Platelet membrane phospholipids in euthymic bipolar disorder patients: are they affected by lithium treatment?

Background: Abnormalities in cell membrane processes and intracellular signal transduction pathways may be implicated in the pathophysiology of bipolar disorder. In this study, we attempted to investigate, in euthymic bipolar patients: 1) in vivo signal transduction abnormalities of the phosphatidylinositol pathway in platelets; and 2) possible in vivo effects of lithium treatment on platelet membrane phospholipids. Methods: We determined the relative absorbances of eight individual classes of platelet membrane phospholipids, using two-dimensional thin-layer chromatography in high-performance plates, followed by scanning laser densitometry, in a group of 10 lithium-treated euthymic bipolar patients and 11 normal controls. Results: The mean relative absorbance of phosphatidylinositol-4,5-bisphosphate (PIP2) was lower in the patient group (0.29 ± 0.08% vs. 0.39 ± 0.12%; t = 2.35, df = 19, p = .03); no significant differences between patients and controls were found for the other phospholipids. Conclusions: This study provides in vivo evidence that bipolar patients on lithium treatment exhibit a decreased relative amount of PIP2 in the platelet cell membranes compared to normal controls.