Mitochondrial ring-phenomenon of keratinocytes in psoriasis vulgaris after dithranol therapy

The antipsoriatic drug anthralin accumulates in keratinocyte mitochondria, dissipates mitochondrial membrane potential, and induces apoptosis through a pathway dependent on respiratory competent mitochondria

Anthralin is a potent topical drug, inducing clearance of psoriatic plaques. Anthralin disrupts mitochondrial function and structure, but its mechanism of action remains undefined. This study aimed to determine whether anthralin induced keratinocyte apoptosis as well as to investigate molecular mechanisms and the role of mitochondria. We studied human keratinocytes and human 143B rho(0) cells, which lack mitochondrial DNA and a functional respiratory chain. We show that anthralin disrupts mitochondrial membrane potential (DeltaPsim) and causes endogenous cytochrome c release, resulting in the activation of caspase-3 and characteristic morphological changes of apoptosis. Disruption of DeltaPsim and cytochrome c release were independent of mitochondrial permeability transition or caspase activation. Human 143B rho(0) cells were resistant to anthralin-induced cell death, disruption of DeltaPsim, and cytochrome c release compared with the isogenic 143B rho+ cell line. Using the intrinsic fluorescence of anthralin, rapid accumulation within mitochondria was observed independent of DeltaPsim. Using assays that measure individual respiratory chain complexes, we show that anthralin specifically interacts with ubiquinone pool. These data indicate that anthralin induces apoptosis through a novel mitochondrial pathway dependent on oxidative respiration and involving electron transfer with the ubiquinone pool. These studies identify keratinocyte apoptosis as a potentially important mechanism involved in the clearance of psoriasis.

Unusual mitochondrial reaction in psoriatic keratinocytes

Electron microscopic investigation of skin biopsies revealed that keratinocytes in clinically uninvolved skin from psoriatic patients show the same mitochondrial ring phenomenon after the application of dithranol as has been observed in the cutaneous lesions proper. In various other skin diseases no mitochondrial reaction was evident after dithranol treatment, nor was it seen in chronic dermatitis when dithranol was not applied. It appears, therefore, that this morphological phenomenon is specific to psoriasis and may provide information concerning functional alterations in the pathogenesis of this disease.