Highest-resolution model to date of brain receptor behind marijuana's high

November 16, 2016

Science Daily/UT Southwestern Medical Center

Researchers at UT Southwestern Medical Center report the most detailed 3-D structure to date of the brain receptor that binds and responds to the chemical at the root of marijuana's high.

Their high-resolution structure of the human cannabinoid receptor 1 (CB1) and its binding site for the chemical tetrahydrocannabinol (THC) should lead to a better understanding of how marijuana affects the brain. The research also could aid discovery of new treatments for conditions that target the receptor, said Dr. Daniel Rosenbaum, Assistant Professor of Biophysics and Biochemistry at UT Southwestern.

"What is most exciting from a therapeutic standpoint is that the same receptor pocket that binds THC also binds cannabinoid inhibitors that have been studied as possible treatments for conditions such as obesity," said Dr. Rosenbaum, senior author of the study published online by Nature. "The structure is an important step toward explaining how cannabinoids initiate signals in the brain that affect the release of neurotransmitters that relay messages between the brain's neurons," Dr. Rosenbaum said. "This 3-D structure provides high-resolution details of the binding pocket in the CB1 receptor, where plant cannabinoids like THC, cannabinoids made in the body, and synthetic cannabinoid inhibitors all work to modulate receptor function and physiology." He said the CB1 receptor is the target for cannabinoid inhibitor drugs now under study as possible treatments for epilepsy, pain control, obesity, and other conditions.

In a competing study released last month by the journal Cell, a U.S.-Chinese team of researchers reported a 3-D structure of the CB1 receptor at a resolution of 2.8 angstroms. The UT Southwestern study reports a higher resolution of 2.6 angstroms. (One angstrom is equivalent to one hundred-millionth of a centimeter.) The higher the resolution, the finer the details of the relationship between atoms of the protein.

"The resolution is very important. Our structure shows a different and better resolved structure at the important binding pocket that is of interest to scientists involved in drug development," Dr. Rosenbaum said. "Overall, these two structures are complementary, but we believe our structure may provide a better framework for understanding how cannabinoids and inhibitors bind to the receptor."

The Cell study examined the CB1 receptor bound to a synthetic chemical created to stabilize the receptor. In contrast, the UT Southwestern research team successfully imaged the receptor bound to the drug taranabant, which was tested as a possible anti-obesity treatment in clinical trials. Those trials ended due to side effects such as anxiety and depression, Dr. Rosenbaum said.

CB1 and the related CB2, which still lacks a high-resolution structural solution, are both members of the human G protein-coupled receptor family. Members of that receptor family control signaling pathways involving hormones, neurotransmitters, and sensory stimuli such as light and odors.

The team's success depended on overcoming the receptor protein's resistance to crystallization, which is required for the diffraction measurements used in X-ray crystallography. The researchers also conducted computer simulations of how THC might bind to the CB1 receptor, he said.

The next step is to obtain structures of CB1 actually bound to THC, he said.

https://www.sciencedaily.com/releases/2016/11/161116131935.htm

How marijuana impairs memory

March 1, 2012

Science Daily/Cell Press

A major downside of the medical use of marijuana is the drug's ill effects on working memory, the ability to transiently hold and process information for reasoning, comprehension and learning. Researchers provide new insight into the source of those memory lapses. The answer comes as quite a surprise: Marijuana's major psychoactive ingredient (THC) impairs memory independently of its direct effects on neurons.

The findings offer important new insight into the brain and raise the possibility that marijuana's benefits for the treatment of pain, seizures and other ailments might some day be attained without hurting memory, the researchers say.

With these experiments in mice, "we have found that the starting point for this phenomenon -- the effect of marijuana on working memory -- is the astroglial cells," said Giovanni Marsicano of INSERM in France.

"This is the first direct evidence that astrocytes modulate working memory," added Xia Zhang of the University of Ottawa in Canada.

The new findings aren't the first to suggest astroglia had been given short shrift. Astroglial cells (also known as astrocytes) have been viewed as cells that support, protect and feed neurons for the last 100 to 150 years, Marsicano explained. Over the last decade, evidence has accumulated that these cells play a more active role in forging the connections from one neuron to another.

The researchers didn't set out to discover how marijuana causes its cognitive side effects. Rather, they wanted to learn why receptors that respond to both THC and signals naturally produced in the brain are found on astroglial cells. These cannabinoid type-1 (CB1R) receptors are very abundant in the brain, primarily on neurons of various types.

Zhang and Marsicano now show that mice lacking CB1Rs only on astroglial cells of the brain are protected from the impairments to spatial working memory that usually follow a dose of THC. In contrast, animals lacking CB1Rs in neurons still suffer the usual lapses. Given that different cell types express different variants of CB1Rs, there might be a way to therapeutically activate the receptors on neurons while leaving the astroglial cells out, Marsicano said.

"The study shows that one of the most common effects of cannabinoid intoxication is due to activation of astroglial CB1Rs," the researchers wrote.

The findings further suggest that astrocytes might be playing unexpected roles in other forms of memory in addition to spatial working memory, Zhang said.

The researchers hope to explore the activities of endogenous endocannabinoids, which naturally trigger CB1Rs, on astroglial and other cells. The endocannabinoid system is involved in appetite, pain, mood, memory and many other functions. "Just about any physiological function you can think of in the body, it's likely at some point endocannabinoids are involved," Marsicano said.

And that means an understanding of how those natural signaling molecules act on astroglial and other cells could have a real impact. For instance, Zhang said, "we may find a way to deal with working memory problems in Alzheimer's."

https://www.sciencedaily.com/releases/2012/03/120301143424.htm

Turned-off Cannabinoid Receptor Turns on Colorectal Tumor Growth

August 4, 2008

Science Daily/University of Texas M. D. Anderson Cancer Center

New preclinical research shows that cannabinoid cell surface receptor CB1 plays a tumor-suppressing role in human colorectal cancer, scientists report in the Aug. 1 edition of the journal Cancer Research.

CB1 is well-established for relieving pain and nausea, elevating mood and stimulating appetite by serving as a docking station for the cannabinoid group of signaling molecules. It now may serve as a new path for cancer prevention or treatment.

"We've found that CB1 expression is lost in most colorectal cancers, and when that happens a cancer-promoting protein is free to inhibit cell death," said senior author Raymond DuBois, M.D., Ph.D., provost and executive vice president of The University of Texas M. D. Anderson Cancer Center.

DuBois and collaborators from Vanderbilt-Ingram Cancer Center also show that CB1 expression can be restored with an existing drug, decitabine. They found that mice prone to developing intestinal tumors that also have functioning CB1 receptors develop fewer and smaller tumors when treated with a drug that mimics a cannabinoid receptor ligand. Ligands are molecules that function by binding to specific receptors. Agonists are synthetic molecules that mimic the action of a natural molecule.

"Potential application of cannabinoids as anti-tumor drugs is an exciting prospect, because cannabinoid agonists are being evaluated now to treat the side-effects of chemotherapy and radiation therapy," DuBois said. "Turning CB1 back on and then treating with a cannabinoid agonist could provide a new approach to colorectal cancer treatment or prevention."

Cannabinoids are a group of ligands that serve a variety of cell-signaling roles. Some are produced by the body internally (endocannabinoids). External cannabinoids include manmade versions and those present in plants, most famously the active ingredient in marijuana (THC).

Receptor shutdown by methylation

Endocannabinoid signaling is important to the normal functioning of the digestive system and has been shown to protect the colon against inflammation. Since chronic inflammation is a known risk factor for colorectal cancer, the researchers decided to look into the role of cannabinoid receptors in a mouse model of colon cancer.

"People have looked at cannabinoids in cancer earlier, mainly in cell culture experiments," DuBois said. "The molecular mechanisms for loss of the receptor and its effect on cancer have not been previously shown."

First, the team found that CB1 was largely absent in 18 of 19 human tumor specimens and in 9 of 10 colorectal cancer cell lines. Further experimentation showed that the gene that encodes the CB1 protein was not damaged, but shut down chemically by the attachment of methyl groups - a carbon atom surrounded by three hydrogen atoms - to the gene encoding CB1.

Treating cell lines with decitabine, a demethylating agent approved for some types of leukemia, removed the methyl groups, restoring gene expression in 7 of 8 cell lines and full expression of CB1 protein in three lines.

Next, the group found that deletion of the CB1 gene in a strain of mice that spontaneously develops precancerous polyps resulted in a 2.5-to-3.8-fold increase in the number of polyps and a 10-fold increase in the number of large growths, those most likely to develop into cancer.

Treating mice that had the CB1 receptor with an endocannabinoid agonist resulted in a decline in polyps ranging from 16.7 percent to 50 percent. The reduction was greater for larger polyps.

CB1 thwarts survivin, a protein that protects cancer

Cannabinoids previously had been shown to kill cancer cells in lab experiments by inducing apoptosis - programmed cell death. The team confirmed the role of CB1 in apoptosis, showing that tumor cells with high CB1 expression were sensitive to apoptosis when treated by a cannabinoid agonist. Cell lines with silenced CB1 resisted cell death.

A series of experiments showed that CB1 increases cancer cell death by stifling a protein called survivin. Survivin is overexpressed in nearly every human tumor but is barely detectable in normal tissue, DuBois noted. Overexpression of survivin is associated with poor outcome and reduced apoptosis in colorectal cancer patients. The researchers pinpointed a cell signaling pathway by which activated CB1 cuts down survivin.

"Just increasing the levels of cannabinoids to treat colorectal cancer won't work if the CB1 receptor is not present," DuBois said. This suggests that treating first with a demethylating agent, such as decitabine, to reactivate CB1 in the tumor and following up with a cannabinoid might be an effective attack on colorectal cancer.

Scarcity of CB1 also is associated with Huntington's disease, Alzheimer's disease and multiple sclerosis. Further investigation, the researchers note, is needed to define its role in those diseases and other types of cancer. The team also analyzed the other main cannabinoid receptor, CB2, and found no role for it in colorectal cancer.

They also treated the mice with a CB1 antagonist, a compound that binds to the receptor but does not activate it. Mice with CB1 blocked in this manner also showed an increase in the number and size of polyps. A CB1 antagonist called rimonabant is currently marketed overseas for weight loss. The researchers note that a patient's risk for colorectal cancer should be assessed when use of such drugs is being considered.

The study was funded by grants from the National Cancer Institute and the National Colorectal Cancer Research Alliance.

https://www.sciencedaily.com/releases/2008/08/080801074056.htm

Separating the Therapeutic Benefits of Cannabis from its Mood-altering Side-effects

November 30, 2007

Science Daily/Queen Mary, University of London

Scientists from Queen Mary, University of London, have discovered a new way to separate the therapeutic benefits of cannabis from its mood-altering side-effects.

Cannabis contains a chemical called THC, which binds to, and activates, proteins in the brain known as ‘CB1 cannabinoid receptors’. Activating these receptors can relieve pain and prevent epileptic seizures; but it also causes the mood-altering effect experienced by people who use cannabis as a recreational drug.

Now, Professor Maurice Elphick and Dr Michaela Egertová from Queen Mary’s School of Biological and Chemical Sciences may have found a way of separating out the effects of cannabis – a discovery which could lead to the development of new medicines to treat conditions such as epilepsy, obesity and chronic pain. The research is described in the December issue of the journal Molecular Pharmacology.

Working in collaboration with scientists based in the USA*, they have identified a protein that binds to the CB1 receptors in the brain. But unlike THC, this ‘Cannabinoid Receptor Interacting Protein’ or CRIP1a, suppresses the activity of CB1 receptors.

Professor Elphick explains: “Because CRIP1a inhibits the activity of the brain’s cannabinoid receptors, it may be possible to develop drugs that block this interaction, and in turn enhance CB1 activity. This may give patients the pain relief associated with CB1 activity, without the ‘high’ that cannabis users experience.”

Leslie Iversen FRS, Professor of Pharmacology at the University of Oxford and author of The Science of Marijuana, commented on the new findings: “This interesting discovery provides a completely new insight into the regulation of the cannabinoid system in the brain - and could offer a new approach to the discovery of cannabis-based medicines in the future.”

“CB1 Cannabinoid Receptor Activity Is Modulated by the Cannabinoid Receptor Interacting Protein CRIP1a” is published online in the December issue of Molecular Pharmacology.

The Elphick laboratory in the School of Biological & Chemical Sciences at Queen Mary is supported by grants from UK research councils (BBSRC, MRC) and the Wellcome Trust.

https://www.sciencedaily.com/releases/2007/11/071129151109.htm