Cyclosporin metabolism by human gastrointestinal mucosal microsomes.

The in vitro metabolism of the immunosuppressant cyclosporin (CsA) by human gastrointestinal mucosal microsomes has been studied. Macroscopically normal intestinal (n = 4) and liver (n = 2) tissue was obtained from kidney transplant donors, and microsomes prepared. Intestinal metabolism was most extensive with duodenal protein (15% conversion to metabolites M1/M17 after 2 h incubation at 37 degrees C; metabolite measurement by h.p.l.c). Western blotting confirmed the presence of P-4503A (enzyme subfamily responsible for CsA metabolism) in duodenum and ileum tissue, but not in colon tissue. The results of this study indicate that the gut wall may play a role in the first-pass metabolism of CsA, and could therefore be a contributory factor to the highly variable oral bioavailability of CsA.     

Review: first-pass metabolism by the gastrointestinal mucosa

The bioavailability of orally administered drugs may be reduced due to presystemic elimination. The first-pass effect can occur in the gastrointestinal tract, the liver and lung. Although the liver is the main drug metabolizing organ in the body, the gut wall can play an important role in the first-pass metabolism of certain drugs. Both phase I (preconjugation) and phase II (conjugation) reactions have been described. However, while the oxidative metabolic capacity of the intestinal mucosa is considerably smaller than that of the liver, the activity of conjugation reactions in the gut may be close to that of the liver, and in some cases may exceed it. Sulphate conjugation is particularly important for steriod hormones such as ethinyloestradiol, and for the beta-adrenoceptor stimulants isoprenaline and isoetharine. Glucuronidation has been demonstrated to occur in man for morphine, paracetamol and oestrogens. Significant drug--drug interactions have been described involving drugs undergoing sulphate conjugation. The study of intestinal metabolism in vivo is difficult in man since direct methods (for example, hepatic portal vein catheterization) is justified in only a small number of patients. Therefore, much of our present understanding has been derived from various in-vitro studies involving intestinal sheets, mucosal biopsies, isolated enterocytes and microsomal preparations.     

Cyclosporin metabolism in human liver microsomes and its inhibition by other drugs

The metabolism of cyclosporin was studied in human liver microsomes. There was no metabolism in the presence of cytochrome C or carbon monoxide or in the absence of cofactors, suggesting metabolism by cytochrome P-450 enzymes. The metabolism was inhibited by ketoconazole and erythromycin, by the steroids methylprednisolone and oestradiol, and by the calcium antagonists diltiazem, nifedipine, prenylamine and verapamil. These in vitro findings correlate well with previously published clinical reports suggesting that these drugs may inhibit the metabolism of cyclosporin in vivo. Our observations suggest that metabolic interactions between cyclosporin and other drugs in vivo may be predicted in vitro under proper experimental conditions.     

Nanoparticle uptake by the rat gastrointestinal mucosa: quantitation and particle size dependency

Polystyrene microspheres in the size range 50 nm to 3 microns were fed by gavage to female Sprague Dawley rats daily for 10 days at a dose of 1.25 mg/kg-1. Previous histological evidence of the uptake of these particles and their absorption across the gastrointestinal tract and passage via the mesentery lymph supply and lymph nodes to the liver and spleen was confirmed by analysis of tissues for the presence of polystyrene by gel permeation chromatography. Measurement of radioactivity of tissues following administration of 100 nm and 1 micron I125-labelled polystyrene latex particles for 8 days was corroborative although less secure because of the potential lability of the labelled particles. The extent of absorption of 50 nm particles under the conditions of these experiments was 34% and of the 100 nm particles 26% (as measured by determination of polystyrene content), of which total, about 7% (50 nm) and 4% (100 nm), was in the liver, spleen, blood and bone marrow. Particles larger than 100 nm did not reach the bone marrow, and those larger than 300 nm were absent from blood. No particles were detected in heart or lung tissue.     

Cyclosporin pharmacokinetics in the elderly.

Cyclosporin is an immunosuppressant used in organ transplantation and selected autoimmune diseases such as rheumatoid arthritis. In both these indications, the elderly represent an important and growing segment of the patient population. Cyclosporin is primarily eliminated via biotransformation by cytochrome P450 (CYP)3A in the gut wall and liver. Additionally, P-glycoprotein (mdr-1) located in the gastrointestinal epithelium can affect affect blood drug concentrations after oral administration of cyclosporin, presumably by counter-transporting the drug from the systemic circulation back into the gastrointestinal lumen. Theoretically, age-related alterations in either of these pathways could affect cyclosporin disposition in the elderly. These general pharmacological considerations together with the narrow therapeutic index of cyclosporin between minimally immunosuppressive concentrations and those associated with adverse events, underscore the need for dedicated pharmacokinetic studies in the elderly. Single dose studies have demonstrated that cyclosporin pharmacokinetics are not different in healthy elderly individuals compared with healthy young adults, nor is the between-subject variability in pharmacokinetic parameters more heterogenous in healthy elderly individuals. Similarly, there were no apparent differences in cyclosporin disposition in elderly patients with rheumatoid arthritis compared with healthy young and elderly individuals. Whether pharmacokinetic variability may be increased in elderly patients has not been rigorously addressed and requires investigation in a larger patient population for a definitive conclusion. A population pharmacokinetic study of cyclosporin in organ transplant patients, including elderly allograft recipients up to 75 years of age, did not identify age as a covariable influencing cyclosporin pharmacokinetics. Hence, the available pharmacokinetic data in the elderly do not reveal any major differences from the disposition characterised in younger individuals. It is generally recognised that the elderly are more prone to drug-related adverse experiences and are at greater risk for drug-drug interactions secondary to polypharmacy. The former factor may underlie, in part, the increased incidence of renal adverse events reported in patients with rheumatoid arthritis over 65 years of age receiving cyclosporin. Clinical experience with cyclosporin in elderly organ transplant recipients has not revealed a tolerability profile remarkably different from those in younger patients. Polypharmacy may have specific relevance for elderly patients treated with cyclosporin since this agent is a substrate of both CYP3A and P-glycoprotein, both of which are important in the elimination of many commonly used drugs. This implies that the clinician prescribing cyclosporin for an elderly patient must exercise a heightened awareness for potential drug-drug interactions which could affect the pharmacokinetics of cyclosporin. Based on the available cyclosporin pharmacokinetic data in adults, no age-related administration adaptations appear necessary for its use in the elderly.     

抗氧化剂与胃肠黏膜屏障损伤

<正>1 氧自由基及损伤作用含有一个不成对电子的分子或原子团称自由基。部分氧分子为活性氧簇(reactive oxygen spe- cies,ROS),包括过氧化氢、超氧阴离子自由基、羟自由基、一氧化氮黄嘌呤氧化酶(XO)自由基等。体内自由基的产生和清除应是平衡的,人体才能保持健康。如果自由基产生过多或清除自由基的能力下降,体内就会有多余的自由基(特别是氧自由基),会损伤细胞成分,导致疾病和衰老的发生。 ROS是许多疾病的特征。自由基和多种疾病有关, 包括与胃肠黏膜屏障损伤密切相关。各器官均有防御ROS形成即清除氧自由基的机制,从而可快速修复氧自由基造成的损伤。体内自由基清除体系主要包括抗氧化酶和抗氧化剂两类。自由基也涉及信号传导通路,如XO既参与传导,同时也是自由基清除剂。     

The in vitro metabolism of ethinyloestradiol, mestranol and levonorgestrel by human jejunal mucosa.

1 Ethinyloestradiol was extensively metabolised in vitro by human jejunal mucosa to form ethinyloestradiol sulphate. 2 The amount of conjugation was directly related to the weight of biopsy tissue. 3 The degree of conjugation of mestranol and levonorgestrel was much lower than for ethinyloestradiol suggesting that the 17-position of the steroid nucleus is relatively inaccessible for conjugation. 4 No Phase I metabolism of ethinyloestradiol or levonorgestrel was apparent in the conditions used in these experiments.     

Protection of the upper gastrointestinal mucosa: the role of antacids

Experiments performed in animals and in healthy human subjects suggest that antacids increase prostaglandin synthesis and have a cytoprotective effect on gastroduodenal mucosa. To investigate this hypothesis, the ability was evaluated of an antacid containing an aluminium/magnesium hydroxide combination (Maalox TC) to modify prostanoid production at the gastric level in 28 patients with gastric antral ulcer of various sizes in different stages of activity with or without erosive gastritis. After the antacid treatment, a significant prostaglandin E2 reduction was observed, together with a significant 6-keto-prostaglandin F1 alpha increase, but there was no thromboxane B2 variation at antrum level, nor any significant modification of prostanoid production at body level. The decreased prostaglandin E2 levels, detected after treatment with the antacid combination, may be due to lesion improvement, decreased synthesis or increased catabolism by mucosal cells, to a drop in this prostaglandin production by inflammatory cells. As far as 6-keto-prostaglandin F1 alpha is concerned, the obtained data confirm the results reported by other authors in healthy human subjects. The increase of this prostaglandin could enhance blood flow, resulting in a protective effect.     

Nutraceuticals for protection and healing of gastrointestinal mucosa

Natural medicinal products have been used for millennia for the treatment of several ailments. Although many have been superseded by conventional pharmaceutical approaches, there is currently a resurgence in the interest in natural products by the general public and the use of complementary and alternative medicine is increasing rapidly in developed countries. Also, pharmaceutical industries are more and more interested in examining their potential as sources of novel medicinal compounds which may act as growth factor or show immunomodulatory or anti-microbial activity. The subgroup of natural bioactive compounds that bridge the gap between food products and drugs are termed nutraceuticals or functional foods. In contrast with most standard medicinal compounds, nutraceuticals are generally used to prevent rather than to treat disease. Many of the claims for such products are supported by very limited scientific evidence. However, there has recently been a great interest at evaluating the mechanism by which natural products exert their beneficial effects in the gastrointestinal tract. In particular, a major area of interest is for the use of biologically active chemical components of plants, i.e. phytochemicals, in a number of gastrointestinal disorders. While the major focus of phytochemical research has been on cancer prevention, several products of plant origin are being used and/or under study for a variety of other gastrointestinal problems. In this review we discuss the scientific evidence supporting the potential use of nutraceuticals as agents capable to prevent or accelerate healing of gastrointestinal mucosal damage, with a focus on polyphenol extracts obtained from apple.     

Effect of potassium-magnesium citrate on upper gastrointestinal mucosa

Background:

Potassium supplements may cause mucosal damage of the gastrointestinal tract.

Aim:

To evaluate the effect of a new potassium supplement, potassium-magnesium citrate (K-Mag), on upper gastrointestinal mucosa and to compare it with an older potassium supplement, potassium citrate (Urocit-K).

Methods:

A randomized and double-blind study was conducted utilizing 36 healthy adults. Subjects were randomized into three groups: K-Mag (70 mmol/day K, 35 mmol/day citrate and 17.6 mmol/day Mg); Urocit-K (70 mmol/day K and 23.4 mmol/day citrate), and placebo. All subjects took 5 tablets b.d. of the allocated drug and 2 mg t.d.s. of glycopyrrolate for 7 days. On day 8, stool was examined for occult blood, a symptom score was calculated and an oesophagogastroduo-denoscopy was performed. Mucosal lesions were scored at five anatomic sites.

Results:

Demographic characteristics and symptom score were similar in the three groups (< 10% with more than mild symptoms). There were no significant differences in the endoscopic scores at any site examined nor in the total scores among the three groups. Erosion or ulcers were found in 18% of K-Mag, 23% of Urocit-K and 17% of the placebo group.

Conclusion:

Short-term use of K-Mag does not appear to induce lesions in the upper gastrointestinal mucosa and its oral tolerance is similar to Urocit-K or placebo.

     

PAF formation by human gastrointestinal mucosa/submucosa in-vitro: release by ricinoleic acid, and inhibition by 5-aminosalicylic acid.

Human isolated gastrointestinal mucosa/submucosa incubated with ricinoleic acid (12.5-100 micrograms mL-1) or the calcium ionophore A23187 (10 micrograms mL-1) released platelet-activating factor (PAF) as determined by a scintillation proximity assay after extraction and purification. 5-Aminosalicylic acid (25-100 micrograms mL-1) inhibited PAF release by ricinoleic acid in a concentration-dependent manner, and 50 micrograms mL-1 reduced the effect of A23187. We suggest that PAF may play a role in the laxation and mucosal damage by ricinoleic acid released from castor oil.     

In vitro genotoxicity of ethanol and acetaldehyde in human lymphocytes and the gastrointestinal tract mucosa cells.

The influence of ethanol and acetaldehyde on DNA in human lymphocytes, gastric mucosa (GM) and colonic mucosa (CM) was investigated by using the comet assay. All kinds of cells were exposed to ethanol and acetaldehyde in two regimens: the cells were incubated with either chemical and analysed or they were exposed first to ethanol, washed and then exposed to acetaldehyde and analysed. Lymphocytes were exposed to ethanol at final concentrations of 30 mM and acetaldehyde at 3 mM. GM cells were incubated with ethanol at 1 M and acetaldehyde at 100 mM. CM cells were exposed to ethanol at 10 mM and acetaldehyde at 100 mM. In combined exposure, the cells were subsequently exposed to ethanol and acetaldehyde at all combination of the concentrations of the agents. Ethanol caused DNA strand breaks, which were repaired during 4 hr, except when this agent was applied in GM cells at a concentration of 1 M. A dose-dependent decrease in the tail moment of all types of acetaldehyde-treated cells was observed. Similar results were obtained when a recognized DNA crosslinking agent, formaldehyde, was used. These results suggest that acetaldehyde may form crosslinks with DNA. These crosslinks were poorly repaired. CM cells showed the highest sensitivity of all cell types to ethanol than lymphocytes and GM cells. There were no differences in the sensitivity to acetaldehyde of all the cell types. Our results clearly indicate that ethanol and acetaldehyde can contribute to cancers of the digestive tract.     

生脉超微颗粒对大鼠胃肠黏膜超微结构的影响

目的：观察生脉超微颗粒对大鼠胃肠黏膜的影响。方法：将生脉超微颗粒制成水混悬液，连同生脉超微过滤液及生脉饮汤剂，分别灌胃给予大鼠1个月。结果：病理结果显示，给药期大鼠胃贲门、幽门、十二指肠部分见轻度间质性炎症外，其余肠段未见明显病理改变。电镜结果显示，与空白对照组比较，3个给药组大鼠十二指肠黏膜超微结构异常均有显著性差异，胃黏膜超微结构异常没有显著性差异；灌胃生脉饮汤剂大鼠十二指肠黏膜面的微束颗粒直径为0．1～2μm，而生脉超微颗粒、生脉超微过滤液的粒径为1～2．5μm。停药3d后各组胃、十二指肠黏膜超微结构异常没有显著性差异。结论：停药后未见生脉超微颗粒的微粉长期黏附于胃肠道的趋势。     

多巴胺在胃肠道黏膜保护中的作用及机制

多巴胺在胃肠道分布广泛,与胃肠道的运动、分泌等功能密切相关.动物实验和人体研究均证实多巴胺具有明显的胃肠道黏膜保护作用. 其机制可能是通过作用于多巴胺受体而影响胃的分泌、运动和黏膜血流.不同的受体亚型作用相异.人类的胃十二指肠黏膜中以多巴胺D4亚型的mRNA表达为多.D4的激动剂喹吡罗对MPTP溃疡模型大鼠胃肠道黏膜的保护作用显著强于阻滞剂氯氮平.多巴胺受体亚型功能的深入研究,将为开发新型胃肠道黏膜保护剂提供依据.     

Cyclosporin A attenuates skeletal muscle damage induced by crotoxin in rats.

This work was undertaken to determine the role of the calcineurin pathway on the necrosis of skeletal muscle induced by crotoxin, the major component of the venom of Crotalus durissus terrificus. Rats were treated with cyclosporin A (CsA), a calcineurin inhibitor, for 5 days and, in the 6th day, received an intramuscular injection of crotoxin into the tibialis anterior muscle. Rats were also treated with diclofenac, a non-steroidal anti-inflammatory drug, for 5 days and, on the 6th day, injected with crotoxin. All treated groups were sacrificed 24 h after injection of crotoxin. Tibialis anterior and soleus muscles were removed, frozen and stored in liquid nitrogen. Histological sections were stained with Toluidine Blue and assayed for acid phosphatase. The results show that CsA, but not diclofenac, is able to significantly minimize myonecrosis promoted by crotoxin. In conclusion, CsA attenuates skeletal muscle necrosis induced by crotoxin, indicating that the calcineurin pathway is essential for crotoxin myotoxic activity. The myoprotective effect of CsA is not related to its anti-inflammatory effect since diclofenac, a cyclo-oxygenase inhibitor, was not able to produce myoprotection.