Similar to
asbestos fibers, nonregulated
mineral fibers can cause
malignant mesothelioma (MM). Recently, increased proportions of women and young individuals with MM were identified in southern Nevada, suggesting that environmental exposure to carcinogenic fibers was causing the development of MM.
Palygorskite, a fibrous
silicate mineral with a history of possible carcinogenicity, is abundant in southern Nevada. In this study, our aim was to determine whether
palygorskite was contributing to the development of MM in southern Nevada. While
palygorskite, in vitro, displayed some cytotoxicity toward primary human mesothelial (HM) cells and reduced their viability, the effects were roughly half of those observed when using similar amounts of
crocidolite asbestos. No Balb/c (0/19) or MexTAg (0/18) mice injected with
palygorskite developed MM, while 3/16 Balb/c and 13/14 MexTAg mice injected with
crocidolite did. Lack of MM development was associated with a decreased acute inflammatory response, as injection of
palygorskite resulted in lower percentages of macrophages (p = .006) and neutrophils (p = .02) in the peritoneal cavity 3 d after exposure compared to injection of
crocidolite. Additionally, compared to mice injected with
crocidolite,
palygorskite-injected mice had lower percentages of M2 (
tumor-promoting) macrophages (p = .008) in their peritoneal cavities when exposed to fiber for several weeks. Our study indicates that
palygorskite found in the environment in southern Nevada does not cause MM in mice, seemingly because
palygorskite, in vivo, fails to elicit
inflammation that is associated with MM development. Therefore,
palygorskite is not a likely contributor to the MM cases observed in southern Nevada.