Report Date: August 2012
The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
Black cohosh (Actaea racemosa) is an herbal supplement that is sold over-the-counter for the management of menopausal symptoms, menstrual irregularities, and arthritis. Liver injury with features mimicking autoimmune hepatitis has been reported following the use of BCH (Nisbet and O'Connor, 2007; Guzman et al., 2009). BCH was nominated by both the National Cancer Institute and the National Institute of Environmental Health Sciences for toxicity evaluation based on its widespread use by pre- and post-menopausal women as an alternative to hormone replacement therapy. The National Toxicology Program has previously conducted a 90-day toxicity study in three week-old female Wistar Han rats using an ethanolic extract of BCH at doses of 0, 15, 125, 250, 500, and 1000 mg/kg by gavage (Mercado-Feliciano et al., 2012). Results from that study indicated that BCH exposure produced decreased thymus weights and minimal thymic cell apoptosis. The changes in the thymus suggest the potential for immunotoxicity.
The NTP requested that a dose range-finding study be performed to establish the potential effects of BCH on the immune system. These studies were conducted in female B6C3F1/N mice. Five BCH dose levels (62.5, 125, 250, 500, and 1000 mg/kg) were utilized in the 28 day oral gavage study. BCH was prepared weekly as a solution in the vehicle 0.5% methylcellulose.
Administration of BCH did not adversely affect interim body weights during the course of these studies, although significant increases in body weight gain were observed. In the majority of the studies conducted, no effects were observed on the weights of the major organs of the immune system, the thymus and the spleen, although absolute spleen weights were increased at doses ≥ 500 mg/kg in one study. Liver weights were significantly increased at the high dose (1000 mg/kg). Mixed effects on hematology were observed. Mean corpuscular volume, mean corpuscular hemoglobin, and the percent of neutrophils in the blood were increased at the 500 mg/kg and/or 1000 mg/kg BCH doses. Thymus cell numbers and absolute numbers of various thymus cell subpopulations were all significantly decreased at the 250 mg/kg dose level only. Spleen cell numbers were unaffected, however decreases in the absolute numbers of splenic B cells, total T cells, T cell subsets, natural killer cells, and macrophages were all observed at the 1000 mg/kg dose. Treatment with BCH had no overall effect on the plaque assay, sheep red blood cell enzyme-linked immunosorbent assay, or keyhole limpet hemocyanin ELISA, suggesting a lack of effect on humoral immunity. Mixed results were observed in evaluations of cell-mediated immunity. The mixed leukocyte response was increased in one study and unaffected in another study. No effects were observed on the anti-CD3 mediated proliferative response or on the delayed-type hypersensitivity response to Candida albicans, however, increases in cytotoxic T-lymphocyte activity were observed at doses greater than or equal to 125 mg/kg. Innate immunity, as evaluated by examining the cytotoxic activity of NK cells and the functional activity of the mononuclear phagocytic system was not affected by treatment with BCH. Finally, no overall effects were observed on bone marrow cell numbers, bone marrow colony-forming units, or the various populations of bone marrow differentials when evaluated as absolute values.