Bifidobacterium longum CCM 7952 Promotes Epithelial Barrier Function and Prevents Acute DSS-Induced Colitis in Strictly Strain-Specific Manner

BACKGROUND

Reduced microbial diversity has been associated with inflammatory bowel disease (IBD) and probiotic bacteria have been proposed for its prevention and/or treatment. Nevertheless, comparative studies of strains of the same subspecies for specific health benefits are scarce. Here we compared two Bifidobacterium longum ssp. longum strains for their capacity to prevent experimental colitis.

METHODS

Immunomodulatory properties of nine probiotic bifidobacteria were assessed by stimulation of murine splenocytes. The immune responses to B. longum ssp. longum CCM 7952 (Bl 7952) and CCDM 372 (Bl 372) were further characterized by stimulation of bone marrow-derived dendritic cell, HEK293/TLR2 or HEK293/NOD2 cells. A mouse model of dextran sulphate sodium (DSS)-induced colitis was used to compare their beneficial effects in vivo.

RESULTS

The nine bifidobacteria exhibited strain-specific abilities to induce cytokine production. Bl 372 induced higher levels of both pro- and anti-inflammatory cytokines in spleen and dendritic cell cultures compared to Bl 7952. Both strains engaged TLR2 and contain ligands for NOD2. In a mouse model of DSS-induced colitis, Bl 7952, but not Bl 372, reduced clinical symptoms and preserved expression of tight junction proteins. Importantly, Bl 7952 improved intestinal barrier function as demonstrated by reduced FITC-dextran levels in serum.

CONCLUSIONS

We have shown that Bl 7952, but not Bl 372, protected mice from the development of experimental colitis. Our data suggest that although some immunomodulatory properties might be widespread among the genus Bifidobacterium, others may be rare and characteristic only for a specific strain. Therefore, careful selection might be crucial in providing beneficial outcome in clinical trials with probiotics in IBD.

Redox state alters anti-cancer effects of wedelolactone

Wedelolactone is one of the active plant polyphenolic compounds. Anti-tumor effects of this drug have been demonstrated recently. We have described that wedelolactone acts as catalytic inhibitor of DNA topoisomerase IIα. The aim of this study was to further characterize the mechanism of its anti-tumor effects. We showed that wedelolactone inhibits binding of DNA topoisomerase IIα to plasmid DNA and antagonizes formation of etoposide-induced DNA cleavage complex. The inhibition of topoisomerase IIα by wedelolactone is reversible by excess of the enzyme but not DNA. The in vitro inhibitory effect of wedelolactone on the topoisomerase IIα activity is redox-dependent as it diminished in the presence of reducing agents. Cytotoxicity of wedelolactone was partially inhibited by N-acetylcysteine and glutathione ethyl ester in breast cancer MDA-MB-231 and MDA-MB-468 cells while the inhibitory effect of catalase was observed only in the former cell line. Finally, we found that wedelolactone can be oxidized in the presence of copper ions resulting in DNA strand break and abasic site formation in vitro. However, wedelolactone induced neither DNA damage in MDA-MB-231 cells nor mutations in bacterial cells detectable by Ames test suggesting that wedelolactone may not be an effective inducer of DNA damage. We conclude that the topoisomerase IIα inhibitory- and DNA damaging activities of wedelolactone in vitro depend on its redox state. Pro-oxidant activity could, however, explain only part of wedelolactone-induced cytotoxicity. Therefore, the major cellular target(s) of wedelolactone and the exact mechanism of wedelolactone-induced cytotoxicity still remain to be identified.

Isolation and characterization of two rumen Streptococcus bovis bacteriophages

A method for the isolation of Streptococcus bovis bacteriophages from ruminal fluid of calves is described. Thirty to 2 x 10(3) phages per ml infecting Streptococcus bovis strains 4/1 and 47/3 were isolated directly from ruminal fluid. Two bacteriophages were characterized on the basis of plaque morphology, host ranges, electron microscopic morphology and DNA restriction endonuclease digestion patterns. The F1 and F3 phages formed clear plaques of different sizes. The plaque size of the F1 phage was about 1-1.5 mm in diameter, while the plaques of the F3 phage were larger (1.5-2.5 mm in diameter). Both phages are placed in group B of Bradley's scheme and have different host ranges. The first isolation of Streptococcus bovis phage DNA is reported. Restriction analysis of their DNAs showed that phages F1 and F3 had different numbers of cleavage sites in their genomes and that they were not identical.