Psoriatic epidermis

Kizaki, H., Matsuo, L. and Sakurada, T. (1977). Xanthine oxidase and guanase activities in normal and psoriatic epidermis. Clin. Chim. Acta 75, 1-4. 

Molin, L. and Wester, P.O. (1973). Iron content in normal and psoriatic epidermis. Acta Dermato-Veneteol. 53, 473-476. 

Marstein, S., Jellum, E., and Eldjam, L. The concentration of pyroglutamic acid (2-pyrrolidone-5-carboxylic acid) in normal and psoriatic epidermis determined on a microgram scale by gas chromatography, Clin. Chim. Acta, 49, 389, 1973. 

Disturbances in lipid metabolism occur in the skin in psoriasis. Increased phospholipase A2 activity is seen in lesional and nonlesional skin, while phospholipase C activity is elevated in lesional skin.183-184 Increased elongase activity is also observed in psoriatic epidermis. A local increase in AA occurs, and this appears to be preferentially metabolized by the lipoxygenases, resulting in a marked increase in 12-HETE and LTB4, while there appears to be a relative or absolute reduction in metabolism by the COX pathway.185 Leukotriene B4 is a very potent chemoattractant, and topical application causes epidermal hyperproliferation in addition to neutrophil microabscesses.186 A defective transmembranous cell-signaling system is also suggested by elevation of both IP3 and DAG in the psoriatic plaque.187... 

Study of Cell Adhesion in Psoriatic Epidermis, J. Ultrastr. Res. (1968) 23, 15-23. 

Is the increased epidermal thickness accompanied by an increase in size of the epidermal cell (hypertrophy) Or are there just more cells (hyperplasia) Despite histologic (H2) and electron microscopic (B36) impressions to the contrary, biochemical evidence indicates that the cell size in the psoriatic lesion is no different than normal. This conclusion is based on measurements indicating that both normal and psoriatic epidermis contain approximately two-thirds water by weight (H2, M15, S17) and, therefore, have the same wet dry weight ratio in conjunction with DNA measurements which have been made in normal and psoriatic skin. 

The process of nucleic acid breakdown presumably starts a little before entry of the cell into the granular layer. Histochemically, however, most lysosomal enzymes are strongest at the level of the granular layer (B28). The amount of DNA in psoriatic epidermis is equivalent per unit weight to normal epidermis, but about one-third of the nuclear DNA is still present in the parakeratotic horny layer of psoriasis while practically none is found in normal stratum corneum. RNA is much increased in psoriatic epidermis (M12, R5), and it also can be found in increased amounts in the psoriatic scale (Table 6). 

Psoriatic epidermis with its great mitotic activity and increased thickness bears several resemblances to epidermis at the edges of a wound. 

Fetal pig epidermis contains hyaluronic acid and chondroitin 4-sulfate containing mucopolysaccharide (S15) as does human epidermis (M13), and some of the enzymes of uronic acid metabolism are present in human epidermis (F24). Also Barker et al. (B6) have shown uptake of radioactive sulfate into epidermis, and Braun-Falco et al. (B33) have shown that psoriatic epidermis is more active than normal epidermis in accumulating radioactive sulfate in vitro. There is also a suggestion that methionine sulfur may be preferentially accumulated in psoriatic lesions (B26, L6). There seems to be little doubt, therefore, that mucopolysaccharides are formed, and there is some suggestion that they may be formed in greater amounts in psoriatic skin lesions. The next section will consider the possibility that they are of importance in the cell membrane and intercellular contact. 

More promising have been recent attempts to show a difference by the response of the skin to injury. Reid (R3) and Reid and Jarrett (R4) have shown an increased erythema response of normal-appearing skin of psoriasis patients to applications of vitamin A with increased release of acid phosphatase in the uninvolved but psoriatic epidermis. Braun-Falco et al. (B32) found an increased number of cells incorporating tritiated thymidine after Scotch tape stripping. While Hell and Hodgson (H13) noted increased uptake of thymidine in vitro by uninvolved skin of psoriatic subjects. There may in the future be a way of reliably... 

The most plausible explanation is that the serum enzymes are a reflection of leakage of the enzymes into the serum from the damaged epidermal cells since the above enzymes are precisely those that are most elevated within the psoriatic epidermis. Another source for these enzymes might be the erythrocyte, but all authors agree (H25, M3, R20, W5)... 

Another enzyme found to be present in increased amounts in psoriatic serum as compared to normal is a phosphodiesterase studied by Zaruba et al. (Z3). Again this enzyme is found in elevated amounts in psoriatic epidermis and presumably the increase of enzyme in the serum is the result of leakage from the epidermis. With this enzyme, which is presumably bound to microsomes and mitochondria, it is a little more difficult to understand exactly how it leaks out of the cell. 

CXCR2 CXCLl High levels CXCLl and CXCL8 found in psoriatic epidermis... 

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