Associations between prenatal exposure to polychlorinated biphenyls and neonatal thyroid-stimulating hormone levels in a Mexican-American population, Salinas Valley, California.
BACKGROUND
Studies have reported that prenatal exposure to polychlorinated biphenyls (PCBs) may alter neurodevelopment in both humans and animals. Furthermore, prenatal exposure to some PCB congeners and commercial mixtures has been shown to decrease free and total thyroxine (T(4)) blood levels in animals. Because thyroid hormones (TH) are essential for normal neurologic development, it has been suggested that the deleterious neurodevelopmental effect of PCBs may occur through TH disruption. PCBs may in turn affect TH levels by inducing the microsomal enzyme uridinediphosphate glucuronosyltransferase (UDP-GT), which is involved in TH elimination.


OBJECTIVE
Our goals were to group PCB congeners based on their potential to induce microsomal enzymes in animals, and to examine the relationship between neonatal TSH levels and prenatal exposure to PCB congeners grouped according to their structure and potential mechanisms of action.


METHODS
We measured the concentration of 34 PCB congeners in serum samples collected from 285 pregnant women and the thyroid-stimulating hormone (TSH) levels in their children's blood collected shortly after birth.


RESULTS
We found no association between the sum of PCB congeners, the toxic equivalents, or structure-based groupings (mono- or di-ortho substituted congeners), and TSH blood concentration. However, we found a positive association between the sum of congeners suspected to be UDP-GT inducers (more specifically cytochrome P450 2B inducers) in animals and neonatal TSH levels. In individual congener analyses, PCBs 99, 138, 153, 180, 183, 187, 194, and 199 were positively associated with neonatal TSH levels after adjustment for covariates. PCBs 194 and 199 remained significant after adjustment for multiple hypothesis testing.


CONCLUSIONS
Our results support grouping PCB congeners based on their potential mechanism of action of enzyme induction when investigating associations with TH. Findings also suggest that PCBs affect TH homeostasis even at the low background level of exposure found in the CHAMA-COS (Center for the Health Assessment of Mothers and Children of Salinas) population.
Chevrier
Jonathan
J
Center for Children's Environmental Health Research, School of Public Health, University of California, Berkeley, California 94704-7380, USA.
Eskenazi
Brenda
B
Bradman
Asa
A
Fenster
Laura
L
Barr
Dana B
DB
D000293:Adolescent; D000328:Adult; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects*; D004781:Environmental Exposure / Q000009:adverse effects*; D005260:Female; D014453:Glucuronosyltransferase / Q000187:drug effects*; D006801:Humans; D007231:Infant, Newborn; D017058:Mexican Americans; D008875:Middle Aged; D011078:Polychlorinated Biphenyls / Q000737:chemistry / Q000145:classification / Q000633:toxicity*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000097:blood / Q000453:epidemiology / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood / Q000187:drug effects*
D013972:Thyrotropin; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D014453:Glucuronosyltransferase