Jonas Burén

The human visceral fat depot has a unique inflammatory profile.

Obesity can be considered as a low‐grade inflammatory condition, strongly linked to adverse metabolic outcomes. Obesity‐associated adipose tissue inflammation is characterized by infiltration of macrophages and increased cytokine and chemokine production. The distribution of adipose tissue impacts the outcomes of obesity, with the accumulation of fat in visceral adipose tissue (VAT) and deep subcutaneous adipose tissue (SAT), but not superficial SAT, being linked to insulin resistance. We hypothesized that the inflammatory gene expression in deep SAT and VAT is higher than in superficial SAT. A total of 17 apparently healthy women (BMI: 29.3±5.5 kg/m2) were included in the study. Body fat (dual‐energy X‐ray absorptiometry) and distribution (computed tomography) were measured, and insulin sensitivity, blood lipids, and blood pressure were determined. Inflammation‐related differences in gene expression (real‐time PCR) from VAT, superficial and deep SAT biopsies were analyzed using univariate and multivariate data analyses. Using multivariate discrimination analysis, VAT appeared as a distinct depot in adipose tissue inflammation, while the SAT depots had a similar pattern, with respect to gene expression. A significantly elevated (P < 0.01) expression of the CC chemokine receptor 2 (CCR2) and macrophage migration inhibitory factor (MIF) in VAT contributed strongly to the discrimination. In conclusion, the human adipose tissue depots have unique inflammatory patterns, with CCR2 and MIF distinguishing between VAT and the SAT depots.

Insulin action and signalling in fat and muscle from dexamethasone-treated rats.

Glucocorticoids initiate whole body insulin resistance and the aim of the present study was to investigate effects of dexamethasone on protein expression and insulin signalling in muscle and fat tissue. Rats were injected with dexamethasone (1mg/kg/day, i.p.) or placebo for 11 days before insulin sensitivity was evaluated in vitro in soleus and epitrochlearis muscles and in isolated epididymal adipocytes. Dexamethasone treatment reduced insulin-stimulated glucose uptake and glycogen synthesis by 30-70% in epitrochlearis and soleus, and insulin-stimulated glucose uptake by approximately 40% in adipocytes. 8-bromo-cAMP-stimulated lipolysis was approximately 2-fold higher in adipocytes from dexamethasone-treated rats and insulin was less effective to inhibit cAMP-stimulated lipolysis. A main finding was that dexamethasone decreased expression of PKB and insulin-stimulated Ser(473) and Thr(308) phosphorylation in both muscles and adipocytes. Expression of GSK-3 was not influenced by dexamethasone treatment in muscles or adipocytes and insulin-stimulated GSK-3beta Ser(9) phosphorylation was reduced in muscles only. A novel finding was that glycogen synthase (GS) Ser(7) phosphorylation was higher in both muscles from dexamethasone-treated rats. GS expression decreased (by 50%) in adipocytes only. Basal and insulin-stimulated GS Ser(641) and GS Ser(645,649,653,657) phosphorylation was elevated in epitrochlearis and soleus muscles and GS fractional activity was reduced correspondingly. In conclusion, dexamethasone treatment (1) decreases PKB expression and insulin-stimulated phosphorylation in both muscles and adipocytes, and (2) increases GS phosphorylation (reduces GS fractional activity) in muscles and decreases GS expression in adipocytes. We suggest PKB and GS as major targets for dexamethasone-induced insulin resistance.

Postprandial regulation of blood lipids and adipose tissue lipoprotein lipase in type 2 diabetes patients and healthy control subjects

BACKGROUND/AIM In type 2 diabetes and other insulin-resistant conditions, postprandial hypertriglyceridaemia is an important metabolic perturbation. To further elucidate alterations in the clearance of triglyceride-rich lipoproteins in type 2 diabetes we focused on the nutritional regulation of adipose tissue lipoprotein lipase (LPL). SUBJECTS AND METHODS Eight subjects with type 2 diabetes and eight age-, sex- and body mass index (BMI)-matched control subjects underwent subcutaneous abdominal adipose tissue biopsies in the fasting state and 3.5 h following a standardized lipid-enriched meal. LPL activity and mass were measured in adipose tissue and also in plasma after an intravenous injection of heparin. RESULTS Postprandial, but not fasting, triglycerides were significantly higher in the diabetic subjects than in the control subjects (3.0+/-0.4 vs 2.0+/-0.2 mmol/l, P=0.028). Adipose tissue LPL activity was increased following the meal test by approximately 35-55% (P=0.021 and 0.004, respectively). There was no significant difference between the groups in this respect. The specific enzyme activity of LPL was not altered in the postprandial state. Fasting and postprandial adipose tissue LPL activity as well as post-heparin plasma LPL activity tended to be lower among the diabetes patients (NS). There was a significant and independent inverse association between insulin resistance (homeostasis model assessment insulin resistance (HOMA-IR) index) vs post-heparin plasma LPL activity and postprandial triglyceride levels, respectively. Adipose tissue LPL activity was related to insulin action in vitro on adipocyte glucose transport, but not to HOMA-IR. CONCLUSION Following food intake adipose tissue LPL activity is enhanced to a similar degree in patients with type 2 diabetes and in healthy control subjects matched for BMI, age and gender. If LPL dysregulation is involved in the postprandial hypertriglyceridaemia found in type 2 diabetes, it should occur in tissues other than subcutaneous fat.

Insulin resistance, endocrine function and adipokines in type 2 diabetes patients at different glycaemic levels: potential impact for glucotoxicity in vivo

Objective  To evaluate the interplay between hyperglycaemia, insulin resistance, hormones and adipokines in patients with type 2 diabetes mellitus (T2DM).

No difference in markers of adipose tissue inflammation between overweight women with polycystic ovary syndrome and weight-matched controls

BACKGROUND Previous studies have indicated that peripheral circulating markers of inflammation are elevated in women with polycystic ovary syndrome (PCOS), but thus far no studies concerning markers of inflammation in adipose tissue have been published. The aim of the study was to investigate whether patients with PCOS display increased expression of inflammatory markers in adipose tissue. METHODS Twenty overweight patients with PCOS, 10 lean patients with PCOS and 20 overweight controls had subcutaneous fat biopsies and blood samples taken. Adipose tissue levels of mRNA of inflammatory markers were determined by use of real-time PCR. RESULTS Overweight patients with PCOS had higher relative adipose tissue chemokine ligand 2 (P < 0.01), and its cognate receptor (P < 0.05), tumour necrosis factor-α (P < 0.001), interleukin (IL)-10 (P < 0.001) and IL-18 (P < 0.001) and the monocyte/macrophage markers CD14 (P < 0.01) and CD163 (P < 0.01) mRNA levels compared with lean women with PCOS. There were no differences between overweight patients with PCOS and overweight control subjects in this respect. Within the PCOS group, markers of adipose tissue inflammation correlated significantly with obesity-related metabolic disturbances, but when data were adjusted for age and BMI, most correlations were lost. CONCLUSIONS Overweight, rather than the PCOS diagnosis per se, appears to be the main explanatory variable for elevated adipose tissue inflammation in patients with PCOS.

Depot- and ethnic-specific differences in the relationship between adipose tissue inflammation and insulin sensitivity

Objective  It is unclear whether there are differences in inflammatory gene expression between abdominal and gluteal subcutaneous adipose tissue (SAT), and between black and white women. We therefore tested the hypotheses that SAT inflammatory gene expression is greater in the abdominal compared to the gluteal depot, and SAT inflammatory gene expression is associated with differential insulin sensitivity (SI) in black and white women.

Is insulin resistance caused by defects in insulin's target cells or by a stressed mind?

The importance of understanding insulin action is emphasized by the increasing prevalence of insulin resistance in various populations and by the fact that it plays an important pathophysiological role in many common disorders, for example, diabetes, obesity, hypertension and dyslipidemia. The primary factors responsible for the development of insulin resistance are so far unknown, although both genetic and environmental factors are involved. The genetic defects responsible for the common forms of insulin resistance, for example, in type 2 diabetes, are largely unidentified. Some studies from our group as well as by other investigators suggest that cellular insulin resistance is reversible and that it may be secondary to factors in the in vivo environment. These may include insulin‐antagonistic action of hormones like catecholamines, glucocorticoids, sex steroids and adipokines as well as dysregulation of autonomic nervous activity and they could contribute to the early development of insulin resistance. Some of these factors can directly impair glucose uptake capacity and this might be due to alterations in key proteins involved in insulins intracellular signaling pathways. This article briefly summarizes proposed mechanisms behind cellular and whole‐body insulin resistance. In particular, we question the role of intrinsic defects in insulins target cells as primary mechanisms in the development of insulin resistance in type 2 diabetes and we suggest that metabolic and neurohormonal factors instead are the main culprits. Copyright

Tissue-Specific Increases in 11β-Hydroxysteroid Dehydrogenase Type 1 in Normal Weight Postmenopausal Women

With age and menopause there is a shift in adipose distribution from gluteo-femoral to abdominal depots in women. Associated with this redistribution of fat are increased risks of type 2 diabetes and cardiovascular disease. Glucocorticoids influence body composition, and 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) which converts inert cortisone to active cortisol is a putative key mediator of metabolic complications in obesity. Increased 11βHSD1 in adipose tissue may contribute to postmenopausal central obesity. We hypothesized that tissue-specific 11βHSD1 gene expression and activity are up-regulated in the older, postmenopausal women compared to young, premenopausal women. Twenty-three pre- and 23 postmenopausal, healthy, normal weight women were recruited. The participants underwent a urine collection, a subcutaneous adipose tissue biopsy and the hepatic 11βHSD1 activity was estimated by the serum cortisol response after an oral dose of cortisone. Urinary (5α-tetrahydrocortisol+5β-tetrahydrocortisol)/tetrahydrocortisone ratios were higher in postmenopausal women versus premenopausal women in luteal phase (P<0.05), indicating an increased whole-body 11βHSD1 activity. Postmenopausal women had higher 11βHSD1 gene expression in subcutaneous fat (P<0.05). Hepatic first pass conversion of oral cortisone to cortisol was also increased in postmenopausal women versus premenopausal women in follicular phase of the menstrual cycle (P<0.01, at 30 min post cortisone ingestion), suggesting higher hepatic 11βHSD1 activity. In conclusion, our results indicate that postmenopausal normal weight women have increased 11βHSD1 activity in adipose tissue and liver. This may contribute to metabolic dysfunctions with menopause and ageing in women.

Sex- and Depot-specific Lipolysis Regulation in Human Adipocytes: Interplay between Adrenergic Stimulation and Glucocorticoids

The purpose of this investigation was to explore interactions between adrenergic stimulation, glucocorticoids, and insulin on the lipolytic rate in isolated human adipocytes from subcutaneous and omental fat depots, and to address possible sex differences. Fat biopsies were obtained from 48 nondiabetic subjects undergoing elective abdominal surgery. Lipolysis rate was measured as glycerol release from isolated cells and proteins involved in lipolysis regulation were assessed by immunoblots. Fasting blood samples were obtained and metabolic and inflammatory variables were analyzed. In women, the rate of 8-bromo-cAMP- and isoprenaline-stimulated lipolysis was approximately 2- and 1.5-fold higher, respectively, in subcutaneous compared to omental adipocytes, whereas there was no difference between the two depots in men. Dexamethasone treatment increased the ability of 8-bromo-cAMP to stimulate lipolysis in the subcutaneous depot in women, but had no consistent effects in fat cells from men. Protein kinase A, Perilipin A, and hormone sensitive lipase content in adipocytes was not affected by adipose depot, sex, or glucocorticoid treatment. In conclusion, catecholamine and glucocorticoid regulation of lipolysis in isolated human adipocytes differs between adipose tissue depots and also between sexes. These findings may be of relevance for the interaction between endogenous stress hormones and adipose tissue function in visceral adiposity and the metabolic syndrome.

Neonatal overfeeding induced by small litter rearing causes altered glucocorticoid metabolism in rats.

Elevated glucocorticoid (GC) activity may be involved in the development of the metabolic syndrome. Tissue GC exposure is determined by the tissue-specific GC-activating enzyme 11β-hydroxysteriod dehydrogenase type 1 (11β-HSD1) and the GC-inactivating enzyme 5α-reductase type 1 (5αR1), as well as 5β-reductase (5βR). Our aim was to study the effects of neonatal overfeeding induced by small litter rearing on the expression of GC-regulating enzymes in adipose tissue and/or liver and on obesity-related metabolic disturbances during development. Male Sprague-Dawley rat pup litters were adjusted to litter sizes of three (small litters, SL) or ten (normal litters, NL) on postnatal day 3 and then given standard chow from postnatal week 3 onward (W3). Small litter rearing induced obesity, hyperinsulinemia, and higher circulating corticosterone in adults. 11β-HSD1 expression and enzyme activity in retroperitoneal, but not in epididymal, adipose tissue increased with postnatal time and peaked at W5/W6 in both groups before declining. From W8, 11β-HSD1 expression and enzyme activity levels in retroperitoneal fat persisted at significantly higher levels in SL compared to NL rats. Hepatic 11β-HSD1 enzyme activity in SL rats was elevated from W3 to W16 compared to NL rats. Hepatic 5αR1 and 5βR expression was higher in SL compared to NL rats after weaning until W6, whereupon expression decreased in the SL rats and remained similar to that in NL rats. In conclusion, small litter rearing in rats induced peripheral tissue-specific alterations in 11β-HSD1 expression and activity and 5αR1 and 5βR expression during puberty, which could contribute to elevated tissue-specific GC exposure and aggravate the development of metabolic dysregulation in adults.