Effects of Dexamethasone on Primarily Cultured Newly Differentiated Rat Adipocytes from Different Adipose Tissue Regions

Cortisol in tissue and systemic level as a contributing factor to the development of metabolic syndrome in severely obese patients

CONTEXT

Adrenal and extra-adrenal cortisol production may be involved in the development of metabolic syndrome (MetS).

OBJECTIVE

To investigate the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the expression of HSD11B1, nuclear receptor subfamily 3, group C, member 1 (glucocorticoid receptors) α (NR3C1α) and β (NR3C1β) in the liver, subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) of severely obese patients with and without MetS.

METHODS

The study included 37 severely obese patients (BMI ≥ 40 kg/m(2)), 19 with MetS (MetS+ group) and 18 without (MetS- group), studied before and during bariatric surgery. Before the day of surgery, urinary free cortisol (UFC) and diurnal variation of serum and salivary cortisol were estimated. During surgery, biopsies of the liver, VAT and SAT were obtained. The expression of HSD11B1, NR3C1α and NR3C1β was evaluated by RT-PCR.

RESULTS

UFC and area under the curve for 24-h profiles of serum and salivary cortisol were lower in the MetS- group. In the MetS- group, mRNA levels of HSD11B1 in liver exhibited a negative correlation with liver NR3C1α (LNR3C1α) and VAT expression of HSD11B1 was lower than the MetS+ group.

CONCLUSIONS

We observed a downregulation of the NR3C1α expression and lower VAT mRNA levels of HSD11B1 in the MetS- group, indicating a lower selective tissue cortisol production and action that could protect these patients from the metabolic consequences of obesity. In the MetS- group, a lower activity of the HPA axis was also detected. Taken together, cortisol in tissue and systematic level might play a role in the development of MetS in severely obese patients.

Metabolism of Different Adipose Tissues in Vivo in the Rat

To explore regional differences in triglyceride retention in white adipose tissues of growing male rats, the mass of adipocytes from epididymal, retroperitoneal, inguinal, and mesenteric tissues were followed with time. In order to attempt to explain regional differences, adipose tissue metabolism was studied in vivo and in vitro. (U-14C) oleic acid in sesame oil was given by gastric gavage to conscious male and female rats, and accumulation and half-life of radioactivity measured. Lipoprotein lipase activity and lipolysis were studied in vitro. Adipocyte triglyceride mass increased linearly in all the depots during 4 months of observation.The increase in mass was more pronounced in retroperitoneal (0.31 microg) and epididymal (0.30 microg) than in mesenteric (0.11 microg) or inguinal (0.05 microg) adipocytes. In the fed state label from (U-14C) oleic acid first increased with time in liver, muscle, and adipose tissues. In the liver radioactivity peaked at 4 hours, and was not measurable in either liver or muscle after a time point between 24 hours to 1 week. In contrast label continued to increase in adipose tissues up to about 16 hours to 24 hours, suggesting transfer of label by recirculation from liver and muscle to adipose tissues. Thereafter the radioactivity decreased. When expressed per adipocyte uptake of label was not significantly different between white adipose tissues. The rate of decrease between 7 days and 4 months was, however, more rapid in mesenteric and inguinal than, particularly, epididymal, and, probably, retroperitoneal adipocytes. These results were partly parallel to in vitro data on lipoprotein lipase activity, which was not different between depots, and the rate of lipolysis, which was higher in mesenteric than other adipocytes. These results suggest that differences in weight increase of adipose tissue regions are due mainly to differences in the rate of mobilization of adipocyte triglycerides. When expressed per gram triglyceride, uptake and mobilization of label were clearly more rapid in mesenteric than other white adipose tissues. This is probably explained by a combination of a higher adipocyte density plus the metabolic characteristics of adipocytes in this depot. Since mesenteric adipose tissue is smaller than the other depots studied, the absolute contribution of this tissue to the energy supply of the body is probably not different from that of other adipose tissues, however. A large uptake and short half life was observed in interscapular adipose tissue. This region contains brown adipocytes, and the results therefore suggest that lipid uptake for thermogenic purposes is of a considerable magnitude. It was concluded that among white adipose tissues, the mesenteric tissue has a rapid turnover of triglyceride. This is probably due to a combination of a high density and specific metabolic characteristics of these adipocytes. Factors in the microenvironment of adipocytes probably contribute to the high turnover either directly, or by modification of cellular characteristics.

A novel selective 11beta-hydroxysteroid dehydrogenase type 1 inhibitor prevents human adipogenesis

Glucocorticoid excess increases fat mass, preferentially within omental depots; yet circulating cortisol concentrations are normal in most patients with metabolic syndrome (MS). At a pre-receptor level, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activates cortisol from cortisone locally within adipose tissue, and inhibition of 11beta-HSD1 in liver and adipose tissue has been proposed as a novel therapy to treat MS by reducing hepatic glucose output and adiposity. Using a transformed human subcutaneous preadipocyte cell line (Chub-S7) and human primary preadipocytes, we have defined the role of glucocorticoids and 11beta-HSD1 in regulating adipose tissue differentiation. Human cells were differentiated with 1.0 microM cortisol (F), or cortisone (E) with or without 100 nM of a highly selective 11beta-HSD1 inhibitor PF-877423. 11beta-HSD1 mRNA expression increased across adipocyte differentiation (P<0.001, n=4), which was paralleled by an increase in 11beta-HSD1 oxo-reductase activity (from nil on day 0 to 5.9+/-1.9 pmol/mg per h on day 16, P<0.01, n=7). Cortisone enhanced adipocyte differentiation; fatty acid-binding protein 4 expression increased 312-fold (P<0.001) and glycerol-3-phosphate dehydrogenase 47-fold (P<0.001) versus controls. This was abolished by co-incubation with PF-877423. In addition, cellular lipid content decreased significantly. These findings were confirmed in the primary cultures of human subcutaneous preadipocytes. The increase in 11beta-HSD1 mRNA expression and activity is essential for the induction of human adipogenesis. Blocking adipogenesis with a novel and specific 11beta-HSD1 inhibitor may represent a novel approach to treat obesity in patients with MS.

Visceral obesity: a "civilization syndrome"

The controversial question of the relationship between obesity and disease has been considerably clearer after the demonstration in several prospective, epidemiological studies that the subgroup of central, visceral obesity is particularly prone to develop cardiovascular disease, stroke, and non-insulin dependent diabetes mellitus. Visceral obesity is associated with multiple central endocrine aberrations. The hypothalamo-adrenal axis is apparently sensitive to stimuli, sex steroid hormone secretion blunted, and hyperandrogenicity is found in women. In addition, there seem to be signs of central dysfunctions in the regulation of hemodynamic factors after stress, and growth hormone secretion appears to be particularly blunted. Several of these endocrine abnormalities are associated with insulin resistance, particularly glycogen synthesis in muscle. Fiber composition with low type I/type II ratio might be secondary to the prevailing hyperinsulinemia, but low capillary density in muscle may well be of importance. In combination with elevated turn-over of free fatty acids (FFA) this will probably provide powerful mechanisms whereby insulin resistance is created. Portal FFA, from the highly lipolytic visceral depots may, in addition, affect hepatic metabolism to induce increased gluconeogenesis, production of very low density lipoproteins as well as to perhaps inhibit clearance of insulin. By these mechanisms a Metabolic Syndrome Visceral adipocytes seem to have a high density of several steroid hormone receptors, directing steroid hormone effects particularly to these depots. The net effect of cortisol is apparently a stimulation of lipid storage, with opposing effects of sex steroid hormones which also facilitate lipid mobilization, regulations most often found at the gene transcription level. Growth hormone inhibits cortisol effects on lipid accumulation, and amplifies the lipid mobilizing effects of steroid hormones. The combined perturbations of hormonal secretions will therefore probably direct triglycerides toward visceral depots. Circulatory and nervous regulatory mechanisms require, however, more attention. The multiple central endocrine and nervous aberrations of visceral obesity suggest neuroendocrine dysregulations, and have features characteristic of the hypothalamic arousal seen after certain types of stress, alcohol intake, and smoking. Such factors can be traced to subjects with visceral fat accumulation. Standardized stress, eliciting a "defeat reaction" in primates is followed by an apparently identical syndrome. This integrated picture of the multiple symptoms of visceral obesity is based on epidemiological, clinical, experimental, cellular, and molecular evidence. The ingredients of positive energy balance, including physical inactivity, stress, smoking, and alcohol consumption are frequent features of modern, urbanized society. Visceral obesity may therefore be an expression of a "Civilization Syndrome."

Body fat distribution, insulin resistance, and metabolic diseases

Obesity has now developed into a world-wide epidemic and is associated with large economic costs and prevalent diseases, particularly with central body fat distribution. Insulin resistance almost invariably occurs, and might be a major trigger for disease-generating mechanisms either directly or via generation of other disease precursors ("risk factors"). The hypothalamo-pituitary-adrenal (HPA) axis seems to be hypersensitive in abdominal obesity, a statement supported by increased responses to challenges from the adrenals to central regulatory centers. Furthermore, the feedback control by central glucocorticoid receptors, probably a secondary, functional consequence of an elevated HPA axis activity, because the receptor gene appears normal. Secretion of sex steroid and growth hormones is diminished, which might be consequence of elevated HPA axis activity. Hyperandrogenicity in women is probably of adrenal origin and another consequence of the sensitivity of the HPA axis. The endocrine abnormalities thus are periodically elevated cortisol and androgen (women) concentrations, as well as low secretions of gender-specific steroid and growth hormones. Since elevated cortisol, and low sex-steroid and growth hormone secretions, probably direct storage fat to visceral depots, the multiple endocrine abnormalities probably cause enlargement of these depots. Furthermore, these hormonal abnormalities most likely at least contribute to the creation of insulin resistance with additional effects of elevated fatty acids from central fat depots, which are sensitive to lipid mobilization agents. This chain of events indicates the central role of the hypersensitive HPA axis. Known causes of sensitization of this axis have been identified in subjects with abdominal obesity, including depression, anxiety, alcohol, and smoking. A common cause of HPA axis activation is perceived stress, with a depressive, defeatist, or "helplessness" reaction. In subjects with abdominal preponderance of body fat stores a number of psychosocial and socioeconomics handicaps have been identified, hypothetically predisposing to such reactions. In a primate model (monkeys), mild psychosocial stress is followed by identical psychological, endocrine, anthropometric, and metabolic abnormalities as in humans with abdominal preponderance of body fat stores, including early signs of diabetes and cardiovascular disease. These findings strongly support the interpretation that a stress reaction activating the HPA axis is involved also in the human syndrome. Interventions with normalization of the endocrine perturbations are followed by clear improvements of the multiple abnormalities in both clinical, experimental, cellular and molecular studies, suggesting that the pathogenesis of abdominal preponderance of body fat and its endocrine, anthropometric and metabolic abnormalities are indeed consequences of the endocrine abnormalities identified.

Growth hormone treatment of hypophysectomized rats increases catecholamine-induced lipolysis and the number of beta-adrenergic receptors in adipocytes: no differences in the effects of growth hormone on different fat depots

Growth hormone (GH) has a lipolytic effect in adipose tissue but this effect may differ in adipose tissue from various fat depots. This latter possibility was investigated in the present study, in which the effects of GH in vivo on catecholamine-induced lipolysis and the number of beta-adrenergic receptors in isolated adipocytes from different fat depots of hypophysectomized rats were investigated. Female and male Sprague-Dawley rats were hypophysectomized or sham-operated at 45 days of age. One week after the operation, hormonal replacement therapy with L-thyroxine and hydrocortisone acetate was given. In addition, groups of rats were treated with GH (1.33 mg/kg per day, given as two daily subcutaneous injections). After 1 week of hormonal treatment, adipocytes were isolated from the parametrial, epididymal and inguinal fat pads, and glycerol release after catecholamine-stimulation and 125I-cyanopindolol binding were measured. Hypophysectomy resulted in a marked decrease in the lipolytic response to catecholamines. GH treatment significantly increased catecholamine-induced lipolysis with similar effects in adipocytes from parametrial or epididymal and inguinal fat depots in both female and male rats. There were no differences between norepinephrine compared with isoproterenol-induced responses. 125I-cyanopindolol binding was reduced after hypophysectomy and normalized by GH treatment, without differences between parametrial and inguinal adipose tissue regions. We conclude that the lipolytic effects of GH in the rat may partly be mediated by a stimulatory effect on beta-adrenergic receptors in adipocytes. In addition, GH exerted similar effect on catecholamine induced lipolysis and beta-adrenergic receptors in adipocytes from parametrial, epididymal and inguinal fat depots.

Glucocorticoid hormone binding to rat adipocytes

Previous quantification of glucocorticoid receptor (GR) binding in adipose tissue has been performed in cytosol preparations, which did not allow the determination of the total number of GR in the cell. Therefore, GR binding was determined in intact adipocytes. Dexamethasone (dex) was used as a ligand in adipocytes isolated from epididymal (Epi), retroperitoneal (Ret), inguinal (Ing) and mesenteric (Mes) adipose tissue regions in male rats. The binding was saturable and specific with a Kd in the nanomolar range, not different from previously reported affinity of binding in cytosol preparations from adipocytes. Binding capacity rose after removal of endogenous glucocorticoids either by adrenalectomy (ADX) or culture in a glucocorticoid-free medium. Binding capacity of adipocytes was in general higher in Mes adipose cells than in adipocytes from Epi, Ing and Ret tissues from intact and ADX animals when expressed per unit of triglyceride weight of adipose tissues. This seemed to be largely explainable by a higher cellular density in Mes than in other adipose tissues. When comparisons were performed with binding per adipocyte, intraabdominal (Epi, Ret and Mes) cells bound more dex than adipocytes from subcutaneous (Ing) adipose tissue. It is suggested that in comparison with other adipose tissues Mes tissue has a higher density of the GR in situ, due mainly to a higher cellular density. Intraabdominal adipocytes in general seem to have a higher GR density than subcutaneous cells. This might explain the high activity of glucocorticoid-regulated metabolic pathways in intraabdominal particularly Mes adipose tissue.