Effect of tetra-hydroxylated bile acid on size and insulin sensitivity of subcutaneous adipocytes in healthy lean cats

Abstract

Obesity leads to insulin resistance and is a major risk factor for the development of diabetes mellitus in cats. Prevention of obesity and obesity-induced insulin resistance is difficult, and reliable long-term strategies are currently lacking. Retinoid-related orphan receptor gamma (RORγ) was recently identified as an important transcription factor in the development of large insulin-resistant adipocytes in mice and humans. RORγ negatively affects adipocyte differentiation through expression of its target gene matrix metalloproteinase 3 (MMP3) and promotes the development of large insulin-resistant adipocytes. Preliminary studies in mice showed that RORγ can be inhibited by its ligand tetra-hydroxylated bile acid (THBA). In the present study, serum THBA levels were determined in healthy and diabetic cats. Moreover, potential side effects and the effects of THBA supplementation on adipocyte size, mRNA expression of RORγ, MMP3, interleukin 6, tumor necrosis factor α, adiponectin and leptin in feline subcutaneous adipocytes and insulin sensitivity were investigated in healthy normal weight cats. Thirteen healthy and 13 diabetic cats were used for determination of serum THBA level, and six healthy normal-weight cats were included in a feeding trial. Similar THBA levels were determined in serum of healthy and diabetic cats. Supplementation of 5 mg/kg THBA for 8 wk did not cause any negative effect on feeding behavior, general condition and blood parameters of tested cats. It significantly reduced adipocyte size and mRNA expression of MMP3, interleukin 6, and tumor necrosis factor α in adipocytes, while mRNA expression of adiponectin significantly increased and mRNA expression of RORγ and leptin remained unchanged. Administration of THBA did not influence fasting blood glucose levels or the response of cats to acute insulin administration. Based on these results, THBA is palatable and is considered safe for use in cats. It reduces expression of MMP3 and promotes the development of small adipocytes with increased expression of adiponectin and reduced expression of interleukin 6 and tumor necrosis factor α. Further studies are recommended to evaluate the effect of THBA on adipocyte size and insulin sensitivity in obese cats.