Percutaneous penetration of octyl salicylate from representative sunscreen formulations through human skin in vitro.

The human skin penetration of [14C]octyl salicylate from two representative sunscreen vehicles was determined in vitro. 3H-sucrose was incorporated into all formulations and provided a marker for membrane integrity. When applied as a finite dose in an oil-in-water emulsion vehicle containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.65+/-0.16% of the applied dose (representing a total amount permeated of 1.58+/-0.36 microg/cm2). When applied as an infinite dose in the oil-in-water emulsion vehicle the average total absorption of 14C over 48 hr was 0.47+/-0.22% of the applied dose (representing a total amount permeated of 27.54+/-13.91 microg/cm2). When applied as a finite dose in a representative hydroalcoholic formulation containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.59+/-0.09% of the applied dose (representing a total amount permeated of 1.58+/-0.25 microg/cm2). When applied as an infinite dose in the hydroalcoholic formulation the average total absorption of 14C over 48 hr was 0.23+/-0.05% of the applied dose (representing a total amount permeated of 11.28+/-2.55 microg/cm2). The penetration of [14C]salicylic acid [applied at a concentration of 2.7% (w/w), in the oil-in-water emulsion] was also determined. When applied as a finite dose the average total absorption of 14C over 48 hr was 1.14+/-0.23% of the applied dose (representing a total amount permeated of 1.65+/-0.39 microg/cm2). These results suggest that the in vitro human skin permeation of octyl salicylate is relatively low. The amounts of octyl salicylate and salicylic acid permeated when applied in similar vehicles were remarkably similar over 48 hr (1.58 microg/cm2 and 1.65 microg/cm2, respectively). This suggests the possibility that the 14C label appearing in the receptor fluid may, in both cases, represent salicylic acid. If this is the case, then it is possible that the amount of octyl salicylate permeating through the skin is much less than that suggested by the data obtained here. This supposition is, however, entirely speculative and has yet to be confirmed experimentally.

Protective effects of glutathione on diethyldithiocarbamate (DDC) cytotoxicity: a possible mechanism.

Rat cerebral astrocytes grown in culture were exposed to 35 micrograms diethyldithiocarbamate (DDC)/ml of medium for 1 hr and treated with 0 or 10 mM reduced glutathione (GSH) 1 hr post-DDC. DDC treatment resulted in a 90% reduction in cell adherence within 24 hr and complete inhibition of growth. The most pronounced ultrastructural lesion in DDC-treated cells was on mitochondria. Numerous lipofuscin-like deposits were seen in these cells. In addition, DDC treatment resulted in a greater than 400% increase in cellular copper. The activity of the selenoenzyme glutathione peroxidase was reduced by about 40% with no concomitant effect on cytosolic superoxide dismutase activity. The data suggest that DDC cytoxicity is peroxidative in nature, presumably due to the massive influx of copper into the astrocyte. GSH treatment 1 hr after exposure of the cells to DDC completely prevented the DDC-induced reduction in cell adherence and growth inhibition. Ultrastructurally, cells post-treated with GSH prevented much of the damage caused by DDC. This protection was associated with marked reduction in cellular copper and a return to control glutathione peroxidase activity.

Bidirectionality of mixed lymphocyte stimulation (Mls) response. Effects of Mlsb stimulator cells on Mlsa helper cells.

The activation of BALB/c lymphocytes in the mixed lymphocyte reaction to Mls-disparate APC has been shown to encompass up to 20% of the mature resting helper T lymphocyte population. In addition to these overtly Mls-responsive cells, our studies have revealed a second population that respond to the Mls difference of DBA/2 spleen cells in conjunction with the mitogen Con A. This part of the Mls response is therefore latent. As mitogen and Mls-stimulating effect act in synergy, it is likely that both stimuli act on the same cell, and hence the Mls effect can be regarded as a regulatory interaction between APC and Th cell. By use of congenic BALB.Mlsa mice, the regulatory effect has been mapped to the Mls locus. The regulatory influence has also been demonstrated in DBA/2 Th cells (Mlsa) stimulated simultaneously with mitogen and Mls-disparate (Mlsb) APC, consistently causing inhibition of mitogen-induced proliferation in this reverse Mls direction. This antagonistic effect has also been linked to the Mls locus. We conclude that the Mls reaction governed by the a and b alleles is bidirectional, producing synergy with class II-dependent activation signals in the direction of Mlsa----Mlsb, and antagonism in the direction Mlsb----Mlsa. Both the classical Mls and the reverse Mls effects have been demonstrated at the clonal level. These results are in accord with the previously proposed hypothesis that the Mls molecule serves as a down-regulatory stimulus in the activation of Th cells. Mls responses of Mlsb T cells are explained as the consequence of a diminished down-regulation by Mlsa APC. Conversely, the reverse Mls response described here can be considered a consequence of inordinately high down-regulation of the Mlsa T cell responses by Mlsb APC.

Mls and the helper T-cell repertoire. I. Mls as a regulator of T-helper cell activation.

We provide evidence that the Mls reaction involves a broad cross-section of the helper cell population. In addition to those cells reacting overtly to Mls stimulatory spleen cells, there is a second large population of helper cells that are affected by an Mls difference. This latent Mls effect is manifested by either synergy or antagonism in mitogen-mediated, Ia-dependent T-cell activation, depending on Mlsa or Mlsb phenotypes of stimulator cells, respectively. Our data can be explained by attributing to Mls alleles the function of differential regulation of autoreactivity of T cells. The results show that the concept of the Mls exerting a negative signal deserves serious consideration.

Ly-6 A/E antigen of murine T cells is associated with a distinct pathway of activation. Requirements for interferon and exogenous interleukin 2.

The Ly-6 pathway of T cell activation was analyzed to identify its essential requirements. Using a monospecific chicken antiserum to Ly-6E, fully cross-reactive to its allelic counterpart, Ly-6A, but unreactive with other members of the Ly-6 family, we have found that interferon (IFN)-alpha/beta or gamma, Ly-6 antibody and interleukin 2 (IL 2) act synergistically in inducing T cell proliferation. The action of IFN can be attributed to induction of Ly-6A/E antigen on T cells, as described previously, and this induction is transcriptionally controlled. Exposure of T cells with elevated Ly-6 concentrations to chicken anti-Ly-6 antibody leads to expression of IL 2 receptors. Consequently, the addition of IL 2 drives T cell proliferation. Thus, in BALB/c mice the minimum requirements for activation by the Ly-6 pathway are IFN (as a means of inducing Ly-6). Ly-6 antibody (as inducer of IL 2 receptors) and IL 2. In mice of the Ly-6.2 haplotype, IFN is not an absolute requirement. This may be related to the fact that these animals, in contrast to those of Ly-6.1 haplotype, express Ly-6 constitutively on a substantial proportion of resting T cells. Thus, T cells of C57BL/6 or DBA/2 mice can be induced to proliferate with Ly-6 antibody and IL 2 alone, although IFN pretreatment enhances this response. In BALB/c mice the IL 2-driven proliferative response induced through the Ly-6 pathway occurs selectively in the L3T4- population.