4-Hydroxyisoleucine: effects of synthetic and natural analogues on insulin secretion.
4-Hydroxyisoleucine, a peculiar amino acid extracted from fenugreek seeds and never found in mammalian tissues, exhibits interesting insulinotropic activity. To investigate the structural requirements for this stimulating effect, the insulinotropic activity of the major isomer (2S,3R,4S) of 4-hydroxyisoleucine, in the presence of 8. 3 mM glucose, was compared to that of (1) its minor isomer (2R,3R, 4S) (2) its lactone form, (3) classical structurally related amino acids, and (4) synthetic monomethylated analogues. In the isolated, ex vivo, perfused rat pancreas, only the major isomer of 4-hydroxyisoleucine (200 microM) potentiated insulin release. On incubated isolated rat islets, the threshold concentration for a significant increase (P<0.05) in insulin release was 200 microM for (2S,3R,4S) 4-hydroxyisoleucine, 500 microM for (2S,4R) and (2S,4S) gamma-hydroxynorvalines as well as (2S,3S) and (2S,3R) gamma-hydroxyvalines, and 1 mM or more for other congeners. In conclusion, the insulinotropic properties of 4-hydroxyisoleucine, in the micromolar range, are seen only in the presence of the linear major isoform; they also require carbon alpha in S-configuration, full methylation and carbon gamma-hydroxylation.
Broca
C
C
UMR 9921 du Centre National de la Recherche Scientifique, Montpellier, France. broca@zeus.sc.univ-montp1.fr
Manteghetti
M
M
Gross
R
R
Baissac
Y
Y
Jacob
M
M
Petit
P
P
Sauvaire
Y
Y
Ribes
G
G
D000818:Animals; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D007532:Isoleucine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D008297:Male; D008745:Methylation; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry; D010946:Plants, Medicinal / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D012639:Seeds / Q000737:chemistry; D013329:Structure-Activity Relationship
C104672:4-hydroxyisoleucine; D007328:Insulin; D010936:Plant Extracts; D007532:Isoleucine