José J.M.A. Hurk

Studies on the plasma membrane of normal and psoriatic keratinocytes

A method is described for the preparation of isolated keratinocytes suitable for subsequent biochemical studies. Scanning electron microscopy showed that the maturation process is accompanied by an increase in cell size and a shortening and eventual loss of microvilli. Psoriatic keratinocytes are distinguishable by exhibiting longer microvilli at all levels of maturation.

Lysosomal hydrolases of the epidermis. 6. Changes in disease.

The activities of 14 acid hydrolases have been measured in normal and diseased human epidermis. Our findings were as follows: (i) Increased hydrolase activity was common in lesions; the clinically uninvolved skin of patients, however, invariably showed normal values. (2) The pattern of change was independent of the nature of the disease, the arylsulphatases and β‐glucosidase usually showing the greatest elevations. (3) The magnitude of the changes differed from disease to disease, being most marked in the lesions of psoriasis. (4) Ichthyosiform erythroderma was exceptional in showing elevated levels of the galactosidases and cathepsins B, and D. We suggest that (with the exception of ichthyosiform erythroderma) the abnormalities which we have observed may be related to the proliferative rate of the epidermis.

Studies on the plasma membrane of normal and psoriatic keratinocytes. 5. Lectin binding

The glycocalyx of epidermal keratinocytes from psoriatic patients has been investigated by means of lectins. Striking changes were found in the levels of glucose and/or mannose (concanavalin A) and of N‐acetylglucosamine and/or sialic acid (wheat germ agglutinin) on the surface of cells from the psoriatic lesion. Smaller but significant changes were seen in the clinically uninvolved epidermis of the patient. A marked increase in the affinity of the cell surface for Ulex europus agglutinin (fucose‐specific) confirms our previous reports of structural alterations in fucose‐containing oligosaccharides in psoriasis.

LICHEN PLANUS; AN INBOEN ERROR OF METABOLISM

Summary.— The Km of the enzyme glucose‐6‐phosphate dehydrogenase for its substrate glucose‐6‐phosphate has been determined in normal human skin and skin from lichen planus patients. There was a clear difference between the 2 groups comparable to that found in congenital erythrocyte glucose‐6‐phosphate dehydrogenase deficiency. The results are discussed in relation to the aetiology and clinical picture of lichen planus.

Plasma vitamin A levels in the common dermatoses

The plasma vitamin A levels of 164 patients with skin disease and 102 comparable control subjects were measured by means of a modern fluorimetric technique.

Acid hydrolases in psoriatic epidermis

This laboratory is currently investigating the levels of acid hydrolase activity in the epidermis of various skin lesions, and our findings will be published in full in due course. The results which we have obtained for psoriasis, however, seem sufficiently remarkable to warrant preliminary publication. Epidermal slices were cut using a keratotome set for a depth of 0-2 mm, frozen in liquid nitrogen, and stored at — 20°C prior to analysis. Specimens were homogenized at 20 mg/ml in bovine serum albumin (i mg/ml), centrifuged, and the activity of fourteen acid hydrolases determined in the supernatant using techniques already described (Mier & van den Hurk, I975a-c). The activity of each enzyme in eight specimens of psoriatic lesion, seven specimens of uninvolved epidermis from psoriatic patients, and thirty-six specimens from healthy controls is shown in Table i. Although there is a tendency for all enzymes to be increased in the lesion (suggesting a greater number of lysosomes in comparison to normal epidermis), it is clear that there are striking and specific increases in the levels ofarylsulphatases A and Band of ^-glucosidase. These enzymes are increased 34fold, 22-fold and 11-fold over the respective mean control values; there is no overlap with the normal range. The values for the uninvolved psoriatic epidermis, by contrast, are identical to the controls. Since lysosomal hydrolases are (at least in some tissues) inducible enzymes, these findings point to the accumulation of a metabolite which contains ;S-glucoside residues and which is sulphated. The most likely candidate, on the rather scanty evidence currently available, seems to be a sulphated glycolipid. These compounds are characteristically located in the plasma membrane, where they may be associated with membrane-bound enzymes (Karlsson, Samuelsson & Steen, 1974). Thus our findings are consistent with, and may be causally related to the defects which have been described in adenyl cyclase (Hsia et al, 1972; Wright et al, 1973; Yoshikawa et al, 1975; Mui, Hsia & Halprin, 1975) and in the membrane-bound ATP hydrolytic activity (Mahrle & Orfanos, 1974) of the psoriatic lesion. The authors wish to thank Professor J.W.H.Mali and the medical staff of this Department for their help in providing the clinical material used in this work.

Lectin binding studies on suspensions of isolated epidermal keratinocytes

The sugar composition of the surface of isolated human keratinocytes has been investigated using lectins. A method is described in which the FITC‐labelled lectin is displaced with competing sugar prior to measurement. This avoids errors due to aspecific binding and utilizes the minimum biological sample. Evidence is presented which indicates that little cell surface glycoconjugate is lost during the preparation of the keratinocyte suspension from human epidermal slices using the technique described here. Values for keratinocytes are similar to those reported for fibroblast lines, being much higher than those found using erythrocytes or lymphocytes.

4. OVERALL PROFILE IN COMPARISON WITH DERMIS AND OTHERTISSUES Lysosomal hydrolases of the epidermis

The activities of fifteen acid hydrolases have been measured in seven tissues of the guinea‐pig; fourteen of these were also assayed in the epidermis of four other mammalian species. The most striking finding was that the proportion of acid phosphatase was consistently much higher in epidermis than in the other tissues investigated.

Plasma vitamin A levels in the dyskeratoses

No significant difference was found between the plasma vitamin A levels of patients with dyskeratoti skin disease and those of comparable control subjects.

A lysosomal storage disorder of the epidermis characterized by a deficiency of α-mannosidase and an accumulation of mannose-rich materials

Laboratory investigation of a patient diagnosed as ichthyosiform erythroderma bullosa revealed the following abnormalities: