The effect of ketoconazole on the jejunal permeability and CYP3A metabolism of (R/S)-verapamil in humans.

AIMS: The purpose of this human intestinal perfusion study was to investigate the effect of ketoconazole on the jejunal permeability and first-pass metabolism of (R)- and (S)-verapamil in humans. METHODS: A regional single-pass perfusion of the jejunum was performed using a Loc-I-Gut(R) perfusion tube in six healthy volunteers. Each perfusion lasted for 200 min and was divided into two periods of 100 min each. The inlet concentration of (R/S)-verapamil was 120 mg l-1 in both periods, and ketoconazole was added at 40 mg l-1 in period 2. (R/S)-verapamil was also administered as a short intravenous infusion of 5 mg, over a period of 10 min. The appearance ratios of the CYP3A formed metabolites (R)- and (S)-norverapamil were also estimated in the outlet jejunal perfusate. RESULTS: The effective jejunal permeability (Peff) of both (R)- and (S)-verapamil was unaffected by the addition of ketoconazole in period 2 suggesting that ketoconazole had no effect on the P-glycoprotein mediated efflux. However, the appearance ratio of both (R)- and (S)-norverapamil in the outlet jejunal perfusate decreased in the presence of ketoconazole. The rate of absorption into plasma of (R)- and (S)-verapamil increased despite the low dose of ketoconazole added, indicating an inhibition of the gut wall metabolism of (R/S)-verapamil by ketoconazole. CONCLUSIONS: Ketoconazole did not affect the jejunal Peff of (R/S)-verapamil, but it did increase the overall transport into the systemic circulation (bioavailability), probably by inhibition of the gut wall metabolism of verapamil. This might be due to ketoconazole being less potent as an inhibitor of P-glycoprotein than of CYP3A4 in vivo in humans.

Eosinophil cationic protein and histamine after intestinal challenge in patients with cow's milk intolerance.

BACKGROUND: Mast cells and eosinophils are key cells in the development of active symptoms in allergic diseases and other inflammatory conditions, and they mediate their action through the release of very potent granule constituents. METHODS: Five patients with milk-related gastrointestinal symptoms diagnosed by double-blind placebo-controlled milk challenges, but with negative responses to skin prick tests and RASTs with milk, and eight healthy control subjects were investigated. Repeated perfusion studies were performed with a two-balloon, six-channel tube by using milk, casein, and whey as antigens. Luminal eosinophil cationic protein, histamine, and albumin were measured by radioimmunoassay. RESULTS: Luminal cow's milk induced a pronounced increase in intestinal secretion of histamine and eosinophil cationic protein in patients, but not control subjects, during the first 20 minutes after challenge (histamine from 123 +/- 12 to 543 +/- 175 ng/cm, hr; eosinophil cationic protein from 80 +/- 23 to 686 +/- 262 ng/cm, hr). Albumin, as a marker of plasma leakage, was also significantly increased. CONCLUSION: These data indicate that mast cells and eosinophils are effector cells not only in patients with allergic disease but also in patients intolerant to foods and lacking circulating antibodies. The underlying mechanisms may be a reaction mediated by locally appearing antibodies or an immunologic activation resembling that found in intestinal disorders such as celiac disease.

Jejunal permeability and hepatic extraction of fluvastatin in humans.

OBJECTIVES: The primary objective was to investigate the effective permeability and the hepatic extraction of fluvastatin, a new 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, during a jejunal perfusion in humans. The secondary objective was to investigate the relationship between human jejunal effective permeability values and physicochemical properties for four different drugs. METHODS: Nine healthy male volunteers were included in the study, which consisted of two sequential study parts. In the first part, the jejunal effective permeability of fluvastatin, antipyrine, metoprolol, and atenolol was assessed with use of the regional jejunal perfusion approach (150 minutes, 2.0 ml/min). After a washout period of at least 5 days, the same subjects received an intravenous infusion of fluvastatin (20 minutes, 2.0 mg). Plasma samples were taken in both parts of the study and were analyzed for the content of fluvastatin. RESULTS: The mean hepatic extraction of fluvastatin was 67% after the jejunal perfusion and 73% after the intravenous infusion. The half-life of fluvastatin was approximately 60 minutes after both administration routes. The jejunal effective permeability and the fraction absorbed both correlated (r2 = 0.968, p < 0.05; and r2 = 0.994, p < 0.05) with the partition coefficient (log D, pH 6.5) but not with the molecular size or the hydrogen bond number. CONCLUSION: Fluvastatin is extracted by the liver to a large extent (about 70%) and has a short half-life after both oral and intravenous administration. In this study, the human jejunal effective permeability and the fraction absorbed for these four drugs were better predicted by log D (pH 6.5) than both the molecular size and the hydrogen bond number.

Effects of luminal antigen on intestinal albumin and hyaluronan permeability and ion transport in atopic patients.

BACKGROUND: Increased luminal transport of proteins and fluid is part of the inflammatory reaction in inflammatory disease of the bowel and of the airways in allergic diseases and asthma. The objective of this study was to determine intestinal appearance rates of albumin and hyaluronan in vivo in atopic patients allergic to birch, as well as changes in net jejunal transport of monovalent ions and water induced by the antigen. METHODS: Secretion studies were performed with the use of a segmental jejunal perfusion system with a small two-balloon, six-channel tube. The intestinal mucosa was challenged with birch allergen in patients allergic to birch and in matched control subjects (n = 12 in both groups). RESULTS: In patients, but not in control subjects, the luminal antigen induced a net increase in albumin of 2689 +/- 567 micrograms/cm/hr and in hyaluronan of 2609 +/- 737 ng/cm/hr (p < 0.01 vs control subjects in both cases). Furthermore, basal net absorption of Cl- ions, Na+ ions, and water was converted to a net secretion after antigen challenge. CONCLUSION: Exposure to antigen normally acting on the respiratory tract induced increased permeability of the gastrointestinal mucosa. This would suggest less organ specificity and more general allergic recognition shared by several immunocompetent tissues in the body, probably mediated by circulating IgE antibodies.

Increased levels of hyaluronan and albumin after intestinal challenge in adult patients with cow's milk intolerance.

BACKGROUND: The mechanisms for adverse reactions to foods in the gastrointestinal tract are poorly understood. Presently, only limited possibilities are available for identification of adverse immunological reactions to different foods. OBJECTIVE: The intestinal inflammatory reactions in adult patients with a history of milk-related gastrointestinal symptoms were studied after intestinal challenges by a jejunal perfusion technique and compared with the reactions in a control group. METHODS: Five skin-prick test and radioallergosorbent test negative and lactose tolerant patients with a history of milk-related gastrointestinal symptoms, verified by double-blind placebo-controlled challenge, and eight healthy controls were investigated. Perfusions were performed allowing analyses of a well-defined 'closed' jejunal segment. Milk perfusions were performed in patients and controls after an overnight fast. Ten millilitres of milk were administered to the segment at 3 mL/min. The jejunal fluid levels of hyaluronan (hyaluronic acid) and albumin were measured. RESULTS: In the five patients the milk challenges induced as a mean fivefold increased levels of hyaluronan compared with prestimulation values, whereas no such increases were seen in the control subjects. Albumin, as a marker of plasma leakage, was also increased in the patients but not in the control subjects. CONCLUSION: The underlying mechanisms for locally increased levels of hyaluronan and also albumin in the intestinal lumen may be secretion of lymph rich in hyaluronan and reflect the mucosal oedema. This capacity of the intestinal mucosa to react with lymph leakage towards a locally infused allergen may be a possible way to delineate gastrointestinal reactions in food-related disorders.

Human proximal duodenal ion and water transport. Role of enteric nervous system and carbonic anhydrase.

Intestinal ion transport is mediated by the interaction of enterocyte function, the enteric nervous system, humoral agents, and mucosal production of carbonic anhydrase. Our purpose was to examine the effect of the carbonic anhydrase inhibitor acetazolamide and inhibition of the enteric nervous system with the topical anesthetic lidocaine on basal and prostaglandin E2-stimulated ion and water transport and transmucosal electrical potential difference. At rest, mean basal (95% confidence intervals) net ion secretion into the human proximal duodenum was: Cl- 670 (288-1052), Na+ 818 (410-1225), K+ 32 (14-51) mumol/cm/hr. Basal net water transport was 30 (14.6-45.3) ml/hr, and the potential difference (PD) was 7.0 (3.6-10.9) mV, lumen negative. Intraluminal prostaglandin E2 increased the secretion of all ions, water, and the PD. After pretreatment with acetazolamide and luminal administration of lidocaine, basal ion transport was unchanged, but the response to luminal PGE2 was inhibited. It is concluded that: (1) at rest there is a net secretion of Na+, K+, Cl-, and water by the human proximal duodenum; and (2) PGE2-stimulated water electrolyte secretion is dependent in part upon mucosal carbonic anhydrase activity and the enteric nervous system.

Acetazolamide inhibits basal and stimulated HCO3- secretion in the human proximal duodenum.

BACKGROUND/AIMS: Carbonic anhydrase activity plays a role in electrolyte transport in many tissues. This study examined the effect of the carbonic anhydrase inhibitor acetazolamide on human basal and prostaglandin E2- and acid-stimulated duodenal mucosal bicarbonate secretion and transmucosal electrical potential difference. METHODS: Seven healthy volunteers participated in four separate experiments. The variables included oral acetazolamide vs. control test and, as agonists of bicarbonate secretion, either luminal acidification or luminal prostaglandin E2. The proximal 4 cm of the duodenum (i.e., the duodenal bulb) was isolated between balloons as previously described and perfused with an HCO(3-)-containing (24 mmol/L) balanced electrolyte glucose-containing (10 mmol/L) solution. RESULTS: Acetazolamide treatment significantly decreased mean basal HCO3- secretion and basal transmucosal potential difference. After luminal acidification, duodenal mucosal bicarbonate increased significantly after both acetazolamide treatment (mean, 626; 95% CI, 91-1160 mumol.cm-1.h-1) and in the control tests (mean, 868; 95% CI, 652-1084 mumol.cm-1.h-1). However, acetazolamide treatment significantly decreased prostaglandin E2-stimulated HCO3- secretion from 461 (95% CI, 307-615) to 222 (95% CI, 121-324) mumol.cm-1.h-1. CONCLUSIONS: Duodenal mucosal carbonic anhydrase activity has an important function in the regulation of basal and prostaglandin E2-stimulated human duodenal mucosal bicarbonate transport.

Endogenous dopamine and duodenal bicarbonate secretion in humans.

BACKGROUND: Catechol-O-methyltransferase (COMT) inhibition prevents tissue degradation of catecholamines including dopamine. This study was undertaken to investigate the effect of intraluminal nitecapone, a peripherally acting COMT inhibitor, on duodenal mucosal bicarbonate secretion in humans and to compare the effect with that of the prostaglandin E1 analogue misoprostol. METHODS: The duodenal bulb was isolated by means of a three-balloon six-channel tube as previously described. Basal bicarbonate secretion and secretion after intraluminal administration of 30 and 150 mg nitecapone were determined in 11 healthy subjects. In 7 of these subjects, effects of intraluminal administration of 30 and 150 micrograms of misoprostol were studied in a second experiment. RESULTS: Even the lower dose of misoprostol increased duodenal bicarbonate secretion from 121 +/- 12 to 221 +/- 36 and the lower dose of nitecapone from 149 +/- 18 to 277 +/- 48 microEq.cm-1 x h-1, respectively (P < 0.05). With 150 micrograms of misoprostol or 150 mg of nitecapone there was a further increase in secretion to 296 +/- 33 (P < 0.01) and 421 +/- 36 (P < 0.001) microEq.cm-1 x h-1, respectively. The rise in bicarbonate secretion in response to nitecapone was associated with some increase in the release of prostaglandin E2 to the luminal perfusate. CONCLUSIONS: It seems likely that peripheral COMT inhibition increases duodenal mucosal bicarbonate secretion and protection by inhibition of mucosal degradation of dopamine, an increase similar in magnitude to that obtained by a prostaglandin E1 analogue.

Intestinal reactivity in allergic and nonallergic patients: an approach to determine the complexity of the mucosal reaction.

BACKGROUND: To determine whether inflammatory markers and mediators were released in response to different intestinal antigens, studies were performed in atopic patients allergic to birch, patients allergic to psyllium powder (ispaghula), and patients intolerant to milk. METHODS: Allergy to birch and psyllium powder was documented by the presence of circulating IgE antibodies and positive skin tests. Patients intolerant to milk had negative outcomes of radioallergosorbent tests and skin tests but positive results of double-blind, placebo-controlled tests. Challenge of the intestine with different antigens was achieved by perfusion of a jejunal segment occluded between balloons. Basal and antigen-activated release of mast cell/basophil and eosinophil products and of substances emanating from the plasma and interstitial fluid was compared in perfusate fluid from patients (n = 8) and matched healthy controls (n = 8). RESULTS: Perfusate levels of albumin and hyaluronan (previous name hyaluronic acid) were increased threefold to fivefold by antigen in all patients, but not in controls. Eosinophilic cationic protein increased in patients but also in ispaghula controls. Histamine was released in response to milk, but not in patients allergic to birch or ispaghula. Prostaglandin E2 increased in milk- and birch-sensitive patients. In response to ispaghula, however, it was released in both patients and controls. CONCLUSIONS: We conclude that subclinical intestinal challenge with antigen induces an increase in the appearance rate of albumin and hyaluronan in the intestinal lumen both in atopic patients (with target organs such as the lungs or nose and eyes) and in patients with intestinal intolerance to milk. These changes in permeation are similar to those reported from other organs such as the lung. They may reflect a common response in early phase I reactions that are either IgE-mediated or occur in response to food antigens without any obvious involvement of an IgE-mediated mechanism. Subclinical provocation with intestinal antigens should prove useful for further elucidation of mechanisms underlying intestinal mucosal reactions to exogenous stimuli.