Enhancing effect of DQ-2511 on gastric emptying of spontaneously hypertensive rats

Rapid Gastric emptying in spontaneously hypertensive rats

OBJECTIVE

To assess the rate of gastric emptying in spontaneously hypertensive rats (SHR) and to evaluate rapid gastric emptying as a possible predisposing factor for hypertension. Rapid gastric emptying of carbohydrates, known to elevate postprandial serum glucose, has been reported to occur in many insulin-resistant states, including hypertension. SHR exhibit insulin resistance similar to human hypertensive patients. No prior studies have assessed gastric emptying of an oral glucose solution in SHR as compared with control Wistar Kyoto rats (WKY).

METHODS

Using scintigraphic imaging, gastric emptying of a physiologic, orally consumed glucose solution was assessed in 12 SHR and 12 control WKY at 5 weeks of age, prior to the development of hypertension, and at 12 weeks of age after hypertension was fully established.

RESULTS

At 5 weeks, the gastric half-emptying time (GHET) was 67.8 ± 9.8 min for the SHR vs. 109.3 ± 18 ( P  = 0.042) minutes for the WKY controls. At 12 weeks, the GHET was 37.29 ± 10.3 min for the SHR vs. 138.53 ± 37.6 ( P  = 0.016) min for the WKY controls.

CONCLUSION

Gastric emptying was significantly more rapid in the SHR before and after the development of hypertension. Even though SHR are known to have increased sympathetic activity associated with their development of hypertension, this increased sympathetic activity does not inhibit gastric emptying. SHR are a promising animal model for investigating therapeutic agents for treating hypertension aimed at slowing the rate of gastric emptying.

P2X7 receptor antagonist improves gastrointestinal disorders in spontaneously hypertensive rats

The purinergic system participates in the control of blood pressure. Hypertension promotes the occurrence of gastrointestinal disorders such as intestinal inflammation and gastric emptying delay. This study aimed i) to investigate the participation of the P2X7 receptor blocker Brilliant Blue G (BBG) on gastric emptying of solids and changes in oxidative stress in the gastric fundus, duodenum, and colon of spontaneously hypertensive rats (SHR) and ii) to study the putative relationship of this effect with the renin-angiotensin system. Rats were divided into five groups: Control, SHR, SHR+BBG, SHR+BBG+ATP, and SHR+BBG+ANG II. In the gastrointestinal tract, we assessed gastric emptying (GE) and oxidative stress markers (NOx, MPO, GSH, SOD). We observed a decrease in the GE rate (P<0.05) in SHR vs control rats (21.8±2.0% vs 42.8±3.5%). The decrease in GE was returned (P<0.05) to control levels by BBG in SHR rats (21.8±2.0% vs 41.6±3.2%). Co-administration of ATP or ANG II together with BBG bypassed the effect of the P2X7 antagonist on GE in SHR (P<0.05) (21.9±5.0% vs 25.6±3.0% vs 41.6±3.2%). The MPO activity increased (P<0.05) in the gastric fundus of SHR compared to control rats (6.12±2.26 vs 0.077±0.02 UMPO/mg tissue); this effect was prevented (P<0.05) by BBG (0.55±0.15 vs 6.12±2.26 UMPO/mg tissue). Data demonstrated that blockage of P2X7 receptors with BBG can improve the GE delay and oxidative stress biomarkers in SHR animals. This preventive effect of BBG on GE delay was abrogated by ANG II and ATP, thus prompting crosstalk between renin-angiotensin and the purinergic signaling systems underlying this phenomenon.

Heme deficiency of soluble guanylate cyclase induces gastroparesis

BACKGROUND

Soluble guanylate cyclase (sGC) is the principal target of nitric oxide (NO) to control gastrointestinal motility. The consequence on nitrergic signaling and gut motility of inducing a heme-free status of sGC, as induced by oxidative stress, was investigated.

METHODS

sGCβ1 (H105F) knock-in (apo-sGC) mice, which express heme-free sGC that has basal activity, but cannot be stimulated by NO, were generated.

KEY RESULTS

Diethylenetriamine NONOate did not increase sGC activity in gastrointestinal tissue of apo-sGC mice. Exogenous NO did not induce relaxation in fundic, jejunal and colonic strips, and pyloric rings of apo-sGC mice. The stomach was enlarged in apo-sGC mice with hypertrophy of the muscularis externa of the fundus and pylorus. In addition, gastric emptying and intestinal transit were delayed and whole-gut transit time was increased in the apo-sGC mice, while distal colonic transit time was maintained. The nitrergic relaxant responses to electrical field stimulation at 1-4 Hz were abolished in fundic and jejunal strips from apo-sGC mice, but in pyloric rings and colonic strips, only the response at 1 Hz was abolished, indicating the contribution of other transmitters than NO.

CONCLUSIONS & INFERENCES

The results indicate that the gastrointestinal consequences of switching from a native sGC to a heme-free sGC, which cannot be stimulated by NO, are most pronounced at the level of the stomach establishing a pivotal role of the activation of sGC by NO in normal gastric functioning. In addition, delayed intestinal transit was observed, indicating that nitrergic activation of sGC also plays a role in the lower gastrointestinal tract.

The 13C-octanoic acid breath test: validation of a new noninvasive method of measuring gastric emptying in rats

Currently available rat models for measuring gastric emptying are hampered by the necessity to kill the animals at the end of each experiment, which makes repetitive testing impossible. We have developed and validated a noninvasive test model, adapted from the 13C-octanoic breath test in humans, for repetitive measurements of gastric emptying in rats. Male Wistar rats were trained on a fixed protocol to eat a piece of pancake doped with 1 microg 13C-octanoic acid after 12 h fasting, and to stay thereafter in cylindrical glass cages. Breath tests were performed by a fully automated system of computer-guided switching valves, which collected consecutive breath samples. All breath samples were analysed by gas chromatography and isotope mass spectrometry. The area under the curve (AUC) from the cumulative 13CO2 excretion from 0 to 6 h was determined by the trapezium method to calculate the gastric half-emptying times (t(1/2)). Inter-day variability was determined. The effect of subcutaneous or intraperitoneal injection of saline was studied. The test was further validated for pharmacological interventions by oral administration of cisapride and parenteral administration of atropine, to induce, respectively. acceleration and delay of gastric emptying. Mean gastric emptying times +/- SD of 24 rats were 119.3 +/- 28.2 min, 138.7 +/- 26.0 min, and 124.5 +/- 30.9 min on three different test days. The mean coefficient of variation of three repeated measurements in the same 24 rats was 17.5%. No significant differences were observed after subcutaneous or intraperitoneal injection of saline. In a second test series of eight rats, cisapride significantly accelerated gastric emptying (mean t(1/2) 112.7 +/- 33.1 min, P < 0.05), while atropine caused a significant delay (mean t(1/2) 205.9 +/- 24.9 min, P < 0.05) when compared to control test results (mean t(1/2) 140.7 +/- 16.7 min) in the same rats. We validated the 13C-octanoic breath test to study gastric emptying in rats. This test method obviates the necessity to kill laboratory animals and allows repetitive measurements of gastric emptying to study its physiology or pathophysiology as well as the effect of pharmacological agents.

Modulation of gastrointestinal afferent sensitivity by a novel substituted benzamide (ecabapide)

The effects of ecabapide, a novel substituted benzamide compound (3-[2-(3,4-dimethoxyphenyl)ethylcarbamoylmethyl]amino-N-methylb enzamide) that has gastrointestinal prokinetic action, were examined on the discharge of extrinsic afferent nerves supplying the stomach and jejunum in anaesthetized rats. Ecabapide (60 and 180 microg kg(-1), i.v.) had no effect on the baseline discharge of vagal gastric distension-sensitive afferents or the stimulus-response profile to gastric distension. Ecabapide also had no effect on either spontaneous jejunal mesenteric afferent nerve discharge or responses to intestinal distension. Ecabapide (180 microg kg(-1)) significantly inhibited the maximum discharge of jejunal afferents induced by cholecystokinin (CCK8; 50 pmol, i.v.), whereas it failed to inhibit the excitatory action of 2-methyl-5-hydroxytryptamine (2Me-5-HT; 10 microg, i.v.), a selective 5-HT3 receptor agonist. A model of acute focal intestinal ischaemia was used to evaluate the actions of ecabapide on the discharge of activated jejunal afferents. Ischaemia produced a substantial increase in afferent discharge which was reproducible when the duration of ischaemia was limited to less than 10 min and repeated every 15 min. Ecabapide at doses of 60 and 180 microg kg(-1) significantly reduced ischaemia-induced increases in afferent discharge. In addition to its therapeutic efficacy as a gastrointestinal prokinetic agent, these findings show also that ecabapide may also have an inhibitory action on the discharge of intestinal afferents activated by ischaemia.

Identification of cytochromes P450 involved in human liver microsomal metabolism of ecabapide, a prokinetic agent

1. In vitro studies identified the hepatic cytochrome P450 (CYP) enzyme(s) involved in the major metabolism of ecabapide in human. 2. Ecabapide mainly underwent N-dealkylation to form M1 and 6-hydroxylation of the benzamide moiety to form M6. 3. The rates of formation of the major metabolites M1 and M6 were significantly correlated with CYP3A-selective testosterone 6beta-hydroxylase activities in 14 different human liver microsomes. The formation of both metabolites was markedly decreased by ketoconazole, miconazole or troleandomycin (TAO), CYP3A-selective inhibitors, and also was inhibited by anti-CYP3A antibodies. 4. These results strongly indicate that CYP3A is the predominant isozyme responsible for the major metabolism of ecabapide in human liver microsomes. 5. Marginal inhibition of the formation of M1 and M6 by nifedipine, a substrate of CYP3A with a Ki > 100 microM, suggested that nifedipne has a limited potential to inhibit the major metabolic pathways of ecabapide.

Pharmacology of the gastric pro-kinetic drug ecabapide (DQ-2511)

The pharmacology of ecabapide (DQ-2511; 3-[2-(3,4-dimethoxyphenyl)ethylcarbamoylmethyl]amino-N-methylbe nzamide) is reviewed. Evidence from basic studies in animal models suggests that the drug acts on peripheral mechanisms of neural control. In the stomach, ecabapide acts to suppress firing in vagal afferent nerves and thereby reduce the flow of sensory information into the dorsal vagal complex. The enhancement of the efferent discharge provoked by ecabapide was completely blocked by bilateral vagotomy, as suggested by increased firing in vagal efferent fibres, preceded by suppression of activity in the sensory limb of the putative vago-vagal reflex pathway. The mechanism of action of ecabapide in suppressing discharge in vagal afferent terminals appears to mimic that of nitric oxide by stimulating formation of cGMP and activation of an inhibitory transduction cascade in the sensory fibres. In this respect the mechanism of its pro-kinetic action differs from other promoter agents. In addition to selective actions in the stomach, evidence from electrophysiological studies of enteric neurons in the small intestine suggests that ecabapide might have actions similar to those of other substituted benzamides on synaptic transmission in the intramural nervous system of this specialized region of the digestive tract. These actions include enhanced release of acetylcholine at excitatory synapses and suppression of the release of noradrenaline at inhibitory synapses.

Actions of Daiichi DQ-2511 on electrical and synaptic behavior of enteric neurons in the guinea-pig small intestine

Intracellular recording of electrical and synaptic behavior of neurons in the enteric nervous system of guinea-pig small intestine was used to evaluate actions of DQ-2511 (3-[[[2-(3, 4-dimethoxyphenyl)ethyl]carbamoyl]methyl]amino-N-methylbenzamide). DQ-2511 is a new drug with gastrointestinal prokinetic action. DQ-2511 was most effective in the nanomolar range. The drug depolarized some of the neurons and this was accompanied by increased input resistance and augmented excitability. DQ-2511 in nanomolar concentrations increased the amplitude of fast excitatory postsynaptic potentials at nicotinic synapses. Slow inhibitory postsynaptic potentials, produced by release of norepinephrine from sympathetic postganglionic fibers, were suppressed by DQ-2511. This appeared to reflect presynaptic suppression of release of norepinephrine because postsynaptic responses to exogenously applied norepinephrine were unaffected. The results suggest that the prokinetic action of DQ-2511 on gastrointestinal transit might emerge from actions that augment excitatory synaptic transmission in the microcircuits of the enteric nervous system while suppressing inhibitory sympathetic neurotransmission.

Identification of major biliary and urinary metabolites of ecabapide in rats

1. The structures of major biliary and urinary metabolites of ecabapide in rat were identified by comparison with authentic standards using lc-ms and 1H-nmr spectrometry. 2. A major metabolite was found in the bile obtained from rat after an oral dose of 14C-ecabapide and identified as the amidaldehyde derivative. In the urine, two polar metabolites were characterized as the phenolic sulphates. Further, two lipophilic metabolites were identified as alcohol derivatives, and two others as oxamic acids. 3. From these results, it was estimated that the first step in the metabolism of ecabapide in rat was oxidative N-dealkylation to produce the amidaldehyde. This amidaldehyde was further metabolized by two routes, one by reduction of the amidaldehyde into the corresponding alcohol followed by mono-demethylation and subsequent aromatic O-sulphation, the second by oxidation of the amidaldehyde into the oxamic acid followed by mono-demethylation and subsequent aromatic O-sulphation.

Comparative evaluation of DQ-2511, a novel gastroprokinetic agent, with cisapride in ameliorative action on experimentally induced delayed gastric emptying

We compared the main pharmacological effect of DQ-2511 (3-[[[2-(3,4-dimethoxyphenyl)- ethyl]carbamoyl]methyl]amino-N-methylbenzamide), a novel gastroprokinetic agent, with that of cisapride. Single oral administration of DQ-2511 (3-10 mg kg-1) caused similar significant improvements to delays in gastric emptying of semi-solid meals evoked by cholecystokinin-octapeptide (CCK8: 5 micrograms kg-1, i.v.) in monkeys, to that with cisapride (3 mg kg-1). A 2-week oral treatment of unilaterally vagotomized rats with DQ-2511 (1-10 mg kg-1) lessened delays in gastric emptying, whereas cisapride (0.3-10 mg kg-1) had no effect under the same experimental protocols. In anesthetized rats, bolus intravenous injection of either compound (60 micrograms kg-1) enhanced gastric motility determined by means of strain gauge force transducers. Electrophysiological investigations revealed that bolus injection of DQ-2511 (6-60 micrograms kg-1) depressed the afferent discharge rate of the ventral gastric branch of the vagus nerve, while cisapride showed no effect. These results suggest that the mechanism of ameliorative action of DQ-2511 on delayed gastric emptying may differ from that of cisapride.

Effects of DQ-2511 on neutral activity in afferent and efferent loops of gastric vago-vagal reflex pathways in the rat

1. DQ-2511 is a new substituted benzamide compound that has gastric prokinetic properties. Actions of the drug on neural discharge in the innervation of the stomach of anaesthetized rats were studied. Standard extracellular methods of multi-unit recording were used to study rates of firing in afferent and efferent filaments teased from gastric branches of the vague nerve. 2. Decreased firing in gastric vagal efferents was associated with increased rates of discharge in the gastric afferents. 3. Intravenous application of DQ-2511 resulted in increased frequency of firing in the efferents in association with decreased rate of discharge in afferent fibres. 4. Application of cholecystokinin octapeptide (CCK8) suppressed activity in the gastric efferents which occurred coincident with the elevated discharge in the afferents. Pretreatment with DQ-2511 blocked the actions of CCK8. 5. The results suggest that the gastric prokinetic action of DQ-2511 may involve suppression of activation of afferents in the sensory component of gastric inhibitory vago-vagal reflex pathways.