title: Bone mineral density directly correlates with elevated serum leptin in haemodialysis patients.
abstract: BACKGROUND
  Experimentally, leptin has a positive effect on bone mass when infused intravenously, but a negative one after intracerebroventricular administration. Renal failure increases its serum level above the concentration beyond which its transport to the brain may be saturated. Thus, we tested, in a chronic haemodialysis population, the hypothesis of a positive relationship between serum leptin and bone mineral density (BMD) when serum levels are above this threshold.
  
  
  METHODS
  Serum leptin (using a two-site RIA), and BMD at the femoral neck, midshaft, and ultradistal radius, as measured by DEXA, were assessed in 17 female and 16 male chronic dialysis patients, with comparable calcium and phosphate metabolism, age and dialysis duration.
  
  
  RESULTS
  Polynomial regression analysis showed a U-shaped correlation between BMD Z-score, with an inflexion point, which may correspond to the concentration threshold at which leptin blood-brain carrier is saturated. Linear regression analysis showed no correlation between BMD and serum leptin levels below these points but a significant positive correlation between BMD at the two radius sites and leptin levels above these points. The correlation remained significant after adjustment for BMI, serum PTH and duration of dialysis. Leptin levels were twice as high in female patients and associated with higher BMD Z-scores close to zero.
  
  
  CONCLUSIONS
  This study suggests a bone-sparing effect of serum leptin in haemodialysis patients only when the serum levels of leptin were higher than the presumed threshold of blood-brain transport saturation. Higher leptin levels in post-menopausal female haemodialysis patients than in male patients may account for their slower bone loss with ageing.
authors.affiliation: Service de Néphrologie, CHU Amiens, France.
authors.forename: Abderrahmane
authors.initials: A
authors.lastname: Ghazali
authors.forename: Franck
authors.initials: F
authors.lastname: Grados
authors.forename: Roxana
authors.initials: R
authors.lastname: Oprisiu
authors.forename: Delia
authors.initials: D
authors.lastname: Bunea
authors.forename: Philippe
authors.initials: P
authors.lastname: Morinière
authors.forename: Najeh
authors.initials: N
authors.lastname: El Esper
authors.forename: Isabelle
authors.initials: I
authors.lastname: El Esper
authors.forename: Michel
authors.initials: M
authors.lastname: Brazier
authors.forename: Jean Claude
authors.initials: JC
authors.lastname: Souberbielle
authors.forename: Albert
authors.initials: A
authors.lastname: Fournier
authors.forename: Thierry
authors.initials: T
authors.lastname: Thomas
mesh_terms: D000368:Aged; D015519:Bone Density / Q000502:physiology*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood / Q000503:physiopathology* / Q000628:therapy; D020738:Leptin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis
chemical_list: D020738:Leptin