Emerging therapeutic targets in bipolar mood disorder

A systematic review of existing data on long-term lithium therapy: neuroprotective or neurotoxic?

Lithium is an efficacious agent for the treatment of bipolar disorder, but it is unclear to what extent its long-term use may result in neuroprotective or toxic consequences. Medline was searched with the combination of the word 'Lithium' plus key words that referred to every possible effect on the central nervous system. The papers were further classified into those supporting a neuroprotective effect, those in favour of a neurotoxic effect and those that were neutral. The papers were classified into research in humans, animal and in-vitro research, case reports, and review/opinion articles. Finally, the Natural Standard evidence-based validated grading rationale was used to validate the data. The Medline search returned 970 papers up to February 2006. Inspection of the abstracts supplied 214 papers for further reviewing. Eighty-nine papers supported the neuroprotective effect (6 human research, 58 animal/in vitro, 0 case reports, 25 review/opinion articles). A total of 116 papers supported the neurotoxic effect (17 human research, 23 animal/in vitro, 60 case reports, 16 review/opinion articles). Nine papers supported no hypothesis (5 human research, 3 animal/in vitro, 0 case reports, 1 review/opinion articles). Overall, the grading suggests that the data concerning the effect of lithium therapy is that of level C, that is 'unclear or conflicting scientific evidence' since there is conflicting evidence from uncontrolled non-randomized studies accompanied by conflicting evidence from animal and basic science studies. Although more papers are in favour of the toxic effect, the great difference in the type of papers that support either hypothesis, along with publication bias and methodological issues make conclusions difficult. Lithium remains the 'gold standard' for the prophylaxis of bipolar illness, however, our review suggests that there is a rare possibility of a neurotoxic effect in real-life clinical practice even in closely monitored patients with 'therapeutic' lithium plasma levels. It is desirable to keep lithium blood levels as low as feasible with prophylaxis.

Epidemiology of bipolar disorders

Bipolar, or manic-depressive, disorders are frequent and severe mental illnesses associated with considerable morbidity and mortality. Epilepsy and bipolar disorder could probably share some aspects of pathophysiology because manic as well as depressive symptoms are seen in patients with seizures, and a number of antiepileptic drugs are effectively used in the acute and prophylactic treatment of bipolar disorder. Epidemiologic research suggests a dimensional composition of bipolar illness at the population level. Apart from the DSM-IV diagnostic features of bipolar I (mania and depression) and bipolar II (hypomania and depression), the concept of bipolar spectrum disorders comprises a range of bipolar conditions with less obvious manifestations with estimated lifetime prevalence rates ranging from 2.8 to 6.5%. Expanding the definition of bipolar II disorders shows that half of the patients currently diagnosed with a unipolar depressive episode could suffer from unrecognized bipolar II disorder, and about the same number of mild depressive patients could be minor bipolars. Research efforts to refine the diagnostic criteria of bipolar disorder aim at an earlier and complete recognition of the disease to provide appropriate pharmacological and nonpharmacological treatment early in the course of the illness to anticipate individual suffering, suicidal behavior, and increased socioeconomic costs for society. This article also discusses risk factors, comorbid conditions, course of illness, as well as the individual and socioeconomic impact of bipolar disorders.

CONCLUSIONS

The findings suggest reconceptualizing bipolar illnesses as highly recurrent, malignant disorders that occur far more frequently than previously thought. Interdisciplinary knowledge transfer could help to increase our understanding of the pathophysiology of these disorders as well as provide grounds for better recognition and treatment of patients with manic and/or depressive symptoms.

Inhibition of phosphoglucomutase activity by lithium alters cellular calcium homeostasis and signaling in Saccharomyces cerevisiae

Phosphoglucomutase is a key enzyme of glucose metabolism that interconverts glucose-1-phosphate and glucose-6-phosphate. Loss of the major isoform of phosphoglucomutase in Saccharomyces cerevisiae results in a significant increase in the cellular glucose-1-phosphate-to-glucose-6-phosphate ratio when cells are grown in medium containing galactose as carbon source. This imbalance in glucose metabolites was recently shown to also cause a six- to ninefold increase in cellular Ca2+ accumulation. We found that Li+ inhibition of phosphoglucomutase causes a similar elevation of total cellular Ca2+ and an increase in 45Ca2+ uptake in a wild-type yeast strain grown in medium containing galactose, but not glucose, as sole carbon source. Li+ treatment also reduced the transient elevation of cytosolic Ca2+ response that is triggered by exposure to external CaCl2 or by the addition of galactose to yeast cells starved of a carbon source. Finally, we found that the Ca2+ over-accumulation induced by Li+ exposure was significantly reduced in a strain lacking the vacuolar Ca2+-ATPase Pmc1p. These observations suggest that Li+ inhibition of phosphoglucomutase results in an increased glucose-1-phosphate-to-glucose-6-phosphate ratio, which results in an accelerated rate of vacuolar Ca2+ uptake via the Ca2+-ATPase Pmc1p.