Significance of the goblet-cell mucin layer, the outermost luminal barrier to passage through the gut wall

The effects of dietary compound plant extracts on growth performance, liver and intestine health, and immune related genes expression in hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

The study explored on the effect of dietary compound plant extract supplementation on the growth performance, serum biochemical indicators, liver and intestinal morphological and gene expression levels in the head kidney and spleen of the hybrid grouper (Epinephelus lanceolatus♂× Epinephelus fuscoguttatus♀). The compound plant extracts (BDG) was a mixture of Bupleurum edulis extract, dandelion extract and Ginkgo biloba extract in a ratio of 1:4:1. Basal diets supplemented with BDG at 0, 0.75, 1.5, 3 and 6 g/kg were fed hybrid grouper for 8 weeks. The results showed that dietary 0.75 and 1.5 g/kg BDG supplementation could significantly increase the WGR and SGR of hybrid grouper (P < 0.05). And dietary 0.75 g/kg BDG could also significantly decrease serum aspartate aminotransferase, glucose and lactate dehydrogenase in hybrid grouper (P < 0.05). Dietary BGD supplementation protected the integrity of liver and intestinal morphological structure, reduced the accumulation of liver fat. Dietary BDG supplementation might enhance the immunity of hybrid grouper by regulating the expression of antioxidant and inflammation-related genes in head kidney and spleen of hybrid grouper. Our study demonstrated that the growth promoting effect of Bupleurum extract, dandelion extract and Ginkgo biloba extract in the ratio of 1:4:1 as a compound feed additive was better than any of them as a feed additive alone, and the dosage was less. The optimal additive dosage of BDG was 0.75 g/kg in hybrid grouper diets.

Utility of in vitro and in vivo systems for studying the permeability of capsaicin and nonivamide through different intestinal regions

1. The present study determined and compared the permeability of capsaicin and nonivamide along the length of the intestine in rats. Accordingly, the purpose was to evaluate this synthetic analog as a clinical substitute for capsaicin.. 2. Permeabilities of capsaicin and nonivamide were measured in experiments utilizing Ussing chambers and in vivo methods. Capsaicin concentrations were examined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). 3. Both capsaicin (0.80 × 10^-6cm/s) and nonivamide (0.22 × 10^-6cm/s, p > 0.05) had poor permeabilities across the jejunal membrane. The permeability of nonivamide (10.12 × 10^-6cm/s) was significantly greater than that of capsaicin (5.34 × 10^-6cm/s, p < 0.05) across the iliac membrane. In contrast, the permeability of nonivamide (8.42 × 10^-6cm/s) across the colonic membrane was markedly lower than that of capsaicin (14.48 × 10^-6cm/s, p < 0.05). In accordance with the in vitro study, the drug concentration-time curve of nonivamide was significantly higher in the ileum (F = 14.18, p < 0.05) but lower in the colon (F = 11.86, p < 0.05) compared with capsaicin. 4. The results demonstrate that capsaicin and nonivamide exhibit varying permeabilities across several different intestinal tissues. The relevance of such extended investigations to healthcare is underscored by the lower cost of nonivamide versus capsaicin, along with potential application in prevention and management of the disease.

Absorption-Enhancing Effect of Nitric Oxide on the Absorption of Hydrophobic Drugs in Rat Duodenum

Nitric oxide (NO), an endogenous gas that plays a versatile role in the physiological system, has the ability to increase the intestinal absorption of water-soluble compounds through the paracellular route. However, it remains unclear whether NO can enhance the absorption of hydrophobic drugs through the transcellular route. In this study, we examined the absorption-enhancing effect of NO on intestinal permeability of hydrophobic drugs in rat intestine. The pretreatment of rat gastrointestinal sacs with NOC7, a NO-releasing reagent, significantly increased the permeation of griseofulvin from mucosa to serosa in the sacs prepared from the duodenum, but not in those prepared from the other regions such as jejunum, ileum, and colon. The absorption-enhancing effect of NOC7 on the duodenal permeation varied depending on the hydrophobicity of the drugs used. Furthermore, NOC7 treatment was found to be apparently ineffective on the griseofulvin permeation in the duodenum pretreated with dithiothreitol (DTT) that was used as a mucus remover, even though the permeation was increased by pretreatment with DTT alone. These results suggest that NO increases the absorption of hydrophobic drugs through the transcellular route in the duodenum by modulating the mucus layer function.

The intestinal mucus layer is a critical component of the gut barrier that is damaged during acute pancreatitis

Gut barrier failure has been implicated in the progression from single-organ injury to multiple-organ failure. The unstirred mucus layer is a major component of the physiological gut barrier; its role in acute pancreatitis (AP) is not clearly defined. Rats underwent biliopancreatic duct ligation-induced AP; two controls were used: biliopancreatic duct ligation with drainage and sham duct ligation. After 4.5 h, serum and ascitic amylase activity was measured. Mucus was analyzed for reactive nitrogen intermediate-mediated damage, reactive oxygen species-induced damage, and total antioxidant capacity. Mucus coverage and villous injury were assessed histologically. Ileum permeability was measured by diffusion of a fluorescent Dextran probe. Histology and morphology of the mucus layer were validated in a mouse AP model (intraductal taurocholate plus cerulein). Biliopancreatic duct ligation increased serum α-amylase, ascitic volume, and ascitic α-amylase. Intestinal permeability was increased, which was associated with loss of the unstirred mucus layer but not villous injury. These changes correlated with increased reactive oxygen species- and- reactive nitrogen intermediate-mediated mucus damage as well as decreased mucus total antioxidant capacity but were not present in the two control groups. Using a different model of AP in mice, the finding of mucus layer disruption was recapitulated at 6 h after AP, but by 24 h, rebound hypersecretion of inspissated mucus was seen. These results support the hypothesis that damage to the unstirred mucus layer with evidence of oxidative stress occurs during AP-induced gut barrier failure.

Absorption of Etoposide (VP-16-213) from the Small Intestine of the Rat. The Potential Role of Mucus as an Absorption Rate Limiting Barrier

The absorption of etoposide (VP-16-213) was investigated in a perfused intestinal loop. The absorbed amount of drug was determined by collecting the blood draining the loop via cannulation of the efferent jejunal vein. The absorption rate of VP-16-213 strongly depended on the composition of the perfusion medium. The addition of taurocholate to an aqueous etoposide solution enhanced the absorption rate. When N-acetylcysteine was added to an aqueous solution, the absorption rate dropped significantly.

Dietary nickel chloride restrains the development of small intestine in broilers

The aim of this study was to determine the effects of dietary NiCl2 on the development of the small intestine in broilers by the methods of light microscopy, histochemistry and enzyme-linked immunosorbent assay. A total of 240 one-day-old avian broilers were divided into four groups and fed on a corn-soybean basal diet or the same basal diet supplemented with 300, 600 and 900 mg/kg of nickel chloride (NiCl2) for 42 days. Results showed that the small intestinal villus height, crypt depth and villus/crypt ratio were significantly decreased, and also the small intestinal goblet cells numbers and insulin-like growth factor-1 (IGF-1) and epidermal growth factor (EGF) contents were significantly decreased in the 300-, 600- and 900-mg/kg groups when compared with those of the control group. In conclusion, dietary NiCl2 in excess of 300 mg/kg reduced the villus height, crypt depth, the goblet cells population and the IGF-1 and EGF contents in the small intestine, indicating that the normal development and function of the small intestine were finally impaired in broilers. This study firstly provided the new experimental information for future studies on the effects of NiCl2 on the intestinal function in humans and other animals.

Breakdown of mucin as barrier to digestive enzymes in the ischemic rat small intestine

Loss of integrity of the epithelial/mucosal barrier in the small intestine has been associated with different pathologies that originate and/or develop in the gastrointestinal tract. We showed recently that mucin, the main protein in the mucus layer, is disrupted during early periods of intestinal ischemia. This event is accompanied by entry of pancreatic digestive enzymes into the intestinal wall. We hypothesize that the mucin-containing mucus layer is the main barrier preventing digestive enzymes from contacting the epithelium. Mucin breakdown may render the epithelium accessible to pancreatic enzymes, causing its disruption and increased permeability. The objective of this study was to investigate the role of mucin as a protection for epithelial integrity and function. A rat model of 30 min splanchnic arterial occlusion (SAO) was used to study the degradation of two mucin isoforms (mucin 2 and 13) and two epithelial membrane proteins (E-cadherin and toll-like receptor 4, TLR4). In addition, the role of digestive enzymes in mucin breakdown was assessed in this model by luminal inhibition with acarbose, tranexamic acid, or nafamostat mesilate. Furthermore, the protective effect of the mucin layer against trypsin-mediated disruption of the intestinal epithelium was studied in vitro. Rats after SAO showed degradation of mucin 2 and fragmentation of mucin 13, which was not prevented by protease inhibition. Mucin breakdown was accompanied by increased intestinal permeability to FITC-dextran as well as degradation of E-cadherin and TLR4. Addition of mucin to intestinal epithelial cells in vitro protected against trypsin-mediated degradation of E-cadherin and TLR4 and reduced permeability of FITC-dextran across the monolayer. These results indicate that mucin plays an important role in the preservation of the mucosal barrier and that ischemia but not digestive enzymes disturbs mucin integrity, while digestive enzymes actively mediate epithelial cell disruption.

Sevelamer hydrochloride binds phosphate released from phytate in chicks fed 1α-hydroxy cholecalciferol

OBJECTIVE

Hyperphosphatemia in animal models of human renal disease has been linked to increased risk of death. Phosphate binders (e.g., sevelamer hydrochloride) and plant-based, low phosphate diets are used to reduce dietary phosphate load; however, animal models show that treatment with active forms of vitamin D(3) (e.g., calcitriol, a renal disease therapy) renders plant phytate phosphate available for absorption. Using an established chick model, the effectiveness of sevelamer in preventing the apparent absorption of liberated phytate phosphate during active vitamin D use was investigated in two separate experiments.

DESIGN

One-day-old chicks were fed ad libitum a basal diet containing deficient levels of inorganic phosphate (0.13%), but adequate in total phosphate (0.40%, 0.23% as phytate phosphate), with or without the inclusion of sevelamer hydrochloride (a phosphate binder), available inorganic phosphate, or active vitamin D as 1α-(OH) D(3).

MAIN OUTCOME MEASURES

Plasma phosphate (mg/dL), total bone ash (%), and weight gain (g).

RESULTS

Adding inorganic phosphate (0.36%) or 1α-(OH) D(3) increased plasma phosphate 49% and 48%, respectively (P < .0001), and bone ash 23% and 19%, respectively (P < .001). The addition of 1% sevelamer to the basal diet with added inorganic phosphate or 1α-(OH) D(3) significantly decreased plasma phosphate by 28% and 20%, respectively (P < .01).

CONCLUSION

Active vitamin D increased the availability of phytate phosphate for intestinal absorption in an animal model; however, sevelamer effectively reduced the availability of phosphate liberated from phytate. These data imply that sevelamer has phytate phosphate binding efficacy.

Intestinal mucus layer preservation in female rats attenuates gut injury after trauma-hemorrhagic shock

BACKGROUND

We tested the hypothesis that females are more resistant to trauma-hemorrhagic shock (T/HS)-induced gut injury than males, and this is related to better preservation of their intestinal mucus layer, which is influenced in turn by the estrus cycle stage at the time of injury.

METHODS

Male, proestrus and diestrus female rats underwent a laparotomy (trauma) and 90 minutes of shock ( approximately 35 mm Hg). At 3 hours after reperfusion, terminal ileum was harvested and stained with Carnoy's Alcian Blue for mucus assessment, hematoxylin and eosin, and periodic acid schiff for villous and goblet cell morphology and injury. Ileal permeability was measured in separate intestinal segments using the ex vivo everted gut sac technique.

RESULTS

When compared with males, proestrus female rats were significantly more resistant to T/HS-induced morphologic gut injury, as reflected in both a lower incidence of villous injury (14% vs. 22%; p < 0.05) and a lesser grade of injury (1.0 vs. 2.8; p < 0.05) as well as preservation of gut barrier function (17.9 vs. 32.2; p < 0.05). This resistance to gut injury was associated with significant preservation of the mucus layer (87% vs. 62%; p < 0.05) and was influenced by the estrus cycle stage of the female rats. There was a significant inverse correlation between mucus layer coverage and the incidence (r = 0.9; p < 0.0001) and magnitude (r = 0.89; p < 0.0001) of villous injury and gut permeability (r = 0.74; p < 0.001).

CONCLUSIONS

The resistance of female rats to T/HS-induced intestinal injury and dysfunction was associated with better preservation of the intestinal mucus barrier and was to some extent estrus cycle-dependent. Preservation of the mucus barrier may protect against shock-induced gut injury and subsequent distant organ injury by limiting the ability of luminal contents such as bacteria and digestive enzymes from coming into direct contact with the epithelium.

Site of drug absorption after oral administration: Assessment of membrane permeability and luminal concentration of drugs in each segment of gastrointestinal tract

This study was conducted to assess the site of drug absorption in the gastrointestinal (GI) tract after oral administration. Drug permeability to different regions of rat intestine, jejunum, ileum and colon, was measured by in situ single-pass perfusion method. It was revealed that the epithelial surface area should not be a determinant of the regional difference in the intestinal permeability of highly permeable drugs. Effects of the mucus layer at the surface of the epithelium and the fluidity of the epithelial cell membrane on the drug permeability were investigated. These factors are demonstrated to contribute to the regional differences in intestinal drug permeability. The luminal drug concentration in each segment of the GI tract after oral administration was measured directly in fasted rats. Water ingested orally was absorbed quickly in the jejunum and the luminal fluid volume was diminished in the middle to lower part of the small intestine. According to the absorption of water luminal concentration of atenolol, a drug with low permeability, was elevated and exceeded the initial dose concentration. In contrast, the concentration of highly permeable drugs, antipyrine and metoprolol, decreased quickly in the upper part of the intestine and a significant amount of drugs was not detected in the lower jejunum and the ileum. From the time-profiles of luminal drug concentration, fraction of dose absorbed from each segment of the GI tract was calculated. Both antipyrine and metoprolol were found to be absorbed quickly at the upper part of the small intestine. In addition, the possible contribution of gastric absorption was demonstrated for these drugs. The pattern of site-dependent absorption of atenolol showed the higher absorbability in the middle and lower portion of the jejunum. These informations on site-dependent absorption of drugs are considered to be important for effective oral delivery systems.

Increased luminal mucin does not disturb glucose or ovalbumin absorption in rats fed insoluble dietary fiber

We tested whether increased mucin secretion due to ingestion of insoluble dietary fiber (IDF) affects small intestinal nutrient absorption in rats. Polystyrene foam (PSF) with a true expansion ratio of 54.9 was used as a model for IDF with high bulk-forming properties. In Expt. 1, rats were fed a control diet or diet containing 50 g PSF/kg for 1, 3, 5, or 7 d. Small intestinal mucin fractions were isolated, and O-linked oligosaccharide chains were measured. The luminal mucin content reached a maximum within 5 d after PSF ingestion. In Expt. 2, rats were fed a control diet or diet containing 50 g PSF/kg for 7 d, and then all rats were switched to the control diet for 1, 3, or 5 d. The increased capacity for luminal mucin secretion disappeared within 5 d after ceasing PSF ingestion. In Expt. 3, rats were fed a control diet or diet containing 70 g PSF/kg for 7 d. Glucose (1g/kg) was administered orally after 12 h of food deprivation. The blood glucose concentrations did not differ between the groups. In Expt. 4, rats were fed a control diet or diet containing 90 g PSF/kg for 14 d. At d 7, portal cannulae were installed. A mixed solution of glucose (1g/kg) and ovalbumin (OVA, 250 mg/kg) was orally administered after 12 h of food deprivation, and responses of portal glucose and OVA concentrations were monitored for 120 min. Although luminal mucin contents were almost doubled in the 9% PSF group compared with the control group, neither portal glucose nor OVA concentration differed at any time point. The results suggest that the short-term ingestion of IDF significantly increases the luminal mucin content, but that this does not disturb nutrient absorption.

Interaction of bile salts with gastrointestinal mucins

The properties of three mucins were examined to identify the structural features responsible for their functional difterences. Bovine submaxillary mucin (BSM), porcine gastric mucin (PGM), and rat intestinal mucin (RIM) were each characterized, and high carbohydrate contents were found for RIM and PGM. The amino acid compositions were typical of mucin glycoproteins, with over half comprising small, neutral amino acids. Thereafter, each mucin was equilibrated with three different series of concentrations of the bile salts sodium taurocholate, sodium taurodeoxycholate, and sodium taurochenodeoxycholate. Following multiple centrifugations, the supernatant and mucin pellet concentrations of the bile salts were measured. The bile salt pellet concentration was plotted as a function of supernatant concentration, and from the slopes, the excluded volumes were calculated as 25, 29-44, and 28 55 mL/g for BSM, RIM, and PGM, respectively. The intercepts were 8-10, 2-3, and 1-3 mM for BSM, RIM, and PGM, respectively, which represents an estimate of the bound concentration of bile salt. Differences among the bile salts were observed in the excluded volume and amount bound, but no trends were evident. The bile salts may interact as aggregates with the hydrophobic areas and carbohydrate side chains of the mucins, providing favorable sites for association. The binding at low concentrations with exclusion at high concentrations is significant for modulating the absorption of lipid aggregates from the intestine. Finally, the differences among the mucins reflect the unique structure function relationship of these gastrointestinal mucins.

Excluded volume effect of rat intestinal mucin on taurocholate/phosphatidylcholine mixed micelles

The interaction of bile salt/phospholipid mixed micelles with an intestinal mucin has been investigated to provide the foundation for the transport of ingested fat and poorly water-soluble drugs through the intestinal mucous layer. Egg phosphatidylcholine (PC) was equilibrated with sodium taurocholate (TC) to generate several series of solutions, which had different intermicellar concentrations of TC. Within each series, each solution had the same IMC and thereby micelle sizes, but varied with respect to micelle concentration. These solutions were combined with isolated rat intestinal mucin, equilibrated, and then separated by centrifugation. The supernatant and mucin pellet were assayed for PC and TC, and the diffusion coefficient of PC was measured in the supernatant by PFG-SE NMR spectroscopy. For each series, four linear relationships were found; TC supernatant concentration plotted as a function of PC supernatant concentration; TC pellet concentration plotted as a function of PC pellet concentration; TC pellet concentration plotted as a function of TC supernatant concentration; and PC pellet concentration plotted as a function of PC supernatant concentration. Theoretical analysis of these results indicated that mucin excludes from 25 to 80% of the bile salt/phospholipid mixed micelles with greater exclusion observed with larger micelle size. There is preferential association of the taurocholate with intestinal mucin, when present in the mixed micelle region of the phase diagram. The association coupled with exclusion would allow mucin to modulate the concentration of bile salt at the epithelial surface.

Transport of lipophilic drug molecules in a new mucus-secreting cell culture model based on HT29-MTX cells

PURPOSE

A new mucus-secreting in vitro drug absorption model based on monolayers of goblet-cell like sub-clones of the human colon carcinoma cell line HT29 obtained by methotrexate (MTX) treatment was investigated.

METHODS

Twelve sub-clones were isolated and characterized by light microscopy (LM), transelectron microscopy (TEM), confocal laser scanning microscopy (CLSM), transepithelial electrical resistance (TEER) and the transport of a paracellular marker FITC-Dextran (Mw 4400) (FD-4).

RESULTS

Significant differences of microscopical appearance, TEER-values and permeability of FD-4 between the sub-clones were evident. However, two of them, namely MTX-D1 and MTX-E12. formed tight confluent monolayers with a thick mucus-layer on the apical surface. They were used to compare the apparent permeability coefficient (Papp) of a series of lipophilic drugs, which should be affected by the mucus-layer, namely barbiturates (barbituric acid, barbital, phenobarbital, methylphenobarbital and heptabarbital) and testosterone, as a reference, to mucus-free Caco-2 cells. The permeability of drugs with a partition coefficient (log P) > 1 was decreased in the mucus-producing cell lines. Testosterone, the most lipophilic compound, showed a decrease of up to 43%.

CONCLUSIONS

We demonstrated that the mucus layer is a significant barrier to drug absorption for lipophilic drugs. In conclusion, our model may serve as a suitable in-vitro cell culture model to study the influence of the mucus layer on drug diffusion.

Interaction of bile salt and phospholipids with bovine submaxillary mucin

PURPOSE

The purpose of this study was to determine the distribution and diffusion of sodium taurocholate-phospholipid micelles with mucin in order to provide the foundation for understanding the transport of ingested fat and poorly water-soluble drugs through the intestinal mucous layer.

METHODS

Sodium taurocholate (NaTC) was dispersed with egg phosphatidylcholines (PC) to yield mixed micelles of a specific size and concentration. A preliminary study was conducted to determine the time required for equilibration of PC/TC micellar solutions with mucin. PC/TC micellar solutions were dialyzed against fixed and variable concentrations of bovine submaxillary mucin after which the concentration of PC and NaTC was measured by an assay for total phosphorus and by HPLC, respectively. In addition, a quantitative assay of TC and PC by NMR was developed and used to estimate the mobile fraction of lipids in the samples. Finally, pulsed-field gradient spin echo NMR self-diffusion measurements were made of the water, TC, and PC in the samples obtained from dialysis.

RESULTS

TC/PC micellar solutions achieved equilibrium with mucin in 7 days. Mucin did not affect the equilibrium concentration of PC or TC, except at high concentrations of mucin (5%), and then the effect was small. NMR quantitation was valid for PC and TC systems containing small micelles, but deviated significantly with systems containing large micelles. Mucin decreased the diffusivity of water and the phospholipids, but the effect was relatively small. Mucin dramatically affected the mobility of TC, which prevented a straightforward interpretation of the calculated diffusion coefficients.

CONCLUSIONS

Mucin has a minor effect on the equilibrium distribution of phospholipids and bile salts. However, lipids are readily accommodated by mucus, which can significantly increase the permeability of the mucous layer, particularly for poorly water-soluble drugs.

The physical properties of biogels and their permeability for macromolecular drugs and colloidal drug carriers

Macromolecular drugs, either free or complexed with colloidal drug carriers, have created a great deal of interest during the last decade. If one wants to administer these new therapeutics via the oral, nasal, and cervical routes or through the conductive airways, one of the first barriers to overcome is the mucus layer that adheres to the related epithelia. In this review, the physicochemical properties of biogels, macromolecular drugs, and colloidal drug carriers that play a major role in transport through biogels are reviewed. Also, methods of studying the mobility of macromolecular drugs and colloidal drug carriers in and through biogels are addressed.

Developmental changes in distribution of the mucous gel layer and intestinal permeability in rat small intestine

BACKGROUND

From the developmental aspects, the distribution of fluorescein isothiocyanate dextran 70,000 (FTTC-dextran) and mucous gel across the lumen of small intestine was observed as an investigation into the role of mucous gel on intestinal permeability. Furthermore, the effect of N-acetyl cysteine (NAC), a mucolytic agent, on intestinal permeability was examined.

METHODS

In suckling and weaned rats, FTTC-dextran (750 mg/kg body wt) was gavage-fed. After 3 hours, blood samples were taken by cardiac puncture to analyze plasma FTTC-dextran by fluorescence spectrometry. Samples of small intestine with luminal contents were frozen and sectioned in a cryostat for fluorescence microscopy; the same sections were placed in a 0.2% celloidin solution to preserve mucous gel and were stained by periodic acid-Schiff reaction for light microscopy. In weaned rats, intestinal permeability was examined with different concentrations of intraluminally instilled NAC.

RESULTS

The plasma level of FTTC-dextran showed a significant increase (p < .01) in suckling rats compared with the weaned rats. Morphologic findings were similar in both the jejunum and ileum: The spaces between villi were not entirely filled with mucus but filled with FTTC-dextran in suckling rats, whereas the spaces were filled with mucus and not filled with FTTC-dextran in weaned rats. Intestinal permeability in groups with NAC were significantly higher (p < .01) than that in group without NAC.

CONCLUSIONS

These results suggest that an increase in the mucous gel layer that coats the epithelial lining according to the maturation of the gastrointestinal tract is one of the most important factors for a restriction in intestinal permeability.

Adhesive mucous gel layer and mucus release as intestinal barrier in rats

BACKGROUND

Although it has been reported that total parenteral nutrition induces an increased intestinal permeability and a decreased mucous gel layer covering the intestinal epithelium, the role of mucous gel on intestinal permeability has not been well understood. We examined the in vivo effects of N-acetyl cysteine (NAC) as mucolytic agent and colchicine as suppressant of the mucus production on the intestinal transmission of fluorescein isothiocyanate dextran 70,000 (FITC-dextran).

METHODS

Rats were divided into four groups. In each group, FITC-dextran (750 mg/kg) with or without NAC (3000 mg/kg) was injected into the small intestinal lumen 3 hours after intraperitoneal injection of saline or colchicine (Col, 10 mg/kg). Thirty minutes after injection of FITC-dextran, blood samples were taken from portal vein to analyze plasma fluorescein concentration by fluorescence spectrometry. Samples of small intestine were sectioned in a cryostat for fluorescence microscopy, and the identical sections were stained by periodic acid-Schiff reaction.

RESULTS

Plasma FITC-dextran level in NAC group was higher than that in control group (p < .01), that in Col + NAC group was higher than that in Col group (p < .01) and that in Col + NAC group was higher than that in NAC group (p < .05). The spaces between villi were filled with mucous gel in the control and Col groups, whereas those were not entirely filled with mucous gel in NAC and Col + NAC groups. FITC-dextran and mucous gel showed complementary distribution in all rats. The villous interstitial edema was recognized in NAC group and the villi were disrupted in Col + NAC group.

CONCLUSIONS

These results suggest that intestinal permeability is possibly affected not only by the mucous gel covering the intestinal epithelium but also by mucus release from goblet cells of the small intestine.

Total parenteral nutrition decreases luminal mucous gel and increases permeability of small intestine

The distribution of fluorescein isothiocyanate dextran 70,000 (FITC-dextran) and mucous gel across the lumen of small intestine was observed as an investigation into the role of mucous gel on permeability in total parenteral nutrition (TPN). Thirty-two rats were randomly divided into two groups fed with either TPN or oral rat food. On day 4 or 7, FITC-dextran (750 mg/kg body weight) was given through the gastroduodenal tube. After 1 hour, blood samples were taken by aortic puncture to analyze plasma FITC-dextran by fluorescence spectrometry. Samples of small intestine with luminal contents were frozen and sectioned in a cryostat for fluorescence microscopy; the same sections were placed in a 0.2% celloidin solution for 3 minutes to preserve mucous gel and stained by periodic acid-Schiff reaction for light microscopy. The plasma level of FITC-dextran after 1 hour of this marker injection showed a significant increase (p < .01) in the TPN group compared with the rat food group on days 4 and 7. Morphologic findings on days 4 and 7 were similar in both the jejunum and ileum: The mucous gel filled the spaces between villi and FITC-dextran centered in the lumen in the rat food group, whereas the mucous gel decreased and FITC-dextran filled the spaces between villi in the TPN group. FITC-dextran and mucous gel showed complementary distributions in both groups. These data suggest that TPN decreases luminal mucous gel and increases permeability of small intestine in rats.

Possible changes in luminal surface charge densities of small intestine membrane in the 4-7.4 pH range exhibit varied influence on the absorption rate constants of the ionized and un-ionized species of sulfadiazine in rats

The overall apparent first-order rate constants (Kab) of small intestinal absorption of sulfadiazine were determined in rats in situ at various pHs (4.01-7.42) of the recirculation fluids at 32 degrees. The purpose of the study was to verify our hypothesis that the rate-determining step for the absorption of sulfonamides involves the formation of an "activated complex" consisting of a transient association of the sulfonamide molecules with the surface protein of the microvillus membrane. The Kab versus Fu (where Fu is the fraction of un-ionized sulfadiazine at a given pH) profile prepared according to the equation Kab = Ki+Fu(Ku-Ki), where Ki and Ku are the first-order rate constants of absorption of the ionized and un-ionized species, respectively, was clearly resolvable into two linear segments: one based on the data in the 4.01-6.43 pH range and the other based on the data in the 6.43-7.42 pH range. In view of the fact that the combined molar concentration of aspartic acid and glutamic acid in the microvillus membrane protein is about twice that of arginine and lysine, the resolution of the data into two linear segments suggested that the negative charge density of the microvillus surface membrane protein in the 6.43-7.42 pH range is greater than that in the 4.01-6.43 pH range. The Ku and Ki values of sulfadiazine were determined in each pH range. It was noted that Ku was greater than Ki in each pH range, and that Ki in the 4.01-6.43 pH range was greater than that in the 6.43-7.42 pH range.(ABSTRACT TRUNCATED AT 250 WORDS)

A drug absorption model based on the mucus layer producing human intestinal goblet cell line HT29-H

A new drug absorption model based on monolayers of the human intestinal goblet cell line HT29-H grown on permeable filters has been characterized. HT29-H cells have been shown (a) to form monolayers of mature goblet cells under standard cell culture conditions, (b) to secrete mucin molecules, (c) to produce a mucus layer that covers the apical cell surface, and (d) that this mucus layer is a significant barrier to the absorption of the lipophilic drug testosterone. This is the first demonstration of an intact human mucus layer with functional barrier properties produced in cell culture. The results indicate that monolayers of HT29-H cells provide a valuable complement to mucus-free drug absorption models based on absorptive cell lines such as Caco-2 cells.

A study of macromolecular diffusion through native porcine mucus

A diffusion chamber technique based on time-lag analysis for the estimation of effective diffusion coefficients of radiolabelled macromolecules of varying molecular weights through native mucus gel is reported. For all solutes studied, a reduction in effective diffusion coefficients was observed with a retardation of solute flux in both aqueous and mucus layers. Over the molecular weight range of solutes investigated (126-186,000 Daltons), a consistent effect of molecular weight was evident with regard to the retarding effect of mucus. No apparent or absolute molecular weight cut-off for macromolecular transfer was exhibited. However, at high molecular weights (greater than 30,000 Daltons) the retardation was greatly enhanced. The results confirm that mucus can be regarded as a gel with finite pores, but that it does not constitute an absolute barrier to even high molecular weight solutes.

Electrochemical determination of the permeability of porcine mucus to model solute compounds

An electrochemical approach to the determination of permeability through native mucus gel of simple electrochemically active solutes is reported. For all the solutes studied, a reduction in effective diffusion coefficients was observed, with retardation of solute flux by a factor of at least two. However, NADH and the dicarboxylic acid derivative of ferrocene demonstrated a substantial, almost ten-fold, reduction in permeability through mucus. Results for the controls were in reasonable agreement with literature values where available. No consistent effect of molecular weight was evident with regard to the barrier properties of mucus over the molecular weight range of solutes investigated (34-660 daltons). The results suggest that mucus is acting more than as a gel support for an unstirred water layer.

Diffusion coefficient in native mucus gel of rat small intestine

The diffusion coefficients of [3H] water, urea, benzoic acid, antipyrine, aminopyrine, alpha-methyl-glucoside, L-phenylalanine and of hydrogen ions were measured at 38 degrees C in native mucus gel from rat small intestine. The diffusion in the gel was reduced to 37-53% (for hydrogen ions to 7%) compared with buffer solution. In addition, the buffering capacity of the gel retarded the permeation of hydrogen ions before a steady state flux was attained. A model calculation revealed that in the preparation a gel layer of 80 microns thickness represents 23% of the total permeation resistance for substances with high epithelial permeability. The aqueous part of the pre-epithelial diffusion resistance amounts to 77% of the total resistance.

Effects of fusarenon-X and T-2 toxin on intestinal absorption of monosaccharide in rats

In order to delineate the effects of Fusarenon-X (FX) and T-2 toxin (T-2) on intestinal absorption of monosaccharide, jejunal absorption in vivo and uptake in vitro of 3-0-methyl glucose (m-glucose) and L-glucose were studied in rats. Jejunal absorption in vivo was assessed by determining the rate of appearance of the sugars in plasma of the mesenteric vein draining the jejunal segment, which was perfused with the medium containing radiolabelled m-glucose or L-glucose. Jejunal uptake in vitro was assessed by determining the m-glucose or L-glucose uptake by the everted jejunum taken from toxin-treated rats. m-Glucose absorption was reduced 1 or 3 h after either toxin was injected into the jejunal lumen. A reduction of m-glucose absorption was also noted after intravenous injection of the toxins, although the timing and magnitude of the reduction were slightly different from those seen after the luminal injection. These results suggest that both toxins impair the jejunal function relating to monosaccharide absorption in the early stages of intoxication. The reduction in m-glucose absorption was associated with a reduction in L-glucose absorption and unchanged or increased uptake of L-glucose. The active transport component, which was indicated by the difference between absorption or uptake of the two sugars, was also reduced in association with the reduction of m-glucose absorption. These results suggest that the toxins cause specific damage in the active transport system for monosaccharides on the one hand, and impairment of their diffusional movement from the epithelial layer to the mesenteric vein on the other.

Effect of mucin and polymeric gums on uptake of fluorescein esters

The effect of three biopolymers on the mass transport of fluorescein esters into cultured epithelial cell monolayers was determined. The method involved measurement of the rate of accumulation of fluorescein after extracellular introduction of its relatively nonfluorescent ester derivatives. Calibration of the intracellular fluorescence along with cell enumeration allowed estimation of the molar velocity of uptake on a per cell basis. Fick's law with modified Michaelis-Menten kinetics provided a kinetic description of the sequential transport and cellular metabolism and permitted estimation of the permeability, maximum velocity, Vm, and apparent Michaelis-Menten constant, Km. From the uptake studies, the calculated Vm and Km decreased with increasing chain length of the ester which is consistent with deacylation of the enzyme being the rate limiting step of the enzymatic conversion. The estimated permeabilities of the controls were variable, in part due to the insensitivity of the functional relationship between the estimated parameters. All biopolymers caused a reduction in the calculated permeability, with guar gum and xanthan gum being more effective at a higher concentration than bovine submaxillary mucin. The results support the conclusion that polymers reduce the rate of mass transport through an increase in the resistance of the diffusional boundary layer.

Odorant stimulation of secretory and neural processes in the salamander olfactory mucosa

Topical application of the odorants guaiacol (10(-3) mol/l, 1-30 min) and 2-isobutyl-3-methoxypyrazine (IBMP, 10(-5)-10(-3) mol/l, 15 min) caused time- and concentration-dependent reductions in the secretory granule content of acinar cells of the superficial Bowman's glands (sBG) and moderate to extensive vacuolation in acinar cells of sBG and deep olfactory glands (dG). Topical application of 9.8 mg/ml scopolamine 10 min before 10(-4) mol/l IBMP significantly reduced the amount of secretory granule depletion from sBG compared to that seen with IBMP alone and resulted in less extensive vacuolation in sBG and dG acinar cells. The i.p. injection of 42 mg/kg propranolol 10 min before topical application of 10(-4) mol/l IBMP had no effect on the action of IBMP. Guaiacol and IBMP also had time- and concentration-dependent effects on the secretory activity of sustentacular cells in the olfactory epithelium. The protrusion of secretory material into the mucociliary matrix that covers the epithelial surface and vacuolation within the secretory material resulted from odorant application. Scopolamine and propranolol had no effects on the action of IBMP on sustentacular cell secretory activity. When applied in the vapor phase, guaiacol elicited action potentials recorded from individual olfactory receptor neurons; the impulse frequency was concentration-dependent and showed tonic and phasic components when the duration of stimulation was varied. Low to moderate concentrations of IBMP delivered in the vapor phase evoked monophasic negative slow voltage transients recorded from the surface of the olfactory mucosa. The amplitudes of these transients increased with increasing stimulus concentrations. Higher concentrations or longer stimulus durations evoked longer-latency positive-voltage generating processes and negative afterpotentials. The properties of the electrophysiological responses to both odorants were characteristic of responses evoked by a wide variety of 'typical' odorants.

Closed rat jejunal segment in situ: role of pre-epithelial diffusion resistance (unstirred layer) in the absorption process and model analysis

After intraluminal injection of 0.5 ml buffer solution into closed jejunal segments (length, 3-5 cm) of anesthetized rats the appearance rates of a series of labeled substances in jejunal venous blood were measured for 30 min in situ (initial concentration, 0.02-10 mmol/l or 1 GBq/l tritiated water). The appearance rates quickly rose to a maximum and then declined almost exponentially. Model analysis of the descending of branch of the curves by two one-compartment models (perfect luminal mixing, radial diffusion without convection) revealed a relative pre-epithelial diffusion resistance of nearly 100% for benzoic acid, salicylic acid, L-lysine (0.02 and 1 mmol/l), alpha-methyl-D-glucoside, and L-phenylalanine; 80% to 95% for aniline and butanol; 50% to 80% for benzyl alcohol, theophylline, aminopyrine, antipyrine, dodecanol, and D-galactose; approximately 40% for tritiated water; approximately 30% for L-lysine (10 mmol/l); 10% to 20% for urea and benzylamine; and approximately 4% for erythritol. The shape of the curves was well described by a two-compartment model (intestinal lumen and "tissue", radial luminal diffusion without convection); the variability of the data, however, prevented closer analysis of the parameters of this model. Since pre-epithelial diffusion (unstirred layer) in the closed jejunal segment without peristalsis is the rate limiting step in the absorption process of highly permeant substances, information on intestinal epithelium can be obtained only with poorly permeant substances.

Occurrence, absorption and metabolism of short chain fatty acids in the digestive tract of mammals

Short chain fatty acids (SCFA) also named volatile fatty acids, mainly acetate, propionate and butyrate, are the major end-products of the microbial digestion of carbohydrates in the alimentary canal. The highest concentrations are observed in the forestomach of the ruminants and in the large intestine (caecum and colon) of all the mammals. Butyrate and caproate released by action of gastric lipase on bovine milk triacylglycerols ingested by preruminants or infants are of nutritional importance too. Both squamous stratified mucosa of rumen and columnar simple epithelium of intestine absorb readily SCFA. The mechanisms of SCFA absorption are incompletely known. Passive diffusion of the unionized form across the cell membrane is currently admitted. In the lumen, the necessary protonation of SCFA anions could come first from the hydration of CO2. The ubiquitous cell membrane process of Na+-H+ exchange can also supply luminal protons. Evidence for an acid microclimate (pH = 5.8-6.8) suitable for SCFA-protonation on the surface of the intestinal lining has been provided recently. This microclimate would be generated by an epithelial secretion of H+ ions and would be protected by the mucus coating from the variable pH of luminal contents. Part of the absorbed SCFA does not reach plasma because it is metabolized in the gastrointestinal wall. Acetate incorporation in mucosal higher lipids is well-known. However, the preponderant metabolic pathway for all the SCFA is catabolism to CO2 except in the rumen wall where about 80% of butyrate is converted to ketone bodies which afterwards flow into bloodstream. Thus, SCFA are an important energy source for the gut mucosa itself.

Immunological control of drug absorption from the gastrointestinal tract: the mechanism whereby intestinal anaphylaxis interferes with the intestinal absorption of bromthymol blue in the rat

Rats were immunized intraperitoneally with ovalbumin and the disappearance of bromthymol blue (BTB) from the intestinal lumen, its accumulation in the tissue, and its net absorption were examined by means of an in-situ recirculation technique during local anaphylaxis. The disappearance of BTB from the intestinal lumen and its net absorption were significantly reduced, but there was no significant effect on its accumulation in the tissue. The pH value of the luminal solution and the perfusate volume were not influenced by intraluminal challenge with the antigen in ovalbumin-immunized rats. In addition, no significant effect was observed on intestinal permeability to BTB in the in-vitro everted sac technique. The intestinal blood flow, measured by a hydrogen clearance method, was not reduced significantly by the intraluminal exposure to antigen. There was enhanced Evans Blue leakage and mucus release in the perfusate after intraluminal challenge with ovalbumin in ovalbumin-immunized rats, but not in non-immunized rats. A significant increase of BTB binding with macromolecular substances in the perfusate was observed during the local anaphylaxis. These findings suggest that the decreased absorption of BTB is due to the interaction with the macromolecular substances in the perfusate during local anaphylaxis.

Histological and histochemical studies of the secretory components of the salamander olfactory mucosa: effects of isoproterenol and olfactory nerve section

Secretory components of the salamander olfactory mucosa, sustentacular cells (SC), and Bowman's glands (BG), were examined histologically and histochemically. In the aquatic larval salamander, SC in sensory grooves contained secretory granules; the submucosa contained a single layer of homogeneous, ductless glands. In the land-dwelling adult salamander, SC spanning a flat epithelial sheet contained vesicles. Subjacent to the epithelium in both dorsal and ventral mucosae lay BG whose ducts opened at the surface of the epithelium. In the ventral mucosa, two additional layers of olfactory glands (OG) lying below the BG were identified; ducts were not observed in association with the OG. The beta-adrenergic agonist isoproterenol caused depletion of secretory granules from BG and OG of larval, young, and adult salamanders but had no discernible effect on SC. Histochemical techniques (Alcian blue at pH 2.5 and pH 1.0, high-iron diamine, and the periodic acid-Schiff reaction) demonstrated that SC contained neutral, acidic, and small amounts of sulfated mucopolysaccharides (MPS), BG and OG contained only neutral MPS. In contrast, glands under adjacent respiratory epithelium contained both acidic and sulfated MPS. Unilateral olfactory nerve section ( ONX ) caused changes in the histochemical reactivity of acidic and sulfated MPS in SC on the ipsilateral and later on the contralateral side. Neutral MPS staining became enhanced first in the OG that lay under the BG, then in BG cells, and later in the deepest OG layer. Ipsilateral changes preceded contralateral ones. At 24 days post- ONX , some acinar cells in the deep OG contained acidic but not sulfated MPS.

Steady state bioavailability of a new oral formulation of Hydergine in geriatric patients

The relative bioavailability of the newly developed formulation of co-dergocrine mesylate (Hydergine special, 1 x 4 mg) was determined in elderly patients under steady state conditions, with conventional Hydergine forte tablets (2 x 2 mg) as a reference. Both formulations were given once a day for 8 days in a randomised cross-over design. The areas under the curve showed that the bioavailability of the new tablet was about 30% higher (28 +/- 6.3%) than that of Hydergine forte. Th peak plasma concentration was reached 3 +/- 0.9 h after administration. Because of its greater relative bioavailability higher plasma levels were found 2-24 hours after the Hydergine special formulation than after Hydergine forte tablets.