Inhibition of Insulin Degrading Enzyme by Racecadotril in the Brain of Wistar Rats

Abstract

Racecadotril is an enkephalinase inhibitor used to treat abdominal discomfort in the clinic. The blood-glucose lowering action of racecadotril has been observed in rats; however, the mechanisms remain obscure. 8-week-old Wistar rats were intravenously injected with racecadotril and the levels of insulin in the brain were measured. Additionally, brain homogenates were co-incubated with racecadotril or thiorphan to evaluate insulin degrading enzyme (IDE) activity. Otherwise, rats were pretreated by intracerebroventricular (i. c. v.) injection of insulin antibody or glibenclamide at a dose sufficient to inhibit K_ATP channels prior to injection of racecadotril. Moreover, rats were vagotomized to evaluate the role of the cholinergic nerve. Racecadotril significantly decreased the plasma glucose in rats; this action of racecadotril was abolished by i. c. v. pretreatment with insulin antibody or glibenclamide. Also, i. c. v. injection of thiorphan, the active form of racecadotril, lowered blood glucose, but this effect disappeared in the presence of the insulin antibody. In rat brain homogenates, racecadotril and thiorphan inhibited IDE activity and increased the cerebral insulin level. The blood-glucose lowering action of racecadotril or thiorphan was diminished in vagotomized rats. Our results suggest that racecadotril lowers blood glucose mainly through inhibition of IDE activity and increases endogenous insulin in the brain. Subsequently, the increased insulin might activate insulin receptor, which opens the K_ATP channel and induces peripheral insulin release through the vagal nerve. Thus, we provide the new finding that racecadotril has the ability to inhibit IDE in rat brain.

Key words

blood glucose - cerebral insulin - K_ATP channels - rececadotril - thiorphan

References

• 1 Matheson AJ, Noble S. Racecadotril.  Drugs. 2000;  59 829-835 Discussion 827–836
• 2 Xu Y, Huang J, Liu F, Gao S, Guo Q. Quantitative analysis of racecadotril metabolite in human plasma using a liquid chromatography/tandem mass spectrometry.  J Chromatogr B Analyt Technol Biomed Life Sci. 2007;  852 101-107
• 3 Xu F, Yang L, Xu G. A rapid and validated HPLC method to quantify racecadotril metabolite, thiorphan, in human plasma using solid-phase extraction.  J Chromatogra B Analyt Technol Biomed Life Sci. 2008;  861 130-135
• 4 Nagpal J, Gogia S. Racecadotril.  Indian Pediatr. 2004;  41 1218-1224
• 5 Rougeot C, Messaoudi M, Hermitte V, Rigault AG, Blisnick T, Dugave C, Desor D, Rougeon F. Sialorphin, a natural inhibitor of rat membrane-bound neutral endopeptidase that displays analgesic activity.  Proc Natl Acad Sci USA. 2003;  100 8549-8554
• 6 Pasternak GW. Multiple morphine and enkephalin receptors: biochemical and pharmacological aspects.  Ann NY Acad Sci. 1986;  467 130-139
• 7 Evans AA, Tunnicliffe G, Knights P, Bailey CJ, Smith ME. Delta opioid receptors mediate glucose uptake in skeletal muscles of lean and obese-diabetic (ob/ob) mice.  Metabolism. 2001;  50 1402-1408
• 8 Liu IM, Liou SS, Chen WC, Chen PF, Cheng JT. Signals in the activation of opioid mu-receptors by loperamide to enhance glucose uptake into cultured C2C12 cells.  Horm Metab Res. 2004;  36 210-214
• 9 Wu HT, Chang CK, Cheng KC, Chang CH, Yeh CH, Cheng JT. Increase of plasma insulin by racecadotril, an inhibitor of enkephalinase, in Wistar rats.  Horm Metab Res. 2010;  42 261-267
• 10 Gerozissis K. Brain insulin, energy and glucose homeostasis; genes, environment and metabolic pathologies.  Eur J Pharmacol. 2008;  585 38-49
• 11 Koch L, Wunderlich FT, Seibler J, Könner AC, Hampel B, Irlenbusch S, Brabant G, Kahn CR, Schwenk F, Brüning JC. Central insulin action regulates peripheral glucose and fat metabolism in mice.  J Clin Invest. 2008;  118 2132-2147
• 12 Pocai A, Lam TK, Gutierrez-Juarez R, Obici S, Schwartz GJ, Bryan J, Aguilar-Bryan L, Rossetti L. Hypothalamic K(ATP) channels control hepatic glucose production.  Nature. 2005;  434 1026-1031
• 13 Yang TT, Ling SM, Tsao CW, Cheng JT. Opening of ATP-sensitive potassium channel by insulin in the brain-induced insulin secretion in Wistar rats.  Horm Metab Res. 2010;  42 110-114
• 14 Chang CH, Tsao CW, Huang SY, Cheng JT. Activation of imidazoline I(2B) receptors by guanidine to increase glucose uptake in skeletal muscle of rats.  Neurosci Lett. 2009;  467 147-149
• 15 Ko WC, Liu IM, Chung HH, Cheng JT. Activation of I(2)-imidazoline receptors may ameliorate insulin resistance in fructose-rich chow-fed rats.  Neurosci Lett. 2008;  448 90-93
• 16 Hamel FG, Bennett RG, Duckworth WC. Regulation of multicatalytic enzyme activity by insulin and the insulin-degrading enzyme.  Endocrinology. 1998;  139 4061-4066
• 17 Norgren R, Smith GP. Central distribution of subdiaphragmatic vagal branches in the rat.  J Comp Neurol. 1988;  273 207-223
• 18 Chipkin RE, Kreutner W, Billard W. Potentiation of the hypoglycemic effect of insulin by thiorphan, an enkephalinase inhibitor.  Eur J Pharmacol. 1984;  102 151-154
• 19 Gerozissis K. Brain insulin and feeding: a bi-directional communication.  Eur J Pharmacol. 2004;  490 59-70
• 20 Gerozissis K. Brain insulin: regulation, mechanisms of action and functions.  Cell Mol Neurobiol. 2003;  23 1-25
• 21 Plum L, Belgardt BF, Bruning JC. Central insulin action in energy and glucose homeostasis.  J Clin Invest. 2006;  116 1761-1766
• 22 Obici S, Zhang BB, Karkanias G, Rossetti L. Hypothalamic insulin signaling is required for inhibition of glucose production.  Nat Med. 2002;  8 1376-1382
• 23 Prodi E, Obici S. Minireview: the brain as a molecular target for diabetic therapy.  Endocrinology. 2006;  147 2664-2669
• 24 Spillantini MG, Geppetti P, Fanciullacci M, Michelacci S, Lecomte JM, Sicuteri F. In vivo ‘enkephalinase’ inhibition by acetorphan in human plasma and CSF.  Eur J Pharmacol. 1986;  125 147-150
• 25 Lecomte JM, Costentin J, Vlaiculescu A, Chaillet P, Marcais-Collado H, Llorens-Cortes C, Leboyer M, Schwartz JC. Pharmacological properties of acetorphan, a parenterally active “enkephalinase” inhibitor.  J Pharmacol Exp Ther. 1986;  237 937-944
• 26 Giros B, Gros C, Schwartz JC, Danvy D, Plaquevent JC, Duhamel L, Duhamel P, Vlaiculescu A, Costentin J, Lecomte JM. Enantiomers of thiorphan and acetorphan: correlation between enkephalinase inhibition, protection of endogenous enkephalins and behavioral effects.  J Pharmacol Exp Ther. 1987;  243 666-673
• 27 Hisamitsu T, de Groat WC. The inhibitory effect of opioid peptides and morphine applied intrathecally and intracerebroventricularly on the micturition reflex in the cat.  Brain Res. 1984;  298 51-65
• 28 Manolopoulou M, Guo Q, Malito E, Schilling AB, Tang WJ. Molecular basis of catalytic chamber-assisted unfolding and cleavage of human insulin by human insulin-degrading enzyme.  J Biol Chem. 2009;  284 14177-14188
• 29 Duckworth WC, Bennett RG, Hamel FG. Insulin degradation: progress and potential.  Endocr Rev. 1998;  19 608-624
• 30 Taylor CA, Varandani PT. Insulin degradation. XXVIII. Immunocytochemical localization of glutathione-insulin transhydrogenase in the pancreas, kidney and liver of normal and streptozotocin-diabetic rats and of lean and obese (ob/ob) mice.  Diabetologia. 1981;  21 464-469
• 31 Farris W, Mansourian S, Chang Y, Lindsley L, Eckman EA, Frosch MP, Eckman CB, Tanzi RE, Selkoe DJ, Guenette S. Insulin-degrading enzyme regulates the levels of insulin, amyloid beta-protein, and the beta-amyloid precursor protein intracellular domain in vivo.  Proc Natl Acad Sci USA. 2003;  100 4162-4167
• 32 Edland SD. Insulin-degrading enzyme, apolipoprotein E, and Alzheimer's disease.  J Mol Neurosci. 2004;  23 213-217
• 33 Erdos EG, Skidgel RA. Neutral endopeptidase 24.11 (enkephalinase) and related regulators of peptide hormones.  FASEB J. 1989;  3 145-151
• 34 Qiu WQ, Folstein MF. Insulin, insulin-degrading enzyme and amyloid-beta peptide in Alzheimer's disease: review and hypothesis.  Neurobiol Aging. 2006;  27 190-198
• 35 Mouri A, Zou LB, Iwata N, Saido TC, Wang D, Wang MW, Noda Y, Nabeshima T. Inhibition of neprilysin by thiorphan (I. c. v.) causes an accumulation of amyloid beta and impairment of learning and memory.  Behav Brain Res. 2006;  168 83-91
• 36 Nonogaki K. New insights into sympathetic regulation of glucose and fat metabolism.  Diabetologia. 2000;  43 533-549
• 37 Teff KL. Visceral nerves: vagal and sympathetic innervation.  JPEN J Parenter Enteral Nutr. 2008;  32 569-571
• 38 Matsuhisa M, Yamasaki Y, Shiba Y, Nakahara I, Kuroda A, Tomita T, Iida M, Ikeda M, Kajimoto Y, Kubota M, Hori M. Important role of the hepatic vagus nerve in glucose uptake and production by the liver.  Metabolism. 2000;  49 11-16

Correspondence