Cerebrospinal fluid xenin levels during body mass reduction: no evidence for obesity-associated defective transport across the blood-brain barrier.

Abstract

Recent studies have shown that xenin can act in the hypothalamus, reducing food intake through a leptin- and melanocortin system-independent mechanism. To evaluate the impact of body mass reduction on the blood and cerebrospinal fluid (CSF) levels of xenin. Thirteen obese patients (11 women) selected for roux-in-Y gastric bypass surgery were evaluated before and approximately 8 months after surgery. Xenin was determined in serum and CSF by radioimmunoassay. As compared with lean subjects, obese patients have increased blood levels of xenin, which reduce after surgery. There are significant correlations between blood xenin and blood leptin and insulin levels. CSF concentration of xenin is ∼10-fold lower than blood levels, and is significantly higher in obese subjects as compared with lean ones, returning to normal levels after body mass reduction. There is a significant linear correlation between CSF and blood levels of xenin. Xenin is present in the human CSF in a concentration ∼10-fold lower than the blood. Both blood and CSF xenin are correlated with blood levels of important markers of adiposity, leptin and insulin. The levels of CSF xenin are linearly correlated with blood xenin, independently of patient body mass, suggesting that either its transport across the blood-brain barrier is not saturated in the concentration range detected in this study or that there is a coordinated release of xenin from the periphery and the CNS.