The degradation of guar gum by a faecal incubation system

Applications of polysaccharides in enzyme-triggered oral colon-specific drug delivery systems: A review

Enzyme-triggered oral colon-specific drug delivery system (EtOCDDS1) can withstand the harsh stomach and small intestine environments, releasing encapsulated drugs selectively in the colon in response to colonic microflora, exerting local or systematic therapeutic effects. EtOCDDS boasts high colon targetability, enhanced drug bioavailability, and reduced systemic side effects. Polysaccharides are extensively used in enzyme-triggered oral colon-specific drug delivery systems, and its colon targetability has been widely confirmed, as their properties meet the demand of EtOCDDS. Polysaccharides, known for their high safety and excellent biocompatibility, feature modifiable structures. Some remain undigested in the stomach and small intestine, whether in their natural state or after modifications, and are exclusively broken down by colon-resident microbiota. Such characteristics make them ideal materials for EtOCDDS. This article reviews the design principles of EtOCDDS as well as commonly used polysaccharides and their characteristics, modifications, applications and specific mechanism for colon targeting. The article concludes by summarizing the limitations and potential of ETOCDDS to stimulate the development of innovative design approaches.

Recent updates on guar gum derivatives in colon specific drug delivery

Colon specific delivery of therapeutics have gained much attention of pharmaceutical researchers in the recent past. Colonic specific targeting of drugs is used not only for facilitating absorption of protein or peptide drugs, but also localization of therapeutic agents in colon to treat several colonic disorders. Among various biopolymers, guar gum (GG) exhibits pH dependent swelling, which allows colon specific release of drug. GG also shows microbial degradation in the colonic environment which makes it a suitable excipient for developing colon specific drug delivery systems. The uncontrolled swelling and hydration of GG can be controlled by structural modification or by grafting with another polymeric moiety. Several graft copolymerized guar gum derivatives are investigated for colon targeting of drugs. The efficacy of various guar gum derivatives are evaluated for colon specific delivery of drugs. The reviewed literature evidenced the potentiality of guar gum in localizing drugs in the colonic environment. This review focuses on the synthesis of several guar gum derivatives and their application in developing various colon specific drug delivery systems including matrix tablets, coated formulations, nano or microparticulate delivery systems and hydrogels.

Guar gum as a microbially degradable component for an oral colon delivery system based on a combination strategy: formulation and in vitro evaluation

Oral colon delivery has widely been pursued exploiting naturally occurring polysaccharides degraded by the resident microbiota. However, their hydrophilicity may hinder the targeting performance. The aim of the present study was to manufacture and evaluate a double-coated delivery system leveraging intestinal microbiota, pH, and transit time for reliable colonic release. This system comprised a tablet core, a hydroxypropyl methylcellulose (HPMC) inner layer and an outer coating based on Eudragit® S and guar gum. The tablets were loaded with paracetamol, selected as a tracer drug because of the well-known analytical profile and lack of major effects on bacterial viability. The HPMC and Eudragit® S layers were applied by film-coating. Tested for in vitro release, the double-coated systems showed gastroresistance in 0.1 N HCl followed by lag phases of consistent duration in phosphate buffer pH 7.4, imparted by the HPMC layer and synergistically extended by the Eudragit® S/guar gum one. In simulated colonic fluid with fecal bacteria from an inflammatory bowel disease patient, release was faster than in the presence of β-mannanase and in control culture medium. The bacteria-containing fluid was obtained by an experimental procedure making multiple tests possible from a single sampling and processing run. Thus, the study conducted proved the feasibility of the delivery system and ability of guar gum to trigger release in the presence of colon bacteria without impairing the barrier properties of the coating. Finally, it allowed an advantageous simulated colonic fluid preparation procedure to be set up, reducing the time, costs, and complexity of testing and enhancing replicability.

Butyrate-producing colonic clostridia: picky glycan utilization specialists

Butyrate-producing human gut microbiota members are recognized for their strong association with a healthy immune-homeostasis and protection from inflammatory disorders and colorectal cancer. These effects are attributed to butyrate, the terminal electron sink of glycan fermentation by prevalent and abundant colonic Firmicutes from the Lachnospiraceae and Oscillospiraceae families. Remarkably, our insight into the glycan utilization mechanisms and preferences of butyrogenic Firmicutes remains very limited as compared with other gut symbionts, especially from the Bacteroides, Bifidobacterium, and Lactobacillus genera. Here, we summarize recent findings on the strategies that colonic butyrate producers have evolved to harvest energy from major dietary fibres, especially plant structural and storage glycans, such as resistant starch, xylans, and mannans. Besides dietary fibre, we also present the unexpected discovery of a conserved protein apparatus that confers the growth of butyrate producers on human milk oligosaccharides (HMOs), which are unique to mother’s milk. The dual dietary fibre/HMO utilization machinery attests the adaptation of this group to both the infant and adult guts. These finding are discussed in relation to the early colonization of butyrogenic bacteria and the maturation of the microbiota during the transition from mother’s milk to solid food. To date, the described butyrogenic Firmicutes are glycan utilization specialists that target only a few glycans in a highly competitive manner relying on co-regulated glycan utilization loci. We describe the common pillars of this machinery, highlighting butyrate producers as a source for discovery of biochemically and structurally novel carbohydrate active enzymes.

Interactions between dietary fibre and the gut microbiota

Research characterising the gut microbiota in different populations and diseases has mushroomed since the advent of next-generation sequencing techniques. However, there has been less emphasis on the impact of dietary fibres and other dietary components that influence gut microbial metabolic activities. Dietary fibres are the main energy source for gut bacteria. However, fibres differ in their physicochemical properties, their effects on the gut and their fermentation characteristics. The diversity of carbohydrates and associated molecules in fibre-rich foods can have a major influence on microbiota composition and production of bioactive molecules, for example SCFAs and phenolic acids. Several of these microbial metabolites may influence the functions of body systems including the gut, liver, adipose tissues and brain. Dietary fibre intake recommendations have recently been increased (to 30 g daily) in response to growing obesity and other health concerns. Increasing intakes of specific fibre and plant food sources may differentially influence the bacteria and their metabolism. However, in vitro studies show great individual variability in the response of the gut microbiota to different fibres and fibre combinations, making it difficult to predict which foods or food components will have the greatest impact on levels of bioactive molecules produced in the colon of individuals. Greater understanding of individual responses to manipulation of the diet, in relation to microbiome composition and production of metabolites with proven beneficial impact on body systems, would allow the personalised approach needed to best promote good health.

Degradation of guar in an up-flow anaerobic sludge blanket reactor: Impacts of salinity on performance robustness, granulation and microbial community

Guar is extensively used during shale gas exploitation and is a major component in the flowback water. The viscosity of guar has adverse effects for the treatment of flowback water. This study investigated the degradation of guar at different salinities with an up-flow anaerobic sludge blanket (UASB) reactor. The effects of salinity on guar degradation, granular characteristics and microbial community were also studied. Results showed that more than 79% of guar was removed at hydraulic retention time (HRT) of 10 h, even at a concentration of 10000 mg L^-1 of NaCl. Increasing salinity decreased granular size and hydrophobicity, but improved the secretion of EPS (especially for protein). Low salt condition 2500 mg L^-1 presented faster degradation rate of guar. Salinity resulted in insignificant difference on bacterial community, but decreased the abundance of methanogens. Bacteroides, Prolixibacter and Pelolinea are essential genera in guar degradation. The results demonstrated the potential of UASB in the treatment of flowback water.

Guar gum modified upconversion nanocomposites for colorectal cancer treatment through enzyme-responsive drug release and NIR-triggered photodynamic therapy

Multimodal therapeutic approach towards colorectal cancer (CRC) holds great promise. There is, however, no convincing strategy reported to date that employs a multimodal strategy in CRC treatment. The present study reports an intense green-emitting core-shell photoluminescent upconversion (CSGU) nanocrystal engineered to synergistically perform photodynamic and enzyme-triggered delivery of the chemotherapeutic agent for an enhanced therapeutic outcome on HT-29 colon carcinoma cells in vitro. The photodynamic activity is achieved by the energy transfer between CSGU and the chemically conjugated Rose Bengal (RB) molecules that are further protected by a mesoporous silica (MS) layer. The chemical assay demonstrates a remarkable FRET mediated generation of ¹O₂ under NIR (980 nm) excitation. The outermost MS layer of the nanoplatform is utilized for the loading of the 5FU anticancer drug, which is further capped with a guar gum (GG) polysaccharide polymer. The release of the 5FU is specifically triggered by the degradation of the GG cap by specific enzymes secreted from colonic microflora, which otherwise showed 'zero-release behavior' in the absence of any enzymatic trigger in various simulated gastro-intestinal (GI) conditions. Furthermore, the enhanced therapeutic efficacy of the nanoplatform (CSGUR-MSGG/5FU) was evaluated through in vitro studies using HT-29 CRC cell lines by various biochemical and microscopic assays by the simultaneous triggering effect of colonic enzyme and 980 nm laser excitation. In addition, the strong visible emission from the nanoplatform has been utilized for NIR-induced cellular bioimaging.

Two binding proteins of the ABC transporter that confers growth of Bifidobacterium animalis subsp. lactis ATCC27673 on β-mannan possess distinct manno-oligosaccharide-binding profiles

Human gut bifidobacteria rely on ATP-binding cassette (ABC) transporters for oligosaccharide uptake. Multiple oligosaccharide-specific solute-binding protein (SBP) genes are occasionally associated with a single ABC transporter, but the significance of this multiplicity remains unclear. Here, we characterize BlMnBP1 and BlMnBP2, the two SBPs associated to the β-manno-oligosaccharide (MnOS) ABC transporter in Bifidobacterium animalis subsp. lactis. Despite similar overall specificity and preference to mannotriose (K_d ≈80 nM), affinity of BlMnBP1 is up to 2570-fold higher for disaccharides than BlMnBP2. Structural analysis revealed a substitution of an asparagine that recognizes the mannosyl at position 2 in BlMnBP1, by a glycine in BlMnBP2, which affects substrate affinity. Both substitution types occur in bifidobacterial SBPs, but BlMnBP1-like variants prevail in human gut isolates. B. animalis subsp. lactis ATCC27673 showed growth on gluco and galactomannans and was able to outcompete a mannan-degrading Bacteroides ovatus strain in co-cultures, attesting the efficiency of this ABC uptake system. By contrast, a strain that lacks this transporter failed to grow on mannan. This study highlights SBP diversification as a possible strategy to modulate oligosaccharide uptake preferences of bifidobacterial ABC-transporters during adaptation to specific ecological niches. Efficient metabolism of galactomannan by distinct bifidobacteria, merits evaluating this plant glycan as a potential prebiotic.

Guar Gum Stimulates Biogenic Sulfide Production at Elevated Pressures: Implications for Shale Gas Extraction

Biogenic sulfide production is a common problem in the oil industry, and can lead to costly hydrocarbon processing and corrosion of extraction infrastructure. The same phenomenon has recently been identified in shale gas extraction by hydraulic fracturing, and organic additives in fracturing fluid have been hypothesized to stimulate this process. Constraining the relative effects of the numerous organic additives on microbial metabolism in situ is, however, extremely challenging. Using a bespoke bioreactor system we sought to assess the potential for guar gum, the most commonly used gelling agent in fracturing fluids, to stimulate biogenic sulfide production by sulfate-reducing microorganisms at elevated pressure. Two pressurized bioreactors were fed with either sulfate-amended freshwater medium, or low-sulfate natural surface water, in addition to guar gum (0.05 w/v%) and an inoculum of sulfate-reducing bacteria for a period of 77 days. Sulfide production was observed in both bioreactors, even when the sulfate concentration was low. Analysis of 16S rRNA gene sequences indicate that heterotrophic bacteria closely associated with the genera Brevundimonas and Acinetobacter became enriched early in the bioreactor experiments, followed by an increase in relative abundance of 16S rRNA genes associated with sulfate-reducing bacteria (Desulfosporosinus and Desulfobacteraceae) at later time points. Results demonstrate that guar gum can stimulate acid- and sulfide-producing microorganisms at elevated pressure, and may have implications for the potential role in microbially induced corrosion during hydraulic fracturing operations. Key differences between experimental and in situ conditions are discussed, as well as additional sources of carbon and energy for biogenic sulfide production during shale gas extraction. Our laboratory approach can be tailored to better simulate deep subsurface conditions in order to probe the role of other fracturing fluid additives and downhole parameters on microbial metabolisms observed in these systems. Such baseline studies will prove essential for effective future development of shale gas worldwide.

The GH5 1,4-β-mannanase from Bifidobacterium animalis subsp. lactis Bl-04 possesses a low-affinity mannan-binding module and highlights the diversity of mannanolytic enzymes

Background

β-Mannans are abundant and diverse plant structural and storage polysaccharides. Certain human gut microbiota members including health-promoting Bifidobacterium spp. catabolize dietary mannans. Little insight is available on the enzymology of mannan deconstruction in the gut ecological niche. Here, we report the biochemical properties of the first family 5 subfamily 8 glycoside hydrolase (GH5_8) mannanase from the probiotic bacterium Bifidobacterium animalis subsp. lactis Bl-04 (BlMan5_8).

Results

BlMan5_8 possesses a novel low affinity carbohydrate binding module (CBM) specific for soluble mannan and displays the highest catalytic efficiency reported to date for a GH5 mannanase owing to a very high k_cat (1828 ± 87 s^-1) and a low K_m (1.58 ± 0.23 g · L^-1) using locust bean galactomannan as substrate. The novel CBM of BlMan5_8 mediates increased binding to soluble mannan based on affinity electrophoresis. Surface plasmon resonance analysis confirmed the binding of the CBM10 to manno-oligosaccharides, albeit with slightly lower affinity than the catalytic module of the enzyme. This is the first example of a low-affinity mannan-specific CBM, which forms a subfamily of CBM10 together with close homologs present only in mannanases. Members of this new subfamily lack an aromatic residue mediating binding to insoluble cellulose in canonical CBM10 members consistent with the observed low mannan affinity.

Conclusion

BlMan5_8 is evolved for efficient deconstruction of soluble mannans, which is reflected by an exceptionally low K_m and the presence of an atypical low affinity CBM, which increases binding to specifically to soluble mannan while causing minimal decrease in catalytic efficiency as opposed to enzymes with canonical mannan binding modules. These features highlight fine tuning of catalytic and binding properties to support specialization towards a preferred substrate, which is likely to confer an advantage in the adaptation to competitive ecological niches.

Electronic supplementary material

The online version of this article (doi:10.1186/s12858-015-0055-4) contains supplementary material, which is available to authorized users.

Progress in the development of gelling agents for improved culturability of microorganisms

Gelling agents are required for formulating both solid and semisolid media, vital for the isolation of microorganisms. Gelatin was the first gelling agent to be discovered but it soon paved the way for agar, which has far superior material qualities. Source depletion, issues with polymerase-chain-reaction and inability to sustain extermophiles etc., necessitate the need of other gelling agents. Many new gelling agents, such as xantham gum, gellan gum, carrageenan, isubgol, and guar gum have been formulated, raising the hopes for the growth of previously unculturable microorganisms. We evaluate the progress in the development of gelling agents, with the hope that our synthesis would help accelerate research in the field.

Safety assessment and caloric value of partially hydrolyzed guar gum

Guar gum and partially hydrolyzed guar gum (PHGG) are food ingredients that have been available for many years. PHGG is the partially hydrolyzed product from guar gum obtained from the Indian cluster bean (Cyanopsis tetragonolopus). The gum (CAS Registry No. 9000-30-0) is composed of galactomannan, a gel-forming polysaccharide with a molecular weight ranging from 200 to 300 kDa. The intact and partially hydrolyzed forms have multiple food applications. The intact material can be used to control the viscosity, stability, and texture of foods. PHGG is highly soluble and has little physical impact on foods. Both forms are indigestible but are excellent sources of fermentable dietary fiber. The caloric value of intact guar gum is accepted as 2.0, whereas the caloric value of PHGG has not been firmly established. It is the goal of this paper to review the chemistry, safety, in vivo effects, and caloric value of PHGG.

Expression and characterization of a Bifidobacterium adolescentis beta-mannanase carrying mannan-binding and cell association motifs

The gene encoding β-mannanase (EC 3.2.1.78) BaMan26A from the bacterium Bifidobacterium adolescentis (living in the human gut) was cloned and the gene product characterized. The enzyme was found to be modular and to contain a putative signal peptide. It possesses a catalytic module of the glycoside hydrolase family 26, a predicted immunoglobulin-like module, and two putative carbohydrate-binding modules (CBMs) of family 23. The enzyme is likely cell attached either by the sortase mechanism (LPXTG motif) or via a C-terminal transmembrane helix. The gene was expressed in Escherichia coli without the native signal peptide or the cell anchor. Two variants were made: one containing all four modules, designated BaMan26A-101K, and one truncated before the CBMs, designated BaMan26A-53K. BaMan26A-101K, which contains the CBMs, showed an affinity to carob galactomannan having a dissociation constant of 0.34 μM (8.8 mg/liter), whereas BaMan26A-53K did not bind, showing that at least one of the putative CBMs of family 23 is mannan binding. For BaMan26A-53K, k(cat) was determined to be 444 s(-1) and K(m) 21.3 g/liter using carob galactomannan as the substrate at the optimal pH of 5.3. Both of the enzyme variants hydrolyzed konjac glucomannan, as well as carob and guar gum galactomannans to a mixture of oligosaccharides. The dominant product from ivory nut mannan was found to be mannotriose. Mannobiose and mannotetraose were produced to a lesser extent, as shown by high-performance anion-exchange chromatography. Mannobiose was not hydrolyzed, and mannotriose was hydrolyzed at a significantly lower rate than the longer oligosaccharides.

Polysaccharides for Colon Targeted Drug Delivery

Colon targeted drug delivery has the potential to deliver bioactive agents for the treatment of a variety of colonic diseases and to deliver proteins and peptides to the colon for their systemic absorption. Various strategies, currently available to target the release of drugs to colon, include formation of prodrug, coating of pH-sensitive polymers, use of colon-specific biodegradable polymers, timed released systems, osmotic systems, and pressure controlled drug delivery systems. Among the different approaches to achieve targeted drug release to the colon, the use of polymers especially biodegradable by colonic bacteria holds great promise. Polysaccharidases are bacterial enzymes that are available in sufficient quantity to be exploited in colon targeting of drugs. Based on this approach, various polysaccharides have been investigated for colon-specific drug release. These polysaccharides include pectin, guar gum, amylose, inulin, dextran, chitosan, and chondroitin sulphate. This family of natural polymers has an appeal to drug delivery as it is comprised of polymers with a large number of derivatizable groups, a wide range of molecular weights, varying chemical compositions, and, for the most part, low toxicity and biodegradability yet high stability. The most favorable property of these materials is their approval as pharmaceutical excipients.

In vitroevaluation and pharmacokinetics in dogs of guar gum and Eudragit FS30D-coated colon-targeted pellets of indomethacin

A pH- and enzyme-dependent colon-targeted multi-unit delivery system of indomethacin was developed by coating guar gum and Eudragit FS30D sequentially onto drug-loaded pellets in a fluidized bed coater. In vitro studies showed that smaller coating weight gain of guar gum resulted in reduced release lag time t10 (10% release time), but favored degradation by enzymes (galactomannanase). A cumulative weight gain (CWG) of 44% provided sufficient enzymatic sensitivity and protection of the core. Under gradient pH conditions (pH = 1.2, 6.8, 7.4 and 6.5 for 2, 2, 1 and 15 h, respectively), indomethacin was released from Eudragit FS30D-coated pellets quickly after changing pH to 7.4. For guar gum/Eudragit FS30D double-coated pellets, only about 5% of the drug was released after another 1 h, showing retarding effect by guar gum coating. After changing pH to 6.5 and addition of galactomannanase, enzyme-dependent drug release was observed. Pharmacokinetic study in beagle dogs showed that fastest absorption with the smallest Tmax and Tlag was observed for uncoated pellets. The Tmax and Tlag of Eudragit FS30D-coated pellets were postponed to about 2.5 and 1 h, respectively. After a further guar gum coating, Tlag was further postponed to about 2.8 h, about 2 h of additional lag time on the basis of Eudragit FS30D coating. It is indicated that the guar gum/Eudragit FS30D-coated system has potential to be used to deliver drugs to the colon.

Guar Gum as Potential Film Coating Material for Colon-specific Delivery of Fluorouracil

The potential of guar gum as a film coating material for colon-specific delivery of 5-fluorouracil is evaluated in this study. The guar gum-based multi-unit pellet system is prepared by coating guar gum and pH-sensitive polymer Eudragit FS30D sequentially around drug-loaded non-pareil cores in a fluid-bed coater. The outer Eudragit FS coating protects the system against gastrointestinal environment and dissolves rapidly in distal small intestine, where a lumen pH of over 7 triggers the dissolution of the enteric polymer. The inner guar gum coating works as a time-controlled retardant and offers additional protection of the pellets until it is degraded by microbial enzymes at the proximal colon. In vitro results indicate that guar gum is a feasible coating material to achieve timed and enzyme-triggered fluorouracil release. Pharmacokinetic study in beagle dogs shows delayed absorption of about 5 h and limited absorption fraction as a result of guar gum and Eudragit FS coating.

New oral delivery systems for treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is often localized to specific sites in the gastrointestinal tract (GIT). As a result, this disease can be treated with oral site-specific (targeted) drug delivery systems. Targeted delivery systems for treatment of IBD are designed to increase local tissue concentrations of antiinflammatory drugs from lower doses compared with systemic administration. This review addresses the impact disease has or may have on oral targeted delivery for treatment of IBD as well as a number of delivery approaches currently used in marketed products or under investigation. Delivery systems reviewed rely on temporal control, changes in pH along the GIT, the action of local enzymes to trigger drug release, and changes in intraluminal pressure. Dissolution of enteric polymer coatings due to a change in local pH and reduction of azo-bonds to release an active agent are both used in commercially marketed products. Newer approaches showing promise in treating IBD are based on polysaccharides. These materials are most effective when used as compression coatings around core tablets, which contain the active agent. More complex polymeric prodrugs systems are also under investigation. If the dose of the drug is sufficiently low, this approach may also prove useful in improving treatment of IBD.

Increasing viscosity of the intestinal contents alters small intestinal structure and intestinal growth, and stimulates proliferation of enterotoxigenic Escherichia coli in newly-weaned pigs

Sources of viscous soluble fibre, such as barley and oats, have often been included in the weaning diet of the pig to accelerate development of the large intestine. Inclusion of a non-fermentable, viscous compound, sodium carboxymethylcellulose (CMC), in a low-fibre weaning diet was tested to assess the influence of digesta viscosity on the gut in the absence of increased fermentation. Two CMC sources, of low and high viscosity, were added to cooked rice-based diet at 40 g/kg total diet. A third control rice diet did not contain any CMC. Diets were fed for 13 d following weaning at 3 weeks of age. Addition of CMC to the diet significantly increased the intestinal viscosity of digesta within the small (P<0.001) and large (P<0.05) intestine. No simple association was found between increases in intestinal viscosity and effects on intestinal morphology and whole-body growth. The average empty-body-weight gain and the small intestinal villus height increased with low-viscosity CMC, but decreased with the high-viscosity CMC group. The full large intestinal weight increased in all pigs fed CMC. Dietary CMC (both low- and high-viscosity) increased the percentage moisture of digesta and faeces, and was associated with increased faecal shedding of enterotoxigenic haemolytic Escherichia coli. Feed ingredients in weaning diets that excessively increase the viscosity of the intestinal digesta may be detrimental to pig health and production.

Low swelling, crosslinked guar and its potential use as colon-specific drug carrier

PURPOSE

(a) To reduce the swelling properties of guar gum (GG) by crosslinking it with glutaraldehyde (GA), while maintaining its degradation properties in the presence of typical colonic enzymes, (b) to characterize the modified GG and to examine its degradation properties in vitro and in vivo, and (c) to assess, by drug probes with different water solubilities, the potential of the crosslinked GG to serve as a colon-specific drug carrier.

METHODS

GG was crosslinked with increasing amounts of GA under acidic conditions to obtain different products with increasing crosslinking densities. These products were characterized by measuring (a) their swelling properties in simulated gastric and intestinal fluids, (b) their crosslinking densities, (c) the release kinetics of three different drugs: sodium salicylate (SS), indomethacin (Indo) and budesonide (Bud) from the crosslinked products into buffer solutions, with or without a mixture of galactomannanase and alpha-galactosidase, and (d) their in vivo degradation in the cecum of conscious rats with and without antibiotic treatment.

RESULTS

Significant reduction in GG swelling properties, in both simulated gastric and intestinal fluids, was accomplished by its crosslinking with GA. The crosslinking density of the modified GG products was GA concentration-dependent. The release of SS from crosslinked GG discs was completed within 120 minutes. During the same period of time and for more than 10 hours the release of Indo and Bud was negligible. The release rate of the latter two drugs was enhanced when galactomannanase and alpha-galactosidase were added to the dissolution media. Discs made of the crosslinked GG were implanted in the cecum of rats and their degradation was assessed after 4 days. The extent of degradation was dependent on the amount of GA used for the crosslinking. After 4 days the same discs were recovered intact from rats exposed to antibiotic treatment and from simulated gastric and intestinal fluids.

CONCLUSIONS

Reducing the enormous swelling of GG by crosslinking it with GA resulted in a biodegradable hydrogel which was able to retain poorly water soluble drugs, such as Indo and BUD, but not highly water soluble drugs, such as SS, in artificial gastrointestinal fluids. A variety of hydrogels with increasing crosslinking densities were produced and tested for their potential use as colon-specific drug platforms in vitro and in vivo. Their performance did not depend on creating physical barriers by means of compression.

Estimation of the fermentability of dietary fibre in vitro: a European interlaboratory study

Five European laboratories tested a simple in vitro batch system for dietary fibre fermentation studies. The inoculum was composed of fresh human faeces mixed with a carbonate-phosphate buffer complex supplemented with trace elements and urea. Five dietary fibre sources (cellulose, sugarbeet fibre, soyabean fibre, maize bran and pectin) were used by each laboratory on three occasions to determine pH, residual non-starch polysaccharides (NSP) and short-chain fatty acid production during fermentation. Cellulose and maize bran degradabilities were very low (7.2(SE 10.8) and 6.2 (SE 9.1)% respectively after 24 h), whereas pectin and soyabean fibre were highly degraded (97.4 (SE 4.4) and 91.1 (SE 3.4)% respectively after 24 h). Sugarbeet fibre exhibited an intermediate level of degradability (59.5 (SE 14.9)%). Short-chain fatty acid production was closely related to NSP degradation (r 0.99). Although each variable was ranked similarly by all laboratories, some differences occurred with respect to absolute values. However, the adaptation of donors to the experimental substrates was not an influential factor. Interlaboratory differences could be reduced either by adding less substrate during incubations or using less-diluted inocula. In vitro fermentations with inocula made from human faeces and from rat caecal contents gave similar results. There was a close correspondence between the data obtained in the present experiment and those previously published in in vivo studies in the rat using the same fibres. The in vitro batch system tested during the present study provides a rapid means of obtaining quantitative estimates of the fermentation and the estimation of the energy content of new sources of dietary fibre.

Pharmacology of dietary fibre

"Dietary fibre" includes a range of relatively poorly digested food substances mainly composed of non-starch polysaccharides. Pectins and gums are multi-branched hydrophilic substances, forming viscous solutions that delay gastric emptying and nutrient absorption from the small bowel. They are used to delay gastric emptying and improve glycemic control in diabetes, as well as to alleviate constipation. Other fibres, including cellulose and lignins, are insoluble and have little effect on gastric emptying and small bowel transit. They markedly accelerate colonic transit and are frequently used as laxatives. Other important, less well-characterised effects of fibre include lowering of blood cholesterol, increase in satiety and possibly reduction in colon neoplasia.

Targeting drugs to the colon: delivery systems for oral administration

The oral delivery of drugs to the colon has applications in a variety of therapeutic areas. This review is concerned with the approaches taken to achieve a universal system for delivery. The design of such a system requires the identification and exploitation of a unique feature of the colonic environment. The use of transit times, pH and bacterial enzymes are critically assessed. In addition, the system must provide protection for the drug during transit to the colon. Upper gastro-intestinal physiology and the transit of pharmaceuticals through these regions are reviewed with reference to their relevance in achieving site specificity.

Effect of human faecal donor on in vitro fermentation variables

Homogenized and diluted human faeces (66.6 g/l) collected from six individuals were incubated with four standard substrates (oat bran, wheat bran, kidney beans (Phaseolus vulgaris), and guar gum) for 4, 8, 12, and 24 h. Neutral detergent fibre (NDF) digestibility coefficients, short-chain fatty acid (SCFA) production (mmol/g organic matter (OM], and gas production (ml/g OM) were significantly affected by donor, substrate, and donor X substrate interactions, within an incubation time, but substrate fermentability rankings were similar at 24 h for all six donors. Substrate differed in NDF digestibilities at all incubation times, whereas SCFA and gas productions differed only at 8, 12, and 24 h. The results indicate that inoculum source (donor) can influence in vitro fermentation variables but not the substrate fermentability ranking at 24 h. It is recommended that several donors, at least three, be used to improve the accuracy of in vitro estimates of colonic fermentation.

The relation between bacterial degradation of viscous polysaccharides and stool output in human beings

1. The relation between bacterial degradation of three viscous polysaccharides (guar gum, ispaghula and xanthan gum) by colonic bacteria in vitro and their effects on colonic function were investigated by comparing the results of anaerobic in vitro incubations with fresh faeces from seven healthy volunteers (measuring viscosity, pH and gas production) with the effects of feeding all three polysaccharides to the same volunteers for 1 week each (14-15 g/d) on faecal mass and whole-gut transit time. 2. Guar gum was rapidly fermented in vitro by faecal bacteria from all volunteers with concomitant loss of viscosity, reduction in pH and generation of gases. Ispaghula maintained its viscosity during incubation, but the pH fell significantly. The results of xanthan gum incubations showed considerable individual variation. 3. Only ispaghula significantly increased faecal mass, whilst none of the gums significantly affected stool frequency or transit time. Statistical analysis of the pooled results showed that although transit time and faecal output were inversely related, feeding viscous polysaccharides could influence these indices independently. Stool frequency was significantly correlated with the transit time, but not the faecal output. 4. Transit time was reduced by gum feeding to a significantly greater extent in those subjects whose faecal bacteria reduced or removed the viscosity of that gum, than in those subjects where the viscosity was maintained. In contrast, there was a smaller increase in faecal mass when the viscosity of the appropriate cultures was removed than when it was maintained or reduced. Increases in stool frequency were significantly associated with hydrogen production from in vitro cultures.

Effect of human faecal inoculum on in vitro fermentation variables

1. Homogenized and diluted faeces (66.6 g/l) collected from one human source on three different months was incubated with four standard substrates (oat bran, wheat bran, red kidney beans (Phaseolus vulgaris) and guar gum) for 4, 8, 12 and 24 h. 2. Neutral-detergent fibre and organic matter (OM) digestibility measurements and gas production (ml gas/g OM) were influenced by substrate and incubation period but not by day of collection. 3. Production of short-chain fatty acids (SCFA) (mmol/g OM) was a function of substrate and incubation period but not day of collection at 4, 8 and 12 h. Rapidly fermentable substrates such as red kidney beans and guar gum did not ferment beyond 12 h and SCFA values were not different at 24 h. 4. Substrates differed in amount, rate and type of SCFA produced. 5. The results indicate that human faeces collected on different occasions were sufficiently uniform to yield similar in vitro fermentation findings among collections. Therefore, it is concluded that human faecal material is a practical source of micro-organisms to evaluate the fermentation properties of substrates.