| 1. |
- Elksnis, Andris, et al.
(författare)
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Heterogeneity of Metabolic Defects in Type 2 Diabetes and Its Relation to Reactive Oxygen Species and Alterations in Beta-Cell Mass
- 2019
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Ingår i: Frontiers in Physiology. - : Frontiers Media S.A.. - 1664-042X. ; 10
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Forskningsöversikt (refereegranskat)abstract
- Type 2 diabetes (T2D) is a complex and heterogeneous disease which affects millions of people worldwide. The classification of diabetes is at an interesting turning point and there have been several recent reports on sub-classification of T2D based on phenotypical and metabolic characteristics. An important, and perhaps so far underestimated, factor in the pathophysiology of T2D is the role of oxidative stress and reactive oxygen species (ROS). There are multiple pathways for excessive ROS formation in T2D and in addition, beta-cells have an inherent deficit in the capacity to cope with oxidative stress. ROS formation could be causal, but also contribute to a large number of the metabolic defects in T2D, including beta-cell dysfunction and loss. Currently, our knowledge on beta-cell mass is limited to autopsy studies and based on comparisons with healthy controls. The combined evidence suggests that beta-cell mass is unaltered at onset of T2D but that it declines progressively. In order to better understand the pathophysiology of T2D, to identify and evaluate novel treatments, there is a need for in vivo techniques able to quantify beta-cell mass. Positron emission tomography holds great potential for this purpose and can in addition map metabolic defects, including ROS activity, in specific tissue compartments. In this review, we highlight the different phenotypical features of T2D and how metabolic defects impact oxidative stress and ROS formation. In addition, we review the literature on alterations of beta-cell mass in T2D and discuss potential techniques to assess beta-cell mass and metabolic defects in vivo.
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| 2. |
- Elksnis, Andris, et al.
(författare)
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Imatinib protects against human beta-cell death via inhibition of mitochondrial respiration and activation of AMPK
- 2021
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Ingår i: Clinical Science. - : Portland Press. - 0143-5221 .- 1470-8736. ; 135:19, s. 2243-2263
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Tidskriftsartikel (refereegranskat)abstract
- The protein tyrosine kinase inhibitor imatinib is used in the treatment of various malignancies but may also promote beneficial effects in the treatment of diabetes. The aim of the present investigation was to characterize the mechanisms by which imatinib protects insulin producing cells. Treatment of non-obese diabetic (NOD) mice with imatinib resulted in increased beta-cell AMP-activated kinase (AMPK) phosphorylation. Imatinib activated AMPK also in vitro, resulting in decreased ribosomal protein S6 phosphorylation and protection against islet amyloid polypeptide (IAPP)-aggregation, thioredoxin interacting protein (TXNIP) up-regulation and beta-cell death. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) mimicked and compound C counteracted the effect of imatinib on beta-cell survival. Imatinib-induced AMPK activation was preceded by reduced glucose/pyruvate-dependent respiration, increased glycolysis rates, and a lowered ATP/AMP ratio. Imatinib augmented the fractional oxidation of fatty acids/malate, possibly via a direct interaction with the beta-oxidation enzyme enoyl coenzyme A hydratase, short chain, 1, mitochondrial (ECHS1). In non-beta cells, imatinib reduced respiratory chain complex I and II-mediated respiration and acyl-CoA carboxylase (ACC) phosphorylation, suggesting that mitochondrial effects of imatinib are not beta-cell specific. In conclusion, tyrosine kinase inhibitors modestly inhibit mitochondrial respiration, leading to AMPK activation and TXNIP down-regulation, which in turn protects against beta-cell death.
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| 3. |
- Elksnis, Andris, 1993-
(författare)
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Pharmaceutical Protection of Beta-Cells in Diabetes : Using Tyrosine Kinase Inhibition and NOX4 Inhibitors
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diabetes mellitus is a complex and heterogenous disease, with loss of beta-cell function and mass being a characteristic of not only type 1 diabetes (T1D), but also type 2 diabetes (T2D). In T1D, inappropriate inflammatory signaling is thought to participate in the autoimmune suppression and destruction of beta-cells. In T2D progressive insulin resistance with resulting glucolipotoxicity, increased inflammation and oxidative stress, drives islet amyloid formation and subsequent beta-cell exhaustion and failure. Even under best managed care, disease progression and eventual complications are unavoidable. New interventions that aim to improve beta-cell survival are highly needed. This thesis investigates two such possible interventions: the tyrosine kinase inhibitor Imatinib, and selective NADPH-oxidase inhibition.Imatinib mesylate, used in treatment of chronic myeloid leukemia and other malignancies, was soon after its introduction reported to possess anti-diabetic properties in both T1D and T2D patients undergoing treatment. Imatinib has been shown to prevent and reverse diabetes in NOD mice and improve glucose tolerance in high fat diet treated rats. In paper I, we aimed to characterize the mechanisms by which imatinib protects beta-cells. We found that imatinib inhibits complex I and II of the respiratory chain, leading to improved beta-cell survival through AMPK activation, reduced amyloid formation and protection against TXNIP upregulation.Oxidative stress may play a pivotal role in the development of beta-cell dysfunction and failure in T2D. The NADPH-oxidases are a family of 7 enzymes (NOX1-5 and DUOX 1-2), that produce reactive oxygen species that are important in various physiological processes but may, if excessively activated, also be a source for oxidative stress in T2D. In paper II, we evaluate novel selective NOX inhibitors as protective agents against in vitro induced human beta-cell stress. Selective NOX4 inhibition protected beta-cells against both cytokines and high-glucose + palmitate. In paper III we found that NOX4 inhibition increased mitochondrial membrane potential, mitochondrial reactive oxygen species and ATP/ADP ratio in a human beta-cell line, and this was paralleled with protection against human islet cell death when challenged with high-glucose and palmitate. Finally, in paper IV, we attempt to apply these findings in vivo, by transplanting athymic diabetic mice with human islets and treating them with a NOX4 inhibitor over a period of 4 weeks. Treated mice achieved lower blood glucose levels and water consumption throughout the treatment period, and apoptotic rates of insulin-positive human cells, measured as co-localization of insulin and cleaved caspase-3, were greatly reduced.
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| 4. |
- Elksnis, Andris, et al.
(författare)
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Pharmacological Inhibition of NOX4 Improves Mitochondrial Function and Survival in Human Beta-Cells
- 2021
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Ingår i: Biomedicines. - : MDPI. - 2227-9059. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have reported beneficial effects of NADPH oxidase 4 (NOX4) inhibition on beta-cell survival in vitro and in vivo. The mechanisms by which NOX4 inhibition protects insulin producing cells are, however, not known. The aim of the present study was to investigate the effects of a pharmacological NOX4 inhibitor (GLX7013114) on human islet and EndoC-beta H1 cell mitochondrial function, and to correlate such effects with survival in islets of different size, activity, and glucose-stimulated insulin release responsiveness. We found that maximal oxygen consumption rates, but not the rates of acidification and proton leak, were increased in islets after acute NOX4 inhibition. In EndoC-beta H1 cells, NOX4 inhibition increased the mitochondrial membrane potential, as estimated by JC-1 fluorescence; mitochondrial reactive oxygen species (ROS) production, as estimated by MitoSOX fluorescence; and the ATP/ADP ratio, as assessed by a bioluminescent assay. Moreover, the insulin release from EndoC-beta H1 cells at a high glucose concentration increased with NOX4 inhibition. These findings were paralleled by NOX4 inhibition-induced protection against human islet cell death when challenged with high glucose and sodium palmitate. The NOX4 inhibitor protected equally well islets of different size, activity, and glucose responsiveness. We conclude that pharmacological alleviation of NOX4-induced inhibition of beta-cell mitochondria leads to increased, and not decreased, mitochondrial ROS, and this was associated with protection against cell death occurring in different types of heterogeneous islets. Thus, NOX4 inhibition or modulation may be a therapeutic strategy in type 2 diabetes that targets all types of islets.
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| 5. |
- Elksnis, Andris, et al.
(författare)
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The selective NOX4 inhibitor GLX7013159 decreases blood glucose concentrations and human beta-cell apoptotic rates in diabetic NMRI nu/nu mice transplanted with human islets
- 2023
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Ingår i: Free radical research. - : Taylor & Francis. - 1071-5762 .- 1029-2470. ; 57:6-12, s. 460-469
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Tidskriftsartikel (refereegranskat)abstract
- NADPH oxidase 4 (NOX4) inhibition has been reported to mitigate diabetes-induced beta-cell dysfunction and improve survival in vitro, as well as counteract high-fat diet-induced glucose intolerance in mice. We investigated the antidiabetic effects of the selective NOX4 inhibitor GLX7013159 in vivo in athymic diabetic mice transplanted with human islets over a period of 4 weeks. The GLX7013159-treated mice achieved lower blood glucose and water consumption throughout the treatment period. Furthermore, GLX7013159 treatment resulted in improved insulin and c-peptide levels, better insulin secretion capacity, as well as in greatly reduced apoptotic rates of the insulin-positive human cells, measured as colocalization of insulin and cleaved caspase-3. We conclude that the antidiabetic effects of NOX4 inhibition by GLX7013159 are observed also during a prolonged study period in vivo and are likely to be due to an improved survival and function of the human beta-cells.
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| 6. |
- Espes, Daniel, 1985-, et al.
(författare)
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GABA induces a hormonal counter-regulatory response in subjects with long-standing type 1 diabetes
- 2021
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Ingår i: BMJ Open Diabetes Research & Care. - : BMJ Publishing Group Ltd. - 2052-4897. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Experimentally, gamma-aminobutyric acid (GABA) has been found to exert immune-modulatory effects and induce beta-cell regeneration, which make it a highly interesting substance candidate for the treatment of type 1 diabetes (T1D). In many countries, including those in the European Union, GABA is considered a pharmaceutical drug. We have therefore conducted a safety and dose escalation trial with the first controlled-release formulation of GABA, Remygen (Diamyd Medical).Research design and methods: Six adult male subjects with long-standing T1D (age 24.8 +/- 1.5 years, disease duration 14.7 +/- 2.2 years) were enrolled in an 11-day dose escalation trial with a controlled-release formulation of GABA, Remygen. Pharmacokinetics, glucose control and hormonal counter-regulatory response during hypoglycemic clamps were evaluated at every dose increase (200 mg, 600 mg and 1200 mg).Results: During the trial there were no serious and only a few, transient, adverse events reported. Without treatment, the counter-regulatory hormone response to hypoglycemia was severely blunted. Intake of 600 mg GABA more than doubled the glucagon, epinephrine, growth hormone and cortisol responses to hypoglycemia.Conclusions: We find that the GABA treatment was well tolerated and established a counter-regulatory response to hypoglycemia in long-standing T1D. Further studies regarding not only the clinical potential of Remygen for beta-cell regeneration but also its potential use as hypoglycemic prophylaxis are warranted. Trail registration number and EudraCT2018-001115-73.
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| 7. |
- Hill, Henrik, et al.
(författare)
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Endogenous Levels of Gamma Amino-Butyric Acid Are Correlated to Glutamic-Acid Decarboxylase Antibody Levels in Type 1 Diabetes
- 2022
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Ingår i: Biomedicines. - : MDPI AG. - 2227-9059. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the central nervous system (CNS) and outside of the CNS, found in the highest concentrations in immune cells and pancreatic beta-cells. GABA is gaining increasing interest in diabetes research due to its immune-modulatory and beta-cell stimulatory effects and is a highly interesting drug candidate for the treatment of type 1 diabetes (T1D). GABA is synthesized from glutamate by glutamic acid decarboxylase (GAD), one of the targets for autoantibodies linked to T1D. Using mass spectrometry, we have quantified the endogenous circulating levels of GABA in patients with new-onset and long-standing T1D and found that the levels are unaltered when compared to healthy controls, i.e., T1D patients do not have a deficit of systemic GABA levels. In T1D, GABA levels were negatively correlated with IL-1 beta, IL-12, and IL-15 15 and positively correlated to levels of IL-36 beta and IL-37. Interestingly, GABA levels were also correlated to the levels of GAD-autoantibodies. The unaltered levels of GABA in T1D patients suggest that the GABA secretion from beta-cells only has a minor impact on the circulating systemic levels. However, the local levels of GABA could be altered within pancreatic islets in the presence of GAD-autoantibodies.
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| 8. |
- Krizhanovskii, Camilla, et al.
(författare)
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EndoC-beta H1 cells display increased sensitivity to sodium palmitate when cultured in DMEM/F12 medium
- 2017
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Ingår i: Islets. - : Informa UK Limited. - 1938-2014 .- 1938-2022. ; 9:3, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- Aims - Human pancreatic islets are known to die in response to the free fatty acid of sodium palmitate when cultured in vitro. This is in contrast to EndoC-beta H1 cells, which in our hands are not sensitive to the cell death-inducing effects sodium palmitate, making these cells seemingly unsuitable for lipotoxicity studies. However, the EndoC-beta H1 cells are routinely cultured in a nutrient mixture based on Dulbecco's Modified Eagle Medium (DMEM), which may not be the optimal choice for studies dealing with lipotoxicity. The aim of the present investigation was to define culture conditions that render EndoC-beta H1 cells sensitive to toxic effects of sodium palmitate. Methods - EndoC-beta H1 cells were cultured at standard conditions in either DMEM or DMEM/F12 culture medium. Cell death was analyzed using propidium iodide staining and flow cytometry. Insulin release and content was quantified using a human insulin ELISA. Results - We presently observe that substitution of DMEM for a DMEM/Ham's F12 mixture (50%/50% vol/vol) renders the cells sensitive to the apoptotic effects of sodium palmitate and sodium palmitate + high glucose leading to an increased cell death. Supplementation of the DMEM culture medium with linoleic acid partially mimicked the effect of DMEM/F12. Culture of EndoC-beta H1 cells in DMEM/F12 resulted also in increased proliferation, ROS production and insulin contents, but markers for metabolic stress, autophagy or amyloid deposits were unaffected. Conclusions - The culture conditions for EndoC-beta H1 cells can be modified so these cells display signs of lipotoxicity in response to sodium palmitate.
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| 9. |
- Wang, Xuan, 1984-, et al.
(författare)
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The novel NADPH oxidase 4 selective inhibitor GLX7013114 counteracts human islet cell death in vitro
- 2018
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Ingår i: PLOS ONE. - : PUBLIC LIBRARY SCIENCE. - 1932-6203. ; 13:9
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Tidskriftsartikel (refereegranskat)abstract
- It has been proposed that pancreatic beta-cell dysfunction in type 2 diabetes is promoted by oxidative stress caused by NADPH oxidase (Nox) over-activity. The aim of the present study was to evaluate the efficacy of novel Nox inhibitors as protective agents against cytokine- or high glucose + palmitate-induced human beta-cell death. The Nox2 protein was present mainly in the cytoplasm and was induced by cytokines. Nox4 protein immunoreactivity, with some nuclear accumulation, was observed in human islet cells, and was not affected by islet culture in the presence of cytokines or high glucose + palmitate. Nox inhibitors with partial or no isoform selectivity (DPI, dapsone, GLX351322, and GLX481372) all reduced ROS production of human islet cells exposed to high glucose + palmitate. This was paralleled by improved viability and reduced caspase 3 activation. The Nox1 selective inhibitor ML171 failed to reduce human islet cell death in response to both cytokines and high glucose + palmitate. The selective Nox2 inhibitor Phox-12 also failed to protect against cytokines, but protected partially against high glucose + palmitate-induced cellular death. The highly selective Nox4 inhibitor GLX7013114 protected islet cells against both cytokines and high glucose + palmitate. However, as no osmotic control for high glucose was used, we cannot exclude the possibility that the high glucose effect was due to osmosis. It is concluded that Nox4 may participate in stress-induced islet cell death in human islets in vitro. We propose that Nox4 mediates pro-apoptotic effects in intact islets under stressful conditions and that selective Nox4-inhibition may be a therapeutic strategy in type 2 diabetes.
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