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We read with considerable interest the paper by Sheil et al. who reported the successful application of the subcutaneous route for the probiotic attenuation of colitis.
We agree with the corresponding commentary of Ghosh et al. regarding the need to study mechanisms underlying probiotic interactions. Recently, we further standardized a method to compare the anti-inflammatory pot...
We agree with the corresponding commentary of Ghosh et al. regarding the need to study mechanisms underlying probiotic interactions. Recently, we further standardized a method to compare the anti-inflammatory potential of orally administered LAB in a murine model of acute TNBS-induced colitis. This model allowed us to discriminate ‘protective’ strains, showing between 30 and 70% reduction of the inflammatory score from strains, which did not significantly attenuate the experimental colitis. We could select very performing strains of Lactobacillus salivarius and Lactobacillus rhamnosus that consistently lowered colitis. In comparison, a strain of Lactobacillus acidophilus, Lactococcus lactis and Streptococcus gordonii never showed any improvement. For all five strains we investigated the protective effect of a single intra-peritoneal injection of 5 x 107 live microorganisms, 24 hour prior to the induction of colitis. Surprisingly, the protection by the LAB strains via this systemic route closely matched the efficiency of the oral route (figure 1).
Figure 1. LAB protection on macroscopic damages induced by TNBS. The impact of oral (open bars) or intra-peritoneal (hatched bars) route of LAB administration on the reduction of TNBS-induced colitis in mice . Results are expressed as a % reduction of the mean macroscopic inflammation 7 of mice treated with LAB, in relation to the mean score of non-treated mice. Colitis index is assessed 48 h after the TNBS administration. Each bar represents an independent experiment of control (n=10) and LAB treated mice (n=10).
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When evaluating both routes simultaneously, the anti-inflammatory effect was of comparable magnitude. Moreover, the prophylactic impact of the intra-peritoneal Lactobacillus salivarius strain was established up to 2 hours before TNBS administration. It is noteworthy that 2 delayed injections could lead to protection but caused marked weight loss (23 %, p<_0.05 versus="versus" _15="_15" _="_" and="and" _11="_11" respectively="respectively" for="for" control="control" oral="oral" route="route" group="group" with="with" alleged="alleged" fever.="fever." p="p"/>
Our findings clearly confirm those of Sheil et al, showing strain specific in vivo probiotic effects distant from the target tissue, suggesting relationships between the type of LAB (or LAB components) and peritoneal immuno-competent cells. Pereyra et al. reported transient dose-dependant induction of a/b like interferon (IFN) in serum of intraperitoneal injected Lactobacillus bulgaricus while Streptococcus thermophilus did not. Recent observations showed that heat treatment of an orally administered probiotic cocktail abolished the colitis protection in a DSS model, while irradiation improved it. Consequently, cellular integrity appears to be necessary to explain at least some part of the effect, although cell walls and peptidoglycans of killed bacteria cannot be considered as passive. Possibly both "good" and "bad" signals are given out by LAB, and the immune system is integrating all of them. Those ‘mixed’ signals will no doubt be specific for each strain as well as dose dependent. Differences in physico-chemical status could explain the mortality seen by Sheil et al, especially when using heat-treated bacteria. Pereyra et al. established that the maximal non-lethal quantity of injected live LAB was 5 x 107 but it can be hypothesized that toxicity may also differ with strain and viability status.
Both pro- and anti-inflammatory components of probiotics have been reported to interact with systemic immune cells, showing effects comparable to other well-known anti-inflammatory or therapeutic molecules. It is therefore most probable that systemic delivery of specific live or killed probiotics may influence the delicate balance between Th1 and Th2 immunity, and subsequently have an impact on the local immunity. Clear relationships, however, are not obvious. A first example is the case of subcutaneous CpG DNA that promoted a Th1-response and was able to alleviate some symptoms of DSS colitis but caused inflammation when administered after the onset of colitis. Secondly, different experimental models of colitis supported a potential benefit of probiotic DNA, although it seems very premature to restrict this probiotic effect to nucleic acids only.
As emphasized by Gosh et al, approaches involving fractional studies are essential tools to complete the knowledge obtained from in vitro and ex vivo models and assist in understanding the interactions between LAB and the immune system. These studies may reveal common mechanisms active in inflammation, tolerance and allergy models. Even if this study confirms the importance of the systemic route for certain probiotic activity, we cannot neglect the possible influence of the local and innate immunity, the general status of the gut flora and the role of the epithelial cells in the cross-talk between both.
We are indebted to Rhodia Food for financial support.
1 B Sheil, J McCarthy, L O’Mahony, M W Bennett, P Ryan, J J Fitzgibbon, B Kiely, J K Collins, and F Shanahan
Is the mucosal route of administration essential for probiotic function? Subcutaneous administration is associated with attenuation of murine colitis and arthritis
Gut 2004; 53: 694-700
2 S Ghosh, D van Heel, and R J Playford
Probiotics in inflammatory bowel disease: is it all gut flora modulation?
Gut, May 2004; 53: 620 - 622
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