Serum and cellular interleukin-6 in haemodialysis patients: relationship with energy expenditure.

Background: Inflammation is a highly prevalent condition among end-stage renal disease (ESRD) patients and it has been implicated with several metabolic derangements. Considering the harmful effect of hypermetabolism on nutritional status and clinical outcomes of ESRD patients, we aimed to investigate the relationship between proinflammatory cytokine interleukin-6 (IL-6) and energy expenditure in this population.

Methods: This cross-sectional study enrolled 80 adult haemodialysis patients for the evaluation of serum IL-6 and energy expenditure. The production of IL-6 by peripheral blood mononuclear cells (PBMCs) (spontaneous and endotoxin-stimulated production) was examined in a subgroup of 30 haemodialysis patients and in 11 healthy control subjects. IL-6 was measured by immunoenzymatic assay. The resting energy expenditure was evaluated by means of indirect calorimetry. Body composition was assessed by bioelectrical impedance analysis and skinfold thicknesses.

Results: Serum IL-6 [6.3 (2.2-163.5) pg/ml] correlated positively with age (R = 0.26; P = 0.02) and C-reactive protein (R = 0.31; P < 0.01). Resting energy expenditure correlated positively with lean body mass (R = 0.68; P < 0.001) and BMI (R = 0.44; P < 0.001), and negatively with Kt/V (R = -0.37; P < 0.01). In the multivariate analysis, controlling for age and lean body mass, serum IL-6 was positively associated with resting energy expenditure (n = 80; beta = 2.4; P = 0.01). The production of IL-6 by PBMCs did not reach statistically significant differences between patients and controls [spontaneous production 6541 (96-7739) pg/ml vs 3410 (50-7806) pg/ml, respectively; and stimulated production 6530 (579-7671) pg/ml vs 5304 (1527-7670) pg/ml, respectively]. IL-6 secreted by monocytes showed no association with either serum IL-6 or resting energy expenditure.

Conclusion: Serum IL-6 was associated with an increase of energy expenditure in haemodialysis patients.