Lithium, red blood cell choline and clinical state. A prospective study in manic-depressive patients

Testing competing path models linking the biochemical variables in red blood cells from Li+-treated bipolar patients

OBJECTIVES

Red blood cells (RBCs) from Li+-treated bipolar patients have shown abnormalities in intracellular Li+ concentration ([Li+]i), Na+/Li+ exchange rates, and membrane phospholipid levels. Based on Li+-loaded RBC studies, we hypothesized that Li+-treated bipolar patients also have varied intracellular free Mg2+ concentrations ([Mg2+]f) as compared with normotensive patients. We addressed how these experimentally determined values are intercorrelated. Assuming that Li+ treatment alters these biochemical parameters, we provide hypothetical pathways based upon structural equation modeling statistics.

METHODS

In RBCs from 30 Li+-treated bipolar patients, we determined [Li+]i, serum [Li+] ([Li+]e), Na+/Li+ exchange parameters, membrane phospholipid levels, [Mg2+]f, and Li+ membrane binding affinities. Comprehensive statistical analyses assessed correlations among the biochemical data. We used path analysis statistics to propose potential pathways in which the data were correlated.

RESULTS

We found significant correlations within the three Na+/Li+ exchange parameters and percentage composition of the membrane phospholipids. Additional correlations existed between [Mg2+]f and Vstd, Km, or phospholipid composition, between [Li+]i and percentage of phosphatidylcholine, and between percentage of phosphatidylserine and Km. Based on these findings, we hypothesized and statistically determined the most probable pathway through which these parameters were intercorrelated.

CONCLUSIONS

Significant correlations existed between the biochemical parameters that describe the cell membrane abnormality and the Li+/Mg2+ competition hypotheses. Using path analysis statistics, we identified a biochemical pathway by which Li+ may assert its cellular effects. This study serves as an illustrative example how path analysis is a valuable tool in determining the direction of a certain biochemical pathway.

Lithium distribution in red blood cells and plasma: NMR studies of rat blood

To understand the interaction of lithium (Li+) with a coadministered drug in both the blood and the brain, we have treated rats with either Li+ alone or Li+ and a codrug. In this paper we address the important problem of quantitation of intra and extracellular Li+ ion contents in blood by the 7Li-NMR technique and the use of a shift reagent (SR). Although Li+ can be studied by atomic absorption techniques, these techniques involve tedious separation of intra- and extracellular components prior to chemical analysis. Magnetic resonance studies on rat blood, in the dose range of 0.5 to 10 meq/kg, indicate that the intracellular red blood cell Li+ predominates in the lower dose range of 0.5-1.0 meq/kg. As the lithium dose increases, a significantly larger amount of Li+ accumulates in the extracellular volume. Our studies on a number of animals at various doses of LiCl indicate that 7Li-NMR of blood samples provide a reliable, noninvasive quantification of red blood cell and plasma Li+ concentrations. The NMR method was further used to study the effect of coadministered drugs such as thioridazine on the intra- and extracellular Li+ concentration of RBCs.

The functional neuroanatomy of mood disorders

Mood disorders may be associated with global and regional changes in cerebral blood flow and metabolism. The accumulated functional neuroimaging findings in mood disorders were reviewed in order to examine a proposed neuroanatomic model of pathophysiology. Global cerebral blood flow and glucose metabolism appear normal, but may be decreased in late-life depression. Regional cerebral blood flow and glucose metabolism deficits are present, and may be indicators of brain regions participating in neuroanatomic circuits involved in mood disorders. Decreased pre-frontal cortex blood flow and metabolism in depressed unipolar and bipolar patients are the most consistently replicated findings, and correlate with severity of illness. Basal ganglia abnormalities have been found in depressed unipolar and bipolar patients, involving decreased blood flow and metabolism. Temporal lobe abnormalities are present in bipolar disorder patients, and perhaps unipolar depression. There is conflicting evidence of abnormalities in other limbic regions. Cognitive impairment may correlate with decreased metabolism in frontal and cerebellar areas. The relationship between functional neuroimaging findings and clinical course, and therefore state and trait characteristics, has not been systematically investigated. Antidepressant medications, but not ECT, seem to reverse some of the identified functional brain changes in the depressed state. The structural, neurotransmitter and neuropathological correlates of these functional abnormalities are yet to be determined. Functional abnormalities in frontal, subcortical and limbic structures appear to be part of the pathophysiology of mood disorders.

Lithium treatment in affective disorders: The significance of strongly elevated erythrocyte choline levels

In manic-depressive patients treated with lithium salts the transport of choline over the erythrocyte membrane is strongly inhibited, resulting in dramatically increased erythrocyte choline levels (for review see ref. 1). Whether or not there is a relationship between this effect and treatment response is not clear. Data on this issue are scarce possibly because the measurement of treatment response in lithium prophylaxis is very difficult and time consuming. Also the effect on erythrocyte choline is specific for lithium and not for manic-depressive illness. We will address here the question of a possible relation between erythrocyte choline and clinical effects of lithium.

Erythrocyte choline concentration in bipolar disorder: a predictor of clinical course and medication response

Erythrocyte choline concentrations were measured in hospitalized patients with bipolar disorder, manic phase, and control subjects. There was a significant elevation in mean erythrocyte choline in the patients with mania. This elevation in erythrocyte choline was due to a subgroup of patients with especially high values. Significant clinical differences were apparent between the patients with "high" and those with "low" erythrocyte choline concentrations. The subgroup of manic patients with elevated erythrocyte choline had a more severe illness at admission, a worse outcome at discharge, and required significantly more neuroleptic during hospitalization than their low choline counterparts; that is, they were less likely to respond well to lithium alone. Furthermore, the bipolar patients with low erythrocyte choline concentrations, as a whole, had more than four times as many previous manic episodes than depressive episodes, while the patients with high choline values had approximately the same number of past manias and depressions. These results are discussed in light of the evidence implicating cholinergic neurotransmission in the pathophysiology of affective disorders. In addition, the design of future clinical studies of erythrocyte choline and its possible clinical utility are discussed.

Erythrocyte choline concentrations in psychiatric disorders

Erythrocyte choline has been used as a potential indirect measure of cholinergic function in the central nervous system (CNS). We review the literature and present some new data on erythrocyte choline concentrations in patients with neuropsychiatric disorders. Our data and most of the reviewed studies report modest elevations in mean erythrocyte choline values in patients with affective illnesses, psychoses, dementia, and other neuropsychiatric disorders when compared to controls. Within each disorder, the increased mean erythrocyte choline concentrations are due to subgroups of patients with especially high values. These subgroups of patients with elevated erythrocyte choline levels appear to have clinical characteristics that distinguish them from patients with normal choline values. Finally, the dramatic rise in erythrocyte choline concentration produced by lithium therapy is reviewed, and the implication of this effect, in particular, the possibility that pretreatment or posttreatment erythrocyte choline concentrations may predict response to lithium, is discussed.

Effects of bipolar affective disorder and lithium administration on the cholinergic system in human blood

Several processes relating to the cholinergic system that are present in human blood were measured in samples obtained from patients with bipolar affective disorder, both before and during treatment with lithium, and from controls. The biochemical measurements include RBC and plasma choline concentrations, the kinetics of RBC choline uptake, plasma non-specific cholinesterase and RBC and plasma acetylcholinesterase. The RBC choline level is increased and the Vmax of the RBC choline uptake system is decreased in samples from lithium-free bipolar patients during manic episodes. There are no differences from control in the plasma choline levels or in the acetylcholinesterase enzyme activities in blood samples from the lithium-free or lithium-treated patients. Plasma non-specific cholinesterase is below control levels in all patients. Lithium treatment increases the RBC choline concentration to more than ten-times control levels and reduces the Vmax and the affinity for choline of the RBC choline transport system. In vitro addition of lithium does not replicate the effects of in vivo administration of lithium. Possible mechanisms for these effects of lithium are discussed.

Cholinergic processes in blood samples from patients with major psychiatric disorders

Cholinergic processes were measured in plasma and red blood cells (RBC) obtained from patients with mania, depression, and schizophrenia. RBC choline levels were elevated in manic patients, and lithium treatment led to a further increase. RBC choline transport was below normal in manic patients, and lithium treatment further reduced choline transport in addition to reducing the apparent affinity for choline. RBC acetylcholinesterase was low in depressed and schizophrenic patients, but not in manic patients, whereas plasma acetylcholinesterase was reduced only in depressed patients. Plasma nonspecific cholinesterase was below normal in all groups of patients. These results indicate unique patterns of differences from controls in the cholinergic system in blood samples from patients with different psychiatric illnesses.

1H NMR methods for the noninvasive study of metabolism and other processes involving small molecules in intact erythrocytes

1H NMR methods are described with which resolved resonances can be obtained for many of the small molecules in intact erythrocytes. In one method, the more intense hemoglobin resonances are suppressed by transfer of saturation throughout the hemoglobin spin system by cross relaxation following a selective saturation pulse. In a second method, the hemoglobin resonances are eliminated with the spin-echo pulse sequence by using a between-pulse delay time long enough for complete elimination of the hemoglobin resonances by spin-spin relaxation. Selected examples of the study of erythrocyte biochemistry by 1H NMR are discussed.