Structure-function relations in the inhibition of murine contact hypersensitivity by amiloride

Is Androgenetic Alopecia a Photoaggravated Dermatosis?

Progressive thinning of the scalp hair in androgenetic alopecia (AGA) results in a gradual decline in natural protection of the scalp from ultraviolet radiation (UVR). A number of pathologic conditions of the scalp are evidently related to UVR, particularly photosensitive diseases and disorders of the chronically photodamaged bald scalp. The most important chronic effects of UVR are photocarcinogenesis and solar elastosis. Besides these, erosive pustular dermatosis and 'red scalp' are distinct disorders peculiar to the balding scalp. While the consequences of sustained UVR on the unprotected scalp are well appreciated, the effects of UVR on hair loss have widely been ignored. However, clinical observations and theoretical considerations suggest that UVR may have negative effects: acute telogen effluvium from UVR has been described, and the production of porphyrins by Propionibacterium sp. in the pilosebaceous duct, with photoactivation of porphyrins leading to oxidative tissue injury, has been implicated in follicular microinflammation. Alternatively, keratinocytes themselves may respond to physicochemical stress from UVR, besides irritants and pollutants, by producing radical oxygen species and nitric oxide and by releasing proinflammatory cytokines, eventually leading to injury of the putative site of follicular stem cells in the superficial portion of the hair follicle. Since all of these processes involved in hair loss share the common feature that they are induced or exacerbated by exposure to sunlight, it is proposed that AGA is a photoaggravated dermatosis that requires photoprotection.

Amiloride blockades lipopolysaccharide-induced proinflammatory cytokine biosynthesis in an IkappaB-alpha/NF-kappaB-dependent mechanism. Evidence for the amplification of an antiinflammatory pathway in the alveolar epithelium

It has been previously reported that amiloride suppresses inflammatory cytokine biosynthesis. However, the molecular mechanism involved has yet to be ascertained. Therefore, the immunoregulatory potential mediated by amiloride and the underlying signaling transduction pathway was investigated. Exposure of alveolar epithelial cells to amiloride or its analog, 5-(N,N-hexamethylene)-amiloride (HMA), reduced, in a dose-dependent manner, lipopolysaccharide (LPS)-induced secretion of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. This inhibitory effect was associated with the augmentation of a counter antiinflammatory response, mediated by IL-6 and IL-10. Analysis of the mechanism implicated revealed the involvement of an inhibitory kappaB (IkappaB-alpha)/nuclear factor kappaB (NF- kappaB)-sensitive pathway. Amiloride and HMA suppressed the phosphorylation of IkappaB-alpha mediated by LPS, thereby allowing its cytosolic accumulation. Furthermore, both inhibitors interfered with the nuclear translocation of selective NF-kappaB subunits, an effect associated with blockading the DNA-binding activity of NF-kappaB. Recombinant IL-10 blockaded LPS-induced biosynthesis of IL-1beta and TNF-alpha and reduced NF-kappaB activation. Immunoneutralization of endogenous IL-10 reversed the inhibitory effect of amiloride on proinflammatory cytokines and restored the DNA-binding activity of NF-kappaB. These results indicate that amiloride acts as a novel dual immunoregulator in the alveolar epithelium: it downregulates an inflammatory signal and at the same time upregulates an antiinflammatory response. This biphasic effect is IL-10 sensitive and is associated with the selective targeting of the IkappaB-alpha/NF-kappaB signaling transduction pathway.

Inhibition of irritation and contact hypersensitivity by ethacrynic acid

The immunosuppressive effect of topical ethacrynic acid (ECA) was tested on both the induction and elicitation phases of contact sensitization in a mouse model. ECA (0.5% in vehicle) reduced the sensitization response by >50% when the sensitizer was either dinitrochlorobenzene (DNCB), oxazalone (OX) or para-phenylenediamine (PPD), and was applied 1 day later to the ECA-pretreated skin site. The immunosuppressive effect of combining ECA with either hydrocortisone or with cis-urocanic acid was also tested. An additive suppressive effect was observed with ECA in both combinations. The effect of ECA (1% in vehicle) on blocking the elicitation phase was also examined in a mouse ear edema assay. ECA was highly effective in preventing the challenge response in mice previously sensitized to either DNCB, OX or PPD. ECA (1% in vehicle) was also tested for its ability to inhibit contact irritation. ECA (1% in vehicle) was highly effective in preventing ear edema due to topically applied skin irritants including arachidonic acid, capsaicin, lactic acid, phorbol myristate acetate, trans-retinoic acid, and sodium lauryl sulfate. ECA may be useful for both prophylaxis and therapeutic treatment of diverse skin conditions including contact dermatitis, eczema, and other related allergic skin disorders.

Inhibition of irritation and contact hypersensitivity by phenoxyacetic acid methyl ester in mice

New anti-irritant treatments are required to prevent irritation and sensitization reactions to consumer medicines and dermatological drugs. We report here that phenoxyacetic acid methyl ester (PAME) is an effective agent to prevent and treat irritant and allergic contact dermatitis. Balb/c mice skin-treated with 1% PAME do not lose weight relative to vehicle-treated mice, nor is it irritating to mouse skin. Topical PAME prevents skin irritation to a wide variety of irritants including: arachidonic acid, capsaicin, sodium lauryl sulfate (SLS), disodium laureth sulfosuccinate and tetradecanoylphorbol-13-acetate. Histological studies showed that 1% PAME greatly diminished dermal neutrophilic infiltration and dermal capillary vessel dilation, and prevented epidermal hyperproliferation and hyperkeratosis that accompanies detergent (SLS)-induced skin irritation. Topical PAME inhibited ear swelling following ear challenge during the elicitation phase of contact hypersensitivity in mice sensitized with 1-chloro-2, 4-dinitrochlorobenzene (DNCB), oxazolone and the hair coloring dye rho-phenylenediamine (PPD). Finally, topical administration of 1% PAME prior to PPD or DNCB sensitization prevented the induction phase of contact hypersensitivity. These results indicate that PAME represents a potential new category of potent topical anti-inflammatory agents.

Diffuse alopecia with stem cell folliculitis: chronic diffuse alopecia areata or a distinct entity?

A 34-year-old woman presented with an 8-year history of slowly progressive diffuse nonscarring alopecia with loss of hair density. Scalp biopsy specimens showed increased miniaturized follicles and an asymmetric wedge-shaped lymphocytic infiltrate concentrated on the stem cell-rich region at the point of entry of sebaceous ducts and at bulge-like regions of multiple follicles. Several hair bulbs emerging at the stem cell compartment also were inflamed, but the hair bulbs in the deeper dermis and subcutis were spared. I speculate whether these findings may represent a stem cell folliculitis similar to the reaction pattern previously observed in graft versus host disease and in androgenetic alopecia. The additional presence of peribulbar lymphocytic inflammation could indicate that the patient had a variant of alopecia areata. The clinical presentation of a slowly progressive diffuse alopecia without progression to clinically recognizable alopecia areata and the prominent lymphocytic inflammation involving the stem cell compartment may prompt a reexamination of similar cases currently classified as chronic diffuse alopecia areata. The concept that lymphocytes can inhibit stem cell function without destroying the stem cells themselves needs consideration.

Several different ion channel modulators abrogate contact hypersensitivity in mice

A major obstacle in transdermal delivery of drugs is the development of adverse skin sensitization reactions. We tested the concept that ion channel modulators as a class of agents suppress contact hypersensitivity in a mouse model. Mice were sensitized to several contact sensitizing chemicals including dinitrochlorobenzene (DNCB) and a sensitizing drug, nadolol. We report our successful use of several ion channel modulators in suppressing contact hypersensitivity, including amiloride, ethacrynic acid (ECA), nifedipine and verapamil. For this purpose, Balb/c female mice were sensitized with DNCB, and abrogation of induction of contact hypersensitivity reaction (CHR) was examined by topical pretreatment of the target-sensitized skin with amiloride, nifedipine and pairwise combinations of these agents with ECA, a potassium ion channel blocker. Abrogation of induction of CHR was observed in all cases. In addition, suppression of contact hypersensitivity was observed in nadolol-sensitized mice pretreated with either verapamil or nifedipine. The results indicate that ion channel inhibitors are broadly effective inhibitors of allergic contact dermatitis and may be useful for facilitating the transdermal delivery of therapeutic drugs that have sensitization potential.

Fenspiride and membrane transduction signals in rat alveolar macrophages

Fenspiride inhibits the calcium signal evoked by the inflammatory peptide formyl-Met-Leu-Phe (fMLP) in peritoneal macrophages, but at concentrations (approximately 1 mM) far above the therapeutic range (approximately 1 microM). Here, in rat alveolar macrophages, high fenspiride concentrations (1 mM) were required to inhibit the calcium signals evoked by the calcium agonist Bay K8644 or by ionomycin. Moreover, fenspiride (1 mM) was a poor inhibitor of the cell membrane depolarization induced by gramicidine D. By contrast, fenspiride blocked Na+-H+ antiport activation by (i) fMLP with an IC50 = 3.1 +/- 1.9 nM and (ii) PMA (phorbol 12-myristate 13-acetate) with an IC50 = 9.2 +/- 3.1 nM. Finally, protein kinase C (PKC) activity of macrophage homogenate was not significantly modified by 10 or 100 microM fenspiride (at 100 microM: 2.57 +/- 1.60 vs. 2.80 +/- 1.71 pmol/10(6) cells/min). In conclusion, fenspiride inhibits fMLP- and PMA-induced pH signals in rat alveolar macrophages, probably by acting distally on the PKC transduction signal. This pH antagonistic action may be relevant for the antiinflammatory mechanism of fenspiride and requires further investigation.