Harvard Medical School researchers have analyzed the molecular crosstalk between pain fibers in the gut and goblet cells that line the walls of the intestine. The work shows that chemical signals from pain neurons induce goblet cells to release protective mucus that coats the gut and shields it from damage. The findings show that intestinal pain is not a mere detection-and-signaling system, but plays a direct protective role in the gut. CREDIT Chiu Lab/Harvard Medical School

Pain has been long recognized as one of evolution’s most reliable tools to detect the presence of harm and signal that something is wrong — an alert system that tells us to pause and pay attention to our bodies. 

But what if pain is more than just a mere alarm bell? What if pain is in itself a form of protection?

A new study led by researchers at Harvard Medical School suggests that may well be the case in mice. 
 
The research, published Oct. 14 in Cell, shows that pain neurons in the mouse gut regulate the presence of protective mucus under normal conditions and stimulate intestinal cells to release more mucus during states of inflammation.  

The work details the steps of a complex signaling cascade, showing that pain neurons engage in direct crosstalk with mucus-containing gut cells, known as goblet cells.  
 
“It turns out that pain may protect us in more direct ways than its classic job to detect potential harm and dispatch signals to the brain. Our work shows how pain-mediating nerves in the gut talk to nearby epithelial cells that line the intestines,” said study senior investigator Isaac Chiu, associate professor of immunobiology in the Blavatnik Institute at HMS. “This means that the nervous system has a major role in the gut beyond just giving us an unpleasant sensation and that it’s a key player in gut barrier maintenance and a protective mechanism during inflammation.” 

A direct conversation 

Our intestines and airways are studded with goblet cells. Named for their cup-like appearance, goblet cells contain gel-like mucus made of proteins and sugars that acts as protective coating that shields the surface of organs from abrasion and damage.  The new research found that intestinal goblet cells release protective mucus when triggered by direct interaction with pain-sensing neurons in the gut. 

In a set of experiments, the researchers observed that mice lacking pain neurons produced less protective mucus and experienced changes in their intestinal microbial composition — an imbalance in beneficial and harmful microbes known as dysbiosis. 
 
To clarify just how this protective crosstalk occurs, the researchers analyzed the behavior of goblet cells in the presence and in the absence of pain neurons. 
 
They found that the surfaces of goblet cells contain a type of receptor, called RAMP1, that ensures the cells can respond to adjacent pain neurons, which are activated by dietary and microbial signals, as well as mechanical pressure, chemical irritation or drastic changes in temperature.  
 
The experiments further showed that these receptors connect with a chemical called CGRP, released by nearby pain neurons, when the neurons are stimulated. These RAMP1 receptors, the researchers found, are also present in both human and mouse goblet cells, thus rendering them responsive to pain signals. 

Experiments further showed that the presence of certain gut microbes activated the release of CGRP to maintain gut homeostasis. 

“This finding tells us that these nerves are triggered not only by acute inflammation, but also at baseline,” Chiu said. “Just having regular gut microbes around appears to tickle the nerves and causes the goblet cells to release mucus.” 
 
This feedback loop, Chiu said, ensures that microbes signal to neurons, neurons regulate the mucus, and the mucus keeps gut microbes healthy. 

In addition to microbial presence, dietary factors also played a role in activating pain receptors, the study showed. When researchers gave mice capsaicin, the main ingredient in chili peppers known for its ability to trigger intense, acute pain, the mice’s pain neurons got swiftly activated, causing goblet cells to release abundant amounts of protective mucus.

By contrast, mice lacking either pain neurons or goblet cell receptors for CGRP were more susceptible to colitis, a form of gut inflammation. The finding could explain why people with gut dysbiosis may be more prone to colitis. 
 
When researchers gave pain-signaling CGRP to animals lacking pain neurons, the mice experienced rapid improvement in mucus production. The treatment protected mice against colitis even in the absence of pain neurons. 

The finding demonstrates that CGRP is a key instigator of the signaling cascade that leads to the secretion of protective mucus.  

“Pain is a common symptom of chronic inflammatory conditions of the gut, such as colitis, but our study shows that acute pain plays a direct protective role as well,” said study first author Daping Yang, a postdoctoral researcher in the Chiu Lab. 

A possible downside to suppressing pain 

The team’s experiments showed that mice lacking pain receptors also had worse damage from colitis when it occurred.  
 
Given that pain medications are often used to treat patients with colitis, it may be important to consider the possible detrimental consequences of blocking pain, the researchers said.  

“In people with inflammation of the gut, one of the major symptoms is pain, so you might think that we’d want to treat and block the pain to alleviate suffering,” Chiu said. “But some part of this pain signal could be directly protective as a neural reflex, which raises important questions about how to carefully manage pain in a way that does not lead to other harms.” 

Additionally, a class of common migraine medications that suppress the secretion of CGRP may damage gut barrier tissues by interfering with this protective pain signaling, the researchers said. 

“Given that CGRP is a mediator of goblet cell function and mucus production, if we are chronically blocking this protective mechanism in people with migraine and if they are taking these medications long-term, what happens?” Chiu said. “Are the drugs going to interfere with the mucosal lining and people’s microbiomes?”

Goblet cells have multiple other functions in the gut. They provide a passage for antigens — proteins found on viruses and bacteria that initiate a protective immune response by the body — and they produce antimicrobial chemicals that protect the gut from pathogens. 
 
“One question that arises from our current work is whether pain fibers also regulate these other functions of goblet cells,” Yang said. 

Another line of inquiry, Yang added, would be to explore disruptions in the CGRP signaling pathway and determine whether malfunctions are at play in patients with genetic predisposition to inflammatory bowel disease. 

The image shows neurons (red) in the smooth muscle layers (green) of the mouse colon CREDIT Peng Zeng.

Neurons that sense pain protect the gut from inflammation and associated tissue damage by regulating the microbial community living in the intestines, according to a study from researchers at Weill Cornell Medicine.

The researchers, whose report appears Oct. 14 in Cell, found in a preclinical model that pain-sensing neurons in the gut secrete a molecule called substance P, which appears to protect against gut inflammation and related tissue damage by boosting the population of beneficial microbes in the gut. The researchers also found that these pain-sensing nerves are diminished in number, with significant disruptions to their pain-signaling genes, in people who have inflammatory bowel disease (IBD).

“These findings reshape our thinking about chronic inflammatory disease, and open up a whole new approach to therapeutic intervention,” said study senior author Dr. David Artis, director of the Jill Roberts Institute for Research in Inflammatory Bowel Disease, director of the Friedman Center for Nutrition and Inflammation and the Michael Kors Professor of Immunology at Weill Cornell Medicine.

The study’s first author, Dr. Wen Zhang, a postdoctoral researcher in the Artis laboratory, added, “Defining a previously unknown sensory function for these specific neurons in influencing the microbiota adds a new level of understanding to host-microbiota interactions”.

IBD covers two distinct disorders, Crohn’s disease and ulcerative colitis, and is believed to affect several million people in the United States. Typically it is treated with drugs that directly target elements of the immune system. Scientists now appreciate that gut-dwelling bacteria and other microbes also help regulate gut inflammation.

As Dr. Artis’s laboratory and others have shown in recent years, the nervous system, which is “wired” into most organs, appears to be yet another powerful regulator of the immune system at the body’s barrier surfaces. In the new study, Dr. Artis and his team specifically examined pain neurons that innervate—extend their nerve endings into—the gut.

These gut-innervating pain neurons, whose cell bodies sit in the lower spine, express a surface protein called TRPV1, which serves as a receptor for pain-related signals. TRPV1 can be activated by high heat, acid, and the chili-pepper compound capsaicin, for example—and the brain translates this activation into a sense of burning pain. The researchers found that silencing these TRPV1 receptors in gut nerves, or deleting TRPV1-expressing neurons, led to much worse inflammation and tissue damage in IBD mouse models, whereas activating the receptors had a protective effect.

The investigators observed that the worsened inflammation and tissue damage in TRPV1-blocked mice were associated with changes in the relative populations of different species of gut bacteria. When this altered bacterial population was transplanted into normal mice, it caused the same worsened susceptibility to inflammation and damage. By contrast, broad-spectrum antibiotic treatment could reverse this susceptibility even in TRPV1-blocked mice. This result demonstrated that TRPV1-expressing nerves protect the gut mainly by helping to maintain a healthy gut microbe population.

The scientists found strong evidence that a large part of this microbe-influencing effect of TRPV1-expressing nerves comes from a molecule the nerves secrete called substance P—which they observed could reverse, on its own, most of the harmful effects of blocking TRPV1. Experiments also suggested that the signaling between neurons and microbes was two-way—some bacterial species could activate TRPV1-expressing nerves to get them to produce more substance P.

To confirm the relevance to humans, the researchers examined gut tissue from IBD patients, and found abnormal TRPV1 and substance P gene activity as well as fewer signs of TRPV1 nerves overall.

“These patients had disrupted pain-sensing nerves, which may have contributed to their chronic inflammation,” Dr. Zhang said.

Precisely how substance P exerts its effects on the gut microbe population, and how these microbes “talk back,” are questions that the researchers are now trying to answer in ongoing studies. But the results so far suggest that the next generation of anti-inflammatory drugs for IBD and other disorders could be compounds that target the nervous system.

“A lot of current anti-inflammatory drugs work in only some patients, and pharma companies really haven’t known why,” Dr. Artis said. “Maybe it’s because, when it comes to chronic inflammation, we’ve been seeing only some of the picture—and now the rest, including the role of the nervous system, is starting to come into focus.”

How to Stop Your Pain With the Egoscue Method (Featuring Brian Bradley)

New molecules are lead candidates for an alternative to narcotics, say UCSF researchers

A newly identified set of molecules alleviated pain in mice while avoiding the sedating affect that limits the use of opiates, according to a new study led by researchers at UC San Francisco.
The molecules act on the same receptor as clonidine and dexmedetomidine—drugs commonly used in hospitals as sedatives—but are chemically unrelated to them and may not be addictive.  

Clonidine and dexmedetomidine are also both effective pain killers but so sedating that they are rarely used for pain relief outside of the hospital.   

“We showed that it’s possible to separate the analgesic and sedative effects related to this receptor, said Brian Shoichet, PhD, professor in the School of Pharmacy, and one of four senior authors of the study, which appears in the Sept. 30, 2022, issue of Science. “That makes it a very promising target for drug development.”

The research is part of a five-year grant from the Defense Advanced Research Projects Agency (DARPA), and began shortly before the COVID-19 pandemic, with the aim of finding effective painkillers that can be used together or in conjunction with opioids. 

The work brings together researchers from a variety of disciplines; Shoichet’s co-authors include UCSF anatomy chair Allan Basbaum, PhD, chemist Peter Gmeiner of Freidrichs Alexander University in Germany, structural biologist Yang Du, PhD, of the Chinese University of Hong Kong, and molecular biologist Michel Bouvier, PhD, of the University of Montreal.

“Together, we were able to take this from the most fundamental level to identifying new molecules that might be relevant, and then to demonstrating that, in fact, they are relevant,” said Basbaum. “That doesn’t happen very often.” 

6 Molecules Out of 300 Million

Shoichet was encouraged to look for substances that would activate this adrenergic receptor, called alpha2a, by Basbaum, who had studied it in his lab and showed that it is tied to pain relief. 

To start the search for molecules that would bind firmly to the receptor, Shoichet computationally combed through a virtual library of over 300 million molecules, eliminating those that were too bulky for the small receptor. The remaining thousands were virtually “docked,” one by one, on a computer model of the receptor.

Through a series of tests, Shoichet narrowed the field from an initial 48 candidates to six, based on how they bound to the receptor in cultured human and mouse cells. Each of the final six was tested on three different mouse models for acute and chronic pain, and successfully alleviated pain in all three instances. 

The pain-relieving molecules, which were from chemically different families, are also entirely novel. None of them had previously been synthesized. 

Whereas the older drugs, like dexmedetomidine, activate a broad spectrum of neuronal pathways, the new molecules trigger only a selective subset of these, Shoichet said. The molecules also concentrate in the brain, and bind tightly to the receptor, making them good candidates for further development. 

Hope for 1 in 5 Americans

Basbaum cautions that it may take several years of research before any of the compounds could be tested in clinical trials. The researchers don’t yet understand possible side effects of the new molecules, and whether there might be unintended consequences from long-term use. 

He believes, however, that it’s unlikely the compound is addictive. “Substance abuse happens when the drug generates a reward, which we didn’t see any evidence of,” he said. 

While opioids clearly help patients with pain from surgery or cancer, Basbaum noted that the majority of the 50 million Americans with chronic pain have other conditions, like back injuries, joint pain, and inflammatory disease, that often aren’t helped by the drugs. New analgesics could completely change the outlook for these patients.

“If we can create a drug that works in combination with a much lower dose of opiate, that would be the dream,” he said. “The need for that is huge.”

A soft, bioresorbable, implantable device developed by researchers from Pusan National University provides a focused, reversible, and precise cooling effect to block pain signals from peripheral nerves CREDIT Pusan National University

Owing to their high efficacy, opioids are used widely for the management of neuropathic pain, despite the increasing rates of opioid addiction and deaths due to overdose. To avoid these side effects, there is an urgent need for pain management approaches that can substitute opioid use.

It is well known that cold temperatures numb the sensation in our nerves. Evidence suggests that cooling peripheral nerves can in fact reduce the velocity and amplitude of neural signals that cause pain, leading to pain relief. What’s great about this approach is that if made possible, it will be completely reversible and non-addictive.

To this end, a team of researchers led by Professor Min-Ho Seo from Pusan National University developed a soft, bioresorbable, implantable device with the potential to cool peripheral nerves in a minimally invasive, focused manner. “Scientists already knew that low temperatures could numb the nerves in the body. But demonstrating this phenomenon with a small device at a clinical level was not an easy task,” said Prof. Seo while discussing the study, which was published in Volume 377 Issue 6601 of Science on June 30, 2022.

To develop the device, the team designed a microfluidics system formed with a bioresorbable material—poly(octanediol citrate)—with interconnects carrying a liquid coolant to a serpentine chamber. To top it off, a Magnesium temperature sensor for real-time temperature monitoring was incorporated at its distal end. The intensity and localization of the cooling effect was regulated by perfluoro pentane (PFP) and dry nitrogen gas (N₂)—the two components of the liquid coolant, as well as the geometry of the serpentine chamber.

Next, the team tested the device by implanting it into the sciatic nerves of living rat models with neuropathic pain associated with spared nerve injury. After a three-week evaluation, the team found that the device successfully delivered cooling power to the peripheral nerves of the rats, which led to a reduction in their pain. Fortunately, the delivery of the cooling power occurred in a minimally invasive, stable, and precise manner. What’s more, this application was localized and reversible, and remained effective for almost 15 minutes during one session.

On being submerged in phosphate-buffered saline solution at 75°C, the device, which was made of bioresorbable materials, dissolved within 20 days and got eliminated in approximately 50 days. These findings imply that it has the potential to naturally degrade and get resorbed in the human body.

So, what are the future applications of this device? “The developed device can be used to treat pain after surgery. Since it is connected to an external source of fluid and power like a commercial intravenous (IV) device, it can easily be controlled by the patient. This way, our implantable device will be able to provide targeted and individualized relief without the drawbacks of the addictive pain medications,” said Prof. Seo in response.

With such progress underway, patients with neuropathic pain will finally be able to receive safe and sustainable treatment, without the risk of adverse effects associated with opioid use!