Anorexigen (TNF-alpha, cholecystokinin) and orexigen (neuropeptide Y) plasma levels in peritoneal dialysis (PD) patients: their relationship with nutritional parameters.

BACKGROUND: Malnutrition has definitely been related to mortality among dialysis patients. Persistent loss of appetite is one of the major symptoms found in these patients. It is also well recognized that several substances produce anorexia or disorders of the hunger-satiety cycle in several diseases. The aim of this study was to identify the role of anorexigen substances (TNF-alpha and cholecystokinin or CCK) and an orexigen substance (neuropeptide Y or NPY) in anorexia and malnutrition among 55 clinically stable peritoneal dialysis (PD) patients.
RESULTS: High TNF-alpha plasma levels were found in 41 of 42 patients (97.6%) with a mean of 70.5+/-32.3 pg/ml. Patients with anorexia (n=11) or anorexia with nausea or vomiting (n=5) had higher TNF-alpha values than patients without these symptoms (75.9+/-34 vs 52.1 +/-24.5 pg/ml, P<0.05). Eight patients with a prior diagnosis of acid pylori disease showed higher TNF-alpha values (87.2+/-24.3) than 30 unaffected patients (63.6+/-30.5, P<0.05). TNF-alpha showed a significant negative linear correlation with retinol binding protein (RBP) (r=-0.37, n=34, P<0.05), and venous pH (r=-0.4, n=42, P<0.01); also, TNF-alpha values higher than 65 pg/ml were inversely associated with transferrin, cholesterol, blood urea nitrogen (BUN) and CCK. Patients with prealbumin levels lower than 30 mg/dl, a BMI lower than 30 kg/m2, nPCR lower than 1.1 g/kg/day and urea KT/V lower than 2.2 showed higher serum TNF-alpha levels. Patients who had been on CAPD treatment for longer periods showed higher TNF-alpha values. High plasma CCK levels were found in 38 of 45 patients (84%), mean 45.9+/-32.3 pg/ml. Patients with anorexia had no difference in CCK values compared with those without. A direct association was found between CCK levels and some nutritional markers (albumin, fibronectin, triglycerides, folic acid and nPCR in non diabetic patients). Although CCK has a recognized anorectic effect, this direct association might be because of an abnormal stimulation of CCK glucose feedback (trypsin) due to continuous peritoneal glucose absorption. This suggests that CCK could be an immediate food intake marker in PD patients. The NPY plasma levels were normal in 33 patients, high in 6 and low in 11. Patients with anorexia showed lower NPY levels than those without. NPY values greater than 50 pg/ml were directly associated with higher transferrin, prealbumin, RBP, nPCR and urea KT/V values. Importantly, a negative linear correlation between NPY and TNF-alpha was found (r=-0.42, n= 41, P<0.01). There was no significant relationship between residual renal clearance and the serum levels of the three peptides.
CONCLUSION: In conclusion, our data suggest that high TNF-alpha and low NPY serum levels are associated with anorexia. High TNF-alpha, low CCK and low NPY serum levels are also related to a poor nutritional status. Further research on these circulating substances is required.