Germline Effects of Maternal Smoking: A New Study Shows Permanent Impairments to Sperm
Sobinoff et al, “Damaging legacy: maternal cigarette smoking has long-term consequences for male offspring fertility”
Dr. McLaughlin's profile page at University of Newcastle
Eileen McLaughlin, Ph.D, is Deputy Head of Faculty at the School of Environmental and Life Sciences, University of Newcastle, Australia. She has a long-standing interest in the environmental health of human germ cells, both egg and sperm. For example, her work has established that many chemicals used in everyday items such as glues, dyes and pesticides, are potentially toxic to eggs. "There are increasing numbers of women in their 30s who are having difficulty producing a sufficient number of good eggs to conceive. The evidence suggests that this may be influenced by lifetime exposure, probably at very low levels, to environmental toxicants," she says.
But not all toxicants exist at a low level, some can be acute and continuous, including drugs and cigarette smoke. Recently, her lab turned to the question of whether in utero exposure to cigarette smoke can affect the long-term quality of the exposed male’s sperm. This study represents the first comprehensive animal model of maternal smoking on male offspring reproductive function.
In an eye-opening set of findings, their mouse study suggested that maternal cigarette smoke exposure during the gestational/weaning period results in the formation of a reduced spermatogonial stem cell population, impaired spermatogenic development and Sertoli cell dysfunction. Germ cell DNA damage was also among the important findings.
Interviewed by Jill Escher, October 2014
Germline effects of toxicants, including maternal smoking, is the primary subject of this website, so of course I was delighted to learn of your recent paper. What is the history of this project, why did your team suspect cigarette smoke could cause long-term damage to offspring’s sperm?
My group has a long standing interest in oxidative stress – It is well known that human sperm are also affected by oxidative stress (1) and we have already published data to show that the administration of chemicals found in cigarette smoke and that exposure to cigarette smoke in vivo causes oxidative stress and damage to eggs and ovarian follicle development (2,3).
So when we started our project looking at offspring exposed to maternal smoking it was logical to examine both male and females. The female work is still in progress.
1) Aitken RJ, Wingate JK, De Iuliis GN, McLaughlin EA. Mol Hum Reprod. 2007 Apr;13(4):203-11. Analysis of lipid peroxidation in human spermatozoa using BODIPY C11.
2) Sobinoff AP, Pye V, Nixon B, Roman SD, McLaughlin EA. Toxicol Appl Pharmacol. 2012 Apr 1;260(1):70-80 Jumping the gun: smoking constituent BaP causes premature primordial follicle activation and impairs oocyte fusibility through oxidative stress.
3) Sobinoff AP, Beckett EL, Jarnicki AG, Sutherland JM, McCluskey A, Hansbro PM, McLaughlin EA. Toxicol Appl Pharmacol. 2013 Sep 1;271(2):156-67. Scrambled and fried: cigarette smoke exposure causes antral follicle destruction and oocyte dysfunction through oxidative stress.
Could you summarize the major findings of the project and how they fit in with broader research in the area of germline exposures to toxicants?
Smoking in pregnancy remains a world-wide problem with significant minority of young women continuing to smoke despite large scale targeted smoking cessation programs. The effects of in utero of maternal smoking on the male germline have been somewhat controversial – largely due to the long time between exposure and diagnosis of male infertility and retrospective collection of maternal smoking histories and other confounding factors such as diet, alcohol and other environmental exposures.
Obviously it would be ethically unacceptable to expose babies in utero to toxicants in cigarette smoke hence our development of an animal model system. As such this is the first study replicating human maternal smoke exposure and its effects on pups exposed in utero and while lactating. The lactational aspects of the study is important as accidental exposure to dioxin during breast feeding appears to affect human sperm production (4).
4) Mocarelli P1, Gerthoux PM, Needham LL, Patterson DG Jr, Limonta G, Falbo R, Signorini S, Bertona M, Crespi C, Sarto C, Scott PK, Turner WE, Brambilla P Environ Health Perspect. 2011 May;119(5):713-8. doi: 10.1289/ehp.1002134. Epub 2010 Dec 13. Perinatal exposure to low doses of dioxin can permanently impair human semen quality.
Your paper stated that future work should address multigenerational effects of maternal cigarette exposure, including defects in fertility and increased cancer susceptibility in offspring and subsequent generations. But what about developmental impacts?
As part of this study we have been collaborating with respiratory physiologists and immunologists and they have been concentrating on other developmental aspects of the animals. This work is also being written up for publication and will be forthcoming.
Have you considered that epigenetic impairments, including imprinting defects, could affect offspring neurodevelopment and behavior? Dr. Bhide at Florida State University found increased “ADHD-like” behavior in F2 mice of nicotine-exposed pregnancies.
Yes and we have also considered looking at epigenetic changes in male and female offspring as part of a larger study.
What chemicals in cigarette smoking are mutagenic? Or otherwise damaging to sperm, or other cells for that matter?
Given our past work in females we would be concerned about the polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP) and the activation of the detoxification pathways which are likely to produce very reactive metabolites which could cause direct DNA damage.
Epimutagenic—again there is evidence to suggest that cigarette smoke also contains epimutagens such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) which could influence gene expression in offspring (5)
5) Pulling LC1, Vuillemenot BR, Hutt JA, Devereux TR, Belinsky SA Cancer Res. 2004 Jun 1;64(11):3844-8. Aberrant promoter hypermethylation of the death-associated protein kinase gene is early and frequent in murine lung tumors induced by cigarette smoke and tobacco carcinogens.
Can you tell me more about the high mitochondrial DNA mutational load in the testes of adult offspring? How might that manifest in the health of the offspring?
The data published in this paper was part of a pilot study in which we have begun to look at the mitochondria in the testes and oocyte. We are concerned that the damaged mitochondrial DNA will lead to a) a loss if the production of ATP (the cells power supply) – this would correlate with the poor swimming ability of the sperm and b) the production of reactive oxygen species which could lead to oxidative stress – this would correlate with the higher levels of nuclear DNA damage we found in the sperm of pups who had been exposed to maternal cigarette smoke. As males typically don’t pass on their mitochondria to their offspring – mitochondria are transmitted via the egg to offspring - this would likely result in subfertility in the fathers and DNA damage in the offspring which may predispose to disease including cancer.
What about eggs? Is there evidence in other studies that maternal smoking causes long-term damage to fetal germ cells, either in terms of mutation, epimutation, or other pathology?
Those studies are in progress at the moment – our preliminary results suggest that the eggs may be damaged and that this results in increased rates of miscarriage in subsequent generations.
In the United States, young people are increasingly turning to e-cigarettes, which is marketed as a safer alternative to traditional cigarettes. But I’ve seen at least one study demonstrating adverse effects of the vapor on methylation in sperm. Have you seen such studies? Should we be concerned about this popular new drug?
Yes – we agree that little to no research has been conducted on the safety of e-cigarettes and no research on their effects on offspring – so we have planned to conduct similar studies to those we have published on maternal and offspring reproductive health.
What about the idea of taking a cohort of human male non-smokers known to have been cigarette-exposed in utero and analyzing their sperm for morphological, genetic, and epigenetic defects, as compared to controls?
Yes this is an excellent idea – more difficult to do as most studies have been conducted in couples attending assisted reproduction clinics – thus they may also have other factors predisposing towards infertility. So a randomised controlled trial would be a good alternative – however it is often difficult to control for other environmental exposures and lifestyle factors.
Aside from cigarette smoke, what other acute exposures concern you, with regard to germline health? What other drugs should we be concerned about? My primary interest lies in synthetic hormone drugs, such as those I had been exposed to in utero, but what others might warrant our concern?
Our other studies have been restricted to known ovarian toxicants (6) – but we have observed effects on oocyte quality and ovarian follicular development after exposure to 4-vinylcyclohexene diepoxide (VCD) ovotoxic metabolite of 4-vinylcyclohexene used as a solvent for epoxides in industry, methoxychlor (MXC) a synthetic organochlorine insecticide , and menadione (MEN) a synthetic quinone vitamin K3.
6). Sobinoff AP1, Pye V, Nixon B, Roman SD, McLaughlin EA. Toxicol Sci. 2010 Dec;118(2):653-66. Adding insult to injury: effects of xenobiotic-induced preantral ovotoxicity on ovarian development and oocyte fusibility.
Why Pregnant Women Who Smoke Might Have Kids With Worse Sperm
(Time Magazine, October 2014)