| 31. |
- Badian, Reza A., et al.
(författare)
-
Comparison of novel wide-field in vivo corneal confocal microscopy with skin biopsy for assessing peripheral neuropathy in type 2 diabetes
- 2023
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 72:7, s. 908-917
-
Tidskriftsartikel (refereegranskat)abstract
- Diabetic peripheral neuropathy (DPN) is a serious complication of diabetes, where skin biopsy assessing intraepi-dermal nerve fiber density (IENFD) plays an important diagnostic role. In vivo confocal microscopy (IVCM) of the corneal subbasal nerve plexus has been proposed as a noninvasive diagnostic modality for DPN. Direct compari-sons of skin biopsy and IVCM in controlled cohorts are lacking, as IVCM relies on subjective selection of images depicting only 0.2% of the nerve plexus. We compared these diagnostic modalities in a fixed-age cohort of 41 participants with type 2 diabetes and 36 healthy participants using machine algorithms to create wide-field image mosaics and quantify nerves in an area 37 times the size of prior studies to avoid human bias. In the same partici-pants, and at the same time point, no correlation between IENFD and corneal nerve density was found. Corneal nerve density did not correlate with clinical measures of DPN, including neuropathy symptom and disability scores, nerve conduction studies, or quantitative sensory tests. Our findings indicate that corneal and intraepidermal nerves likely mirror different aspects of nerve degeneration, where only intraepidermal nerves appear to reflect the clinical status of DPN, suggesting that scrutiny is warranted concerning methodologies of studies using corneal nerves to assess DPN.
|
|
| 32. |
- Baker, DJ, et al.
(författare)
-
Glycogen phosphorylase inhibition in type 2 diabetes therapy: a systematic evaluation of metabolic and functional effects in rat skeletal muscle
- 2005
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 54:8, s. 2453-2459
-
Tidskriftsartikel (refereegranskat)abstract
- Inhibition of hepatic glycogen phosphorylase is a promising treatment strategy for attenuating hyperglycemia in type 2 diabetes. Crystallographic studies indicate, however, that selectivity between glycogen phosphorylase in skeletal muscle and liver is unlikely to be achieved. Furthermore, glycogen phosphorylase activity is critical for normal skeletal muscle function, and thus fatigue may represent a major development hurdle for this therapeutic strategy. We have carried out the first systematic evaluation of this important issue. The rat gastrocnemius-plantaris-soleus (GPS) muscle was isolated and perfused with a red cell suspension, containing 3 μmol/l glycogen phosphorylase inhibitor (GPi) or vehicle (control). After 60 min, the GPS muscle was snap-frozen (rest, n = 11 per group) or underwent 20 s of maximal contraction (n = 8, control; n = 9, GPi) or 10 min of submaximal contraction (n = 10 per group). GPi pretreatment reduced the activation of the glycogen phosphorylase a form by 16% at rest, 25% after 20 s, and 44% after 10 min of contraction compared with the corresponding control. AMP-mediated glycogen phosphorylase activation was impaired only at 10 min (by 21%). GPi transiently reduced muscle lactate production during contraction, but other than this, muscle energy metabolism and function remained unaffected at both contraction intensities. These data indicate that glycogen phosphorylase inhibition aimed at attenuating hyperglycaemia is unlikely to negatively impact muscle metabolic and functional capacity.
|
|
| 33. |
- Baker, DJ, et al.
(författare)
-
The experimental type 2 diabetes therapy glycogen phosphorylase inhibition can impair aerobic muscle function during prolonged contraction
- 2006
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 55:6, s. 1855-1861
-
Tidskriftsartikel (refereegranskat)abstract
- Glycogen phosphorylase inhibition represents a promising strategy to suppress inappropriate hepatic glucose output, while muscle glycogen is a major source of fuel during contraction. Glycogen phosphorylase inhibitors (GPi) currently being investigated for the treatment of type 2 diabetes do not demonstrate hepatic versus muscle glycogen phosphorylase isoform selectivity and may therefore impair patient aerobic exercise capabilities. Skeletal muscle energy metabolism and function are not impaired by GPi during high-intensity contraction in rat skeletal muscle; however, it is unknown whether glycogen phosphorylase inhibitors would impair function during prolonged lower-intensity contraction. Utilizing a novel red cell–perfused rodent gastrocnemius-plantaris-soleus system, muscle was pretreated for 60 min with either 3 μmol/l free drug GPi (n = 8) or vehicle control (n = 7). During 60 min of aerobic contraction, GPi treatment resulted in ∼35% greater fatigue. Muscle glycogen phosphorylase a form (P < 0.01) and maximal activity (P < 0.01) were reduced in the GPi group, and postcontraction glycogen (121.8 ± 16.1 vs. 168.3 ± 8.5 mmol/kg dry muscle, P < 0.05) was greater. Furthermore, lower muscle lactate efflux and glucose uptake (P < 0.01), yet higher muscle Vo2, support the conclusion that carbohydrate utilization was impaired during contraction. Our data provide new confirmation that muscle glycogen plays an essential role during submaximal contraction. Given the critical role of exercise prescription in the treatment of type 2 diabetes, it will be important to monitor endurance capacity during the clinical evaluation of nonselective GPi. Alternatively, greater effort should be devoted toward the discovery of hepatic-selective GPi, hepatic-specific drug delivery strategies, and/or alternative strategies for controlling excess hepatic glucose production in type 2 diabetes.
|
|
| 34. |
- Banfi, C, et al.
(författare)
-
Transcriptional regulation of plasminogen activator inhibitor type 1 gene by insulin: insights into the signaling pathway
- 2001
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:7, s. 1522-1530
-
Tidskriftsartikel (refereegranskat)abstract
- Impairment of the fibrinolytic system, caused primarily by increases in the plasma levels of plasminogen activator inhibitor (PAI) type 1, are frequently found in diabetes and the insulin-resistance syndrome. Among the factors responsible for the increases of PAI-1, insulin has recently attracted attention. In this study, we analyzed the effects of insulin on PAI-1 biosynthesis in HepG2 cells, paying particular attention to the signaling network evoked by this hormone. Experiments performed in CHO cells overexpressing the insulin receptor indicate that insulin increases PAI-1 gene transcription through interaction with its receptor. By using inhibitors of the different signaling pathways evoked by insulin-receptor binding, it has been shown that the biosynthesis of PAI-1 is due to phosphatidylinositol (PI) 3-kinase activation, followed by protein kinase C and ultimately by mitogen-activated protein (MAP) kinase activation and extracellular signal–regulated kinase 2 phosphorylation. We also showed that this pathway is Ras-independent. Transfection of HepG2 cells with several truncations of the PAI-1 promoter coupled to a CAT gene allowed us to recognize two major response elements located in the regions between −804 and −708 and between −211 and −54. Electrophoretic mobility shift assay identified three binding sites for insulin-induced factors, all colocalized with putative Sp1 binding sites. Using supershifting antibodies, the binding of Sp1 could only be confirmed at the binding site located just upstream from the transcription start site of the PAI-1 promoter. A construct comprising four tandem repeat copies of the −93/−62 region of the PAI-1 promoter linked to CAT was transcriptionally activated in HepG2 cells by insulin. These results outline the central role of MAP kinase activation in the regulation of PAI-1 induced by insulin.
|
|
| 35. |
- Barbarroja, Nuria, et al.
(författare)
-
Increased dihydroceramide/ceramide ratio mediated by defective expression of degs1 impairs adipocyte differentiation and function
- 2015
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 64:4, s. 1180-1192
-
Tidskriftsartikel (refereegranskat)abstract
- Adipose tissue dysfunction is an important determinant of obesity-associated, lipid-induced metabolic complications. Ceramides are well-known mediators of lipid-induced insulin resistance in peripheral organs such as muscle. DEGS1 is the desaturase catalyzing the last step in the main ceramide biosynthetic pathway. Functional suppression of DEGS1 activity results in substantial changes in ceramide species likely to affect fundamental biological functions such as oxidative stress, cell survival, and proliferation. Here, we show that degs1 expression is specifically decreased in the adipose tissue of obese patients and murine models of genetic and nutritional obesity. Moreover, loss-of-function experiments using pharmacological or genetic ablation of DEGS1 in preadipocytes prevented adipogenesis and decreased lipid accumulation. This was associated with elevated oxidative stress, cellular death, and blockage of the cell cycle. These effects were coupled with increased dihydroceramide content. Finally, we validated in vivo that pharmacological inhibition of DEGS1 impairs adipocyte differentiation. These data identify DEGS1 as a new potential target to restore adipose tissue function and prevent obesity-associated metabolic disturbances.
|
|
| 36. |
- Barg, Sebastian, et al.
(författare)
-
A Subset of 50 Secretory Granules in Close Contact With L-Type Ca(2+) Channels Accounts for First-Phase Insulin Secretion in Mouse beta-Cells.
- 2002
-
Ingår i: Diabetes. - 1939-327X .- 0012-1797. ; 51 Suppl 1, s. 74-82
-
Tidskriftsartikel (refereegranskat)abstract
- Capacitance measurements were applied to mouse pancreatic beta-cells to elucidate the cellular mechanisms underlying biphasic insulin secretion. We report here that only <50 of the beta-cell's >10,000 granules are immediately available for release. The releasable granules tightly associate with the voltage-gated alpha(1C) Ca(2+) channels, and it is proposed that the release of these granules accounts for first-phase insulin secretion. Subsequent replenishment of the releasable pool by priming of previously nonreleasable granules is required for second-phase insulin secretion. The latter reaction depends on intragranular acidification due to the concerted action of granular bafilomycin-sensitive v-type H(+)-ATPase and 4,4-diisothiocyanostilbene-2,2-disulfonate--blockable ClC-3 Cl(-) channels. Lowering the cytoplasmic ATP/ADP ratio prevents granule acidification, granule priming, and refilling of the releasable pool. The latter finding provides an explanation to the transient nature of insulin secretion elicited by, for example, high extracellular K(+) in the absence of metabolizable fuels.
|
|
| 37. |
|
|
| 38. |
- Barg, Sebastian, et al.
(författare)
-
Tight coupling between electrical activity and exocytosis in mouse glucagon-secreting alpha-cells
- 2000
-
Ingår i: Diabetes. - 1939-327X .- 0012-1797. ; 49:9, s. 1500-1510
-
Tidskriftsartikel (refereegranskat)abstract
- alpha-Cells were identified in preparations of dispersed mouse islets by immunofluorescence microscopy. A high fraction of alpha-cells correlated with a small cell size measured as the average cell diameter (10 microm) and whole-cell capacitance (<4 pF). The alpha-cells generated action potentials at a low frequency (1 Hz) in the absence of glucose. These action potentials were reversibly inhibited by elevation of the glucose concentration to 20 mmol/l. The action potentials originated from a membrane potential more negative than -50 mV, had a maximal upstroke velocity of 5 V/s, and peaked at +1 mV. Voltage-clamp experiments revealed the ionic conductances underlying the generation of action potentials. alpha-Cells are equipped with a delayed tetraethyl-ammonium-blockable outward current (activating at voltages above -20 mV), a large tetrodotoxin-sensitive Na+ current (above -30 mV; peak current 200 pA at +10 mV), and a small Ca2+ current (above -50 mV; peak current 30 pA at +10 mV). The latter flowed through omega-conotoxin GVIA (25%)- and nifedipine-sensitive (50%) Ca(2+)-channels. Mouse alpha-cells contained, on average, 7,300 granules, which undergo Ca(2+)-induced exocytosis when the alpha-cell is depolarized. Three functional subsets of granules were identified, and the size of the immediately releasable pool was estimated as 80 granules, or 1% of the total granule number. The maximal rate of exocytosis (1.5 pF/s) was observed 21 ms after the onset of the voltage-clamp depolarization, which is precisely the duration of Ca(2+)-influx during an action potential. Our results suggest that the secretory machinery of the alpha-cell is optimized for maximal efficiency in the use of Ca2+ for exocytosis.
|
|
| 39. |
- Barker, Adam, et al.
(författare)
-
Association of genetic loci with glucose levels in childhood and adolescence a meta-analysis of over 6,000 children
- 2011
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 60:6, s. 1805-1812
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE-To investigate whether associations of common genetic variants recently identified for fasting glucose or insulin levels in nondiabetic adults are detectable in healthy children and adolescents. RESEARCH DESIGN AND METHODS-A total of 16 single nucleotide polymorphisms (SNPs) associated with fasting glucose were genotyped in six studies of children and adolescents of European origin, including over 6,000 boys and girls aged 9-16 years. We performed meta-analyses to test associations of individual SNPs and a weighted risk score of the 16 loci with fasting glucose. RESULTS-Nine loci were associated with glucose levels in healthy children and adolescents, with four of these associations reported in previous studies and five reported here for the first time (GLIS3, PROX1, SLC2A2, ADCY5, and CRY2). Effect sizes were similar to those in adults, suggesting age-independent effects of these fasting glucose loci. Children and adolescents carrying glucose-raising alleles of G6PC2, MTNR1B, GCK, and GLIS3 also showed reduced p-cell function, as indicated by homeostasis model assessment of beta-cell function. Analysis using a weighted risk score showed an increase [beta (95% CI)] in fasting glucose level of 0.026 mrnol/L (0.021-0.031) for each unit increase in the score. CONCLUSIONS-Novel fasting glucose loci identified in genome-wide association studies of adults are associated with altered fasting glucose levels in healthy children and adolescents with effect sizes comparable to adults. In nondiabetic adults, fasting glucose changes little over time, and our results suggest that age-independent effects of fasting glucose loci contribute to long-term interindividual differences in glucose levels from childhood onwards. Diabetes 60:1805-1812, 2011
|
|
| 40. |
- Barker, CJ, et al.
(författare)
-
XPR1 Mediates the Pancreatic β-Cell Phosphate Flush
- 2021
-
Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 70:1, s. 111-118
-
Tidskriftsartikel (refereegranskat)abstract
- Glucose-stimulated insulin secretion is the hallmark of the pancreatic β-cell, a critical player in the regulation of blood glucose concentration. In 1974, the remarkable observation was made that an efflux of intracellular inorganic phosphate (Pi) accompanied the events of stimulated insulin secretion. The mechanism behind this “phosphate flush,” its association with insulin secretion, and its regulation have since then remained a mystery. We recapitulated the phosphate flush in the MIN6m9 β-cell line and pseudoislets. We demonstrated that knockdown of XPR1, a phosphate transporter present in MIN6m9 cells and pancreatic islets, prevented this flush. Concomitantly, XPR1 silencing led to intracellular Pi accumulation and a potential impact on Ca2+ signaling. XPR1 knockdown slightly blunted first-phase glucose-stimulated insulin secretion in MIN6m9 cells, but had no significant impact on pseudoislet secretion. In keeping with other cell types, basal Pi efflux was stimulated by inositol pyrophosphates, and basal intracellular Pi accumulated following knockdown of inositol hexakisphosphate kinases. However, the glucose-driven phosphate flush occurred despite inositol pyrophosphate depletion. Finally, while it is unlikely that XPR1 directly affects exocytosis, it may protect Ca2+ signaling. Thus, we have revealed XPR1 as the missing mediator of the phosphate flush, shedding light on a 45-year-old mystery.
|
|
