Abstract
Dear Sir, Lee and co-workers presented a study of multiple myeloma among Swedish construction workers. The only occupational exposure related to myelomawas diesel exhaust1 and this association was consistent with results from several previous studies. However, I think there is at least 1 chemical compound that ought to be further emphasized in the discussion with regard to a relationship between diesel exhaust exposure and the occurrence of myeloma. Pristane (2,6,10,14-tetramethypentadecane) is a branched chain hydrocarbon which is thought to be derived from the phytol moiety of chlorophyll. The content in crude mineral oils is 0.5% or less.2 Today pristane, injected intraperitoneally, is the most widely used oil in order to induce chronic inflammation and experimental plasma cell tumors and multiple myeloma in mice.3 Emissions of pristane from 2 heavy duty diesel vehicles (a bus and a truck) were investigated. The emissions varied between 15 and 380 g/km when different fuels were used.4 Pristane has been measured within the greater Los Angeles urban area (mean 68 and max 390 ng/m)5 and also in New York City after 9/11 (range 16 to 68 ng/m).6 Inhalation of diesel exhaust causes an increase of interleukin-6 (IL-6) in bronchial wash among human volunteers.7 Furthermore IL-6 is a critical and specific factor in plasma cell tumor development. One strong evidence is the fact that IL-6 knockout mice are refractory to plasma cell tumor induction by pristane.3 Human adipose tissue produce substantial amounts of IL-6 and this secretion might represent 10–30% of circulating levels. Plasma levels of IL-6 are highly correlated with body mass8 and this fact may explain the positive relation between BMI and multiple myeloma observed in some epidemiological studies. In conclusion further studies are needed in order to explore different chemical compounds in diesel exhaust in order to understand the relation between exposure and occurrence of multiple myeloma. Further developments of engines, fuels and lubrication must aim to reduce exhaust regarding specific and general emissions. Yours sincerely, Bengt SJOGREN
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