Brain lithium concentrations in bipolar disorder patients: preliminary (7)Li magnetic resonance studies at 3 T.

BACKGROUND: This study was conducted to investigate the feasibility of human brain (7)Li MRS investigations at a high magnetic field (3 T), and to further explore the relationship between brain and serum lithium measures in lithium-treated bipolar patients. METHODS: Eight bipolar disorder type I patients (5 males, 3 females; mean age +/- SD = 33 +/- 9 years) were studied. A 3-T scanner, using a dual-tuned ((1)H and (7)Li) echoplanar imaging (EPI) compatible radiofrequency (RF) birdcage coil was used. (7)Li magnetic resonance spectroscopy (MRS) signal was acquired at the frequency of 49.64 MHz using an imaging selective in vivo spectroscopy (ISIS) sequence (TR = 15 sec, 128 averages), and quantitation was obtained in reference to an external standard. RESULTS: The mean +/- SD oral lithium dose was 1265 +/- 442 mg/day, and the mean +/- SD 12-hour serum level was 0.69 +/- 0.19 mEq/L. The measured brain lithium concentrations varied from 0.23 to 0.55 mEq/L (mean +/- SD = 0.35 +/- 0.11 mEq/L). The brain-serum ratios varied from 0.30 to 0.80 (mean +/- SD = 0.52 +/- 0.16). Subjects on single daily doses of lithium at bedtime (n = 5) had higher brain-serum lithium ratios compared with those on twice-a-day schedules (n = 3) (0.61 +/- 0.12 and 0.37 +/- 0.07, respectively; Mann--Whitney U test, Z = -2.24, p =.03). CONCLUSIONS: This study demonstrated for the first time the feasibility of (7)Li MRS human studies at 3 T. Future studies should examine a possible role for this methodology in investigations of lithium refractoriness and prediction of treatment outcome in bipolar patients.

Increased platelet membrane phosphatidylinositol-4,5-bisphosphate in drug-free depressed bipolar patients.

Prior investigations in bipolar disorder patients have suggested abnormalities in the cellular phosphoinositide second messenger system. This study was conducted to examine the levels of platelet membrane phosphoinositides in drug-free bipolar patients in the depressed state (n=9) and healthy controls (n=19). Bipolar patients had significantly increased levels of platelet membrane phosphatidylinositol-4,5-bisphosphate (PIP(2)) compared to healthy individuals (0.67+/-0.14 and 0.44+/-0.17%, respectively, t-test=3.71, d.f.=26, P=0.001). No significant differences in the levels of phosphatidylinositol-4-phosphate (PIP) (0.65+/-0.17 and 0.58+/-0.20%, respectively, t-test=1.02; d.f.=26; P=0.32) or phosphatidylinositol (PI) (5.92+/-1.23 and 5.56+/-1.45%, respectively, t-test=0.68; d.f.=26; P=0.51) were found. These findings provide the first demonstration of increased PIP(2) platelet levels in bipolar patients in the depressed state, and provide additional evidence that the phosphoinositide second messenger system may be a site of abnormality in bipolar disorder.

Concurrent measures of protein kinase C and phosphoinositides in lithium-treated bipolar patients and healthy individuals: a preliminary study.

This study examined the hypothesis that lithium inhibits the PI signaling pathway in humans during in vivo administration by concurrently measuring PKC isozymes and platelet membrane phosphoinositides in lithium-treated patients and healthy individuals. The platelet membrane and cytosolic levels of PKC alpha, beta I, beta II, delta, and epsilon were measured using Western blotting. The relative platelet membrane contents of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP(2)) were measured with two-dimensional thin-layer chromatography. Nine euthymic lithium-treated bipolar subjects and 11 healthy control subjects were studied. Compared to control subjects, lithium-treated bipolar patients had significantly lower levels of cytosolic PKC alpha isozyme (t-test=-3.24, d.f.=17, P=0.01) and PIP(2) platelet membrane levels (t-test=-2.51, d.f.=18, P=0.02), and a trend toward reduced levels of cytosolic PKC beta II isozyme (t=-2.17, d.f.=17, P=0.05). There was no significant correlation between PIP(2) and any of the PKC isozymes. These preliminary findings suggest that chronic lithium treatment may decrease the levels of both cytosolic PKC alpha isozyme and membrane PIP(2) in platelets of bipolar disorder patients.

Effects of lithium on platelet membrane phosphoinositides in bipolar disorder patients: a pilot study.

RATIONALE: In vitro and in vivo animal studies suggest that the intracellular phosphatidylinositol (PI) pathway is an important target for the effects of lithium. OBJECTIVES: We conducted a preliminary study to examine the in vivo effects of lithium treatment on platelet membrane phosphoinositides in bipolar disorder subjects, in an attempt to examine further the hypothesis that lithium has significant in vivo effects on the PI pathway in these patients. METHODS: We quantitated PI, phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2) in platelet membranes of seven subjects (five male, two female; mean age= 27.9+/-5.7 years), initially while they were unmedicated, and a second time after at least 21 days of lithium treatment (mean+/-SD=28.7+/-7.1 days). RESULTS: The mean+/-SD values for PI were 5.63+/-2.25% and 5.21+/-1.06%; for PIP 0.68+/-0.20% and 0.55+/-0.11%; and for PIP2 0.60+/-0.21% and 0.38+/-0.15%, before and after lithium treatment, respectively. The decrease in PIP2 values after lithium treatment was statistically significant (Wilcoxon signed ranks test, Z=-2.37, P=0.02). CONCLUSION: This longitudinal study suggests that therapeutic doses of lithium significantly decrease platelet membrane PIP2 levels in vivo in bipolar disorder subjects, which may be related to lithium's mechanism of action in bipolar disorder.

Reproducibility of in vivo measures of platelet membrane phospholipids in human subjects.

Membrane phospholipid abnormalities in the brain neurons may be implicated in the pathophysiology of neuropsychiatric disorders. In the absence of methods to directly examine the levels of brain membrane phospholipids in vivo in human subjects, peripheral cells and platelets have been used as models in this field. We previously reported a method to determine the relative amounts of eight individual platelet membrane phospholipid classes using two-dimensional thin-layer chromatography, and scanning-laser densitometry (Mallinger et al., 1993). Here we report the test/retest reproducibility of these platelet membrane phospholipid measures in healthy human subjects (n = 12) who were studied on two different occasions separated by a 3-week interval. The mean intra-subject coefficients of variation were 3.1-18%, and the intra-class correlation coefficients (ICCs) were 0.41-0.68. These findings are consistent with a low to moderate variability, and moderate reliability of these individual platelet membrane phospholipid measures over the period studied. When this method is applied for longitudinal studies of psychiatric populations, the degree of variability has to be considered in the interpretation of the results.

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 phosphatidyl-inositol-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.

Low rate of membrane lithium transport during treatment correlates with outcome of maintenance pharmacotherapy in bipolar disorder.

Lithium is transported across cell membranes by an exchange diffusion process (Na(+)-Li+ countertransport) that is inhibited during lithium treatment. We hypothesized that low rates of lithium efflux (a potential manifestation of strong transport inhibition) would be associated with better clinical outcome of maintenance pharmacotherapy. We measured the erythrocyte (RBC) apparent rate constant for lithium efflux (kexch) in 22 patients with bipolar disorder who had been euthymic on lithium for 1 month. Subsequently, clinical mood ratings and in vivo RBC: plasma lithium ratios (LiR) were determined monthly. Outcome was categorized according to whether subjects completed 1 year of successful maintenance treatment (n = 10), experienced a recurrent affective episode (n = 8), or dropped out (n = 4). The kexch at the outset of the study was significantly lower (potentially because of greater transport inhibition) in 1-year completers than in patients with recurrences or those who dropped out (median kexch = 0.09, 0.24, and 0.27 h-1, respectively; P < .03). Moreover, 77% of patients with a kexch of 0.11 h-1 or lower were successfully maintained on lithium for 1 year, whereas only 23% of those with a kexch greater than or equal to 0.12 h-1 had a successful treatment outcome. LiR measured during the course of maintenance treatment was significantly higher (suggesting greater transport inhibition) in 1-year completers than in noncompleters (recurrences and dropouts). Measurement of kexch at an early point in treatment may provide a means for prospectively identifying those bipolar patients at greater risk for failure of maintenance lithium therapy.

Platelet membrane phosphatidylinositol-4,5-bisphosphate alterations in bipolar disorder--evidence from a single case study.

Abnormalities in the cellular phosphatidylinositol (PI) pathway have been proposed to be implicated in the pathophysiology of bipolar disorder. A platelet model was used to study phosphatidylinositol-4,5-bisphosphate (PIP2) membrane values in a bipolar disorder patient in different mood states, in a single case study. The patient was studied unmedicated, initially in the euthymic and later in the manic states, and subsequently on lithium after remission of manic symptoms. The relative percentage of PIP2 in the platelet membranes increased with cycling from the euthymic into the manic state. After lithium treatment, PIP2 decreased, and was similar to the euthymic state. This study further demonstrates the feasibility of this method, as well as its applicability to longitudinal studies in bipolar disorder, and suggests promising directions for future research in this area.

Analysis of complex mixtures of phospholipid classes from cell membranes using two-dimensional thin-layer chromatography and scanning laser densitometry.

Increasing recognition of the important roles served by membrane phospholipids in cellular metabolic and signal transduction processes has stimulated interest in examining potential phospholipid abnormalities in patients with psychiatric disorders. This report describes a method, based on several novel modifications of existing techniques, for concurrently analyzing nanomolar amounts of nine phospholipid classes in a single aliquot of membrane extract. With this method, diverse phospholipid classes are first separated by two-dimensional thin-layer chromatography, and then determined using two-dimensional scanning laser densitometry. The method is able to quantitate even small amounts of specific phospholipid classes, corresponding to < 10 ng of lipid phosphorus. The sensitivity of this method allows it to be readily applied to clinical studies involving membranes from cell types that are obtainable only in small quantities.