The adipose tissue metabolism: role of testosterone
Testosterone (T) and dehydroepiandrosterone (DHEA) are fat-reducing hormones, even though they exert this effect by different mechanisms. In particular, T inhibits lipid uptake and lipoprotein-lipase (LDL) activity in adipocytes, and stimulates lipolysis by increasing the number of lipolytic beta-adrenergic receptors. An indirect sign of these effects is the decrease of adipocyte leptin production. Lastly, T inhibits differentiation of adipocyte precursor cells. Concerning DHEA, this hormone does not seen to have any of T effects; however, DHEA stimulates resting metabolic rate (RMR) and lipid oxidation, and enhances glucose disposal, by increasing the expression of GLUT-1 and GLUT-4 on fat cell plasma membrane. The insulin-like effect of DHEA would be associated to a decrease of plasma insulin concentrations and, thus, to an increase of the molar ratio between lipolytic hormones and insulin. Noteworthy, the fat-reducing effect of both T and DHEA seems to be more evident at the level of visceral adipose tissue.
Int J Obes Relat Metab Disord 2000 Jun;24 Suppl 2:S59-63
Dehydroepiandrosterone sulfate and beta-cell function: enhanced glucose-induced insulin secretion and altered gene expression in rodent pancreatic beta-cells.
Administration of dehydroepiandrosterone (DHEA), or its sulfated form (DHEAS), controls hyperglycemia in diabetic rodents without directly altering insulin sensitivity. We show that DHEAS enhanced glucose-stimulated insulin secretion when administered in vivo to rats or in vitro to beta-cell lines, without changing cellular insulin content. Insulin secretion increased from 3 days of steroid exposure in vitro, suggesting that DHEAS did not directly activate the secretory processes. DHEAS selectively increased the beta-cell mRNA expression of acyl CoA synthetase-2 and peroxisomal acyl CoA oxidase in a time-dependent manner. Although DHEAS is a peroxisomal proliferator, it did not alter the mRNA expression of peroxisomal proliferator-activated receptor (PPAR) alpha or beta, or enhance the activity of transfected PPAR alpha, beta, or gamma in vitro. Thus, DHEAS directly affected the beta-cell to enhance glucose-stimulated insulin secretion and increased the mRNA expression of specific beta-cell mitochondrial and peroxisomal lipid metabolic enzymes. This effect of DHEAS on insulin secretion may contribute to the amelioration of hyperglycemia seen in various rodent models of diabetes.
Diabetes 2000 Dec;49(12):2012-20
DHEA and the intracrine formation of androgens and estrogens in peripheral target tissues: its role during aging.
Human and some other primates are unique since their adrenals secrete large amounts of dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S), which are converted into androstenedione (4-dione) and then into potent androgens and estrogens in peripheral tissues, therefore providing autonomous intracrine control to target tissues that can adjust the formation and metabolism of active sex steroids according to local requirements. Knowledge in this area has recently made rapid progress with the elucidation of the structure of most of the tissue-specific cDNAs and genes that encode the steroidogenic enzymes responsible for the transformation of these inactive precursor steroids into androgens and/or estrogens. It is estimated that 30% to 50% of total androgens in men are synthesized in peripheral intracrine tissues from inactive adrenal precursors while, in women, peripheral estrogen formation is even more important, the best estimate being 75% before menopause and 100% after menopause. The marked reduction in the formation of DHEA-S by the adrenals during aging, especially before the age of 50 years, results in a dramatic fall in the formation of active sex steroids in peripheral target tissues, a situation which is thought to be associated with a long series of age-related decreases such as insulin resistance, obesity, osteoporosis, cardiovascular diseases, loss of muscle mass, cancer and other diseases. We have demonstrated for the first time a series of medically important beneficial effects of DHEA administered for 12 months to post-menopausal women. Most interestingly, the bone mineral density significantly increased. This relatively rapid change was associated with an increase in plasma osteocalcin, a marker of bone formation, while a decrease in bone resorption reflected by a decrease in urinary hydroxyproline excretion was observed in parallel. In addition, the estrogenic stimulation of vaginal cytology in the absence of any sign of stimulatory effect on the endometrium is also of potentially major interest for the prevention and management of menopause. Furthermore, the inhibitory effect of DHEA on the growth of human breast cancer xenografts in vivo in nude mice supports the beneficial use of DHEA as hormone replacement therapy in women.
Steroids 1998 May-Jun;63(5-6):322-8
Age-related changes of the hypothalamic-pituitary-adrenal axis: pathophysiological correlates.
The aim of this review was to examine the evidence for age-related changes of the hypothalamic-pituitary-adrenal (HPA) axis in both physiological and pathological aging, on the basis of the many data in the literature, as well as of our personal findings. A statistically significant circadian rhythmicity of serum cortisol was maintained in elderly subjects, even if with a reduced amplitude of the 24 h fluctuations and a trend to an increase of the serum levels in the evening and at night-time, in comparison with young controls. Furthermore, an age-related impairment of HPA sensitivity to steroid feedback was present in elderly people. The occurrence of senile dementia amplified the changes already present in physiological aging. While the cortisol secretion was generally well maintained in aging, the adrenal production of dehydroepiandrosterone and of its sulfate (DHEAS) exhibited an age-related decline. Therefore, the cortisol/DHEAS molar ratio was significantly higher in elderly subjects and even more in demented ones, than in young controls. Due to the opposite effects of cortisol and DHEAS on the brain and particularly on the hippocampal region, the imbalance between glucocorticoids and androgens occurring in physiological and even more in pathological aging, may have adverse effects on the function of this region, whose key role in learning and memory is well known.
Eur J Endocrinol 2001 Apr;144(4):319-29
Effects of age on serum dehydroepiandrosterone sulfate, IGF-I, and IL-6 levels in women.
Data from animal and in vitro studies suggest that the growth-promoting effects of the adrenal androgen dehydroepiandrosterone sulfate (DHEAS) may be mediated by stimulation of insulin-like growth factor-I (IGF-I) and/or inhibition of interleukin 6 (IL-6), a cytokine mediator of bone resorption. This study tests the hypotheses that there are effects of age on serum DHEAS, IGF-I, and IL-6 levels, and that levels of IGF-I and IL-6 are related to DHEAS levels. The study included 102 women: 27 premenopausal and 75 postmenopausal, including 35 postmenopausal women with osteoporosis, as defined by bone mineral density scores by dual X-ray energy absorptiometry. DHEAS levels decreased significantly with age (r = -0.52, P < 0.0001) and IGF-I levels decreased significantly with age (r = -0.49, P < 0.0001). IL-6 levels increased significantly with age (r = 0.36, P = 0.008). IGF-I was positively correlated to DHEAS levels (r = 0.43, P < 0. 0001, n = 102) and IL-6 levels were negatively correlated to DHEAS levels (r = -0.32, P = 0.021, n = 54). Levels of DHEAS and IGF-I were correlated with T scores of the spine and some hip sites. In a multiple variable model to predict DHEAS, age was an important predictor (P < 0.001), but osteoporosis status, IGF-I, and IL-6 were not. The median DHEAS level was lower in the postmenopausal osteoporotic women (67 microg/dl, n = 35) than in the nonosteoporotic postmenopausal women (106.3 microg/dl, n = 40, P = 0. 03), but this was not significant after correction for age. Age accounted for 32% of the variance in DHEAS levels. In summary, DHEAS levels decreased with age and had a positive association with IGF-I levels and a negative association with IL-6 levels. DHEA deficiency may contribute.
Calcif Tissue Int 2000 Jun;66(6):414-8
Leg extensor power and dehydroepiandrosterone sulfate, insulin-like growth factor-I and testosterone in healthy active elderly people.
We examined the association between quadriceps muscle function and serum levels of dehydroepiandrosterone sulphate (DHEAS), insulin-like growth factor I (IGF-I) and testosterone in a group of healthy elderly people. Fifty-three independent, community-dwelling elderly subjects (26 men and 27 women) aged from 66 to 84 years volunteered to participate in the study. Physical activity (PA) was evaluated by a questionnaire. Quadriceps maximal muscle power (Wmax) and optimal shortening velocity (v(opt)) were measured on a friction-loaded non-isokinetic cycle ergometer. The Wmax is expressed in relation to body mass (W(max/kg), W x kg(-1)), and in relation to the mass of the two quadriceps muscles (W(max/Quadr), W x kg(Quadr(-1))). In women, when adjusted for age, anthropometric measurements and PA indices, IGF-I correlated significantly with W(max/kg) (partial correlation: r = 0.59; P = 0.001), W(max/Quadr) (r = 0.58; P = 0.002) and v(opt) (r = 0.53; P = 0.004), whereas DHEAS was correlated significantly with W(max/kg) (r = 0.54; P = 0.003) and W(max/Quadr) (r = 0.58; P = 0.002). No such correlation was found in men. These findings indicate that in healthy elderly women lower values for quadriceps muscle Wmax and v(opt) are related, independently of age, anthropometric measurements and PA indices, to lower circulating levels of DHEAS and IGF-I.
Eur J Appl Physiol 2000 May;82(1-2):83-90
Sexual dimorphism in the influence of advanced aging on adrenal hormone levels: the Rancho Bernardo Study.
In recent years, adrenal function and aging has been the subject of intense interest. This cross-sectional study examines age and gender differences in plasma levels of cortisol, dehydroepiandrosterone (DHEA), DHEA-sulfate (DHEAS), and the molar ratio of cortisol/DHEAS in 50 to 89-yr-old community-dwelling adults. Plasma hormone levels were assayed in samples obtained between 0730 h and 1100 h from 857 men and 735 nonestrogen-using,
postmenopausal women. Hormone levels were stratified by 10-yr age groups and compared by two-factor (gender and age) ANOVA. Overall, age and BMI-adjusted DHEA and DHEAS [collectively DHEA(S)] levels were 40% lower and cortisol levels 10% higher in women than men, resulting in a 1.7-fold higher cortisol/DHEAS molar ratio for women (both, P < 0.001). Cortisol levels increased progressively (20% overall) with age in both men and women (both, P < 0.01). Although DHEA(S) levels declined 60% and the cortisol/DHEAS ratio increased 3-fold across the 40-yr age range for both men and women (all P < 0.001), the pattern of the change differed (all P < 0.01 for interaction). For men, DHEA(S) fell in a curvilinear fashion, with the degree of change decreasing with each decade. In contrast, DHEA(S) levels in women fell 40% from the 50s to 60s, were unvarying from 60-80 years of age, and declined an additional 18% in the 80s. The cortisol/DHEAS ratio increased in a linear fashion for men, but was flat during the 60-80-year age range for women. Despite these differences in the effect of aging, levels of DHEA(S) remained lower and cortisol and the cortisol/DHEAS ratio higher, in women than men throughout the 50-89-year age range. These results were independent of adiposity, smoking, and alcohol consumption. In summary, among older, healthy adults DHEA(S) levels are lower and cortisol levels higher in women than men. The age-related decline in adrenal androgens persists into advanced age for both men and women, but exhibits a sexually dimorphic pattern. In contrast, cortisol levels in men and women show a parallel, linear increase with aging. These findings may have important implications for a host of age-related processes that exhibit gender differences, including brain function, bone metabolism, and cardiovascular disease.
J Clin Endocrinol Metab 2000 Oct;85(10):3561-8
Effects of dehydroepiandrosterone on collagen and collagenase gene expression by skin fibroblasts in culture.
Dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S) are the most abundant steroids in humans whose low levels are related to aging, greater incidence of various cancers, immune dysfunction, atherosclerosis and osteoporosis. It has been shown that collagen and collagenase gene expression decreases in fibroblasts taken from more aged donors. In this paper, to investigate the relationship between DHEA and skin aging, we examined the effects of DHEA on the regulation of collagen, collegians and stromelysin-1 genes in cultured human skin fibroblasts. In collagen assay, DHEA slightly increased collagen production in a dose-related fashion, its maximal effect occurred at 10(-5) M DHEA (P>0.05). In the presence of DHEA, steady-state levels of alpha1 (I) procollagen mRNA increased to 1.6-fold of the non-treated group, while those of fibronectin were not. Interestingly, DHEA differently regulated collagenase and stromelysin-1 gene expression. The steady-state levels of collagenase mRNA decreased in response to DHEA by 40%, whereas those of stromelysin-1 mRNA increased up to 2.4-fold, compared to controls. Similar results were obtained for chloramphenicol acetyltransferase assay (CAT); maximal promoter activation of stromelysin-1 gene occurred at 10(-6) M DHEA, 4.5-fold higher than control. CAT assay revealed that treatment with 10(-5) M DHEA resulted in a strong (approximately 70%) inhibition of the collagenase promoter activity. In our experiments, the effects of DHEA on these gene expressions were higher at pharmacologic concentration (>/=10(-5) M) than those at physiologic concentration (10(-8)-10(-6) M). This study suggests that the level of DHEA may be related to the process of skin aging through the regulation of production and degradation in extracellular matrix.
J Dermatol Sci 2000 Jun;23(2):103-10
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