The Lung-Brain Axis
DESCRIPTION:
Lung-Brain Axis: Nicotine damages the brain! A new effect of nicotine: in smoking and e-cigarettes. Mechanisms, inflammation and the immune system.
Lung-brain axis: How nicotine damages the brain
Smoking is harmful; that is well known. Less well known is that the damage does not end where one might expect it to. A new study in Science Advances describes a lung-brain axis through which nicotine directly interferes with the brain’s iron metabolism. Specialised lung cells release exosomes that disrupt iron metabolism. (Exosomes are tiny vesicles (30–150 nm) secreted by cells that act as messenger molecules for intercellular communication. They transport signals relating to tissue regeneration and wound healing, for example. The health consequences of this signalling pathway extend to dementia and also affect vapers.
What happens throughout the body when smoking: the current understanding
Smoking is a holistic risk factor; the effects of nicotine do not affect the lungs alone. Within seconds of inhalation, nicotine reaches the brain via the bloodstream. It binds to target molecules (nicotinic acetylcholine receptors) and triggers the release of dopamine, the biochemical basis of nicotine dependence.
The well-known health consequences of tobacco and smoking for the brain therefore follow several pathways:
Blood vessel walls: The alkaloid causes blood vessels to constrict, increases heart rate and blood pressure, promotes atherosclerosis, and thus chronically reduces the oxygen supply to the brain. This increases the risk of vascular dementia.
Inflammation: Cigarette smoke activates immune cells and causes persistent chronic inflammation. This inflammatory burden is considered the link between tobacco use and cognitive decline.
Oxidative stress: Tobacco smoke contains substances that generate high concentrations of free radicals and overload the antioxidant defence systems, directly damaging neurons.
These mechanisms were long considered a complete explanation. The current study shows: they are not.
Underestimated lung cells
The lungs contain a group of highly specialised cells: pulmonary neuroendocrine cells (PNECs). They function both as chemical sensors and as producers of neurotransmitters and hormones. They detect stimuli in the airways, respond to oxygen deprivation and communicate with distant target organs via chemical signals.
PNECs account for less than 1% of all lung cells. Due to their rarity, they have been difficult to culture. The research team at the University of Chicago generated PNECs from human pluripotent stem cells, known as induced pulmonary neuroendocrine cells (iPNECs), thereby enabling mechanistic analyses on a sufficient scale for the first time.
The new signalling pathway: exosomes disrupt iron metabolism
When iPNECs were exposed to the alkaloid in the laboratory, they released large numbers of transport vesicles. These alkaloid-stimulated exosomes contained high levels of cerotransferrin, an iron-binding molecule (glycoprotein).
Neurons that took up these exosomes responded with altered iron metabolism:
· Transferrin receptor 1 (TFR1): Upregulated, increased iron uptake into the cell
· Divalent metal transporter 1 (DMT1): More iron enters the cell
· Duodenal cytochrome b (DcytB): Altered iron chemistry (reduction)
The consequences: iron homeostasis is disrupted, triggering oxidative stress; energy reserves (ATP) are depleted; and neurons are damaged. Additionally, levels of alpha-synuclein, a protein molecule whose accumulation is a hallmark of Parkinson’s disease, increased. When TFR1 was inhibited, these effects were mitigated. Iron import is the critical step.
Why is a disrupted iron metabolism serious?
Iron is essential in the brain: for nerve fibre insulation (myelination), for the production of dopamine and serotonin, and for energy production within cells (mitochondria). However, excessively high iron concentrations are toxic.
Excess free iron promotes the formation of reactive oxygen species. This process leads to ferroptosis, a form of cell death (caused by lipid peroxidation of the cell membrane). Elevated iron concentrations in brain regions are well documented in Alzheimer’s, Parkinson’s and other neurodegenerative diseases.
In short, nicotine binds to PNECs, which then release a massive number of signals that disrupt iron metabolism in the brain, with markers similar to those seen in neurological diseases.
Why electronic cigarettes are just as harmful
This signalling pathway is triggered by nicotine itself, not by the combustion products of tobacco smoke. This clearly has a direct implication for vaping.
Those who switch from smoking to vaping avoid tar, carbon monoxide and other harmful substances found in tobacco smoke. However, vaping does not bypass the lung-brain pathway. Vaping nicotine-containing liquids triggers the same biological cascade: nicotine – PNEC – exosomes – iron metabolism in the brain. Quitting smoking, rather than simply replacing it with vaping, is the only effective step.
This is particularly relevant because e-cigarettes are regarded, especially among young people, as a supposedly safe alternative. The data show that the risk of brain changes arises from nicotine, regardless of the route of administration. Lung cancer risks resulting from chronic inflammation in the airways affect both forms of consumption equally.
Interpretation of the results
The study demonstrates a molecular signalling pathway in cell cultures and in a mouse model! It measures markers associated with neurodegeneration. This does not yet provide evidence of an effect in humans.
Further investigations would be necessary for this: exosome profiles in the blood of smokers and comparisons with cognitive changes over decades. Such data does not exist. What the study achieves: it identifies a new signalling pathway, identifies TFR1 as a therapeutic target and shows that the lungs are more actively involved in cerebral pathology than previously assumed.
Smoking cessation: What actually helps
The pharmaceutical industry promotes varenicline, bupropion and nicotine replacement products with impressive-sounding relative risk reductions. However, even with medication, absolute abstinence rates after 12 months are usually around 20–25%. Cochrane reviews confirm statistically significant effects, so the results are more modest than the advertising messages suggest. Spontaneous abstinence and the role of self-efficacy beliefs are systematically glossed over in literature closely linked to the pharmaceutical industry.
Withdrawal symptoms, irritability, sleep disturbances and concentration problems have biological causes and subside within weeks for most people. Adrenaline and dopamine, which nicotine releases in the short term, create a feeling of relaxation. Every cigarette alleviates the tension caused by the previous withdrawal, a vicious circle that psychotherapy can break from the outside.
Behavioural therapy therefore achieves comparable long-term effects in well-controlled studies: motivational interviewing, relapse prevention training and addressing the functions of smoking, stress regulation, social integration, identity, and tackling what medication structurally overlooks: the psychological reason why someone smokes.
Conclusion
Smoking damages the brain in more ways than previously known. The lung-brain axis, mediated by specialised cells, shows that the lungs are not passive victims of tobacco use but active transmitters of misdirected signals. Nicotine, not the combustion process, is the trigger. This applies to smokers as well as to anyone who considers vaping an alternative. Those who quit are protecting their brains, now with an additional argument that can be substantiated at a molecular level.
Source
Thakur A, Zhang K, Chen J et al. (2026). Pulmonary neuroendocrine cell-derived exosomes regulate iron homeostasis and oxidative stress in lung neurons. Science Advances. DOI: 10.1126/sciadv.ady2696
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