Application of in vitro skin penetration measurements to confirm and refine the quantitative skin sensitization risk assessment of methylisothiazolinone

Draize human repeat insult patch test (HRIPT): Seven decades of pitfalls and progress

Allergic contact dermatitis, a Type IV delayed hypersensitivity reaction, can result in dermatologic signs/symptoms for patients/workers. The likelihood of this phenomenon has been estimated/predicted for numerous chemicals/drugs by animal model and human patch testing protocols developed over the last century. Karl Landsteiner initiated testing with guinea pig studies; further studies based on his initial concept were in continual development. John Draize extended Landsteiner's guinea pig studies (which led to development of blood transfusions) to a human assay documenting irritant and allergic contact dermatitis potential - for drugs, chemicals, mixtures and products. We performed a literature search of major Draize derived protocols of the human repeat insult patch test (HRIPT). Our results reveal minor and major differences between protocols and lack of international standardization. Key clarification and principles post-Draize modified and improved usefulness of the HRIPT. Without a standard method of performing the HRIPT, it is problematic to generalize results of studies summarized here. Furthermore, we suggest a potential standardization procedure/protocol combining the work of the most satisfactory HRIPT methods. As the HRIPT constitutes a key parameter in current quantitative risk assessment for chemicals/drugs, such standardization should aid potential prediction of allergic contact dermatitis potential.

Imaging and quantifying drug delivery in skin - Part 1: Autoradiography and mass spectrometry imaging

In this two-part review we present an up-to-date description of different imaging methods available to map the localization of drugs on skin as a complement of established ex-vivo absorption studies. This first part deals with invasive methods which are grouped in two classes according to their underlying principles: i) methods using radioactivity such as autoradiography and ii) mass spectrometry methods such as MALDI and SIMS. For each method, a description of the principle is given along with example applications of imaging and quantifying drug delivery in human skin. Thanks to these techniques a better assessment of the fate of drugs is obtained: its localization on a particular skin structure, its potential accumulation, etc. A critical comparison in terms of capabilities, sensitivity and practical applicability is included that will help the reader to select the most appropriate technique depending on the particular problem to be solved.

Evaluation of the effects of feeding glyphosate-tolerant soybeans (CP4 EPSPS) on the testis of male Sprague-Dawley rats

Glyphosate tolerant soybeans represent a large portion of soybeans grown and fed to farm animals around the world. Despite their widespread use for many years, some have raised questions regarding their safety because the soybeans were genetically modified. The CP4 EPSPS gene which imparts resistance to topical application of the herbicide glyphosate was introduced into soybeans. Application of glyphosate to soybean fields will reduce weed pressure and increase soybean yield. To assess their safety on the rat reproduction system, male Sprague Dawley rats were fed either glyphosate-tolerant (GM) soybean (40-3-2) or near-isogenic, non-GM (A5403) (control) soybean meal. The processed soybean meal was added to formulated rodent diets at 20% (w/w) and fed to rats for 90 days. Some rats from the control group were separately administered mitomycin C for 40 days and served as positive controls in the sperm abnormality test. Body weights and behavior were monitored daily, serum enzymes and histologic and EM appearance of the testis, and sperm morphology were also examined. After 90 days of feeding, no adverse effects were observed in rats fed glyphosate-tolerant soybeans.

Formulation and Artificial Sebum Effects on the Percutaneous Absorption of Zinc Pyrithione through Excised Human Skin

BACKGROUND

Zinc pyrithione (ZnPT) is deposited on the skin as a fine particulate and must reach microorganisms localized in the stratum corneum and hair follicles in molecular form to exert its broad-spectrum antimicrobial/antifungal activity. Dissolution of ZnPT particles followed by molecular speciation results in the organic portion, i.e. pyrithione, being more susceptible to skin penetration than the inorganic component, i.e. zinc, or the chelate itself, i.e. ZnPT.

OBJECTIVES

To further test the hypothesis that ZnPT skin penetration is rate-limited by dissolution and molecular speciation, the effect of different formulations and artificial sebum on the in vitro percutaneous absorption of radiolabel associated with Zn[14C]PT was investigated.

METHOD

In vitro penetration of [14C]PT into and through excised human skin was measured following application of Zn[14C]PT prepared as suspensions in distinct vehicles including water-based carboxymethylcellulose (CMC), diluted body wash comprised of surfactants, and castor oil, in the presence and absence of artificial sebum.

RESULTS

The steady-state flux and cumulative absorption of Zn[14C]PT increased 4- to 5-fold when deposited from a body wash or castor oil compared to a water-based CMC suspension. Tritiated water flux measured before and after treatment showed that neither the surfactant vehicle nor castor oil significantly altered barrier function versus water alone. An artificial sebum layer on the skin potentiated Zn[14C]PT and 3H2O absorption when dosed from both aqueous formulations, but not from castor oil.

CONCLUSION

These data are consistent with the hypothesis that ZnPT percutaneous absorption, as measured by [14C]PT kinetics, is controlled by particle dissolution and molecular speciation.