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Aims/hypothesisType 2 diabetes is characterised by reduced beta cell mass (BCM). However, it remains uncertain whether the reduction in BCM in type 2 diabetes is due to a decrease in size or number of beta cells. Our aim was to examine the impact of beta cell size and number on islet morphology in humans with and without type 2 diabetes.MethodsPancreas samples were obtained from 64 Japanese adults with (n = 26) and without (n = 38) type 2 diabetes who underwent pancreatectomy. Using pancreatic tissues stained for insulin, we estimated beta cell size based on beta cell diameter. Beta cell number was estimated from the product of fractional beta cell area and pancreas volume divided by beta cell size. The associations of beta cell size and number with islet morphology and metabolic status were examined.ResultsBoth beta cell size (548.7 ± 58.5 vs 606.7 ± 65.0 μm3, p < 0.01) and number (5.10 × 108 ± 2.35 × 108 vs 8.16 × 108 ± 4.27 × 108, p < 0.01) were decreased in participants with type 2 diabetes compared with those without diabetes, with the relative reduction in beta cell number (37%) being greater than for beta cell size (10%). Beta cell number but not size was positively correlated with BCM in participants with and without type 2 diabetes (r = 0.97 and r = 0.98, both p < 0.01) and negatively correlated with HbA1c (r = −0.45, p < 0.01).Conclusions/interpretationBoth beta cell size and number were reduced in participants with type 2 diabetes, with the relative reduction in beta cell number being greater. Decrease in beta cell number appears to be a major contributor to reduced BCM in type 2 diabetes.

Aims/hypothesis The role of beta cell mass in the balance of glucose control and hypoglycaemic burden in people with type 1 diabetes is unclear. We applied positron emission tomography (PET) imaging with radiolabelled exendin to compare beta cell mass among people with type 1 diabetes and either low glucose variability (LGV) or high glucose variability (HGV). Methods All participants with either LGV ( n =9) or HGV ( n =7) underwent a mixed-meal tolerance test to determine beta cell function and wore a blinded continuous glucose monitor for a week. After an i.v. injection with [ 68 Ga]Ga-NODAGA-exendin-4, PET images were acquired for the quantification of pancreatic uptake of radiolabelled exendin. The mean standardised uptake value (SUVmean) of the pancreas was used to determine the amount of beta cell mass. Results Participants with LGV had lower HbA 1c (46.0 mmol/mol [44.5–52.5] [6.4% (6.3–7)] vs 80 mmol/mol [69.0–110] [9.5% (8.5–12.2)], p =0.001) and higher time in range (TIR) (75.6% [73.5–90.3] vs 38.7% [25.1–48.5], p =0.002) than those with HGV. The SUVmean of the pancreas was higher for the LGV than for the HGV group (5.1 [3.6–5.6] vs 2.9 [2.1–3.4], p =0.008). The AUC C-peptide :AUC glucose ratio was numerically, but not statistically, higher in the LGV compared with the HGV group (2.7×10 −2 [6.2×10 −4 –5.3×10 −2 ] vs 9.3×10 −4 [4.7×10 −4 –5.2×10 −3 ], p =0.21). SUVmean correlated with the AUC C-peptide :AUC glucose ratio (Pearson r =0.64, p =0.01), as well as with the TIR ( r =0.64, p =0.01) and the SD of interstitial glucose levels ( r =−0.66, p =0.007). Conclusion/interpretation Our data show higher beta cell mass in people with type 1 diabetes and LGV than in those with HGV, independent of beta cell function. Graphical abstract

Aims/hypothesisSecond-generation antipsychotic (SGA) drugs have been associated with the development of type 2 diabetes and the metabolic syndrome in patients with schizophrenia. In this study, we aimed to investigate the effects of two different SGA drugs, olanzapine and aripiprazole, on metabolic state and islet function and plasticity.MethodsWe analysed the functional adaptation of beta cells in 12-week-old B6;129 female mice fed an olanzapine- or aripiprazole-supplemented diet (5.5–6.0 mg kg−1 day−1) for 6 months. Glucose and insulin tolerance tests, in vivo glucose-stimulated insulin secretion and indirect calorimetry were performed at the end of the study. The effects of SGAs on beta cell plasticity and islet serotonin levels were assessed by transcriptomic analysis and immunofluorescence. Insulin secretion was assessed by static incubations and Ca2+ fluxes by imaging techniques.ResultsTreatment of female mice with olanzapine or aripiprazole for 6 months induced weight gain (p<0.01 and p<0.05, respectively), glucose intolerance (p<0.01) and impaired insulin secretion (p<0.05) vs mice fed a control chow diet. Aripiprazole, but not olanzapine, induced serotonin production in beta cells vs controls, likely by increasing tryptophan hydroxylase 1 (TPH1) expression, and inhibited Ca2+ flux. Of note, aripiprazole increased beta cell size (p<0.05) and mass (p<0.01) vs mice fed a control chow diet, along with activation of mechanistic target of rapamycin complex 1 (mTORC1)/S6 signalling, without preventing beta cell dysfunction.Conclusions/interpretationBoth SGAs induced weight gain and beta cell dysfunction, leading to glucose intolerance; however, aripiprazole had a more potent effect in terms of metabolic alterations, which was likely a result of its ability to modulate the serotonergic system. The deleterious metabolic effects of SGAs on islet function should be considered while treating patients as these drugs may increase the risk for development of the metabolic syndrome and diabetes.

Type 2 diabetes (T2DM) is characterized by insulin resistance and beta-cell dysfunction. Although insulin resistance is assumed to be a main pathophysiological feature of the development of T2DM, recent studies have revealed that a deficit of functional beta-cell mass is an essential factor for the pathophysiology of T2DM. Pancreatic fat contents increase with obesity and are suggested to cause beta-cell dysfunction. Since the beta-cell dysfunction induced by obesity or progressive decline with disease duration results in a worsening glycemic control, and treatment failure, preserving beta-cell mass is an important treatment strategy for T2DM. In this mini-review, we summarize the current knowledge on beta-cell mass, beta-cell function, and pancreas fat in obesity and T2DM, and we discuss treatment strategies for T2DM in relation to beta-cell preservation.

The critical role of the beta cell in the pathogenesis of type 2 diabetes is now well established. When examined in patients with type 2 diabetes and individuals at increased risk, reductions in beta cell mass and abnormalities of beta cell function can both be demonstrated. The question of whether one alone is sufficient or both are necessary for the development of hyperglycaemia has been debated. Based on human and animal studies, it appears that neither alone is sufficient. Rather, for glucose to rise to the level at which diabetes would be diagnosed, defects in beta cell mass and in beta cell function are required.

Aims/hypothesis Stem cell-derived islets (SC-islets) are being used as cell replacement therapy for insulin-dependent diabetes. Non-invasive long-term monitoring methods for SC-islet grafts, which are needed to detect misguided differentiation in vivo and to optimise their therapeutic effectiveness, are lacking. Positron emission tomography (PET) has been used to monitor transplanted primary islets. We therefore aimed to apply PET as a non-invasive monitoring method for SC-islet grafts. Methods We implanted different doses of human SC-islets, SC-islets derived using an older protocol or a state-of-the-art protocol and SC-islets genetically rendered hyper- or hypoactive into mouse calf muscle to yield different kinds of grafts. We followed the grafts with PET using two tracers, glucagon-like peptide 1 receptor-binding [ 18 F]F-dibenzocyclooctyne-exendin-4 ([ 18 F]exendin) and the dopamine precursor 6-[ 18 F]fluoro- l -3,4-dihydroxyphenylalanine ([ 18 F]FDOPA), for 5 months, followed by histological assessment of graft size and composition. Additionally, we implanted a kidney subcapsular cohort with different SC-islet doses to assess the connection between C-peptide and stem cell-derived beta cell (SC-beta cell) mass. Results Small but pure and large but impure grafts were derived from SC-islets. PET imaging allowed detection of SC-islet grafts even <1 mm 3 in size, [ 18 F]exendin having a better detection rate than [ 18 F]FDOPA (69% vs 44%, <1 mm 3 ; 96% vs 85%, >1 mm 3 ). Graft volume quantified with [ 18 F]exendin ( r 2 =0.91) and [ 18 F]FDOPA ( r 2 =0.86) strongly correlated with actual graft volume. [ 18 F]exendin PET delineated large cystic structures and its uptake correlated with graft SC-beta cell proportion ( r 2 =0.68). The performance of neither tracer was affected by SC-islet graft hyper- or hypoactivity. C-peptide measurements under fasted or glucose-stimulated conditions did not correlate with SC-islet graft volume or SC-beta cell mass, with C-peptide under hypoglycaemia having a weak correlation with SC-beta cell mass ( r 2 =0.52). Conclusions/interpretation [ 18 F]exendin and [ 18 F]FDOPA PET enable non-invasive assessment of SC-islet graft size and aspects of graft composition. These methods could be leveraged for optimising SC-islet cell replacement therapy in diabetes. Graphical Abstract

Streptozotocin (STZ) is a cytotoxic glucose analogue that causes beta cell death and is widely used to induce experimental diabetes in rodents. The sensitivity of beta cells to STZ is species-specific and human beta cells are resistant to STZ. In experimental islet transplantation to rodents, STZ-diabetes must be induced before transplantation to avoid destruction of grafted islets by STZ. In human islet transplantation, injection of STZ before transplantation is inconvenient and costly, since human islet availability depends on organ donation and frail STZ-diabetic mice must be kept for unpredictable lapses of time until a human islet preparation is available. Based on the high resistance of human beta cells to STZ, we have tested a new model for STZ-diabetes induction in which STZ is injected after human islet transplantation. Human and mouse islets were transplanted under the kidney capsule of athymic nude mice, and 10–14 days after transplantation mice were intraperitoneally injected with five consecutive daily doses of STZ or vehicle. Beta-cell death increased and beta-cell mass was reduced in mouse islet grafts after STZ injection. In contrast, in human islet grafts beta cell death and mass did not change after STZ injection. Mice transplanted with rodent islets developed hyperglycemia after STZ-injection. Mice transplanted with human islets remained normoglycemic and developed hyperglycemia when the graft was harvested. STZ had no detectable toxic effects on beta cell death, mass and function of human transplanted islets. We provide a new, more convenient and cost-saving model for human islet transplantation to STZ-diabetic recipients in which STZ is injected after islet transplantation.

Aims/hypothesisLow birthweight is associated with a high risk of diabetes, but there are no reports discussing birthweight and pancreatic tissues in humans. The purpose of this study was to examine the correlation between birthweight and beta and alpha cell mass in humans.MethodsSixty-four Japanese adults with and without diabetes who underwent pancreatectomy and were able to recall their weight history including birthweight were included. Pancreatic tissues were stained for insulin and glucagon, and fractional beta cell area (BCA) and alpha cell area (ACA) were quantified. Islet size and density and beta cell replication were also quantified and their associations with birthweight were evaluated.ResultsIn participants without diabetes, there was a weak positive correlation between birthweight and BCA (R = 0.34, p = 0.03). The group with a history of childhood obesity, but not the group with a history of obesity in adulthood only, showed higher BCA compared with those without a history of obesity (1.78 ± 0.74% vs 0.99 ± 0.53%, p = 0.01), and the correlation coefficient between birthweight and BCA increased after excluding those with a history of childhood obesity (R = 0.51, p < 0.01). In those with diabetes, there was no correlation between birthweight and BCA. No correlation was found between birthweight and ACA in either those with or without diabetes.Conclusions/interpretationBirthweight and beta, but not alpha, cell mass are positively correlated in non-diabetic adults, and a history of childhood obesity may affect beta cell mass.

Arachidonic acid (AA) is a polyunsaturated 20-carbon fatty acid present in phospholipids in the plasma membrane. The three primary pathways by which AA is metabolized are mediated by cyclooxygenase (COX) enzymes, lipoxygenase (LOX) enzymes, and cytochrome P450 (CYP) enzymes. These three pathways produce eicosanoids, lipid signaling molecules that play roles in biological processes such as inflammation, pain, and immune function. Eicosanoids have been demonstrated to play a role in inflammatory, renal, and cardiovascular diseases as well type 1 and type 2 diabetes. Alterations in AA release or AA concentrations have been shown to affect insulin secretion from the pancreatic beta cell, leading to interest in the role of AA and its metabolites in the regulation of beta-cell function and maintenance of beta-cell mass. In this review, we discuss the metabolism of AA by COX, LOX, and CYP, the roles of these enzymes and their metabolites in beta-cell mass and function, and the possibility of targeting these pathways as novel therapies for treating diabetes.

Aims/hypothesisHigh-mobility group box 1 (HMGB1), an evolutionarily conserved chromosomal protein, was rediscovered to be a ‘danger signal’ (alarmin) that alerts the immune system once released extracellularly. Therefore, it has been recognised contributing to the pathogenesis of autoimmune diabetes, but its exact impact on the initiation and progression of type 1 diabetes, as well as the related molecular mechanisms, are yet to be fully characterised.MethodsIn the current report, we employed NOD mice as a model to dissect the impact of blocking HMGB1 on the prevention, treatment and reversal of type 1 diabetes. To study the mechanism involved, we extensively examined the characteristics of regulatory T cells (Tregs) and their related signalling pathways upon HMGB1 stimulation. Furthermore, we investigated the relevance of our data to human autoimmune diabetes.ResultsNeutralising HMGB1 both delayed diabetes onset and, of particular relevance, reversed diabetes in 13 out of 20 new-onset diabetic NOD mice. Consistently, blockade of HMGB1 prevented islet isografts from autoimmune attack in diabetic NOD mice. Using transgenic reporter mice that carry a Foxp3 lineage reporter construct, we found that administration of HMGB1 impairs Treg stability and function. Mechanistic studies revealed that HMGB1 activates receptor for AGE (RAGE) and toll-like receptor (TLR)4 to enhance phosphatidylinositol 3-kinase (PI3K)–Akt–mechanistic target of rapamycin (mTOR) signalling, thereby impairing Treg stability and functionality. Indeed, high circulating levels of HMGB1 in human participants with type 1 diabetes contribute to Treg instability, suggesting that blockade of HMGB1 could be an effective therapy against type 1 diabetes in clinical settings.Conclusions/interpretationThe present data support the possibility that HMGB1 could be a viable therapeutic target to prevent the initiation, progression and recurrence of autoimmunity in the setting of type 1 diabetes.