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Psoralens have been used previously in an attempt to repigment vitiliginous skin. Recent reports indicate psoralens, activated by long wavelength ultraviolet light (black light), inhibit DNA synthesis in various cell types. This suggested to us a possible new therapeutic use for psoralens in proliferative epidermal diseases such as psoriasis. This study shows that trioxsalen plus black light markedly inhibits epidermal DNA synthesis. Trioxsalen or black light alone has no significant effect. Our own preliminary clinical studies show improvement of chronic plaque type psoriatic lesions in eight of 11 patients using topically applied trioxsalen and black light. We suggest that further critical clinical investigation of psoralens either topically or systemically in combination with black light for proliferative skin diseases is warranted.

Duell, E. A. (Western Reserve University, Cleveland, Ohio), Sakae Inoue, and Merton F. Utter. Isolation and properties of intact mitochondria from spheroplasts of yeast. J. Bacteriol. 88:1762–1773. 1964.—Functionally intact mitochondria can be obtained in good yields by osmotic disruption of spheroplasts formed from yeast by treatment with an enzyme mixture from the snail digestive tract. The useful range of this method is extended greatly by pretreatment of the yeast cells with 2-mercaptoethylamine and ethylene-diaminetetraacetate. The concentration of the yeast suspension can be increased greatly, the incubation period can be shortened considerably, and the requirement for log-phase cells is obviated. Mitochondria prepared by this method have been compared with those obtained by mechanical disruption in terms of respiratory control, specific activity on a wide range of oxidizable substrates, heterogeneity during centrifugation, and structures observed by electron microscopy. In all cases, the mitochondria obtained from spheroplasts appear to be much less damaged by the preparative procedures.

Previously we suggested that incomplete differentiation, accelerated proliferation and glycogen accumulation in epidermis of psoriatic lesions might be due to deficient adenosine 3',5'-monophosphate (cyclic AMP) in epidermis of the lesion. Therefore, we measured endogenous cyclic AMP in involved and uninvolved epidermis of 25 psoriasis patients and normal epidermis of 25 control subjects. A statistically significant decrease in cyclic AMP was found in involved psoriatic epidermis when compared with uninvolved psoriatic and control epidermis. Because cyclic AMP regulates glycogen metabolism and promotes differentiation of cancer cells in culture while limiting their proliferation, the cyclic AMP deficiency may play a pathophysiological role in the rapid epidermal cell cycle kinetics of psoriasis. Therefore, topical application of cyclic AMP analogues or agents which promote cyclic AMP synthesis or retard its hydrolysis might be used therapeutically to either normalize psoriatic differentiation or prevent psoriasis from occurring.

Adenyl cyclase was found in a 17,000 g particulate fraction of gently homogenized newborn rat epidermis. Isoproterenol produced a statistically significant 40% (P <.005) stimulation of this enzyme. We have previously shown a 205% stimulation of the enzyme by isoproterenol with intact epidermis from adult rats; thus it is apparent that the broken-cell preparation of epidermal adenyl cyclase has a decreased sensitivity to the hormone, which is characteristic of many adenyl cyclases from various tissues. Sodium fluoride, a stimulator of most adenyl cyclases, produced a 139% increase in enzyme activity. Propranolol, a beta-adrenergic antagonist, prevented the stimulation of epidermal adenyl cyclase by the beta-adrenergic agonist, isoproterenol. Thus the second criterion used to characterize a hormonally induced response, in this case the betaadrenergic inhibition of epidermal cell division, mediated by adenosine 3′,5′-monophosphate (cyclic AMP) appears to have been satisfied.

Epidermal cell division appears to be slowed by beta adrenergic stimulation. The satisfaction of Sutherland's four criteria of an adenosine 3′, 5′ = monophosphate (cyclic AMP) mediated event shows that the inhibition is due to an increase intra-epidermal cyclic AMP. Since increasing cyclic AMP slows epidermal cell division and mediates glycogen breakdown, we suggest that psoriasis may be a polygenic-environmentally induced defect in the adenyl cyclase-cyclic AMP cascade. Such a defect could explain that seemingly paradoxical occurrence of the 12-fold acceleration in the rate of cell division, low phosphorylase activity, and glycogen buildup in the epidermis of a psoriatic lesion. Our approach to the detection of a possibly defective adenyl cyclase-cyclic AMP-cyclic AMP dependent protein kinase cascade and how such a defect, if it is found, might be corrected by therapy is discussed.

We envision the epidermal chalone mechanism as an epinephrine-activated cascade of intra-epidermal molecular events whereby the feedback control of epidermal cell division is mediated via adenosine 3′,5′-monophosphate (cyclic AMP). Sutherland's first criterion of a cyclic AMP mediated event appears to have been satisfied in that isoproterenol (1 × 10-6M) produced a threefold (P < 0.001) rise in cyclic AMP level within three minutes in epidermal target tissue which was followed by inhibition of epidermal cell division. Since keratinocytes comprise approximately 95% of epidermal volume, we suggest that the majority of cyclic AMP measured was synthesized in keratinocytes.

Dibutyryl adenosine 3′,5′-monophosphate (cyclic AMP), but not sodium butyrate or adenosine 5′-monophosphate (5′-AMP) produced a dose-dependent epidermal mitotic inhibition. Previously we showed that isoproterenol inhibits epidermal mitosis, stimulates adenyl cyclase activity in broken epidermal cells, and stimulates cyclic AMP formation in intact epidermis. This data and results from the present study strongly suggest that cyclic AMP is one and possibly a major mediator of epidermal mitotic control. Our findings together with recent evidence that cyclic AMP inhibits cell growth rate while promoting differentiation in cultured cells suggests the following: (1) the rate of epidermal proliferation may be inversely proportional to the intraepidermal cyclic AMP level; (2) the 12-fold accelerated proliferation rate and glycogen accumulation of psoriatic epidermis might be due to low intraepidermal cyclic AMP concentrations.