Case Studies

Additive toxicity of limonene and 50% oxygen and the role of glutathione in detoxification in human lung cells

Limonene has many commercial applications and has been introduced as an environmentally acceptable solvent replacing halogenated hydrocarbons. Occupational exposure to limonene presumably occurs simultaneously with other chemicals including oxidative agents and may exert a heavy strain on cellular detoxifying capacity resulting in synergistic effects. The present study used oxygen as an example of an ubiquitous oxidative and radical forming agent and investigated the combination effects with limonene on human lung cells. Mechanistic information was gained by comparing the toxicity of limonene with a major oxidation product, limonene 1,2-epoxide, and by the involvement of glutathione in cellular detoxification. At cell culture conditions most similar to the in vivo situation oxygen did not increase the toxicity of limonene beyond an additive effect. The results further indicated that limonene 1,2-epoxide was not the active compound in limonene toxicity. Experimental evidence suggests that detoxification of limonene in human lung cells primarily occurs by mechanisms not involving the glutathione system and point to possible long-term effects of limonene exposure. The present knowledge indicates clearly that the mechanism of action of limonene on biological systems and particularly in combination with oxidative compounds still remains to be elucidated. In light of the frequent exposure of humans to such combinations further investigations into this issue are highly recommended.

Contact allergy to oxidized d-limonene among dermatitis patients

d-Limonene, obtained as a by-product from the citrus juice industry, was introduced on the market as a more environmentally friendly defatting and cleaning agent than the traditionally used organic solvents. Autoxidation of d-limonene readily occurs to give a variety of oxygenated monocyclic terpenes that are strong contact allergens. The aim of the present study was to investigate the prevalence of contact allergy to air exposed d-limonene among dermatitis patients. A fraction consisting of d-limonene hydroperoxides was also tested. Screening with oxidized d-limonene will detect cases of allergic contact dermatitis. Additional cases were detected when testing with the fraction of limonene hydroperoxides. The proportion of positive patch test reactions to oxidized d-limonene was comparable to that seen for several of the allergens within the standard series. An increased use of d-limonene containing allergenic oxidation products in industry where high concentrations are used, as well as in domestic exposure, might result in contact sensitization and dermatitis. Patients reacting to d-limonene often reacted to fragrance mix, balsam of Peru and colophony in the standard series.