Leptin induces secretion of pro-inflammatory cytokines by human keratinocytes in vitro - a possible reason for increased severity of psoriasis in patients with a high body mass index.

Investigations about prevalence of obesity in psoriasis patients are increased nowadays. Higher serum levels of leptin in patients with psoriasis who are overweight or obese suggest that leptin may serve as a molecular link between psoriasis and metabolic comorbidities. However, the pathological functions of leptin in psoriasis are not clearly understood. We investigated the influence of being overweight or obese on the risk of psoriasis, and the relationship between serum leptin levels and the severity of psoriasis in Chinese Han patients. We also investigated biological effects of leptin on the proliferation and secretion of pro-inflammatory cytokines by human keratinocytes in vitro. Obesity was a significant risk factor for psoriasis in the Chinese Han population; however, we did not observe a significant correlation between Psoriasis Area and Severity Index (PASI) and body mass index (BMI). We observed a positive correlation between the serum leptin level and PASI in overweight and obese male patients with psoriasis. Strong leptin immunoreactivity was detected in the epidermis of psoriatic lesions, particularly in keratinocytes. Leptin significantly increased the proliferation and secretion of pro-inflammatory cytokines by keratinocytes in vitro. In conclusion, this study suggests leptin as a novel molecular link between psoriasis and obesity, which may help to explain the more server conditions of psoriasis in patients with obesity.