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Oxytocin dampens the brain’s food-related reward circuitry


 

REPORTING FROM ENDO 2019

– Oxytocin shows promise as a weight-loss medication, with encouraging results in animal models and small human studies. Now, new imaging results show that the hormone inhibits food-related reward circuitry in the brain, tackling the hedonic, nonnutritive eating that can contribute to overweight and obesity in a calorie-rich environment.

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“It is clear by now that obesity is a very serious health concern,” Liya Kerem, MD, said in a video interview at the annual meeting of the Endocrine Society. “The most adopted strategy, which is lifestyle modification, does not help [with losing or maintaining] weight in many cases, so we really need to find new treatments for obesity.”

Functional magnetic resonance imaging (fMRI) is a good tool for investigating the neurobiologic basis of overeating, said Dr. Kerem, a pediatric endocrinology fellow at Massachusetts General Hospital, Boston. In previous studies, fMRI has shown that “individuals with obesity have hyperactivation of the reward circuitry in the brain.”

Oxytocin is produced in the hypothalamus and is active in many brain areas associated with reward processing, said Dr. Kerem. Animal studies have shown a decrease in food intake and weight gain with oxytocin administration.

The hormone, which is generally seen as very safe, has had limited study in humans as a weight-loss strategy. Findings from one small study have shown that in men, a single intranasal dose of 24 IU of oxytocin resulted in less hunger-driven eating as well as lower consumption of a postmeal palatable snack, with the latter representing hedonic eating, said Dr. Kerem. A second small pilot study showed that significant weight loss occurred in obese humans after 8 weeks of daily oxytocin administration.

Findings from another study showed that participants who were overweight or obese, unlike their normal-weight counterparts, had reduced activation in the ventral tegmental area (VTA) after oxytocin administration. The VTA is an important region in the brain’s reward network, explained Dr. Kerem.

She and her colleagues used fMRI to probe dynamic changes in brain reward circuitry under the effect of oxytocin. They wanted to understand how oxytocin would “change the dialog between the VTA and the key brain areas involved in processing visual food stimuli.”

The hypothesis was that oxytocin would reduce functional connectivity between the VTA and other brain areas that are important for food reward and sensory processing when the participants were exposed to pictures of high-calorie food.

To test that hypothesis, the researchers showed the participants 100 each of four different kinds of images: high-calorie foods, low-calorie foods, nonfood images, and “fixation” images, used for calibration. The 10 participants had a mean body mass index of 29 kg/m2, and the mean age was 31 years.

Oxytocin did indeed attenuate functional connectivity between the VTA and several brain regions that are “key food motivation areas,” said Dr. Kerem. In particular, connections between the VTA and the insula were reduced with oxytocin. The insula is the “gustatory hub of the brain, key to subjective perception of food stimuli,” she explained.

Other attenuated associations included the oral area of the somatosensory cortex; the operculum, which shows fMRI activation to taste; the temporal gyrus, which is important for sensory processing; and, importantly, both the amygdala and hippocampus, known to be important for stimulus-reward learning, said Dr. Kerem. “We found that oxytocin targets exactly that hyperactivation in an overweight and obese population.”

It “reduced the functional connectivity between the VTA, a key hedonic brain region that drives efforts to obtain desired foods, and multiple brain areas involved in the cognitive, sensory, and emotional processing of food cues in men with overweight and obesity,” she said at a press conference highlighting the research. She emphasized that the effect was seen only with exposure to high-calorie food images. “Targeting hyperactivation of reward areas with oxytocin may inhibit overeating behavior,” she added.

Dr. Kerem and her colleagues are currently enrolling men and women for a larger clinical trial of oxytocin for weight loss.

Dr. Kerem reported no conflicts of interest. One of the study’s coauthors is a consultant for OXT Therapeutics, which is investigating obesity-related uses for oxytocin.

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