Tolerability profile of topical cannabidiol and palmitoylethanolamide: a compilation of single-centre randomized evaluator-blinded clinical and in vitro studies in normal skin.

BACKGROUND: An increasing number of studies have investigated the adverse effect profile of oral cannabinoids; however, few studies have provided sufficient data on the tolerability of topical cannabinoids in human participants. AIM: To assess the tolerability profile of several commercial topical formulations containing cannabidiol (CBD) and palmitoylethanolamide (PEA) on the skin of healthy human participants. METHODS: Three human clinical trials and one in vitro study were conducted. The potential for skin irritation, sensitization and phototoxicity of several products, were assessed via patch testing on healthy human skin. The products assessed included two formulations containing CBD and PEA, one containing hemp seed oil and four concentrations of CBD alone. Ocular toxicity was tested using a traditional hen's egg chorioallantoic membrane model with three CBD, PEA and hemp seed oil formulations. RESULTS: There was no irritation or sensitization of the products evident via patch testing on healthy participants. Additionally, mild phototoxicity of a hemp seed oil product was found at the 48-h time point compared with the negative control. The in vitro experiment demonstrated comparable effects of cannabinoid products with historically nonirritating products. CONCLUSION: These specific formulations of CBD- and PEA-containing products are nonirritating and nonsensitizing in healthy adults, and further encourage similar research assessing their long-term safety and efficacy in human participants with dermatological diseases. There are some limitations to the study: (i) external validity may be limited as formulations from a single manufacturer were used for this study, while vast heterogeneity exists across unregulated, commercial CBD products on the market; and (ii) products were assessed only on normal, nondiseased human skin, and therefore extrapolation to those with dermatological diseases cannot be assumed.

Raised epidermal phospholipase A2 activity in rheumatoid arthritis.

Epidermal phospholipase A2 (PLA2) in RA patients was significantly higher than in normals (p less than 0.0001) but lower than in psoriatic patients (p less than 0.05). No relationship was observed between PLA2 activity and commonly used measures of rheumatoid disease activity in a cross-sectional study. However, in a longitudinal study change in PLA2 activity correlated strongly with changes in disease activity.

Inhibition of normal and psoriatic epidermal phospholipase A2 by picomolar concentrations of recombinant human lipocortin I.

Normal human and psoriatic epidermal phospholipase A2 (PLA2) was inhibited by human recombinant lipocortin I when the substrate was present in a several million-fold molar excess. Inhibition was not total, even at relatively high concentrations of lipocortin I. It is therefore suggested that human epidermis contains two species of PLA2: one that is controlled by lipocortin I and one that is not.

Modulation of phospholipase A2 activity in extracts of lesion-free psoriatic epidermis by alkaline phosphatase and a protein phosphatase inhibitor.

Phospholipase A2 activity is raised in non-lesional psoriatic epidermis compared with normal epidermis. It has been shown that the activity of this enzyme is controlled by an inhibitory protein the inhibitory effect of which is increased by dephosphorylation. Treatment of epidermal extracts with alkaline phosphatase reduced the phospholipase A2 activity, both in normal and in lesion-free psoriatic epidermis. Inclusion of pyrophosphate, a protein phosphatase inhibitor, in the homogenizing medium caused the activity of phospholipase A2 in epidermal extracts from normal and lesion-free epidermis to be raised to the same high level. These results are consistent with the hypothesis that the raised phospholipase A2 activity in psoriatic epidermis is due to hyperphosphorylation of an endogenous inhibitor as a result of defective control of a phosphorylation/dephosphorylation mechanism. The relevance of these findings to other work is discussed.

Lipids in the laminated layer of liver, lung and daughter hydatid cysts of equine Echinococcus granulosus (Cestoda).

Lipids extracted from the laminated layers of horse liver and lung hydatids, including a daughter liver cyst, were analysed using TLC. No differences in lipid composition was detected in 11 liver cysts, whether from the same or different livers, and di- and triacylglycerols, cholesterol, wax and steryl esters, oleic acid, sphingomyelin, phosphatidyl choline, phosphatidyl inositol and ceramide hexosides were detected. The daughter cyst differed from its "parent" cyst in lacking diacylglycerols and wax and steryl esters. The lung cyst differed from the liver cysts in that cholesterol, wax and steryl esters and diacylglycerols were not detected.

Epidermal lipids.

Synopsis From the time an epidermal cell leaves the basal layer to the time it is desquamated, the cell lipids change dramatically, both qualitatively and quantitatively. The most abundant lipid class in basal cells is phospholipid with the remaining lipid being accounted for by roughly equal proportions of cholesterol, non-esterified fatty acid, triacylglycerol and glycolipid: minor components include cholesteryl esters and ceramide. In contrast, approximately half of the lipid in a desquamated cell consists of ceramide, with the remainder consisting largely of cholesterol and non-esterified fatty acid. Immediately before desquamation, small concentrations of cholesteryl sulphate and glycolipid have been found and there is evidence that these polar lipids are important components of the water barrier and also contribute towards the physical integrity of the lower part of the stratum corneum. The change in lipid content as cornification proceeds is no less dramatic than the change in lipid composition. A basal cell contains about 10 pg lipid, whereas a desquamated stratum corneum cell contains approximately six times this amount. The change in lipid composition of a cell undergoing cornification results, therefore, largely from de novo synthesis of lipid, especially cholesterol, non-esterified fatty acid and ceramide. Les lipides de l'épiderme.

Characterization and activity of phospholipase A2 in normal human epidermis and in lesion-free epidermis of patients with psoriasis or eczema.

The kinetic properties of phospholipase A2 isolated from single large specimens of normal human epidermis and 'uninvolved' (lesion-free) psoriatic epidermis were determined. The enzymes from the two sources behaved identically with respect to changes in protein concentration, Ca2+ concentration and pH, but the enzymes responded differently to changes in substrate concentration. Furthermore, the specific activity of the enzyme derived from lesion-free psoriatic epidermis was higher than that from normal epidermis under all conditions used. Increased specific activity of the enzyme in the lesion-free epidermis was also found when biopsy specimens taken from thirty-five patients with psoriasis vulgaris at varying severity were compared with biopsies of normal epidermis from thirty-one control volunteers (P less than 0.001). Mixing experiments, in which homogenates of lesion-free psoriatic epidermis and control epidermis were combined, suggested that the relatively low activity of the enzyme in normal epidermis was due to the presence of an inhibitor. As the activity of the enzyme was not elevated in the lesion-free epidermis from twelve cases of eczema, which is also an inflammatory condition of the epidermis and superficial dermis, it is suggested that the raised phospholipase A2 activity demonstrated in the lesion-free epidermis of psoriasis may play an important role in the pathogenesis of the disease.

Utilization of epidermal phospholipase A2 inhibition to monitor topical steroid action.

The effect of several steroid creams on epidermal phospholipase A2 (PLA2) activity in symptomless psoriatic and normal epidermis was studied. The magnitude of PLA2 inhibition produced by the steroids was directly proportional to the initial level of the enzyme activity. This differential inhibition resulted in PLA2 activity approaching or attaining the normal range regardless of its initial level. Clobetasol propionate 0.05% (Dermovate) produced more enzyme inhibition than betamethasone valerate 0.1% (Betnovate) but there was no difference in inhibition between this latter steroid and clobetasone butyrate 0.05% (Eumovate). All were more inhibitory than hydrocortisone I% (Efcortelan).

Epidermal phospholipase A2 activity is raised in the uninvolved skin of psoriasis.

In uninvolved epidermis from nine psoriatic subjects, the mean phospholipase A2 activity was significantly greater (P less than 0.01) than in nine controls. The increased activity of this enzyme could lead to an increase in the concentration of free arachidonic acid which, in turn, could lead to increased concentrations of inflammatory mediators.

Lipid composition of the superficial stratum corneum cells of pig epidermis.

Stratum corneum was removed from the surface of pig skin using a wet brushing technique. The material so obtained was fractionated into cell clumps, discrete cells and fine material by differential filtration through nylon gauzes. Ceramide, cholesterol and free fatty acid accounted for about 95% of the lipid present in each fraction: phospholipid and glycolipid were not detected. Material removed by successive brushings showed no detectable differences in lipid composition.

The plasma membrane of Malpighian cells from pig epidermis: isolation and lipid and protein composition.

A plasma membrane fraction from Malpighian cells has been isolated by differential and density gradient centrifugation of a pig epidermal homogenate. It was enriched in the marker enzymes 2-naphthylamidase, 5'-nucleotidase, phosphodiesterase I and acid phosphatase and depleted of NADH-ferricyanide reductase and cytochrome c oxidase. It had a protein to lipid ratio of 3:2 by weight. The protein composition was complex with compounds ranging from a molecular weight of 150,000 down to 13,000. Major components with molecular weights 120,000 to 90,000 were glycoproteins. Two other components had molecular weights of 39,000 (actin ?) and 24,000. There were minor components with molecular weights from 63,000 to 46,000. About 76% of the total lipid was present as phospholipid, which was enriched in sphingomyelin. Most of the neutral lipids were accounted for by cholesterol, triacylglycerols and fatty acids: very little glycosphingolipid was present. The preparation was probably derived from non-desmosomal areas of the plasma membrane of Malpighian cells, as desmosomes were not seen in the preparation.

Changes in dry weight and projected area of human epidermal cells undergoing keratinization as determined by scanning interference microscopy.

Cells, obtained from human leg by successive treatments with trypsin, were air dried on microscope slides before mounting in glycerol. Dry weights and projected areas of individual cells were measured using a Vickers M 86 scanning microinterferometer. The dry weights of cells varied from 100 pg for basal cells to 700 pg for large squames. Corresponding projected areas varied from 100 to 1500 mum2.

Brittle fracture of epidermal cells by liquid shear.

A suspension of epidermal cells obtained from pig tail skin by trypsinization was subjected to high liquid-shear forces in a French press. The material issuing from the press was examined by phase-contrast microscopy, transmission electron microscopy and scanning electron microscopy. The cytoskeleton of tonofibrils retained the shape of cell fragments, and subcellular organelles remained enmeshed in the network of tonofibrils. Examination of some cell fragments by scanning electron microscopy revealed the internal organization of the tonofibrils. The relevance of these findings to the problem of isolating subcellular fractions from epidermis is discussed.

The lipid composition of sebaceous glands as a reflection of gland size.

Following 4 h incubation in vitro, the patterns of incorporation of [I-14C] acetate into the lipid classes of human sebaceous glands which were dissected from small skin biopsies have been established for glands of different size. It has been shown that in the larger sebaceous glands proportionately more of the labelled acetate is incorporated into squalene at the expense of triglycerides. Experiments are presented as a result of which we conclude that this in vitro phenomenon, observed with [I-14C] acetate incorporation, does reflect parallel changes in the proportions of these lipids actually present in glands of different size. It is suggested that the larger sebaceous glands of the acne patient elaborate sebum which has an enhanced potential for inducing comedo formation by virtue of an increased concentration of squalene. This work also demonstrates that, in the interpretation of in vitro studies of sebaceous gland lipogenesis utilizing labelled precursors, the size of the sebaceous glands must be carefully considered whenever patterns of incorporation are being compared.

Lipid compositions of cells isolated from pig, human, and rat epidermis.

Epidermal slices from pig, human, and rat skin were treated with dilute buffered trypsin solution (0.005%, w/v), and suspensions of mixed basal and spinous cells were obtained in good yield. Total lipids accounted for approximately 8% of the pig, 10% of the human, and 20% of the rat epidermal cell (dry weight). Phospholipids in pig, human, and rat cells accounted for, respectively, 62%, 53%, and 35% of the total lipids. Phosphatidylcholine (34-38%), phosphatidylethanolamine (18-23%), and sphingomyelin (17-21%) were major compounds in all species. The major neutral lipids were sterols (mostly cholesterol) and triglycerides. Free fatty acids were a major lipid class in pig and human cells, whereas wax esters were a major component in rat epidermal cells. Nearly half (45%) of the sterols in rat cells but less than 10% of those in pig and human cells were esterified. Cholest-7-ene-3beta-ol accounted for 20% of the total sterols in rat cells. Cholesteryl sulfate and ceramide were minor lipids in the three species. The predominant glycosphingolipid (greater than 99%) was glucosylceramide, which accounted for 7% and 9%, respectively, of the total lipids in pig and human cells. A significant proportion (pig, 17%; human, 11%) of the fatty acids in the glucosylceramides were C26:0 and C28:0.