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      Selecting GLP-1 agonists in the management of type 2 diabetes: differential pharmacology and therapeutic benefits of liraglutide and exenatide

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          Abstract

          Failure of secretion of the incretin hormone glucagon-like peptide-1 (GLP-1) plays a prominent role in type 2 diabetes, and restoration of GLP-1 action is an important therapeutic objective. Although the short duration of action of GLP-1 renders it unsuited to therapeutic use, 2 long-acting GLP-1 receptor agonists, exenatide and liraglutide, represent a significant advance in treatment. In controlled trials, both produce short-term glucose-lowering effects, with the reduction in hemoglobin A 1c of up to 1.3%. These responses are often superior to those observed with additional oral agents. However, unlike sulfonylureas, thiazolidinediones, or insulin, all of which lead to significant weight gain, GLP-1 receptor agonists uniquely result in long-term weight loss of around 5 kg, and higher doses may enhance this further. Reduction in blood pressure of 2–7 mm Hg also has been observed. Both drugs produce transient mild gastrointestinal side effects; although mild hypoglycemia can occur, this is usually in combination with other hypoglycemic therapies. However, serious hypoglycemia and acute pancreatitis are rare. The once-daily dosage of liraglutide makes it more convenient than twice-daily dosage of prandial exenatide, and a superior glucose-lowering effect was observed in the only head-to-head comparison reported so far. Besides cost, these considerations currently favor liraglutide over exenatide. Further studies are needed to confirm long-term safety, and most importantly, that short-term benefits translate into long-term reductions of diabetes-related cardiovascular events and other complications.

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          Most cited references 3

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          Actions of glucagon-like peptide-1 on KATP channel-dependent and -independent effects of glucose, sulphonylureas and nateglinide.

          This study examined the effects of glucagon-like peptide-1 (GLP-1) on insulin secretion alone and in combination with sulphonylureas or nateglinide, with particular attention to K(ATP) channel-independent insulin secretion. In depolarised cells, GLP-1 significantly augmented glucose-induced K(ATP) channel-independent insulin secretion in a glucose concentration-dependent manner. GLP-1 similarly augmented the K(ATP) channel-independent insulin-releasing effects of tolbutamide, glibenclamide or nateglinide. Downregulation of protein kinase A (PKA)- or protein kinase C (PKC)-signalling pathways in culture revealed that the K(ATP) channel-independent effects of sulphonylureas or nateglinide were critically dependent upon intact PKA and PKC signalling. In contrast, GLP-1 exhibited a reduced but still significant insulin-releasing effect following PKA and PKC downregulation, indicating that GLP-1 can modulate K(ATP) channel-independent insulin secretion by protein kinase-dependent and -independent mechanisms. The synergistic insulin-releasing effects of combinatorial GLP-1 and sulphonylurea/nateglinide were lost following PKA- or PKC-desensitisation, despite GLP-1 retaining an insulin-releasing effect, demonstrating that GLP-1 can induce insulin release under conditions where sulphonylureas and nateglinide are no longer effective. Our results provide new insights into the mechanisms of action of GLP-1, and further highlight the promise of GLP-1 or similarly acting analogues alone or in combination with sulphonylureas or meglitinide drugs in type 2 diabetes therapy.
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            Influence of initial hyperglycaemia, weight and age on the blood glucose lowering efficacy and incidence of hypoglycaemic symptoms with a single-tablet metformin-glibenclamide therapy (Glucovance) in type 2 diabetes.

            To evaluate the efficacy and incidence of hypoglycaemic symptoms associated with fixed combinations of metformin and glibenclamide (glyburide in the USA) formulated within a single tablet (tablet strengths 250 mg/1.25 mg, 500 mg/2.5 mg and 500 mg/5 mg), in comparison with metformin 500 mg and glibenclamide 2.5-5 mg monotherapy, in clinically important patient subgroups within the type 2 diabetic population. A total of 1856 patients from three randomized, double-blind, multicentre, parallel-group clinical trials were stratified at baseline according to HbA1C ( or = 8%), age ( or = 65 years) and body mass index (BMI; or = 28 kg/m2). The effects of study treatments on HbA1C and the incidence of hypoglycaemic symptoms were determined in each subgroup. The combination treatments were more effective than either monotherapy irrespective of baseline HbA1C, age or BMI in each trial. Antihyperglycaemic effects were greater in patients with HbA1C > or = 8% at baseline, especially with the combinations. The majority of hypoglycaemic symptoms with glibenclamide-containing treatments occurred in patients with HbA1C < 8% at baseline. Neither age nor BMI had a marked effect on the efficacy of the combination treatments, and there was no increase in hypoglycaemic symptoms in older patients. Single-tablet metformin-glibenclamide combination treatment is more effective than metformin or glibenclamide monotherapy, and is well tolerated in patients with hyperglycaemia inadequately controlled by diet and exercise or antidiabetic monotherapy, irrespective of their severity of hyperglycaemia at baseline, age or weight.
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              Human glucagon gene promoter sequences regulating tissue-specific versus nutrient-regulated gene expression.

              The glucagon-like peptides (GLPs) are synthesized and secreted in a nutrient-dependent manner in rodents; however, the factors regulating human GLP-1 and GLP-2 biosynthesis remain unclear. To understand how nutrients regulate human proglucagon gene expression, we studied the expression of a human proglucagon promoter-growth hormone (GH) transgene in 1.6 human glucagon-GH transgenic mice. Fasting-refeeding significantly decreased and increased the levels of circulating mouse insulin and transgene-derived hGH (P < 0.05 fasting vs. refeeding) and decreased and upregulated, respectively, the levels of endogenous mouse proglucagon RNA in the ileum but not in the jejunum or colon. High-fiber feeding significantly increased the levels of glucose-stimulated circulating hGH and upregulated levels of mouse intestinal proglucagon gene expression in the jejunum, ileum, and colon (P < 0.05, 0 vs. 30% fiber diet). In contrast, neither fasting-refeeding nor a high-fiber diet upregulated the expression of the human proglucagon promoter-hGH transgene. These findings demonstrate that human proglucagon gene regulatory sequences specifying tissue-specific expression in gut endocrine cells are not sufficient for recognition of energy-derived signals regulating murine glucagon gene expression in enteroendocrine cells in vivo.
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                Author and article information

                Journal
                Ther Clin Risk Manag
                Therapeutics and Clinical Risk Management
                Therapeutics and Clinical Risk Management
                Dove Medical Press
                1176-6336
                1178-203X
                2010
                2010
                7 September 2010
                : 6
                : 401-411
                Affiliations
                [1 ]Department of Diabetes and Endocrinology, Peninsula College of Medicine and Dentistry, Plymouth, United Kingdom;
                [2 ]Department of Clinical Biochemistry and Metabolic Medicine, Royal Liverpool University Hospital, Liverpool, United Kingdom
                Author notes
                Correspondence: Jonathan Pinkney, Department of Diabetes and Endocrinology, Peninsula College of Medicine and Dentistry, University Medicine, Level 7 Derriford Hospital, Plymouth Hospitals NHS Trust, Crownhill, Plymouth PL8 6DH, United Kingdom, Tel +44-1752793498, Email jonathan.pinkney@ 123456pms.ac.uk
                Article
                tcrm-6-401
                2940748
                20856686
                © 2010 Pinkney et al, publisher and licensee Dove Medical Press Ltd.

                This is an Open Access article which permits unrestricted noncommercial use, provided the original work is properly cited.

                Categories
                Review

                Medicine

                weight loss, diabetes, glycemic control, blood pressure

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