Transmission electron microscopy of the preclinical phase of experimental phytophotodermatitis.
OBJECTIVE
To examine the epidermis in induced phytophotodermatitis using transmission electron microscopy in order to detect histologic changes even before lesions are visible by light microscopy.


BACKGROUND
In the first six hours after the experimental induction of phytophotodermatitis, no changes are detectable by light microscopy. Only after 24 hours can keratinocyte necrosis and epidermal vacuolization be detected histologically, and blisters form by 48 hours.


METHODS
The dorsum of four adult rats (Rattus norvegicus) was manually epilated. After painting the right half of the rat with the peel juice of Tahiti lemon, they were exposed to sunlight for eight minutes under general anesthesia. The left side was used as the control and exposed to sunlight only. Biopsies were performed immediately after photoinduction and one and two hours later, and the tissue was analyzed by transmission electron microscopy.


RESULTS
No histological changes were seen on the control side. Immediately after induction, vacuolization in keratinocytes was observed. After one hour, desmosomal changes were also observed in addition to vacuolization. Keratin filaments were not attached to the desmosomal plaque. Free desmosomes and membrane ruptures were also seen. At two hours after induction, similar changes were found, and granular degeneration of keratin was also observed.


CONCLUSIONS
The interaction of sunlight and psoralens generates a photoproduct that damages keratinocyte proteins, leading to keratinocyte necrosis and blister formation.


CONCLUSIONS
Transmission electron microscopy can detect vacuolization, lesions of the membrane, and desmosomes in the first two hours after experimental induction of phytophotodermatitis.
Department of Dermatology, Federal and Catholic University of Pelotas, Pelotas, RS, Brazil. hiramalmeidajr@hotmail.com
Hiram Larangeira de
HL
Almeida
Miriam Nakagami
MN
Sotto
Luis Antonio Suita de
LA
Castro
Nara Moreira
NM
Rocha
D000818:Animals; D001768:Blister / Q000139:chemically induced / Q000473:pathology; D002957:Citrus; D017484:Dermatitis, Phototoxic / Q000473:pathology*; D003896:Desmosomes / Q000648:ultrastructure*; D004195:Disease Models, Animal; D004817:Epidermis / Q000648:ultrastructure*; D004890:Erythema / Q000139:chemically induced / Q000473:pathology; D005638:Fruit; D046529:Microscopy, Electron, Transmission / Q000592:standards*; D009336:Necrosis / Q000139:chemically induced / Q000473:pathology; D051381:Rats