Decreased hyaluronic acid synthesis, a sensitive indicator of cortisol action on fibroblast

Chronic tympanic membrane perforation: a better animal model is needed

Developments in the treatment of chronic tympanic membrane perforation have been hindered by the lack of an ideal animal model. It is not appropriate to test such treatments on acute perforations as the majority of these heal spontaneously. An ideal animal model would be one that most closely resembles the human clinical situation. It should be inexpensive, readily available, and easy to create. There have been a number of attempts to create a chronic tympanic membrane perforation model with limited success. All published attempts at chronic tympanic membrane perforations have been reviewed and the limitations of each model are discussed. A number of areas for research exist for further developing a chronic tympanic membrane perforation model. These areas include a perforation model in the presence of bacteria and eustachian tube dysfunction. Understanding the molecular and genetic mechanisms of chronic otitis media and potential treatments will also be useful.

The effects of Musk T on peroxisome proliferator-activated receptor [PPAR]-alpha activation, epidermal skin homeostasis and dermal hyaluronic acid synthesis

Peroxisome proliferators activated receptors (PPARs) are a family of nuclear hormone receptors that heterodimer with the retinoid X receptor and function as transcriptional regulators of genes. Topically Applied PPAR-alpha agonists possess receptor mediated, pro-differentiating/anti-proliferative effects, lipid metabolism stimulation, and anti-inflammatory activity, which suggest that they could be beneficial for the treatment of a variety of cutaneous diseases. Hyaluronan (HA), a high-molecular-weight linear glycosaminoglycan consisting of alternating D: -glucuronic acid and N-acetyl-D: -glucosamine residues, is one of the major extracellular matrix components in skin. Among the family of HA synthase genes (HAS1, 2, 3) so far identified, one group has demonstrated that the expressions of HAS2 and HAS3 play crucial roles in the regulation of HA synthesis in human skin fibroblasts and keratinocytes, respectively, but the precise regulatory mechanisms are still unknown. We examine Musk T called Ethylene brassylate, Astratone or 1,4-Dioxacycloheptadecane-5,17-dione, which used as just a perfume ingredient, plays a role as PPAR-alpha ligand in vitro and stimulates skin barrier recovery, ceramide synthesis, beta-Glucocerebrosidase, involucrin expression in epidermis in vivo; and examine that Musk T stimulates HAS expression and HA synthesis in human skin fibroblast. Through these experiments, we conclude that Musk T is PPAR-alpha ligand, effects on keratinocyte differentiation, intercellular lipid synthesis in epidermis, HA synthesis stimulation in dermis.

The neutral red release assay: a review

The neutral red release (NRR) assay is a cytotoxicity test that can be used to measure the immediate toxic effects of test substances on the cell membrane, resulting in the leaking of intracellular contents. The assay has already been used for several years to evaluate the cytotoxicities of various kinds of products, such as cosmetics, pharmaceuticals, industrial chemicals and household products. It has undergone in-house validation by many companies, and has been found to be particularly useful for identifying substances that are potentially capable of causing adverse reactions on coming into brief contact with the eye or the skin at relatively high concentrations, such as might occur in an adventitious splash into the eye or onto the skin, followed by a quick rinse. Because of the relatively long existence of the NRR assay, its practicality and its proven usefulness for particular purposes, ECVAM decided to review the status of the method, in order to decide whether prevalidation and formal validation studies on the test might be profitable. The review of the status of the test was carried out by performing a comprehensive review of the literature, and by conducting a survey involving companies and institutes with experience in using the test. Both the review and the survey revealed that the assay could provide extremely valuable information when it was used for particular purposes, such as for the evaluation and comparison of immediate toxic effects on the eye or the skin caused by certain products or chemicals such as surfactants. Most of those who responded in the survey favoured a prevalidation/validation study.

Short-term impact of corticosteroids on hyaluronan and epithelial hyperplasia in the rabbit cornea after photorefractive keratectomy

PURPOSE

To investigate the impact of corticosteroids on subepithelial hyaluronan deposition and corneal epithelium thickness in the first 10 days after photorefractive keratectomy (PRK) and to analyze a possible contralateral effect of corticosteroids.

METHODS

Thirty-two New Zealand white rabbits were assigned into two groups and had a transepithelial 5.0-mm diameter, 8.00-diopter myopic PRK performed on one eye. The corticosteroid treatment group (16 animals) received 0.1 mL of methylprednisolone 4% subconjunctivally on the operation table, followed by 0.1% dexamethasone eye drops six times a day during the postoperative period. The sodium chloride (NaCl) treatment group received topical isotonic NaCl eye drops six times a day. In each treatment group, eight animals were killed after 3 and 9 days, respectively. The harvested specimens were stained for hyaluronan and the epithelial thickness was measured.

RESULTS

In contrast to the epithelial thickness, the subepithelial hyaluronan did not show a significant increase during the observation period. The corticosteroid treated group showed at both time-points significantly less subepithelial hyaluronan formation as well as a significantly thinner epithelium, when compared with the NaCl-treated group. At 9 days, the corticosteroid-treated group showed a mild epithelial hyperplasia in only one of eight eyes, whereas this was a common finding in the NaCl-treated group. We detected no hyaluronan deposits in any contralateral-untreated eye, and the epithelial thickness did not differ significantly between any of the four contralateral-untreated eye groups.

CONCLUSIONS

Corticosteroid medication during the first 10 days after operation reduces the amount of subepithelial hyaluronan production and inhibits the epithelial proliferation, and epithelial hyperplasia is prevented. Neither a contralateral hyaluronan deposition nor a contralateral corticosteroid effect could be detected.

Discrimination of the toxic potential of chemically differing topical glucocorticoids using a neutral red release assay with human keratinocytes and fibroblasts

In inflammatory skin disease, hydrocortisone and prednisolone double esters are about equipotent to conventional medium potency topical glucocorticoids, such as betamethasone valerate. Local adverse effects, in particular skin atrophy, are a potential problem with topical glucocorticoids. Recently, cell cultures have shown promise as a means of assessing local tolerance. To investigate the toxic potential of hydrocortisone, hydrocortisone-17-butyrate, hydrocortisone aceponate, prednicarbate, triamcinolone acetonide, betamethasone valerate and desoximethasone, human keratinocytes and fibroblasts were exposed to these agents in vitro, using a modified neutral red release assay. In addition, the morphology of these cells was assessed by light microscopy. Although all the topical glucocorticoids tested proved toxic to both cell types, there were major differences between glucocorticoids in their effect on fibroblasts. Hydrocortisone and the non-halogenated double-ester-type glucocorticoids were less toxic than the conventional medium potency topical glucocorticoids tested (betamethasone valerate and desoximethasone). In particular, hydrocortisone aceponate was less toxic than betamethasone valerate (P < or = 0.05). In general, the effect of topical glucocorticoids on the cells, based on neutral red release, was more marked with keratinocytes than with fibroblasts. Although the ranking order with respect to the toxic potential was similar, a clear-cut difference was not observed between non-halogenated double-ester-type glucocorticoids and betamethasone valerate. Morphological changes due to glucocorticoid exposure followed the same pattern with both keratinocytes and fibroblasts. The neutral red release assay is able to discriminate between the cytotoxic effects of chemically differing topical glucocorticoids on human keratinocytes and fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo prevention of corticosteroid-induced skin atrophy by tretinoin in the hairless mouse is accompanied by modulation of collagen, glycosaminoglycans, and fibronectin

In an earlier study we showed that tretinoin could prevent corticosteroid-induced skin atrophy in hairless mice. In this study, we examined the histochemical, biochemical, and immunochemical changes that accompanied the atrophy and its prevention. Mice were treated dorsally for 3 weeks in the morning and afternoon (AM:PM) as follows: 1) vehicle:vehicle, 2) steroid:vehicle, 3) steroid:tretinoin. Tretinoin concentration was 0.05% in an ethanol:propylene glycol vehicle. The steroid was clobetasol propionate (0.05%). The normally sparse dermal glycosaminoglycans were further reduced by steroid:vehicle treatment and increased to greater than vehicle:vehicle amounts by steroid:retinoid. Mast cells were similarly affected. Biochemical quantification of glycosaminoglycans confirmed the histochemical findings. Collagen, non-collagenous protein, and total protein content were reduced by the steroid. The latter two were returned to more normal levels by tretinoin whereas with collagen there was only a trend toward normal levels. Fibronectin, which was increased by the steroid:vehicle treatment, was reduced to more normal levels by steroid:tretinoin. We conclude that tretinoin has the ability to prevent the major steroid-induced biomechanical changes in hairless mouse dermal connective tissue that contribute to atrophy.

Animal model for persistent tympanic membrane perforations

Topically applied hydrocortisone was used to develop an animal model for persistent tympanic membrane (TM) perforations. Hydrocortisone suspension was applied on the margins of TM perforations of standardized size in rats once daily for 10 days. The healing patterns of the TMs were mapped weekly and, when the perforations were about to close, daily. After 50 days, all hydrocortisone-treated perforations were open, whereas the controls closed within 9 to 12 days. At 3 months, when one third of the perforations still were open, the TMs were studied by otomicroscopy and light microscopy. All TMs were thickened and covered by keratin and wax. The thickened epidermal layer at the border of the TM perforations that remained open also draped the surface of the perforation facing the middle ear cavity. The thickened connective tissue layer contained abundant fibroblasts with their axes of length oriented at random. Both application of 1.4% hyaluronan and wounding of the perforation border enhanced the healing rate of the hydrocortisone-induced chronic TM perforation.

Hydrocortisone delay of tissue repair of experimental tympanic membrane perforations

The effects of topically applied hydrocortisone on experimental tympanic membrane (TM) perforations in rats were evaluated by otomicroscopy and light microscopy. Standardized TM perforations, occupying the whole upper rear quadrant, were performed, and a 2% hydrocortisone suspension (CORT) was applied once daily for 10 consecutive days. Application of CORT caused a delayed healing pattern, and even at 1 month only 2 of 12 perforations had healed. The keratinizing squamous epithelial cells of the TM appeared hypertrophic, whereas hyperplasia, characterizing a nontreated healing TM perforation, was less prominent. The connective tissue layer of the CORT-treated TM was invaded by abundant inflammatory cells, mainly polymorphonuclear leukocytes. Also, when applied to an intact TM, CORT caused hypertrophy of the epidermal cells and an inflammatory reaction within the TM.