With the development of reliable in chemico/in vitro assays, manufacturers and formulators are now able to determine whether or not a substance is a skin sensitizing agent without the need for animal testing. Each of the available assays recapitulates some element of the adverse outcome pathway (AOP) associated with a skin sensitization response in humans. Using an integrated testing strategy that incorporates these approaches for identifying skin sensitization hazard risk (as outlined by the Globally Harmonized System of Classification and Labelling of Chemicals) ensures regulatory compliance as well as consumer safety and satisfaction.

Overview of Direct Peptide Reactivity Assay (DPRA)

The Direct Peptide Reactivity Assay is an in chemico test that recapitulates the first key event within the skin sensitization adverse outcome pathway. After multiple exposures to a skin sensitizer, the sensitizing material may bind to proteins in the skin which increases the potential for a sensitizing reaction. The DPRA replicates this response by measuring the reactivity of a material towards synthetic protein peptides made with lysine and cysteine. This is performed with a known molar ratio of test chemical and synthetic peptide. Reactivity quantification is based on the percent peptide depletion of lysine and cysteine measured using High Performance Liquid Chromatography (HPLC) or Ultra High-Performance Liquid Chromatography (UPLC). Based on the results of the assay, the test material is categorized into one of four reactivity classes with regard to skin sensitization potential: None or Minimal Reactivity, Low Reactivity, Moderate Reactivity or High Reactivity. The results of the DPRA can be used to make predictions about the skin sensitization potential of a variety of materials.

The DPRA should be used in conjunction with additional assays to confidently determine a substance’s safety and skin sensitization potential as some materials may not be suitable for this assay. Because the DPRA lacks metabolic capacity, chemicals requiring enzymatic activation to become skin sensitizers (such as pro-haptens) are unsuitable for evaluation via this method. In addition, materials that readily react with proteins outside of a sensitization response (e.g., metal compounds, oxidative chemicals) or preferentially react with amino acids other than cysteine and lysine may provide false positives or negatives, respectively.

Our Capabilities

CPT is a state-of-the-art testing facility, including laboratories that specialize in Analytical, Clinical, and In-Vitro Toxicology testing.  Our entire testing facility is at your disposal for evaluating skin sensitization potential.

In our highly experienced and specialized departments, we test a wide range of articles including pharmaceuticals, raw materials, cosmetic and personal care products. Our experts offer our clients guidance on the best testing strategies to ensure consumer safety and satisfaction as well as regulatory compliance.

Our Departments

In response to the multifaceted nature of safety testing, we are proud to provide our clients with support that can be tailored to meet your individual and evolving needs. The product(s) under evaluation and desired claims will determine which department(s) ultimately assist your product testing endeavors. Our clients typically take advantage of the diverse expertise that CPT offers by calling upon our specialists from a variety of departments, including:

  • Clinical – CPT performs safety and efficacy tests to support pre-market testing, performance validation, and claims such as ‘dermatologist-tested’ and ‘ophthalmologist-tested.’
  • In-Vitro Safety – We offer alternative testing methods to meet the needs of the various industries when it comes to non-animal or animal-tree toxicology evaluations.
  • Microbiology – From preservative efficacy to stability testing, CPT has a variety of testing approaches at your disposal for microbial contamination potential and preservative testing evaluations for cosmetics.
  • Photobiology – CPT is the industry leader in photobiology testing, from supporting SPF and Water-Resistant claims to PhotoAllergy and Phototoxicity assays.
  • Analytical – Our analytical team provides support at all levels of product evaluation, from raw materials to stability shelf-life testing to “free-of” and low-level detection claims. Our experts will ensure that all regulatory requirements are met.

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