Glial-derived growth factor signaling pathway in infantile hypertrophic pyloric stenosis

BACKGROUND/PURPOSE: Glial-derived growth factor (GDNF), which is the ligand of RET is reported to be essential for the development of enteric nervous system. A GDNF knockout mouse model has shown that the gastric region is a critical passing site between GDNF-RET-independent neuroblasts (colonizing the esophagus) and GDNF-RET-dependent neuroblasts (colonizing the small and large bowel). The earliest GDNF site of production is the mesenchyme and the outer smooth muscle cell (SMC) layer of the developing bowel. In the mature gastrointestinal tract the presence of GDNF is restricted to enteric glial cells. The aim of this study was to investigate the expression of GDNF and RET in infantile hypertrophic pyloric stenosis (IHPS). METHODS: Full-thickness muscle biopsy specimens were obtained from 8 IHPS patients at pyloromyotomy and from 8 age-matched controls without gastrointestinal disease. Indirect immunohistochemistry was performed using avidin-biotin-peroxidase complex method with anti-GDNF and anti-RET antibodies. Quantitative analysis was performed using sandwich-type enzyme-linked immunosorbent assay (ELISA) for GDNF. RESULTS: GDNF- and RET-positive nerve fibers were absent or markedly reduced in IHPS compared with controls. GDNF was expressed strongly by smooth muscle cells of both muscular layers in IHPS, whereas no GDNF expression was detected in pyloric muscle of controls. The quantity of total GDNF in IHPS was significantly higher than in controls (P < .01). CONCLUSIONS: The lack or markedly decreased number of GDNF-positive nerve fibers in IHPS supports the hypothesis of a selective immaturity of the enteric glia in the muscular layers in IHPS. The strong expression of GDNF in smooth muscle cells in IHPS and the increased levels of GDNF in IHPS suggest a compensatory mechanism by which the smooth muscle cells continue to produce GDNF until maturation of the enteric glial cells occurs.     

In vitro metabolism of the calmodulin antagonist DY-9760e (3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate) by human liver microsomes: involvement of cytochromes p450 in atypical kinetics and potential drug interactions.

Human cytochrome P450 (P450) isozyme(s) responsible for metabolism of the calmodulin antagonist 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e) and kinetic profiles for formation of its six primary metabolites [M3, M5, M6, M7, M8, and DY-9836 (3-[2-[4-(3-chloro-2-methylphenyl)piperazinyl]ethyl]-5,6-dimethoxyindazole)] were identified using human liver microsomes and recombinant P450 enzymes. In vitro experiments, including an immunoinhibition study, correlation analysis, and reactions with recombinant P450 enzymes, revealed that CYP3A4 is the primary P450 isozyme responsible for the formation of the DY-9760e metabolites, except for M5, which is metabolized by CYP2C9. Additionally, at clinically relevant concentrations, CYP2C8 and 2C19 make some contribution to the formation of M3 and M5, respectively. The formation rates of DY-9760e metabolites except for M8 by human liver microsomes are not consistent with a Michaelis-Menten kinetics model, but are better described by a substrate inhibition model. In contrast, the enzyme kinetics for all metabolites formed by recombinant CYP3A4 can be described by an autoactivation model or a mixed model of autoactivation and biphasic kinetics. Inhibition of human P450 enzymes by DY-9760e in human liver microsomes was also investigated. DY-9760e is a very potent competitive inhibitor of CYP2C8, 2C9 and 2D6 (Ki 0.25-1.7 microM), a mixed competitive and noncompetitive inhibitor of CYP2C19 (Ki 2.4 microM) and a moderate inhibitor of CYP1A2 and 3A4 (Ki 11.4-20.1 microM), suggesting a high possibility for human drug-drug interaction.