Influence of feeding regimens on rat gut fluids and colonic metabolism of diclofenac-β-cyclodextrin

Commensal flora triggered target anti-inflammation of alginate-curcumin micelle for ulcerative colitis treatment

Ulcerative colitis (UC) is a chronic, idiopathic inflammatory bowel disease characterized by dysregulation of colon immune response. Curcumin (Cur) has strong anti-inflammatory activities, but the application is severely hindered by the extremely hydrophobicity and pitiful bioavailability. Alginate (Alg), a natural polysaccharide with ideal solubility and biosafety, was introduced to prepare the esterified alginate-curcumin conjugate (Alg-Cur) and constructed stable Alg-Cur micelle in physiological solutions. Compared with crystalline Cur, the target anti-inflammatory activities of Alg-Cur were systematically investigated. The results showed that Alg-Cur exerted effective anti-inflammatory effects in Raw 264.7 cells. After oral administration, 92.32 % of Alg-Cur reached colon, and the ester bonds were quickly sheared by abundant esterase produced by commensal anaerobic flora. The released Cur was quickly absorbed in-situ in monomolecular state, and effectively ameliorated the colonic inflammation and tissue damage by inhibiting the TLR4 expression in colonic epithelial cell, reducing the transcription and expression of the pro-inflammation cytokines downstream, as well as the infiltration of lymphocytes, macrophages and neutrophils. The Alg-Cur micelle effectively enhanced the hydrophilicity and bioavailability of Cur, and the commensal flora triggered Cur release showed great potential for UC treatment.

Exploring gastric drug absorption in fasted and fed state rats

The small intestine is generally considered the major site of absorption after oral drug administration. Absorption from the stomach is often disregarded, though passive diffusion across the gastric mucosal barrier is theoretically possible. In this study, an in situ gastric bolus administration model was used to study the gastric absorption of pharmaceutical compounds in fasted and fed state rats. Three drugs [paracetamol (neutral), diclofenac (acidic) and posaconazole (basic)] were administered directly into the stomach as solution (paracetamol and diclofenac) or suspension (posaconazole). Transfer to the intestine was blocked by ligating the pylorus; as a reference, non-ligated conditions were used. Blood samples were collected and gastric absorption was assessed by the appearance of compounds in the systemic circulation. Paracetamol and diclofenac were readily absorbed from the fasted and fed state rat stomach. For paracetamol, the relative contribution of gastric absorption was higher in the fed state compared to the fasted state. Posaconazole absorption was negligible. Since the ability of the stomach to absorb pharmaceutical compounds was clearly confirmed, the present study warrants further research to quantify the contribution of gastric absorption to total gastrointestinal drug absorption.

Diclofenac-β-cyclodextrin for colonic drug targeting: In vivo performance in rats

The aim of this in vivo study was to assess the ability of the prodrug conjugate diclofenac-β-cyclodextrin to release diclofenac in the colon following oral administration, using sulfapyridine (a metabolite of sulfasalazine) as a marker of colonic absorption. Two groups of rats were used; the test rats received a suspension containing the two prodrugs, diclofenac-β-cyclodextrin and sulfasalazine, while the control rats received a suspension containing the corresponding free drugs, sodium diclofenac and sulfapyridine. The rats were fasted overnight with free access to water before and throughout the first 12h of the study. Blood was collected from the tail vein at pre-determined time points and the plasma analyzed for the concentrations of diclofenac and sulfapyridine. Following the oral administration of the two prodrugs, a more extended absorption profile was observed and Cmax was achieved 10h post-dose, in contrast to rapid absorption of the free drugs (tmax of diclofenac being 1.3h, and that of sulfapyridine being 2.1h). In addition to a later tmax, conjugation of diclofenac to β-cyclodextrin also resulted in a reduced Cmax and a reduced AUC. The same tmax for diclofenac-β-cyclodextrin as for sulfasalazine confirms the colonic metabolism of diclofenac-β-cyclodextrin. This study shows the potential of this new cyclodextrin-based prodrug to target and release diclofenac specifically in the colon following oral administration.