Actions of a Recombinant GLP-1 Albumin Protein
Actions of a Recombinant GLP-1 Albumin Protein
Peptide hormones exert unique actions via specific G protein-coupled receptors; however, the therapeutic potential of regulatory peptides is frequently compromised by rapid enzymatic inactivation and clearance from the circulation. In contrast, recombinant or covalent coupling of smaller peptides to serum albumin represents an emerging strategy for extending the circulating t1/2 of the target peptide. However, whether larger peptide-albumin derivatives will exhibit the full spectrum of biological activities encompassed by the native peptide remains to be demonstrated. We report that Albugon, a human glucagon-like peptide (GLP)-1-albumin recombinant protein, activates GLP-1 receptor (GLP-1R)-dependent cAMP formation in BHK-GLP-1R cells, albeit with a reduced half-maximal concentration (EC50) (0.2 vs. 20 nmol/l) relative to the GLP-1R agonist exendin-4. Albugon decreased glycemic excursion and stimulated insulin secretion in wild-type but not GLP-1R mice and reduced food intake after both intracerebroventricular and intraperitoneal administration. Moreover, intraperitoneal injection of Albugon inhibited gastric emptying and activated c-FOS expression in the area postrema, the nucleus of the solitary tract, the central nucleus of the amygdala, the parabrachial, and the paraventricular nuclei. These findings illustrate that peripheral administration of a larger peptide-albumin recombinant protein mimics GLP-1R-dependent activation of central and peripheral pathways regulating energy intake and glucose homeostasis in vivo.
Glucagon-like peptide (GLP)-1 is a 30-amino acid peptide hormone secreted from gut endocrine cells in response to nutrient ingestion that promotes nutrient assimilation through regulation of gastrointestinal motility and islet hormone secretion. Infusion of GLP-1 into normal or diabetic human subjects stimulates insulin and inhibits glucagon secretion, thereby indirectly modulating peripheral glucose uptake and control of hepatic glucose production. GLP-1 also produces anorectic effects, and short-term infusion of GLP-1 is associated with diminished appetite and reduced energy consumption in normal, obese, and diabetic human subjects. Taken together, the actions of GLP-1 to reduce glycemia while preventing concomitant weight gain have attracted considerable interest in pharmaceutical approaches to enhancing GLP-1 action for the treatment of type 2 diabetes.
A major challenge for the therapeutic use of regulatory peptides, including native GLP-1, is a short circulating t1/2, due principally to rapid enzymatic inactivation and/or renal clearance. Although infusion of native GLP-1 is highly effective in lowering blood glucose in subjects with type 2 diabetes, a single subcutaneous injection of the native peptide is quickly degraded and disappears from the circulation within minutes. Hence, the majority of pharmaceutical approaches to the development of GLP-1 mimetic agents have focused on the development of long-acting degradation-resistant peptides. The naturally occurring lizard salivary gland peptide exendin-4 (Ex-4) is a potent GLP-1 receptor (GLP-1R) agonist and exhibits therapeutic efficacy in studies of patients with type 2 diabetes. Similarly, a fatty acylated human GLP-1 analog, liraglutide, exhibits a more sustained duration of action and potently reduces glycemic excursion in diabetic subjects.
Although degradation-resistant GLP-1R agonists appear to be promising agents for the treatment of diabetes, the need for once- or twice-daily injection of these peptides has fostered complementary efforts directed at identification of more potent longer-acting agents with sustained efficacy in vivo. Given the long circulating t1/2 of albumin-linked drugs, a GLP-1-albumin protein should exhibit a much more prolonged circulating t1/2 and hence requires a reduced frequency of parenteral administration, relative to native GLP-1. Nevertheless, the molecular interaction with the GLP-1R, volume of distribution, and access to the central nervous system (CNS) would be predicted to be markedly different for a much larger albumin-based molecule.
Whether all of the desirable actions of native GLP-1, including the activation of the CNS centers regulating food intake and gastrointestinal motility, would be mimicked by a much larger GLP-1-albumin protein is currently unclear. Accordingly, we have examined the biological actions of Albugon, a recombinant GLP-1-human serum albumin (HSA) fusion protein, using a combination of cell line studies in vitro and both wild-type and GLP-1R mice in vivo.
Peptide hormones exert unique actions via specific G protein-coupled receptors; however, the therapeutic potential of regulatory peptides is frequently compromised by rapid enzymatic inactivation and clearance from the circulation. In contrast, recombinant or covalent coupling of smaller peptides to serum albumin represents an emerging strategy for extending the circulating t1/2 of the target peptide. However, whether larger peptide-albumin derivatives will exhibit the full spectrum of biological activities encompassed by the native peptide remains to be demonstrated. We report that Albugon, a human glucagon-like peptide (GLP)-1-albumin recombinant protein, activates GLP-1 receptor (GLP-1R)-dependent cAMP formation in BHK-GLP-1R cells, albeit with a reduced half-maximal concentration (EC50) (0.2 vs. 20 nmol/l) relative to the GLP-1R agonist exendin-4. Albugon decreased glycemic excursion and stimulated insulin secretion in wild-type but not GLP-1R mice and reduced food intake after both intracerebroventricular and intraperitoneal administration. Moreover, intraperitoneal injection of Albugon inhibited gastric emptying and activated c-FOS expression in the area postrema, the nucleus of the solitary tract, the central nucleus of the amygdala, the parabrachial, and the paraventricular nuclei. These findings illustrate that peripheral administration of a larger peptide-albumin recombinant protein mimics GLP-1R-dependent activation of central and peripheral pathways regulating energy intake and glucose homeostasis in vivo.
Glucagon-like peptide (GLP)-1 is a 30-amino acid peptide hormone secreted from gut endocrine cells in response to nutrient ingestion that promotes nutrient assimilation through regulation of gastrointestinal motility and islet hormone secretion. Infusion of GLP-1 into normal or diabetic human subjects stimulates insulin and inhibits glucagon secretion, thereby indirectly modulating peripheral glucose uptake and control of hepatic glucose production. GLP-1 also produces anorectic effects, and short-term infusion of GLP-1 is associated with diminished appetite and reduced energy consumption in normal, obese, and diabetic human subjects. Taken together, the actions of GLP-1 to reduce glycemia while preventing concomitant weight gain have attracted considerable interest in pharmaceutical approaches to enhancing GLP-1 action for the treatment of type 2 diabetes.
A major challenge for the therapeutic use of regulatory peptides, including native GLP-1, is a short circulating t1/2, due principally to rapid enzymatic inactivation and/or renal clearance. Although infusion of native GLP-1 is highly effective in lowering blood glucose in subjects with type 2 diabetes, a single subcutaneous injection of the native peptide is quickly degraded and disappears from the circulation within minutes. Hence, the majority of pharmaceutical approaches to the development of GLP-1 mimetic agents have focused on the development of long-acting degradation-resistant peptides. The naturally occurring lizard salivary gland peptide exendin-4 (Ex-4) is a potent GLP-1 receptor (GLP-1R) agonist and exhibits therapeutic efficacy in studies of patients with type 2 diabetes. Similarly, a fatty acylated human GLP-1 analog, liraglutide, exhibits a more sustained duration of action and potently reduces glycemic excursion in diabetic subjects.
Although degradation-resistant GLP-1R agonists appear to be promising agents for the treatment of diabetes, the need for once- or twice-daily injection of these peptides has fostered complementary efforts directed at identification of more potent longer-acting agents with sustained efficacy in vivo. Given the long circulating t1/2 of albumin-linked drugs, a GLP-1-albumin protein should exhibit a much more prolonged circulating t1/2 and hence requires a reduced frequency of parenteral administration, relative to native GLP-1. Nevertheless, the molecular interaction with the GLP-1R, volume of distribution, and access to the central nervous system (CNS) would be predicted to be markedly different for a much larger albumin-based molecule.
Whether all of the desirable actions of native GLP-1, including the activation of the CNS centers regulating food intake and gastrointestinal motility, would be mimicked by a much larger GLP-1-albumin protein is currently unclear. Accordingly, we have examined the biological actions of Albugon, a recombinant GLP-1-human serum albumin (HSA) fusion protein, using a combination of cell line studies in vitro and both wild-type and GLP-1R mice in vivo.
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