Estimating the contribution by skin to systemic metabolism

Comparative assessment of local tolerance of alcohols commonly used in alcohol-based hand rubs for hand hygiene

Hand hygiene plays a key role in nosocomial infection prevention. To achieve users' adherence, products' dermal tolerance is essential. We aimed at making a comparative assessment of skin irritation and phototoxicity of the 3 alcohols commonly used in alcohol-based hand rubs (Ethanol, Propan-2-ol, Propan-1-ol) at 60, 70, 80 or 85% w/w in water or with co-formulates (hydrating, emollient and skin protective agents). In vitro validated OECD methods 439 and 432 were used. For irritation, EpiSkin™ Small Model was the chosen Reconstructed Human Epidermis (RhE). For phototoxicity, co-formulates alone or in mixture with and without alcohol were tested using BALB/c 3T3 cell cultures. Whilst Ethanol and Propan-2-ol could not be differentiated and displayed good skin tolerance profiles, Propan-1-ol based products lead to significant viability impairments of RhE at 60, 70 or 80% and at 60% in the presence of co-formulates. However, these results could not be reproduced in another RhE model. Taking also into account bibliographic data on Propan-1-ol, this suggests that our results are probably related to a lack of specificity of the used RhE. Therefore, it can be relevant in case of significant results to use two different RhE models before performing any classification and/or performing any complementary tests.

Characterization and modulation of sex steroid metabolizing activity in normal human keratinocytes in primary culture and HaCaT cells

Skin, the largest organ of the human body, synthesizes active sex steroids from adrenal C19 precursor steroids. Normal human breast epidermal keratinocytes in primary culture were used to evaluate the enzymatic activities responsible for the formation and degradation of active androgens and estrogens during keratinocyte differentiation. Enzymatic activities, including 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD), 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) were measured using [3H] steroids as substrates. After 10-60 days in culture, no 3beta-HSD activity was detected, but all other activities were measured, demonstrating the ability of keratinocytes to convert androstenedione (4-DIONE) into the potent androgen dihydrotestosterone (DHT). Furthermore, marked changes in enzymatic activity were observed during cell differentiation: 17beta-HSD was first detected during the third week of culture, the level of activity reaching a peak during the fourth week. This peak was followed by a progressive decrease during keratinization. On the other hand, 5alpha-reductase and 3alpha-HSD activities were first detected during the fourth week of culture. The enzymatic activities involved in the formation and degradation of sex steroids were also characterized in the immortalized human keratinocyte cell line HaCaT. It was then found that HaCaT cells possess a pattern of steroid metabolizing enzymes similar to that of human epidermal keratinocytes in culture. Since glucocorticoids are known to exert potent pharmacological effects on the skin, the effect of dexamethasone (DEX) on cell proliferation and enzymatic activities was determined using HaCaT cells. DEX causes a 55% decrease in HaCaT cell proliferation (IC50: 10nM) whereas DEX caused a three- to five-fold stimulation of oxidative 17beta-HSD activity in intact cells in culture (ED50: 30 nM) and this stimulatory effect was competitively blocked by the glucocorticoid antagonist RU486. A four-fold increase in type 2 17beta-HSD mRNA levels was also observed as measured by real-time PCR, correlating with the increase in oxidative activity. No effect of DEX on the other enzymatic activities (3beta-HSD, 5alpha-reductase, and 3alpha-HSD) was observed. Since increased levels of inflammatory cytokines have been detected in some skin diseases then these cytokines might play a role in the differentiation of keratinocytes. In this regard, we found that interleukin-4 (IL-4) induced the expression of 3beta-HSD in HaCaT cells, thus allowing the cells to produce a different set of sex steroids from adrenal C19 precursors. The present data thus indicate that HaCaT cells are a useful model to further study the regulation of the enzymes involved in the metabolism of sex steroids in keratinocytes.

Mechanisms of drug reactions: the metabolic track

Hypersensitivity syndrome (HSR) describes a drug-induced symptom complex consisting of fever, rash, and internal organ involvement. Although these reactions are rare, they are very important because of their severity and unpredictability. The metabolic conversion of drugs to chemically-reactive products is now established as a prerequisite for many idiosyncratic drug reactions. In the setting of HSR, an imbalance in the rates of formation of reactive metabolites and of enzymatic detoxification can lead to accumulation of these byproducts. Reactive metabolites could act as haptens eliciting an immune response, covalently bind target proteins causing cell death, or interact with nucleic acids leading to mutations. The lymphocyte toxicity assay (LTA) provides an in vitro assessment of host susceptibility to reactive metabolites of a given drug. It has validated the clinical finding of increased risk of HSR in first degree relatives of patients. It is hoped that the LTA will be used to predict host susceptibility before drug exposure. Ultimately it is hoped that the genetic defects that lead to drug reactions will be identified. This would improve drug development safety and allow primary prevention of serious reactions.