胃內(nèi)滯留漂浮給藥系統(tǒng)中使用草藥根除幽門螺旋桿菌的研究進(jìn)展

1、胃內(nèi)滯留漂浮給藥系統(tǒng)中使用草藥根除幽門螺旋桿菌的研究進(jìn)展 09-12-14 09:57:00 編輯：studa20 作者：Shreeraj H. SHAH, Jayvadan K. PATEL, Nirav V. PATEL【關(guān)鍵詞】 幽門螺旋桿菌; 胃滯留劑; 漂浮劑型; 草藥; 黑柯子; 黃連素Helicobacter pylori are very common pathogenic bacteria colonizing about half of all populations and associated with the development of serious gastro

2、duodenal diseases like gastric lymphoma, peptic ulcers and acute chronic gastritis. Current drug regimes are not wholly effective. Other problems related with the current drug regimes are lack of patient compliance, side effects and bacterial resistance. Thus, drug delivery to the site of residence

3、in the gastric mucosa may help in solving the problems associated with the current drug therapy. Gastric retentive delivery systems potentially allow increased penetration and thus increased drug concentration at the site of action. Floating drug delivery systems, expandable or swellable drug delive

4、ry systems and bioadhesive systems are the major areas of interest to formulate gastroretentive drug delivery system against H. pylori. Generally, problems with these formulations are lack of specificity and the dependence on mucus turnover, so they fail to persist in the stomach. Gastric mucoadhesi

5、ve systems are hailed as a promising technology to address this issue, penetrating the mucus layer and prolonging activity at the mucusepithelial interface. Gastroretentive delivery strategies, specifically with regard to their application as a delivery system to target Helicobacter, are a very attr

6、active field which can cure these troublesome infections. H. pylori is a Gramnegative, microaerophilic, spiral and flagellated bacterium, with unipolarsheathed flagella that provides motility. Its spiral shape and high motility allows it to penetrate mucus, resist gastric emptying and remain in the

7、host gastrointestinal (GI) tract. It is now firmly established that infection with this bacterium is the cause of chronic active gastritis. Its isolation radically changed the conceptualisation of several chronic gastrointestinal illnesses including gastritis and peptic ulcers, and elimination of th

8、e causative organism became the goal of therapies 1. Estimates from the WHO in 1994 claimed that about half of the worlds population was infected with H. pylori and although most infections are silent, a portion of the infected population will subsequently present with associated disease including c

9、hronic gastritis, peptic and duodenal ulcers. About 550 000 new cases a year of gastric cancerabout 55% of the worldwide totalwere attributed to H. pylori, and it was predicted that by 2020 to enter the top ten of leading causes of death worldwide2, 3. H. pylori is a very diverse specy and cancer ri

10、sks may be increased with strains having virulenceassociated genes (cytotoxinassociated gene, CagA), host genetics and environmental factors. The incidence of infection is higher in developing countries with up to 80%90% of adults being infected whereas in developed countries prevalence ranges from

11、10%50%4.1 Mechanism of H. pylori infections Infection with H. pylori occurs predominately in childhood mainly between the ages 1 to 5, via oral ingestion of the bacterium, and lasts until the end of life with intrafamilial transmission being the major route in developed countries. The possible route

12、s of transmission are food and water. The major feature of H. pylori infection is progressive injury to the gastric mucosa and its function5, 6. The bacterium adheres to the gastric epithelial cells, producing a direct injurious effect that is then amplified by production and release of a vacuolatin

13、g cytotoxin (VacA)7, 8. H. pylori produces a variety of enzymes and is characterised by a high urease activity. Urea is broken down into bicarbonate and ammonia that protects the bacterium in the acid environment of the stomach. The ammonium ions produced can be toxic to the gastric superficial epit

14、helial cells. Urease stimulates inflammatory cytokine production and activates mononuclear phagocytes. Although, after colonisation, the host immune defences are stimulated, and there is increased secretory IgA (sIgA) detected in the gastric mucosa and raised specific IgG, while the infected host is

15、 not able to eliminate the organism. Colonisation results in persistent gastric inflammation but the clinical course of infection can be very variable9.2 Current treatment of H. pylori infections The treatment for eradication of H. pylori is complicated, requiring a minimum of two antibiotics in com

16、bination with gastric acid inhibitors. Although H. pylori is sensitive to many antibiotics in vitro, no single agent is effective alone in vivo. Firstly, the bacterium resides below the gastric mucus adherent to the gastric epithelium and thus access of drugs to this site is limited. Secondly, the s

17、train may have acquired resistance to the commonly used antimicrobial drugs10. These infections are currently treated with a firstline triple therapy treatment, consisting of one proton pump inhibitor (PPI) and two antibiotics. None of the antibiotics used achieves sufficient eradication when used a

18、lone and also require adjuvant therapy11. This consists of agents increasing pH within the stomach to allow local action of antibiotics not active at low pH, and PPIs are used at a dose equivalent to 20 mg omeprazole twice daily. It was suggested that ranitidine bismuth citrate (RBC) regimens may be

19、 less influenced by antibiotic resistance than PPIbased therapies12. The most effective therapies combine two antibiotics including clarithromycin and amoxicillin with a gastric acid inhibitor. However, increasing resistance to current antibiotics is driving research to produce alternatives to the c

20、ommonly used therapies. In addition to increasing levels of antibiotic resistance, the hostile environment of the stomach, reducing antibiotic bioavailability at the site of action, contributes to failures in treatment13. Current recommended regimes are not wholly effective, for example, triple ther

21、apy with bismuth, metronidazole and amoxicillin or tetracycline has an eradication efficiency of 60%80%, and patient compliance, sideeffects and bacterial resistance can be problematic with this regime14. Alternatives proposed include quadruple therapies, based on, for example, colloidal bismuth sub

22、citrate, tetracycline, metronidazole and omeprazole15. Patient compliance with such a complicated dosage regime could be improved by combining the therapies in a single dosage form, and a capsule containing bismuth biskalcitrate, metronidazole and tetracycline (Helicide) has been developed in an eff

23、ort to improve patient compliance and has currently received approval16. There is concern regarding acquired resistance to two of the commonly prescribed antibiotics: clarithromycin and metronidazole. Although not as widespread, resistance to metronidazole can also be problematic but it can be overc

24、ome in some cases by lengthening the duration of treatment17.3 Drug delivery systems for gastric retention Major problems in the eradication of H. pylori are the presence of antibioticresistant bacteria requiring multiple drugs with complicated dosing schedules and bacterial residence in an environm

25、ent where high drug concentrations are difficult to achieve. In order to ensure that the therapy is adequately delivered to the unique niche of the gastric mucosa, development of oral dosage forms with prolonged gastric residence is desirable. Gastric retentive delivery systems have been studied for

26、 a number of years, and generally requirements of such strategies are that the vehicle maintains a controlled release of drug and exhibits prolonged residence time in the stomach. Overcoming the physiological barriers of the human GI tract is a major challenge facing successful development of gastri

27、c retentive systems and leads to problems with reproducibility. In addition to the thick protective mucus layer, gastrointestinal motility patterns are another obstacle facing drug delivery to the stomach. In the fasted state, the interdigestive myoelectric motor complex (IMMC) is a 2hour cycle of p

28、eristaltic activity that regulates motility patterns18. Phase of the IMMC is also called the housekeeper wave and consists of strong, intense contractions designed to remove debris such as undigested food from the stomach19, 20. Gastric residence time will depend on which phase of IMMC is active. In

29、 the fed state, the stomach churns food to sizes less than 1 mm, which is then emptied to the duodenum. Type of the food determines its residence time in the stomach with liquids emptying rapidly and solids much more slowly. Gastric residence time is generally longer in the fed rather than fasted st

30、ate. The gastric residence time of dosage forms is also influenced by posture, age, gender, disease status and concomitant medication. A number of different techniques have been explored to increase gastric retention including high density and magnetic systems, but the three main systems are floatin

31、g systems, bio/mucoadhesive systems and swelling systems.4 Floating drug delivery systems Various approaches had been made since the late 1970s to utilise floating behaviour in order to prolong residence. Designs include hydrodynamically balanced systems (HBS), microspheres, gasgenerating systems an

32、d raftforming systems. Originally, such systems were proposed to reduce fluctuations in drug levels and provide sustained release as the duration of most oral sustained release preparations is 812 hours, due to a relatively short GI transit time21, 22. HBS has a bulk density lower than gastric fluid

33、s and contain one or more colloids formulated into a single unit with the drug and other additives, which swell on contact with water and facilitate floating23, 24. A density of less than 1.0 g/mL is required. A triplelayer floating tablet system was proposed containing a swellable gasgenerating lay

34、er, a swellable drugcontaining layer (with tetracycline and metronidazole) and a rapidly dissolving layer containing bismuth salts. The system was capable of providing sustained release of the antibiotics in vitro at pH 1.8 and demonstrated buoyancy in vitro, however no in vivo results are reported.

35、 Tablets containing a 12 ratio of hydroxypropylcellulose to amoxicillin, with a gasgenerating system, failed to improve efficacy. These large singlelayer tablets remained buoyant in vitro but bioavailability was reduced to 80.5% as compared with conventional capsules in fasted humans25. Intersubject

36、 variability in gastric transit times with floating tablets and HBS results in unreliable and irreproducible residence times in the stomach and remains a significant problem with such systems. This can be addressed by using multipleunit divided systems such as microspheres. As these can spread evenl

37、y through the stomach contents, they can avoid the problems of variable and early gastric emptying or bursting associated with the singleunit systems. Polymers used in formulation of floating multipleunits include caesingelatin acrylic polymers such as Eudragits and alginates26. Alginic acid is a po

38、lysaccharide consisting of Dmannuronic acid and Lguluronic acid. It forms a bioadhesive and stable gel with divalent cations such as calcium and the sodium salt been used in a variety of oral and topical formulations. Floating alginate systems such as Gaviscon form a buoyant gel which floats on the

39、gastric contents alleviating symptoms of heartburn. Its stability in acidic media has made it a popular choice for gastric retentive delivery systems. For example, floating multiple units consisting of a calcium alginate core, separated from a calcium alginate/polyvinyl alcohol (PVA) membrane by an

40、air compartment displayed prolonged gastric retention after a meal. Alginate beads are commonly prepared by extruding alginate, dropwise, into a solution containing Ca2+. The resultant beads are porous and can be used to encapsulate a variety of drugs with a wide range of physicochemical properties2

41、7. Adequate control of drug release from such formulations often requires some modification to the matrix. For example, foambased floating microspheres can be prepared by adding polypropylene foam powder to an organic solution containing dissolving polymer (Eudragit RS or polymethyl methacrylate, PM

42、MA) and drug. Upon solvent evaporation, freeflowing microspheres are formed with extended release profiles28. Two types of alginate floating beads containing metronidazole were compared; one formulation contained chitosan and the other contained vegetable oils. In vitro release was complete from all

43、 formulations within two hours. Following administration to guinea pigs, it was concluded that after three hours chitosancontaining particles resulted in increased drug levels in the gastric mucosa as compared with metronidazole solution29. A multipleunit floating dosage form formulated using calciu

44、m alginate was prepared by dropping sodium alginate solution into calcium chloride and the resultant particles were freezedried. Amoxicillin was incorporated into these beads by addition of drug to the calcium chloride solution. Once the sodium alginate was extruded into the solution, the resultant

45、gel beads were left for thirty minutes before extraction and freezedrying. Amylose was also added to the formulation in an attempt to reduce the release rate. Amoxicillin release showed an initial burst effect and the release was described by Higuchi kinetics, implying that it is controlled by diffu

46、sion of the drug through a porous matrix. Gammascintigraphic studies showed evidence of gastric retention of the floating beads in all seven subjects even following normal food intake. A major limitation with such systems is the requirement for sufficient volumes of gastric acid within the stomach t

47、o enable the devices to float. It may be that using a single approach to localise delivery in the stomach may not be sufficient to resist the forces of gastric emptying. It was therefore envisaged that a floating dosage form with mucoadhesive polymers could extend the period of gastric retention, ex

48、ploiting the retentive properties of the floating system and the ability of bioadhesive formulations to adhere to inflamed tissue. Floating, bioadhesive microsphere systems containing acetohydroxamic acid (AHA), a cytoplasmic urease inhibitor, were prepared. A solution of AHA and the acrylic polymer

49、 (Eudragit E) in ethanol/dichloromethane was added to an aqueous PVA solution to form an oilinwater emulsion. The drug and polymer precipitated due to preferential diffusion of ethanol into the aqueous phase. After evaporation of the dichloromethane, the particles were dried and an air cavity was pr

50、oduced inside the spheres giving the particles the ability to float30. These particles were spraycoated with the mucoadhesive polymer, polycarbophil. Floating ability was demonstrated in vitro and demonstrated greater percentage growth inhibition of H. pylori in vitro than free drug. Release rates w

51、ere extended due to the polycarbophil coating31. Similar preparations using polybisphenolA carbonate as the coating polymer also showed buoyancy, extended drug release and inhibition of growth of H. pylori in vitro. Clearance of an inoculated strain of H. pylori from the stomach of gerbils following

52、 oral delivery of the encapsulated drug was shown to be better than free drug, presumably due to better retention. Although AHA has been shown to be effective at reducing gastritis in a Mongolian gerbil model, further studies are needed to prove that established antibiotics could also be successfull

53、y encapsulated into, and released from, such formulations and their efficacy demonstrated in human models30.5 Herbal and integrative drugs against H. pylori infections5.1 Black myrobalan The aqueous extract of black myrobalan (Terminalia chebula Retz) has been shown to have uniform antibacterial act

54、ivity against ten clinical strains of H. pylori32, 33. This activity was bactericidal after 3 h and was stable after autoclaving. Although Sato and coworkers34 reported gallic acid and ethyl gallate in T. chebula Retz and have shown antibacterial activity of ethanol extracts of this plant against bo

55、th methicillin resistant and sensitive Staphylococcus aureus and other bacteria, the components of T. chebula Retz aqueous extracts responsible for the observed bacteriocidal activity remain unknown35. The antibacterial activity of aqueous extracts of black myrobalan against H. pylori was significan

56、tly higher than that of ether and alcoholic extracts. The aqueous extract preserved its antibacterial activity after autoclaving for 30 min at 121 and was inhibitory at 125150 mg/L. When the plant powder was tested directly against H. pylori, without grinding and (or) extraction and using Colombia A

57、gar plates, the mean inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values were 150 and 175 mg/L, respectively.5.2 Ginger Ginger root (Zingiber officinale Rosc.) has been used traditionally for the treatment of gastrointestinal ailments such as motion sickness, dyspepsia

58、 and hyperemesis gravidarum, and is also reported to have chemopreventative activity in animal models36. The gingerols are a group of structurally related polyphenolic compounds isolated from ginger and known to be the active constituents. Since H. pylori is the primary etiological agent associated

59、with dyspepsia, peptic ulcer disease and the development of gastric and colon cancer, the antiH. pylori effects of ginger and its constituents were tested in vitro37. A methanol extract of the dried powdered ginger rhizome, fractions of the extract and the isolated constituents, 6, 8 and 10gingerol and 6shogoal, were tested against 19 strains of H. pylor