The parity-related protection against breast cancer is compromised by cigarette smoke during rat pregnancy: observations on tumorigenesis and immunological defenses of the neonate.
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AuthorsSteinetz, Bernard G.
Ng, Sheung Pui
Zelikoff, Judith T.
Bosland, Maarten C.
MetadataShow full item record
AbstractEarly pregnancy is a powerful negative risk factor for breast cancer (BCa) in women. Pregnancy also protects rats against induction of BCa by carcinogens such as N-methyl-N-nitrosourea (MNU), making the parous rat a useful model for studying this phenomenon. Smoking during early pregnancy may lead to an increased risk of BCa in later life, possibly attributable to carcinogens in cigarette smoke (CS), or to reversal of the parity-related protection against BCa. To investigate these possibilities, 50-day-old timed first-pregnancy rats were exposed to standardized mainstream CS (particle concentration = 50 mg/m3) or to filtered air (FA) 4 h/day, Day 2-20 of gestation. Age-matched virgin rats were similarly exposed to CS or FA. At age 100 days, the CS or FA-exposed, parous and virgin rats were injected s.c. with MNU (50 mg/kg body wt), or with MNU vehicle. Mammary tumors (MTs) first appeared in virgin rats 9 weeks post-MNU injection. While no MTs were detected in FA-exposed parous rats until 18 weeks post-MNU, MTs appeared in the CS-exposed parous rats as early as 10 wks (P < 0.02). As no MTs developed in CS-exposed rats not injected with MNU, CS did not act as a direct mammary carcinogen. Serum prolactin concentration on Day 19 of pregnancy in CS-exposed dams was reduced by 50% compared with FA-exposed dams (P < 0.005). CS exposure during a pregnancy may thus 'deprotect' rats, enhancing their vulnerability to MNU-induced BCa. Prenatal CS exposure had no detectable effect on the immune responses of the pups examined at 3, 8 or 19 weeks of age. However, prolactin concentration in stomach contents (milk) of 3-day-old pups suckled by CS-exposed dams was decreased when compared with that of FA-exposed dams (P < 0.032). As milk-borne prolactin modulates development of the central nervous and immune systems of neonatal rats, CS exposure of the dams could adversely affect later maturation of these systems by reducing milk prolactin.
CitationCarcinogenesis 2006, 27 (6):1146-1152
DescriptionLifestyle modulation of cancer & cancer biomarkersLifestyle element evaluated: early pregnancyOutcome studied (cancer or cancer biomarker): breast cancerMethod of biomarker analysis: hormone assays, cytokine assays, lymphocyte proliferation assayStudy type (in vitro, animals, humans): Sprague-Dawley rats Confounders controlled for: smoking Impact on outcome: (P < 0.005) decrease in serum immunoactive prolactin concentration on Day 19 of pregnancy in the rats exposed to CS as compared with FA controls. However, a significant decrease (P Ό 0.032) was observed in the concentration of immunoactive prolactin in the milk of CS- versus FA-exposed dams. KEYWORDS CLASSIFICATION: Animals;cytology;Carcinogens;Female;Killer Cells,Natural;lifestyle modulation of cancer & cancer biomarkers;Lymphocytes;mechanisms of carcinogenesis;metabolism;Male;Mammary Neoplasms,Animal;Methylnitrosourea;New York;prevention & control;Pregnancy;Pregnancy,Animal;Prolactin;Rats;Rats,Sprague-Dawley;Research;Sex Factors;Smoking.