against thapsigargin-evoked cell death and caspase-3 activation. Moreover, inhibitors of glycogen synthase kinase-3 (GSK-3), kenpaullone and SB216763, abrogated rotenone-induced, but not H2O2-induced, cytotoxicity. Thus the cytoprotective effects of lithium and valproate against H2O2-induced cell death is likely independent of GSK-3 inhibition. On the other hand, chronic lithium or valproate treatment did not ameliorate cytotoxicity induced by rotenone, H2O2, and thapsigargin in SVG astroglial and U87 MG glioma cell lines. Our results suggest that lithium and valproate may decrease vulnerability of human neural, but not glial, cells to cellular injury evoked by oxidative stress possibly arising from putative mitochondrial disturbances implicated in bipolar disorder.