The Neurobiology Of Major Depression

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In the past year, we have further elucidate pathophysiological mechanisms in the premature coronary artery disease and osteoporosis of patients with major depression, most of whom were medication free and in remission from depression. These included specific interrelated abnormalities in (a) inflammation, including diffuse changes in the acute phase response; (b) blood clotting and clot lysis; (c) insulin sensitivity, body composition, and in the levels of plasma lipids and glucose; (d) inflammatory-related pathologic losses in bone mineral density; and (e) in the sustained hypersecretion of overnight plasma NE. We also found glucocorticoid receptor gene polymorphisms in patients with major depression associated with visceral obesity, relationships between increased stress-reactivity, and clustering of haplotypes of the CRH gene in rhesus macaques, and in the role of plasma cortisol levels on abnormalties of the 5HT2a serotonin receptor in patients with major depression. In normal weight,medication free, and remitted patients with major depression studied on at least two occasions, we found a consistent increase in positive acute phase markers of inflammation and a decrease in negative acute phase markers. These included increases in plasma levels of C-reactive protein, serum amaloid A, complement C3, and C4, increases in the clotting factor fibrinogen, and increases in plasminogen activator inhibitor-1 (PAI-1), a compound that profoundly interrupts the breakdown of clots already formed. The negative acute phase markers transferrin, albumin, and apo AII were significantly reduced. Patients with major depression also had significant increases in clotting factor fVIII, the factor altered in hemophilia, and in the levels of thrombin-antithrombin complexes, a real-time measure of ongoing clotting. All of these abnormalities could potentially occur as a consequence of the pathological alterations in the CRH system. We also found that remitted patients with major depression had consistent metabolic alterations consisting of decreased insulin sensitivity, increased levels of plasma insulin and glucose, and increased levels of LDL cholesterol and triglycerides. In addition, compared to carefully age, weight and height matched controls, patients with major depression had significantly more adipose tissue and a significant decrease in overall lean body mass. Thus, medication-free remitted patients with major depression are in proinflammatory and prothrombotic states, as well as showing stigmata of the insulin resistance syndrome. Taken together, these findings indicate that despite having normal weight, patients with major depression have a CRH-related, CNS-driven metabolic syndrome. Since not all overweight non-depressed subjects have the metabolic syndrome, we postulate that qualitatively similar but more subtle CNS abnormalities may be required for the full expression of the metabolic syndrome. We have relicated our New England Journal findings showing that a large group of premenopausal women with major depression have either premature osteoporosis and/or osteopenia compared to premenopausal controls carefully matched for BMI and age. Compared to controls, patients with major depression, in association with their bone loss, had a significant increase in the plasma levels of proinflammatory mediators, and a significant decrease in the levels of anti-inflammatory mediators, suggesting that inflammation plays a key role in the bone loss of major depression. The pattern of bone loss in these patients was similar to the unusual one which we described previously, manifested in bone loss greater at the hip than the spine. Studies in experimental animals indicate that this pattern is especially present in animal models of chronic inflammation. Given the role of CRH in the overall inflammatory response, and the presence of a coexistence of pro-inflammatory and metabolic stigmata in patients with major depression, we hypothesize that further study will show that pathologic bone loss is also a component of the metabolic syndrome. The glucocorticoid receptor is closely linked to the CRH system. We showed activation of the glucocorticoid receptor significantly stimulates the amygdala CRH system that plays a key role in conditioned fear responses and their resistance to extinction. It is also known that glucocorticoid receptor gene polymorphisms are associated with glucocorticoid hypersensitivity and visceral obesity, changes leading to both the premature onset of the insulin resistance syndrome and osteoporosis. On this basis, we tested the hypothesis that the glucocorticoid receptor in patients with major depression may be associated with polymorphisms that enhance glucorticoid receptor responsiveness (eg. Bcl1, N363S, rs33388, rs33389). We found that in premenopausal women with major depression, the G/G genotype of the Bc11 polymorphism was significantly more common than in healthy controls. In addition, G/G homozygotes had higher waist/hip ratios than did non G/G carriers. The waist/hip ratio is a sensitive marker for visceral obesity and its metabolic and proinflammatory stigmata. CRH also plays a significant role in the predisposition to alcoholism, a condition frequently associated with major depression. To further explore the potential role of the CRH system in parameters important to the predisposition to alcoholism (and some forms of major depression), we explored the role of CRH gene variation in stress-reactivity in rhesus macaques. We sequenced the rhesus macaque CRH locus (rhCRH) and performed cladistic clustering of haplotypes. Animals were genotyped for a single-nucleotide polymorphism disrupting a glucocorticoid response element, rhCRH -2232 C>G, and the effects of this allele on CSF levels of CRH, plasma levels of ACTH, and behavior were assessed. We showed that -2232C>G alters DNA x protein interactions and confers abnormal sensitivity of the CRH promoter to glucocorticoids in vitro. Consistent with the known effects of glucocorticoids on CRH expression in the brain, carriers of the G allele had higher levels of ACTH. Infants carrying the G allele were more exploratory and bold, and among adolescent and adult male macaques, the G allele was associated with exploratory/bold responding to an unfamiliar male. Adults with the C/G genotype also exhibited increased alcohol consumption in the social group, a model for high-risk alcohol-seeking behavior. In summary, we have systematically studied the role of the stress system (with emphasis on CRH)in behavioral, physiological, and genomic paramaters of relevance to major depression and related disorders. We have found systematic metabolic, pro-inflammatory, and hemostatic change that are characteristic of the metabolic syndrome. Because in the general population,the presence of obesity is linked to the metabolic syndrome, this entity has been named as a global crisis by the WHO on the basis of the global epidemic in obesity. However, our patients have the metabolic syndrome even though they are of normal weight, on the basis of a primary CNS defect. Since not all obese patients have the metabolic syndrome, a subtle CNS defect may thus also be obligatory for the metabolic syndrome in obese patients. We are poised to intervene with antalarmin, our CRH antagonist, a compound that could change the landscape of treating the affective and systemic maniferstations of major depression. Given the specific systematic stigmata of major depression, we postulate that patients with this illness be followed carefully, including periodic bone scans, and treated with prophylactic statins or insulin sensitizers. Given the fact that approximately 25 million Americans have affective illness,these matters are of urgent public health significance