Attenuation of obesity-induced inflammation in mice orally administered with salmon cartilage proteoglycan, a prophylactic agent

Obesity is associated with chronic inflammation of adipose tissue and causes development of type 2 diabetes. M1 macrophage population was increased in adipose tissue of obese mouse. M1 macrophages induce insulin resistance through the secretion of proinflammatory cytokines. Our previous studies demonstrated that salmon cartilage proteoglycan (PG) suppresses excess inflammation in various mouse inflammatory diseases. In this study, we examined the effect of PG on type 2 diabetes using high-fat-diet (HFD) induced obese mouse model. Oral PG administration enhanced the population of small adipocytes (area less than 1000 μm2) without body and tissue weight gain. In addition, PG administration suppressed mRNA expression of TNF-α, IL-6 and CXCL2 in adipose tissue. The proportion of M1 macrophages was decreased by PG administration. In addition, PG administration suppressed hyperglycemia after intraperitoneal glucose injection. Fasted serum insulin level was decreased in PG-administered mice. Moreover, insulin-stimulated phosphorylation of Akt was enhanced in the liver and gastrocnemius skeletal muscle of PG-administered mice. These data suggested that PG administration improves hyperglycemia and insulin sensitivity in obese mice by modulation of M1 macrophages which secrete proinflammatory cytokines in adipose tissue and activation of Akt in liver and skeletal muscle.