Impaired oxygen utilization. A new mechanism for the hepatotoxicity of ethanol in sub-human primates.

The role of oxygenation in the pathogenesis of alcoholic liver injury was investigated in six baboons fed alcohol chronically and in six pair-fed controls. All animals fed alcohol developed fatty liver with, in addition, fibrosis in three. No evidence for hypoxia was found, both in the basal state and after ethanol at moderate (30 mM) or high (55 mM) levels, as shown by unchanged or even increased hepatic venous partial pressure of O2 and O2 saturation of hemoglobin in the tissue. In controls, ethanol administration resulted in enhanced O2 consumption (offset by a commitant increase in splanchnic blood flow), whereas in alcohol fed animals, there was no increase. At the moderate ethanol dose, the flow-independent O2 extraction, measured by reflectance spectroscopy on the liver surface, tended to increase in control animals only, whereas a significant decrease was observed after the high ethanol dose in the alcohol-treated baboons. This was associated with a marked shift in the mitochondrial redox level in the alcohol-fed (but not in control) baboons, with striking rises in splanchnic output of glutamic dehydrogenase and acetaldehyde, reflecting mitochondrial injury. Increased acetaldehyde, in turn, may aggravate the mitochondrial damage and exacerbate defective O2 utilization. Thus impaired O2 consumption rather than lack of O2 supply characterizes liver injury produced by high ethanol levels in baboons fed alcohol chronically.

Effects of the enantiomers of lansoprazole (AG-1749) on (H+ + K+)-ATPase activity in canine gastric microsomes and acid formation in isolated canine parietal cells.

The effects of the enantiomers of 2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridyl]methyl]-sulfinyl ]- 1H-benzimidazole (lansoprazole, AG-1749) on acid formation in isolated canine parietal cells and (H+ + K+)-ATPase activity in canine gastric microsomes were investigated. Both the (+)-and the (-)-enantiomer of lansoprazole inhibited the acid formation stimulated by dibutyryl cyclic AMP (db-cAMP) in isolated canine parietal cells in a concentration-dependent manner with IC50 values of 59 and 82 nM, respectively. The enantiomers showed concentration-dependent inhibition of (H+ + K+)-ATPase with IC50 values of 4.2 and 5.2 microM, respectively. On the other hand, the IC50 values of lansoprazole for db-cAMP-stimulated acid formation and (H+ + K+)-ATPase were 59 nM and 2.1 microM, respectively. These results suggest that the two enantiomers of lansoprazole have antisecretory action due to inhibition of (H+ + K+)-ATPase.

Spizofurone (AG-629) increases gastric mucosal blood flow in dogs: a possible mechanism of its anti-ulcer effect.

The effect of spizofurone (AG-629), a new anti-ulcer agent, on gastric mucosal blood flow was investigated in anesthetized dogs and the effects were compared with those of prostaglandin E2. Intravenous administration of spizofurone in doses of 15 and 30 mg/kg caused a dose-related increase in gastric mucosal blood flow. Spizofurone (1-10 mg/ml) given intragastrically for 15 min produced a sustained increase in gastric mucosal blood flow in a concentration-dependent manner; with 3 mg/ml there was about a 50% increase in gastric mucosal blood flow at the peak and a 2 h duration of action. The mode of action of spizofurone was similar to that of prostaglandin E2. The reduction in the gastric mucosal blood flow as induced by indomethacin was markedly improved by spizofurone. The topical action of spizofurone was confirmed in an in situ experiment using a stomach flap fixed to a lucite chamber. These results indicate that spizofurone increases gastric mucosal blood flow after systemic and topical administration, and this increase in gastric mucosal blood flow would account for the anti-ulcer effects of this drug.

EM574, an erythromycin derivative, improves delayed gastric emptying of semi-solid meals in conscious dogs.

The gastroprokinetic effects of de(N-methyl)-N-isopropyl-8, 9-anhydroerythromycin A 6,9-hemiacetal (EM574), a non-peptide motilin receptor agonist, were investigated in conscious dogs in a normal state and with experimentally-induced gastroparesis. Gastric emptying of semi-solid meals was assessed indirectly from acetaminophen absorption with simultaneous recording of gastric antral motility. In the normal state, post-prandial intraduodenal administration of EM574 (0.03 mg/kg) [corrected] stimulated antral motility and significantly enhanced gastric emptying as potently as did intravenous porcine motilin (0.003 mg/kg/h). Intraduodenal cisapride at 1 mg/kg denal cisapride at 1 mg/kg elicited antral contractions and tended to accelerate gastric emptying but at 3 mg/kg, gastric emptying was not enhanced despite a further increase in the motor index. In dogs with gastroparesis induced by intraduodenal oleic acid or intravenous dopamine, EM574 (0.03 mg/kg) increased antral motility and reversed the delayed gastric emptying completely. Cisapride (1 mg/kg) partially ameliorated the impaired emptying under these conditions. In atropinized dogs, no acceleration of gastric emptying by EM574 was observed. These results indicate that EM574 potently accelerates gastric emptying of caloric meals in dogs in a normal state and with experimentally-induced gastroparesis, and also suggest that the effect is mediated through stimulation of a cholinergic neural pathway.

Spizofurone, a new anti-ulcer agent, increases alkaline secretion in isolated bullfrog duodenal mucosa.

The effect of spizofurone, a new anti-ulcer agent, on alkaline secretion was studied in an isolated sheet of bullfrog (10(-4)-10(-3) M) as well as prostaglandin E2 (PGE2, 10(-8)-10(-5) M) added to the nutrient solution increased alkaline secretion, transmucosal potential difference (PD) and short-circuit current (Isc), in a concentration-dependent manner. The maximum increases in alkaline secretion stimulated by spizofurone and PGE2 were much the same. Spizofurone also showed this effect when added to the secretory solution while PGE2 did not. Treatment with indomethacin partly but significantly inhibited the effect of spizofurone, but did not affect that of PGE2. These results indicate that the increase in alkaline secretion in bullfrog duodenal mucosa seen in the presence of spizofurone is mediated, at least in part, by stimulation of endogenous PGs synthesis.

Gastric mucosal protection by spizofurone.

The protective effect of spizofurone (AG-629) on the rat gastric mucosa was studied in the presence of various stimuli. Spizofurone given orally markedly inhibited gastric lesions induced by ethanol (ED50 = 6.5 mg/kg). Spizofurone inhibited ethanol-induced gastric lesions even when administered intraperitoneally (i.p.), but the onset of action after oral administration was shorter. Spizofurone given orally or i.p. in a dose range of 25-200 mg/kg inhibited indomethacin-induced gastric antral ulcers in re-fed rats. Furthermore, spizofurone potentiated the inhibitory effect of prostaglandin E2 on indomethacin-induced gastric antral ulcers. Spizofurone given i.p. prevented a decrease in potential difference and the formation of gastric lesions induced by intragastric instillation of 30 mM aspirin in 0.1 N HCl. Spizofurone given i.p. inhibited the increase in net fluxes of H+ and Na+ caused by intragastric instillation of 15% ethanol in 0.1 N HCl. These findings indicate that spizofurone, like prostaglandin E2, exerts gastric mucosal protection and even potentiates the anti-ulcer effect of prostaglandin E2. The gastric mucosal protection by spizofurone is ascribed in part to preservation of the mucosal barrier.

EM574, an erythromycin derivative, is a motilin receptor agonist in the rabbit.

This study was performed to examine whether an erythromycin derivative, de(N-methyl)-N-isopropyl-8,9-anhydroerythromycin A 6,9-hemiacetal (EM574) is a motilin receptor agonist in the rabbit gastrointestinal tract. EM574 and porcine motilin induced contractions in segments of isolated rabbit intestine with pEC50 values of 8.26 +/- 0.04 and 8.69 +/- 0.07, respectively, but not in rat or guinea pig preparations. The sensitivity and efficacy of the response to both compounds in rabbits decreased aborally and was insensitive to pretreatment with atropine or tetrodotoxin, but was markedly suppressed under Ca(2+)-free conditions. EM574 and porcine motilin specifically displaced [125I-Tyr23]canine motilin bound to gastric antral smooth muscle homogenates with plC50 values of 8.21 +/- 0.13 and 9.20 +/- 0.11, respectively. The pEC50 value for the contractile response and plC50 value for the receptor binding for motilin, EM574, erythromycin A and three other derivatives correlated well (r = 0.94, P < 0.01). Tissue section autoradiography in the antrum revealed that specific labeled motilin binding sites were localized in the circular muscle layer and myenteric plexus, and could be reduced in the presence of an excess of EM574. These results indicate that EM574 is a potent motilin receptor agonist in the rabbit gastrointestinal tract.

Bioactive metabolites of EM574 and EM523, erythromycin derivatives having strong gastrointestinal motor stimulating activity.

Two motilides, EM574 (N-demethyl-N-isopropyl-8,9-anhydroerythromycin A 6,9-hemiacetal) and EM523 (N-demethyl-N-ethyl-8,9-anhydroerythromycin A 6,9-hemiacetal) have strong gastrointestinal motor stimulating (GMS) activity. When administered orally to dogs, these agents showed strong GMS activity, but their plasma levels were very low and the metabolites which have been determined so far using the radio-labeled compounds show only weak GMS activity. The findings suggested that unknown bioactive metabolites might be responsible for the GMS activity. From the liver of dogs given EM574 intravenously, two bioactive metabolites, EM574 P1 and P2, were isolated by solvent extraction and chromatography as detected by contractile activity. They both showed the same UV spectra as EM574 and the molecular ion peaks at m/z 760 (MH+) and 602 (MH(+)-cladinose) in the FAB-MS. From 2D-NMR experiments, the structures of EM574 P1 and P2 were unveiled to be the 15- and 14-hydroxyl derivatives of EM574, respectively. EM523 P1 and P2 were also isolated in the same procedure. In order to prepare these bioactive metabolites, EM574 and EM523 were converted enzymatically with dog liver homogenates in the presence of co-enzymes to give the corresponding P1 and P2. The structures of the metabolites are shown in Fig 1. They exhibited stronger contractile activity in vitro and GMS activity in vivo than the parent compounds.

Microbial conversion of EM574 and EM523, gastrointestinal motor stimulating agents.

EM574 exerts gastrointestinal motor stimulating (GMS) activity even after being converted to its metabolites P1 and P2 in dogs. These metabolites were isolated from dog liver using a series of chromatographic procedures. Their structures were determined to be the 15- and 14-hydroxyl derivatives of EM574, respectively, by spectral analysis. Large scale preparation by microbial transformation was investigated for further evaluation of the metabolites, because the amounts obtained by oxidation with dog liver homogenate were limited. Three strains of actinomycetes, Amycolatopsis tolypophorus IFO 13151, Dactylosporangium variesporum IFO 14104 and Nocardia capreola IFO 12847, were found to have the aiming oxidative potency. HPLC analysis of the crude extracts from these three cultures showed that the bioactive metabolites, EM574 P1 and P2 were produced. They were isolated from the culture broth with the other bioactive products EM574 P3 and P4. These bioactive products were prepared by large scale cultivation. EM574 P3 and P4 showed GMS activity comparable to that of EM574 P1 and P2. The structures of EM574 P3 and P4 were elucidated by spectral analysis and found to be the 3"-O-demethyl derivatives of EM574 P2 and EM574, respectively. Moreover, the absolute configuration at the C14 position of P2 was determined to be R by spectral analysis of the 6-membered cyclic carbonate of EM574 P2.

The effects of varying acidity on Helicobacter pylori growth and the bactericidal efficacy of ampicillin.

BACKGROUND: Penicillins inhibit cell wall synthesis; therefore, Helicobacter pylori must be dividing for this class of antibiotics to be effective in eradication therapy. Identifying growth responses to varying medium pH may allow design of more effective treatment regimens. AIM: To determine the effects of acidity on bacterial growth and the bactericidal efficacy of ampicillin. METHODS: H. pylori were incubated in dialysis chambers suspended in 1.5-L of media at various pHs with 5 mM urea, with or without ampicillin, for 4, 8 or 16 h, thus mimicking unbuffered gastric juice. Changes in gene expression, viability and survival were determined. RESULTS: At pH 3.0, but not at pH 4.5 or 7.4, there was decreased expression of ~400 genes, including many cell envelope biosynthesis, cell division and penicillin-binding protein genes. Ampicillin was bactericidal at pH 4.5 and 7.4, but not at pH 3.0. CONCLUSIONS: Ampicillin is bactericidal at pH 4.5 and 7.4, but not at pH 3.0, due to decreased expression of cell envelope and division genes with loss of cell division at pH 3.0. Therefore, at pH 3.0, the likely pH at the gastric surface, the bacteria are nondividing and persist with ampicillin treatment. A more effective inhibitor of acid secretion that maintains gastric pH near neutrality for 24 h/day should enhance the efficacy of amoxicillin, improving triple therapy and likely even allowing dual amoxicillin-based therapy for H. pylori eradication.

Effect of prostaglandins on mucosal blood flow and aspirin-induced damage in the canine stomach.

This study deals with the action in anesthetized dogs of prostaglandin E2 and F2 alpha given into the celiac artery and the femoral vein on gastric mucosal blood flow and on gastric mucosal damage induced by aspirin. In the non-stimulated stomach, infusion of prostaglandin E2 or F2 alpha into the celiac artery resulted in a marked increase in mucosal blood flow and a sustained decrease, respectively. In contrast, an infusion of prostaglandin E2 into the femoral vein produced a decrease in mucosal blood flow, whereas prostaglandin F2 alpha produced a biphasic response: a transient increase followed by a decrease. It was observed that intravenously infused prostaglandin E2, while reducing mucosal blood flow, significantly diminished mucosal lesions, altered transmucosal potential differences and H+ back-diffusion induced by a topical application of aspirin. The findings indicate that the action of prostaglandins on gastric mucosal blood flow alters depending on the route of administration and that prostaglandins seem to exert gastric cytoprotection through mechanisms other than an increase in mucosal blood flow.

Differences in the antisecretory actions of the proton pump inhibitor AG-1749 (lansoprazole) and the histamine H2-receptor antagonist famotidine in rats and dogs.

Antisecretory effects of a substituted benzimidazole, (+/-)-2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridyl]methyl] sulfinyl]-1H-benzimidazole (AG-1749) were compared with those of a histamine H2-receptor antagonist, famotidine. AG-1749 inhibited acid formation regardless of the stimulant in isolated canine parietal cells, while famotidine inhibited the histamine-stimulated acid formation selectively. In pylorus-ligated rats, AG-1749 suppressed basal acid secretion, histamine-, bethanechol-, pentagastrin-, 2-deoxy-D-glucose- and stress (restraint and water-immersion)-induced acid secretion; ID50 values were 1.0-6.0 mg/kg. On the other hand, famotidine only partially inhibited the acid secretion induced by 2-deoxy-D-glucose or stress, although it suppressed the acid secretion stimulated by other secretagogues several times more potently than AG-1749. The antisecretory effect of AG-1749 lasted longer than that of famotidine, especially in the case of bethanechol-stimulated acid secretion. In Heidenhain pouch dogs, both AG-1749 and famotidine potently inhibited histamine-, bethanechol-, pentagastrin- and peptone meal-stimulated acid secretion, but the inhibitory effect of famotidine was short-lived in the case of bethanechol- and pentagastrin-stimulated acid secretion. These results suggest that AG-1749 persistently inhibits acid secretion induced by both peripheral and central stimuli and suggest that the antisecretory effect of famotidine depends on the nature of the stimuli.

Antiphosphodiesterase activity and nonspecific smooth muscle relaxation tested on intestinal smooth muscles.

Mitochondrial, microsomal and soluble fractions separated from the guinea pig taenia and from the dog longitudinal smooth muscle were used as phosphodiesterase preparation. Each preparation had low and high Km values, indicating the existence of at least two kinds of phosphodiesterase. Papaverine and Aspaminol (1, 1-diphenyl-3-piperidinobutanol hydrochloride), hydralazine, caffeine Na benzoate and aminophylline were used at test drugs. Aspaminol had little inhibitory effect on phosphodiesterase. Ki value of papaverine almost equalled the concentration (M) which was necessary to produce 50% relaxation. Relaxation of the guinea pig taenia by papaverine was preceded by an increase of intracellular cyclic AMP,. Therefore, the action of papaverine is likely to be mediated by an increase in cyclic AMP, which is caused by inhibition of the phosphodiesterase-catalyzed breakdown of cyclic AMP. There was little correlation between relaxing activities of the drugs used and their antiphosphodiesterase activities. Relaxation of the smooth muscle induced by the smooth muscle relaxants excepting papaverine is not due to inhibition of phosphodiesterase.

Ethanol oxidation by deermice mitochondria under physiologic conditions.

Mitochondria obtained from alcohol dehydrogenase-positive or - negative deermice do not oxidize significant amounts of ethanol at pH 7.4. A slight activity, equivalent to less than 0.3% of the elimination rate in alcohol dehydrogenase-negative deermice was observed at pH 10; it was strongly inhibited by cyanide and thiourea, and was not dependent on exogenous NAD. Whereas ethanol oxidation by the cytosol of alcohol dehydrogenase-positive deermice was time-dependent, that of mitochondria from alcohol dehydrogenase-negative deermice was not. These findings indicate that deermice mitochondria do not oxidize ethanol at physiological pH, and that the mitochondrial system is not likely to play a significant physiologic role.

Role of peroxisomal fatty acid beta-oxidation in ethanol metabolism.

The contribution of peroxisomal fatty acid beta-oxidation to ethanol metabolism was examined in deermice hepatocytes. Addition of 1 mM oleate to hepatocytes isolated from fasted alcohol dehydrogenase (ADH)-positive deermice in the presence of 4-methylpyrazole or to hepatocytes from fasted or fed ADH-negative deermice produced only a slight and statistically not significant increase in ethanol oxidation. Lactate (10 mM), which is not a peroxisomal substrate, showed a greater effect on ethanol oxidation. There was also a lack of oleate effect on the oxidation of ethanol by hepatocytes of ADH-positive deermice. Furthermore, in ADH-negative deermice, the catalase inhibitor azide (0.1 mM) did not inhibit the increase in ethanol oxidation by oleate and lactate. The rate of oleate oxidation by hepatocytes from fasted ADH-negative deermice was much lower than that of ethanol. These results indicate that in deermice hepatocytes, peroxisomal fatty acid oxidation does not play major role in ethanol metabolism.

Comparison of the motor-stimulating action of EM523, an erythromycin derivative, and prostaglandin F2 alpha in conscious dogs.

The effect of EM523 [de(N-methyl)-N-ethyl-8,9-anhydroerythromycin A 6,9-hemiacetal], an erythromycin derivative, on gastrointestinal motility was investigated using conscious dogs in the fasting state, and it was compared with those of motilin and prostaglandin F2 alpha (PGF2 alpha). EM523 and motilin given as i.v. infusions induced strong contractions in the stomach that migrated along the intestine. On the other hand, PGF2 alpha stimulated intestinal contractions, but its effect on gastric motility was weak. EM523 had 1/50 the potency of motilin and 6 times the potency of PGF2 alpha for stimulation of intestinal motility. Atropine at 0.1 mg/kg, i.v. strongly inhibited gastrointestinal contractions induced by EM52 EM523 or motilin and partly inhibited PGF2 alpha-induced intestinal motility. ICS-205-930, a 5HT3-receptor antagonist, at a dose of 1 mg/kg, i.v. strongly inhibited EM523 or motilin-induced gastric contractions but did not affect the action of PGF2 alpha. Infusion of EM523 at 100 micrograms/kg/hr induced strong migrating contractions even when motility was depressed by dopamine infusion or laparotomy. Infusion of PGF2 alpha at 300 micrograms/kg/hr stimulated intestinal but not gastric motility under these conditions. The results of this study indicate that the cholinergic pathway and 5HT3 receptors are involved in EM523 and motilin-induced migrating gastrointestinal contractions, whereas the cholinergic pathway seems to be only partly involved in PGF2 alpha-induced intestinal contractions.