Stability of Cephalosporin Prodrug Esters in Human Intestinal Juice: Implications for Oral Bioavailability

The levels of degradation of cefetamet pivoxil (CAT), cefuroxime axetil (CAE), and cefpodoxime proxetil (CPD) in 0.6 M phosphate buffer (pH 7.4) and human intestinal juice (pH 7.4) at 37°C over 24 h were compared. Significant differences in the time courses of degradation and in the patterns of degradation products were observed. (i) The relative proportions of the Δ2- and Δ3-cephalosporins were roughly reversed in the two incubation media. In phosphate buffer, the major degradation product was the Δ2-cephalosporin (CAT = 61%; CAE = 74%; CPD = 85%), while in intestinal juice it was the Δ3-cephalosporin (CAT = 86%; CAE = 75%; CPD = 87%). (ii) Generally, the degradation of the prodrug esters progressed faster in intestinal juice than in phosphate buffer (e.g., for CAT the half-lives [t_1/2s] were 0.78 and 4.3 h, respectively). (iii) The two diastereoisomers of CAE and CPD were degraded at different rates in intestinal juice (for the CAE diasteroisomers, t_1/2s = 0.37 and 0.93 h; for the CPD diastereoisomers, t_1/2s = 0.18 and 0.98 h) but were degraded at similar rates in phosphate buffer (for the CAE diastereoisomers, t_1/2 = 1.6 h; for the CPD t_1/2 diastereoisomers, = 2.2 h). It is concluded that (i) the Δ2 isomerization does not significantly affect the bioavailability of prodrug esters since enzymatic hydrolysis in the intestinal fluid proceeds mainly to the active Δ3-cephalosporin and (ii) the high degree of stereoselectivity of the enzymatic ester hydrolysis should make it possible to increase the bioavailabilities of certain prodrug esters (CAE, CPD) by using the more stable diasterioisomer.     

T cell activation causes diarrhea by increasing intestinal permeability and inhibiting epithelial Na+/K+-ATPase

Inflammatory bowel disease (IBD) is associated with mucosal T cell activation and diarrhea. We found that T cell activation with anti-CD3 mAb induces profound diarrhea in mice. Diarrhea was quantified by intestinal weight-to-length (wt/l) ratios, mucosal Na(+)/K(+)-ATPase activity was determined and ion transport changes were measured in Ussing chambers. Anti-CD3 mAb increased jejunal wt/l ratios by more than 50% at 3 hours, returning to base line after 6 hours. Fluid accumulation was significantly reduced in TNF receptor-1 (TNFR-1(-/-)), but not IFN-gamma knockout mice. Anti-CD3 mAb decreased mucosal Na(+)/K(+)-ATPase activity, which was blocked by anti-TNF mAb and occurred to a lesser degree in TNFR-1(-/-) mice. Neither alpha nor beta subunits of Na(+)/K(+)-ATPase decreased in abundance at 3 hours. Intestinal tissue from anti-CD3-treated mice exhibited increased permeability to mannitol at 1 hour and decreases in electroneutral Na(+) absorption, Na(+)-dependent glucose absorption, and cAMP-stimulated anion secretion at 3 hours. Furthermore, enteral fluid accumulation was observed in CFTR(-/-) mice, indicating a minor role of active anion secretion. These data suggest that diarrhea in IBD is due to TNF-mediated malabsorption rather than to secretory processes. T cell activation induces luminal fluid accumulation by increasing mucosal permeability and reducing epithelial Na(+)/K(+)-ATPase activity leading to decreased intestinal Na(+) and water absorption.     

Behavioural phenotypes: An emerging specialist role for nurses

The idea that behaviour can be influenced by genetics is not new and developments in the field of behavioural genetics suggest this is an area of increasing relevance to healthcare professionals who support people who have learning disabilities associated with genetic disorders. This paper considers both the evidence for behavioural phenotypes and the possible roles healthcare professionals have when supporting affected individuals and their families. The paper argues that nurses in all areas of health care need to have a foundation of skill and knowledge of behavioural phenotypes to ensure effective care is provided for individuals and their families. In addition, the paper proposes that a specialist nursing role is essential in providing direct support to clients and their families as well as in providing a consultancy and educational role to the health and social care professionals who support these families.     

Molecular mechanism of a thumb domain hepatitis C virus nonnucleoside RNA-dependent RNA polymerase inhibitor

A new pyranoindole class of small-molecule inhibitors was studied to understand viral resistance and elucidate the mechanism of inhibition in hepatitis C virus (HCV) replication. HCV replicon variants less susceptible to inhibition by the pyranoindoles were selected in Huh-7 hepatoma cells. Variant replicons contained clusters of mutations in the NS5B polymerase gene corresponding to the drug-binding pocket on the surface of the thumb domain identified by X-ray crystallography. An additional cluster of mutations present in part of a unique beta-hairpin loop was also identified. The mutations were characterized by using recombinant replicon variants engineered with the corresponding amino acid substitutions. A single mutation (L419M or M423V), located at the pyranoindole-binding site, resulted in an 8- to 10-fold more resistant replicon, while a combination mutant (T19P, M71V, A338V, M423V, A442T) showed a 17-fold increase in drug resistance. The results of a competition experiment with purified NS5B enzyme with GTP showed that the inhibitory activity of the pyranoindole inhibitor was not affected by GTP at concentrations up to 250 microM. Following de novo initiation, the presence of a pyranoindole inhibitor resulted in the accumulation of a five-nucleotide oligomer, with a concomitant decrease in higher-molecular-weight products. The results of these studies have confirmed that pyranoindoles target the NS5B polymerase through interactions at the thumb domain. This inhibition is independent of GTP concentrations and is likely mediated by an allosteric blockade introduced by the inhibitor during the transition to RNA elongation after the formation of an initiation complex.