Distinct hypoglycemic effect of different formulations of a fixed ratio of basal insulin plus glucagon-like peptide-1 receptor agonist in a patient with pancreatic diabetes

Fixed-ratio combination injection therapy (FRC) is a fixed-ratio mixture containing basal insulin and glucagon-like peptide-1 receptor agonist (GLP-1 RA) in a single injection for the treatment of patients with type 2 diabetes. The two types of FRC products contain different concentrations and mixing ratios of basal insulin and GLP-1 RA. Both products demonstrated satisfactory blood glucose control throughout the day, with less hypoglycemia and weight gain. However, few studies have examined the differences in the actions of the two formulations. Herein, we present a case of a 71-year-old man with pancreatic diabetes and significantly impaired intrinsic insulin secretion capacity, who demonstrated a marked difference in glycemic control following treatment with two different FRC formulations. Treatment with IDegLira, an FRC product, demonstrated suboptimal glucose control in the patient. However, after a change in therapy to another FRC product, IGlarLixi, his glucose control markedly improved, even with a decrease in the injection dose. This difference could have been due to lixisenatide, a short-acting GLP-1RA contained in IGlarLixi, which exerts a postprandial hypoglycemic effect irrespective of intrinsic insulin secretion capacity. In conclusion, IGlarLixi has the potential to achieve good fasting and postprandial glucose control with a once-daily injection, even in patients with type 2 diabetes who have a reduced intrinsic insulin secretion capacity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13340-023-00621-5.

l-Asparaginase regulates mTORC1 activity via a TSC2-dependent pathway in pancreatic beta cells

Eif2ak4, a susceptibility gene for type 2 diabetes, encodes GCN2, a molecule activated by amino acid deficiency. Mutations or deletions in GCN2 in pancreatic β-cells increase mTORC1 activity by decreasing Sestrin2 expression in a TSC2-independent manner. In this study, we searched for molecules downstream of GCN2 that suppress mTORC1 activity in a TSC2-dependent manner. To do so, we used a pull-down assay to identify molecules that competitively inhibit the binding of the T1462 phosphorylation site of TSC2 to 14-3-3. l-asparaginase was identified. Although l-asparaginase is frequently used as an anticancer drug for acute lymphoblastic leukemia, little is known about endogenous l-asparaginase. l-Asparaginase, which is expressed downstream of GCN2, was found to bind 14-3-3 and thereby to inhibit its binding to the T1462 phosphorylation site of TSC2 and contribute to TSC2 activation and mTORC1 inactivation upon TSC2 dephosphorylation. Further investigation of the regulation of mTORC1 activity in pancreatic β-cells by l-asparaginase should help to elucidate the mechanism of diabetes and insulin secretion failure during anticancer drug use.

Obesity and risk for its comorbidities diabetes, hypertension, and dyslipidemia in Japanese individuals aged 65 years

Diabetes, hypertension, and dyslipidemia are obesity-related comorbidities that contribute to the development of cardiovascular disease, one of the leading causes of death. In addition to obesity, the underweight condition is a concern because it can give rise to sarcopenia, particularly after the age of 65 years. We examined the risk for diabetes, hypertension, and dyslipidemia due to obesity in individuals of this age. We retrospectively investigated the relation between obesity and its three major comorbidities in 10,852 individuals aged 65 years who underwent health checkups implemented by Kobe City between April 2017 and March 2021. The prevalence of diabetes, hypertension, and dyslipidemia with and without hyper-low-density lipoprotein-cholesterolemia was 9.7%, 41.0%, 63.8%, and 19.5%, respectively, and the prevalence of these conditions increased with increasing obesity. The risk for diabetes and hypertension was increased markedly (odds ratios of 12.95 and 19.44, respectively), and that for dyslipidemia with and without hyper-low-density lipoprotein-cholesterolemia was modestly increased (odds ratios of 2.59 and 3.65, respectively) at a BMI of ≥ 35 kg/m² compared with normal weight. Analysis by gender revealed that the obesity-related risk for dyslipidemia with hyper-low-density lipoprotein-cholesterolemia was small compared with other comorbidities in women, while the risk for all comorbidities elevated similarly in men. Our results suggest the importance of public health intervention for obesity to suppress its comorbidities, especially diabetes and hypertension, at this age.

Histone deacetylase 6 regulates insulin signaling in pancreatic β cells

The reduction of pancreatic β cell mass is one of the key factors for the onset of type 2 diabetes. Many reports have indicated that insulin signaling is important for type 2 diabetes, but the mechanism by which insulin signaling is altered in pancreatic β cells remains unclear. This study was designed to examine the role of histone deacetylases (HDACs) in the regulation of insulin signaling in pancreatic β cells. We found that insulin signaling was downregulated by inhibition of HDAC6. HDAC6 expression was specifically observed in pancreatic β cells and was decreased in the pancreatic islets of a type 2 diabetes mouse model. When a mouse pancreatic β cell line (MIN6 cells) was treated with palmitic acid to mimic the effect of a high-fat diet on pancreatic β cells, HDAC6 was imported into the nucleus. These results suggest that HDAC6 plays an important role in the regulation of insulin signaling in pancreatic β cells. Therefore, clarifying the regulation of insulin signaling by HDAC6 may be a valuable approach for the treatment of type 2 diabetes.

GCN2 regulates pancreatic β cell mass by sensing intracellular amino acid levels

EIF2AK4, which encodes the amino acid deficiency-sensing protein GCN2, has been implicated as a susceptibility gene for type 2 diabetes in the Japanese population. However, the mechanism by which GCN2 affects glucose homeostasis is unclear. Here, we show that insulin secretion is reduced in individuals harboring the risk allele of EIF2AK4 and that maintenance of GCN2-deficient mice on a high-fat diet results in a loss of pancreatic β cell mass. Our data suggest that GCN2 senses amino acid deficiency in β cells and limits signaling by mechanistic target of rapamycin complex 1 to prevent β cell failure during the consumption of a high-fat diet.

Casein kinase 2 phosphorylates and stabilizes C/EBPβ in pancreatic β cells

During the development of type 2 diabetes, endoplasmic reticulum (ER) stress leads to pancreatic β cell failure. CCAAT/enhancer-binding protein (C/EBP) β is highly induced by ER stress and AMP-activated protein kinase (AMPK) suppression in pancreatic β cells, and its accumulation reduces pancreatic β cell mass. We investigated the phosphorylation state of C/EBPβ under these conditions. Casein kinase 2 (CK2) was found to co-localize with C/EBPβ in MIN6 cells. It phosphorylated S222 of C/EBPβ, a previously unidentified phosphorylation site. We found that C/EBPβ is phosphorylated by CK2 under AMPK suppression and ER stress, which are important from the viewpoint of the worsening pathological condition of type 2 diabetes, such as decreased insulin secretion and apoptosis of pancreatic β cells.

Compensatory hyperinsulinemia in high-fat diet-induced obese mice is associated with enhanced insulin translation in islets

A high-fat diet (HF) is associated with obesity, insulin resistance, and hyperglycemia. Animal studies have shown compensatory mechanisms in pancreatic β-cells after high fat load, such as increased pancreatic β-cell mass, enhanced insulin secretion, and exocytosis. However, the effects of high fat intake on insulin synthesis are obscure. Here, we investigated whether insulin synthesis was altered in correlation with an HF diet, for the purpose of obtaining further understanding of the compensatory mechanisms in pancreatic β-cells. Mice fed an HF diet are obese, insulin resistant, hyperinsulinemic, and glucose intolerant. In islets of mice fed an HF diet, more storage of insulin was identified. We analyzed insulin translation in mouse islets, as well as in INS-1 cells, using non-radioisotope chemicals. We found that insulin translational levels were significantly increased in islets of mice fed an HF diet to meet systemic demand, without altering its transcriptional levels. Our data showed that not only increased pancreatic β-cell mass and insulin secretion but also elevated insulin translation is the major compensatory mechanism of pancreatic β-cells.

Pancreatic β-cell failure mediated by mTORC1 hyperactivity and autophagic impairment

Hyperactivation of the mammalian target of rapamycin complex 1 (mTORC1) in β-cells is usually found as a consequence of increased metabolic load. Although it plays an essential role in β-cell compensatory mechanisms, mTORC1 negatively regulates autophagy. Using a mouse model with β-cell-specific deletion of Tsc2 (βTsc2(-/-)) and, consequently, mTORC1 hyperactivation, we focused on the role that chronic mTORC1 hyperactivation might have on β-cell failure. mTORC1 hyperactivation drove an early increase in β-cell mass that later declined, triggering hyperglycemia. Apoptosis and endoplasmic reticulum stress markers were found in islets of older βTsc2(-/-) mice as well as accumulation of p62/SQSTM1 and an impaired autophagic response. Mitochondrial mass was increased in β-cells of βTsc2(-/-) mice, but mitophagy was also impaired under these circumstances. We provide evidence of β-cell autophagy impairment as a link between mTORC1 hyperactivation and mitochondrial dysfunction that probably contributes to β-cell failure.

Ras-related C3 botulinum toxin substrate 1 (RAC1) regulates glucose-stimulated insulin secretion via modulation of F-actin

AIMS/HYPOTHESIS

The small G-protein ras-related C3 botulinum toxin substrate 1 (RAC1) plays various roles in mammalian cells, such as in the regulation of cytoskeletal organisation, cell adhesion, migration and morphological changes. The present study examines the effects of RAC1 ablation on pancreatic beta cell function.

METHODS

Isolated islets from pancreatic beta cell-specific Rac1-knockout (betaRac1(-/-)) mice and RAC1 knockdown INS-1 insulinoma cells treated with small interfering RNA were used to investigate insulin secretion and cytoskeletal organisation in pancreatic beta cells.

RESULTS

BetaRac1(-/-) mice showed decreased glucose-stimulated insulin secretion, while there were no apparent differences in islet morphology. Isolated islets from the mice had blunted insulin secretion in response to high glucose levels. In RAC1 knockdown INS-1 cells, insulin secretion was also decreased in response to high glucose levels, consistent with the phenotype of betaRac1(-/-) mice. Even under high glucose levels, RAC1 knockdown INS-1 cells remained intact with F-actin, which inhibits the recruitment of the insulin granules, resulting in an inhibition of insulin secretion.

CONCLUSIONS/INTERPRETATION

In RAC1-deficient pancreatic beta cells, F-actin acts as a barrier for insulin granules and reduces glucose-stimulated insulin secretion.