ABSTRACTRecent studies have suggested that the topical application of probiotic bacteria can improve skin health or combat disease. We have utilized a primary human keratinocyte culture model to investigate whether probiotic bacteria can inhibitStaphylococcus aureusinfection. Evaluation of the candidate probioticsLactobacillus reuteriATCC 55730,Lactobacillus rhamnosusAC413, andLactobacillus salivariusUCC118 demonstrated that bothL. reuteriandL. rhamnosus, but notL. salivarius, reducedS. aureus-induced keratinocyte cell death in both undifferentiated and differentiated keratinocytes. Keratinocyte survival was significantly higher if the probiotic was applied prior to (P< 0.01) or simultaneously with (P< 0.01) infection withS. aureusbut not when added after infection had commenced (P> 0.05). The protective effect ofL. reuteriwas not dependent on the elaboration of inhibitory substances such as lactic acid.L. reuteriinhibited adherence ofS. aureusto keratinocytes by competitive exclusion (P= 0.026).L. salivariusUCC118, however, did not inhibitS. aureusfrom adhering to keratinocytes (P> 0.05) and did not protect keratinocyte viability.S. aureusutilizes the α5β1 integrin to adhere to keratinocytes, and blocking of this integrin resulted in a protective effect similar to that observed with probiotics (P= 0.03). This suggests that the protective mechanism forL. reuteri-mediated protection of keratinocytes was by competitive exclusion of the pathogen from its binding sites on the cells. Our results suggest that use of a topical probiotic prophylactically could inhibit the colonization of skin byS. aureusand thus aid in the prevention of infection.

In this study, we investigated whether probiotic lysates can modify the tight-junction function of human primary keratinocytes. The keratinocytes were grown on cell culture inserts and treated with lysates from Bifidobacterium longum, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus fermentum, or Lactobacillus rhamnosus GG. With the exception of L. fermentum (which decreased cell viability), all strains markedly enhanced tight-junction barrier function within 24 h, as assessed by measurements of transepithelial electrical resistance (TEER). However, B. longum and L. rhamnosus GG were the most efficacious, producing dose-dependent increases in resistance that were maintained for 4 days. These increases in TEER correlated with elevated expression of tight-junction protein components. Neutralization of Toll-like receptor 2 abolished both the increase in TEER and expression of tight-junction proteins induced by B. longum, but not L. rhamnosus GG. These data suggest that some bacterial strains increase tight-junction function via modulation of protein components but the different pathways involved may vary depending on the bacterial strain.

. Ochratoxin A increases permeability through tight junctions by removal of specific claudin isoforms.

In the present study, we have investigated the role of cholesterol in maintaining the barrier properties of the model intestinal cell line Caco-2. We have extracted membrane cholesterol using methyl-beta-cyclodextrin and demonstrated that maximally, methyl-beta-cyclodextrin lowered cell cholesterol levels by 40-45%. Depletion of cell cholesterol was accompanied by an 80-90% decrease in monolayer transepithelial electrical resistance and a significant increase in the paracellular permeability of dextrans of 4, 10 and 40 kDa. The increase in dextran permeability was most pronounced for the two lower molecular mass species. In addition to the decline in the barrier properties of the monolayers, extraction of cell cholesterol produced an increase in the Triton X-100 solubility of claudin 3, claudin 4 and occludin, and the loss of all three proteins from the plasma membrane (tight junctions). In contrast, removal of cholesterol had no detectable influence on the detergent solubility or morphological distribution of claudin 1. These results indicate that membrane cholesterol is a critical factor in maintaining the barrier property of epithelial monolayers. More specifically, cholesterol appears to stabilize the association of certain proteins with the tight junctions.

Few studies have evaluated the potential benefits of the topical application of probiotic bacteria or material derived from them. We have investigated whether a probiotic bacterium, Lactobacillus rhamnosus GG, can inhibit Staphylococcus aureus infection of human primary keratinocytes in culture. When primary human keratinocytes were exposed to S. aureus, only 25% of the keratinocytes remained viable following 24 h of incubation. However, in the presence of 10 8 CFU/ml of live L. rhamnosus GG, the viability of the infected keratinocytes increased to 57% (P ‫؍‬ 0.01). L. rhamnosus GG lysates and spent culture fluid also provided significant protection to keratinocytes, with 65% (P ‫؍‬ 0.006) and 57% (P ‫؍‬ 0.01) of cells, respectively, being viable following 24 h of incubation. Keratinocyte survival was significantly enhanced regardless of whether the probiotic was applied in the viable form or as cell lysates 2 h before or simultaneously with (P ‫؍‬ 0.005) or 12 h after (P ‫؍‬ 0.01) S. aureus infection. However, spent culture fluid was protective only if added before or simultaneously with S. aureus. With respect to mechanism, both L. rhamnosus GG lysate and spent culture fluid apparently inhibited adherence of S. aureus to keratinocytes by competitive exclusion, but only viable bacteria or the lysate could displace S. aureus (P ‫؍‬ 0.04 and 0.01, respectively). Furthermore, growth of S. aureus was inhibited by either live bacteria or lysate but not spent culture fluid. Together, these data suggest at least two separate activities involved in the protective effects of L. rhamnosus GG against S. aureus, growth inhibition and reduction of bacterial adhesion.

Epithelial tight junctions play a central role in cell-cell adhesion and are necessary for the selective paracellular movement of ions. Claudins are key components of tight junctions and their expression is altered in gut epithelia in a variety of inflammatory enteropathies, including ulcerative colitis and Crohn's disease. Psoriasis is a chronic inflammatory skin disease affecting approximately 2% of the western population, with significantly increased occurrence in individuals with Crohn's disease. Initial studies investigated the expression of claudins in skin of healthy volunteers and patients with chronic plaque psoriasis. We report here that claudins-1 and -3 are the major protein species present in the epidermis of healthy skin; they are expressed on the surface of epidermal keratinocytes, consistent with their localization to tight junctions. In plaques of psoriasis, claudin-1 was not identifiable in the epidermis, although typical staining patterns were observed in clinically normal, uninvolved skin of patients with psoriasis. Claudin-3 was present in the epidermal granular cell layer in normal skin, but was only identified within the cytosol of epidermal keratinocytes in both involved and uninvolved skin of psoriasis patients. We examined further whether exposure of keratinocytes in vitro to pro-inflammatory cytokines mimicked the observed changes in claudin expression seen in chronic plaque psoriasis; lipopolysaccharide, interferon-gamma and tumour necrosis factor-alpha had no effect on claudin protein expression or distribution. Addition of interleukin-1beta, however, resulted in down-regulation of claudins-1 and -3. Tumour necrosis factor-alpha and interleukin-1beta were further used in an in vivo model of skin inflammation; interleukin-1beta alone modulated claudin protein expression in this system. These data demonstrate that epidermal claudin expression is altered in chronic plaque psoriasis and that expression is in part modulated by interleukin-1beta.

1 Intestinal xenobiotic transporters are a signi®cant barrier to the absorption of many orally administered drugs. P-glycoprotein (PGP) is the best known, but several others, including members of the multidrug resistance-associated protein (MRP) family, are also expressed. De®nitive information on their precise e ect on intestinal drug permeability is scarce due to a lack of speci®c inhibitors and the di culty of studying non-PGP activity in the presence of high PGP expression. 2 We have investigated the in vitro use of intestinal tissues from PGP knockout (mdr1a (7/7)) mice as a tool for dissecting the mechanisms of intestinal drug e ux. The permeability characteristics of digoxin (DIG), paclitaxel (TAX) and etoposide (ETOP) were measured in ileum from mdr1a (7/7) and wild-type (FVB) mice mounted in Ussing chambers. 3 DIG and TAX exhibited marked e ux across FVB tissues (B-A : A-B apparent permeability (P app ) ratio 10 and 17 respectively) which was absent in mdr1a (7/7) tissues, con®rming that PGP is the sole route of intestinal e ux for these compounds. The A-B P app of both compounds was 3 ± 5 fold higher in mdr1a (7/7) than in FVB. 4 Polarized transport of ETOP in FVB tissues was reduced but not abolished in mdr1a (7/7) tissues. Residual ETOP e ux in mdr1a (7/7) tissues was abolished by the MRP inhibitor MK571, indicating involvement of both PGP and MRP. 5 MK571 abolished calcein e ux in mdr1a (7/7) tissues, while quinidine had no parallel e ect in FVB tissues, suggesting involvement of MRP but not PGP. 6 Tissues from mdr1a (7/7) mice provide a novel approach for investigating the in¯uence of PGP ablation on intestinal permeability and for resolving PGP and non-PGP mechanisms that modulate drug permeability.

These data encourage further investigation of ABC transporters as potentially important regulators of HF epithelial biology. Clinically, pharmacological modulation of the activity of selected intrafollicular ABC transporters may permit novel therapeutic interventions, such as protecting HF stem cells from chemotherapy-induced damage, counteracting cholesterol-associated hypertrichosis, and manipulating the intrafollicular prostaglandin balance in androgenetic alopecia.