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Title: Development and evaluation of novel CCK peptide analogues for the treatment of obesity and type II diabetes
Author: Frizelle, Pamela
ISNI:       0000 0004 2720 6068
Awarding Body: University of Ulster
Current Institution: Ulster University
Date of Award: 2010
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Cholecystokinin-8 (CCK-8) is an important gastrointestinal (GI) peptide that is released from endocrine I-cells in response to feeding. CCK-8 promotes satiety, reducing food intake via the CCK1 receptor. It is also responsible for initiating insulin release from pancreatic beta cells. The hypothesis underlying this thesis was that CCK-8 properties may be exploitable for treatment for obesity and type 11 diabetes. CCK-8 is rapidly released by feeding but has a half life of only 1-2 min because of rapid degradation by aminopeptidase A. In the present study, the aminopeptidase A inhibitor, bestatin was shown to prevent N-terminal degradation of CCK-8 in mouse plasma. Furthermore, novel N-terminally modified CCK-S analogues, such as aceylated(Ac)-CCK-8 and pyroglutamyl p(GluGln)-CCK-S, as well as analogues with secondary pegylated[PEG] and palmitate[PAL] modifications, resisted enzyme degradation. These results suggested that amino terminal protection prevented enzymatic breakdown, raising the possibility of prolonged satiety effects in vivo. Indeed, novel N-terminally modified analogues of CCK-8 reduced food intake for a prolonged time and to a greater extent than native CCK-8. Further to this, these analogues significantly increased insulin secretion from clonal pancreatic BRIN-BD11 cells compared to native CCK-8. Acute in vivo studies also showed that CCK-8 and related analogues reduced the plasma glucose excursion when administered with glucose in normal and obese diabetic (ob/ob) mice. Long term studies involving daily injections of the analogue, p(GluGln)CCK- S, in normal, high fat fed and obese diabetic (ob/ob) mice resulted in significant reduction of both food intake and body weight as well as enhanced glucose tolerance and improved insulin sensitivity. Furthermore, intermittent treatment of obese and high fat fed mice with p(GluGln)CCK-8 significantly decreased body weight and improved glucose tolerance. Secondary modifications of this CCK-8 analogue, whereby a PEGylated moiety was attached to the C-terminus to promote binding to plasma proteins and extend the half life, were also assessed in vivo. p(GluGln)CCK- 8[PEG] exerted similar beneficial effects as p(GluGln)CCK-8 but no superior actions were recorded, possibly due to the low doses of analogue administered. The long term effects of p(GluGln)CCK-8 were examined in combination with other peptide therapeutics known to enhance either the secretion or action of insulin. The combination of p(GluGln)CCK-8 with glucagons like peptide (GLP-l) mimetic exendin-4 produced significantly greater benefic ial effects than either peptide alone. In acute studies, this combination significantly improved glucose tolerance in normal and obese diabetic mice (ob/ob) and potently stimulated insulin secretion from clonal pancreatic BRIN-BDll cells. Daily administration of the combination p(GluGln)CCK-8 plus exendin-4 to high fat fed mice decreased food intake, reduced body weight, increased insulin sensitivity and enhanced glucose tolerance. In other experiments, the gastric inhibitory polypeptide (GIP) receptor antagonist, Pro3GIP[PEG] was administered daily in eqimolar doses with p(GluGln)CCK-8 in high fat fed mice. These mice exhibited reduced food intake, decreased body weight and marked improvements in glucose tolerance and insulin sensitivity. However, each peptide alone produced prominent effects with no appreciable additive effects being observed in combination. In conclusion, this thesis has provided evidence that N-terminal modification of CCK-8 confers enzyme resistance, prolonged action and enhanced biological effects in animal models of obesity-diabetes. The ability to decrease food intake, promote weight loss and improve glucose homeostasis suggests that novel analogues, such as p(GluGln)CCK-8, might be exploitable clinically alone or in combination for the treatment of obesity and type 11 diabetes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available