Researchers find new target for chronic pain treatment

Researchers at the UNC School of Medicine have found a new target for treating chronic pain: an enzyme called PIP5K1C. In a paper published today in the journal Neuron, a team of researchers led by Mark Zylka, PhD, Associate Professor of Cell Biology and Physiology, shows that PIP5K1C controls the activity of cellular receptors that signal pain.

By reducing the level of the enzyme, researchers showed that the levels of a crucial lipid called PIP₂ in pain-sensing neurons is also lessened, thus decreasing pain.

They also found a compound that could dampen the activity of PIP5K1C. This compound, currently named UNC3230, could lead to a new kind of pain reliever for the more than 100 million people who suffer from chronic pain in the United States alone.

In particular, the researchers showed that the compound might be able to significantly reduce inflammatory pain, such as arthritis, as well as neuropathic pain – damage to nerve fibers. The latter is common in conditions such as shingles, back pain, or when bodily extremities become numb due to side effects of chemotherapy or diseases such as diabetes.

The creation of such bodily pain might seem simple, but at the cellular level it’s quite complex. When we’re injured, a diverse mixture of chemicals is released, and these chemicals cause pain by acting on an equally diverse group of receptors on the surface of pain-sensing neurons.

“A big problem in our field is that it is impractical to block each of these receptors with a mixture of drugs,” said Zylka, the senior author of the Neuron article and member of the UNC Neuroscience Center. “So we looked for commonalities – things that each of these receptors need in order to send a signal.” Zylka’s team found that the lipid PIP₂ (phosphatidylinositol 4,5-bisphosphate) was one of these commonalities.

“So the question became: how do we alter PIP₂ levels in the neurons that sense pain?” Zylka said. “If we could lower the level of PIP₂, we could get these receptors to signal less effectively. Then, in theory, we could reduce pain.”

Many different kinases can generate PIP₂ in the body.  Brittany Wright, a graduate student in Zylka’s lab, found that the PIP5K1C kinase was expressed at the highest level in sensory neurons compared to other related kinases. Then the researchers used a mouse model to show that PIP5K1C was responsible for generating at least half of all PIP₂ in these neurons.

“That told us that a 50 percent reduction in the levels of PIP5K1C was sufficient to reduce PIP₂ levels in the tissue we were interested in – where pain-sensing neurons are located” Zylka said. “That’s what we wanted to do – block signaling at this first relay in the pain pathway.”

Once Zylka and colleagues realized that they could reduce PIP₂ in sensory neurons by targeting PIP5K1C, they teamed up with Stephen Frye, PhD, the Director of the Center for Integrative Chemical Biology and Drug Discovery at the UNC Eshelman School of Pharmacy.

They screened about 5,000 small molecules to identify compounds that might block PIP5K1C. There were a number of hits, but UNC3230 was the strongest. It turned out that Zylka, Frye, and their team members had come upon a drug candidate. They realized that the chemical structure of UNC3230 could be manipulated to potentially turn it into an even better inhibitor of PIP5K1C. Experiments to do so are now underway at UNC.

How Cone Snail Venom Minimizes Pain

The venom from marine cone snails, used to immobilize prey, contains numerous peptides called conotoxins, some of which can act as painkillers in mammals. A recent study in The Journal of General Physiology provides new insight into the mechanisms by which one conotoxin, Vc1.1, inhibits pain. The findings help explain the analgesic powers of this naturally occurring toxin and could eventually lead to the development of synthetic forms of Vc1.1 to treat certain types of neuropathic pain in humans.

Neuropathic pain, a form of chronic pain that occurs in conjunction with injury to—or dysfunction of—the nervous system, can be debilitating and difficult to treat, and the medical community is eager to find better methods to minimize what can be a serious condition. Neuropathic pain is associated with changes in the transmission of signals between neurons, a process that depends on several types of voltage-gated calcium channels (VGCCs). However, given the importance of these VGCCs in mediating normal neurotransmission, using them as a pharmacological target against neuropathic pain could potentially lead to undesirable side effects.

In previous studies, David Adams and colleagues from RMIT University in Melbourne showed that Vc1.1 acted against neuropathic pain in mice; they found that, rather than acting directly to block VGCCs, Vc1.1 acts through GABA type B (GABA_B) receptors to inhibit N-type (Ca_v2.2) channels.

Now, Adams and colleagues show that Vc1.1 also acts through GABA_B receptors to inhibit a second, mysterious class of neuronal VGCCs that have been implicated in pain signaling but have not been well understood—R-type (Ca_v2.3) channels. Their new findings not only help solve the mystery of Ca_v2.3 function, but identify them as targets for analgesic conotoxins.

Pain’s Benefit to Squid May Hold Clues to Chronic Human Pain

For the longfin inshore squid, pain can mean the difference between life and death, according to a new study. That’s because pain prompts injured squid to behave in ways that help it survive encounters with a fish predator, researchers said.

That finding may also provide hints as to why other animals, including humans, experience long-lasting or chronic pain, behavior experts say.

It’s long been thought that pain causes an animal to act self-protectively, says Robert Elwood, an animal behavior researcher at Queen’s University Belfast who was not involved in the study. Pain teaches an organism to avoid situations that will bring it on. It seems obvious, but it hasn’t really been tested until now, Elwood said in an email interview.

In a study published today in Current Biology, researchers report that the sensitivity with which injured squid reacted to aggressive moves from a predator, in this case a black sea bass, gave the squid better odds of surviving an attack.

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Pain curbs sex drive in female mice, but not in males

Now, researchers from McGill University and Concordia University in Montreal have investigated, possibly for the first time in any species, the direct impact of pain on sexual behaviour in mice. Their study, published in the April 23 issue of The Journal of Neuroscience, found that pain from inflammation greatly reduced sexual motivation in female mice in heat — but had no such effect on male mice.

“We know from other studies that women’s sexual desire is far more dependent on context than men’s – but whether this is due to biological or social/cultural factors, such as upbringing and media influence, isn’t known,” says Jeffrey Mogil, a psychology professor at McGill and corresponding author of the new study. “Our finding that female mice, too, show pain-inhibited sexual desire suggests there may be an evolutionary biology explanation for these effects in humans – and not simply a sociocultural one.”

To conduct the study, the researchers placed mice in a mating chamber divided by a barrier with openings too small for male mice to squeeze through. This enabled the females to decide whether, and for how long, to spend time with a male partner. Female mice in pain spent less time on the “male side” of the testing chamber, and as a result less sexual behaviour occurred. The researchers found that the sexual motivation of the female mice could be revived, however with a pain-relieving drug (pregabalin) or with either of two known desire-enhancing drugs.

Male mice, for their part, were tested in an undivided chamber in which they had free access to a female partner in heat. Their sexual behaviour was entirely unaffected by the same inflammatory pain. There were no differences in pain perception between the sexes, the researchers determined.

“Chronic pain is very often accompanied by sexual problems in humans,” says Prof. Yitzchak Binik, a professor of psychology at McGill and Director of the Sex and Couple Therapy Service at the McGill University Health Center. “This research provides an animal model of pain-inhibited sexual desire that will help scientists study this important symptom of chronic pain.”

Melissa Farmer, now a postdoctoral fellow at Northwestern University, led the study as a doctoral student at McGill under the supervision of Prof. Mogil, a pain researcher, and Prof. Binik, a human sexual-disorder researcher.

Prof. James Pfaus of Concordia University’s Centre for Studies in Behavioral Neurobiology, an expert on rodent sexual behaviour, also co-authored the study. “The sex differences in pain reactivity open new doors to understanding how sexual responses are organized in the brain,” Prof. Pfaus said. “In fact, the growing trend towards personalized medicine requires us to understand how particular ailments, along with their treatments, might impact the sexual lives of women and men.“

Computers See Through Faked Expressions of Pain Better Than People

A joint study by researchers at the University of California, San Diego and the University of Toronto has found that a computer system spots real or faked expressions of pain more accurately than people can.

The work, titled “Automatic Decoding of Deceptive Pain Expressions,” is published in the latest issue of Current Biology.

“The computer system managed to detect distinctive dynamic features of facial expressions that people missed,” said Marian Bartlett, research professor at UC San Diego’s Institute for Neural Computation and lead author of the study. “Human observers just aren’t very good at telling real from faked expressions of pain.”

Senior author Kang Lee, professor at the Dr. Eric Jackman Institute of Child Study at the University of Toronto, said “humans can simulate facial expressions and fake emotions well enough to deceive most observers. The computer’s pattern-recognition abilities prove better at telling whether pain is real or faked.”

The research team found that humans could not discriminate real from faked expressions of pain better than random chance – and, even after training, only improved accuracy to a modest 55 percent. The computer system attains an 85 percent accuracy.

“In highly social species such as humans,” said Lee, “faces have evolved to convey rich information, including expressions of emotion and pain. And, because of the way our brains are built, people can simulate emotions they’re not actually experiencing – so successfully that they fool other people. The computer is much better at spotting the subtle differences between involuntary and voluntary facial movements.”

“By revealing the dynamics of facial action through machine vision systems,” said Bartlett, “our approach has the potential to elucidate ‘behavioral fingerprints’ of the neural-control systems involved in emotional signaling.”

The single most predictive feature of falsified expressions, the study shows, is the mouth, and how and when it opens. Fakers’ mouths open with less variation and too regularly.

“Further investigations,” said the researchers, “will explore whether over-regularity is a general feature of fake expressions.”

In addition to detecting pain malingering, the computer-vision system might be used to detect other real-world deceptive actions in the realms of homeland security, psychopathology, job screening, medicine, and law, said Bartlett.

“As with causes of pain, these scenarios also generate strong emotions, along with attempts to minimize, mask, and fake such emotions, which may involve ‘dual control’ of the face,” she said. “In addition, our computer-vision system can be applied to detect states in which the human face may provide important clues as to health, physiology, emotion, or thought, such as drivers’ expressions of sleepiness, students’ expressions of attention and comprehension of lectures, or responses to treatment of affective disorders.”

Shedding a light on pain: A technique developed by Stanford bioengineers could lead to new treatments

The mice in Scott Delp’s lab, unlike their human counterparts, can get pain relief from the glow of a yellow light.

Right now these mice are helping scientists to study pain – how and why it occurs and why some people feel it so intensely without any obvious injury. But Delp, a professor of bioengineering and mechanical engineering, hopes one day the work he does with these mice can also help people who are in chronic, debilitating pain.

"This is an entirely new approach to study a huge public health issue," Delp said. "It’s a completely new tool that is now available to neuroscientists everywhere." He is the senior author of a research paper published Feb. 16 in Nature Biotechnology.

A switch for pain

The mice are modified with gene therapy to have pain-sensing nerves that can be controlled by light. One color of light makes the mice more sensitive to pain. Another reduces pain. The scientists shone a light on the paws of mice through the Plexiglas bottom of the cage.

Graduate students Shrivats Iyer and Kate Montgomery, who led the study, say it opens the door to future experiments to understand the nature of pain and also touch and other sensations that are part of our daily lives but little understood.

"The fact that we can give a mouse an injection and two weeks later shine a light on its paw to change the way it senses pain is very powerful," Iyer said.

For example, increasing or decreasing the sensation of pain in these mice could help scientists understand why pain seems to continue in people after an injury has healed. Does persistent pain change those nerves in some way? If so, how can they be changed back to a state where, in the absence of an injury, they stop sending searing messages of pain to the brain?

Leaders at the National Institutes of Health agree that the work could have important implications for treating pain. “This powerful approach shows great potential for helping the millions who suffer pain from nerve damage,” said Linda Porter, the pain policy adviser at the National Institute of Neurological Disorders and Stroke and a leader of the NIH’s Pain Consortium.

"Now, with a flick of a switch, scientists may be able to rapidly test new pain-relieving medications and, one day, doctors may be able to use light to relieve pain," she said.

Accidental discovery

The researchers took advantage of a technique called optogenetics, which involves light-sensitive proteins called opsins that are inserted into the nerves. Optogenetics was developed by Delp’s colleague Karl Deisseroth, a co-author of the journal article. He has used the technique as a way of activating precise regions of the brain to better understand how the brain functions. Deisseroth is a professor of bioengineering, psychiatry and behavioral sciences.

Delp, who has an interest in muscles and movement, saw the potential for using optogenetics not just for studying the brain – interesting though those studies may be – but also for studying the many nerves outside the brain. These are the nerves that control movement, pain, touch and other sensations throughout our body, and that are involved in diseases such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s Disease.

A few years ago Stanford Bio-X, which encourages interdisciplinary projects such as this one, supported Delp and Deisseroth in their efforts to use optogenetics to control the nerves that excite muscles. In the process of doing that work, Delp said, his student at the time, Michael Llewellyn, occasionally found that he had placed the opsins into nerves that signal pain rather than those that control muscle.

That accident sparked a new line of research. Delp said, “We thought, ‘Wow, we’re getting pain neurons; that could be really important.’” He suggested that Montgomery and Iyer focus on those pain nerves that had been a byproduct of the muscle work.

A faster approach

A key component of the work was a new approach to quickly incorporate opsins into the nerves of mice. The researchers started with a virus that had been engineered to contain the DNA that produces the opsin. Then they injected those modified viruses directly into mouse nerves. Weeks later, only the nerves that control pain had incorporated the opsin proteins and would fire, or be less likely to fire, in response to different colors of light.

The speed of the viral approach makes it very flexible, both for this pain work and for future studies. Researchers are developing newer forms of opsins with different properties, such as responding to different colors of light. “Because we used a viral approach we could, in the future, quickly turn around and use newer opsins,” said Montgomery, who is a Stanford Bio-X fellow.

This entire project, which spans bioengineering, neuroscience and psychiatry, is one Delp says could never have happened without the environment at Stanford that supports collaboration across departments. The pain portion of the research came out of support from NeuroVentures, which was a project incubated within Bio-X to support the intersection of neuroscience and engineering or other disciplines. That project was so successful it has spun off into the Stanford Neurosciences Institute, of which Delp is now a deputy director.

Delp said that many challenges must be met before results of these experiments – either new drugs based on what they learn, or optogenetics directly – could become available to people but that he always has that as a goal.

"Developing a new therapy from the ground up would be incredibly rewarding," he said. "Most people don’t get to do that in their careers."

Delp and Deisseroth have started a company called Circuit Therapeutics to develop therapies based on optogenetics.