Browsing by Person "O'Harte, Finbarr P. M."

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A stable analogue of glucose-dependent insulinotropic polypeptide, GIP(LysPAL16), enhances functional differentiation of mouse embryonic stem cells into cells expressing islet-specific genes and hormones
(De Gruyter, 2006-07) Marenah, Lamin; McCluskey, Jane T.; Abdel-Wahab, Yasser H.; O'Harte, Finbarr P. M.; McClenaghan, Neville H.; Flatt, Peter R.
Embryonic stem (ES) cells can be differentiated into insulin-producing cells by conditioning the culture media. However, the number of insulin-expressing cells and amount of insulin released is very low. Glucose-dependent insulinotropic polypeptide (GIP) enhances the growth and differentiation of pancreatic beta-cells. This study examined the potential of the stable analogue GIP(LysPAL16) to enhance the differentiation of mouse ES cells into insulin-producing cells using a five-stage culturing strategy. Semi-quantitative PCR indicated mRNA expression of islet development markers (nestin, Pdx1, Nkx6.1, Oct4), mature pancreatic beta-cell markers (insulin, glucagon, Glut2, Sur1, Kir6.1) and the GIP receptor gene GIP-R in undifferentiated (stage 1) cells, with increasing levels in differentiated stages 4 and 5. IAPP and somatostatin genes were only expressed in differentiated stages. Immunohistochemical studies confirmed the presence of insulin, glucagon, somatostatin and IAPP in differentiated ES cells. After supplementation with GIP(LysPAL16), ES cells at stage 4 released insulin in response to secretagogues and glucose in a concentration-dependent manner, with 35-100% increases in insulin release. Cellular C-peptide content also increased by 45% at stages 4 and 5. We conclude that the stable GIP analogue enhanced differentiation of mouse ES cells towards a phenotype expressing specific beta-cell genes and releasing insulin.
Demonstration of glycated insulin in human diabetic plasma and decreased biological activity assessed by euglycemic-hyperinsulinemic clamp technique in humans.
(American Diabetes Association, 2003-02) Hunter, Steven J.; Boyd, Alison C.; O'Harte, Finbarr P. M.; McKillop, Aine M.; Wiggam, M. Ivan; Mooney, Mark H.; McCluskey, Jane T.; Lindsay, John R.; Ennis, Cieran N.; Gamble, Raymond; Sheridan, Brian; Barnett, Christopher R.; McNulty, Helene; Bell, Patrick M.; Flatt, Peter R.
The presence and biological significance of circulating glycated insulin has been evaluated by high-pressure liquid chromatography (HPLC), electrospray ionization mass spectrometry (ESI-MS), radioimmunoassay (RIA), receptor binding, and hyperinsulinemic-euglycemic clamp techniques. ESI-MS analysis of an HPLC-purified plasma pool from four male type 2 diabetic subjects (HbA(1c) 8.1 +/- 0.2%, plasma glucose 8.7 +/- 1.3 mmol/l [means +/- SE]) revealed two major insulin-like peaks with retention times of 14-16 min. After spectral averaging, the peak with retention time of 14.32 min exhibited a prominent triply charged (M+3H)(3+) species at 1,991.1 m/z, representing monoglycated insulin with an intact M(r) of 5,970.3 Da. The second peak (retention time 15.70 min) corresponded to native insulin (M(r) 5,807.6 Da), with the difference between the two peptides (162.7 Da) representing a single glucitol adduct (theoretical 164 Da). Measurement of glycated insulin in plasma of type 2 diabetic subjects by specific RIA gave circulating levels of 10.1 +/- 2.3 pmol/l, corresponding to approximately 9% total insulin. Biological activity of pure synthetic monoglycated insulin (insulin B-chain Phe(1)-glucitol adduct) was evaluated in seven overnight-fasted healthy nonobese male volunteers using two-step euglycemic-hyperinsulinemic clamps (2 h at 16.6 micro g x kg(-1) x min(-1), followed by 2 h at 83.0 micro g x kg(-1) x min(-1); corresponding to 0.4 and 2.0 mU x kg(-1) x min(-1)). At the lower dose, the exogenous glucose infusion rates required to maintain euglycemia during steady state were significantly lower with glycated insulin (P < 0.01) and approximately 70% more glycated insulin was required to induce a similar rate of insulin-mediated glucose uptake. Maximal responses at the higher rates of infusion were similar for glycated and control insulin. Inhibitory effects on endogenous glucose production, insulin secretion, and lipolysis, as indicated by measurements of C-peptide, nonesterified free fatty acids, and glycerol, were also similar. Receptor binding to CHO-T cells transfected with human insulin receptor and in vivo metabolic clearance revealed no differences between glycated and native insulin, suggesting that impaired biological activity is due to a postreceptor effect. The present demonstration of glycated insulin in human plasma and related impairment of physiological insulin-mediated glucose uptake suggests a role for glycated insulin in glucose toxicity and impaired insulin action in type 2 diabetes.