Modulation of heme oxygenase/carbon monoxide system affects the inhibitory neurotransmission involved in gastrointestinal motility of streptozotocin-treated diabetic rats

Chronic treatment with epigallocatechin gallate reduces motor hyperactivity and affects in vitro tested intestinal motility of spontaneously hypertensive rats

BACKGROUND

Green tea catechins seem to contribute toward reducing body weight and fat.

OBJECTIVE

We aimed to investigate whether chronic administration of (-)-epigallocatechin-3-gallate (EGCG), the most abundant catechin of green tea, reduces weight gain in spontaneously hypertensive rats (SHR), an animal model of metabolic syndrome, by increasing motor activity and/or by altering gastrointestinal motility.

DESIGN

Nine-week-old SHR were randomly assigned to two groups and treated by gavage for 3 weeks with vehicle dimethyl sulfoxide or EGCG (200 mg/kg/day). Age-matched Wistar-Kyoto (WKY) control rats were treated with vehicle alone. The effect of chronic administration of EGCG was evaluated on open-field motor activity and on ex vivo colonic and duodenal motility. Moreover, in vitro acute effect of 20-min incubation with EGCG (100 µM) or vehicle was evaluated in colonic and duodenal specimens from untreated WKY rats and SHR.

RESULTS

Vehicle-treated SHR were normoglycemic and hyperinsulinemic, and showed a reduction of plasma adiponectin when compared to vehicle-treated WKY rats. In addition, consistent with fasting glucose and insulin values, vehicle-treated SHR were more insulin resistant than age-matched vehicle-treated WKY rats. Chronic treatment for 3 weeks with EGCG improved insulin sensitivity, raised plasma adiponectin levels, and reduced food intake and weight gain in SHR. Vehicle-treated SHR showed increased open-field motor activity (both crossings and rearings) when tested after each week of treatment. The overall hyperactivity of vehicle-treated SHR was significantly reduced to the levels of vehicle-treated WKY rats after 2 and 3 weeks of EGCG treatment. Colonic and duodenal preparations obtained from SHR chronically treated in vivo with EGCG showed reduced responses to carbachol (0.05-5 µM) and increased inhibitory response to electrical field stimulation (EFS, 1-10 Hz, 13 V, 1 msec, 10-sec train duration), respectively. In vitro acute EGCG incubation (100 µM, 20 min) of colonic and duodenum strips obtained from untreated SHR and WKY rats showed a reduced contractile colonic response to a fixed dose of carbachol (1.5 µM) only in SHR with respect to its own vehicle, whereas the inhibitory duodenal response to a fixed EFS frequency (5 Hz) was significantly reduced in both WKY rats and SHR groups with respect to their own vehicle.

CONCLUSIONS

These data suggest that EGCG affects body weight gain in rats and this effect seems to be due to the altered intestinal motility and not to increased motor activity.

Carbon Monoxide (CO) Released from Tricarbonyldichlororuthenium (II) Dimer (CORM-2) in Gastroprotection against Experimental Ethanol-Induced Gastric Damage

The physiological gaseous molecule, carbon monoxide (CO) becomes a subject of extensive investigation due to its vasoactive activity throughout the body but its role in gastroprotection has been little investigated. We determined the mechanism of CO released from its donor tricarbonyldichlororuthenium (II) dimer (CORM-2) in protection of gastric mucosa against 75% ethanol-induced injury. Rats were pretreated with CORM-2 30 min prior to 75% ethanol with or without 1) non-selective (indomethacin) or selective cyclooxygenase (COX)-1 (SC-560) and COX-2 (celecoxib) inhibitors, 2) nitric oxide (NO) synthase inhibitor L-NNA, 3) ODQ, a soluble guanylyl cyclase (sGC) inhibitor, hemin, a heme oxygenase (HO)-1 inductor or zinc protoporphyrin IX (ZnPPIX), an inhibitor of HO-1 activity. The CO content in gastric mucosa and carboxyhemoglobin (COHb) level in blood was analyzed by gas chromatography. The gastric mucosal mRNA expression for HO-1, COX-1, COX-2, iNOS, IL-4, IL-1β was analyzed by real-time PCR while HO-1, HO-2 and Nrf2 protein expression was determined by Western Blot. Pretreatment with CORM-2 (0.5-10 mg/kg) dose-dependently attenuated ethanol-induced lesions and raised gastric blood flow (GBF) but large dose of 100 mg/kg was ineffective. CORM-2 (5 mg/kg and 50 mg/kg i.g.) significantly increased gastric mucosal CO content and whole blood COHb level. CORM-2-induced protection was reversed by indomethacin, SC-560 and significantly attenuated by celecoxib, ODQ and L-NNA. Hemin significantly reduced ethanol damage and raised GBF while ZnPPIX which exacerbated ethanol-induced injury inhibited CORM-2- and hemin-induced gastroprotection and the accompanying rise in GBF. CORM-2 significantly increased gastric mucosal HO-1 mRNA expression and decreased mRNA expression for iNOS, IL-1β, COX-1 and COX-2 but failed to affect HO-1 and Nrf2 protein expression decreased by ethanol. We conclude that CORM-2 released CO exerts gastroprotection against ethanol-induced gastric lesions involving an increase in gastric microcirculation mediated by sGC/cGMP, prostaglandins derived from COX-1, NO-NOS system and its anti-inflammatory properties.

Hemin and Zinc Protoporphyrin IX Affect Granisetron Constipating Effects In Vitro and In Vivo

Granisetron is a 5-HT3 receptors antagonist used in the management of emesis associated with anticancer chemotherapy. It affects intestinal motility with constipating effect. Since the pathway heme oxygenase/carbon monoxide (HO/CO) is involved in gastrointestinal motility, we evaluated the possible interplay between granisetron and agents affecting HO/CO pathways such as zinc protoporphyrin IX (ZnPPIX), an HO inhibitor, or hemin, an HO-1 inducer. ZnPPIX (10 µM) or hemin (10 µM), but not granisetron (0.1, 0.3, 1 µM), affected spontaneous basal activity recorded in rat duodenal strips, in noncholinergic nonadrenergic conditions. Granisetron restored spontaneous basal activity after ZnPPIX, but not after hemin. ZnPPIX decreased and hemin increased the inhibition of activity after electrical field stimulation (EFS), but they did not affect the contraction that follows the relaxation induced by EFS called off contraction. Granisetron did not alter the response to EFS per se but abolished both ZnPPIX and hemin effect when coadministered. In vivo study showed constipating effect of granisetron (25, 50, 75 µg/kg/sc) but no effect of either ZnPPIX (50 µg/kg/i.p.) or hemin (50 µM/kg/i.p.). When coadministered, granisetron effect was abolished by ZnPPIX and increased by hemin. Specimens from rats treated in vivo with hemin (50 µM/kg/i.p.) showed increased HO-1 protein levels. In conclusion, granisetron seems to interact with agents affecting HO/CO pathway both in vitro and in vivo.

Rosiglitazone reverses increased duodenal inhibitory response in spontaneously hypertensive rats

BACKGROUND

Thiazolidinediones (TZDs) including rosiglitazone (ROSI) are insulin sensitizing agents with beneficial gastrointestinal effects. However, no studies are available on TZDs effect in gastrointestinal motility. We evaluated the effects of ROSI on gastrointestinal inhibitory neurotransmission focusing on the modulatory roles of nitric oxide synthase/nitric oxide (NOS/NO) and heme oxygenase/carbon monoxide (HO/CO) pathways.

METHODS

Spontaneously hypertensive rats (SHR) were used as model of insulin resistance. Duodenal strips were obtained from vehicle-treated SHR, ROSI-treated SHR (5 mg kg(-1) by gavage daily per 6 weeks), and Wistar Kyoto (WKY). Inhibitory responses to electrical field stimulation (EFS) were evaluated in the presence of HO inhibitor zinc protoporphyrin IX (ZnPPIX, 10 μmol L(-1)) or NOS inhibitor N(G)-nitro-L-arginine (L-NNA, 100 μmol L(-1)), alone and in combination. Protein levels of HO and NOS isoforms were evaluated by immunohistochemistry and western blot analysis.

KEY RESULTS

Basal responses to EFS were significantly increased in duodenum strips from vehicle-treated SHR vs WKY. This effect was reversed in ROSI-treated SHR. The EFS-mediated relaxation was comparably reduced by ZnPPIX in WKY and SHR, but not in ROSI-treated SHR animals. The L-NNA reduced EFS response to a similar extent in WKY and ROSI -treated SHR, but its effect was significantly higher in vehicle-treated SHR. Expression of HO-1 protein was significantly lower, whereas HO-2 protein levels were unchanged in ROSI-treated SHR with respect to vehicle-treated SHR. Finally, increased levels of nNOS in vehicle-treated SHR were reduced in ROSI-treated SHR.

CONCLUSIONS & INFERENCES

Chronic ROSI treatment reverses increased SHR duodenal inhibitory response acting on CO and NO components.

Non-adrenergic non-cholinergic inhibition of gastrointestinal smooth muscle and its intracellular mechanism(s)

Relaxation of gastrointestinal smooth muscle caused by release of non-adrenergic non-cholinergic (NANC) transmitters from enteric nerves occurs in several physiologic digestive reflexes. Likely candidate NANC inhibitory agents include nitric oxide (NO), adenosine triphosphate (ATP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), carbon monoxide (CO), protease-activated receptors (PARs), hydrogen sulfide (H2S), neurotensin (NT) and beta-nicotinamide adenine dinucleotide (beta-NAD). Multiple NANC transmitters work in concert, are pharmacologically coupled and are closely coordinated. Individual contribution varies regionally in the gastrointestinal tract and between species. NANC inhibition of gastrointestinal smooth muscle involves several intracellular mechanisms, including increase of cyclic guanosine monophosphate (cGMP), increase of cyclic adenosine monophosphate (cAMP) and hyperpolarization of the cell membrane via direct or indirect activation of potassium ion (K+) channels.