Renal extraction and acute effects of glucagon-like peptide-1 on central and renal hemodynamics in healthy men.

The present experiments were performed to elucidate the acute effects of intravenous infusion of glucagon-like peptide (GLP)-1 on central and renal hemodynamics in healthy men. Seven healthy middle-aged men were examined on two different occasions in random order. During a 3-h infusion of either GLP-1 (1.5 pmol·kg⁻¹·min⁻¹) or saline, cardiac output was estimated noninvasively, and intraarterial blood pressure and heart rate were measured continuously. Renal plasma flow, glomerular filtration rate, and uptake/release of hormones and ions were measured by Fick's Principle after catheterization of a renal vein. Subjects remained supine during the experiments. During GLP-1 infusion, both systolic blood pressure and arterial pulse pressure increased by 5±1 mmHg (P=0.015 and P=0.002, respectively). Heart rate increased by 5±1 beats/min (P=0.005), and cardiac output increased by 18% (P=0.016). Renal plasma flow and glomerular filtration rate as well as the clearance of Na⁺ and Li⁺ were not affected by GLP-1. However, plasma renin activity decreased (P=0.037), whereas plasma levels of atrial natriuretic peptide were unaffected. Renal extraction of intact GLP-1 was 43% (P<0.001), whereas 60% of the primary metabolite GLP-1 9-36amide was extracted (P=0.017). In humans, an acute intravenous administration of GLP-1 leads to increased cardiac output due to a simultaneous increase in stroke volume and heart rate, whereas no effect on renal hemodynamics could be demonstrated despite significant extraction of both the intact hormone and its primary metabolite.

Pharmacokinetics, pharmacodynamics, and cytotoxicity of recombinant orally-administrated long-lasting GLP-1 and its therapeutic effect on db/db mice.

Recombinant orally long-acting glucagon-like peptide 1 (rolGLP-1), a novel analog of native GLP-1 that can stimulate insulin secretion, was constructed via site-directed mutagenesis by our laboratory. This study was designed to investigate the pharmacokinetics, pharmacodynamics, and the cytotoxicity of rolGLP-1. Diabetic db/db mice were given 125I-rolGLP-1 through a single dose of oral administration to evaluate the pharmacokinetics of rolGLP-1 by trichloroacetic acid-Radioactive assay (TCA-RA). Separately, rolGLP-1 was orally administered to the db/db mice daily for 28 days to evaluate its therapeutic effect. In addition, the safety of rolGLP-1 was assessed based on cytotoxicity testing on the cell line SH-SY5Y by both the MTT assay and the cell counts method. The results showed that the half-life of rolGLP-1 in db/db mice was 68.2 h, which is longer than that of native GLP-1. Results after the 28 day treatment showed glucose homeostasis was improved. Furthermore, rolGLP-1 was also proved to mitigate insulin resistance, alleviate hyperinsulinemia and decreased glycosylated hemoglobin content. Lastly, no visible adverse events were observed in cytotoxicity treatments on SH-SY5Y. Our results revealed that oral administration of rolGLP-1 harbored a longer half-life and a good therapeutic effect for type 2 db/db mice. All the results suggest the capacity and safety of rolGLP-1 for further use as an anti-diabetic agent for type 2 diabetes.This study was supported by Project 863 of China (2008AA02Z205).

Metabolism and excretion of the once-daily human glucagon-like peptide-1 analog liraglutide in healthy male subjects and its in vitro degradation by dipeptidyl peptidase IV and neutral endopeptidase.

Liraglutide is a novel once-daily human glucagon-like peptide (GLP)-1 analog in clinical use for the treatment of type 2 diabetes. To study metabolism and excretion of [(3)H]liraglutide, a single subcutaneous dose of 0.75 mg/14.2 MBq was given to healthy males. The recovered radioactivity in blood, urine, and feces was measured, and metabolites were profiled. In addition, [(3)H]liraglutide and [(3)H]GLP-1(7-37) were incubated in vitro with dipeptidyl peptidase-IV (DPP-IV) and neutral endopeptidase (NEP) to compare the metabolite profiles and characterize the degradation products of liraglutide. The exposure of radioactivity in plasma (area under the concentration-time curve from 2 to 24 h) was represented by liraglutide (≥89%) and two minor metabolites (totaling ≤11%). Similarly to GLP-1, liraglutide was cleaved in vitro by DPP-IV in the Ala8-Glu9 position of the N terminus and degraded by NEP into several metabolites. The chromatographic retention time of DPP-IV-truncated liraglutide correlated well with the primary human plasma metabolite [GLP-1(9-37)], and some of the NEP degradation products eluted very close to both plasma metabolites. Three minor metabolites totaling 6 and 5% of the administered radioactivity were excreted in urine and feces, respectively, but no liraglutide was detected. In conclusion, liraglutide is metabolized in vitro by DPP-IV and NEP in a manner similar to that of native GLP-1, although at a much slower rate. The metabolite profiles suggest that both DPP-IV and NEP are also involved in the in vivo degradation of liraglutide. The lack of intact liraglutide excreted in urine and feces and the low levels of metabolites in plasma indicate that liraglutide is completely degraded within the body.