A study in mice has linked mothers’ exposure to smoke to their offsprings’ development of cerebral palsy and cognitive problems.
The study, “Maternal Cigarette Smoke Exposure Worsens Neurological Outcomes in Adolescent Offspring with Hypoxic-Ischemic Injury,” was published in the journal Frontiers in Molecular Neuroscience.
Depriving a fetus of oxygen, either before or around the time of birth, can cause hypoxic-ischemic brain damage. The cause of this injury, oxygen deprivation to the brain, has been linked to diseases such as cerebral palsy and seizures. A hallmark of cerebral palsy is increased cell death in parts of the brain that are responsible for movement and memory.
A lot of oxygen is required for the brain to develop properly. Cells components known as mitochondria need it to create energy.
Scientists say a hypoxic-ischemic brain injury can rapidly decrease energy production. This increases brain damage and the production of molecules called free radicals that further damage mitochondria.
Previous studies have shown that when a pregnant woman smokes, it can lead to lack of oxygen and brain damage in a fetus.
An Australian study took the findings further. It found a connection between a mother’s exposure to smoke and an increase in brain cell death in her adult offspring. The study was also done in mice.
The same researchers decided to see if a mother’s exposure to smoke would lead to severe neurological damage in her offspring after a hypoxic-ischemic brain injury early in the offspring’s life. Researchers did the study to clarify the mechanism through which diseases such as cerebral palsy can develop from a mother smoking.
“By identifying the mechanism, we will be better able to identify potential preventative strategies and improve the neurological outcome in babies of smoking mothers,” Hui Chen, a senior lecturer at the University of Technology Sydney, said in a press release. He was the study’s lead author.
The team exposed half of a group of female mice to cigarette smoke before they mated, while they were pregnant, and while they were producing milk for their offspring. The other half of the mice breathed normal room air.
Ten days after the babies’ births, researchers blocked the left heart artery of half of them in each group, then exposed them to 8 percent oxygen — much less than normal. This led to hypoxic-ischemic brain injury.
The team looked at the babies’ condition 40-44 days after birth. The offspring of mothers exposed to smoke had grown less than those whose mothers had breathed normal air.
Researchers used grip traction and foot fault tests to assess offsprings’ movement function. Mice whose mothers had been exposed to smoke had less forelimb muscle strength and movement coordination than those in the control group.
Offspring with hypoxic-ischemic brain damage had even worse muscle strength, regardless of whether their mothers had been exposed to smoke. This indicated that both smoke exposure to mothers and brain damage in offspring led to less movement function.
“In this study, even without postnatal” hypoxic-ischemic brain injury, mice whose mothers had been exposed to smoke “displayed both motor [movement] and cognitive dysfunction, as has been previously observed in human studies,” the researchers wrote. Exposing mothers to smoke did not significantly worsen most of the functional problems in their brain-damaged offspring “except for short-term memory function,” the team wrote.
Exposing mothers to smoke also increased their offsprings’ anxiety levels, the study showed. In contrast, a brain injury did not increase their anxiety levels. In fact, an injury actually normalized anxiety levels in mice whose mothers had been exposed to smoke.
“We found that pups from smoking mothers are more clumsy at adolescent age, have less strength in their limbs, are more anxious, and have poor memory function, which may affect their learning ability,” Chen said.
Exposure to smoke was also associated with increased levels of cell death biomarkers, which were even higher when an offspring had a brain injury. Another findings was that brain-damaged mice had higher levels of biomarkers of inflammation and mitochondria breakdown. This suggested that a brain injury can exacerbate cell death stemming from a mother’s exposure to smoke.
The team concluded that a mother’s exposure to smoke and an offspring’s early brain injury can lead to conditions such as cerebral palsy. The lesson is that mothers should quit smoking well ahead of pregnancy, they said.
“What we have observed so far is that in order to avoid harm to their baby, mothers need to give up smoking several months or even years before their pregnancy, as smoking will affect the quality of their eggs before they are even fertilised,” Chen said.
One of the ways to prevent a fetus from being brain-damaged would be to give mothers antioxidant supplements, the team said. These would counter the free radicals that mitochondria damage generates.
A previous study that the Australians conducted showed that giving pregnant mothers exposed to cigarette smoke antioxidant therapy improved their offsprings’ health outcomes.
“The next step will be to use such a treatment to improve functional outcomes in pups from the smoking mothers,” Chen said. “However, the message for the public is if you want a healthy baby, you need to stop smoking long before you plan for the pregnancy.”