Love hormone delivered in a nasal spray can combat obesity
[Dec 6, 2021: Olga Khazan]
Studies have been conducted is by putting oxytocin in a nasal spray and attempting to shoot it directly toward the brain. (CREDIT: Creative Commons)
Scientists suspect that one element of the obesity epidemic is that the brains of obese people respond differently to images of delicious, calorically dense foods. Obese individuals’ brains seem to light up at the sight of donuts, pizza, and other calorie bombs, even when they’re no longer hungry.
Some studies have suggested that this heightened activity might predispose people to overeating. Today, nearly 40 percent of American adults are obese, and obesity is predicted to become the leading cause of cancer among Americans, replacing smoking, within five or 10 years. (It’s still not clear yet which comes first—the obesity or the overactive brain activity.) “Part of the reason for the obesity epidemic is that people eat when they’re not hungry,” says Elizabeth Lawson, an associate professor of medicine at Harvard Medical School and a neuroendocrinologist at Massachusetts General Hospital.
A remedy for this over-activation in the brain might come from an unexpected source: oxytocin, the brain chemical often associated with love and social relationships. Oxytocin is sometimes called the “love hormone” because it’s released during sex, childbirth, and breastfeeding. People who are in the early stages of falling in love have higher levels of oxytocin than normal. The drug ecstasy also increases concentrations of the hormone in the blood.
Oxytocin has a variety of other surprising functions. A form of the chemical, Pitocin, induces labor, and another form might help treat stomach pain. Early studies have suggested that the hormone might boost social skills among kids with autism. Now Lawson and other researchers are investigating whether oxytocin might also prevent overeating.
Metabolic effects of oxytocin: OT is secreted from the posterior lobe of the pituitary gland and binds to its receptor in peripheral tissues. In adipose tissue, it induces fatty acid oxidation and lipolysis, and formation of small adipocytes. Small adipocytes increase secretion of adiponectin and decrease leptin secretion, which improve insulin sensitivity in adipose tissue, liver, and muscles. In pancreas, it induces insulin secretion via phosphoinositide (PI) turnover and activation of protein kinase C, and regeneration of pancreatic β-cells. In liver and muscles, it enhances glucose uptake by stimulation of intracellular release of calcium, and activation of phosphoinositid-3-kinase (PI3K), calcium-calmodulin kinase kinase (Ca-CAMKK), and AMP-activated protein kinase (AMPK).
Lawson and her colleagues recently showed images of high-calorie foods to 10 overweight and obese men. She found that the regions of the brain involved in eating for pleasure lit up when the men viewed the images. A dose of oxytocin, compared with a placebo, weakened the activity in those regions, and it also reduced the activity between them. Meanwhile, oxytocin didn’t have that effect when the men viewed images of low-calorie foods or household items. Lawson’s colleagues presented the research, which has not yet been published in a peer-reviewed journal, last month at Endo 2019, the Endocrine Society’s annual meeting.
“One of the key ways oxytocin works in limiting the amount of food that we eat is that it speeds up the satiety process, or reaching fullness,” says Pawel Olszewski, an associate professor of physiology at the University of Waikato, in New Zealand, who was not involved with Lawson’s study. “Then, oxytocin works through brain areas that are associated with the pleasure of eating, and it decreases our eating for pleasure.”
That’s just one of the ways oxytocin shows potential as an obesity treatment. Previously, Lawson and her colleagues found that the hormone improves insulin sensitivity and encourages the body to use fat as fuel. Lawson’s other studies have shown that oxytocin reduces activation in the hypothalamus, an area of the brain that controls hunger, and increases activation in areas of the brain associated with impulse control. To Lawson, the results together suggest that the hormone creates less of a need to eat, reduces the compulsion to eat for fun, and improves impulse control when it comes to actually reaching for that second slice of cake. Oxytocin, in other words, appears to make food seem less rewarding.
Other researchers have found that oxytocin might weaken alcoholics’ dependence on alcohol, drawing parallels to the hormone’s effects on how some obese people’s brains perceive food. A study published in the journal PLOS showed that oxytocin cut the desire to drink among alcohol-dependent rats. It’s not clear what this anti-drinking element of oxytocin has to do with its love-hormone properties, if anything.
So why can’t we just pick up bottles of oxytocin at CVS? For one thing, most of these studies have been very small; 10 is a minuscule sample size. They’ve been largely conducted on men, so future research would need to be expanded to women. The mechanism behind oxytocin’s effects on eating behavior and metabolism needs to be clarified, and the safety of using the hormone long term needs to be established.
The way that Lawson’s and many other studies have been conducted is by putting oxytocin in a nasal spray and attempting to shoot it directly toward the brain. Lawson is currently conducting an NIH-funded randomized controlled trial that will administer oxytocin to obese men and women for eight weeks.
Early tests show one squirt in each nostril is enough to stop us from thinking about food. Scientists think the spray could help tackle the global obesity crisis. For example, more than one in three adults in the US and one in four adults in Britain are obese.
Forty volunteers, men and women, sprayed oxytocin into both nostrils before being shown images of food, couples being romantic, or scenery.
Researchers measured their reactions to the photographs after using the oxytocin spray and again after using a placebo spray.
The results, which were published in the journal Appetite, showed that responses to food images were much slower after the hormone spray but hardly changed with the placebo spray.
Researchers said this suggests our brains are much less preoccupied with the need for calories when taking oxytocin.
Animal studies have found that daily oxytocin use triggers significant weight loss.
The hormone is thought to dampen activity in part of the brain's reward system – called the ventral tegmental area. Researchers think the nasal spray could be a future weight loss aid.
The scientists said in a report: 'These findings may have important implications for people with obesity.'
However, oxytocin is not without its risks. Possible side-effects of the hormone include nausea, low blood pressure and even abnormal heart rhythms.
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