Percutaneous Penetration Enhancers: An Overview

Transdermal drug delivery is the controlled release of drugs through the skin to obtain therapeutic levels systematically. Several technological advances have been made in the recent decades to enhance percutaneous drug penetration. This overview focuses on the physical, biochemical, and chemical means of penetration enhancement, as well as the classification and mechanisms of chemical penetration enhancers, their application in transdermal drug delivery, and trends and development in penetration enhancement.

The patterns of melanosome distribution in keratinocytes of human skin as one determining factor of skin colour

BACKGROUND

One determining factor of skin colour is the distribution pattern of melanosomes within keratinocytes. Melanosomes in keratinocytes of light skin as in Caucasians are distributed as membrane-bound clusters, whereas the melanosomes in keratinocytes of dark skin as in African/American individuals tend to be larger and distributed individually. It has been shown that melanin content, melanin composition and the size of melanosomes in the human epidermis vary considerably with both ethnicity and chronic sun exposure.

OBJECTIVES

To assess quantitatively the distribution pattern of melanosomes that have been transferred to keratinocytes in the photoprotected (volar forearm) skin from normal Asian individuals and to compare these data with those from light-skinned Caucasian and dark-skinned African/American individuals.

METHODS

Electron microscopy was used.

RESULTS

We have demonstrated that melanosomes within keratinocytes of Asian skin are distributed as a combination of individual and clustered melanosomes with a proportion of 62.6% vs. 37.4%, respectively. This contrasts with dark and light skin keratinocytes where melanosomes are predominantly individual (88.9%) and clustered (84.5%), respectively. Analysis of mean +/- SD melanosome size also revealed a progressive variation in size with ethnicity, melanosomes in dark skin being the largest (1.44 +/- 0.67 microm(2) x 10-2) followed in turn by those in Asian skin (1.36 +/- 0.15 microm(2) x 10-2) and Caucasian skin (0.94 +/- 0.48 microm(2) x 10-2). In addition, it was shown that the melanosomes that are individually distributed tend to have a larger size than the clustered melanosomes.

CONCLUSIONS

The present data indicate that there may be a size gradient of melanosomes encompassing the global complexion coloration and that the melanosome distribution in keratinocytes of Asian skin is intermediate between that in light Caucasian and dark African/American skin.

A predominant IgG4 subclass may be responsible for false-negative direct immunofluorescence in bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is an immune-mediated blistering disease, usually characterized immunopathologically by the linear deposition of IgG and C3 along the basement membrane zone (BMZ) of skin. However, positive deposition of C3 but negative staining for IgG on direct immunofluorescence (DIF) studies has been noted in some patients.

METHODS

Twelve patients known to have BP but with absence of staining for IgG were included in this study. Frozen sections of skin specimens from the 12 patients were subjected to IgG DIF, as well as a sandwich double antibody method of staining for IgG, IgG subclasses, and light chains. Enzyme-linked immunosorbent assay (ELISA) using commercially available human IgG subclasses was used to analyze the subclass restriction of FITC-labeled antihuman IgG conjugates.

RESULTS

Of the 12 skin specimens with positive C3 and negative IgG on DIF, nine were positive for IgG with the double antibody sandwich method. In addition, all 12 specimens had positive linear staining for the subclass IgG4 along the BMZ with this method. There was no IgG light chain restriction. Two commercially obtained antihuman IgG conjugates, both commonly used in our laboratory for DIF testing, were analyzed for separate IgG subclass specificity by ELISA. Both conjugates showed high reactivity to IgG1 and IgG3 with less reactivity to IgG2 and IgG4.

CONCLUSION

These results suggest that the following factors contribute to false-negative staining for IgG on DIF in some BP patients: (i): subthreshold IgG in skin specimens; (ii) limited reactivity of commercial antihuman IgG conjugates to the IgG4 subclass; and (iii) decreased sensitivity of DIF compared with double antibody methods for the detection of IgG. The use of sandwich double antibody immunofluorescence methods to test for IgG and/or IgG subclasses may be helpful in definitively diagnosing BP in patients with negative IgG and positive C3 staining on DIF.