Lithium transport across the RBC membrane. A study of genetic factors

Comparison of lithium concentrations in red blood cells and plasma in samples collected for TDM, acute toxicity, or acute-on-chronic toxicity

BACKGROUND

Lithium salts (Li+) are still one of the most appropriate treatments in manic-depressive disorders. Since Li+ has a narrow therapeutic index, plasma levels must be closely monitored to verify maintenance pharmacotherapy, to prevent side effects, to evaluate compliance and to avoid increasing rates of relapse. Although it has been reported that Li+ concentrations in red blood cells (RBC) should be a better indicator of brain levels, therapeutic drug monitoring (TDM) of Li+ is not based on its routine assessment.

OBJECTIVE

The aim of this retrospective study was to compare Li+ concentrations in RBC and plasma and the calculated ratio (LiR= RBC/plasma concentrations) in the three groups of patients.

METHODS

During the past 3 years, 309 Li+ measures were collected corresponding to 165 patients classified into three subgroups (TDM, acute or acute-on-chronic intoxication). Li+ plasma (Cplasma) and RBC (CRBC) concentrations were determined by atomic absorption spectrophotometry.

RESULTS

Results showed that Li+ concentrations in plasma are significantly correlated to Li+ concentration in RBC (r=0.81, P<0.0001). Although a wide inter- and intra-variability was found, Cplasma, CRBC and LiR were statistically different in the three groups. Compared with TDM, Cplasma was more elevated in cases of acute intoxication whereas Li+ accumulated preferentially in RBC in cases of acute-on-chronic intoxication.

CONCLUSION

This study shows the interest of determining Li+ in RBC and plasma for TDM, and that LiR could be a sensitive marker of intoxication and of Li+ impregnation.

Natural variation in passive sodium permeability in human erythrocytes

The rate of influx of 22Na+ into human erythrocytes (RBC) varies greatly depending upon the donor. A high rate of influx may be related to a congenital predisposition to essential hypertension. In Northern Europeans, we find a threefold difference in the rate of 22Na+ influx between those with the least (LP) and most highly permeable (HP) RBC (from less than 0.15 to greater than 0.60 mmol Na+/liter RBC/hr). In order to further define determinants of these apparently hereditary differences in passive membrane Na+ transport, we identified two groups of normal laboratory and hospital personnel differing markedly (greater than twofold) in RBC 22Na+ influx rate. We find that the loop diuretics furosemide and bumetanide decrease by about 50% the influx of 22Na+ into HP RBC, but have a lesser influence on LP RBC. Impermeant polyanions such as citrate and pyrophosphate also specifically diminish 22Na+ influx into HP, but not LP, RBC. Therefore, the exaggerated 22Na+ influx into HP RBC probably occurs through a discrete pathway (perhaps via "Na/K/Cl cotransport"), which appears to be almost absent in LP RBC. The differences between HP and LP RBC most likely do not involve polymorphisms of RBC anion transport per se. The rate of RBC anion (35SO4(2-)) transport is the same in HP and LP RBC and is equally inhibited by furosemide and (to a lesser extent) bumetanide. Furthermore, the potent inhibitor of RBC anion transport, DIDS (diisothiocyanostilbene disulfonate) does not affect RBC Na+ permeability in either group. Nonetheless, the preferential reduction of Na+ permeation of HP RBC by loop diuretics may be of help in experimentally distinguishing HP from LP phenotypes. This information may be crucial in unraveling the structural basis of intrinsic differences in cell membrane Na+ permeability and their possible relationship to essential hypertension.

The effect of lithium on the membrane molecular dynamics of normal human erythrocytes

Erythrocytes from normal adults with no personal or family history of bipolar affective disorder were analyzed by fluorescence spectroscopy to determine what effect, if any, acute in vitro incubation with lithium had on erythrocyte membrane dynamics. The effects on erythrocyte membrane molecular dynamics of varying concentrations of Li2CO3 (0.25-2.0 meq/liter), varying incubation temperatures (25-40 degrees C), and varying incubation times (5-185 min) were investigated. Following incubation with Li2CO3, the erythrocytes were labeled with either 4-phenylspiro-[furan-2(3H),--1'phthalan]--3,3'-dione (fluorescamine), which binds to membrane surface primary amines, or 12(9)anthroyl stearate [12(9)AS], which inserts deep in the membrane hydrocarbon core. The membrane molecular dynamics were then determined by fluorescence anisotropy measurements. These studies demonstrate that clinically relevant concentrations of Li+ incubated with intact normal human erythrocytes significantly alters molecular dynamics on the erythrocyte membrane surface, with less striking changes in the hydrocarbon core. A possible interpretation of these findings is that hydrated Li+ alters the electrostatic interaction of membrane surface molecules, as well as the surrounding solvent (water) structure, with a resultant increase in the molecular motion of these molecules. Alterations in membrane receptor motion could potentially alter receptor functional activity. If similar motional alterations were to occur in the interior of a membrane channel, such as an ionophore, the functional activity of the channel could also be potentially altered. These findings provide additional insight into possible biological actions of Li+, as well as potential molecular alterations in bipolar affective disorder erythrocytes.

Cholinesterases in primary affective disorders

Cholinesterase activities were measured in plasma (ChE) and in intact erythrocytes (AChE) in patients suffering from manic-depressive illness, their first degree relatives who were well, and unrelated normal volunteers. All the subjects were in a normal mood state at the time of testing. Plasma cholinesterase activity was found to be significantly lower than normal in bipolar (BP), unipolar (UP), other affective disorder (OA) and well subjects belonging to manic-depressive families. Intact erythrocyte cholinesterase (true cholinesterase) activity was also found to be significantly lower than normal in all the above mentioned patients and their relatives. Half of the BP subjects were on lithium treatment and their cholinesterase activities were similar to those patients not on lithium treatment. The data suggest a significant role of cholinergic mechanisms in the etiology of manic-depressive illness.

Erythrocyte membrane sodium-potassium and magnesium ATPase in primary affective disorder

Erythrocyte membrane Mg2+ ATPase and Na+-K+ ATPase were measured in patients with affective disorder, their well relatives, and normal controls during euthymic moods. On the average, the Mg2+ ATPase activity was high in subjects belonging to affective disorder families. However, the difference between normal and affective disordered individuals was not statistically significant. Only the well individuals from affective disorder pedigrees as a group had significantly higher than normal Mg2+ ATPase activity (p less than 0.05). The Na+-K+ ATPase activity was similar for all the groups, including normal, bipolar manic-depressive (with or without lithium), unipolar depressive, and well individuals. Lithium treatment did not seem to have any effect on Mg2+ ATPase. Even though the values of Na+-K+ ATPase in the lithium-treated group were high, it is not certain that this was due to lithium per se.

Lithium therapy for mania and depression

The literature on lithium carbonate was reviewed for clues to the processes involved in mania. Lithium has proved effective therapeutically and prophylactically for mania and depressive disorders. Children and adolescents as well as adults tolerate lithium well. Side effects rarely are serious enough to necessitate having lithium therapy. Some success with schizophrenia and schizoaffective disorders has broadened the scope of lithium's therapeutic efficacy but also blunted the expectation for a direct relationship between lithium and the processes involved in mania. Research points to neurotransmitters as contributing to the etiology and symptom pattern of mania.

Exogenous factors influencing the human erythrocyte sodium-lithium countertransport system

It has recently been found that the Na+-Li+ countertransport across the human erythrocyte membrane is increased in patients with essential hypertension. We investigated the influence of hypokalaemia, oral contraceptives, diabetes mellitus and essential hypertension on the activity of this transport system. Normal values for the maximal Na+-Li+ transport rate were 0.25 +/- 0.08 mmol l-1 h-1 (males, n = 18) and 0.23 +/- 0.06 (females, n = 14). We found elevated values in women taking oral contraceptives (0.34 +/- 0.07, n = 10, P less than 0.001), in patients with chronic hypokalaemia due to diuretic or laxative abuse (0.41 +/- 0.16, n = 13, P less than 0.005) and in those with essential hypertension (0.32 +/- 0.08, n = 24, P less than 0.001) (all data mean +/- SD). Thus our results with hypertensive patients support the findings of other investigators. However, oral contraceptives and drug-induced hypokalaemia greatly modify this system, indicating a regulation of the Na+-Li+ countertransport by hormones. Thus the transport rate does not seem to be an appropriate test for the diagnosis of essential hypertension.

Heritability of erythrocyte Na+-Li+ countertransport in relation to essential hypertension

The Na+-Li+ countertransport system in erythrocytes was investigated in patients with essential hypertension and control subjects. Furthermore, studies on the pairs of parent-offspring and husband-wife were added in order to evaluate heritability of the countertransport. The Na+-Li+ countertransport of patients with essential hypertension and normotensive subjects with the family history of hypertension was significantly increased in comparison with that of normotensive subjects without the family history. The correlation coefficient of the countertransport in pairs of parent-offspring was significant but not between husband-wife. These results support the concept of a genetic determinant for the countertransport system.

Blood cells as biological trait markers in affective disorders

Data are reviewed on platelet monoamine oxidase activity, red blood cell/plasma lithium ratio, and tritiated imipramine binding to platelet membranes as trait markers for affective disorders. The results of various studies are not in agreement. Differences in methodological procedure are probably central to such discrepancies. At the present time, no single biological abnormality of blood cells has proved to be a trait marker for affective disorders; thus their use to identify vulnerability to mood disorders or predict favourable response to pharmacological treatment appears to be premature.

Perturbation of sodium-lithium countertransport in red cells

The rate of sodium-lithium countertransport in red cells is thought to be determined by inheritance and to be constant over years in a given person. We have found that the rate is influenced acutely by ultrafiltration and by hemodialysis. In seven patients with endstage renal disease secondary to essential hypertension, the mean rate of sodium-lithium countertransport (+/- S.E.M.) was reduced from 0.18 +/- 0.02 to 0.09 +/- 0.01 mmol per liter of cells per hour (P less than 0.02) by ultrafiltration and from 0.22 +/- 0.03 to 0.12 +/- 0.03 mmol per liter per hour (P less than 0.001) by hemodialysis. When patients' red cells obtained before dialysis were incubated with plasma obtained afterward, the rate of countertransport fell, and when red cells obtained after dialysis were incubated with plasma obtained beforehand, the rate returned to normal. Whereas the rate in red cells from normal subjects was reduced after incubation in post-dialysis plasma from patients, predialysis plasma from the same patients had no such effect. We conclude that the rate of the countertransport system of red cells is dependent on a dialyzable plasma factor.

Trends in research and treatment of affective disorders

Trends in research on affective disorders were reviewed. Studies which described the contribution of neurotransmitters and neuroendocrines to depression, unipolar and bipolar, and manic states were cited. Women more frequently suffer from affective disorders but women's response to different therapies sometimes is more favorable than men's. Age and married status influence sex differences in the incidence of affective disorders. Symptoms of pain and depression intertwine, and response to analgesia may emerge as an index of response to therapy for depression. Trends in pharmacotherapies for affective disorders were reviewed: lithium, tricyclic antidepressants, and MAOI drugs, as well as trends in the employment of ECT and sleep deprivation to relieve symptoms of affective disorders were reviewed.

Essential hypertension: sodium-lithium countertransport in erythrocytes from patients and from children having one hypertensive parent

This report deals with the possibility that there is a specific change of the lithium transport across the membrane of erythrocytes from patients with essential hypertension. Sodium-lithium countertransport was significantly increased (p less than 0.005) in erythrocytes from 17 males with essential hypertension (mean 0.7 mmole (liter cells X hr)-1, range 0.4-1.6) compared to a group of 16 normotensive males (mean, 0.4 mmole (liter cells X hr)-1, range 0.3-0.6). A considerable overlap between the values from patients and controls was found. No significant increase of the transport function was found in a group of 14 female patients (mean 0.4 mmole (liter cells X hr)-1, range 0.2-0.6) compared with 10 normotensive female controls (mean 0.3 mmole (liter c hr)-1, range 0.3-0.6). A considerable overlap between the values from patients and controls was found. No significant increase of the transport function was found in a group of 14 female patients (mean 0.4 mmole (liter cells X hr)-1, range 0.2-0.6) compared with 10 normotensive female controls (mean 0.3 mmole (liter c hr)-1, range 0.3-0.6). A considerable overlap between the values from patients and controls was found. No significant increase of the transport function was found in a group of 14 female patients (mean 0.4 mmole (liter cells X hr)-1, range 0.2-0.6) compared with 10 normotensive female controls (mean 0.3 mmole (liter cells X hr)-1, range 0.1-0.6). Determination of sodium-lithium countertransport in red blood cells from nine children with and 14 without known familial disposition for essential hypertension did not demonstrate a close coupling between genetic disposition and the membrane transport function. In spite of the very small intraindividual variability of the transport function, studies of changes in sodium-lithium counter-transport are hampered by considerable interindividual variability of the transport in red cells from apparently normal individuals.

Current psychopharmacogenetic strategies in primary affective disorders

1. The evidence is substantial that primary affective disorders are genetically inherited. 2. Using pharmacological probes or strategies, biological markers of the gene(s) should be able to be ascertained or induced during remission of illness. 3. Genetic marker criteria are defined and are applied to the scanty existing data. 4. It is concluded that these strategies have yet to yield a clear marker of primary affective disorder.