Daniel Espes

Increased Circulating Betatrophin Concentrations in Patients with Type 2 Diabetes

Betatrophin has recently been described as a key hormone to stimulate beta-cell mass expansion in response to insulin resistance and obesity in mice. The finding has generated an interest in the development of antidiabetic drugs with betatrophin as the active component. However, the circulating levels of betatrophin in patients with type 2 diabetes are not well known. Betatrophin concentrations in plasma of 27 type 2 diabetes patients and 18 gender-, age-, and BMI-matched controls were measured. Study participants were characterized with regard to BMI, waist and hip circumference, blood pressure, and fasting plasma blood lipids, creatinine, glucose, HbA1c, and C-peptide. HOMA2 indices were calculated. Betatrophin was 40% higher in patients with type 2 diabetes (893 ± 80 versus 639 ± 66 pg/mL). Betatrophin positively correlated with age in the controls and with HbA1c in the type 2 diabetes patients. All study participants were insulin resistant with mean HOMA2B IR in both groups exceeding 2 and HOMA2%S < 50%. Control individuals had impaired fasting glucose concentrations. In this report on betatrophin concentrations in type 2 diabetes and insulin resistance, elevated betatrophin levels were measured in the patients with type 2 diabetes. Future studies are clearly needed to delineate the exact role, if any, of betatrophin in regulating human beta-cell mass.

Positron Emission Tomography Ligand [11C]5-Hydroxy-Tryptophan Can Be Used as a Surrogate Marker for the Human Endocrine Pancreas

In humans, a well-developed serotonin system is localized to the pancreatic islets while being absent in exocrine pancreas. Assessment of pancreatic serotonin biosynthesis could therefore be used to estimate the human endocrine pancreas. Proof of concept was tested in a prospective clinical trial by comparisons of type 1 diabetic (T1D) patients, with extensive reduction of β-cells, with healthy volunteers (HVs). C-peptide–negative (i.e., insulin-deficient) T1D subjects (n = 10) and HVs (n = 9) underwent dynamic positron emission tomography with the radiolabeled serotonin precursor [11C]5-hydroxy-tryptophan ([11C]5-HTP). A significant accumulation of [11C]5-HTP was obtained in the pancreas of the HVs, with large interindividual variation. A substantial and highly significant reduction (66%) in the pancreatic uptake of [11C]5-HTP in T1D subjects was observed, and this was most evident in the corpus and caudal regions of the pancreas where β-cells normally are the major constituent of the islets. [11C]5-HTP retention in the pancreas was reduced in T1D compared with nondiabetic subjects. Accumulation of [11C]5-HTP in the pancreas of both HVs and subjects with T1D was in agreement with previously reported morphological observations on the β-cell volume, implying that [11C]5-HTP retention is a useful noninvasive surrogate marker for the human endocrine pancreas.

Pancreatic islet blood flow and its measurement

Abstract Pancreatic islets are richly vascularized, and islet blood vessels are uniquely adapted to maintain and support the internal milieu of the islets favoring normal endocrine function. Islet blood flow is normally very high compared with that to the exocrine pancreas and is autonomously regulated through complex interactions between the nervous system, metabolites from insulin secreting β-cells, endothelium-derived mediators, and hormones. The islet blood flow is normally coupled to the needs for insulin release and is usually disturbed during glucose intolerance and overt diabetes. The present review provides a brief background on islet vascular function and especially focuses on available techniques to measure islet blood perfusion. The gold standard for islet blood flow measurements in experimental animals is the microsphere technique, and its advantages and disadvantages will be discussed. In humans there are still no methods to measure islet blood flow selectively, but new developments in radiological techniques hold great hopes for the future.

Increased levels of irisin in people with long‐standing Type 1 diabetes

Irisin stimulates browning of white adipose tissue and improves metabolic control in mice. Betatrophin, another recently described hormone, improves metabolic control in mice by inducing β–cell proliferation. In vitro, irisin stimulates the expression of betatrophin in rat adipocytes. There is a great interest in developing drugs that target or use these hormones for the treatment of obesity and diabetes. We have previously reported on increased levels of betatrophin in people with Type 1 diabetes, but the levels of irisin are currently unknown.

Interleukin-35 administration counteracts established murine type 1 diabetes – possible involvement of regulatory T cells

The anti-inflammatory cytokine IL-35 is produced by regulatory T (Treg) cells to suppress autoimmune and inflammatory responses. The role of IL-35 in type 1 diabetes (T1D) remains to be answered. To elucidate this, we investigated the kinetics of Treg cell response in the multiple low dose streptozotocin induced (MLDSTZ) T1D model and measured the levels of IL-35 in human T1D patients. We found that Treg cells were increased in MLDSTZ mice. However, the Treg cells showed a decreased production of anti-inflammatory (IL-10, IL-35, TGF-β) and increased pro-inflammatory (IFN-γ, IL-2, IL-17) cytokines, indicating a phenotypic shift of Treg cells under T1D condition. IL-35 administration effectively both prevented development of, and counteracted established MLDSTZ T1D, seemingly by induction of Eos expression and IL-35 production in Treg cells, thus reversing the phenotypic shift of the Treg cells. IL-35 administration reversed established hyperglycemia in NOD mouse model of T1D. Moreover, circulating IL-35 levels were decreased in human T1D patients compared to healthy controls. These findings suggest that insufficient IL-35 levels play a pivotal role in the development of T1D and that treatment with IL-35 should be investigated in treatment of T1D and other autoimmune diseases.

Cotransplantation of Polymerized Hemoglobin Reduces β-Cell Hypoxia and Improves β-Cell Function in Intramuscular Islet Grafts

Background Muscle is a promising alternative site for islet transplantation that facilitates rapid restoration of islet vascularization. However, the development of fibrosis suggests massive cellular death after transplantation. This study tested the hypothesis that islet graft function is limited by hypoxia-related death early after intramuscular transplantation, but that this can be overcome by cotransplantation of an oxygen carrier, that is, polymerized bovine hemoglobin (PolyHb). Methods Two hundred islets were transplanted with or without different doses of PolyHb intramuscularly to nondiabetic C57BL/6 and diabetic C57BL/6 nu/nu mice. &bgr;-cell hypoxia and apoptosis were evaluated by immunohistochemistry after injection of the biochemical marker pimonidazole or by staining for caspase-3, respectively. Blood glucose concentrations were monitored for 30 days after islet transplantation and animals were then subjected to an intravenous glucose tolerance test. Results Substantial hypoxia was observed in control islet grafts during the first 4 days after transplantation. Cotransplantation of PolyHb resulted in a dose-dependent reduction of &bgr;-cell hypoxia, but &bgr;-cell apoptosis was only reduced by cotransplantation of low-dose PolyHb (0.03 mg/g body weight) due to the inflammatory effects of higher PolyHb concentrations. Cotransplantation of low-dose PolyHb resulted in improved islet graft function 30 days after transplantation in diabetic mice, with a glucose tolerance comparable to transplantation of 50% more islets. Conclusion We conclude that cotransplantation of islets with PolyHb can be used to effectively bridge the critical hypoxic phase immediately after transplantation, improve islet graft function, and reduce the number of islets needed for successful intramuscular transplantation.

Betatrophin in Diabetes Mellitus: the Epidemiological Evidence in Humans.

The prevalence of type 2 diabetes is increasing worldwide, and while numerous treatments exist, none of the current pharmacologic therapies is curative. Pharmacologic approaches that increase beta cell mass may present an avenue for actual cure. There have been numerous reports on factors that can induce beta cell proliferation in rodents, whereas there are still very limited data on the occurrence of beta cell proliferation in humans. The recent discovery of the hormone betatrophin, which in mice counteracted glucose intolerance induced by insulin resistance by potently stimulating beta cell proliferation, has boosted the hope for a new target for drug development for the treatment of diabetes mellitus in humans. With the encouraging preclinical findings as a background, this review presents the available clinical data on betatrophin and discusses its possible role in humans.

Striated Muscle as Implantation Site for Transplanted Pancreatic Islets

Islet transplantation is an attractive treatment for selected patients with brittle type 1 diabetes. In the clinical setting, intraportal transplantation predominates. However, due to extensive early islet cell death, the quantity of islets needed to restore glucose homeostasis requires in general a minimum of two donors. Moreover, the deterioration of islet function over time results in few insulin-independent patients after five-year followup. Specific obstacles to the success of islet transplantation include site-specific concerns for the liver such as the instant blood mediated inflammatory reaction, islet lipotoxicity, low oxygen tension, and poor revascularization, impediments that have led to the developing interest for alternative implantation sites over recent years. Within preclinical settings, several alternative sites have now been investigated and proven favorable in various aspects. Muscle is considered a very promising site and has physiologically properties and technical advantages that could make it optimal for islet transplantation.

Rapid Restoration of Vascularity and Oxygenation in Mouse and Human Islets Transplanted to Omentum May Contribute to Their Superior Function Compared to Intraportally Transplanted Islets

Transplantation of islets into the liver confers several site‐specific challenges, including a delayed vascularization and prevailing hypoxia. The greater omentum has in several experimental studies been suggested as an alternative implantation site for clinical use, but there has been no direct functional comparison to the liver. In this experimental study in mice, we characterized the engraftment of mouse and human islets in the omentum and compared engraftment and functional outcome with those in the intraportal site. The vascularization and innervation of the islets transplanted into the omentum were restored within the first month by paralleled ingrowth of capillaries and nerves. The hypoxic conditions in the islets early posttransplantation were transient and restricted to the first days. Newly formed blood vessels were fully functional, and the blood perfusion and oxygenation of the islets became similar to that of endogenous islets. Furthermore, islet grafts in the omentum showed at 1 month posttransplantation functional superiority to intraportally transplanted grafts. We conclude that in contrast to the liver the omentum provides excellent engraftment conditions for transplanted islets. Future studies in humans will be of great interest to investigate the capability of this site to also harbor larger grafts without interfering with islet functionality.

The Cannabinoid Receptor-1 Is an Imaging Biomarker of Brown Adipose Tissue

Recently, the existence of significant deposits of brown adipose tissue (BAT) in human adults was confirmed. Its role in the human metabolism is unknown but could be substantial. Inhibition of the cannabinoid receptor-1 (CB1) by the antagonist rimonabant (SR141716) has been associated with activation of BAT thermogenesis and weight loss in mice and rats. The role of peripheral and central CB1 in the activation of BAT merits further investigation. Here we developed a technique for quantifying CB1 in BAT by PET. Methods: Sections of rat BAT and subcutaneous white adipose tissue (WAT) were stained for CB1 and uncoupling protein-1 by immunofluorescent staining. Binding of the radiolabeled CB1 antagonist (3R,5R)-5-(3-(18F-fluoromethoxy)phenyl)-3-(((R)-1-phenylethyl)amino)-1-(4-(trifluoromethyl)-phenyl)pyrrolidin-2-one (18F-FMPEP-d2) to BAT in vivo and in vitro was assessed in rats by PET. Results: We found that CB1 was colocalized with uncoupling protein-1 in BAT, but neither protein was found in WAT. Binding of the radiotracer to BAT sections (but not WAT) in vitro was high and displaceable by pretreatment with rimonabant. Deposits of BAT in rats had significant binding of 18F-FMPEP-d2 in vivo, indicating high CB1 density. WAT deposits were negative for 18F-FMPEP-d2, consistent with the immunofluorescent staining and in vitro results. Conclusion: 18F-FMPEP-d2 PET can quantify CB1 density noninvasively in vivo in rats. CB1 is therefore a promising surrogate imaging biomarker for assessing the presence of BAT deposits as well as for elucidating the mechanism of CB1 antagonist–mediated weight loss.