Anorexia and serum leptin levels in hemodialysis patients

Hyperleptinemia is a common feature in hemodialysis (HD) patients. However, the role of increased serum leptin levels in the pathogenesis of HD-related anorexia is still controversial. The purpose of the present prospective study was to ascertain whether hyperleptinemia is causally implicated in the pathogenesis of HD-related anorexia.

We measured the serum leptin levels and the serum leptin/body mass index (BMI) ratio in 24 healthy subjects and in 49 end-stage renal disease patients on maintenance HD. HD patients were subdivided into anorexic (14/49, 28.5%) and non-anorexic (35/49, 71.5%) according to a questionnaire discriminating for the presence of anorexia-related symptoms.

Calorie (kcal/kg/day) and protein (g/ kg/day) intakes were significantly lower in anorexic than in non-anorexic patients (20.1 +/- 1.1 vs. 27.9 +/- 1.3, p = 0.004, and 0.82 +/- 0.05 vs. 1.19 +/- 0.05, p = 0.001, respectively). Accordingly, serum albumin, total lymphocyte count, mid-arm muscle circumference, and the protein equivalence of nitrogen appearance (PNA) were significantly lower in anorexic patients. The serum leptin concentration (ng/ml) was significantly higher in HD patients than in controls, in males (15.33 +/- 3.4 vs. 3.7 +/- 0.3, p = 0.003) and in females (42.3 +/- 7.2 vs. 10.5 +/- 1.3, p = 0.03). Similarly, serum leptin/BMI ratio was significantly higher in HD patients than in controls, in males (0.56 +/- 0.1 vs. 0.16 +/- 0.02, p = 0.0028) and in females (1.8 +/- 0.2 vs. 0.4 +/- 0.04, p < 0.0001). However, serum leptin levels were similar in anorexic and in non-anorexic patients, in males (15.3 +/- 5.6 vs. 16.9 +/- 4.2, p = 0.85) and in females (46.6 +/- 12.9 vs. 47.4 +/- 9.4, p = 0.96). No differences were observed between the 2 groups in the serum leptin/BMI ratio, in males (0.59 +/- 0.2 vs. 0.58 +/- 0.14, p = 0.92) and in females (1.5 +/- 0.4 vs. 1.8 +/- 0.3, p = 0.94). Similarly, no statistically significant differences in terms of serum leptin levels and leptin/BMI ratio were observed between patients with dietary energy intake of <30 or > or =30 kcal/kg/day and between those with a dietary protein intake of <1.2 or > or =1.2 g/kg/day. No significant correlations were found between serum leptin levels and PNA, albumin, cholesterol, total lymphocytes number, weight change, C-reactive protein, fibrinogen, ferritin, and complement.

The present results indicate that mechanisms other than increases in serum leptin levels might be involved in the pathogenesis of HD-related anorexia.