Although sporadic effects were observed at lower dose levels, the most consistent effects on the immune response were observed at the 2000 ppm dose level in the F0 generation female and F1 generation male and female animals.
Nonylphenol, an endocrine disruptor, is a polyethoxylated nonylphenol (NP) which is used extensively as a non-ionic detergent surfactant in industrial applications, and undergoes biodegradation during sewage treatment to persistent metabolites, including NP and di- and monethoxylated NP. Nonylphenol was first reported to have estrogenic activity based on its induction of proliferation and up-regulation of the progresterone receptor in human estrogen-sensitive breast tumor cells (Soto et al., 1991, White et al., 1994). Estrogens are potent regulatory factors for many developmental and physiological responses. Untimely exposure to natural or synthetic estrogenic compounds may have serious consequences to the reproductive cycle in humans and animals (Korah, 1993; Ginsburg 1994). The immunological evaluation of nonylphenol-exposed animals was undertaken by the National Toxicology Program/NIEHS in cooperation with the National Center for Toxicological Research (NCTR).
Nonylphenol is one of five endocrine disruptor compounds nominated by the National Toxicology Program (NTP) for reproductive assessment studies, neurotoxicological and immunotoxicological studies, and cancer bioassay studies. The title of this project is "Effects of Endocrine Disrupting Chemicals on Fertility and Reproductive Tract Cancers". These studies were carried out as an interagency agreement between National Environmental Health Science (NIEHS) and National Center for Toxicology Research (NCTR) with the immunotoxicological component being a portion conducted outside of the NCTR facility in Jefferson, Arkansas. Thus, the purpose of these reported studies was to determine the potential effects of nonylphenol on the immune system. The nonylphenol/immunotoxicology code identification from the National Center for Toxicological Research is E2125.14.
The exposure times and the doses, 0, 25, 500 and 2000 ppm, were determined by NCTR. Nonylphenol was procured and administered in feed by personnel at NCTR in Jefferson, Arkansas. The control rats received casein NIH-31C as the feed. The studies were conducted in male and female Sprague Dawley rats, strain 23 CD, from the NCTR breeding colony. The F0 generation female rats received the test article for 65-72 days beginning 7 days into gestation. The F1 generation male and female rats received the test article in utero for 14 days and continued postpartum until 77-82 days. On the day of sacrifice, whole spleens or flushed bone marrow cells were placed in tubes with the appropriate medium, packed in wet ice, and shipped to the Medical College of Virginia (MCV) Campus of Virginia Commonwealth University, Richmond, VA, for assay evaluation on the following day. The assay days of the study were conducted between 9 April 1998 and 19 May 1998
The baseline toxicology studies are summarized in Table ES-1. Exposure to nonylphenol resulted in a statistically significant decrease in terminal body weight, both in the F0 generation female and F1 generation female rats. A decrease of 13% (F0 female) and 16% (F1 female) as compared to the vehicle controls was observed at the highest dose of 2000 ppm.
Exposure to nonylphenol resulted in a statistically significant increase in the relative spleen weight (% body weight) in the F1 generation male and female rats. The increase at the high dose only, 2000 ppm, was 15% and 17%, respectively. In the F1 generation female rat study, a significant increase in relative thymus weight was observed at the 25 ppm (21%) and 2000 ppm (25%) doses.
The F1 generation male and female rats were evaluated for nonylphenol exposure effects on bone marrow cell number, colony-forming units, CFU-E (recombinant erythropoietin), CFU-GM (granulocyte-monocytes progenitors) and CFU-M (macrophage progenitors) and DNA synthesis. A statistically significant decrease of 29% in CFU-E/2 x 105 cells was seen in the F1 generation male rats at 2000 ppm. With the F1 generation female rats, a significant increase in the CFU-GM/1 x 105 cells of 25% was observed at the high dose along with an increase of 34% in the DNA synthesis.
Table ES-2 summarizes the immunology studies. For the F0 generation female rats exposed to nonylphenol, referring to the absolute values of the splenic differential, no alteration in numbers were observed. In the F1 generation male rats, statistically significant increases were seen at the high dose in the spleen cell number (38%), B cells (47%), T suppressor cells (39%) and the macrophage cells (50%). For the F1 generation female rats, statistically significant increases were observed in the T cells, T helper cells and the macrophages, in the middle doses ranging from 38 to 50%.
In the spleen antibody-forming cell (AFC) response to T-dependent antigen, sheep erythrocytes, no alterations were observed in the F0 generation female rats nor the F1 generation male and female rats.
No effect was seen in receptor-mediated proliferation in the F0 generation female rats stimulated with anti CD3. In spleen cells from F1 generation male and female rats, stimulation with the anti-CD3 receptor-mediated proliferation produced a statistically significant dose-dependent increase in proliferation of the unstimulated spleen cells from 44 to 92% and in the stimulated spleen cells from 23 to 69% as compared to the vehicle control.
In the F0 generation female rats and the F1 generation male rats, no statistically meaningful alterations were observed in natural killer cell activity. In the F1 generation female rats, a statistically significant increase was demonstrated only at the 200:1 effector-to-target (67%) 2000 ppm dose group which was not supported by the lytic unit/107 cells. However, the lytic units per spleen were significantly increased up to 112%.
Nonylphenol, when administered in the feed at closes of 25, 500, and 2000 ppm, produced a measurable decrease in terminal body weight at the 2000 ppm dose. The results from the immunotoxicological evaluation demonstrated that nonylphenol exposure did not impact on the immunocompetence of the F0 generation female rats. However, for the F1 generation male and female rats, exposure to nonylphenol for 77 days resulted in minimal increases in T cell numbers and marked increases in T cell function.