Augmentation of zinc ion stimulation of lymphoid cells by calcium and lithium

Lithium: effects in animal models of vanishing white matter are not promising

Vanishing white matter (VWM) is a devastating autosomal recessive leukodystrophy, resulting in neurological deterioration and premature death, and without curative treatment. Pathogenic hypomorphic variants in subunits of the eukaryotic initiation factor 2B (eIF2B) cause VWM. eIF2B is required for regulating the integrated stress response (ISR), a physiological response to cellular stress. In patients' central nervous system, reduced eIF2B activity causes deregulation of the ISR. In VWM mouse models, the extent of ISR deregulation correlates with disease severity. One approach to restoring eIF2B activity is by inhibition of GSK3β, a kinase that phosphorylates eIF2B and reduces its activity. Lithium, an inhibitor of GSK3β, is thus expected to stimulate eIF2B activity and ameliorate VWM symptoms. The effects of lithium were tested in zebrafish and mouse VWM models. Lithium improved motor behavior in homozygous eif2b5 mutant zebrafish. In lithium-treated 2b4he2b5ho mutant mice, a paradoxical increase in some ISR transcripts was found. Furthermore, at the dosage tested, lithium induced significant polydipsia in both healthy controls and 2b4he2b5ho mutant mice and did not increase the expression of other markers of lithium efficacy. In conclusion, lithium is not a drug of choice for further development in VWM based on the limited or lack of efficacy and significant side-effect profile.

Biphasic dose-dependent effect of lithium chloride on survival of human hormone-dependent breast cancer cells (MCF-7)

Lithium, the first element of Group I in the periodic system, is used to treat bipolar psychiatric disorders. Lithium chloride (LiCl) is a selective inhibitor of glycogen synthase kinase-3β (GSK-3β), a serine/threonine kinase that regulates many cellular processes, in addition to its role in the regulation of glycogen synthase. GSK-3β is emerged as a promising drug target for various neurological diseases, type-2 diabetes, cancer, and inflammation. Several works have demonstrated that lithium can either inhibit or stimulate growth of normal and cancer cells. Hence, the present study is focused to analyze the underlying mechanisms that dictate the biphasic oncogenic properties of LiCl. In the current study, we have investigated the dose-dependent effects of LiCl on human breast cancer cells (MCF-7) by assessing the consequences on cytotoxicity and protein expressions of signaling molecules crucial for the maintenance of cell survival. The results showed breast cancer cells respond in a diverse manner to LiCl, i.e., at lower concentrations (1, 5, and 10 mM), LiCl induces cell survival by inhibiting apoptosis through regulation of GSK-3β, caspase-2, Bax, and cleaved caspase-7 and by activating anti-apoptotic proteins (Akt, β-catenin, Bcl-2, and cyclin D1). In contrast, at high concentrations (50 and 100 mM), it induces apoptosis by reversing these effects. Moreover, LiCl also alters the sodium and potassium levels thereby altering the membrane potential of MCF-7 cells. Thus it is inferred that LiCl exerts a dose-dependent biphasic effect on breast cancer cells (MCF-7) by altering the apoptotic/anti-apoptotic balance.

Lithium potentiates antigen-dependent stimulation of lymphocytes only under suboptimal conditions

Immunization of hamsters with DNP-BSA in either Freund's complete or incomplete adjuvant led to the induction of antigen reactive lymph node cells. As assessed by in vitro lymphocyte stimulation assays, antigen in complete adjuvant was more effective than antigen in incomplete adjuvant in inducing immunity. Supplementing antigen-stimulated cultures from animals 14 days post-immunization with LiCl led to no enhancement of tritiated thymidine incorporation into cells from animals immunized with antigen in complete adjuvant, but did enhance antigen-dependent stimulation of cells from animals immunized with antigen + incomplete adjuvant. LiCl was, however, able to enhance stimulation of cells from animals immunized with antigen + complete adjuvant at 22 and 29 days post-immunization, when in vitro responsiveness was declining. Lymph node cells from animals optimally immunized antigen + complete adjuvant were fractionated by passage over Sephadex G-10 columns. Sephadex G-10 non-adherent cells, deficient in cells such as macrophages, exhibited a depressed responsiveness to antigen, compared to unfractionated cells, and responsiveness was not restored by LiCl. Stimulation of cells by antigen was found to be inhibited by supplementing the cultures with theophylline or dibutyryl cyclic AMP and this inhibition could be reversed by LiCl. Lithium would, therefore, appear to be able to influence lymphocyte adenylate cyclase. Thus, LiCl can exert an immunopharmacologic effect on in vitro antigen stimulation primarily when conditions are suboptimal, possibly through an influence on cyclic AMP metabolism.

The requirements for ionized calcium and magnesium in lymphocyte proliferation

The extracellular ionized calcium and magnesium requirements for lectin-induced lymphocyte DNA synthesis were measured in a serum-free system. The use of this system permitted measurements of the ionized calcium and magnesium concentrations with ion-selective electrodes. Maximal DNA synthesis was observed at 270 microM ionized calcium and at 100 microM ionized magnesium in phytohemagglutinin-treated lymphocytes. Lymphocyte DNA synthesis was much more sensitive to reduction of external ionized calcium than to reduction of ionized magnesium. In calcium-free medium (ionized calcium 25 microM), DNA synthesis was reduced by 90%, but in magnesium-free medium (ionized magnesium concentration 7 microM) DNA synthesis was reduced by only 30%. Fifty percent of DNA synthesis stimulated by phytohemagglutinin (PHA) and concanavalin A (Con A) was observed at external ionized calcium concentrations of 97 and 43 microM, respectively. When lymphocytes were stimulated with PHA and the external calcium was chelated with EGTA, 50% inhibition of DNA synthesis was observed at 98 microM ionized calcium. This value agreed well with the free calcium required for PHA activation of DNA synthesis (97 microM). Cytoplasmic calcium, measured with the fluorescent probe Quin 2, increased following lectin exposure if the extracellular ionized calcium concentration was greater than 80 microM. No increase in cytoplasmic calcium could be detected in lectin-treated lymphocytes below 80 microM extracellular ionized calcium, although substantial DNA synthesis was sustained.

Stimulatory and cytotoxic effects of beryllium on proliferation of mouse spleen lymphocytes in vitro

Low concentrations (1-5 microM) of beryllium (Be) salts were weakly mitogenic to mouse spleen cells in vitro as measured by an hydroxyurea-sensitive 2-3fold increase in pulse labelled [3H]-thymidine incorporation into lymphocyte DNA. It is proposed the activation may be induced by a direct interaction of Be2+ with the lymphocyte membranes. Higher concentrations of Be2+ (5-20 microM) produced a gradual loss of the stimulatory response, possibly as the result of either a limited cytotoxic effect or by the established property of intracellularly-accumulated Be2+ to inhibit cell division. In contrast, Concanavalin A-stimulated lymphocyte mitogenesis was markedly decreased by a 20-h preincubation of splenocytes with micromolar concentrations of Be2+, whereas similar pretreatment with lower concentrations (0.1 microM) actually enchanced the subsequent proliferative response. In both cases, supplementary addition of 0.1-1% peritoneal macrophages increased the level of Concanavalin A stimulation. It is concluded, therefore, that inhibition of the proliferative response to accessory cell-dependent mitogens may result from dose-dependent destruction by Be2+ of the macrophage/adherent cell population.