title: Decreased cerebrospinal-fluid/serum leptin ratio in obesity: a possible mechanism for leptin resistance.
abstract: BACKGROUND
  A receptor for leptin has been cloned from the choroid plexus, the site of cerebrospinal-fluid (CSF) production and the location of the blood/cerebrospinal-fluid barrier. Thus, this receptor might serve as a transporter for leptin. We have studied leptin concentrations in serum and (CSF).
  
  
  RESULTS
  We demonstrated by radioimmunoassay and western blot the presence of leptin in human CSF. We then measured leptin in CSF and serum in 31 individuals with a wide range of bodyweight. Mean serum leptin was 318% higher in 8 obese (40.2 [SE 8.6] ng/mL) than in 23 lean individuals (9.6 [1.5] ng/mL, p < 0.0005). However, the CSF leptin concentration in obese individuals (0.337 [0.04] ng/mL) was only 30% higher than in lean people (0.259 [0.26] ng/mL, p < 0.1). Consequently, the leptin CSF/serum ratio in lean individuals (0.047 [0.010]) was 4.3-fold higher than that in obese individuals (0.011 [0.002], p < 0.05). The relation between CSF leptin and serum leptin was best described by a logarithmic function (r = 0 x 52, p < 0.01).
  
  
  CONCLUSIONS
  Our data suggest that leptin enters the brain by a saturable transport system. The capacity of leptin transport is lower in obese individuals, and may provide a mechanism for leptin resistance.
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Caro
authors.forename: J W
authors.initials: JW
authors.lastname: Kolaczynski
authors.forename: M R
authors.initials: MR
authors.lastname: Nyce
authors.forename: J P
authors.initials: JP
authors.lastname: Ohannesian
authors.forename: I
authors.initials: I
authors.lastname: Opentanova
authors.forename: W H
authors.initials: WH
authors.lastname: Goldman
authors.forename: R B
authors.initials: RB
authors.lastname: Lynn
authors.forename: P L
authors.initials: PL
authors.lastname: Zhang
authors.forename: M K
authors.initials: MK
authors.lastname: Sinha
authors.forename: R V
authors.initials: RV
authors.lastname: Considine
mesh_terms: D001692:Biological Transport; D001812:Blood-Brain Barrier; D015153:Blotting, Western; D015992:Body Mass Index; D002352:Carrier Proteins / Q000378:metabolism; D005260:Female; D006801:Humans; D020738:Leptin; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism* / Q000502:physiology; D011863:Radioimmunoassay; D011956:Receptors, Cell Surface; D018121:Receptors, Cytokine / Q000378:metabolism; D054411:Receptors, Leptin
chemical_list: D002352:Carrier Proteins; C515448:LEPR protein, human; D020738:Leptin; D011506:Proteins; D011956:Receptors, Cell Surface; D018121:Receptors, Cytokine; D054411:Receptors, Leptin