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A study in mice shows that a drug makes mammalian pain receptors more like those in birds—and more resistant to some forms of pain.

Researchers have discovered a possible new way to treat pain without the use of opioids. By targeting a specific area of a well-known pain receptor, they were able to reduce pain sensitivity in mice without affecting the receptor’s other functions, such as sensitivity to heat.

Their inspiration? Chickens.

Many chicken farmers know that squirrels and mice won’t eat chicken feed laced with capsaicin—the chemical that gives chili peppers their spiciness. In mammals, capsaicin activates a pain receptor to cause a burning sensation. In most bird species, capsaicin has little effect.

“It turns out that birds are naturally resistant to capsaicin,” says Eric Gross, associate professor of anesthesiology, perioperative and pain medicine at Stanford University School of Medicine.

That fact prompted Gross to wonder whether it was possible for humans to have a genetic variant that made the receptor, known as transient receptor potential cation channel subfamily V member 1, or TRPV1, more birdlike—and more resistant to pain.

Bird and human pain receptors

In a study in the Journal of Clinical Investigation, Gross’s team and their collaborators identified a specific genetic variant of TRPV1 that reduces pain sensitivity in humans. Though this variant is extremely rare, the researchers were able to replicate the effects of the altered gene with a custom-designed drug.

The researchers first used a computational approach to find genetic variants of human TRPV1 that resemble avian TRPV1. When they tested these variants in genetically modified cells, one variant, known as K710N, drastically reduced the receptor’s reaction to capsaicin.

“We were quite amazed that there was such a decrease in activity of TRPV1’s response to capsaicin when we made that genetic variant,” says Gross, who is the senior author of the study. “It was to the point where we actually tried this several times to make sure that was really what we were seeing.”

Spicy chicken feed for mice

Next, they used the CRISPR/Cas9 gene editing technique to create mice with the K710N mutation. The plan was to see if these mice would find palatable the capsaicin-laced bird food that normal mice reject. The response was more immediate than the researchers expected: As soon as the spicy bird food was placed on the floor of their cage, normal mice lifted their paws as much as they could to avoid touching the capsaicin—suggesting that even skin contact caused pain. The K710N mice, meanwhile, lifted their paws much less frequently and were comfortable enough with the capsaicin to sample some spicy bird food.

Based on these and other behavioral responses, Gross estimates that the mutation reduced pain by about 50%.

The TRPV1 receptors in our sensory neurons do more than generate a burning sensation when we eat chili peppers. They also respond to other stimuli such as heat and physical injury—playing an important role in protecting us from danger—and they regulate body temperature.

“You don’t want to take away the full sensation of pain,” Gross says. “You still want to have somebody, if they place their hand over a hot stove or step on a Lego, to have that pain sensation.”

The K710N mice enjoyed a happy medium—they felt less pain but could still sense harmful stimuli and maintain normal body temperatures. “We were able to dial it down rather than take it away completely,” Gross says.

TRPV1 has yet more functions throughout the body, such as protecting against organ damage. The researchers found that the K710N variant retained and even enhanced these protective benefits of TRPV1. Heart cells with the variant, for example, were less likely to die when temporarily deprived of oxygen.

A potential drug for pain

With an understanding of precisely how the K710N mutation changed the structure and function of TRPV1, the researchers were able to design a drug that had the same effect. When they gave the drug, a peptide named V1-cal, to mice by injection or infusion, it reduced their sensitivity to capsaicin and lessened chronic pain from nerve injury. Just like the K710N mutation, the drug had little impact on heat sensation and regulation of body temperature.

Compared with previous attempts at treating pain by targeting TRPV1, the new chicken-inspired drug works more selectively, with fewer side effects.

“People have always used a direct approach, so they looked at ways to specifically activate or block the receptor,” Gross says. “That’s been a challenge because activation of the receptor causes pain, while inactivation may cause unwanted changes in body temperature.”

A high concentration of capsaicin activates and eventually desensitizes the receptor, and has been used in analgesic creams or patches, but the treatments increase pain before reducing it. On the other hand, drugs that block the receptor have failed in clinical trials because they caused people to overheat.

“Instead of directly activating or inactivating the receptor, the drug we developed modulates only a specific area of the receptor,” he says. “We’re able to avoid the side effects that have been plaguing drug discovery for TRPV1 for quite some time.”

Gross’s team hopes to modify the peptide so that it is more stable and can relieve pain longer. In the study, the mice were given the drug by continuous infusion.

As an anesthesiologist, Gross often treats patients with post-operative pain. “We’re really excited to see if this is a potential therapeutic for pain after surgery, and to help us move toward an opioid-free approach.”

Researchers from the Second Hospital of Anhui Medical University in China, the Butantan Institute in Brazil, the University Hospital Munster in Germany, and Emory University also contributed to the work.

The study had funding from the National Institutes of Health, the Stanford Cardiovascular Institute, the National Natural Science Foundation of China, the State Scholarship Fund of China Scholarship Council, the Second Hospital of Anhui Medical University, Sāo Paulo Research Foundation, Coodernacāo de Aperfeiçoamento de Pessoal de Nível Superior-Brasil, the Stanford Diabetes Research Center, the American Heart Association, and the German Research Foundation.

Source: Stanford University

Neglecting the psychological trauma many older adults with HIV/AIDS experience will make it difficult, if not impossible, to end the epidemic, according to a new study.

Once considered a death sentence, HIV/AIDS has evolved into a manageable illness—with the availability of antiretroviral treatments—and people with the disease are living longer. But as this population ages, they are facing mental and psychosocial health challenges that could have a profound effect on their well-being—and on the trajectory of the virus.

“Our findings support the need to target post-traumatic stress disorder and substance dependence and use among older HIV/AIDS-positive people and suggest that resilience might help increase adherence to antiretroviral therapy regimes,” says Kristen D. Krause, an instructor of urban health at the Rutgers School of Public Health and lead author of the study in the Journal of Gay & Lesbian Mental Health.

In 2016, the United Nations set a global target to end HIV as a public health threat by 2030. To succeed, however, antiretroviral therapy (ART) adherence—taking medication as directed and avoiding so-called “pill fatigue”—would – would need to continue. Krause says resilience, namely the ability to thrive amid challenge situations, may play an important role in ART adherence.

To understand the association between HIV-related resilience and mental health, Krause and colleagues at the Rutgers Center for Health, Identity, Behavior and Prevention Studies (CHIBPS) surveyed 250 HIV-positive gay men ages 50 to 69 living in the New York City area between April 2017 and October 2018. Participants were recruited from dating apps, gay-related events, community-based organizations, and word of mouth.

Using an HIV-related resilience assessment tool Krause helped create, researchers asked participants a series of questions about their ability to deal with adversity, whether they had or were experiencing post-traumatic stress disorder (PTSD), how they viewed HIV-related stigma, and whether they’d ever had suicidal thoughts.

The researchers found that people with higher levels of HIV-related resilience were more likely to have lower levels of PTSD and substance dependence and were more likely to feel financially secure.

About 16% of participants were symptomatic for PTSD, 14% met the criteria for severe depression, 18% reported a substance dependency, 18% suffered generalized anxiety disorder, and nearly 33% expressed suicidal tendencies.

A majority of the sample (64.4%) indicated they could barely or could not get by on the money they have.

Krause says the findings point to major gaps in mental health coverage for older people living with HIV/AIDS and support calls for a more holistic approach to health care for this population.

“More and more people are surviving with HIV, and we don’t really know what the long-term effects of that will be,” Krause says. “We’re finding out in real time. Any piece of information that we can collect will help mitigate the negative impacts of HIV later in life.

“As we wait for a vaccine or a cure, it’s important to continue building a toolbox of methods and best practices to bring this epidemic to an end. Resilience is one tool in that box.”

Source: Greg Bruno for Rutgers University