Kerstin Gorzelniak

Weight Loss and the Renin-Angiotensin-Aldosterone System

The renin-angiotensin-aldosterone system has been causally implicated in obesity-associated hypertension. We studied the influence of obesity and weight reduction on the circulating and adipose tissue renin-angiotensin-aldosterone system in menopausal women. Blood samples were analyzed for angiotensinogen, renin, aldosterone, angiotensin-converting enzyme activity, and angiotensin II. In adipose tissue biopsy samples, we analyzed angiotensinogen, renin, renin-receptor, angiotensin-converting enzyme, and angiotensin II type-1 receptor gene expression. Obese women (n=19) had higher circulating angiotensinogen, renin, aldosterone, and angiotensin-converting enzyme than lean women (n=19), and lower angiotensinogen gene expression in adipose tissue. Seventeen women successfully participated in a weight reduction protocol over 13 weeks to reduce daily caloric intake by 600 kcal. Body weight was reduced by −5%, as were angiotensinogen levels by −27%, renin by −43%, aldosterone by −31%, angiotensin-converting enzyme activity by −12%, and angiotensinogen expression by −20% in adipose tissue (all P<0.05). The plasma angiotensinogen decrease was highly correlated with the waist circumference decline (r=0.74; P<0.001). Weight and renin-angiotensin-aldosterone system reductions were accompanied by a −7-mm Hg reduced systolic ambulatory blood pressure. These data suggest that a 5% reduction in body weight can lead to a meaningfully reduced renin-angiotensin-aldosterone system in plasma and adipose tissue, which may contribute to the reduced blood pressure.

Angiotensin Blockade Prevents Type 2 Diabetes by Formation of Fat Cells

Obesity is the prime risk factor for the development of type 2 diabetes. Recent clinical trials have shown that blockade of the renin-angiotensin system, either by inhibiting the angiotensin-converting enzyme or blocking the angiotensin type 1 receptor, may substantially lower the risk for type 2 diabetes. The mechanism underlying this effect is unknown. Based on our recent observation that angiotensin II markedly inhibits adipogenic differentiation of human adipocytes via the angiotensin type I receptor and that expression of angiotensin II-forming enzymes in adipose tissue is inversely correlated with insulin sensitivity, we propose the hypothesis that blockade of the renin-angiotensin system prevents diabetes by promoting the recruitment and differentiation of adipocytes. Increased formation of adipocytes would counteract the ectopic deposition of lipids in other tissues (muscle, liver, pancreas), thereby improving insulin sensitivity and preventing the development of type 2 diabetes.

Co-expression of renin-angiotensin system genes in human adipose tissue.

OBJECTIVE The renin-angiotensin system plays a central role in blood pressure regulation, both by affecting renal function and by modulating vascular tone and structure. Recent studies in rodents demonstrated the existence of several components of this system in adipose tissue. The activity of the renin-angiotensin system appears to be regulated by food intake, suggesting that it may be involved in obesity-associated hypertension. Few data are available on the presence of renin-angiotensin system components in human adipose tissue. MATERIALS AND METHODS In order to explore the expression of renin-angiotensin system genes in human adipose tissue and adipocytes, total RNA was isolated from whole adipose tissue (subcutaneous and omental) or cultured adipocytes (mammary) and subjected to reverse-transcriptase polymerase chain reaction with primers specific for human angiotensinogen, renin, renin-binding protein, angiotensin converting enzyme, chymase and type 1 and type 2 angiotensin receptors. RESULTS Angiotensinogen, angiotensin converting enzyme and type 1 angiotensin receptor genes were widely expressed, both in human adipose tissue and in cultured human adipocytes. Furthermore, we found expression of the chymase and renin-binding protein genes in these samples. CONCLUSIONS Our findings suggest the presence of a local renin -angiotensin system in human adipose tissue, with adipocytes being an important part of this system, and prompt speculation that this local renin-angiotensin system may be involved in obesity-related disorders, including hypertension and the metabolic syndrome.

Hormonal regulation of the human adipose-tissue renin-angiotensin system: relationship to obesity and hypertension.

Objective Adipose tissue secretes vasoactive substances which may contribute to the development of obesity-related hypertension. The aim of this work was to study the expression of renin–angiotensin system genes in adipose tissue of obese hypertensive subjects and the hormonal regulation of these genes. Design Differential expression of renin–angiotensin system genes in subcutaneous abdominal adipocytes of 12 lean normotensive, eight obese normotensive, and 10 obese hypertensive women was determined in a cross-sectional study. In vitro hormonal regulation of these genes was studied in primary human adipocytes obtained by breast reduction from healthy women. Methods In the clinical study, 24-h ambulatory blood pressure measurement and anthropometry were used to characterize the volunteers, and adipocytes were obtained by subcutaneous needle biopsy. The in vitro regulation of renin–angiotensin system genes by hydrocortisone, insulin, thyroxin, estradiol and angiotensin II on primary cultured human mammary adipocytes was studied by quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Results While expression of the angiotensinogen gene was significantly lower in adipocytes from both obese groups, the renin, angiotensin-converting enzyme and angiotensin II type 1 receptor genes were significantly upregulated in obese hypertensives. Hydrocortisone increased angiotensin II type 1 receptor gene and protein expression in a time- and dose-dependent manner in human adipocytes, but had no significant influence on other renin–angiotensin system genes. Expression of these genes was not significantly affected by any of the other tested hormones. Conclusions Renin–angiotensin system genes are differentially regulated in human obesity and hypertension. The role of the adipose-tissue renin–angiotensin system in the development of obesity-associated hypertension or metabolic disease clearly warrants further study.

Angiotensin type 1 receptor antagonists induce human in-vitro adipogenesis through peroxisome proliferator-activated receptor-gamma activation.

Objective In clonal animal cells, certain angiotensin receptor blockers (ARB) activate the peroxisome proliferator-activated receptor-γ (PPARγ). The aim of this work was to validate that observation in human cells and humans. Methods We investigated the induction of in-vitro adipogenesis and the activation of PPARγ-target genes, adiponectin and lipoprotein lipase, by ARB in human preadipocytes. We also studied PPARγ response-element-driven luciferase reporter gene activation in human adipocytes. Finally, we treated 14 obese men for 10 days with placebo crossed over with 150 mg/day irbesartan. Subcutaneous fat was analyzed for mRNA expression of adiponectin and lipoprotein lipase. Results Telmisartan and irbesartan, and to a lesser degree losartan, induced adipogenesis and activated PPARγ-target genes. This stimulation of PPARγ-target genes was prevented by the PPARγ antagonist GW9662. Eprosartan had no effect. Paradoxically, all ARB activated the luciferase reporter gene. PPARγ activity increased approximately two-fold with pioglitazone and 1.5-fold with the ARB in all assays. In the cross-over clinical study, irbesartan lowered blood pressure but had no effect on adiponectin or lipoprotein lipase mRNA expression. Conclusions Our data are the first to show that ARB induce adipogenesis and PPARγ-target gene expression in human adipocytes. Pharmacokinetic differences may contribute to the heterogeneous effects on metabolism and preadipocyte differentiation. In humans, larger doses of ARB, longer treatments, or both may be required to activate PPARγ in adipose cells.

Adipose Tissue Metabolism and CD11b Expression on Monocytes in Obese Hypertensives

At a given degree of adiposity, metabolic and cardiovascular risk varies markedly between individuals. Animal studies suggest that differentially expressed systemic activation of monocytes contributes to the obesity-associated risk variability. We tested the hypothesis that systemic monocyte activation is associated with changes in adipose tissue and skeletal muscle metabolism. In 17 obese hypertensive patients, we assessed CD11b expression on circulating monocytes, gene expression in adipose tissue biopsies, and obtained blood samples and adipose tissue and skeletal muscle microdialysis samples in the fasted state and during a glucose load. Patients were stratified into groups with higher and lower CD11b expression on monocytes. Expression of the macrophage marker CD68 was increased markedly in adipose tissue of subjects with higher CD11b expression. Although no differences in systemic insulin sensitivity were found between both groups, patients with higher peripheral CD11b expression showed a markedly augmented increase in dialysate glucose in adipose tissue during oral glucose tolerance testing and increased adipose tissue lipolysis as well. Our data demonstrate that human monocyte activation is associated with tissue-specific changes in glucose and lipid metabolism. These findings may be explained in part by monocyte/macrophage infiltration of adipose tissue, which appears to interfere with insulin responsiveness.

A gene expression analysis in rat kidney following high and low salt intake

Background The effects of salt intake on renal regulation have been investigated for decades. To find new pathways and to demonstrate the utility of oligonucleotide expression arrays, we studied whole kidneys. Methods Eight Sprague–Dawley rats were divided into two groups. One group received a 6% salt (by weight) diet, while the other group received a 0.3%, otherwise identical, salt diet for 7 days. The rats were sacrificed after 7 days and the left kidney was subjected to RNA extraction. Oligonucleotide expression arrays (Affymetrix) were used to determine downregulation and upregulation, comparing high with low salt intake. Four rats from each group were studied separately. Results The experiments were reproducible. Thirty genes were downregulated with the high-salt diet, while 35 genes were upregulated. The renin gene, beta-2 glycoprotein-1, retinol binding protein, annexin VI, and the PTP2C protein tyrosine phosphatase were among the downregulated genes. The angiotensin II receptor type 1B receptor, HMG-CoA reductase, B7 antigen, and the rat calcium channel beta subunit III were among the upregulated genes. Differentially regulated were the p55 subunit (upregulated) and the p50 subunit (downregulated) of the phosphatidyl inositol 3-kinase enzyme complex. We verified our results by selecting a high-salt downregulated gene (renin) and an upregulated gene (B7 antigen) and subjecting these genes to real-time polymerase chain reaction. The results were consistent. Conclusion Oligonucleotide expression arrays can detect novel genes encoding for proteins not generally associated with responses to varied salt intake. Experiments of this nature have substantial limitations and require detailed verification. However, overall, the utility is promising.

Peripheral endocannabinoid system activity in patients treated with sibutramine.

Objective: The endocannabinoid system (ECS) promotes weight gain and obesity‐associated metabolic changes. Weight loss interventions may influence obesity‐associated risk indirectly through modulation of the peripheral ECS. We investigated the effect of acute and chronic treatment with sibutramine on components of the peripheral ECS.

Compounds used for 'Injection Lipolysis' destroy adipocytes and other cells found in adipose tissue

Background: A widely applied technique to reduce subcutaneous fat pad size involves subcutaneous injection of a phosphatidylcholine preparation (‘injection lipolysis’). As the mode of action is mostly unknown, we planned to study cellular effects of the particular drug used in Germany (Lipostabil®). Methods: Human preadipocytes, adipocytes, vascular and skeletal muscle cells as well as renal epithelial cells were incubated in the compound, morphological changes were described, and cell vitality was measured. Results: A strong cytolytic effect of the compound was signified by lipid release and acridine orange staining of dying adipocyte nuclei. When the undiluted compound was used, more than 90% of cell death occurred after 90 s in preadipocytes, after 6 min in vascular smooth muscle cells, skeletal myotubes and renal epithelial cells, and after 15 min in adipocytes. Dilution slowed down cytolysis, but still >50% of the cells disappeared during 30 min incubation. Neither osmotic effects nor differences in medium acidity were responsible for cell death. Conclusion: Injection lipolysis with phosphatidylcholine as the major injected compound reduces subcutaneous fat pad size through cell and tissue destruction. Beside the lack of a clear risk-benefit analysis, applying this technique represents off-label drug use and application of a drug by a contraindicated route.