title: Evidence for interindividual heterogeneity in the glucose gradient across the human red blood cell membrane and its relationship to hemoglobin glycation.
abstract: OBJECTIVE
  To determine whether interindividual heterogeneity in the erythrocyte (red blood cell [RBC]) transmembrane glucose gradient might explain discordances between A1C and glycemic control based on measured fructosamine.
  
  
  METHODS
  We modeled the relationship between plasma glucose and RBC glucose as the concentration distribution (C(i)-to-C(o) ratio) of a nonmetabolizable glucose analog (14)C-3-O-methyl glucose ((14)C-3OMG) inside (C(i)) and outside (C(o)) RBCs in vitro. We examined the relationship between that distribution and the degree of glycation of hemoglobin in comparison with glycation of serum proteins (fructosamine), the glycation gap. A1C, fructosamine, and in vitro determination of the (14)C-3OMG distribution in glucose-depleted RBCs were measured in 26 fasted subjects.
  
  
  RESULTS
  The C(i)-to-C(o) ratio 0.89 +/- 0.07 for 3-O-methyl-d-glucopyranose (3OMG) ranged widely (0.72-1.04, n = 26). In contrast, urea C(i)-to-C(o) (1.015 +/- 0.022 [range 0.98-1.07], P < 0.0001) did not. Concerning mechanism, in a representative subset of subjects, the C(i)-to-C(o) ratio was retained in RBC ghosts, was not dependent on ATP or external cations, and was reestablished after reversal of the glucose gradient. The 3OMG C(i)-to-C(o) ratio was not correlated with serum fructosamine, suggesting that it was independent of mean plasma glucose. However, C(i)-to-C(o) did correlate with A1C (R(2) = 0.19) and with the glycation gap (R(2) = 0.20), consistent with a model in which differences in internal glucose concentration at a given mean plasma glucose contribute to differences in A1C for given level of glycemic control.
  
  
  CONCLUSIONS
  The data demonstrate interindividual heterogeneity in glucose gradients across RBC membranes that may affect hemoglobin glycation and have implications for diabetes complications risk and risk assessment.
authors.affiliation: Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Cincinnati Medical Center, Cincinnati, Ohio, USA.
authors.forename: Paramjit K
authors.initials: PK
authors.lastname: Khera
authors.forename: Clinton H
authors.initials: CH
authors.lastname: Joiner
authors.forename: Anthony
authors.initials: A
authors.lastname: Carruthers
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lindsell
authors.forename: Eric P
authors.initials: EP
authors.lastname: Smith
authors.forename: Robert S
authors.initials: RS
authors.lastname: Franco
authors.forename: Yancey R
authors.initials: YR
authors.lastname: Holmes
authors.forename: Robert M
authors.initials: RM
authors.lastname: Cohen
mesh_terms: D000328:Adult; D002250:Carbon Radioisotopes; D003920:Diabetes Mellitus / Q000453:epidemiology / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D019270:Fructosamine / Q000493:pharmacokinetics; D005947:Glucose / Q000493:pharmacokinetics*; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006031:Glycosylation; D006151:Guanosine / Q000031:analogs & derivatives; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012307:Risk Factors; D014508:Urea / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D019270:Fructosamine; D005947:Glucose; D006442:Glycated Hemoglobin; D006151:Guanosine; D014508:Urea; D014867:Water; C037626:3'-O-methylguanosine