Lithium transport in red cells of patients with affective disorders

Relevance of red blood cell Lithium concentration in the management of Lithium-treated bipolar and unipolar disorders: a systematic narrative review

BACKGROUND

Despite a variability in response and a narrow therapeutic index, Lithium (Li) remains the gold standard treatment for bipolar disorders (BD), and a treatment of choice for unipolar disorders (UD). Red blood cell Li concentration (RBCLiC) and red blood cell/plasma Li ratio (LiR) have been studied in many areas of mood disorders (such as acute or chronic Li efficacy, adherence, side effects (SE), intoxication management) as well as in several research domains. This systematic review aims to synthesize the existing literature.

METHODS

We conducted a systematic review, based on preferred reporting items for systematic reviews and Metanalysis (PRISMA) guidelines, of articles published between 1972 and February 2023, indexed in the following databases: EMBASE, MEDLINE, Cochrane Library. The search terms were combinations of the following headings: "Lithium AND Plasma AND Erythrocyte AND Mood disorders". The systematic review protocol was published to PROSPERO (CRD42023406154).

RESULTS AND CONCLUSION

Out of the 252 identified studies, 57 met the selection criteria. The articles investigated the interest of RBCLiC and other blood parameters (PLiC and LiR) in various areas: (i) disease management (31 articles) (compliance/adherence (5 articles), SE/toxicity (13 articles), prediction of Li response/therapeutic efficacy for acute episode or for relapse prevention (17 articles)), (ii) Li blood parameters as trait markers of mood disorders subtypes (UD, BDI, BDII) (16 articles), (iii) Li blood parameters as state markers of mood episodes (11 articles), (iv) factors influencing Li blood parameters (age, gender, ethnicity, dosage and duration of Li treatment, co-medications with other treatments, seasonality) associated with RBCLiC or LiR (24 articles), and (v) potential pathophysiological mechanisms (30 articles).

CONCLUSION

Overall, this review suggests that RBCLiC or LiR could be of interest for tolerance monitoring. However, the heterogeneity of methods and results, coupled with the limited amount of data, does not allow clear conclusions to be drawn in the other areas explored in this literature review. Given the potential interest in exploring brain Li pharmacokinetics (PK)s, this review calls for further research.

The molecular basis for Na-dependent phosphate transport in human erythrocytes and K562 cells

The kinetics of sodium-stimulated phosphate flux and phosphate-stimulated sodium flux in human red cells have been previously described (Shoemaker, D.G., C.A. Bender, and R.B. Gunn. 1988. J. Gen. Physiol. 92:449-474). However, despite the identification of multiple isoforms in three gene families (Timmer, R.T., and R.B. Gunn. 1998. Am. J. Physiol. Cell Physiol. 274:C757-C769), the molecular basis for the sodium-phosphate cotransporter in erythrocytes is unknown. Most cells express multiple isoforms, thus disallowing explication of isoform-specific kinetics and function. We have found that erythrocyte membranes express one dominant isoform, hBNP-1, to which the kinetics can thus be ascribed. In addition, because the erythrocyte Na-PO(4) cotransporter can also mediate Li-PO(4) cotransport, it has been suggested that this transporter functions as the erythrocyte Na-Li exchanger whose activity is systematically altered in patients with bipolar disease and patients with essential hypertension. To determine the molecular basis for the sodium-phosphate cotransporter, we reasoned that if the kinetics of phosphate transport in a nucleated erythroid-like cell paralleled those of the Na-activated pathway in anucleated erythrocytes and yet were distinct from those known for other Na-PO(4) cotransporters, then the expressed genes may be the same in both cell types. In this study, we show that the kinetics of sodium phosphate cotransport were similar in anuclear human erythrocytes and K562 cells, a human erythroleukemic cell line. Although the erythrocyte fluxes were 750-fold smaller, the half-activation concentrations for phosphate and sodium and the relative cation specificities for activation of (32)PO(4) influx were similar. Na-activation curves for both cell types showed cooperativity consistent with the reported stoichiometry of more than one Na cotransported per PO(4). In K562 cells, external lithium activation of phosphate influx was also cooperative. Inhibition by arsenate, K(I) = 2.6-2.7 mM, and relative inhibition by amiloride, amiloride analogs, phosphonoformate, and phloretin were similar. These characteristics were different from those reported for hNaPi-3 and hPiT-1 in other systems. PCR analysis of sodium-phosphate cotransporter isoforms in K562 cells demonstrated the presence of mRNAs for hPiT-1, hPiT-2, and hBNP-1. The mRNAs for hNaPi-10 and hNaPi-3, the other two known isoforms, were absent. Western analysis of erythrocytes and K562 cells with isoform-specific antibodies detected the presence of only hBNP-1, an isoform expressed in brain neurons and glia. The similarities in the kinetics and the expression of only hBNP-1 protein in the two cell types is strong evidence that hBNP-1 is the erythrocyte and K562 cell sodium-phosphate cotransporter.

Abnormalities of lithium transport across the erythrocyte membrane in depression and schizophrenia

Three mechanisms of lithium transport across erythrocyte membrane [lithium-sodium countertransport (LSC), lithium-potassium cotransport (LPC), and passive lithium diffusion (PLD)] were estimated in 27 acutely schizophrenic patients, 27 acutely depressed affective patients and in 18 control subjects. The activities of all mechanisms studied were significantly lower in both schizophrenic and depressed patients compared with controls. Analysis by gender showed that in control subjects, mean values of erythrocyte LSC and LPC were significantly higher in males compared with females. The decrease of LSC and LPC in depression and LSC in schizophrenia compared with control subjects was observed only in male patients but not in female ones. The results obtained suggest that lithium transport abnormalities during acute psychotic episodes are not specific to affective patients where lithium exerts its therapeutic action, but are also observed in schizophrenia. These abnormalities are more evident in male patients.

New applications of lithium therapy

Several placebo-controlled double-blind studies have indicated that lithium sometimes augments antidepressants, converting nonresponding patients to responders. Lithium therapy has also benefitted some schizoaffective patients and some alcoholics. Side effects are minimal. Mechanisms involved in lithium's effectiveness have not yet been discovered.

Kinetics of erythrocyte lithium-sodium countertransport in patients with affective illness before and during lithium therapy

Previous investigations have elucidated an erythrocyte lithium-sodium countertransport (LSC) system as the primary mechanism for extruding lithium from the cell, and this activity has been described in terms of Michaelis-Menten kinetics. In most clinical studies the maximum velocity (Vmax) of the LSC has been measured by estimating the rate of lithium efflux from lithium-loaded cells. To date, few studies have examined whether the affinity (Km) of the LSC for lithium might be altered in patients with affective disorders. In the present study we examined LSC kinetic parameters (Vmax, leak, Km, and in vitro lithium ratio) at baseline in 80 patients with affective disorder and 25 healthy control subjects, and after 6 weeks of lithium administration in 33 of the patients. No differences in Vmax were observed between any patient and control group, although Vmax was significantly lower in unipolar depressed men compared to bipolar men (P = 0.043). The affinity (Km) of the transport 'carrier' for lithium did not differentiate between patient and control groups. Chronic lithium administration caused a decreased Vmax in bipolar men (P = 0.015), an increase in the in vitro lithium ratio in bipolar men (P = 0.002) and bipolar women (P = 0.002), and a marginal increase in Km in bipolar men (P = 0.08) and bipolar women (P = 0.06). Although the present data do not demonstrate an underlying difference for Km between affectively ill patients and controls, they do indicate a decrease in the affinity of the transport 'carrier' for lithium after chronic lithium administration.