P. H. Andersen

Faecal enzymes: in vivo human skin irritation.

Digestive enzymes in faeces have been reported to posses skin irritation potential. The present study was designed to investigate the in vivo irritant potentials of faecal concentrations of proteolytic and lipolytic digestive enzymes in bile salt mixtures. In a 21‐day cumulative irritation assay, clinical evaluation and noninvasive bioengineering techniques were used. 5 days occlusive exposure to phosphate buffer (pH = 8) caused no visual skin damage but reflectance spectroscopy demonstrated significant vasodilation (p < 0.01) and increases in transepidermal water loss (TEWL) and skin pH were also observed (p < 0.01). These increases were still present at days 12 and 19. Occlusive exposure to physiologic concentrations of faecal enzymes resulted in significant visual and objective scores at day 5, 12, and 19, with increased readings as a function of exposure time (p < 0.01). The enzyme mixture containing lipase caused delayed onset of skin erythema and epidermal barrier disruption compared to elastase and chymotrypsin containing solutions. Prolonged occlusive exposure to digestive enzymes in faecal concentrations caused severe skin erythema and epidermal barrier disruption in a human model, suggesting a possible etiologic role of digestive enzymes in perianal, circumstomal or diaper dermatitis.

High dissociation constants (pKa) of basic permeants are associated with in vivo skin irritation in man

Previously, we have investigated the relationship between dissociation constant (pKa) and skin irritation potential. In the present experiment, 12 basic compounds, with varying pKa values ranging from 1.4 10 11.2, were applied on the hacks of 12 healthy adult panellists. Cutaneous reactions were measured objectively using reflectance speetrcscopy and transepidermal water loss (TEWL), and evaluated subjectively with a modified Draize scale. A positive correlation between increasing pKa and skin irritation capacity, measured either visually or by reflectance spectroscopy, was found, but only mecamylamine (pKa= 11.2) induced a significant increase in transepidermal water loss. Compounds with low pKa also induced a paradoxical vasoconstriction measured by reflectance spectroscopy. Only high pKa appeared predictive of in vivo skin irritation, and these chemicals apparently induce skin irritation with only minimal disruption of the skin barrier. A simple 1‐variable model is predictive of skin irritation for this series of organic permeants with increasing PKa.

Skin irritation in man: a comparative bioengineering study using improved reflectance spectroscopy

Variable types of skin irritation were induced in 8 human female volunteers, ranging from subclinical to visible erythema with slight oedema. Skin reactions were graded clinically and objectively using transepidermal water loss (TEWL), laser Doppler flowmetry (LDF) and improved reflectance spectroscopy. This last technique enables separation of in vivo erythemas into relatively deoxygenated (venous‐deoxy hem) and oxygenated (arterial oxy hem) haemoglobin components. Compared to uninvolved skin, an empty patch increased oxy hem by 197%± 121%(p < 0.05). Exposure to vehicles also changed skin biophysics. At sodium lauryl sulfate (SLS) and hydrochloric acid (HCL) exposed sites, a linear correlation between concentration and oxy hem. LDF and TEWL was found. These chemicals predominantly increased TEWL values. Nonanoic acid (NON) and imipramine (IMI) also raised oxs hem, LDI and TEWL values linear at increasing concentrations. Although IMI 2.5% clinically was graded as a type ++ response, no significant increase in TEWL was found. The improved reflectance spectroscopic technique proved valid in skin irritation studies, with a higher sensitivity than laser Doppler flowmetry, and allowed irritant vascular reactions to be discriminated into arterial and venous components. Furthermore, our observations clearly demonstrate that clinical indistinguishable skin irritation reactions induce significantly different changes in barrier function (disruption) and vascular status.

The cutaneous corticosteroid vasoconstriction assay : a reflectance spectroscopic and laser-Doppler flowmetric study

Cutaneous vasoconstriction induced by topical corticosteroids was investigated using non‐invasive bioengineering techniques. Corticosteroids of different potency in alcoholic solution were applied topically, under occlusion, and cutaneous blanching was investigated using visual scoring, reflectance spectroscopy (RS) and laser‐DoppIer flowmetry (LDF), The RS technique allowed separation of cutaneous haemoglobin content into arterial oxygenated (OH) and venous deoxygen‐ated haemoglobin (DOH) components.

Chemical and pharmacologic skin irritation in man : a reflectance spectroscopic study

Attention is increasingly being focused on the relationship of dissocial Ion constant (pKa) of chemicals and skin irritation presumably caused by pH effects at epidermal levels. Human skin Studies of irritation have utilized both subjective visual‐palpation scores and reflectance spectroscopy (RS) or laser Doppler velocimetry (LDV) respectively. Several studies document that erythema determined subjectively and objectively correlates with the degree of skin irritancy, but others report lack of correlation between LDV and irritancy scored subjectively. In this study, pharmacologicol and chemical in vivo, skin irritation was evaluated utilizing an improved reflectance spectrophotometer equipped with computerized data analysis. In 16 white females, a model for skin irritation was induced by a 24‐h patch application of 4 basic chemicals, imipramine, norephedrine, nicotine and 8‐aminoquinoline, with pKas ranging from 3.8 to 9.5. Skin pigmentation (melanin) and the relative amounts of oxygenized (arterial) and deoxygenized (venous) hemoglobin present in the erythematous skin were calculated. A clear increase in the hemoglobin content was observed in chemical and vehicle exposed sites. Although skin irritation is a complex phenomenon involving chemical and solution properties, percutaneous absorption and the biological drug response, high pKa (p > 0.01) was predictive of acute skin irritation in man using computerized analysis of reflectance spectroscopy, A high correlation between visual score and RS was found (r= 0.91).

Erythema induced by organic solvents: in vivo evaluation of oxygenized and deoxygenized haemoglobin by reflectance spectroscopy

Objective: (i) using a new non‐invasive technique capable of evaluating quantitatively and qualitatively the haemoglobin content of the skin (ii) to evaluate delipidization induced by organic solvents. Patients: 11 Caucasians treated for 1 min in a randomized manner on the volar forearm with a mixture of chloroform/methanol (2: 1) (CM) and ether/acetone (1:1) (EA) to delipidize the skin. Method erythema was evaluated by computerized remittance spectroscopy immediately after delipidization and hourly for 2 h. Results: only CM application induced subjectively observed and objectively quantified erythema. Erythema was related to a significant increase in oxygenized haemoglobin content due to dilatation of arterioles in the subpapillary plexus (P<0.01). The increased blood flow induced a significant (P<0.01) reduction in de‐oxygenized haemoglobin in venous vessels immediately after CM application. Conclusion: short contact with certain potent solvent mixtures causes erythema, possibly due to massive lipid extraction and damage of the skin barrier. Using computerized remittance spectroscopy the visible erythema was composed of an increase in oxygenized haemoglobin and a relative decrease in deoxygenized haemoglobin.

A corticosteroid, a non‐steroidal anti‐inflammatory drug and an antihistamine modulate in vivo vascular reactions before and during post‐occlusive hyperaemia

Post‐occlusive reactive hyperaemia is the temporary increase of blood flow in a tissue following transient vascular obstruction, and has recently heen proposed as an in vivo method for ranking topical corticosteroid potency. We investigated in vivo vascular reactions before and during postocclusive hyperaemia using laser‐Doppler flowmetry and reflectance spectroscopy (RS). RS enables resolution of in vivo erythema into deoxygenated (venous) [DOH] and oxygenated (arterial) haemoglobin (OH) components (expressed in arbitrary units. All). Using a randomized 24‐h occlusive exposure in 10 healthy volunteers the effects of a corticosteroid (betamethasone‐1 7‐valerate). a non‐steroidal anti‐inflammatory drug (NSAID) [indomethacin], an antihistamine (diphenydramine), or vehicle, were studied before and during post‐occlusive hyperaemia.

A time correlation study between reflectance spectroscopic cutaneous vasoconstriction and plasma corticosteroid concentration

Although cutaneous vasoconstriction assays are used as a primary screen for ranking the in vivo efficacy of new corticosteroids and in vivo human drug delivery studies, little is known about the relationship between the blanching reaction and corticosteroid tissue or plasma concentrations. We measured cutaneous vascular reactions in five volunteers, using an improved reflectance spectroscopic method, and a sensitive radioimmunoassay technique was employed to measure plasma betamethasone concentrations. Using a specially developed betamethasone‐17‐valerate patch prepared in BIO‐PSA®, constant corticosteroid release was ensured, and correlations between cutaneous blanching and plasma corticosteroid concentrations were calculated. Maximal skin blanching was documented 12 h post‐application, whereas plasma corticosteroid concentrations peaked later, at 32 h post‐application, when a paradoxical telangiectatic vasodilatation occurred. At 72 h post‐application, when the plasma corticosteroid concentration was still above the 12 h level, this paradoxical vasodilatation was maximal. The corticosteroid‐induced vascular reactions were mainly due to arterial haemoglobin (Oxy Haem), and both vasoconstriction and vasodilatation were related to changes in Oxy Haem. Our results suggest a dual, probably both time and concentration related, interaction between corticosteroids and dermal vessels in which lower concentrations at 6‐12 h exposure caused vasoconstriction, but as the exposure time increased (24 h) paradoxical vasodilatation was induced, although plasma corticosteroid concentrations were still rising.