Gary J. Stoltz

Heme Oxygenase-1 Protects Interstitial Cells of Cajal from Oxidative Stress and Reverses Diabetic Gastroparesis

BACKGROUND & AIMS Diabetic gastroparesis (delayed gastric emptying) is a well-recognized complication of diabetes that causes considerable morbidity and makes glucose control difficult. Interstitial cells of Cajal, which express the receptor tyrosine kinase Kit, are required for normal gastric emptying. We proposed that Kit expression is lost during diabetic gastroparesis due to increased levels of oxidative stress caused by low levels of heme oxygenase-1 (HO-1), an important cytoprotective molecule against oxidative injury. METHODS Gastric emptying was measured in nonobese diabetic mice and correlated with levels of HO-1 expression and activity. Endogenous HO-1 activity was increased by administration of hemin and inhibited by chromium mesoporphyrin. RESULTS In early stages of diabetes, HO-1 was up-regulated in gastric macrophages and remained up-regulated in all mice that were resistant to development of delayed gastric emptying. In contrast, HO-1 did not remain up-regulated in all the mice that developed delayed gastric emptying; expression of Kit and neuronal nitric oxide synthase decreased markedly in these mice. Loss of HO-1 up-regulation increased levels of reactive oxygen species. Induction of HO-1 by hemin decreased reactive oxygen species, rapidly restored Kit and neuronal nitric oxide synthase expression, and completely normalized gastric emptying in all mice. Inhibition of HO-1 activity in mice with normal gastric emptying caused a loss of Kit expression and development of diabetic gastroparesis. CONCLUSIONS Induction of the HO-1 pathway prevents and reverses cellular changes that lead to development of gastrointestinal complications of diabetes. Reagents that induce this pathway might therefore be developed as therapeutics.

CD206-Positive M2 Macrophages That Express Heme Oxygenase-1 Protect Against Diabetic Gastroparesis in Mice

BACKGROUND & AIMS Gastroparesis is a well-recognized complication of diabetes. In diabetics, up-regulation of heme oxygenase-1 (HO1) in gastric macrophages protects against oxidative stress-induced damage. Loss of up-regulation of HO1, the subsequent increase in oxidative stress, and loss of Kit delays gastric emptying; this effect is reversed by induction of HO1. Macrophages have pro- and anti-inflammatory activities, depending on their phenotype. We investigated the number and phenotype of gastric macrophages in NOD/ShiLtJ (nonobese diabetic [NOD]) mice after onset of diabetes, when delayed gastric emptying develops, and after induction of HO1 to reverse delay. METHODS Four groups of NOD and db/db mice were studied: nondiabetic, diabetic with normal emptying, diabetic with delayed gastric emptying, and diabetic with delayed gastric emptying reversed by the HO1 inducer hemin. Whole mount samples from stomach were labeled in triplicate with antisera against F4/80, HO1, and CD206, and macrophages were quantified in stacked confocal images. Markers for macrophage subtypes were measured by quantitative polymerase chain reaction. RESULTS Development of diabetes was associated with an increased number of macrophages and up-regulation of HO1 in CD206(+) M2 macrophages. Onset of delayed gastric emptying did not alter the total number of macrophages, but there was a selective loss of CD206(+)/HO1(+) M2 macrophages. Normalization of gastric emptying was associated with repopulation of CD206(+)/HO1(+) M2 macrophages. CONCLUSIONS CD206(+) M2 macrophages that express HO1 appear to be required for prevention of diabetes-induced delayed gastric emptying. Induction of HO1 in macrophages might be a therapeutic option for patients with diabetic gastroparesis.

Production of the gaseous signal molecule hydrogen sulfide in mouse tissues

The gaseous molecule hydrogen sulfide (H2S) has been proposed as an endogenous signal molecule and neuromodulator in mammals. Using a newly developed method, we report here for the first time the ability of intact and living brain and colonic tissue in the mouse to generate and release H2S. This production occurs through the activity of two enzymes, cystathionine‐γ‐lyase and cystathionine‐β‐synthase. The quantitative expression of messenger RNA and protein localization for both enzymes are described in the liver, brain, and colon. Expression levels of the enzymes vary between tissues and are differentially distributed. The observation that, tissues that respond to exogenously applied H2S can endogenously generate the gas, strongly supports its role as an endogenous signal molecule.

Ano1, a Ca2+‐activated Cl− channel, coordinates contractility in mouse intestine by Ca2+ transient coordination between interstitial cells of Cajal

Ano1, a Ca2+‐activated Cl− channel, is expressed in interstitial cells of Cajal (ICC) throughout the gut. We report here that it is required to maintain coordinated Ca2+ transients within myenteric ICC of mouse small intestine. Ca2+ transients in Ano1 WT mice were rhythmic and coordinated whereas uncoordinated Ca2+ transients were seen in knockout mice. Ca2+ transients were un‐coordinated following pharmacological block of Ano1 in WT mice using niflumic acid, 5‐nitro‐2‐(3‐phenylpropylamino) benzoic acid and 4,4′‐diisothiocyanato‐2,2′‐stilbenedisulfonic acid disodium salt. Transient knockdown of Ano1 in organotypic cultures with short hairpin RNA to Ano1 in WT tissues also caused loss of coordinated Ca2+ transients. Contractility of Ano1 knockout mouse intestinal segments in organ bath experiments was significantly decreased, less coordinated and non‐rhythmic. Spatiotemporal maps from knockout mouse small intestine also showed loss of phasic contractile activity. This study provides important information on the basic mechanisms driving coordinated contractile activity in the gastrointestinal tract.

Endoscopic full-thickness biopsy of the gastric wall with defect closure by using an endoscopic suturing device: survival porcine study

BACKGROUND The pathogenesis of several common gastric motility diseases and functional GI disorders remains essentially unexplained. Gastric wall biopsies that include the muscularis propria to evaluate the enteric nervous system, interstitial cells of Cajal, and immune cells can provide important insights for our understanding of the etiology of these disorders. OBJECTIVES To determine the technical feasibility, reproducibility, and safety of performing a full-thickness gastric biopsy (FTGB) by using a submucosal endoscopy with mucosal flap (SEMF) technique; the technical feasibility, reproducibility, and safety of tissue closure by using an endoscopic suturing device; the ability to identify myenteric ganglia in resected specimens; and the long-term safety. DESIGN Single center, preclinical survival study. SETTING Animal research laboratory, developmental endoscopy unit. SUBJECTS Twelve domestic pigs. INTERVENTIONS Animals underwent an SEMF procedure with gastric muscularis propria resection. The resultant offset mucosal entry site was closed by using an endoscopic suturing device. Animals were kept alive for 2 weeks. MAIN OUTCOME MEASUREMENTS The technical feasibility, reproducibility, and safety of the procedure; the clinical course of the animals; the histological and immunochemical evaluation of the resected specimen to determine whether myenteric ganglia were present in the sample. RESULTS FTGB was performed by using the SEMF technique in all 12 animals. The offset mucosal entry site was successfully closed by using the suturing device in all animals. The mean resected tissue specimen size was 11 mm. Mean total procedure time was 61 minutes with 2 to 4 interrupted sutures placed per animal. Histology showed muscularis propria and serosa, confirming full-thickness resections in all animals. Myenteric ganglia were visualized in 11 of 12 animals. The clinical course was uneventful. Repeat endoscopy and necropsy at 2 weeks showed absence of ulceration at both the mucosal entry sites and overlying the more distal muscularis propria resection sites. There was complete healing of the serosa in all animals with minimal single-band adhesions in 5 of 12 animals. Retained sutures were present in 10 of 12 animals. LIMITATIONS Animal experiment. CONCLUSIONS FTGB by using the SEMF technique and an endoscopic suturing device is technically feasible, reproducible, and safe. Larger tissue specimens will allow improved analysis of multiple cell types.