Improved stability, insulin-releasing activity and antidiabetic potential of two novel N-terminal analogues of gastric inhibitory polypeptide: N-acetyl-GIP and pGlu-GIP.
OBJECTIVE
This study examined the plasma stability, biological activity and antidiabetic potential of two novel N-terminally modified analogues of gastric inhibitory polypeptide (GIP).


METHODS
Degradation studies were carried out on GIP, N-acetyl-GIP (Ac-GIP) and N-pyroglutamyl-GIP (pGlu-GIP) in vitro following incubation with either dipeptidylpeptidase IV or human plasma. Cyclic adenosine 3'5' monophosphate (cAMP) production was assessed in Chinese hamster lung fibroblast cells transfected with the human GIP receptor. Insulin-releasing ability was assessed in vitro in BRIN-BD11 cells and in obese diabetic ( ob/ ob) mice.


RESULTS
GIP was rapidly degraded by dipeptidylpeptidase IV and plasma (t(1/2) 2.3 and 6.2 h, respectively) whereas Ac-GIP and pGlu-GIP remained intact even after 24 h. Both Ac-GIP and pGlu-GIP were extremely potent ( p<0.001) at stimulating cAMP production (EC(50) values 1.9 and 2.7 nmol/l, respectively), almost a tenfold increase compared to native GIP (18.2 nmol/l). Both Ac-GIP and pGlu-GIP (10(-13)-10(-8) mmol/l) were more potent at stimulating insulin release compared to the native GIP ( p<0.001), with 1.3-fold and 1.2-fold increases observed at 10(-8) mol/l, respectively. Administration of GIP analogues (25 nmol/kg body weight, i.p.) together with glucose (18 mmol/kg) in ( ob/ ob) mice lowered ( p<0.001) individual glucose values at 60 min together with the areas under the curve for glucose compared to native GIP. This antihyperglycaemic effect was coupled to a raised ( p<0.001) and more prolonged insulin response after administration of Ac-GIP and pGlu-GIP (AUC, 644+/-54 and 576+/-51 ng.ml(-1) x min, respectively) compared with native GIP (AUC, 257+/-29 ng.ml(-1) x min).


CONCLUSIONS
Ac-GIP and pGlu-GIP, show resistance to plasma dipeptidylpeptidase IV degradation, resulting in enhanced biological activity and improved antidiabetic potential in vivo, raising the possibility of their use in therapy of Type II (non-insulin-dependent) diabetes mellitus.
O'Harte
F P M
FP
School of Biomedical Sciences, University of Ulster, Coleraine, N. Ireland, UK. fpm.oharte@ulst.ac.uk
Gault
V A
VA
Parker
J C
JC
Harriott
P
P
Mooney
M H
MH
Bailey
C J
CJ
Flatt
P R
PR
D000107:Acetylation; D000818:Animals; D019540:Area Under Curve; D001711:Biotransformation; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D005347:Fibroblasts; D005749:Gastric Inhibitory Polypeptide / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D018698:Glutamic Acid; D006801:Humans; D007004:Hypoglycemic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D008168:Lung; D051379:Mice; D008820:Mice, Obese; D011964:Receptors, Gastrointestinal Hormone / Q000235:genetics / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D011964:Receptors, Gastrointestinal Hormone; D011994:Recombinant Proteins; D018698:Glutamic Acid; D005749:Gastric Inhibitory Polypeptide; C041086:gastric inhibitory polypeptide receptor; D000242:Cyclic AMP