Interim results from a multicenter clinical trial demonstrate insulin secretion from engrafted cells in patients with type 1 diabetes. The safety, tolerability, and efficacy of the implants, which consisted of pancreatic endoderm cells derived from human pluripotent stem cells (PSCs), were tested in 26 patients. While the insulin secreted by the implants did not have clinical effects in the patients, the data are the first reported evidence of meal-regulated insulin secretion by differentiated stem cells in human patients. The results appear December 2 in the journals Cell Stem Cell and Cell Reports Medicine.

“A landmark has been set. The possibility of an unlimited supply of insulin-producing cells gives hope to people living with type 1 diabetes,” says Eelco de Koning of Leiden University Medical Center, a co-author of an accompanying commentary published in Cell Stem Cell. “Despite the absence of relevant clinical effects, this study will remain an important milestone for the field of human PSC-derived cell replacement therapies as it is one of the first to report cell survival and functionality one year after transplantation.”

Approximately 100 years following the discovery of the hormone insulin, type 1 diabetes remains a life-altering and sometimes life-threatening diagnosis. The disease is characterized by the destruction of insulin-producing β-cells in the Islets of Langerhans of the pancreas, leading to high levels of the blood sugar glucose.

Insulin treatment lowers glucose concentrations but does not completely normalize them. Moreover, modern insulin delivery systems can be burdensome to wear for long periods, sometimes malfunction, and often lead to long-term complications. While islet replacement therapy could offer a cure because it restores insulin secretion in the body, this procedure has not been widely adopted because donor organs are scarce. These challenges underscore the need for an abundant alternate supply of insulin-producing cells.

The use of human PSCs has made significant progress toward becoming a viable clinical option for the mass production of insulin-producing cells. In 2006, scientists at Novocell (now ViaCyte) reported a multi-stage protocol directing the differentiation of human embryonic stem cells into immature pancreatic endoderm cells. This stepwise protocol manipulating key signaling pathways was based on embryonic development of the pancreas. Follow-up studies showed that these pancreatic endoderm cells were able to mature further and become fully functional when implanted in animal models. Based on these results, clinical trials were started using these pancreatic endoderm cells.

Now two groups report on a phase I/II clinical trial in which pancreatic endoderm cells were placed in non-immunoprotective (“open”) macroencapsulation devices, which allowed for direct vascularization of the cells, and implanted under the skin in patients with type 1 diabetes. The use of third-party off-the-shelf cells in this stem cell-based islet replacement strategy required immunosuppressive agents, which protect against graft rejection but can cause major side effects, such as cancer and infections. The participants underwent an immunosuppressive treatment regimen that is commonly used in donor islet transplantation procedures.

In Cell Stem Cell, Timothy Kieffer of the University of British Columbia and his collaborators provided compelling evidence of functional insulin-secreting cells after implantation. PEC-01s — the drug candidate pancreatic endoderm cells produced by ViaCyte — survived and matured into glucose-responsive, insulin-secreting cells within 26 weeks after implantation. Over the up to one year of follow-up, patients had 20% reduced insulin requirements, and spent 13% more time in target blood glucose range. Overall, the implants were well tolerated with no severe graft-related adverse events.

“For the first time, we provide evidence that stem cell-derived PEC-01s can mature into glucose-responsive, insulin-producing mature β-cells in vivo in patients with type 1 diabetes,” Kieffer says. “These early findings support future investment and investigation into optimizing cell therapies for diabetes.”

However, two patients experienced serious adverse events associated with the immunosuppression protocol. Moreover, there was no control group and the interventions were not blinded, limiting causal conclusions, and outcomes were highly variable among the small number of participants. In addition, further studies need to determine the dose of pancreatic endoderm cells necessary to achieve clinically relevant benefits for patients.

In Cell Reports Medicine, Howard Foyt of ViaCyte and his collaborators reported engraftment and insulin expression in 63% of devices explanted from trial subjects at time periods ranging from 3 to 12 months after implantation. The progressive accumulation of functional, insulin-secreting cells occurred over a period of approximately 6-9 months from the time of implant.

The majority of reported adverse events were related to surgical implant or explant procedures or to immunosuppressive side effects. Despite potent systemic immune suppression, multiple surgical implantation sites, and the presence of foreign materials, the risk of local infection was exceedingly low, suggesting that this approach is well tolerated in subjects who are at risk for a poor healing response. The researchers are currently working on ways to promote graft vascularization and survival.

“The present study demonstrates definitively for the first time to our knowledge, in a small number of human subjects with type 1 diabetes, that PSC-derived pancreatic progenitor cells have the capacity to survive, engraft, differentiate, and mature into human islet-like cells when implanted subcutaneously,” Foyt says.

Both reports showed that the grafts were vascularized and that cells in the device can survive up to 59 weeks after implantation. Analyses of the grafts revealed that the main islet cell types, including β-cells, are present. Moreover, there was no formation of tumors called teratomas. However, the ratio of different endocrine cell types was atypical compared to mature pancreatic islets, and the total percentage of insulin-positive cells in the device was relatively low.

Regarding safety, most severe adverse events were associated with the use of immunosuppressive agents, emphasizing the life-long use of these drugs as a major hurdle for wider implementation of these types of cell replacement therapies. “An ideal and sunny possible future scenario would be the wide availability of a safe and efficacious stem cell-based islet replacement therapy without the need for these immunosuppressive agents or invasive, high-risk transplantation procedures,” says Françoise Carlotti of Leiden University Medical Center, a co-author of the related commentary.

According to de Koning and Carlotti, many questions remain to be answered. For example, researchers need to determine the differentiation stage at which the cells are most optimal for transplantation, and the best transplantation site. It is also not clear whether the effectiveness and safety of the cells can be maintained over time, and whether it is possible to eliminate the need for immunosuppressive therapy.

“The clinical road to wide implementation of stem cell-derived islet replacement therapy for type 1 diabetes is likely to be long and winding. Until that time, donor pancreas and islet transplantation will remain important therapeutic options for a small group of patients,” de Koning says. “But an era of clinical application of innovative stem-cell based islet replacement therapy for the treatment of diabetes has finally begun.”

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Intranasal insulin induces an increase in the [11C] raclopride binding potential in the striatum, which indicates a decrease in the synaptic dopamine level. © IDM

In the human brain, the hormone insulin also acts on the most important neurotransmitter for the reward system, dopamine. This was shown by researchers from the German Center for Diabetes Research (DZD) in Tübingen. Insulin lowers the dopamine level in a specific region of the brain (striatum *) that regulates reward processes and cognitive functions, among other things. This interaction can be an important driver of the brain’s regulation of glucose metabolism and eating behavior. The study has now been published in the Journal of Clinical Endocrinology & Metabolism.  

Worldwide, more and more people are developing obesity and type 2 diabetes. Studies show that the brain plays an important role in causing these diseases. Dopamine is the most important neurotransmitter for the reward system. The hormone insulin is released after eating and regulates the metabolism in the human body (homeostatic system). It is not yet known how these two systems interact. However, changes in these systems have been linked to obesity and diabetes. In the current study, researchers from the Institute of Diabetes Research and Metabolic Diseases (IDM) of Helmholtz Zentrum München at the University of Tübingen, a partner of the DZD, and Tübingen University Hospital (Innere IV, Director: Prof. Andreas Birkenfeld) examined how the two systems interact specifically in the reward center of the brain, the striatum.  

“Our eating behavior is regulated by the interaction between the reward system and homeostatic systems. Studies indicate that insulin also acts in dopamine-driven reward centers in the brain. It has also been shown that obesity leads to changes in the signaling of the brain that have a negative effect on the glucose metabolism in the whole body,” said first author Stephanie Kullmann. “We now wanted to decipher the interaction between the two systems in humans and find out how insulin regulates the dopamine system.” 

For this purpose, ten healthy, normal-weight men received insulin or a placebo via a nasal spray (randomized, placebo-controlled, blinded crossover study). When insulin is absorbed via the nose, it reaches the brain directly. To study the interaction between insulin and dopamine, the researchers used a unique measurement technique: they combined magnetic resonance imaging to assess functional brain activity and positron emission tomography to assess dopamine levels.   

Analysis of the study showed that the intranasal administration of insulin lowered dopamine levels and led to changes in the brain’s network structure. “The study provides direct evidence of how and where in the brain signals triggered after eating – such as insulin release and the reward system – interact,” said Professor Martin Heni, last author of the study, summarizing the results. “We were able to show that insulin is able to decrease dopamine levels in the striatum in normal-weight individuals. The insulin-dependent change in dopamine levels was also associated with functional connectivity changes in whoe-brain networks. Changes in this system may be an important driver of obesity and related diseases.” 

In further studies, the researchers want to investigate changes in the interaction of dopamine and insulin in obese or diabetic participants. These people often suffer from insulin resistance in the brain. The researchers therefore assume that this resistance prevents the normal insulin-induced regulation of dopamine levels in the reward center. In further steps, they want to restore the normal action of insulin in the brain by behavioral and/or pharmaceutical interventions. 

Insulin is one of the most well known hormones in the human body for its role in regulating blood glucose. While its absence or inaction causes diabetes (Type-I and Type-II), it is also associated with several metabolic disorders such as obesity, hypertension, cancer and aging. Levels of insulin, produced by the pancreas, fluctuate between fasted and fed states in a normal healthy individual. However, abnormally high amounts of insulin could be found either in hyper-insulinemic states (pre-/early-diabetic) or during treatments with clinically administered insulin (for both types of diabetes).

Diabetes is often associated with tissue damage resulting in neuropathy, nephropathy and myopathy among others. This is linked to insulin (in)action since besides its essentiality for maintaining glycemic index, it is critical for controlling tissue growth and repair.

Insulin dependent effects are mediated by an intricate and elaborate network of molecules that convey information, inside all cells, about the presence and concentrations of insulin and constitute the insulin signaling cascade. The flow of information within the different components of insulin signaling cascade dictates the uptake and utilization of glucose for metabolism and tissue growth.

Albeit decades of work elucidated the molecular components of the insulin signaling cascade, how information is conveyed amongst these different molecules in response to varied insulin inputs is still unknown. Besides being fundamentally important to our understanding of action of insulin under fed and fasted states, this is relevant in the context of diabetes, both emergence and treatment.

Moreover, with excess consumption of high calorie diets and aberrant or uncontrolled feeding habits, if/how perturbed information flow in insulin signaling cascade, under these conditions, lead to ‘insulin resistance’ has not been addressed thus far.

The study illustrates robustness of information flow in the signaling cascade in response to normal and abnormal insulin inputs. It demonstrates the importance of normal feed-fast cycles with the discovery of fasted insulin inputs leading to better response to fed insulin inputs. The findings also elucidate the detrimental impact of constant high insulin as in the case of uncontrolled feeding habits, without a fasting phase, and effects on signaling molecules that govern tissue maintenance and growth. The study identifies potential novel regulatory components and parameters whose modulation could lead to better therapeutic interventions in the future to reduce tissue damage, beyond the usual impact on blood glucose.

The study uncovers hitherto unknown mechanisms that regulate robustness of information flow through insulin signaling. In addition to highlighting the importance of normal insulin cycles (during feeding and fasting), it identifies components that could perturb the signaling cascade under situations of hyper-insulinemia as in diabetes and clinical insulin administration. The study also raises the possibility of re-evaluation of insulin dosing (amounts and frequency) to ascertain its impact on molecular components that protect tissues from damage, beyond maintenance of blood glucose levels.

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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.