Environmental estrogens and reproductive health: a discussion of the human and environmental data

Estrogenic activity of certain xenobiotics is an established mechanism of toxicity that can impair reproductive function in adults of either sex, lead to irreversible abnormalities when administered during development, or cause cancer. The concern has been raised that exposure to ambient levels of estrogenic xenobiotics may be having widespread adverse effects on reproductive health of humans and wildlife. The purpose of this review is to evaluate (a) the nature of the evidence supporting this concern, and (b) the adequacy of toxicity screening to detect, and risk assessment procedures to establish safe levels for, agents acting by this mechanism. Observations such as adverse developmental effects after maternal exposure to therapeutic levels of the potent estrogen diethylstilbestrol or male fertility problems after exposure to high levels of the weak estrogen chlordecone clearly demonstrate that estrogenicity is active as a toxic mechanism in humans. High level exposures to estrogenic compounds have also been shown to affect specific wildlife populations. However, there is little direct evidence to indicate that exposures to ambient levels of estrogenic xenobiotics are affecting reproductive health. Reports of historical trends showing decreasing reproductive capacity (e.g., decreased sperm production over the last 50 years) are either inconsistent with other data or have significant methodologic inadequacies that hinder interpretation. More reliable historical trend data show an increase in breast cancer rate, but the most comprehensive epidemiology study to data failed to show an association between exposure to persistent, estrogenic organochlorine compounds and breast cancer. Clearly, more work needs to be done to characterize historical trends in humans and background incidence of abnormalities in wildlife populations, and to test hypotheses about ambient exposure to environmental contaminants and toxic effects, before conclusions can be reached about the extent or possible causes of adverse effects. It is unlikely that current lab animal testing protocols are failing to detect agents with estrogenic activity, as a wide array of estrogen-responsive endpoints are measured in standard testing batteries. Routine testing for aquatic and wildlife toxicity is more limited in this respect, and work should be done to assess the validity of applying mammalian toxicology data for submammalian hazard identification. Current risk assessment methods appear to be valid for estrogenic agents, although the database for evaluating this is limited. In conclusion, estrogenicity is an important mechanism of reproductive and developmental toxicity; however, there is little evidence at this point that low level exposures constitute a human or ecologic health risk. Given the potential consequences of an undetected risk, more research is needed to investigate associations between exposures and effects, both in people and animals, and a number of research questions are identified herein. The lack of evidence demonstrating widespread xenobiotic-induced estrogenic risk suggests that far-reaching policy decisions can await these research findings.     

p107 and p130 associated cyclin A has altered substrate specificity

We demonstrate that p107 and p130 immune complexes exhibit kinase activity. We have tested such immune complexes with four substrates commonly utilized to assay Cdk activity, including all three known members of the retinoblastoma family. Immunodepletion revealed this kinase activity could be abolished by removal of either cyclin A or Cdk2 but was unaffected by removal of Cdk4 or any D-type cyclin. The appearance of p107 associated activity followed the accumulation of p107 protein. In contrast, the kinase activity associated with p130 immune complexes became apparent after mid-G1, coincident with p130 hyperphosphorylation. GST-Rb, GST-p107, and GST-p130 (where GST indicates glutathione S-transferase) were equally suitable substrates in p107 and p130 immune complex kinase assays, yielding activity equal to 25% of the cyclin A activity present. The p107 and p130 associated activity was unable to phosphorylate histone H1, suggesting the p107 and p130 associated cyclin A/Cdk2 may represent a distinct pool with a distinct substrate specificity. The p107 and p130 associated activity was released from the immune complexes upon incubation with ATP and Mg2+ and exhibited the same substrate preference observed with the untreated immune complex. Our data suggest that p107 and p130 recognize, or form by association, a distinct pool of cyclin A/Cdk2 that preferentially phosphorylates retinoblastoma family members.     

Estimation of variance components for somatic cell counts to determine thresholds for uninfected quarters

The objective of this study was to determine the factors affecting somatic cell count (SCC), to estimate variance components of these factors, and to calculate and evaluate the thresholds for intramammary infection based on SCC. The infection status from 22,467 quarter milk samples from 544 cows in seven herds was determined. Infections status was the most important factor affecting SCC. The increase in SCC was more pronounced for major pathogens than for minor pathogens. Even after adjustment for infection status, the interaction between stage of lactation and parity was significant. For culture-negative samples within a lactation, the shape of the SCC curve was inversely related to the shape of the milk production curve. The shape of the SCC curve was flat for first lactation cows compared with the shape of the SCC curve for cows in subsequent lactations. The effect of clinical mastitis on SCC was significant. The use of SCC thresholds for specific parities and stages of lactation to detect intramammary infection improved quality parameters only slightly over a fixed threshold of 200,000 cells/ml.     

Orthopaedic surgery in hemophilic patients with human immunodeficiency virus

Patients registered at the author's hemophilia center between 1982 and 1994 were studied to establish whether major orthopaedic surgical procedures accelerate the fall of CD4 lymphocyte counts of patients with hemophilia who are infected with the human immunodeficiency virus, and whether patients who had surgery had different rates of development of acquired immune deficiency syndrome or death when compared with patients who did not have surgery. The patients were divided into four groups: Group 1, 22 patients who were human immunodeficiency virus positive undergoing orthopaedic surgery; Group 2, 89 patients who were human immunodeficiency virus positive not undergoing orthopaedic surgery; Group 3, 18 patients who were human immunodeficiency virus negative undergoing orthopaedic surgery; and Group 4, 135 patients who were human immunodeficiency virus negative not undergoing orthopaedic surgery. There was no significant difference between the rates of decline of CD4 lymphocyte counts for patients who were human immunodeficiency virus positive who underwent surgery when compared with human immunodeficiency virus positive patients who did not undergo surgery, nor was there any significant difference between the two human immunodeficiency virus negative groups. There were no significant differences in the rate of development of acquired immune deficiency syndrome or mortality rates between patients who had surgery and those who did not.     

Analysis of variant forms of porcine surfactant polypeptide-C by nano-electrospray mass spectrometry

Electrospray (ES) mass spectrometry has been used to analyse preparations of porcine pulmonary surfactant polypeptide-C (SP-C). A number of variant forms of the native 35-residue dipalmitoylated peptide were detected including (a) C-terminally methylated SP-C, (b) C-terminally methylated and methionine oxidized SP-C, (c) N-terminally truncated, C-terminally methylated and methionine oxidized SP-c, (d) C-terminally elongated, C-terminally methylated and methionine oxidized SP-C, and (e) tripalmitoylated, C-terminally methylated and methionine oxidized SP-C. C-terminal methylation and methionine oxidation are probably a consequence of the sample handling procedure. The occurrence of the C-terminally elongated form of SP-C has implications for the in vivo processing of proSP-C and the Tandem mass spectrometry (MS/MS) was used to confirm the amino acid sequence of SP-C and the presence of palmitoyl groups covalently linked to the peptide. Some of the structures of the variant forms of SP-C were determined by MS/MS.