The retention of 14C-labelled poly(acrylic acids) on gastric and oesophageal mucosa: an in vitro study.

Polymers that bind from solution onto gastric mucosa can be used either as a means of facilitating localised drug delivery, or can act as therapeutic agents in their own right (e.g. by forming a protective layer or by inhibiting enzymes). In our previous study [Int. J. Pharm. 236 (2002) 87], the binding and retention of labelled poly(acrylic acid)s on sections of gastric mucosa from pigs was evaluated using 'dynamic flow' conditions and a high molecular weight poly(acrylic acid) was found to bind most avidly. In the current study, 3% solutions of 'low', 'high' and 'ultra high' molecular weight polymers were evaluated in the 'dynamic flow' model for their ability to bind to tissues from the fundic and pyloric regions of the stomach and the oesophagus of pigs. All the polymers tested were retained on each mucosa for extended periods; the high and ultra high molecular weight polymers showed the greatest retention. Examination of the kinetics of polymer elution suggested that two fractions exist, 'bound' and 'unbound' polymer, showing differing retention profiles. The high molecular weight polymer showed the greatest retention on pyloric tissue, particularly on the upper sections. The retention of the ultra high and high molecular weight polymer was similar on the fundic and oesophageal mucosa, and the distribution was even across the tissue. It was concluded that poly(acrylic acid) binding from solution presents a therapeutic opportunity, and the differences in binding and retention of the polymers on the different mucosae could present an opportunity for targeting.     

Enhanced nasal retention of hydrophobically modified polyelectrolytes

Hydrophobically modified polyelectrolytes (HMP) are polymers with a high content of ionizable groups bonded to hydrophobic groups. Copolymers of poly(acrylic acid) and Pluronic surfactants constitute a special class of HMP whereby poly(propylene oxide) segments act as hydrophobes. The poly(propylene oxide) segments possess temperature-dependent aqueous solubility and the solutions of the Pluronic-poly(acrylic acid) copolymers (MW > 3,000,000) undergo a sol-gel transition when kept at body temperature. Due to the presence of the poly(acrylic acid) segments, the Pluronic-poly(acrylic acid) copolymers are bioadhesive. We have examined the hypothesis that the in-situ gelling polymer formulations of Pluronic-poly(acrylic acid) copolymers may have an enhanced retention in the nasal cavity. The effects of putative bioadhesive (Carbomer 934P) and thermogelling (Pluronic F127) polymers on nasal clearance were compared with Pluronic-poly(acrylic acid) copolymers using a rat model. The enhancement of the residence time of fluorescent labels by the Pluronic-poly(acrylic acid) copolymers was shown to be 5-8-fold that of Carbomer, and 3-6-fold that of Pluronic F127. The results unequivocally demonstrate the superior retention of the HMP that combines bioadhesive and thermogelling capabilities over either a bioadhesive polyelectrolyte or a polymer of a low molecular weight that undergoes a sol-gel transition.     

Polymeric microspheres for drug delivery to the oral cavity: an in vitro evaluation of mucoadhesive potential

Polymeric microparticles were fabricated from Carbopol, polycarbophil, chitosan, or Gantrez using a "water-in-oil emulsification" solvent evaporation method. Mean particle sizes, as determined by laser diffraction, were in the range 23-38 microm. Electron microscopy revealed that all microparticles were spherical and of smooth surface morphology. In pH 7.0 phosphate buffered saline, the microspheres exhibited significantly increased swelling ratios and longer half-times of swelling than the corresponding powdered polymers. The relative merits of the potential usefulness of these microspheres as formulation tools for the enhanced retention of a therapeutic entity within the oral mucosa were evaluated by in vitro mucoadhesion tests. Tensile tests showed that all microspheres under consideration were capable of adhering to porcine esophageal mucosa, with particles prepared from the poly(acrylic acid)s exhibiting greater mucoadhesive strength than those constructed from chitosan or Gantrez. However, in elution experiments involving a challenge with artificial saliva, particles of chitosan or Gantrez were retained onto mucosal tissue for longer time periods than those assembled from the poly(acrylic acid)s.     

超氧化物歧化酶对急性胃粘膜损伤的保护作用

制作不同的动物急性胃粘膜损伤模型，应用外源性超氧化物歧化酶（ＳＯＤ）观测对急性胃粘膜损伤的保护作用。发现ＳＯＤ抑制应激、结扎幽门和阿斯匹林性胃溃疡的形成，降低大鼠胃溃疡形成过程中胃粘膜丙二醛（ＭＤＡ）含量，保护胃粘膜上皮并促进其粘液的分泌，但对胃酸的分泌量无明显影响。提示：ＳＯＤ的胃粘膜保护作用，可能与提高胃粘膜的防御能力有关。     

An investigation of mucus/polymer rheological synergism using synthesised and characterised poly(acrylic acid)s

A range of poly(acrylic acid)s with different average degrees of polymerisation and cross-linking densities were synthesised using a solution polymerisation process. The rheological characteristics of aqueous dispersions of these materials and those of mixtures with homogenised pigs gastric mucus were investigated using dynamic oscillatory rheology, and compared to the known mucoadhesive Carbopol 934P. From the storage moduli, the rheological synergy and relative rheological synergy were calculated, and the effects of concentration and pH on this considered. Generally, the larger the molecular weight (and degree of cross-linking), the greater the rheological synergy, with Carbopol 934P giving the most pronounced effect. Rheological synergy was seen to be concentration-dependent, and a maximum concentration to produce an optimum effect was evident. Acid pHs were seen to favour synergy, although in marked contrast to previous literature reports, the optimum mucus-polymer interaction was not observed at the half ionised value (pH = pKa) but at pH regimes that were unique to each polymer type. This could be influenced by the structural constrains imposed on potential hydrogen bonded interactions. It was concluded that synthesising poly(acrylic acid)s with better defined physicochemical properties than commercially available polymers will advance the study of the phenomenon of rheological synergy.     

Gastric mucosal cytoprotection in the rat by cysteine

The free radical scavengers methyl-methionine sulphonium bromide and cysteine (5%) protected the rat gastric mucosa against ischaemic injury produced by reserpine (5 mg kg-1 i.p.). Pretreatment with 1 mL of 5% cysteine by gavage completely protected against injury rats with no ligation and 70% of rats with pyloric ligation after they had been given aspirin (200 mg kg-1 by gavage), a dose that produced gastric mucosal injury in 40% of rats with no ligation and 70% of rats with pyloric ligation after 4 h. Ethanol (1 mL of 40% solution by gavage) after 1 h produced gastric mucosal injury in all animals and pretreatment with 1 mL of 5% cysteine by gavage completely protected 80% of non-ligated and 70% of pyloric-ligated rats against this injury. This protection was not associated with any significant effect on H+ output. The data suggest that cysteine maintains gastric mucin by a mechanism independent of acid secretion.     

GASTRIC MUCOSAL DEFENCE MECHANISM DURING STRESS OF PYLORIC OBSTRUCTION IN ALBINO RATS

1. The integrity of the gastric mucosa and its ability to secrete mucus are believed to be essential for protection of gastric mucosa against ulceration induced by aggressive factors active in any stress situation. This study involves a three-compartmental analysis of gastric mucosal barrier in pylorus-ligated albino rats. 2. Quantitative analyses of histologically identifiable gastric mucosal epithelial neutral glycoproteins and gastric adherent mucus from oxyntic and pyloric gland areas, and components of non-dialysable mucosubstances in gastric secretion were made under stress of pyloric obstruction for 4, 8, and 16 h durations. Epithelial mucin was identified by periodic acid-Schiff (PAS) staining technique and assessed from the ratio of gastric mucosal thickness to the depth of PAS positive materials in it. The remaining visible mucus adhered to the gastric mucosa was estimated by Alcian blue binding technique. The results were compared with that of identical control groups. 3. A significant reduction in mucosal epithelial PAS positive materials after 8 or 16 h of pylorus ligation was observed. 4. The Alcian blue binding capacity of the pyloric gland area was increased significantly after 4 h of pylorus ligation, while after 8 or 16 h it was reduced in both oxyntic and pyloric gland areas. 5. Significant reductions in the rate of gastric secretion and volume, as well as concentration of the components of non-dialysable mucosubstances, were observed, indicating decreased synthesis of mucus glycoproteins. 6. Disruption of the mucosal barrier may have occurred due to decreased mucus synthesis and acid-pepsin accumulation; both could be due to stress associated with gastric distension. 7. The present findings confirm the role of mucus in protecting the underlying gastric epithelium during stress. The adherent mucus offers a first line of defence and epithelial mucus a second line of defence.     

Use of scavenging oxygen-derived free radicals to protect the rat against aspirin- and ethanol-induced erosive gastritis.

Oxygen-derived free radicals are cytotoxic and produce tissue damage. The effect of the radical scavengers allopurinol and dimethyl sulfoxide (DMSO) on aspirin- and ethanol-induced acute gastric mucosal injury was studied in the rat. Orogastric instillation of aspirin at 200 mg/kg produced, after 4 h, gastric mucosal injury in 30% of rats without pyloric ligation [score, 3.1 +/- 0.8 mm2, mean +/- standard error of the mean (SEM); n = 10] and in 80% of rats with this ligation (score, 10.4 +/- 1.2 mm2, mean +/- SEM; n = 10). Gavage with 1 mL of 2 or 5% allopurinol or DMSO at 24 h before and again just before aspirin administration completely protected rats with or without pyloric ligation against injury. Orogastric instillation of ethanol (1 mL of a 40% solution) produced, after 1 h, gastric mucosal injury in all rats with or without pyloric ligation (24.1 +/- 1.7 and 14.1 +/- 1.3 mm2, respectively, mean +/- SEM; n = 10). Gavage with 1 mL of 5% allopurinol or DMSO at 24 h before and again just before ethanol administration completely protected rats with or without pyloric ligation against injury. Protection against the aspirin- and ethanol-induced injury was not associated with any significant effect on the H+ output. The results suggest that oxygen-derived free radicals are directly implicated in the mechanism of aspirin- and ethanol-induced acute gastric mucosal injury and that scavenging these free radicals protects against injury by maintaining the integrity of the gastric mucosa.     

牛乳铁蛋白对实验性胃黏膜损伤及胃溃疡大鼠模型的影响

目的 观察牛乳铁蛋白对实验性大鼠胃黏膜损伤及胃溃疡的保护作用。方法 建立无水乙醇、幽门结扎致大鼠胃黏膜损伤模型,水浸应激、乙酸灼烧致大鼠胃溃疡模型,测定模型大鼠胃黏膜损伤程度、溃疡面积、溃疡指数,以及胃黏膜中氨基己糖、PEG₂含量和血流动力学的变化,观察牛乳铁蛋白对实验性胃黏膜损伤和胃溃疡的保护作用。此外,通过连续喂养正常大鼠牛乳铁蛋白,观察其对大鼠胃液量、胃液酸度和胃蛋白酶活性的影响。结果 牛乳铁蛋白能降低乙醇及幽门结扎致胃黏膜损伤大鼠的溃疡指数,增加乙醇致胃黏膜损伤大鼠受损胃黏膜的氨基己糖和PEG₂含量以及血流量。同时,牛乳铁蛋白还能降低水浸应激以及乙酸灼烧致胃溃疡大鼠胃部的溃疡面积。此外,连续灌胃高剂量牛乳铁蛋白能抑制正常大鼠胃液分泌,减少胃液酸度。结论 牛乳铁蛋白对实验性胃黏膜损伤及胃溃疡大鼠模型胃黏膜损伤具有保护作用。     

银杏叶提取物的胃粘膜保护作用(英文)

目的:研究银杏叶提取物的胃粘膜保护作用.方法:采用大鼠束缚-冷冻应激(RCS)模型和小鼠无水乙醇损伤模型观察GbE对胃粘膜损伤指数的影响;采用幽门结扎法收集胃液,观察GbE对胃液分泌量,胃液酸度和胃蛋白酶活性的影响;采用硫代巴比妥酸(TBA)法测定胃粘膜及血清中丙二醛(MDA)含量.结果:GbE(25,50,100 mg/kg,bid×5 d,ig)剂量依赖性地抑制RCS和无水乙醇引起的胃粘膜损伤.用药组应激后的胃粘膜损伤指数分别为对照组的58％,43％和31％;用药组乙醇诱发的胃粘膜损伤指数降至对照组的62％,36％和26％;GbE尚能增强西米替丁对胃粘膜的保护作用,但对大鼠胃液分泌量、胃液酸度及胃蛋白酶活性GbE并无明显影响.小鼠经无水乙醇ig后1 h,胃粘膜和血清中的MDA含量显著升高(P<0.01),而GbE(25,50,100 mg/kg,ig)预处理则可以明显抑制MDA的升高.结论:GbE具有胃粘膜保护作用,并且与西米替丁在治疗急性胃粘膜损伤方面具有协同作用.     

Pluronic block copolymers and Pluronic poly(acrylic acid) microgels in oral delivery of megestrol acetate

Several Pluronic-based formulations were studied in-vitro and in a rat model with respect to the release and bioavailability of megestrol acetate (MA) after oral administration. It was demonstrated that an aqueous, micellar formulation comprising a mixture of a hydrophobic (L61) and a hydrophilic (F127) Pluronic copolymer, significantly enhanced the bioavailability of MA administered orally at relatively low doses (1-7 mg kg(-1)). Pluronic-based microgels (spherical gel particles of sub-millimetre size) were introduced as MA vehicles. The microgels comprised a cross-linked network of poly(acrylic acid) onto which the Pluronic chains were covalently attached. Microgels of Pluronic L92 and poly(acrylic acid) fabricated into tablet dosage forms exhibited dramatically lowered MA initial burst release. The MA release was pH-dependent owing to the pH sensitivity of the microgel swelling, with the drug retained by the microgel at pH 1.8 and released slowly at pH 6.8. In the rat model, a significant increase in MA bioavailability was observed when the microgel-formulated MA was administered orally at a high dose of 10 mg kg(-1), owing to the enhanced retention of the microgel. The study of the microgel passage through the gastrointestinal tract demonstrated the microgel retention characteristic of a very high molecular weight polymer and the absence of any systemic absorption of the polymer.     

Effect of bioadhesive polymer on phenol red absorption in normal and ulcer rats

The influence of a bioadhesive polymer, poly(acrylic acid) crosslinked with 2,5-dimethyl-1,5-hexadiene (PADH) on the absorption of a poorly absorbable water-soluble dye (phenol red), was studied in normal and ulcer rats. The urinary recovery after oral administration of phenol red solution was significantly increased in normal and indomethacin-ulcer rats pre-administered with bioadhesive polymer. The percentage of urinary recovery in normal, ulcer, normal pre-administered polymer, and ulcer pre-administered polymer rats were 2.7±0.2, 8.3±0.8, 22.6±1.5, and 27.2±1.7%, respectively. The results indicated that PADH can enhance the absorption of water soluble compound but through a different mechanism when compared with sparingly soluble compounds. The polymer has the ability to attach to the mucin/epithelial cell surface, as determined by visual inspection of the rat stomach, however it could only detain a low percentage of phenol red in the polymer as confirmed by the in-vitro affinity study under gastric condition. These findings suggested that the enhancement of absorption of phenol red by the bioadhesive polymer is essentially by the increase of permeability of gastrointestinal (GI) membrane to the transport of phenol red through thinning or damage of the protective mucosal layer.     

Movement of Heparins Across Rat Gastric Mucosa is Dependent on Molecular Weight and pH

Purpose  Movement of unfractionated (UFH) and low molecular weight heparins (LMWHs) through gastric mucosa was compared to determine effect of molecular weight on absorption. Methods  Rat gastric mucosa, mounted in an Ussing chamber, was bathed in oxygenated Kreb’s buffer, containing mannitol on the mucosal (lumen) at pH 7.4 or 4, and glucose on the serosal side (circulation) at pH 7.4. Heparins (10 mg/ml) were added to the mucosal side. Potential difference (PD), resistance, and short circuit current (Isc), were determined. Buffers and tissues were extracted to measure heparin by gel electrophoresis. Results  PD increased on heparin addition and following a lag period, that was longer for UFH at pH 7.4 and LMWHs at pH 4.0, returned to baseline. Isc increased slightly for UFH at pH 4.0 but significantly for LMWHs at pH 7.4. More UFH or LMWHs were recovered from serosal buffers at pH 4.0 and pH 7.4 respectively. Results suggest UFH and LMWHs cross gastric mucosa faster, and active transport is involved, at pH 4.0 and pH 7.4, respectively. Conclusions  Decreasing heparin size, increases movement through gastric mucosa at mucosal buffer pH 7.4 but not pH 4.0. The stomach environment may favor UFH absorption while the intestine environment favors LMWH absorption.     

In vitro inhibition of gastric acid secretion by vasopressin

Interpretation of studies designed to investigate the inhibitory action of vasopressin on gastric acid secretion has proven difficult, as the in vivo models are potentially susceptible to both direct (e.g. mucosal effects) and indirect effects (e.g. changes in mucosal blood flow). In the present series of experiments we studied vasopressin inhibition of both basal and histamine-stimulated acid secretion in rat isolated gastric mucosa, a preparation which is independent of blood flow. Basal and histamine-stimulated levels of acid secretion were 2.32 +/- 0.10 (mean +/- S.E.) and 4.36 +/- 0.41 mu eqH+/h per cm2. Vasopressin inhibited both basal and histamine-stimulated acid secretion; the effect, which was maximal at 15 min post-dosing, was blocked by the specific V1 antagonist d(CH2)5Tyr(Me) AVP. No effect on acid secretion was evident with either the potent V2 agonist, dDAVP, or oxytocin, a neurohypophyseal hormone which can also affect water retention and blood pressure. These studies demonstrate that vasopressin can specifically inhibit mucosal acid secretion; the inhibitory effect is most likely mediated via a V1 vasopressin receptor subtype on the gastric mucosa.     

Regulatory mechanism of gastric acid secretion and mucosal integrity--an analysis with various gene deficient mice

Mechanisms for gastric acid secretion have been elucidated through invention of new methods and new drugs. Current genetic technology have generated knockout (KO) mice lacking receptors such as CCK2, histamine H2, muscarinic M3 and M1, or enzymes such as histidine decarboxylase (HDC) and H+,K(+)-ATPase. Here, we review the functional and morphological changes in the gastric mucosa of such KO mice. In M3R-KO mice (intragastric pH 5.9), carbachol, histamine and gastrin stimulated acid secretion like they did in wild-type mice. Carbachol-stimulated acid secretion was significantly inhibited by famotidine and pirenzepine. The serum gastrin level in M3R-KO mice was increased, yet the stomach weight and the gastric mucosa remained unchanged. In H2R-KO mice (intragastric pH 3.0), serum gastrin and mucosal histamine levels significantly increased. Carbachol significantly stimulated acid secretion, yet histamine and gastrin had little or no effect on acid secretion. The stomach wet weight increased with time after birth and the serum albumin level was decreased. In the gastric mucosa with hyperplasia, numerous enlarged cysts and a marked expression of TGF-alpha were observed, indicating the occurrence of Menetrier's disease like mucosal changes. G/D cell ratio was greatly increased, providing evidence of the increased serum gastrin level. In HDC-KO mice (intragastric pH 4.5), the stomach weight was also increased 6 mo after birth, with no enlarged cysts in the gastric mucosa. CONCLUSION: The above results indicate that KO mice can be used to yield many important findings that selective antagonists cannot reveal.     

Interactions between ethanol and acetylsalicylic acid in damaging the rat gastric mucosa

The interactions between ethanol (EtOH) and acetylsalicylic acid (ASA) in damaging the gastric mucosa were investigated in urethane-anaesthetised rats upon intragastric irrigation. The addition of 5, 10 or 20 mM ASA to 1 and 4 M EtOH instillates strongly aggravated lesion formation in the gastric mucosa and mucosal bleeding. ASA enhanced the back-diffusion of hydrogen ions into the mucosa induced by 1 M EtOH, whereas gastric mucosal blood flow, which is thought to dispose of the back-diffused acid from the mucosa, remained unchanged, thus resulting in an accumulation of acid within the gastric mucosa. ASA did not further enhance the strongly increased back-diffusion of hydrogen ions induced by 4 M EtOH, but it effectively inhibited EtOH-induced stimulation of the gastric mucosal blood flow, thus causing an increase in the ratio between hydrogen ion back-diffusion and gastric mucosal blood flow. The simultaneous presence of EtOH and ASA did not enhance the rates of absorption of each from the instillates. The results indicate that EtOH and ASA have a strong synergistic action in damaging the gastric mucosa in the rat. The mechanism of this interaction may be an increased accumulation of hydrogen ions within the gastric mucosa, resulting in excessive acidification of the mucosal tissue.     

Mechanisms underlying gastric mucosal damage induced by indomethacin and bile-salts, and the actions of prostaglandins.

1 The mechanisms by which -he bile salt, sodium taurocholate, potentiates the formation of gastric mucosal erosions induced by indomethacin has been investigated in the rat. 2 Systemic administration of indomethacin lowered resting mucosal blood flow but had no effect on the acid back-diffusion across the mucosa. 3 Gastric perfusion of taurocholate in acid solution increased acid back-diffusion and lowered the potential differences. This was accompanied by an increase in mucosal blood flow, which may represent a protective mechanism in the mucosa. 4 Administration of indomethacin during acid-taurocholate perfusion reduced this elevated mucosal blood flow without any further change in acid back-diffusion. 5 The results suggest that although a decrease in mucosal blood flow or an increase in acid back-diffusion can lead to a low incidence of erosions, a combination of both produces extensive mucosal damage. 6 The (15S)-methyl analogue of prostaglandin E2 reduced erosion formation induced by indomethacin and acid-taurocholate administration. 7 It is suggested that this protective action of the prostaglandin analogue may be linked to changes in gastric mucosal permeability and in mucosal blood flow.     

Effects of sulfhydryl-related compounds on indomethacin-induced gastric lesions in rats: role of endogenous sulfhydryls in the pathogenesis.

The role of mucosal sulfhydryl (SH) in the pathogenesis of indomethacin-induced gastric lesions was investigated in rats. Indomethacin (25 mg/kg, s.c.) caused high-amplitude gastric contractions, resulting in linear hemorrhagic lesions in the corpus mucosa within 4 hr, but did not induce any changes in the mucosal SH levels. These lesions were prevented significantly by prior s.c. administration of cysteamine, glutathione (GSH) or diethylmaleate (DEM), irrespective of whether the mucosal SH was increased by the former two agents or reduced by the latter. N-Ethylmaleimide (NEM) tended to worsen such lesions without any effect on the mucosal SH contents. Gastric hypermotility caused by indomethacin was inhibited significantly by DEM, cysteamine and GSH, while acid secretion was reduced by DEM and NEM. Both cysteamine and GSH prevented the indomethacin-induced linear lesions even in the stomach perfused with 150 mM HCl, whereas in the animals treated with DEM, nonlinear damage was induced exclusively in the antrum by indomethacin in the presence of acid. We conclude that the mucosal SH has no relation to the ulcerogenicity of indomethacin in the gastric corpus mucosa.     

Effect of the molecular weight of water-soluble polymers on accumulation at an inflammatory site following intravenous injection

The body distribution of noncharged, water-soluble polymers, e.g. poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), and dextran, was studied following their intravenous injection into mice with or without carrageenan-induced inflammatory lesions at the femoral muscle. Inflammation induction did not affect their distribution profile, although polymers of high molecular weight tended to remain in the blood circulation for a longer period than those of low molecular weight. Polymers exhibited longer accumulation at the inflammatory site than at the normal site, regardless of the polymer type and the molecular weight estimated by size exclusion chromatography. Maximum accumulation was observed for the polymer having a molecular weight around 200,000, regardless of the polymer type. Pharmacokinetic studies demonstrated that the accumulation rate of polymers at the inflammatory site was higher than at the normal site and decreased with increasing molecular weight. On the other hand, the higher the molecular weight of polymers, the longer the retention time in the blood circulation. Such trends were observed for all types of polymers used, indicating that the inflammatory site accumulation of polymers injected intravenously is governed solely by the polymer molecular weight. The balance between the accumulation rate of polymers and the blood retention seemed to determine the maximum accumulation of polymers having a certain range of molecular weight.