Transport pathways for lithium ions in neuroblastoma x glioma hybrid cells at 'therapeutic' concentrations of Li+

Lithium: A Promising Anticancer Agent

Lithium is a therapeutic cation used to treat bipolar disorders but also has some important features as an anti-cancer agent. In this review, we provide a general overview of lithium, from its transport into cells, to its innovative administration forms, and based on genomic, transcriptomic, and proteomic data. Lithium formulations such as lithium acetoacetate (LiAcAc), lithium chloride (LiCl), lithium citrate (Li₃C₆H₅O₇), and lithium carbonate (Li₂CO₃) induce apoptosis, autophagy, and inhibition of tumor growth and also participate in the regulation of tumor proliferation, tumor invasion, and metastasis and cell cycle arrest. Moreover, lithium is synergistic with standard cancer therapies, enhancing their anti-tumor effects. In addition, lithium has a neuroprotective role in cancer patients, by improving their quality of life. Interestingly, nano-sized lithium enhances its anti-tumor activities and protects vital organs from the damage caused by lipid peroxidation during tumor development. However, these potential therapeutic activities of lithium depend on various factors, such as the nature and aggressiveness of the tumor, the type of lithium salt, and its form of administration and dosage. Since lithium has been used to treat bipolar disorder, the current study provides an overview of its role in medicine and how this has changed. This review also highlights the importance of this repurposed drug, which appears to have therapeutic cancer potential, and underlines its molecular mechanisms.

A Metabolic Inhibitory Cocktail for Grave Cancers: Metformin, Pioglitazone and Lithium Combination in Treatment of Pancreatic Cancer and Glioblastoma Multiforme

Pancreatic cancer (PC) and glioblastoma multiforme (GBM) are among the human cancers with worst prognosis which require an urgent need for efficient therapies. Here, we propose to apply to treat both malignancies with a triple combination of drugs, which are already in use for different indications. Recent studies demonstrated a considerable link between risk of PC and diabetes. In experimental models, anti-diabetogenic agents suppress growth of PC, including metformin (M), pioglitazone (P) and lithium (L). L is used in psychiatric practice, yet also bears anti-diabetic potential and selectively inhibits glycogen synthase kinase-3 beta (GSK-3β). M, a biguanide class anti-diabetic agent shows anticancer activity via activating AMP-activated protein kinase (AMPK). Glitazones bind to PPAR-γ and inhibit NF-κB, triggering cell proliferation, apoptosis resistance and synthesis of inflammatory cytokines in cancer cells. Inhibition of inflammatory cytokines could simultaneously decrease tumor growth and alleviate cancer cachexia, having a major role in PC mortality. Furthermore, mutual synergistic interactions exist between PPAR-γ and GSK-3β, between AMPK and GSK-3β and between AMPK and PPAR-γ. In GBM, M blocks angiogenesis and migration in experimental models. Very noteworthy, among GBM patients with type 2 diabetes, usage of M significantly correlates with better survival while reverse is true for sulfonylureas. In experimental models, P synergies with ligands of RAR, RXR and statins in reducing growth of GBM. Further, usage of P was found to be lesser in anaplastic astrocytoma and GBM patients, indicating a protective effect of P against high-grade gliomas. L is accumulated in GBM cells faster and higher than in neuroblastoma cells, and its levels further increase with chronic exposure. Recent studies revealed anti-invasive potential of L in GBM cell lines. Here, we propose that a triple-agent regime including drugs already in clinical usage may provide a metabolic adjuvant therapy for PC and GBM.

Demonstration of the mineralocorticoid hormone receptor and action in human leukemic cell lines

We studied the expression of the mineralocorticoid receptor (MCR), and of the amiloride-sensitive sodium channel (ASSC) regulated by the MCR, in human leukemic cell lines. Cell extracts from TF1 (proerythroblastic), HEL (human erythroblastic leukemia) and U937 (myeloblastic) cell line were positive for the ASSC, as a 82 kDa band in Western blots developed with the aid of a polyclonal antibody raised against the peptide QGLGKGDKREEQGL, corresponding to the region 44-58 of the alpha subunit of the epithelial sodium channel (ENaC) cloned from rat colon, linked to KLH. The polyclonal antibody against the MCR revealed a single band of about 102 kDa in extracts from HEL and TF1 cells. The immunofluorescent labelling of the MCR in all cell lines showed a nucleocytoplasmic localization of the receptor but the ASSC was exclusively membrane-bound and these results were confirmed by confocal microscopy. The expression of the MCR in the HEL cells was evident as a predicted band of 843 bp (234 amino acids) in electrophoresis of the PCR product obtained after total RNA had been reverse transcribed and then amplified using the primers 5'-AGGCTACCACAGTCTCCCTG-3' and 5'-GCAGTGTAAAATCTCCAGTC-3' (sense and antisense, respectively). The ENaC was similarly evident with the aid of the primers 5'-CTGCCmATG GATGATGGT-3' (sense) and 5'-GTTCAGCTCGAAGAAGA-3' (antisense) as a predicted band of 520 bp. In both cases, 100% identity was observed between the sequences of the PCR products compared to those from known human sources. The multiplication of the HEL cells was influenced by antagonists (RU 26752, ZK 91587) targeted for specificity to the MCR and this was selectively reversed by the natural hormone aldosterone. These steroids also provoked chromatin condensation in the HEL population. These permit new and novel possibilities to understand the pathobiology of human leukemia and to delineate sodium-water homeostasis in nonepithelial cells.

The uptake of Li+ into human 1321 N1 astrocytomas using 7Li NMR spectroscopy

The uptake of Li+ ions into human 1321 N1 astrocytomas cultured on the surface of microcarrier beads was followed by 7Li NMR spectroscopy. The intracellular and extracellular 7Li resonances were separated by the use of dysprosium tripolyphosphate as a shift reagent. Excellent spectra were obtained from which the uptake of Li+ was found to be approximately ten times faster than that into human erythrocytes using the same technique and a steady-state intracellular Li+ concentration was observed within 60 min. The low intracellular Li+ concentration attained, relative to the extracellular concentration, indicates the presence of an efflux mechanism in astrocytomas that actively transports Li+ against its concentration gradient. The intracellular volume was estimated by quantitative 23Na NMR spectroscopy and the viability of the cells was confirmed by 31P NMR spectroscopy.

The effects of lithium on a neuronal in vitro circadian pacemaker

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KCl concentrations, yielded an increasing magnitude of phase delays with increasing KCl concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.

Compartmentation of phosphorylated precursors of phospholipid biosynthesis in cultured neuroblastoma cells

The continuous turnover of membrane phospholipids requires a steady supply of biosynthetic precursors. We evaluated the effects of decreasing extracellular Na+ concentration on phospholipid metabolism in cultured neuroblastoma (N1E 115) cells. Incubating cultures with 145 to 0 mM NaCl caused a concentration-dependent inhibition of [32P]phosphate uptake into the water-soluble intracellular pool and incorporation into phospholipid. Phospholipid classes were differentially affected; [32P]phosphate incorporated into phosphati-dylethanolamine (PE) and phosphatidylcholine (PC) was consistently less than into phosphatidylinositol (PI) and phosphatidylserine (PS). This could not be attributed to decreased phospholipid synthesis since under identical conditions, there was no effect on arachidonic acid or ethanolamine incorporation, and choline utilization for PC synthesis was increased. The effect of Na+ was highly specific since reducing phosphate uptake to a similar extent by incubating cultures in a phosphate-deficient medium containing Na+ did not alter the relative distribution of [32P]phosphate in phospholipid. Of several cations tested only Li+ could partially (50%) replace Na+. Incubation in the presence of ouabain or amiloride had no effect on [32P]phosphate incorporation into phospholipid. The differential effects of low Na+ on [32P]phosphate incorporation into PI relative to PC and PE suggests preferential compartmentation of [32P]phosphate into ATP in pools used for phosphatidic acid synthesis and relatively less in ATP pools used for synthesis of phosphocholine and phosphoethanolamine, precursors of PC and PE, respectively. This suggestion of heterogeneous and distinct pools of ATP for phospholipid biosynthesis, and of potential modulation by Na+ ion, has important implications for understanding intracellular regulation of metabolism.

Stimulation of cell membrane sodium transport activity by lithium: possible relationship to therapeutic action

Because lithium is extruded from cells by means of coupled exchange for external sodium (Na+-Li+ countertransport), we hypothesized that clinical treatment with this agent could lead to significant augmentation of net cellular sodium influx. We therefore directly measured sodium influx in vitro using erythrocytes (RBCs) from 27 depressed bipolar patients. When cells were loaded with sufficient lithium to maximally stimulate Na+-Li+ countertransport activity (5.1 mmoles/1 RBCs), there was a significant 44% increase in mean sodium influx. To approximate clinical conditions more closely, we also studied sodium influx in a subset of eight subjects after loading cells with 0, 0.40, 0.66, and 1.55 mmoles lithium/1 RBCs. Over this range of lithium concentrations, sodium influx increased progressively. In separate experiments, we found that RBC sodium content measured in eight subjects did not change significantly during a 4-week course of lithium treatment. Thus, excess cellular sodium during such treatment may be extruded by increased activity of the membrane Na+-K+ pump, which has electrogenic properties and thereby could augment the membrane potential. In the nervous system, such an effect could stabilize cell membranes electrophysiologically, and possibly affect processes, such as behavioral sensitization or kindling, proposed to have a role in the development of recurrent affective disorders.

Mechanism of action of lithium on acetylcholine receptor metabolism in skeletal muscle

Changes in the levels of cations within skeletal muscle are thought to mediate the neural regulation of turnover of extrajunctional acetylcholine receptors (AChRs). We have used lithium as a probe of these cation influences because of its resemblance to calcium and other ions. In the present experiments we studied the mechanism of action of lithium on AChR metabolism in cultured mammalian skeletal muscle. We measured the effects of lithium on AChR turnover (using [125I]alpha-bungarotoxin binding), and evaluated the resemblance of lithium and calcium in producing their effects on AChR metabolism. Our results provide insight into the mechanisms of action of lithium and the cellular processes controlling AChR metabolism in muscle. Lithium reduces the number of AChRs in skeletal muscle in vitro to a degree similar to that which we previously reported in vivo. Lithium appears to enter cells via both sodium and calcium channels. It then produces its effect on levels of AChRs primarily by selectively reducing AChR synthesis and insertion into the surface membrane. Lithium induces this change in AChR metabolism in a manner resembling neural and calcium-mediated effects on AChRs. Phosphoinositide pathways may be involved in the lithium-induced effects. Further analysis of the effects of lithium on AChR turnover should provide new information about the mechanisms underlying the cellular control of receptor metabolism.

Sodium-dependent lithium ion efflux from murine neuroblastoma and rat glioma cells: a minor pathway for efflux of lithium ions

Lithium ion efflux by murine neuroblastoma (clone N1E-115) and rat glioma (clone C6) cells was studied to determine the presence of a phloretin-sensitive sodium-lithium countertransport pathway which has been found in human erythrocytes. Although this pathway could be identified in these cultured cells, unlike that in red blood cells, it was a very minor (less than 20%) component of the overall efflux of lithium ions from these cells of nervous tissue origin.

Effects of lithium on electrical activity and potassium ion distribution in the vertebrate central nervous system

Three different regions of the vertebrate central nervous system maintained in vitro (frog spinal cord, guinea pig olfactory cortex and hippocampus) have been used to investigate how Li+ influences membrane potential, membrane resistance, action potentials, synaptic potentials and the transmembrane K+-distribution of neurons and glial cells. In view of the therapeutic action of Li+ in manic-depressive disease, a special effort was made to determine the threshold concentration for the actions of Li+ on the parameters described above. It was observed that Li+ induced a membrane depolarization of both neurons and glial cells, a decrease of action potential amplitudes, a facilitation of monosynaptic excitatory postsynaptic potentials and a depression of polysynaptic reflexes. The membrane resistance of neurons was not altered. Li+ also induced an elevation of the free extracellular potassium concentration and a decrease of the free intracellular potassium concentration. Furthermore, in the presence of Li+ a slowing of the recovery of the membrane potential of neurons and glial cells, and of the extracellular potassium concentration after repetitive synaptic stimulation was observed. The threshold concentrations for the effects of Li+ were below 5 mmol/l in the frog spinal cord and below 2 mmol/l in the guinea pig olfactory cortex and hippocampus. The basic mechanism underlying the action of Li+ may be an interaction with the transport-function of the Na+/K+ pump.