Leptin is a negative acute phase protein in chronic hemodialysis patients

BACKGROUND: Hypoalbuminemia strongly predicts death in hemodialysis patients and results from both inflammation and malnutrition. One potential link between malnutrition and inflammation is appetite suppression triggered by inflammation. Leptin is secreted by adipose tissue and suppresses appetite, and it is also a positive acute phase protein in the rat. Factored for body weight, leptin is known to be increased in hemodialysis patients, but its relationship to inflammation is unknown. METHODS: We examined the relationship between spontaneously occurring activation of the acute phase response and leptin levels in 29 chronic hemodialysis patients. Serum samples were obtained three times weekly for six weeks and then monthly from 29 chronic hemodialysis patients, and the levels of the positive acute phase proteins C-reactive protein (CRP), alpha1-acid glycoprotein (alpha1 AG), serum amyloid A, ceruloplasmin] and the negative acute phase proteins (albumin and transferrin) as well as leptin and interleukin-6 (IL-6) were measured. RESULTS: Positive and negative acute phase proteins were evaluated at the maximum CRP (mean, 9.42 +/- 1.14 mg/dL) and minimum values (mean, 0.41 +/- 0.09 mg/dL). When CRP was elevated, leptin levels were significantly reduced, as were the negative acute phase proteins albumin and transferrin. Serum amyloid A, ceruloplasmin, alpha1 acid glycoprotein, and IL-6 were all significantly increased at the maximum CRP level, compatible with general activation of the acute phase response. The change in leptin correlated negatively with the change in CRP (R = 0.437, P = 0.018), as did changes in albumin (R = 0.620, P < 0.001). CONCLUSIONS: Leptin is not increased as a consequence of inflammation in hemodialysis patients, but behaves as a negative rather than as a positive acute phase protein. Inflammation is unlikely to reduce appetite in dialysis patients through a leptin-mediated mechanism.