Nicotine Blocks Estrogen Production in Women’s Brains

The production of estrogen in the thalamus appears to be curtailed by just one dose of nicotine, equivalent to that in a cigarette, reveals a whole brain analysis of healthy women in the first study of its kind.

The findings were presented at the 35th European College of Neuropsychopharmacology (ECNP) Congress.

The researchers performed both MRI and positron emission tomography (PET) scans in 10 healthy women using a tracer that binds to aromatase, also known as estrogen synthase.

They found that, following an intranasal spray, delivering 1 mg of nicotine, there was a significant reduction in estrogen synthase in both the right and left thalamus.

“For the first time, we can see that nicotine works to shut down the estrogen production mechanism in the brain of women,” said lead researcher Erika Comasco, PhD, Department of Neuroscience, Uppsala University, Sweden, in a release.

“We were surprised to see that this effect could be seen even with a single dose of nicotine, equivalent to just one cigarette, showing how powerful the effects of smoking are on a woman’s brain.”

Emphasizing the preliminary nature of the study and the need for a larger sample, she added: “We’re still not sure what the behavioral or cognitive outcomes are; only that nicotine acts on this area of the brain.

“However, we note that the affected brain system is a target for addictive drugs, such as nicotine.”

Previous research has revealed that women are less successful at quitting smoking than men, and appear to be more resistant to nicotine replacement therapy, and experience more relapses.

There is evidence to suggest that there is a complex interaction between sex and steroid hormones and the reward effect of nicotine, modulated by the dopaminergic system.

Moreover, women who smoke enter menopause earlier than non-smokers, and have lower plasma estrogen levels, Camasco told Medscape Medical News.

Comasco explained that “besides its role in reproductive function and sexual behavior, estrogen has an impact on the brain wherever there are receptors, which is basically regions that are related to emotional regulation, cognitive function, and so on.”

Estrogen, she continued, has two main mechanisms of action, via dopaminergic and serotonergic signaling. However, levels of the hormone cannot be measured directly in the brain.

The researchers therefore turned to estrogen synthase, which regulates the synthesis of estrogen, and is highly expressed in the limbic system, a brain region associated with addiction.

Moreover, estrogen synthase levels can be measured in vivo, and previous animal studies have indicated that nicotine inhibits estrogen synthase.

To investigate its impact in humans, the researchers performed structural MRI and two [11C]cetrozole PET scans in 10 healthy women.

The assessments were performed before and after the nasal administration of 1 mg of nicotine, the dose contained in one cigarette, via two sprays of a nasal spray containing 0.5 mg of nicotine.

A whole brain analysis was then used to determine changes in non-displaceable binding potential of [11C]cetrozole to estrogen synthase between the two scans to indicate the availability of the enzyme at the two time points.

The results showed that, at baseline, high availability of estrogen synthase was observed in the thalamus, hypothalamus, and amygdala, with the highest levels in the right and left thalamus.

However, nicotine exposure was associated with a significant reduction in estrogen binding bilaterally in the thalamus when averaged across the participants (P < .01).

Region-of-interest analysis using within-individual voxel-wise comparison confirmed reduced estrogen synthase levels in both the right and left thalamus (P < .05), as well as in the subthalamic area.

Next, Comasco would like to test the impact of nicotine on estrogen synthase in men.

While men have lower levels of estrogen then women, “the reaction will take place anyway,” she said, although the “impact would be different.”

She would also like to look at the behavioral effects of reductions in estrogen synthase, and look at the effect of nicotine from a functional point of view.

Wim van den Brink, MD, PhD, professor of Psychiatry and Addiction at the Academic Medical Center, University of Amsterdam, Netherlands, commented that this is an “important first finding.”

“Smoking has many adverse effects in men and in women, but this particular effect of nicotine on the reduction of estrogen production in women was not known before,” he added in the release.

However, he underlined that tobacco addition is a “complex disorder” and it is “unlikely that this specific effect of nicotine on the thalamus explains all the observed differences in the development, treatment, and outcomes between male and female smokers.”

“It is still a long way from a nicotine-induced reduction in estrogen production to a reduced risk of nicotine addiction and negative effects of treatment and relapse in female cigarette smokers, but this work merits further investigation,” van den Brink said.

The study was funded by the Science for Life Laboratory/Uppsala University.

No relevant financial relationships were declared.

35th European College of Neuropsychopharmacology (ECNP) Congress. Abstract P.0346. Presented Oct. 16, 2022.

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