Glargine blood biotransformation: in vitro appraisal with human insulin immunoassay.
OBJECTIVE
Glargine, a long-acting insulin analogue, is metabolized in the bloodstream and in subcutaneous tissue. Glargine metabolism and its implications for diabetes therapy remain poorly understood. The aim of our study was to assess in vitro the glargine blood biotransformation and its inter-individual variability.


METHODS
Formation of M1 glargine metabolite in vitro was studied with Elecsys Insulin immunoassay in pools of sera and sera from patients spiked with glargine. Elecsys Insulin assay is specific of human insulin, does not recognize glargine and its M2 metabolite but does recognize its M1 metabolite.


RESULTS
Glargine incubation with serum resulted in M1 metabolite formation which was detected and characterized as an enzymatic process: metabolite kinetics were dependant on temperature, substrate concentration and serum proportion. Carboxypeptidase inhibitors and chelating agents partially inhibited the activity of the enzyme(s). Glargine biotransformation was decreased when blood was collected on EDTA tubes. After 30 min incubation of glargine (100 mU/l) in 69 sera at 37 degrees C, percentage of glargine converted into M1 ranged from 46% to 98% (mean 72%; S.D. 11%).


CONCLUSIONS
Glargine blood biotransformation is an enzymatic process probably involving serum carboxypeptidase(s). Metabolite formation is rapid and non negligible. Inter-individual variability of glargine biotransformation is noteworthy and should be confronted to M1 metabolite bioactivity which has not been fully documented yet.
Agin
A
A
Centre national de la recherche scientifique, UMR 7004, institut de physique biologique, faculté de médecine, université Louis-Pasteur, 67091 Strasbourg, France. arnaud-agin@chru-strasbourg.fr
Jeandidier
N
N
Gasser
F
F
Grucker
D
D
Sapin
R
R
D000595:Amino Acid Sequence; D001711:Biotransformation; D006801:Humans; D007004:Hypoglycemic Agents / Q000097:blood* / Q000493:pharmacokinetics; D007118:Immunoassay; D007328:Insulin / Q000031:analogs & derivatives* / Q000097:blood* / Q000737:chemistry / Q000493:pharmacokinetics; D000069036:Insulin Glargine; D049528:Insulin, Long-Acting; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D015203:Reproducibility of Results
D007004:Hypoglycemic Agents; D007328:Insulin; D049528:Insulin, Long-Acting; D010446:Peptide Fragments; D000069036:Insulin Glargine