Contact allergy to dicyclohexyl carbodiimide and diisopropyl carbodiimide

An Evaluation of the Occupational Health Hazards of Peptide Couplers

Peptide couplers (also known as amide bond-forming reagents or coupling reagents) are broadly used in organic chemical syntheses, especially in the pharmaceutical industry. Yet, occupational health hazards associated with this chemical class are largely unexplored, which is disconcerting given the intrinsic reactivity of these compounds. Several case studies involving occupational exposures reported adverse respiratory and dermal health effects, providing initial evidence of chemical sensitization. To address the paucity of toxicological data, a pharmaceutical cross-industry task force was formed to evaluate and assess the potential of these compounds to cause eye and dermal irritation as well as corrosivity and dermal sensitization. The goal of our work was to inform health and safety professionals as well as pharmaceutical and organic chemists of the occupational health hazards associated with this chemical class. To that end, 25 of the most commonly used peptide couplers and five hydrolysis products were selected for in vivo, in vitro, and in silico testing. Our findings confirmed that dermal sensitization is a concern for this chemical class with 21/25 peptide couplers testing positive for dermal sensitization and 15 of these being strong/extreme sensitizers. We also found that dermal corrosion and irritation (8/25) as well as eye irritation (9/25) were health hazards associated with peptide couplers and their hydrolysis products (4/5 were dermal irritants or corrosive and 4/5 were eye irritants). Resulting outcomes were synthesized to inform decision making in peptide coupler selection and enable data-driven hazard communication to workers. The latter includes harmonized hazard classifications, appropriate handling recommendations, and accurate safety data sheets, which support the industrial hygiene hierarchy of control strategies and risk assessment. Our study demonstrates the merits of an integrated, in vivo -in silico analysis, applied here to the skin sensitization endpoint using the Computer-Aided Discovery and REdesign (CADRE) and Derek Nexus programs. We show that experimental data can improve predictive models by filling existing data gaps while, concurrently, providing computational insights into key initiating events and elucidating the chemical structural features contributing to adverse health effects. This interactive, interdisciplinary approach is consistent with Green Chemistry principles that seek to improve the selection and design of less hazardous reagents in industrial processes and applications.

Comparative dermal toxicity of dicyclohexylcarbodiimide and diisopropylcarbodiimide in rodents

Dicyclohexylcarbodiimide (DCC) and Diisopropylcarbodiimide (DIC) are two representative chemicals in the carbodiimide class of chemicals used in industry as stabilizing agents. There is a potential of dermal exposure to these agents in chemical, pharmaceutical and recombinant DNA industries. The National Toxicology Program conducted a number of animal studies to characterize toxicity and carcinogenicity of DIC and DCC. Dermal administration of DCC and DIC in F344/N rats and B6C3F1 mice for 90-days induced skin irritation at the site of application in a dose-dependent manner. Microscopically, dose-dependent increases in epidermal hyperplasia and chronic inflammation were observed. We further evaluated the effects of dermal exposure of DCC and DIC in p53 haploinsufficient and Tg.AC mouse models. Results revealed the skin as the primary target of DCC and DIC exposure as indicated by dose - dependent skin lesions (hyperplasia, inflammation and necrosis). DCC induced squamous cell papillomas in Tg.AC mice but did not induce any neoplastic lesions in p53 haploinsufficient mice. Dermal application of DIC did not induce any neoplastic lesions in Tg.AC mice and p53 haploinsufficient mice. Based on these studies, it was predicted that DIC would be negative and DCC positive for carcinogenic activity in the traditional two-year bioassay. In the subsequent studies, the carcinogenic potential of DIC only in F344 rats and B6C3F1 mice in a traditional 2-year chronic carcinogenicity bioassay was evaluated by the dermal route. Findings revealed the skin as the major target organ of toxicity in both sexes in rats and in male mice. There were no neoplastic lesions observed in rats or mice with the administration of DIC. In rats, there were clinical signs of toxicity in the highest dose-group which included ataxia, excitability, impaired gait, low muscle tone, abnormal breathing, lethargy, and seizures. This was accompanied by non-neoplastic lesions in the brain and lung only at the highest dose level. In conclusion, both DIC and DCC are dermal toxicants. DIC did not have any carcinogenic activity in transgenic mouse models or in the traditional NTP two-year carcinogenicity studies in F344 rats and B6C3F1 mice. DCC was positive in the Tg.AC mouse model and likely to be carcinogenic in the 2-year bioassay as well.

MHC restriction in contact hypersensitivity to dicyclohexylcarbodiimide

Mouse ear swelling tests were performed using different strains of mice with dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), di-p-tolylcarbodiimide (DTC), and positive control chemicals, such as dinitrochlorobenzene (DNCB) and oxazolone (OXA). The chemicals were examined at different doses up to the minimal irritating concentration determined in a irritancy assay. While BALB/c mice exhibited strong responses for the carbodiimide compounds, C3H/HeN mice demonstrated no reactions. Other strains, C57BL/6 and DBA/1, also showed responses to DCC, but CBA/J mice with the same haplotype as C3H/HeN (H-2(k)) did not. Based on our present findings, there may be a specific unresponsiveness to DCC dependent on the H-2(k) haplotype.

An update on airborne contact dermatitis

This review is an update of 2 previously published articles on airborne contact dermatoses. Because reports in the literature often omit the term 'airborne', 18 volumes of Contact Dermatitis (April 1991-June 2000), 8 volumes of the American Journal of Contact Dermatitis (1992 1999) and 4 volumes of La Lettre du Gerda (1996-1999) were screened, and the cases cited were classified as to history, lesion locations, sensitization sources, and other factors. Reports on airborne dermatitis are increasingly being published, sometimes in relation to specific occupational areas.

Contact hypersensitivity to dicyclohexylcarbodiimide and diisopropylcarbodiimide in female B6C3F1 mice

Dicyclohexylcarbodiimide (DCC) and diisopropylcarbodiimide (DIC) are two commonly used coupling reagents in protein synthesis resulting in exposure of individuals in chemical and pharmaceutical industries as well as research laboratories involved in protein synthesis and recombinant DNA techniques. The objectives of these studies were to determine the irritation and sensitizing potential of these two compounds when applied topically to B6C3F1 mice. Sensitization potential was assessed by the Mouse Ear Swelling Test (MEST) and the murine Local Lymph Node Assay (LLNA). Concentrations used in the contact hypersensitivity assays were determined by primary irritancy studies. DCC and DIC were identified as both irritants and contact sensitizers with the MEST being a more sensitive indicator of sensitization potential. The MEST identified DCC as a sensitizer at concentrations as low as 0.006% (w/v) 24 hr and 48 hr post challenge and DIC at 0.3% (w/v) and 1.5% (w/v) 24 and 48 hr post challenge, respectively. In the LLNA, the lowest concentrations yielding a significant response were 0.06% (w/v) for DCC and 10% (w/v) for DIC.