β-carotene and genistein modulate the phagocytic activity of human pre-adipocytes

Objective: Obesity is exceedingly associated with the development of type 2 diabetes. It is characterized by an increase in fat mass which is accused to cause a chronic pro-inflammatory state. Adipose tissue does not only comprise mature fat-storing adipcoytes, but also immuno-competent cells such as preadipocytes and macrophages. The latter cells also exert the ability to perform phagocytosis and, thus, may have an effect on the local inflammatory status in adipose tissue. In this study, the influence of β-carotene and genistein on the phagocytic activity of SGBS cells, a human preadipocyte cell line, and of freshly isolated primary human pre-adipocytes was investigated.

Methods: Phagocytic activity was measured by incorporation of FITC-labelled E. coli by flow cytometry. For β-carotene, two preparation methods were used: 1) β-carotene dissolved in the organic solvent tetrahydrofurane (THF), and 2) β-carotene incorporated in liposomes. TNF-α and interleukin-6 were measured with ELISA in cell culture supernatants.

Results: β-carotene dissolved in THF had no significant impact on the phagocytic rate of SGBS cells. In contrast, β-carotene incorporated in liposomes together with α-tocopherol as an antioxidant caused a significant increase in phagocytosis. In addition, genistein significantly increased the phagocytic rate in SGBS cells. In primary human preadipocytes, β-carotene in low concentrations increased the phagocytic activity, at higher concentrations the phagocytic activity returned to baseline. The increased phagocytic activity was not associated with an elevated secretion of the pro-inflammatory cytokines TNF-α and interleukin-6.

Conclusions: This study shows that adipose precursor cells possess phagocytic activity. Phytochemicals like β-carotene and genistein increase the phagocytic activity of human preadipocytes without increasing the secretion of pro-inflammatory cytokines. This effect may demonstrate an important anti-inflammatory effect of certain phytochemicals in adipose tissue which may counteract the pro-inflammatory state in obesity.