Effect of body condition, body weight and adiposity on inflammatory cytokine responses in old horses

Advanced age is associated with a low-grade, systemic inflammatory response characterized by increased inflammatory cytokine production both in vitro and in vivo, termed inflamm-aging. It is also known that increased white adipose tissue, associated with obesity, leads to increased production of inflammatory cytokines. To date, it is unknown whether increased adiposity contributes to the age-related increased inflammatory status. Here we show that peripheral blood mononuclear cells (PBMC) from old horses compared to young horses have increased inflammatory cytokine production; moreover, fat old horses compared to thin old horses have even greater frequencies of lymphocytes and monocytes producing inflammatory cytokines. Therefore, we proposed that decreasing adiposity in old horses would reduce age-associated increases of inflammatory cytokines both in vitro and in vivo, and increasing adiposity in old horses would increase these measurements. To test this hypothesis further, eight old obese horses (20-28 year) were assigned to two consecutive treatments, dietary restriction (DR) during weeks 1-12 and increased dietary intake (DI) during weeks 13-30. Body weight, body condition score (BCS) and percent body fat were measured weekly. PBMC were stimulated in vitro and interferon gamma (IFNγ) and tumor necrosis factor alpha (TNFα) production was measured by intracellular staining. Levels of nascent IFNγ and TNFα mRNA expression were examined by RT-PCR. Serum concentrations of TNFα protein were also measured weekly. Reducing body weight and fat in old horses significantly reduced the percent of IFNγ and TNFα positive lymphocytes and monocytes, and serum levels of TNFα protein. Further, when weight and fat increased in these old horses there was a significant increase in inflammatory cytokine production. Regression analysis also revealed significant relationships. These findings demonstrate that age-related obesity potentially plays a role in the dysregulation of inflammatory cytokine production by the immune system with age or inflamm-aging in the horse.