RESUMEN
Preventive actions of probiotics as antidiarrheal agents are well documented, but their mechanisms are poorly understood. Two selected probiotics, Bacillus subtilis CU1 and Lactobacillus plantarum CNCM I-4547, were tested in mouse experimental models of diarrhea and the possible mechanisms of action were investigated. Diarrhea was induced in mice by oral castor oil administration or by i.v. injection of lipopolysaccharide (LPS) of Salmonella enteritis. The antidiarrheal drug loperamide was used as control. Fecal water excretion was quantified for 2 h and paracellular permeability and electrical parameters of the colon were assessed in Ussing chambers. The expression of colonic exchangers or channels and of Toll-like receptor 4 (TLR4) was assessed by immunohistochemistry. Prophylactic treatment with B. subtilis CU1 or with L. plantarum CNCM I-4547 reduced LPS-induced diarrhea. The reduction of water excretion was in the same range as those induced by loperamide. In the castor oil model, this effect was only observed with B. subtilis CU1. The two probiotic treatments abolished the increase in paracellular permeability induced by LPS, but not by castor oil. However, only L. plantarum CNCM I-4547 treatment decreased the colonic expression of TLR-4. After B. subtilis CU1, colonic expression of cystic fibrosis transmembrane conductance regulator (CFTR) was reduced and that of Na+/H+ exchanger 3 (NHE3) increased. B. subtilis CU1 may increase the capacity of the colon to absorb excess of water in diarrheic conditions by acting on CFTR and NHE3 expression. The two probiotics strains showed an impact on diarrhea through limitation of water excretion that may involve paracellular permeability or electrolyte transport for L. plantarum CNCM I-4547 and B. subtilis CU1 respectively.
RESUMEN
The beta-lactam antibiotic ampicillin has a relatively poor oral bioavailability in animals and man (30-40%), and its widespread agricultural use in livestock may be contributing to the emergence of antibiotic resistance in the environment. The aim of this study was to define the absorption mechanism by which ampicillin crosses the small intestinal epithelium. The improved rat everted gut sac system was used, with an emphasis on the role of the PepT1 transporter. The absorption kinetics, effects of pH and the use of competitive substrates failed to provide any substantive evidence that the transporter played a major role in ampicillin absorption. Ethylenediaminetetraacetic acid enhanced the absorption, and tissue levels remained low, suggesting that paracellular transport was predominant. pH and competition studies with glycylsarcosine, the widely used PepT1 substrate, also failed to show any transporter activity. Despite evidence from studies with Caco-2 cells that beta-lactam antibiotics are transported by the PepT1 transporter in rat small intestine, the results rather suggest that paracellular diffusion is the major mechanism of absorption, at least for beta-lactam antibiotics with poor bioavailability, such as ampicillin. We suggest that the use of Caco-2 cells underestimates the role of the paracellular route in the absorption of hydrophilic drugs in vivo, and may exaggerate the role of influx transporters.
