Visceral or central obesity is characterized by an excess of abdominal fat, and is correlated with risk of cardiovascular disease and other health conditions such as type 2 diabetes and dyslipidemia. Central obesity is measured by the waist circumference and is considered to be a stronger predictor of death risk than body mass index. Increases in blood cytokine and chemokine levels are associated with central obesity and is an indication that chronic inflammation is associated with the condition.
Adipocytes have catecholamine-mediated signaling pathways in common with immune and nerve cells, and these pathways are mediated through adrenoceptor (AR) activation. Since catecholamines may mediate inflammatory obesity, researchers decided to study the expression of ARs in peripheral blood mononuclear cells because there may be specific adrenergic patterns associated with central obesity. Blood was collected from donors and the participants were divided into central obesity and a non-central obesity groups based on waist circumference. Participant blood levels of leptin, fasting plasma glucose, triacylglycerol (TAG), and various cholesterol species were measured. Peripheral blood mononuclear cells were isolated for RT-PCR analysis of AR expression. Flow cytometry and immunofluorescence studies were performed to study blood monocyte subsets.
The group with central obesity had higher leptin, total cholesterol, and very low density lipoprotein-cholesterol (VLDL-C) values compared to the group without central obesity. There was also an inverse relationship between central obesity and high-density lipoprotein-cholesterol (HDLP-C). Lower monocyte subset ratios between classical and non-classical monocytes (pro-inflammatory) in the central obesity group indicate a more inflammatory phenotype pattern of monocytes.
Beta-2 AR was downregulated in the central obesity group when compared to the group without central obesity. Beta-2 AR expression was inversely related to TAG, VLDL-C, and leptin, but positively with HDLP-C plasma levels. Overall, the lower expression of beta-2 AR in central obesity, the pro-inflammatory monocyte pattern, and observed correlations with metabolic parameters suggest the utility of beta-2 AR as a marker of obesity in peripheral blood mononuclear cells and the basis to better understand adrenergic mechanisms in inflammatory obesity.
Leite, F., Lima, M., Marino, F., Cosentino, M., & Ribeiro, L. (2017). β2 Adrenoceptors are underexpressed in peripheral blood mononuclear cells and associated with a better metabolic profile in central obesity. International Journal Of Medical Sciences, 14(9), 853-861. doi:10.7150/ijms.19638