The Na,K-ATPase hypothesis for manic-depression. II. The mechanism of action of lithium

Derivation of whole blood biomonitoring equivalents for lithium for the interpretation of biomonitoring data

INTRODUCTION

Lithium salts have numerous industrial uses and are also used in the treatment of bipolar disorders. The main source of lithium exposure to the general population is drinking water and foods. Lithium is nephrotoxic at higher doses. Thus, oral exposure guidelines for lithium have been derived, including ICH's permitted daily exposure (PDE = 0.008 mg lithium/kg-bw/day) adopted by Health Canada and the United States Environmental Protection Agency's (U.S. EPA) provisional peer reviewed toxicity value (PPRTV = 0.002 mg lithium/kg-bw/day), both based on human data.

OBJECTIVE

To derive whole blood biomonitoring equivalents (BEs) associated with PDE and PPRTV to interpret population-level biomonitoring data in health risk context.

METHOD

A simple kinetic relationship based on plasma clearance value (0.5 L/kg-bw/day) and the oral absorption fraction (100%) was used to derive blood BEs for PDE and PPRTV.

RESULTS

This analysis resulted in BE values in plasma and whole blood of 16 and 10 μg/L, respectively, based on the PDE values developed by the Health Canada and of 4.2 and 2.7 μg/L, respectively, based on the PPRTV developed by U.S. EPA.

CONCLUSION

The derived BE values can be used to interpret population-level biomonitoring data.

Lithium and cognitive enhancement: leave it or take it?

RATIONALE

Lithium is established as an effective treatment of acute mania, bipolar and unipolar depression and as prophylaxis against bipolar disorder. Accumulating evidence is also delineating a neuroprotective and neurotrophic role for lithium. However, its primary effects on cognitive functioning remain ambiguous.

OBJECTIVES

The aim of this paper is to review and combine the relevant translational studies, focusing on the putative cognitive enhancement properties of lithium, specifically on learning, memory, and attention.

DISCUSSION

These properties are also discussed in reference to research demonstrating a protective action of lithium against cognitive deficits induced by various challenges to the nervous system, such as stress, trauma, neurodegenerative disorders, and psychiatric disorders.

CONCLUSIONS

It is suggested on the basis of the evidence that the cognitive effects of lithium are best expressed and should, therefore, be sought under conditions of functional or biological challenge to the nervous system.

Dysregulation of ion fluxes in bipolar affective disorder

Bipolar disorder has attracted numerous research from different neurobiological angles. This review will summarize selected findings focusing on the role of disturbed transmem-braneous ion fluxes. Several mood stabilizers exhibit a distinct profile including effects on sodium, calcium and potassium conductance. In summary, some decisive mechanisms of action as calcium antagonism and modulation of potassium currents may play a crucial role in the success of any given mood stabilizer in bipolar disorder.

Combined treatment with lithium and nimodipine in a bipolar I manic syndrome

1. The benefit of a combined treatment with the calcium antagonist nimodipine and lithium in a bipolar I disorder (currently manic, DSM IV 296.44, ICD 10 F 31.1) was explored and documented in a longitudinal single case study. 2. Nimodipine (270 mg/d) was added to lithium (900 mg/d), substituting for previously administered neuroleptics, in an up to then unsatisfactorily treated manic patient. 3. A clear-cut improvement in the patient's condition was achieved within a fortnight, and lasted over the continuation period of this drug regimen. This combined treatment was discontinued after eight weeks and lithium alone was then administered. Within three months another manic episode appeared. 4. Side-effects and changes of lithium blood levels were not observed during the combined treatment with nimodipine and lithium. 5. Further research on the benefits of adding a calcium antagonist, instead of neuroleptics, to lithium therapy for bipolar manic disorder patients who do not respond sufficiently to lithium is recommended. In addition, the benefits of a long term prophylaxis of nimodipine alone or in combination with lithium should be evaluated in those bipolar patients who still show a high relapse frequency on lithium alone.

Effectiveness of the combination verapamil and chlorpromazine in the treatment of severe manic or mixed patients

1. The authors investigated the possible antimanic properties of a Calcium channel blocker, Verapamil, in 15 in-patients admitted consecutively to the female psychiatric ward at Pisa University for a manic episode. 2. The results showed that most of the patients presented a global improvement of the manic symptoms and, in some cases, even a complete clinical remission. 3. Although it was necessary to add chlorpromazine for the severe conditions of several patients, verapamil appeared to speed the positive outcome and to lead to a faster resolution of the symptoms. In addition, the association of verapamil and chlorpromazine did not produce any relevant side-effect. These preliminary findings thus indicate that verapamil by itself does not seem to be sufficient in the treatment of a severe affective episode, but it may constitute an alternative to lithium salts in association with neuroleptics.

The Na,K-ATPase hypothesis for bipolar illness

A cellular model for bipolar illness is presented. It is propounded that alterations in the activity of the membrane sodium- and potassium-activated adenosine triphosphatase pump (Na,K-ATPase) may be responsible for alterations in neuronal excitability and activity. Specifically, a reduction in Na,K-ATPase activity can lead to both mania and depression by increasing membrane excitability and decreasing neurotransmitter release, respectively. Supporting evidence is reviewed, and clinical and research implications are discussed.

Organic mood disorder, manic type, associated with hyponatremia: a case report

OBJECTIVE

Mania and other mood changes are known to be associated with various organic etiologies. This article documents a case of organic mania associated with hyponatremia, a phenomenon which has not been previously reported, and reviews the pertinent medical literature.

METHOD

The mental status of a patient with end stage renal disease and no previous psychiatric history who presented with mania and hyponatremia was carefully monitored while her serum sodium concentration was corrected.

RESULTS

The manic symptoms of the patient presented resolved completely with correction of serum sodium concentration alone.

CONCLUSIONS

The acute episode of hyponatremia experienced by this patient with chronic, end stage renal disease appears to have precipitated the symptoms of mania. This observation may shed some additional light on the pathophysiology of organic mania.

Possible role of endogenous ouabain-like compounds in the pathophysiology of bipolar illness

A large number of studies have documented a mood-state-related decrease in blood cell sodium, potassium-activated adenosine triphosphatase (Na, K-ATPase) activity in acutely ill bipolar patients. While it has been proposed that this enzymatic change may be central to the pathophysiology of bipolar illness, its genesis has remained obscure. Recent advances in the isolation and characterization of endogenously produced ouabain- or digoxin-like compounds suggest a possible mechanism by which these mood-state-related changes can come about. We herein propose that the hypothalamic-pituitary-adrenal dysregulation frequently documented in major mood disorders may underlie a pathological increase in the production of endogenous ouabain-like compounds which excessively suppresses Na, K-ATPase activity and results in pathological mood and energy alteration.

Verapamil and valproic acid treatment of prolonged mania

The case of an adolescent with severe mental retardation, blindness, and a complex of behavioral symptoms consistent with mania is reported. Symptoms include an increased activity level, mood liability, irritability, hyposomia, and severe self-injurious behavior. The successful use of verapamil and valproic acid in the treatment of prolonged mania in this child is described.

Complications of concurrent lithium and electroconvulsive therapy: a review of clinical material and theoretical considerations

Several anecdotal reports and two retrospective chart reviews have examined complications of concurrent lithium and electroconvulsive treatment. Discussions have generally been contradictory or confusing. This article reviews the literature and particularly emphasizes theoretical considerations and mechanisms, concluding (A) that lithium may act synergistically with neuromuscular blockers, but the effect is not clinically significant, and (B) that repeated electroconvulsive seizures may cause a toxic delirium in patients concurrently taking lithium.

The use of sodium and potassium to reduce toxicity and toxic side effects from lithium

Studies in rats find that the animals develop toxic side effects at serum levels which are therapeutic for man. Most of the toxic effects were prevented by feeding sodium and potassium. The rats must ingest and excrete comparatively higher amounts of lithium than humans to maintain these levels. Sodium used alone has been shown to reduce side effects in man, but was found to reduce therapeutic effectiveness at fixed lithium dosages. Evidence is presented to suggest that therapeutic effectiveness can be maintained and toxic side effects and risk of toxicity reduced, by using both sodium and potassium, and by modestly raising the dosage of lithium.

Hypertension and diabetes in obesity: a review and new ideas on the contributing role of ions

Ion metabolism in obesity-associated hypertension is reviewed. A hypothesis is presented which proposes that ion imbalances in obesity may play an etiological role in obesity-associated diabetes mellitus as well. It is suggested that the rise in intracellular calcium--secondary to reduced sodium, potassium-activated adenosine triphosphatase (Na,K-ATPase) activity--may aid in the development of increased vascular tone and decreased glucose tolerance.