Ethanol-induced vascular permeability changes in the jejunal mucosa of the dog

Effect of concomitant oral administration of ethanol on the pharmacokinetics of nicardipine in rats

Ethanol intake can alter pharmacokinetics by increasing the solubility or enhancing the absorption of concomitant drugs. Here, a selective, sensitive and reproducible high-performance liquid chromatography-tandem mass spectrometry method for the quantitative analysis of nicardipine in rat plasma was developed using simple protein precipitation. The calibration curve was linear over a concentration range of 1-2,000 ng/ml (r²  > 0.998). Accuracy ranged from 93.4 to 112.2% and precision was within 12.1% from three independent analytical batches. Stable conditions for the quantification of nicardipine in rat plasma were established in various conditions, including sample storage and handling. The matrix effect was negligible, and recovery was consistent at three different levels of quality control sample. The method was applied to assessment for the effect of ethanol on the pharmacokinetics of nicardipine in rats. The oral bioavailability of nicardipine was increased from 5.4 to 9.4% in Sprague-Dawley rats by concomitant oral administration of ethanol whereas the half-life was not altered. The findings indicated that concomitant ethanol intake can increase systemic drug exposure by increasing gastrointestinal absorption, especially poorly soluble drugs. This study provides an insight for further investigation of the alteration of the pharmacological effect of poorly soluble drugs owing to ethanol intake.

Rodent models of alcoholic liver disease: of mice and men

Alcoholic liver disease (ALD) is a major cause of acute and chronic liver disease worldwide. The progressive nature of ALD is well described; however, the complex interactions under which these pathologies evolve remain to be fully elucidated. Clinically there are no clear biomarkers or universally accepted, effective treatment strategies for ALD. Experimental models of ALD are an important component in identifying underlying mechanisms of alcohol-induced injury to develop better diagnostic markers, predictors of disease progression, and therapeutic targets to manage, halt, or reverse disease progression. Rodents remain the most accessible model for studying ALD pathology. Effective rodent models must mimic the natural history of ALD while allowing examination of complex interactions between multiple hepatic, and non-hepatic, cell types in the setting of altered metabolic or oxidative/nitrosative stress, inflammatory responses, and sensitivity to cytotoxic stress. Additionally, mode and duration of alcohol delivery influence hepatic response and present unique challenges in understanding disease pathology. This review provides an overview of rodent models of ALD, their strengths and weaknesses relative to human disease states, and provides insight of the potential to develop novel rodent models to simulate the course of human ALD.

Animal models and their results in gastrointestinal alcohol research

Alcohol-induced diseases of the gastrointestinal tract play an important role in clinical gastroenterology. However, the precise pathophysiological mechanisms are still largely unknown. Alcohol research depends essentially on animal models due to the fact that controlled experimental studies of ethanol-induced diseases in humans are unethical. Animal models have already been successfully applied to disclose and analyze molecular mechanisms in alcohol-induced diseases, partially by using knockout technology. Because of a lack of transferability of some animal models to the human condition, results have to be interpreted cautiously. For some alcohol-related diseases like chronic alcoholic pancreatitis, the ideal animal model does not yet exist. Here we provide an overview of the most commonly used animal models in gastrointestinal alcohol research. We will also briefly discuss the findings based on animal models as well as the current concepts of pathophysiological mechanisms involved in acute and chronic alcoholic damage of the esophagus, stomach, small and large intestine, pancreas and liver.

Animal models in gastrointestinal alcohol research-a short appraisal of the different models and their results

Alcohol-related diseases of the gastrointestinal tract play an important role in clinical gastroenterology. However, the mechanisms and pathophysiology underlying the effects of ethanol on the organs of the digestive tract are not yet completely understood. Animal models represent an essential tool for investigating alcohol-related diseases because they give researchers the opportunity to use methods that cannot be used in humans, such as knockout technology. However, there is still a need for new animal models resembling the human condition, since for some alcohol-related diseases such as chronic alcoholic pancreatitis, the ideal animal model does not yet exist. In this chapter, we provide an overview of the most commonly used animal models in gastrointestinal alcohol research. We will also briefly discuss the current concepts of the pathophysiological mechanisms involved in acute and chronic alcoholic damage of the oesophagus, stomach, small and large intestine, pancreas and liver.

Increased intestinal permeability to macromolecules and endotoxemia in patients with chronic alcohol abuse in different stages of alcohol-induced liver disease

BACKGROUND/AIMS

No information is yet available about the influence of alcohol abuse on the translocation of larger molecules (Mr>1200) through the intestinal mucosa in man. The present study aimed to determine the intestinal permeability to macromolecules in patients with chronic alcohol abuse and mild to more advanced stages of liver disease, and to measure the concentration of endotoxins in the plasma, as these compounds derive from the intestinal flora and are suspected to contribute to the development of alcoholic liver disease (ALD).

METHODS

The permeability to polyethylene glycol Mr 400, Mr 1500, Mr 4000, and Mr 10,000 and endotoxin plasma concentrations were measured in 54 patients with alcoholic liver disease, 19 of them with cirrhosis, and in 30 non-alcoholic healthy controls.

RESULTS

Permeability to polyethylene glycol Mr 400 was found to be unchanged in patients with ALD in comparison to healthy controls, whereas polyethylene glycol Mr 1500 and Mr 4000 were recovered in about twice as high concentrations in the urine of ALD patients (p<0.01). Polyethylene glycol Mr 10,000 was detected significantly less frequently in urine from healthy controls (0/30) than in urine of patients with alcoholic liver disease (20/54, p<0.01). Endotoxin concentrations in the plasma of alcoholics were increased more than 5-fold compared to healthy controls (p<0.01).

CONCLUSIONS

The results of this study indicate that alcohol abuse impairs the function of the intestinal barrier, which might enhance the translocation of bacterial toxins, thereby contributing to inflammatory processes in alcoholic liver disease.

Effect of alcohol on bacterial translocation in rats

Bacterial translocation has been proposed to be important in the pathophysiology of sepsis, as well as to be a consequence of sepsis. To study the effect of alcohol on bacterial translocation from the gut, normal Sprague-Dawley rats were administered alcohol by gavage by two regimens: Acute (3.7 g/kg, one dose) or Subacute (1 of 2 doses, 2.4 or 3.7 g/kg/day once daily for 14 days). Mesenteric lymph node cultures were performed, and portal venous blood was assayed for endotoxin. Ileal and cecal permeability studies were performed in the Acute and Subacute groups using fluorescein isothiocyanate-labeled dextrans of either 4,000 or 70,000 kDa size. As an index of the effect of systemic endotoxin, tissues from mesenteric lymph nodes, liver, and intestinal Peyer's patches were assayed for the presence of mRNA for tumor necrosis factor. Additionally, because extrapulmonary sepsis has been shown to suppress pulmonary antibacterial defenses, animals in the Subacute group were challenged by aerosol inoculation with Pseudomonas aeruginosa to determine bacterial clearance and alveolar cellular responses. The results show that neither of the alcohol regimens resulted in bacterial growth from mesenteric lymph nodes or portal blood. Animals in the Subacute group had more endotoxin present in portal blood than did the Control group (92.9 pg/ml vs. 40.2 pg/ml; p < 0.02). None of the animals had demonstrable mRNA for tumor necrosis factor in any of the tissues assayed. There were no demonstrable increases in ileal or cecal permeability for either the small or large molecular weight dextran in either alcohol group. Furthermore, there was no delay in the clearance of P. aeruginosa from the lung in the Subacute group, but these animals recruited fewer neutrophils into the airspaces in response to this challenge than did the Control animals. Thus, alcohol intoxication does not result in bacterial translocation from the gut in this model. Despite higher levels of portal venous endotoxin in the animals in the Subacute alcohol group, no adverse systemic consequences of this phenomenon could be demonstrated.

Ethanol-induced jejunal microvascular and morphological injury in relation to histamine release in rabbits

BACKGROUND

To investigate the relation between ethanol-induced jejunal microvascular injury, morphological changes, and histamine release, the present study examined whether the attenuation of microvascular effect of ethanol by 16,16-dimethyl prostaglandin E2 (dmPGE2) (reported by us previously) was associated with an attenuation of epithelial damage and histamine release.

METHODS

Rabbits were used. Mucosal microvascular injury was assessed by determining jejunal plasma protein loss (JPPL), histamine release by measuring histamine concentration of the gut effluent, and epithelial damage by routine histology.

RESULTS

(1) During 90-minute jejunal ethanol perfusion, there was a direct relation between the time course of histamine release and that of JPPL. (2) dmPGE2 attenuated the ethanol-induced JPPL and histamine release, and the decrease in JPPL was directly proportional to the decrease in histamine release. (3) dmPGE2 did not alleviate ethanol-induced epithelial damage. (4) Ketotifen (a mast cell stabilizer), similar to dmPGE2, attenuated ethanol-induced JPPL and histamine release. (5) Ethanol caused histamine release by the jejunum in vitro; this was attenuated by dmPGE2 and also by phloretin (a mast cell stabilizer).

CONCLUSIONS

It appears that (1) ethanol causes JPPL by inducing release of mediators from mucosal mast cells. (2) dmPGE2 attenuates JPPL by stabilizing mast cells. (3) The ethanol-induced mucosal microvascular injury is directly related to histamine release but not to epithelial damage.

The role of histamine1 and histamine2 receptors in the ethanol-induced jejunal plasma protein loss

Histamine and other mediators have been shown to be involved in the ethanol-induced jejunal plasma protein loss. In this study we have investigated whether the histamine (H)-related component of this protein loss is mediated by H1-receptors, H2-receptors or both. Four groups of dogs (n = 12 in each) were studied. They were: untreated, H1 + H2-receptor blockade, H1-receptor blockade and H2-receptor blockade. Chlorpheniramine and ranitidine were used to block H1 and H2-receptor blockade. Chlorpheniramine and ranitidine were used to block H1 and H2-receptors respectively. In all animals, jejunal protein loss was measured over 10 min periods for 90 min. Ethanol increased protein loss in all time periods (p less than 0.001). This protein loss was depressed by H1 + H2-receptors blockade throughout 90 min (p less than 0.01). H1-receptor blockade caused a similar depression of ethanol effect but only during 20 to 40 min (p less than 0.05). In contrast, H2-receptor blockade aggravated the protein losing effect of ethanol throughout 90 min (p less than 0.01). Analyses of data tend to suggest that the ethanol-induced protein loss is mediated principally by H1-receptors, and that a complete inhibition of the histamine-related ethanol-induced protein loss can be achieved only by a simultaneous blockade of both H1 and H2-receptors, and not by H1- or H2-receptor blockade alone.

Acute exposure of small intestine to ethanol induces mucosal leakage and prostaglandin E2 synthesis

The small intestines of healthy volunteers were challenged with ethanol during regional perfusion of a defined jejunal segment. Infusion of 30 mL of 5000 mmol/L ethanol to the perfused jejunal segment gave a maximum ethanol concentration of 973 +/- 98 (SEM) mmol/L in the jejunum lumen. This ethanol challenge induced within 20-30 minutes a 10-fold increase in albumin (P less than 0.001) and a two-fold increase in the glycosaminoglycan hyaluronic acid (P less than 0.05) in the perfusion fluid. Later during the challenge and simultaneously with a decreased jejunal loss of albumin, the jejunal recovery of prostaglandin E2 increased fourfold (P less than 0.01). The jejunal fluid concentrations of histamine and eosinophil cationic protein remained stable during the ethanol challenge. No changes in the jejunal appearance of albumin or other measured substances were seen when the maximum jejunal fluid concentrations of ethanol were less than 400 mmol/L achieved during challenge with smaller amounts of ethanol. The increased jejunal fluid appearance of hyaluronic acid after ethanol challenge indicates increased leakage from the interstitial/lymph fluid of the gut wall due to altered mucosal permeability. The relatively larger jejunal losses of albumin suggest that ethanol induces increased microvascular permeability of the jejunum as well.

Microvascular permeability increases early in the course of acid-induced esophageal injury

To test the hypothesis that microvascular injury is involved in the pathophysiology of acid-induced esophagitis, the effect of acid perfusion on intraluminal plasma protein loss was studied in relation to histological changes. Four groups of opossums (n = 6 in each) were perfused with either normal saline control) or 10, 20, or 100 mmol/L isoosmolar hydrochloric acid at 2 mL/min for 90 minutes using a midesophageal catheter. The distal esophagus was cannulated via a gastrostomy, and the effluent was collected and measured for intraluminal loss of IV injected 125I-bovine serum albumin. Plasma protein loss in the control group was constant with a total loss of 3.40 +/- 0.69 mg/g dry wt. Perfusion of 10, 20, and 100 mmol/L hydrochloric acid increased total protein loss to 8.06 +/- 2.62, 13.94 +/- 2.72, and 27.34 +/- 4.34 mg/g dry wt, respectively. The protein loss was not associated with intraluminal blood loss, as measured by previously injected 51Cr-labeled autologous red blood cells. Histological changes, scored by a blinded observer, were significant only between control animals and those perfused with 100 mmol/L hydrochloric acid. Separate studies using the vascular tracer monastral blue B demonstrated an increase in labeling of lamina propria blood vessels that varied directly with the concentration of acid perfusate, thereby providing direct morphological evidence of microvascular injury. These studies suggest that increased microvascular permeability occurs early in the course of acid-induced esophageal injury.

Nerve-mediated effect of ethanol on sodium and fluid transport in the jejunum of the rat

The hypothesis tested in this study is whether a potential harmful substance such as ethanol causes secretion in the small intestine and, if so, whether the secretion is mediated via intestinal nerve reflexes or a direct effect on the epithelium. The jejunum of anaesthetized Sprague-Dawley rats was perfused in vivo with a modified Krebs-Henseleit solution. Three per cent ethanol had no significant effect, whereas 8% ethanol in the perfusate elicited a net secretion of fluid and sodium in the intestine. This secretion was reversed by ganglionic blockade with hexamethonium (10 mg/kg intravenously). The ethanol absorption from the perfusate, on the other hand, was not affected by the ganglionic blockade. We concluded that ethanol dose-dependently caused a nerve-mediated secretion of sodium and fluid in the rat small intestine. Ethanol was probably absorbed by diffusion.

Mechanism of ethanol-induced jejunal microvascular and morphologic changes in the dog

To study the mechanism of morphologic and microvascular effects of intraluminal ethanol, we perfused jejunal segments of the dog with 6% (wt/vol) ethanol for 0 (control), 10, 20, 30, 60, and 90 min, and measured the time-dependent changes in (a) the prevalence of villi with epithelial damage (i.e., villi with intact blebs plus those with broken blebs) and those without epithelial damage (undamaged villi), (b) the height of the villus core and the patency of lacteals, (c) jejunal albumin loss, and (d) permeability of microvessels of the villus tip by colloidal carbon vascular labeling. We found that (a) the prevalence of villi with epithelial damage or with intact bleb increased progressively during the first 20 min of ethanol perfusion and then declined gradually; (b) the height of the villus core and the patency of lacteals in the undamaged villi and in those with intact bleb decreased during the first 20 min and then gradually increased; and (c) jejunal albumin loss and the prevalence of villi with carbon labeling increased for the first 30 min, after which the former declined gradually whereas the latter remained at a plateau. These findings suggest that contraction of the villus core and compression of the lymphatics are the primary cause of ethanol-induced epithelial damage, which is accentuated by increased microvascular permeability and consequent protein leakage. The mechanism of recovery of most parameters, in spite of continuous ethanol perfusion, remains to be investigated.

Beneficial effects of prostaglandin E2 in endotoxic shock are unrelated to effects on PAF-acether synthesis

The effects of endotoxic shock on the synthesis of PAF-acether by the stomach, duodenum and lung were examined in the rat. Furthermore, the effect of pretreatment with prostaglandin E2 on endotoxin induced PAF-acether synthesis and changes in vascular permeability were examined. Administration of endotoxin resulted in significant increases in PAF-acether synthesis in all tissues studied. Such increases were apparent within 5-15 minutes of the administration of endotoxin, corresponding to the time when significant hypotension, hemoconcentration and increases in gastrointestinal vascular permeability were first observed. Pretreatment with prostaglandin E2 resulted in a significant reduction of endotoxin-induced hypotension, hemoconcentration and changes in vascular permeability in the gastrointestinal tract. However, prostaglandin pretreatment did not significantly alter endotoxin-induced PAF-acether release from the gastrointestinal tissues studied. These results demonstrate that prostaglandin E2 can significantly attenuate several of the systemic and gastrointestinal manifestations of endotoxic shock. The mechanism responsible for these beneficial actions appears to be unrelated to effects of prostaglandin E2 on PAF-acether synthesis.

Histamine is involved in ethanol-induced jejunal microvascular injury in rabbits

To examine for the possible involvement of histamine in the jejunal microvascular effects of ethanol, we investigated the effects of (a) intraluminal ethanol on histamine release by the jejunum and (b) simultaneous inhibition of both histamine1 and histamine2 receptors (using promethazine and cimetidine, respectively) on ethanol-induced intestinal plasma protein loss in rabbits. Ethanol increased histamine release by the jejunum both in vivo (p less than 0.01) and in vitro (p less than 0.05). To investigate the effect of antihistamines on ethanol-induced plasma protein loss, we determined the dose of blockers that would completely inhibit the histamine1 and histamine2 receptors. In the absence of antihistamines, ethanol caused a 10-fold increase in jejunal protein loss over the controls (p less than 0.001). Simultaneous inhibition of histamine1 and histamine2 receptors attenuated (p less than 0.025), but did not abolish, the ethanol-induced protein loss. These data are discussed in relation to the literature, and it is concluded that histamine may play a role in the jejunal microvascular effects of ethanol. As the ethanol-induced protein loss was not completely inhibited, other mediators or mechanisms were probably involved.

16,16-Dimethyl prostaglandin E2 alleviates jejunal microvascular effects of ethanol but not the ethanol-induced inhibition of water, sodium, and glucose absorption

To examine the relation between ethanol-induced microvascular and absorptive changes, we have investigated the effect of 16,16-dimethyl prostaglandin E2 on the jejunal intraluminal plasma albumin loss (which was taken as a measure of microvascular changes) and the inhibition of water, sodium, and glucose transport caused by intraluminal ethanol. A group of 8 dogs received intravenously 16,16-dimethyl prostaglandin E2 at a dose of 0.1 microgram/kg as a bolus followed by 0.05 microgram/kg.hour for 2 h (prostaglandin-treated group). A second group of 8 dogs received no 16,16-dimethyl prostaglandin E2 (untreated group). In each dog of both groups, one jejunal segment was perfused with an ethanol-free solution (control segment) and an adjacent segment was perfused with the same solution containing 6% (wt/vol) ethanol (ethanol-perfused segment). The albumin loss (mg/g dry gut wt.90 min, mean +/- SE) by the control and the ethanol-perfused segments was 0.76 +/- 0.23 and 8.29 +/- 1.27, respectively, in the untreated group, and 0.66 +/- 0.23 and 4.81 +/- 0.67, respectively, in the prostaglandin-treated group. The ethanol-induced increase in albumin loss was significant in both groups, but was significantly lower (p less than 0.05) in the prostaglandin-treated group than in the untreated group. Intraluminal ethanol depressed net water, sodium, and glucose transport by 74%, 52%, and 22%, respectively, in the untreated group, and by 92%, 65%, and 38%, respectively, in the prostaglandin-treated group. The magnitude of this depression did not differ significantly between the two groups. As 16,16-dimethyl prostaglandin E2 attenuated the ethanol-induced plasma albumin loss, but not the inhibition of water, sodium, or glucose transport, we conclude that the microvascular and the absorptive changes produced by ethanol are not mediated by the same mechanism.

Prostaglandins and cellular restitution in the gastric mucosa

Topical application of "barrier breakers," including drugs such as aspirin and ethanol, produces widespread destruction of the surface epithelium of the stomach. Such damage does not usually develop into hemorrhagic erosions because the integrity of the surface epithelium is reestablished within a few minutes to hours by the process of epithelial restitution. This process involves active migration of cells from the gastric pits and upper regions of the glands. Restitution is independent of cell division but probably requires an intact basal lamina (basement membrane). The process also depends, in vivo, on adequate microvascular perfusion and can be prevented by high local concentrations of acid. Prostaglandins do not appear to directly affect the restitution process. It is unlikely that prostaglandins either "cytoprotect" the epithelium or accelerate the rate of epithelial migration. Exogenous prostaglandins can, however, protect against the development of hemorrhagic erosions by maintaining an environment in which restitution can proceed. By preventing disruption of the mucosal microvasculature, prostaglandins ensure that the migrating epithelial cells are provided with nutrients and oxygen necessary for cellular activity.