The hamster flank organ model: is it relevant to man?

Applications and limitations of lipid nanoparticles in dermal and transdermal drug delivery via the follicular route

Lipid nanoparticles (LN) such as solid lipid nanoparticles (SLN) and nanolipid carriers (NLC) feature several claimed benefits for topical drug therapy including biocompatible ingredients, drug release modification, adhesion to the skin, and film formation with subsequent hydration of the superficial skin layers. However, penetration and permeation into and across deeper skin layers are restricted due to the barrier function of the stratum corneum (SC). As different kinds of nanoparticles provide the potential for penetration into hair follicles (HF) LN are applicable drug delivery systems (DDS) for this route in order to enhance the dermal and transdermal bioavailability of active pharmaceutical ingredients (API). Therefore, this review addresses the HF as application site, published formulations of LN which showed follicular penetration (FP), and characterization methods in order to identify and quantify the accumulation of API delivered by the LN in the HF. Since LN are based on lipids that appear in human sebum which is the predominant medium in HF an increased localization of the colloidal carriers as well as a promoted drug release may be assumed. Therefore, sebum-like lipid material and a size of less or equal 640 nm are appropriate specifications for FP of particulate formulations.

Spontaneous comedones on the skin of hairless descendants of Mexican hairless dogs

In the first experiment, the skin sebum and humidity, perspiration ability of sweat glands, and histology of spontaneous comedones were examined in hairless descendants of Mexican hairless dogs. The skin of females showed lower humidity than that of males. Some animals with a large number of comedones exhibited remarkably high skin sebum scores. The comedones were distributed throughout the dorsal skin, and a cluster of lesions was found mainly in the limbs and prepuces. The sweat glands showed no perspiration in the sudorific test. Histologically, both infant and adult animals had lesions of micro- and/or "blackhead" comedones. Plugged follicles containing abundant keratic substances associated well-developed sebaceous glands. Spontaneous comedones in the skin of hairless dogs were grossly and histologically similar to the acne vulgaris observed in human beings. The skin of some adult animals showed a large number of protrusive comedones which were solid cystic structures containing organized substances. In the second experiment, three kinds of antiacne agents (sulfur and camphor, sulfur and resorcinol, and ibuprofen piconol) were applied daily to the test sites for one month. These antiacne agents caused prominent extrusion of keratin plugs from follicular sites. The results suggest that the hairless dogs are a predictive model for evaluating the efficacy of antiacne agents proposed for acne treatment.

The improved organ maintenance of the human sebaceous gland: modeling in vitro the effects of epidermal growth factor, androgens, estrogens, 13-cis retinoic acid, and phenol red

We have previously reported that human sebaceous glands can be maintained for up to 14 d as whole organs with full retention of the physiological rate and pattern of new cell formation, but we have also reported that the newly formed cells did not differentiate normally, causing a progressive loss of lipogenesis in vitro. We now show that this abnormal sebocyte differentiation was attributable to the presence of epidermal growth factor (EGF) and phenol red in our maintenance medium. In their absence, human sebaceous glands apparently retain in vivo rates of cell division and lipogenesis over 7 d of maintenance in addition to a retention of in situ morphology. This is reversible on the re-addition of 10 ng EGF/ml and 10 mg phenol red/ml. The addition of 600 pM 17 beta-estradiol results in a significant fall in the rate of lipogenesis over 7 d of maintenance, without affecting the rate of cell division. This effect is apparently due to abnormal differentiation of newly formed sebocytes. Neither 1 nM testosterone nor 1 nM dihydrotestosterone (DHT) has any effect on rates of cell division of lipogenesis over 7 d. In the presence of phenol red, however, 1 nM testosterone or 1 nM DHT cause a significant reduction in the rate of lipogenesis over 7 d of maintenance. One micromolar 13-cis retinoic acid caused a significant reduction in the rate of lipogenesis over 7 d in both the presence and absence of phenol red. These findings show that we can model the physiological effects of steroids, EGF, and 13-cis retinoic acid in vitro.

Local inhibition of sebaceous gland growth by topically applied RU 58841

The biological activity of a series of nonsteroidal, pure androgen receptor inhibitors was compared using the Syrian hamster ear skin sebaceous gland model. RU 58841, RU 56187, RU 38882 and cyproterone acetate were applied topically for 4 weeks on the ventral ear pinna of sexually mature male Syrian hamsters. Their order of efficacy was as follows: RU 58841 > RU 56187 > RU 38882 > cyproterone acetate. Maximal reduction of 60% in the size of the sebaceous glands was observed in hamsters treated with RU 58841 at a dose of 10 micrograms per day. This degree of inhibition occurred without any systemic side effects as shown by the absence of inhibition on the contralateral untreated ear pinna. Longer treatment did not produce greater inhibition since extending the treatment period from 4 weeks to 12 weeks showed similar data. The effect of RU 58841 was reversible since the inhibited sebaceous glands returned to normal size within 4 weeks after the cessation of the topical applications. The potent localized inhibition of sebaceous glands by RU 58841 demonstrates the excellent potential of this compound as a topical drug for the treatment of acne and other androgen-mediated disorders.

Effects of 13-cis-retinoic acid, all-trans-retinoic acid, and acitretin on the proliferation, lipid synthesis and keratin expression of cultured human sebocytes in vitro

The aim of this study was to determine the effects of 13-cis-RA, all-trans-RA, and acitretin on the proliferation, lipid synthesis, and keratin expression of human sebocytes in vitro and to elucidate possible mechanisms of retinoid action on sebaceous glands at the cellular level. It was found that 13-cis-RA and all-trans-RA decreased sebocyte proliferation in a dose- and time-dependent manner, with a 13-cis-RA-IC50 of 10(-5) M (after 7 d) and 10(-6) M (after 14 d) and an all-trans-RA-IC50 of 10(-7) M (after 14 d; no IC50 after 7 d). Acitretin inhibited sebocyte proliferation only at 10(-5) M. Furthermore, 13-cis-RA was the most potent inhibitor of acetate incorporation into lipids, which indicated lipid synthesis (48.2% reduction), followed by all-trans-RA (-38.6%), and by acitretin (-27.5%). All retinoids tested markedly decreased the synthesis of triglycerides, wax/stearyl esters, and free fatty acids in cultured sebocytes, whereas squalene synthesis remained uninfluenced and cholesterol synthesis slightly increased. On the other hand, keratin 5 was down-regulated, keratin 17 was up-regulated, and the expression of keratin 13 was virtually unaffected by all retinoids tested. Keratins 6 and 16 were down-regulated by 13-cis-RA and by all-trans-RA, keratin 14 was down-regulated by 13-cis-RA only, and keratin 19 was up-regulated by all-trans-RA. These investigations indicate that 13-cis-RA and, to a lesser extent, all-trans-RA are potent inhibitors of both cell proliferation and lipid synthesis in human sebocytes in vitro, whereas acitretin only decreases lipogenesis in this model. In addition, retinoids may modify the differentiation of sebocytes in vitro by modulating keratin expression. Models of cultured human sebocytes are useful tools for further investigations on the sebaceous gland and its activity at the cellular level.