Blood cells as biological trait markers in affective disorders

Is platelet imipramine binding reduced in depression? A meta-analysis

Although it has been suggested that decreased platelet imipramine binding may be a putative biological marker of depressive illness, a number of studies have not confirmed this finding, including a recent multicenter investigation by the World Health Organization (Mellerup and Langer 1990). We performed a meta-analysis of published reports on imipramine binding in groups of depressed and healthy control subjects and found that there was a highly significant decrease in Bmax (maximal binding) values in the depressed subject groups, which was even greater among those who had been free of medication for 4 weeks at the time of investigation. This finding remained highly significant even when only high affinity binding studies (Kd < 1 nmol/L) were considered, although the absolute size of this decrease was smaller.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Platelet imipramine binding in endogenous depressed patients and controls: relationship to platelet MAO and 5HT uptake during successful imipramine treatment

Platelet imipramine binding was measured in 25 unmedicated depressed patients and 25 age- and sex-matched healthy controls. In the patients, the measurement was repeated after 3 weeks and 2 months of imipramine treatment leading to clinical recovery. No significant differences in imipramine binding were found between controls and unmedicated patients. In the latter, imipramine administration produced a progressive change in the binding characteristics, increasing the apparent Kd and decreasing the number of binding sites (Bmax). The results suggest that platelet imipramine binding is not altered in depression and that changes in this parameter are the consequence of the presence of imipramine in the blood stream. However, such changes accompany changes in other biological parameters, such as platelet monoamine oxidase and serotonin uptake, seen in the same patients throughout imipramine treatment, suggesting that the drug acts on a wide range of normal or altered serotonin-related cellular mechanisms while it accelerates the clinical recovery from depression.

Tricyclic antidepressant binding to lymphocyte membranes and changes during depression

The binding of [3H]imipramine, its 2- and 4-nitroderivatives and [3H]desmethylimipramine to lymphocyte membranes was determined. IC50 values for drugs and neurotransmitters to inhibit [3H]imipramine binding to lymphocyte membranes were comparable with those for brain and thrombocyte membranes. The number of [3H]imipramine and [3H]desmethylimipramine binding sites increased in depressive patients, whereas the dissociation constants remained unchanged.

Biochemical aspects of therapy-resistant depression

Despite the relatively high incidence of therapy-resistant depression, there is little clinical evidence to suggest that there are significant biochemical differences between therapy-resistant and therapy-responsive patients. A major problem for investigators is the lack of an internationally recognised definition of resistant depression. Also, it is possible that depressed patients with delusional symptoms or rapidly cycling affective disorders from subgroups that are more likely to be resistant to tricyclic antidepressant treatment and are therefore classified as therapy-resistant. Evidence is presented to show that an abnormality in serotonergic function may characterise some therapy-resistant depressed patients.

Platelet research in psychiatry

The platelet is one of the most researched biological markers in psychiatry. Characteristics of MAO activity, 5-HT uptake, imipramine and alpha 2-adrenergic receptor binding, for example, are similar in platelet and CNS. Methodological factors are not negligible, and range from diagnostic specificity and drug effects to the normal physiological variability of age and hormone-related changes, circadian and seasonal rhythms. As yet, there are no clear state or trait platelet markers in affective disorders and schizophrenia that can be unequivocally used to detect vulnerability to the illness, predict therapeutic response, define clinical diagnostic entities or follow the course of the illness. However, platelet markers are increasingly being used in careful studies to monitor psychopharmacological effects (an in vivo assay of all active metabolites), different ligands can be specific markers for certain aspects of a psychiatric illness (e.g. alpha 2-adrenergic receptors and weight loss), and this homogeneous preparation of human cells is an increasingly important tool in studying mechanisms in pathophysiology. More longitudinal studies are required to establish functional relationships between platelet variables and psychopathology.

Monoamine transport in depression: kinetics and dynamics

There appears to be an abnormality in monoamine transport in major depressive disorders that may be specific to these disorders, although it may not be primarily an aminergic lesion. Kinetic factors alone are insufficient to explain the observed effects of antidepressants on transport mechanisms, or changes in uptake with therapeutic response, suggesting dynamic influences on uptake processes that deserve further exploration. The investigation of these influences may indicate that platelet 5-HT uptake offers diagnostic and theoretical possibilities not adverted to at present and another rationale for the use of platelets in research on mental disorders.