Dr. Benjamin Bickman (2:29)
Welcome to the Metabolic Classroom Podcast. I'm Ben Bickman. Thanks for letting me be your guest professor for the next few minutes. Don't worry about any pop quizzes. I'm here to simply make the science of metabolism clear, practical and engaging before we get started. Just as a reminder, you can listen to both of my podcasts ad free by becoming an insider. Just go to benbickman.com or click on the link at the top of the show. Notes hello and welcome back to the metabolic classroom. I'm your host, Dr. Benjamin Bickman, professor of cell biology and metabolic scientist. Today we are revisiting a topic I've covered before. But honestly, there's just so much fascinating research on this compound that it warrants another deep dive. We're talking about nicotine. And before you click away, I want to be very clear up front, this is not a discussion about smoking. Smoking is unequivocally harmful. The evidence is overwhelming and I would say it's indisputable. What we're exploring today is nicotine itself, the molecule separated from the thousands of other toxic compounds that are found in cigarette smoke. What I've discovered in preparing this episode, or this mini lecture as I prefer to call it, it really was pretty surprising actually. The hole continued to just go deeper and deeper. And I think it's going to surprise you as well. We're going to explore some counterintuitive findings about addiction, dive into nicotine's effects on metabolism just briefly because I touched on that more previously. Examine its anti inflammatory properties and look at some of the remarkable research on conditions like adhd, autism, Tourette syndrome and even cognitive decline. So let's get into it now. Here's something that might challenge everything you thought you knew about cigarette addiction. For decades, we've been told that nicotine is the addictive component of cigarettes, the thing that keeps people coming back. But research from Harvard published in the journal Tobacco Control presents a far more nuanced picture. The researchers. The researchers examined internal toxic tobacco industry documents and found something remarkable. Nicotine, when administered alone, has what they called poor reinforcing effects. In other words, pure nicotine by itself isn't particularly addictive. Think about it. If nicotine were truly the sole driver of addiction, nicotine patches and gum would be irresistibly addictive. People would be going to them as much as they're going to the cigarette. But they're not. Non smokers who try nicotine replacement therapy find it particularly difficult and not very rewarding. So what's actually driving the intense addiction we see with cigarettes? The answer appears to be additives called pyrazines. That's spelled P R Y A Z I N E S or Z I N E S depending on where, which version of English you embrace. These are chemical compounds that the tobacco industry began adding to cigarettes in the 1970s. Particularly to light cigarettes like Marlboro Lights, the industry created what they internally called super juice, a cocktail of pyrozines designed to make cigarettes more appealing and habit forming. Pyrazines work through multiple mechanisms. First, they have chemosensory effects. They create pleasant aromas like nutty, chocolatey or rainbow roasted notes in the cigarette smoke. They smooth out the harsh, irritating effects of smoke on the airways as well. They also stimulate receptors in the nasal lining that may enhance learned behavior and conditioning. And research suggests that they may increase dopamine production in the brain independently of nicotine. The researchers concluded that pyrazines appear to work synergistically with nicotine, optimizing its delivery to the brain while while also enhancing the sensory experience that creates powerful learned associations. They suggested that pyrozines make it easier for non smokers to start, harder for smokers to quit, and easier for former smokers to relapse. That's a heck of a combination. Now, I want to be careful here. This doesn't mean nicotine is harmless or non addictive. It can still possibly create some dependence. But it does suggest that the extreme addictiveness of cigarettes may be more sophisticated product engineering than about nicotine itself. And importantly, it means that nicotine delivered through other means like patches, gums or pouches may not carry the same addiction risk that you would find with cigarette smoke. In fact, I'm being kind of soft in my language. It absolutely doesn't. Now let's get further into this. But before we go into the specific conditions that nicotine can address, we need to understand a fundamental mechanism that explains many of nicotine's effects. That is the cholinergic anti inflammatory pathway. This pathway was discovered by scientists at the Feinstein Institute. And it represents a direct communication line between your nervous system and your immune system. Here's how it works. The vagus nerve. That's the main parasympathetic nerve that runs from your brainstem to your gut and other parts of your body like the adrenal glands or the pancreas. I've talked about it before, but this vagus nerve will release acetylcholine. This acetylcholine binds to something called the alpha 7 nicotinic acetylcholine receptor. And it's found on immune cells like macrophages. When this receptor is activated, it inhibits the production of pro inflammatory cytokines like TNF alpha, interleukin 1, beta and a host of other interleukins. Now here's where nicotine comes in. Nicotine can directly activate these same alpha 7 receptors, essentially mimicking and amplifying this natural anti inflammatory pathway. Research published in Nature demonstrated that the alpha 7 receptor is essential for controlling inflammation and that stimulating it can prevent excessive cytokine release that leads to tissue damage. This has profound implications. It means that nicotine isn't just a stimulant, it's an immunomodulator. And this helps explain why nicotine has shown therapeutic potential in such a wide range of inflammatory conditions, from ulcerative colitis to sepsis to arthritis. Interestingly, this also helps explain why smoking has such a paradoxical relationship with certain diseases. While smoking causes tremendous harm through the toxic compounds that again I'm reiterating and emphasizing, the nicotine component may actually be providing some anti inflammatory benefit, admittedly one that gets lost in the midst of all of the toxic compounds in the smoke. Now, let's talk about metabolism, because this is the metabolic classroom. After all, it's well established that smokers weigh less than non smokers and weight gain after smoking cessation is a major barrier to quitting. But what's actually happening metabolically? Nicotine affects metabolism through several mechanisms. First, it inhibits AMPK activity in the hypothalamus, which decreases appetite and food intake. Second, it increases thermogenesis, your body's heat production, particularly in brown adipose tissue. Research shows smoking can increase 24 hour energy expenditure by about 10%, which translates roughly to an extra 200250 calories burned per day doing nothing. Nicotine also promotes lipolysis, the breakdown of stored fat. Studies have shown it decreases respiratory exchange ratio, meaning the body shifts toward burning more fat as fuel. Research in male rats demonstrated that self administered nicotine suppressed body weight, specifically through increased fat metabolism, independent of changes in food intake or physical activity. However, and this is important, the metabolic picture isn't all positive. Nicotine can also induce insulin resistance. Research shows it increases MTOR signaling in muscle cells, which on one hand could promote more muscle protein synthesis. But it also can, when sustained, lead to impaired insulin signaling and glucose uptake. It can also increase lipolysis in a way that floods the liver with free fatty acids, promoting potentially liver insulin resistance. So the metabolic effects of nicotine are complex and context dependent. It promotes fat burning and energy expenditure, but it also may impair glucose metabolism at the muscle. For someone who is metabolically healthy and using nicotine intermittently, the effects might be quite different than for someone who is using it chronically or has an underlying metabolic condition. Now let's shift from metabolism to the brain. Of course the brain is a very metabolic tissue, but let's look at some of the neurological conditions where nicotine has shown promise. Starting with adhd, there is a striking statistic. People with ADHD are significantly more likely to smoke and become dependent on cigarettes compared to the general population. They start smoking earlier, smoke more heavily, and have a harder time quitting. This has led researchers to hypothesize that individuals with ADHD may be self medicating with nicotine. A controlled double blind study conducted at Duke University tested transdermal nicotine in adults diagnosed with adhd, both smokers and non smokers. The results were intriguing. Nicotine caused a significant reduction in reaction time on continuous performance tests, it reduced variability in attention over time, it improved accuracy of time estimation and clinicians rated global improvements in ADHD symptoms. Importantly, because improvements occurred in non smokers who had never been exposed to nicotine, the effects couldn't be attributed simply to relieving withdrawal symptoms. The nicotine was genuinely enhancing attention and cognitive performance. Another pilot study tested transdermal nicotine in children and adolescents with ADHD. Using a 5 milligram patch for 16 hours daily, they found significant reduction in learning problems and hyperactivity as rated by parents. Side effects included nausea and dizziness but were generally manageable. The mechanism likely involves nicotine effects on dopamine release in the prefrontal cortex. That's the same region targeted by stimulant medications like methylphenidate. Both nicotine and traditional ADHD medications increase dopamine availability, which improves attention regulation and and impulse control. Another area sticking in the brain where nicotine research is generating interest is autism spectrum disorder, particularly for managing aggression and irritability symptoms that can be extremely challenging in individuals with autism and their families. Research has shown that individuals with autism have alterations in their cholinergic system. Specifically, they have significantly fewer nicotinic acetylcholine receptors and in key brain regions, including up to 60 to 70% reductions in certain areas. This has led to the hypothesis that nicotine might help compensate for this deficit. Yale researchers have conducted several studies in this area. In mouse models, they demonstrated that nicotine reduces aggression related behaviors. They then translated this to a case study involving a hospitalized adolescent with severe autism and aggression that hadn't responded to standard treatments. When transdermal nicotine patches were applied when aggression seemed imminent, there was a marked reduction in the need for physical restraints and emergency medications. The treatment was well tolerated with no significant side effects. The researchers subsequently conducted a randomized double blind placebo controlled pilot trial in adults with autism, finding that nicotine patches reduced irritability and aggressive symptoms compared to placebo. Now, I want to emphasize this research is still preliminary and parents should absolutely not be self medicating their children with nicotine products. Just again, let me reiterate, I'm not a clinician and I'm not giving medical advice. I'm just your friendly neighborhood scientist. And with that comment in mind, the evidence does point to an intriguing therapeutic avenue that I think as a scientist, deserves more rigorous investigation.
