Reactive skin is characterized by marked sensitivity to physical (heat, cold, wind) or chemical (topically applied products) stimuli and by the impairment of the skin barrier's ability to repair itself. Several lines of evidence suggest that beyond their capacity to positively influence the composition of intestinal microbiota, some probiotic bacteria can modulate the immune system both at local and systemic levels, thereby improving immune defense mechanisms and ⁄ or down-regulating immune disorders such as allergies and intestinal inflammation. Several recent human clinical trials clearly suggest that probiotic supplementation might be beneficial to the skin. Using a probiotic lysate, Bifidobacterium longum sp. extract (BL), we demonstrated first in vitro, and then in a clinical trial, that this non-replicating bacteria form applied to the skin was able to improve sensitive skin. The effect of BL were evaluated first on two different models. Using ex vivo human skin explant model we found a statistically significant improvement versus placebo in various parameters associated with inflammation such as a decrease in vasodilation, oedema, mast cell degranulation and TNF-alpha release. Moreover, using nerve cell cultures in vitro, we showed that after 6 h of incubation in culture medium (0.3-1%), the probiotic lysate significantly inhibited capsaicin-induced CGRP release by neurones. Then, a topical cream containing the active extract was tested in a randomized, double-blind, placebocontrolled trial. Sixty-six female volunteers with reactive skin were randomly given either the cream with the bacterial extract at 10% (n = 33) or the control cream (n = 33). The volunteers applied the cream to the face, arms and legs twice a day for two months.Skin sensitivity was assessed by stinging test (lactic acid) and skin barrier recovery was evaluated by measuring trans-epidermal water loss following barrier disruption induced by repeated tapestripping at D1, D29 and D57. The results demonstrated that the volunteers who applied the cream with bacterial extract had a significant decrease in skin sensitivity at the end of the treatment. Moreover, the treatment led to increase skin resistance against physical and chemical aggression compared to the group of volunteers who applied the control cream. Notably, the number of strippings required to disrupt skin barrier function was significantly increased for volunteers treated with the active cream. Clinical and self-assessment scores revealed a significant decrease in skin dryness after 29 days for volunteers treated with the cream containing the 10% bacterial extract. Since in vitro studies demonstrated that, on one hand, isolate sensitive neurones release less CGRP under capsaicin stimulation in the presence of the bacterial extract and, on the other hand, increased skin resistance in volunteers applying the test cream, we speculate that this new ingredient may decrease skin sensitivity by reducing neurone reactivity and neurone accessibility. The results of this studi...
The existence of a flux of proton donors from skin (inner part of the forearm) to the electrode was observed in 12 male and female volunteers. This flux was used to collect and identify the ionic species responsible for skin acidity. It was then found that: (i) pK of these proton donors (pK = 6.13 +/- 0.07) was quasi-identical to that of trans-urocanic acid (6.10), and (ii) the amount of urocanic acid present in stratum corneum was sufficient in itself to explain the acidic level as measured with pH meter (R = 0.8484, n = 10, p = 0.00136). As a result, the contribution of other ionic species can be considered as negligible in normal human skin. The data recorded led us to identify three groups (Fast, Medium, and Slow) characterized by different skin surface pH values (low, medium, and close to neutral) and showing a pH gradient in the outer layers of the stratum corneum, or not. Data analysis suggests that these characteristics depend on urocanic acid production rate within the stratum corneum and that this production rate is self-regulated by its urocanic acid content.
Previous isolation and analysis of E. coli RNA polymerase (EC 2.7.7.6) binding sites on X DNA had demonstrated the existence of a sigma-dependent process of recognition of A-T-rich DNA sequences. We have now extended this finding to T5 and T7 DNA and have provided evidence for the double-strandedness of the isolated binding sites. The possible equation of these sites to the genetically defined promoters is discussed.We have reported (1) the isolation of Escherichia coli RNA lpolymerase binding sites on X DNA by taking advantage of their resistance to nuclease digestion. Their nucleotide composition was enriched in A-T (57%) when a low polymerase-to-DNA ratio was used, although at high ratio it was not very different from that of total X DNA (50%). This observation reflected the existence of at least two types of sites (2), the ones with the highest affinity being selected for at low polymeraseto-DNA ratios. Indeed, when using tRNA as a competitor for RNA lolymerase during the digestion step, we observed (3) that, when the binding was done with holoenzyme at 370, a fraction of protected DNA fragments was resistant to displacement by tRNA, as assayed by the filter retention technique (4). This resistant fraction was enriched in A-T. In contrast, no resistance was observed with core enzyme or with holoenzyme incubated at 00. By further purification on acrylamide gels, we were able to resolve two populations of protected DNA fragments (5). The first type of fragments, referred to as peak I, contained 45-52 nucleotide residues, was considerably enriched in A-T (up to 67%), and, most importantly, was observed only when sigma was present during the binding step. The second type of fragments (peak II), containing 7-10 nucleotide residues, showed no dependence on sigma nor was it enriched in A-T. On the basis of its sigma dependence the first population of protected fragments was operationally defined as promoters. The sigma-dependent selection of A-T-rich DNA sequences by RNA polymerase along with an additional temperature requirement in order to form a stable complex, as demonstrated with T7 (6) and X DNA (3), fits well with the idea of a local melting of DNA. (1) The enrichment in A-T observed in the "promoters" (peak-I fragments) decreased with increasing polymerase-to-DNA ratios. This observation had been interpreted in the following way: at high ratios, peak I is contaminated with nonspecific binding sites of average base composition. A]-though of lower affinity than specific ones, these sites still bind tightly enough not to be displaced by DNase at high concentration of polymerase. Therefore, nonspecific sites of average composition should be detectable as peak-I molecules even in the absence of sigma.(2) Although the nucleotide composition of peak-I fragments was consistent with their being double stranded, this point had to be unequivocally established. Because of the high number of T5 promoters (10), making them more easily available in quantities possible to work with, the experiments designed to answ...
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