Abstract

TBTU (2-[1H-benzotriazol-1-yl]-1,1,3,3-tetramethyluronium tetrafluoroborate; CAS No: 125700-67-6) and HBTU (2-[1H-benzotriazol-1-yl]-1,1,3,3-tetramethyluronium hexafluorophosphate; CAS No: 94790-7-1) are increasingly used as coupling reagents for the stepwise synthesis of peptides. There have been isolated reports describing the development of rhinitis, urticaria and contact dermatitis 1–4 caused by these uronium compounds.

We evaluated six workers exposed to TBTU in a laboratory producing a wide variety of biologically active peptides. Three times a week, they weighed 30–50 g of TBTU powder into separate aliquots which were dissolved in dimethylformamide in closed vials and connected to an automated synthesiser. The survey included a detailed questionnaire and skin-prick tests with five common inhalant allergens, natural rubber latex, and reshly prepared dilutions of TBTU, HBTU and hydroxybenzotriazole (HOBt) (1 and 10 mg/ml) in sterile saline. One employee reported work-related asthma and rhinitis, while three others experienced both rhinitis and skin symptoms (transient urticarial rash of the hands and face and persistent eczematous-like skin lesions on the hands). The nasal and skin symptoms markedly decreased after improvement in the plant ventilation system, isolation of the weighing procedure, and implementation of stringent work practices (systematic cleaning procedures, use of respiratory rotectivemasks for weighing operations, protective clothes changed daily, use of long-sleeved gloves). These four symptomatic workers showed an immediate skin-prick test response to TBTU but not to saline solution. Three of them also demonstrated a positive skin reaction to HBTU, while skin testing with HOBt gave negative results. Skin-prick tests with TBTU, HBTU and HOBt were negative in nine unexposed control subjects. Specific IgE antibodies against TBTU and HBTU conjugated to human serum albumin could not be detected in symptomatic workers using the ImmunoCAP technique (personal communication from L Strombeck, Phadia Diagnostics, Uppsala, Sweden).

In the employee reporting work-related asthma, bronchial provocation challenge by tipping TBTU powder elicited an immediate asthmatic reaction and a significant increase in non-specific bronchial responsiveness to histamine. Analysis of induced sputum showed an increase in the percentage of sputum eosinophils (6.3% of 5.326106 cells/ml) at 24 h post-challenge vs 0.3% of 1.896106 cells/ml in the control day sample).the 1.0 mg/ml solution of TBTU induced complete blockage of nasal cavities and an increase in nasal lavage fluid eosinophils (from 0% post-saline to 20.5% in the sample collected 4 h after TBTU instillation).

The results of bronchial challenge with TBTU were consistent with those reported in asthmatic reactions induced by lowmolecular weight agents, although the underlying mechanisms remain largely uncertain. Thus, the bronchial response to TBTU was associated with a significant increase in non-specific bronchial hyperresponsiveness and in sputum eosinophils.

Immediate skin-prick test response to TBTU and HBTU supported a type I allergic response directed against these agents. Specific IgE antibodies could not be detected, which is often the case in workers with occupational asthma caused by low-molecular-weight agents.5 The nature of skin symptoms was consistent both with urticaria resulting from type I allergy and with allergic contact dermatitis due to delayed type IV hypersensitivity. The potentiating effects of other chemicals present in the workplace, such as dimethylformamide, should be further explored.

These findings indicate that uronium salts have a high potential for inducing respiratory and skin hypersensitivity reactions. Stringent work hygiene programs should be implemented to minimise airborne and skin exposure to peptide coupling reagents. Exposed workers should be carefully observed for the development of respiratory and skin symptoms.

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Comments

Evidence Table: Asthma in a chemist due to TBTU (new cause)

10/9/2008