In purple, the tanycytes that form the brain’s cellular gateway to the hormone leptin; in yellow, the appetite-inducing neurons and, in blue, the appetite-suppressing neurons. Leptin targets both neuron types, inhibiting the former and using its appetite-suppressant signal to activate the latter. CREDIT Inserm/Vincent Prévot

Leptin, the satiety or appetite-suppressant hormone, is secreted by the adipose tissue at levels proportional to the body’s fat reserves and regulates appetite by controlling the feeling of fullness.  It is transported to the brain by tanycytes – cells which it enters by attaching to the LepR receptors. Tanycytes are therefore leptin’s gateway to the brain, helping it to cross the blood-brain barrier and deliver satiety information to the neurons.

Previous research has revealed that such transport is impaired in subjects who are obese or overweight. This goes some way to explaining their dysfunctional appetite regulation given that it is more difficult for the information on satiety to reach the brain. In their new study, the researchers took a closer look at this transport mechanism, and more precisely the role played by the LepR receptors.

The key role of satiety hormone receptors in glucose management

In mouse models, the researchers removed the LepR receptor that is located on the surface of the tanycytes. After three months, the mice experienced a marked increase in their fat mass (which doubled over the period) as well as a loss of muscle mass (reduced by more than half). The total amount of weight gained was only fairly moderate. The scientists also regularly measured the animals’ blood sugar levels following the injection of glucose.

They found that in order to maintain blood sugar at normal levels (between 0.70 and 1.10 g/L), the mice secreted more insulin during the first four weeks of the experiment. Three months after removing the receptor, their ability to secrete insulin from the pancreas appeared to be exhausted.

Removing the LepR receptors and impairing leptin transport to the brain therefore led the mice to initially develop a pre-diabetic state. This occurs when the body releases more insulin than usual in order to control blood sugar. Then, in the longer term, the mice became unable to secrete insulin and as such unable to control their blood sugar levels. These data therefore suggest that impaired leptin transport to the brain via the LepR receptors plays a role in the development of type 2 diabetes.

In the last part of their research, the scientists reintroduced leptin to the brain and observed the immediate resumption of its pancreatic function-promoting action – particularly the ability of the pancreas to secrete insulin to regulate blood sugar. The mice quickly regained a healthy metabolism.

This study therefore elucidates the brain’s role in type 2 diabetes and also helps to further research into a disease that until then had not been considered to involve the central nervous system.

“We show that the brain’s perception of leptin is essential for the management of energy homeostasis[1] and blood sugar. We also show that blocking the transport of leptin to the brain impairs the functioning of the neurons that control pancreatic insulin secretion,” concludes Vincent Prévot, research director at Inserm and last author of the study.

To 3D print vascularized hydrogels that can be turned into living tissue, Rice University bioengineers use (top left) a nontoxic liquid polymer that is (top middle) solidified one layer at a time by blue light. Yellow food coloring absorbs the light, allowing for the creation of passageways for flowing blood. Postdoctoral researcher Kristen Means (top right) displays a printed hydrogel that was secured (bottom right and middle) in a plastic housing for graduate student Madison Royse’s (bottom left) blood-flow demonstration using liquid dye. CREDIT Photos by Jeff Fitlow/Rice University

Rice University bioengineers are using 3D printing and smart biomaterials to create an insulin-producing implant for Type 1 diabetics.

The three-year project is a partnership between the laboratories of Omid Veiseh and Jordan Miller that’s supported by a grant from JDRF, the leading global funder of diabetes research. Veiseh and Miller will use insulin-producing beta cells made from human stem cells to create an implant that senses and regulates blood glucose levels by responding with the correct amount of insulin at a given time.

Veiseh, an assistant professor of bioengineering, has spent more than a decade developing biomaterials that protect implanted cell therapies from the immune system. Miller, an associate professor of bioengineering, has spent more than 15 years researching techniques to 3D print tissues with vasculature, or networks of blood vessels.

“If we really want to recapitulate what the pancreas normally does, we need vasculature,” Veiseh said. “And that’s the purpose of this grant with JDRF. The pancreas naturally has all these blood vessels, and cells are organized in particular ways in the pancreas. Jordan and I want to print in the same orientation that exists in nature.”

Type 1 diabetes is an autoimmune disease that causes the pancreas to stop producing insulin, the hormone that controls blood-sugar levels. About 1.6 million Americans live with Type 1 diabetes, and more than 100 cases are diagnosed each day. Type 1 diabetes can be managed with insulin injections. But balancing insulin intake with eating, exercise and other activities is difficult. Studies estimate that fewer than one-third of Type 1 diabetics in the U.S. consistently achieve target blood glucose levels.

Veiseh’s and Miller’s goal is to show their implants can properly regulate blood glucose levels of diabetic mice for at least six months. To do that, they’ll need to give their engineered beta cells the ability to respond to rapid changes in blood sugar levels.

“We must get implanted cells in close proximity to the bloodstream so beta cells can sense and respond quickly to changes in blood glucose,” Miller said.

Ideally, insulin-producing cells will be no more than 100 microns from a blood vessel, he said.

“We’re using a combination of pre-vascularization through advanced 3D bioprinting and host-mediated vascular remodeling to give each implant several shots at host integration,” Miller said.

The insulin-producing cells will be protected with a hydrogel formulation developed by Veiseh, who is also a Cancer Prevention and Research Institute of Texas Scholar. The hydrogel material, which has proven effective for encapsulating cell treatments in bead-sized spheres, has pores small enough to keep the cells inside from being attacked by the immune system but large enough to allow passage of nutrients and life-giving insulin.

“Blood vessels can go inside of them,” Veiseh said of the hydrogel compartments. “At the same time, we have our coating, our small molecules that prevent the body from rejecting the gel. So it should harmonize really well with the body.”

If the implant is too slow to respond to high or low blood sugar levels, the delay can produce a roller coaster-like effect, where insulin levels repeatedly rise and fall to dangerous levels.

“Addressing that delay is a huge problem in this field,” Veiseh said. “When you give the mouse — and ultimately a human — a glucose challenge that mimics eating a meal, how long does it take that information to reach our cells, and how quickly does the insulin come out?”

By incorporating blood vessels in their implant, he and Miller hope to allow their beta-cell tissues to behave in a way that more closely mimics the natural behavior of the pancreas.

A transplant of healthy gut microbes followed by fibre supplements benefits patients with severe obesity and metabolic syndrome, according to University of Alberta clinical trial findings published today in Nature Medicine.

Patients who were given a single-dose oral fecal microbial transplant followed by a daily fibre supplement were found to have better insulin sensitivity and higher levels of beneficial microbes in their gut at the end of the six-week trial. Improved insulin sensitivity allows the body to use glucose more effectively, reducing blood sugar.

“They were much more metabolically healthy,” said principal investigator Karen Madsen, professor of medicine in the Faculty of Medicine & Dentistry and director of the Centre of Excellence for Gastrointestinal Inflammation and Immunity Research.

“These patients were on the best known medications (for metabolic syndrome) and we could improve them further, which shows us there is an avenue for improvement by targeting these different pathways in the microbiome.”

Sixty-one patients with a body mass index of 40 or higher completed the double-blind, randomized trial. Recruited from the bariatric surgery waitlist in Edmonton, all had metabolic syndrome, a condition that includes insulin resistance, high blood glucose, high blood pressure and other complications. It can eventually lead to diabetes.

The microbiome is all of the bugs–micro-organisms, bacteria, viruses, protozoa and fungi–found in the gastrointestinal tract. People with various diseases are known to have altered microbial contents. It is not fully understood whether microbiome changes cause disease or whether disease causes changes in the gut, but it is likely a bit of both, Madsen said. It is known that replacing unhealthy bacteria with healthy bacteria can lead to improved health.

Fecal transplants, which contain microbes from healthy stool donors, are currently used extensively for treating Clostridium difficile, or C. difficile, bacterial infections, and research is underway to test their usefulness in treating other illnesses such as inflammatory bowel disease, mental health and metabolic disorders.

“We know that the gut microbiome affects all of these processes–inflammation, metabolism, immune function,” said Madsen, who is a member of the Women and Children’s Health Research Institute and is one of the University of Alberta leads for the national Microbiome Research Core (IMPACTT).

“The potential for improving human health through the microbiome is immense,” Madsen said. “We are only scratching the surface at the moment.”

This is the first study to show that oral delivery of fecal transplantation is effective in patients with obesity-related metabolic syndrome.

A previous study done in Europe on a small number of male patients with obesity and metabolic syndrome had shown promising results, but the transplants in that study were given through an invasive endoscopy (a tube down the throat) and the patients had milder disease.

The fecal microbial transplants in this study were from four lean, healthy donors, and were taken by mouth in a single dose of about 20 capsules prepared in a U of A lab. The capsules have no taste or odour.

The fibre supplements following the transplant were key to the success, Madsen said.

“When you transplant beneficial microbes, you need to feed them to keep them around,” Madsen explained. “If you give a new microbe and you don’t feed it, if you continue to eat a diet of processed foods and no fibre, then that microbe will likely die.”

Our bodies do not naturally produce the enzymes needed to break down fibre, but that’s what healthy bacteria in the microbiome need to live, thus the supplements. The team experimented with fermentable fibre (the kind found in beans, which produce gas) and non-fermentable fibre (essentially cellulose, found in whole grains).

“Non-fermentable fibre can change gut motility–how fast things move through–as well as acting as a bulking and binding agent that can change levels of bile acids, which could help explain our results,” Madsen explained.

Madsen said the next step will be to do a longer study with more participants in multiple centres to learn how the transplant/fibre combination works and to monitor for changes in medication requirements, weight loss and other indicators. If results continue to show benefit, she said the pills could be available as a potential therapy within five years.

While scientists continue to narrow down which bacteria are the most beneficial for us, Madsen recommends we support the health of our own gut microbiome by eating fewer processed foods and more foods that contain fibre, such as whole grains, fruits and vegetables.

Phase 2 clinical trial results show fewer episodes of low blood sugar and comparable safety

A new once-weekly basal insulin injection demonstrated similar efficacy and safety and a lower rate of low blood sugar episodes compared with a daily basal insulin, according to a phase 2 clinical trial. The study results, which will be presented at ENDO 2021, the Endocrine Society’s annual meeting, compared an investigational drug called basal insulin Fc (BIF) with insulin degludec, a commercially available long-lasting daily insulin, in patients with type 2 diabetes.

“These study results demonstrate that BIF has promise as a once-weekly basal insulin and could be an advancement in insulin therapy,” said Juan Frias, M.D., the study’s principal investigator and the medical director of the National Research Institute in Los Angeles, Calif.

The reduced number of injections with weekly insulin may improve adherence to insulin therapy, which could result in better patient outcomes than for daily basal insulins, Frias said. Once-weekly dosing also may increase the willingness of patients with type 2 diabetes to start insulin therapy when oral medication alone no longer gives adequate blood glucose control, he added.

The 32-week clinical trial was conducted in 399 patients and sponsored by Eli Lilly and Company. All patients had type 2 diabetes and were previous users of basal insulin combined with oral antidiabetic medications.

The patients received random assignments to one of three treatment groups: once-weekly injections of BIF at one of two different dosing algorithms (with different goals for fasting blood glucose levels) or the standard once-daily injections of insulin degludec. One fasting glucose target for patients receiving BIF was 140 milligrams per deciliter (mg/dL) or less, and the other was at or below 120 mg/dL. The fasting glucose target for insulin degludec was 100 mg/dL or less.

Compared with insulin degludec, patients taking BIF achieved similar long-term blood glucose control, as measured by hemoglobin A1c, the researchers reported. Study participants had an average A1c of 8.1 percent at the beginning of the study and at the end of the study had an average improvement in A1c of 0.6 percent for BIF and 0.7 percent for insulin degludec, the data showed.

Additionally, BIF use resulted in significantly lower rates of hypoglycemia, or low blood sugar (less than 70 mg/dL). Severe untreated hypoglycemia is a dangerous complication that can cause seizures, loss of consciousness and death. Frias said BIF has “the potential of a flatter and more predictable action than the current daily basal insulins, which may have contributed to the lower rates of hypoglycemia.”

Regarding safety, BIF had a generally comparable adverse event profile to that of insulin degludec, he said.

“Based on our promising data, further research with BIF has been initiated in patients with type 1 diabetes and other type 2 diabetes patient populations,” Frias said.

At left is a healthy islet with many insulin-producing cells (green) and few glucagon-producing cells (red). At right, this situation is altered in a diabetic islet with a heavy preponderance of glucagon-producing cells (red) and very few insulin-producing cells CREDIT UT Southwestern Medical Center.

Blocking cell receptors for glucagon, the counter-hormone to insulin, cured mouse models of diabetes by converting glucagon-producing cells into insulin producers instead, a team led by UT Southwestern reports in a new study. The findings, published online in PNAS, could offer a new way to treat both Type 1 and Type 2 diabetes in people.

More than 34 million Americans have diabetes, a disease characterized by a loss of beta cells in the pancreas. Beta cells produce insulin, a hormone necessary for cells to absorb and use glucose, a type of sugar that circulates in the blood and serves as cellular fuel.

In Type 2 diabetes, the body’s tissues develop insulin resistance, prompting beta cells to die from exhaustion from secreting excess insulin to allow cells to take in glucose. In Type 1 diabetes, which affects about 10 percent of the diabetic population, beta cells die from an autoimmune attack. Both kinds of diabetes lead to severely elevated blood sugar levels that eventually cause a host of possible complications, including loss of limbs and eyesight, kidney damage, diabetic coma, and death.

Most treatments for diabetes focus on insulin, but its counterpart – the hormone glucagon that is produced by alpha cells in the pancreas – has received comparatively little attention, says study leader May-Yun Wang, Ph.D., assistant professor of internal medicine at UTSW. Glucagon binds to receptors on cells in the liver, prompting this organ to secrete glucose. Some recent studies have suggested that depleting glucagon or blocking its receptor can help research animals or humans with diabetes better manage their glucose levels. But how this phenomenon occurs has been unknown.

To answer this question, Wang and her colleagues, including William L. Holland, Ph.D., a former assistant professor of internal medicine at UTSW who is now at the University of Utah, and Philipp E. Scherer, Ph.D., professor of internal medicine and cell biology at UTSW and director of UTSW’s Touchstone Center for Diabetes Research, used monoclonal antibodies – manmade proteins that act like human antibodies and help the immune system identify and neutralize whatever they bind to – against the glucagon receptor in mouse models of diabetes.

In one model, called PANIC-ATTAC (pancreatic islet beta-cell apoptosis through targeted activation of caspase 8), a genetic mutation causes beta cells to selectively die off when these mice receive a chemical treatment. Once these animals’ beta cells were depleted, the researchers administered monoclonal antibodies against the glucagon receptor. Weekly treatment with the antibodies substantially lowered the rodents’ blood sugar, an effect that continued even weeks after the treatments stopped.

Further investigation showed that the number of cells in the pancreas of these animals significantly increased, including beta cells. Searching for the source of this effect, the researchers used a technique called lineage tracing to label their alpha cells. When they followed these alpha cells through rounds of cell divisions, they found that treatment with monoclonal antibodies pushed some of the glucagon-producing alpha cell population to convert into insulin-producing beta cells.

Although the PANIC-ATTAC model shares the same beta cell loss that occurs in both Type 1 and Type 2 diabetes, it’s missing the autoimmune attack that spurs Type 1 diabetes. To see if beta cells could rebound through alpha cell conversion under these circumstances, the researchers worked with a different mouse model called nonobese diabetic (NOD) mice in which their beta cells become depleted through an autoimmune reaction. When these animals were dosed with monoclonal antibodies, beta cells returned, despite active immune cells.

In a third animal model that more closely mimics a human system, the researchers injected human alpha and beta cells into immunodeficient NOD mice – just enough cells to produce sufficient insulin to make the animals borderline diabetic. When these mice received monoclonal antibodies against the glucagon receptor, their human beta cells increased in number, protecting them against diabetes, suggesting this treatment could do the same for people.

Holland notes that being able to push alpha cells to shift to beta cells could be especially promising for Type 1 diabetics. “Even after decades of an autoimmune attack on their beta cells, Type 1 diabetics will still have plentiful amounts of alpha cells. They aren’t the cells in the pancreas that die,” he says. “If we can harness those alpha cells and convert them into beta cells, it could be a viable treatment for anyone with Type 1 diabetes.”

Being able to produce native insulin, adds Wang, could hold significant advantages over the insulin injections and pumps used by both Type 1 and Type 2 diabetics. Eventually, she says, similar monoclonal antibodies could be tested in diabetics in clinical trials.

“Even though Type 1 and Type 2 diabetics try their very best to keep glucose under control, it fluctuates quite massively throughout the day even with the best state-of-the-art pump,” Wang says. “Giving them back their own beta cells could help restore much better natural regulation, greatly improving glucose regulation and quality of life.”

Scherer holds the Gifford O. Touchstone, Jr. and Randolph G. Touchstone Distinguished Chair in Diabetes Research and the Touchstone/West Distinguished Chair in Diabetes Research.