Factors limiting the oral bioavailability of N-acetylglucosaminyl-N-acetylmuramyl dipeptide (GMDP) and enhancement of absorption in rats by delivery in a water-in-oil microemulsion.

The bioavailability (BA) of radio-labelled N-acetylglucosaminyl-N-acetylmuramyl dipeptide (GMDP) was low when administered by oral gavage as an aqueous solution to conscious male Sprague-Dawley rats (8.3+/-4.4% (mean+/-S.D., n=3)). To assess the likely factors contributing to the poor BA of GMDP, the stability of GMDP in the lumen of the gastrointestinal (GI) tract was examined in vitro, using ex vivo GI contents. GMDP was degraded by the contents of the small intestine, caecum and large intestine but was more stable in stomach contents. The permeability coefficient (p(app)) of GMDP in isolated sections of rabbit ileum was 1.67x10(-6) cm/s in the mucosal to serosal direction and was not significantly different in the serosal to mucosal direction, indicating that GMDP is poorly permeable and passively transported across the intestinal wall. First pass metabolism was considered to be unlikely to be the primary limitation to the oral bioavailability of GMDP and therefore, that the oral bioavailability of GMDP was likely limited by instability in the lumen of the gastrointestinal tract and low intestinal permeability. A water-in-oil (w/o) microemulsion formulation subsequently developed to address these problems was trialed in a preliminary bioavailability study in rats and enhanced the bioavailability of GMDP ten-fold when administered intraduodenally, indicating that w/o microemulsions may represent a viable mechanism for enhancing the bioavailability of poorly GI-stable and poorly permeable peptide-based molecules.

Non-electrostatic factors govern the hydrodynamic properties of articular cartilage proteoglycan.

The hydrodynamic frictional resistance to water flow exerted by articular cartilage proteoglycan is shown to be similar to that of proteoglycan isolated from Swarm rat chondrosarcoma, and independent of the state of aggregation of the proteoglycan. Frictional resistance is dependent, however, on the chain segments of the constituent chondroitin-sulphate and keratan-sulphate chains of the proteoglycan. Frictional resistance offered by chondroitin sulphate was independent of pH over the range 3.2-8.7. This confirms previous studies, associated with varying ionic strength and chemical modification of ionic groups of chondroitin sulphate, which showed that the frictional resistance offered by this molecule is independent of electrostatic factors. Water-structure-breaking and hydrogen-bond-breaking solvents were also without major effects on the flow resistance offered by chondroitin sulphate. An overall secondary structure of chondroitin sulphate was not evident, as it showed no significant difference to dextran in terms of its temperature dependence of relative viscosity. Local regions of rigid secondary structure, as manifested through inter-residue hydrogen bonding between sugar residues, is likely to control flow resistance as periodate-oxidized chondroitin sulphate and periodate-oxidized and reduced preparations showed a significant decrease in their frictional resistance to water.

Sulphated macromolecules produced by in vivo labelling in the rat gastric mucosa.

The aim of this study was to investigate the nature and distribution of sulphated macromolecules of the extracellular matrix in rat gastric mucosa. This was achieved by developing an in vivo labelling system. An intraperitoneal injection of 1 mCi [35S]-sulphate was given for either 4 h (0.01% incorporation into macromolecular fraction) or 8 h (0.13% incorporation). At the end of the labelling period the stomach was removed and the mucosa and submucosa was either taken as a single combined sample or separated into four layers by blunt dissection. Each sample was papain digested and analysed by ion-exchange chromatography. This analysis revealed sulphated species of differing charge existing in differing proportions throughout the mucosa. These sulphated species eluted at NaCl concentrations of approximately 0 (A), 0.19 (B), 0.34 (C) and 0.78 mol/L (D) from a Q-Sepharose ion exchange column. Further analysis by size exclusion chromatography and chemical and enzymatic digestion showed that peaks B and C had molecular weights of 2.4 x 10(5) and 2.8 x 10(5), respectively and were resistant to chondroitinase ABC, heparitinase and nitrous acid digestion. Peak D was found to contain a polydisperse population of molecules with a molecular weight range of approximately 1 x 10(4) to 6 x 10(4). This sample was susceptible to nitrous acid and chondroitinase ABC digestion and was found predominantly in the sample isolated from deeper in the tissue. We have thus developed an in vivo labelling technique for sulphated macromolecules that can be used in the further study of injury to the gastric mucosa.

Changes in sulfated macromolecules produced in vivo during normal and indomethacin-delayed ulcer healing in rats.

The aim of this study was to examine the synthesis of sulfated glycosaminoglycans during normal healing of experimental acetic acid-induced gastric ulcer in rats and to investigate the effect of indomethacin, a drug known to delay ulcer healing, on this synthesis using an in vivo labelling system. Analysis revealed the presence of two major sulfated species in control tissue; a population of sulfated mucins and glycosaminoglycans, predominantly galactosaminoglycans. The incorporation of [35S]sulfate label into glycosaminoglycans synthesized in the granulation tissue of healing ulcers increased significantly (P < 0.05) as compared to day 0 and control levels at day 14. Treatment of animals with indomethacin (1 mg/kg daily) resulted in a further significant (P < 0.01) rise in sulfated glycosaminoglycan synthesis in indomethacin-treated ulcer tissue compared to that found in healing ulcers at day 14. The increased glycosaminoglycan synthesis was due to increased levels of chondroitin sulfate and dermatan sulfate. Glycosaminoglycan synthesis is elevated at the ulcer site during healing of experimental gastric ulcers; however, indomethacin treatment, which delays ulcer healing, significantly increases the synthesis of glycosaminoglycans above that seen in healing ulcers. Changes in the sulfated glycosaminoglycan content of the ulcer may play a role in the healing process and may give further insight into the mechanisms by which indomethacin delays ulcer healing.