Contact sensitizing potential of annatto extract and its two primary color components, cis-bixin and norbixin, in female BALB/c mice
The present studies were performed to examine the contact allergenic effects of an annatto extract (ANT) in female BALB/c mice. ANT at 5-10% induced a greater than threefold increase in lymph node cell proliferation when compared to the control in the LLNA. Moreover, a significant increase in the percent ear swelling at 24h after ANT challenge was observed in the MEST. A significant increase in the percentage of B cells was also observed. To determine which of the two predominant coloring components (norbixin and bixin) in ANT was responsible for the sensitizing effects of ANT, norbixin was subsequently examined, with negative results being observed in both the LLNA and MEST following treatment with norbixin (1-20%). These findings suggested that perhaps bixin was responsible for the positive responses in both the LLNA and MEST following exposure to ANT. Therefore, further studies using a partially purified cis-bixin extract were conducted. Positive responses in both the LLNA and MEST were observed in mice treated with cis-bixin at the concentrations as low as 0.1-0.5%. These results have demonstrated that cis-bixin, but not norbixin, is likely a contact sensitizer and contributes to the contact hypersensitivity effects observed following dermal exposure to ANT in mice.