Dermatotoxicology

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An Overview. Clinical Heterogeneity and Contributing Factors. Chapter 14 Systemic Contact Dermatitis.

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Chapter 15 Allergic Contact Dermatitis. Rational WorkUp. Chapter 18 Systemic Toxicity. Chapter 19 Concepts in Molecular Dermatotoxicology.


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Chapter 21 Photoirritation Phototoxicity Phototoxic Dermatitis. Chapter 23 Chemically Induced Scleroderma. Current Trends in Skin Cancer Research. Chapter 26 Retinoids and Mechanisms of Their Toxicity. Chapter 28 DrugInduced Ocular Phototoxicity. Is It an Irritant? Chapter 30 Sodium Lauryl Sulfate.

Marzulli and Maibach's Dermatotoxicology

Chapter 32 Barrier Creams. Chapter 34 Methods for Percutaneous Absorption. Chapter 36 Pesticide Percutaneous Absorption and Decontamination. Chapter 41 Physiologically Based Pharmacokinetic Modeling. Chapter 45 Kawai Method for Testing Irritation. Literature Review. Do They Work? Chapter 51 Tests for Sensitive Skin. Elicitation Thresholds of Potent Allergens in Humans. A Cross Sensitization Phenomenon. Chapter 66 Animal Models of Contact Urticaria. Patch and Photopatch Testing and Contact Urticaria.

Testing ban and marketing ban of cosmetic products, which were tested on animals, have been in effect since March Controlled studies with human volunteers have provided meaningful data, and their basic principles are discussed in the following. Predicative irritation assays in humans, using a small area of skin, can be done provided that systematic toxicity from absorption is low and informed consent is obtained. Although regulatory agencies do not routinely require testing in humans, human tests are sometimes preferred to animal tests. Test sites generally heal rapidly, within a week or so.

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More severe reactions should be periodically evaluated over a longer time to ensure resolution and determine inflammatory patterns. Some subjects may develop changes in pigmentation level at the test site following severe responses. Detailed consultation before consenting human subjects are extremely important.

The single-application irritation patch test is used for the assessment of acute irritation potential and involves the application of 0. New test materials may be applied for shorter periods 30 minutes to 1 hour , and if tolerated, the exposure time can progressively be increased to 4 hours.

When testing new materials, the application of dilutions should be considered Subjects should routinely be instructed to immediately remove patches if unusual discomfort occurs. Tested sites are assessed for the presence of irritation using a grading scale Table Commercial patches, chambers, gauze squares, or cotton bandage material can be used, and patches are applied to either the upper back or the dorsal surface of the upper arm. Patches are secured with surgical tape without wrapping the trunk of the arm.

This test detects acute skin irritation hazard potential and should be used for hazard classification. It is not intended to predict other types of skin irritant dermatitis, such as cumulative irritant dermatitis Faint but definite erythema, no eruptions or broken skin or no erythema but definite dryness; may have epidermal fissuring.

Well-defined erythema or faint erythema with definite dryness; may have epidural fissuring.

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Moderate erythema, may have a few papules or deep fissures, moderate-to-severe erythema in the cracks. Moderate erythema with barely perceptible edema or severe erythema not involving a significant portion of the patch halo effect around the edges ; may have a few papules or moderate to severe erythema. Severe erythema beet red ; may have generalized papules or moderate to severe erythema with slight edema edges well defined by raising. Moderate to severe erythema with moderate edema confined to patch area or moderate to severe erythema with isolated eschar formations or vesicles.

Source: Hayes, B. The repeat-application cumulative irritation patch test assesses cumulative irritation. The early work of Marzulli and Maibach 75 , Kligman and Wooding 80 and other investigators formed the basis of cumulative irritation assays 78 , Patches were removed after 24 hours, sites were evaluated, and a fresh set of patches were reapplied up to 21 days. Basic principles are similar to the single application, and many investigators have developed their version of it. Shorter study times have also been used in the evaluation of surfactants.

Many investigators have developed their version 62 , These methods do not always predict the safety of consumer products, which may be related to intrinsic differences in the reactivity of healthy skin versus damaged or sensitive skin Soaps are an example in which patch testing may overpredict the reaction in real life. Immersion testing and antecubital washing test, also known as flex wash , are examples of nonpatch irritancy techniques.

Numerous versions of these tests have been used by investigators basically exposing the skin of consented human subjects to different concentrations of detergents for varied amounts of time; the end points are erythema and scaling 78 , 83 , Multiple commercially available devices are used to measure the biophysical properties of skin. These measures provide objective data to be used in conjunction with the clinical evaluation of inflammatory responses detailed discussion is in Chapter 1. Disks are subsequently stained, and the amount of dye found in the cells are quantified and scaled 87 — Phototoxicity photoirritation refers to tissue inflammation caused by the interaction of certain chemicals with light.

Phototoxicity is a nonimmunological, dose-dependent phenomenon that happens when certain chemicals in the skin absorb light and create a pathological irritation. These chemicals may be applied topically or diffused into skin following systemic administration of a drug. The principle of photochemical activation Grotthuss—Draper Law states that light must be absorbed by a chromophore for a chemical reaction to happen.

Therefore, the first step in the evaluation of the photosafety of a chemical is to have an absorption spectrum conducted. If a substance absorbs light within the range of UV and visible light — nm , reactive species can be generated, which can harm the tissue. Additional testing is required to assess the photosafety of a product that is intended for topical use or a systemic medication that diffuses to photoexposed skin Validated testing methods for the assessment of phototoxic properties of chemicals are reviewed here. Skin is optically heterogeneous, and via reflection, refraction, scattering, and absorption, it can modify the amount of radiation reaching deeper structures These protective properties can be affected by the topical application of different products.

Vehicles can decrease the amount of light reflected, scattered, or absorbed They can also affect percutaneous absorption into the skin 92 , Physical and chemical properties of vehicles can affect absorption, and photoproperties of applied medications, therefore testing of vehicles along with the medications is required by regulating agencies The approach to the initial evaluation of phototoxicological properties of a substance is summarized in Figure The ability of chemicals to absorb light is an intrinsic property of that specific chemical.

To measure how strongly a chemical absorbs light in a given wavelength, molar extinction coefficient MEC , also called molar absorptivity , is used. MEC is a constant for any given molecule under a specific set of conditions e. Phototoxicity refers to tissue inflammation caused by the interaction of light and a photoreactive chemical.

Therefore, ROS generation following visible light or UV exposure can indicate the potential phototoxicity of a chemical. ROS assay is designed considering the principle mentioned earlier 44 , This assay has high sensitivity and low specificity, creating many false positives; therefore, a positive result at any concentration would only point out the need for further assessment. Cytotoxicity is expressed as a concentration-dependent uptake of neutral red NR dye 3-aminodimethylaminomethylphenazine hydrochloride 24 hours after treatment with the test chemical and irradiation NR is a weak cationic dye that penetrates cell membranes by nondiffusion and intracellularly accumulates in the lysosomes.

In damaged cells, the alteration of the lysosomal membranes and their fragility by a phototoxic reaction lead to decreased uptake and binding of NR is considered one sequential process. On this bases, viable, damaged, or dead cells can be distinguished. The protocol follows the following steps full details are available on Test Guideline Both sets will go through the entire test procedure under identical conditions except that one plate is irradiated and one plate is kept in the dark.

Dermatotoxicology and Sensitive Skin Syndrome. Predictive In Vitro Testing Corrosion Testing The main principle of corrosion testing is based on the fact that corrosive chemicals damage the SC and barrier function. The Draize Rabbit Skin Irritancy Test The Draize rabbit skin, successfully used since the s 74 and established as the basis for the methods mentioned earlier used in Test Guideline , involves the application of two semioccluded patches of an undiluted chemical to the shaved back of each animal typically, three albino rabbits.

Human Irritation Testing Controlled studies with human volunteers have provided meaningful data, and their basic principles are discussed in the following. Single-Application Irritation Patch Test The single-application irritation patch test is used for the assessment of acute irritation potential and involves the application of 0. Repeat-Application Cumulative Irritation Patch Test The repeat-application cumulative irritation patch test assesses cumulative irritation.

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