Stimulatory Effect Of Insulin Research Articles

Periodic insulin stimulation of Akt: Dynamic steady states and robustness

The periodic secretion of insulin is a salient feature of the blood glucose control system in vivo. Insulin levels in the blood exhibit oscillations on multiple time scales – rapid, ultradian, and circadian – and the improved metabolic regulation resulting from pulsatile insulin release has been well established. Although numerous mathematical models investigating the causal mechanisms of insulin oscillations have appeared in the literature, to date there has been comparatively little attention given to the influence of periodic insulin stimulation on downstream components of the insulin signalling pathway.In this paper, we explore the effect of high frequency periodic insulin stimulation on Akt (also known as PKB), a crucial crosstalk node in the insulin signalling pathway that coordinates metabolic and mitogenic processes in the cell. We analyse a mathematical model of Akt translocation to the plasma membrane under both single step insulin perturbations and periodic insulin stimulation with an emphasis on – but not limited to – the physiological range of parameter values.It was shown that the system rapidly attains a robust dynamic steady state entrained to the periodic insulin stimulation. Moreover, the translocation of Akt to the plasma membrane in the model permits a sufficient level of phosphorylation to trigger downstream metabolic regulators. However, the modelling also indicated that further investigation of this activation process is required to determine whether the response of Akt is a key determinant of the enhanced metabolic control observed under periodic insulin stimulation.

Insulin Stimulates IL-23 Expression in Human Adipocytes: A Possible Explanation for the Higher Prevalence of Psoriasis in Obesity.

Psoriasis is a chronic systemic inflammatory disease involving the production of many pro-inflammatory cytokines derived from immune cells and interacting with different tissues leading to the typical skin lesions. Psoriasis shows a higher prevalence and a worse progression in obese than in lean subjects. The IL-23/IL-17 immune axis has a pivotal role in the pathogenesis of psoriasis and anti-IL-23 monoclonal antibodies are highly effective in its treatment. Since obesity in frequently associated with elevated insulin plasma levels, we have investigated the ability of in vitro differentiated human adipocytes to produce IL-23 at basal conditions and after insulin stimulation. In vitro differentiated human adipocytes were incubated in the absence and presence of different insulin concentrations and the expression of IL-23 was analyzed by real-time PCR and Western blotting. The results of this study show that in vitro differentiated human adipocytes spontaneously express IL-23 mRNA and protein being stimulated by insulin in a dose-dependent manner. The stimulatory effects of insulin on IL-23 expression were specific since it did not stimulate the expression of other well-known cytokines involved in psoriasis pathogenesis such as Il-22 nor LL-37. Furthermore, lipopolysaccharide did not stimulate IL-23 expression in human adipocytes, thus highlightening the specific effects of insulin in the stimulation of IL-23 expression in human adipocytes. Here we show that human adipocytes spontaneously express IL-23 and that insulin stimulates IL-23 production by these cells in a specific manner as other stimuli, known to be involved in psoriasis pathophysiology, are ineffective. These observations could explain the association between psoriasis and obesity, a condition frequently characterized by a state of insulin hypersecretion.

Inhibition of phosphodiesterase 5A by tadalafil improves SIRT1 expression and activity in insulin-resistant podocytes

A decrease in intracellular levels of 3′,5′-cyclic guanosine monophosphate (cGMP) has been implicated in the progression of diabetic nephropathy. Hyperglycemia significantly inhibits cGMP-dependent pathway activity in the kidney, leading to glomerular damage and proteinuria. The enhancement of activity of this pathway that is associated with an elevation of cGMP levels may be achieved by inhibition of the cGMP specific phosphodiesterase 5A (PDE5A) using selective inhibitors, such as tadalafil. Hyperglycemia decreased the insulin responsiveness of podocytes and impaired podocyte function. These effects were associated with lower protein amounts and activity of the protein deacetylase sirtuin 1 (SIRT1) and a decrease in the phosphorylation of adenosine monophosphate-dependent protein kinase (AMPK). We found that PDE5A protein levels increased in hyperglycemia, and PDE5A downregulation improved the insulin responsiveness of podocytes with reestablished SIRT1 expression and activity. PDE5A inhibitors potentiate nitric oxide (NO)/cGMP signaling, and NO modulates the activity and expression of SIRT1. Therefore, we investigated the effects of tadalafil on SIRT1 and AMPK in the context of improving the insulin sensitivity in podocytes and podocyte function in hyperglycemia. Our study revealed that tadalafil restored SIRT1 expression and activity and activated AMPK by increasing its phosphorylation. Tadalafil also restored stimulating effect of insulin on glucose transport in podocytes with high glucose-induced insulin resistance. Additionally, tadalafil improved the function of podocytes that were exposed to high glucose concentrations. Our results display novel mechanisms involved in the pathogenesis of glomerulopathies in diabetes, which may contribute to the development of more effective treatment strategies for diabetic nephropathy.

Genetic and Physiological Effects of Insulin-Like Growth Factor-1 (IGF-1) on Human Urate Homeostasis.

Hyperinsulinemia induces hyperuricemia by activating net renal urate reabsorption in the renal proximal tubule. The basolateral reabsorptive urate transporter GLUT9a appears to be the dominant target for insulin. By contrast, IGF-1 infusion reduces serum urate (SU), through mechanisms unknown. Genetic variants of IGF1R associated with reduced SU have increased IGF-1R expression and interact with genes encoding the GLUT9 and ABCG2 urate transporters, in a sex-specific fashion, which controls the SU level. Activation of IGF-1/IGF-1R signaling in Xenopus oocytes modestly activates GLUT9a and inhibits insulin's stimulatory effect on the transporter, which also activates multiple secretory urate transporters-ABCG2, ABCC4, OAT1, and OAT3. The results collectively suggest that IGF-1 reduces SU by activating secretory urate transporters and inhibiting insulin's action on GLUT9a. Metabolic syndrome and hyperinsulinemia are associated with hyperuricemia. Insulin infusion in healthy volunteers elevates serum urate (SU) by activating net urate reabsorption in the renal proximal tubule, whereas IGF-1 infusion reduces SU by mechanisms unknown. Variation within the IGF1R gene also affects SU levels. Colocalization analyses of a SU genome-wide association studies signal at IGF1R and expression quantitative trait loci signals in cis using COLOC2, RT-PCR, Western blotting, and urate transport assays in transfected HEK 293T cells and in Xenopus laevis oocytes. Genetic association at IGF1R with SU is stronger in women and is mediated by control of IGF1R expression. Inheritance of the urate-lowering homozygous genotype at the SLC2A9 locus is associated with a differential effect of IGF1R genotype between men and women. IGF-1, through IGF-1R, stimulated urate uptake in human renal proximal tubule epithelial cells and transfected HEK 293T cells, through activation of IRS1, PI3/Akt, MEK/ERK, and p38 MAPK; urate uptake was inhibited in the presence of uricosuric drugs, specific inhibitors of protein tyrosine kinase, PI3 kinase (PI3K), ERK, and p38 MAPK. In X. laevis oocytes expressing ten individual urate transporters, IGF-1 through endogenous IGF-1R stimulated urate transport mediated by GLUT9, OAT1, OAT3, ABCG2, and ABCC4 and inhibited insulin's stimulatory action on GLUT9a and OAT3. IGF-1 significantly activated Akt and ERK. Specific inhibitors of PI3K, ERK, and PKC significantly affected IGF-1 stimulation of urate transport in oocytes. The combined results of infusion, genetics, and transport experiments suggest that IGF-1 reduces SU by activating urate secretory transporters and inhibiting insulin's action.

Increased plasma fatty acid clearance, not fatty acid concentration, is associated with muscle insulin resistance in people with obesity

BackgroundAlthough it is well-accepted that increased plasma free fatty acid (FFA) concentration causes lipid overload and muscle insulin resistance in people with obesity, plasma FFA concentration poorly predicts insulin-resistant glucose metabolism. It has been proposed that hyperinsulinemia in people with obesity sufficiently inhibits adipose tissue triglyceride lipolysis to prevent FFA-induced insulin resistance. However, we hypothesized enhanced FFA clearance in people with obesity, compared with lean people, prevents a marked increase in plasma FFA even when FFA appearance is high. MethodsWe assessed FFA kinetics during basal conditions and during a hyperinsulinemic-euglycemic clamp procedure in 14 lean people and 46 people with obesity by using [13C]palmitate tracer infusion. Insulin-stimulated muscle glucose uptake rate was evaluated by dynamic PET-imaging of skeletal muscles after [18F]fluorodeoxyglucose injection. ResultsPlasma FFA clearance was accelerated in participants with obesity and correlated negatively with muscle insulin sensitivity without a difference between lean and obese participants. Furthermore, insulin infusion increased FFA clearance and the increase was greater in obese than lean participants. ConclusionsOur findings suggest plasma FFA extraction efficiency, not just plasma FFA concentration, is an important determinant of the cellular fatty acid load and the stimulatory effect of insulin on FFA clearance counteracts some of its antilipolytic effect.

The pro-proliferative effect of insulin in human breast epithelial DMBA-transformed and non-transformed cell lines is PI3K-, mTOR- and GLUT1-dependent.

Type 2 diabetes mellitus (T2DM) is linked to an increased risk of breast cancer. We aimed to investigate how T2DM-associated characteristics (high levels of glucose, insulin, leptin, inflammatory mediators and oxidative stress) influence breast cancer carcinogenesis, in DMBA-treated (MCF-12ADMBA ) and non-treated breast epithelial (MCF-12A) cell lines. Insulin (50 nM) promotes cell proliferation, 3 H-DG uptake and lactic acid production in both cell lines. The stimulatory effects of insulin upon cell proliferation and 3 H-DG uptake were hampered by rapamycin, LY294001 and BAY-876, in both cell lines. In conclusion, hyperinsulinemia, one important characteristic of T2DM, contributes to the initiation of breast cancer by a PI3K- and mTOR-dependent mechanism involving increased GLUT1-mediated glucose uptake. SIGNIFICANCE: The pro-proliferative effect of insulin in human breast epithelial DMBA-transformed and non-transformed cell lines is PI3K-, mTOR- and GLUT1-dependent.

Pancreatic exocrine insufficiency in diabetes is associated with autonomic dysfunction

Objectives Pancreatic exocrine insufficiency (PEI) is prevalent in diabetes. Pathophysiological theories imply autoimmune destruction, lack of trophic effects of insulin or impaired neuronal stimulation, but the relationship between PEI and autonomic dysfunction is largely unknown. In a pilot study, we aimed to investigate if patients with diabetes and PEI had impaired autonomic function. Methods We measured faecal elastase in 59 patients with type 1 or 2 diabetes, using a cut-off-value <200 μg/g to define PEI. Based on faecal elastase results, patients were stratified into matched case (n = 8) and control groups (n = 13). We used heart rate variability, baroreflex sensitivity and orthostatic hypotension tests to assess autonomic dysfunction. Results All baroreflex sensitivity parameters were reduced in cases with PEI compared with controls (all p < .05). The heart rate variability parameters root mean square of successive RR interval differences (p = .05) and high frequency (p = .04) were also reduced. We found no difference in orthostatic hypotension between the groups. Conclusions In this first-of-its-kind study, we found that diabetes patients with PEI had reduced autonomic function compared with matched controls. Although numbers are small, results support the hypothesis that autonomic dysfunction could be a contributor to PEI in diabetes.

Insulin and 5-Aminoimidazole-4-Carboxamide Ribonucleotide (AICAR) Differentially Regulate the Skeletal Muscle Cell Secretome.

Skeletal muscle is a major contributor to whole-body glucose homeostasis and is an important endocrine organ. To date, few studies have undertaken the large-scale identification of skeletal muscle-derived secreted proteins (myokines), particularly in response to stimuli that activate pathways governing energy metabolism in health and disease. Whereas the AMP-activated protein kinase (AMPK) and insulin-signaling pathways have received notable attention for their ability to independently regulate skeletal muscle substrate metabolism, little work has examined their ability to re-pattern the secretome. The present study coupled the use of high-resolution MS-based proteomics and bioinformatics analysis of conditioned media derived from 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR—an AMPK activator)- and insulin-treated differentiated C2C12 myotubes. We quantified 858 secreted proteins, including cytokines and growth factors such as fibroblast growth factor-21 (Fgf21). We identified 377 and 118 proteins that were significantly altered by insulin and AICAR treatment, respectively. Notably, the family of insulin growth factor binding-proteins (Igfbp) was differentially regulated by each treatment. Insulin- but not AICAR-induced conditioned media increased the mitochondrial respiratory capacity of myotubes, potentially via secreted factors. These findings may serve as an important resource to elucidate secondary metabolic effects of insulin and AICAR stimulation in skeletal muscle.

EFFECT OF THE AQUEOUS EXTRACT OF CLERODENDRUM THOMSONIAE LINN (VERBENACEAE) LEAVES ON TYPE 2 DIABETIC WISTAR RATS INDUCED BY THE MACAPOS1 TYPE DIET AND DEXAMETHASONE

Aim and objective: Clerodendrum thomsoniae leaves are used in Cameroon to manage diabetes and its related disorders. The study aimed at investigating the antidiabetic effect of the aqueous extract on diet and dexamethasone induced diabetic rats. Methods: Young mature leaves of C thomsoniae were dried, finely powdered and submitted to aqueous extraction. The dehydrated extract was tested in rats at 3 doses 312.5, 625 and 1250 mg/kg based on the local use of the plant. The effect of the extract on the fasting blood glucose in normoglycemic rats and MACAPOS 1 type diet induced diabetic rats, using respectively glibenclamide and metformin as positive control groups, were investigated. Results: AECT significantly reduced blood glucose levels in normoglycemic rats (p&lt;0.05) two hours after administration, from 83±2 mg/dL to 57.39±1.7 mg/dL with the dose of 1250 mg/kg. given the highest reduction rate of 30.86%. In normoglycemic rats 30 minutes after oral glucose overload, the maximum reduction rate was observed with glibenclamide 5 mg / kg and calculated at 49.90% followed by 36.39%, for the extract at 1250 mg / kg. After 30 days of repeated oral administration, AECT produced a reduction on blood glucose levels (p&lt;0.05) in type 2 diabetic rats. This reduction in blood sugar was much more expressed with the dose of 1250mg/kg (73.52±0.71 mg/dL) followed by metformin 38mg/kg (70.21±0.89 mg/dL) as the normal control with no significant difference (P &lt; 0.05). Conclusion: These results show that the antidiabetic activity of AECT can be explained by insulin stimulating effect, also give support to the traditional use of this plant. Peer Review History: Received 11 May 2021; Revised 17 June; Accepted 27 June, Available online 15 July 2021 Academic Editor: Dr. Asia Selman Abdullah, Al-Razi university, Department of Pharmacy, Yemen, asia_abdullah65@yahoo.com UJPR follows the most transparent and toughest ‘Advanced OPEN peer review’ system. The identity of the authors and, reviewers will be known to each other. This transparent process will help to eradicate any possible malicious/purposeful interference by any person (publishing staff, reviewer, editor, author, etc) during peer review. As a result of this unique system, all reviewers will get their due recognition and respect, once their names are published in the papers. We expect that, by publishing peer review reports with published papers, will be helpful to many authors for drafting their article according to the specifications. Auhors will remove any error of their article and they will improve their article(s) according to the previous reports displayed with published article(s). The main purpose of it is ‘to improve the quality of a candidate manuscript’. Our reviewers check the ‘strength and weakness of a manuscript honestly’. There will increase in the perfection, and transparency. Received file: Reviewer's Comments: Average Peer review marks at initial stage: 6.5/10 Average Peer review marks at publication stage: 8.0/10 Reviewer(s) detail: Dr. Terhemen Festus Swem, Department of Veterinary Physiology and Biochemistry, College of Veterinary Medicine, Federal University of Agriculture, Makurdi, Benue State, Nigeria, swemfestus422@gmail.com Taha A.I. El Bassossy, Medicinal and Aromatic Plants Department, Desert Research Center, Cairo, Egypt, tahachemist2008@gmail.com Prof. Dr. Ali Gamal Ahmed Al-kaf, Sana'a university, Yemen, alialkaf21@gmail.com Similar Articles: ANTIDIABETIC AND ANTIHYPERLIPIDEMIC ACTIVITY OF DRACAENA CINNABARI BALF. RESIN ETHANOLIC EXTRACT OF SOQATRA ISLAND IN EXPERIMENTAL ANIMALS THE SCOPING REVIEW OF CHINESE AND WESTERN MEDICINE TREATMENT OF DIABETIC FOOT IN ASIA ANTIHYPERGLYCEMIC AND ANTI-OXIDANT POTENTIAL OF ETHANOL EXTRACT OF VITEX THYRSIFLORA LEAVES ON DIABETIC RATS EFFECTS OF EMODIN ON BLOOD GLUCOSE AND BODY WEIGHT IN TYPE 1 DIABETIC RATS

Modifying Effects of Glucose and Insulin/Insulin-Like Growth Factors on Colon Cancer Cells.

There are only a few experimental studies which have investigated effects of glucose alone, and glucose in combination with insulin/insulin-like growth factors (IGF) on the growth of colon cancer. In the present study, we studied in vitro in human colorectal cancer cells originating from four Dukes’ stages of colorectal cancer the effects of glucose, insulin and IGFs on proliferation, migration, cell cycle progression and gene expression of the IGF system. Growth of colon cancer cells originating from a Dukes’ stage A was glucose-dependent, whereas growth of cancer cells from Dukes’ stage B, C and D was glucose-independent. Stimulatory effects of insulin and IGFs on cell growth were observed only in colon cancer cells originating from Dukes’ stage C and D. IGF-II stimulated migration in Dukes’ stage B cells only. The growth stimulatory effects in Dukes’ stage C and D colorectal cancer cells were accompanied by G2/M arrest and associated with an increased IGF-IR/IGF-II receptor ratio. In conclusion, our in vitro data suggest that the stimulating effects of glucose, IGFs and insulin on proliferation differ between colorectal cancer cells from early and late Dukes’ stages. Stimulatory effects of glucose on proliferation appear predominantly present in stage Dukes’ stage A colorectal cancer cells, while in contrast growth factor-mediated stimulation of cell proliferation is more pronounced in Dukes’ late stage (metastasized) colorectal cancer cells. Moreover, our study suggests that a stringent glucose control may be important to control tumor growth in early stages of colorectal cancer, while inhibition of the endocrine actions of the IGFs and insulin become more important in the late (metastasized) stages of colorectal cancer to restrain growth of colon cancer cells.

Palmitic acid induces insulin resistance by a mechanism associated with energy metabolism and calcium entry in neuronal cells.

Palmitic acid (PA) is a saturated fatty acid whose high consumption has been largely associated with the development of different metabolic alterations, such as insulin resistance, metabolic syndrome, and type 2 diabetes. Particularly in the brain, insulin signaling disruption has been linked to cognitive decline and is considered a risk factor for Alzheimer's disease. Cumulative evidence has demonstrated the participation of PA in the molecular cascade underlying cellular insulin resistance in peripheral tissues, but its role in the development of neuronal insulin resistance and the mechanisms involved are not fully understood. It has generally been accepted that the brain does not utilize fatty acids as a primary energy source, but recent evidence shows that neurons possess the machinery for fatty acid β-oxidation. However, it is still unclear under what conditions neurons use fatty acids as energy substrates and the implications of their oxidative metabolism in modifying insulin-stimulated effects. In the present work, we have found that neurons differentiated from human neuroblastoma MSN exposed to high but nontoxic concentrations of PA generate ATP through mitochondrial metabolism, which is associated with an increase in the cytosolic Ca2+ and diminished insulin signaling in neurons. These findings reveal a novel mechanism by which saturated fatty acids produce Ca2+ entry and insulin resistance that may play a causal role in increasing neuronal vulnerability associated with metabolic diseases.

Loss Of Insulin‐like Growth Factor 1 Receptor In Vascular Smooth Muscle Cells Promotes Increased Mirna‐221 And ‐222 In Type 2 Diabetes

Type 2 diabetes mellitus is associated with a 2 to 4 times higher risk of a heart attack or stroke. This increased risk of heart attacks and strokes results from an accelerated development of atherosclerotic plaques. During atherosclerotic plaque development, vascular smooth muscle cells (VSMC) proliferate and migrate leading to thickening of the intima of the arterial walls. This process is accelerated in diabetic patients by increase in two miRNAs, miR-221 and -222. These miRNAs are sensitive to changes in insulin receptor (IR) signaling. Under normal conditions, most of IR subunits are bound to insulin-like growth factor-1 receptor (IGFR) subunits forming heterodimers, which largely function as IGFR homodimers. A loss of IGFR thus promotes increased IR homodimers and an increase in insulin signaling. Our objective is to evaluate the effect of loss of IGFR on miR-221 and -222 expression in VSMCs. We hypothesize that the loss of IGFR coupled with physiological insulin stimulation promotes increased expression of miR-221/-222, which will in turn promote increased VSMC proliferation and migration. IGFR expression was measured in human atherosclerotic plaque samples from diabetic patients and nondiabetic patients. The effects of insulin stimulation coupled with the absence of IGFR was modeled with VSMCs isolated from an VSMC-specific IGFR knockout mouse. Our data demonstrates that arteries from diabetic subjects exhibit a 5.5-fold loss of the insulin-like growth factor receptor (IGFR-1). Murine vascular smooth muscle cells lacking IGFR exhibit a dose-dependent increase in miR-221/222 in response to physiological insulin stimulation. We conclude that loss of IGFR, likely increasing IR holoreceptors, alters insulin signaling to promote increased miR-221/222 in response to physiological insulin. These data provide support for the loss of IGFR as an initiator of the increase in intimal thickening seen in type 2 diabetes associated with miR-221/222.

Hormonal Regulation of Glycine Decarboxylase and its Impact on Cellular Physiology

The amino acid glycine is involved in generation of multiple critical metabolites including glutathione, heme, and creatinine. Interestingly, in both humans and rodents, circulating glycine levels are significantly reduced in obesity, glucose intolerance, type II diabetes and non‐alcoholic fatty liver disease. The glycine cleavage system (GCS) is the predominant glycine degradation pathway in humans. The rate‐limiting enzyme of GCS is glycine decarboxylase (GLDC), and loss‐of‐function mutations of GLDC cause hyperglycinemia. Here, we show that GLDC gene expression is upregulated in livers of mouse models of diabetes and diet‐induced obesity as well as in the fasted state in normal animals. In exploring the hormonal signals that mediate these regulatory events we found that both glucagon and insulin stimulated GLDC gene expression. In primary rat hepatocytes, GLDC expression was strongly stimulated by glucagon and cAMP, and mildly with insulin while in a rat hepatoma cell line, insulin strongly stimulated GLDC expression as compared to cAMP. We identified the cAMP‐response element binding protein 1 (Creb1) and insulin responsive transcription factor Sterol regulatory element binding protein 1c (Srebp‐1c) as mediators of the glucagon and insulin stimulatory effect, respectively. By knocking down or overexpressing GLDC in cell lines we observed GLDC expression levels are strongly linked to intracellular glutathione and reactive oxygen species (ROS) levels. Our findings suggest that the hormonal regulation of GLDC may contribute to compensatory changes in glutathione production as a defense against metabolic disease‐associated oxidative stress.Support or Funding InformationThis work is supported by NIH R21AG050741, Grants Boost OVPR Wayne State University and the Michigan Diabetes Research and Training Center.

Abstract 856: Mitochondrial Protein Kinase B (akt) Translocation Mediates Insulin-stimulated Cardiac Glucose Oxidation

Introduction: Insulin stimulates glucose oxidation, an effect which is associated with simulating pyruvate dehydrogenase (PDH). However, how the insulin signal is transduced from the cell membrane to the mitochondria to stimulate PDH is not known. Protein kinase B (Akt), protein kinase C-delta (PKCδ) and glycogen synthase kinase-3beta (GSK-3β) are main components of the cytosolic insulin signalling pathway and it has been suggested that they can be translocated to the mitochondria following insulin receptor activation in noncardiac tissue. Therefore, we investigated whether any of these kinases has a role mediated cardiac insulin-stimulated glucose oxidation in the heart. Methods and Results: Male and female C57BL/6 mice were anesthetized and hearts were collected and perfused in the isolated working heart mode. Hearts were perfused with [5- 3 H] glucose and [U- 14 C] glucose to simultaneously measure glycolysis and glucose oxidation rates, respectively, in the presence and absence of insulin. Insulin enhanced the phosphorylation and translocation of Akt Ser473 , PKCδ Tyr311 and GSK-3β Ser9 to the cardiac mitochondria along with enhancing PDH activity by decreasing its phosphorylation. Pharmacological inhibition of Akt using AktiVIII completely abolish the stimulatory effect of insulin on cardiac glucose oxidation rates (354 ± 145 vs 2307 ± 185 nmol. g dry wt -1 . min -1 in vehicle-treated hearts, p&lt;0.05). However, pharmacological inhibition of either PKCδ or GSK-3β using Bisindolylmaleimide I or 3F8, respectively, did not have a significant effect on insulin-stimulated glucose oxidation rates. None of the pharmacological inhibitors had any significant effect on cardiac glycolysis. Conclusion: Insulin mediates its stimulatory effect on cardiac glucose oxidation via a mechanism which involve the activation and translocation of Akt to the mitochondria.

A Potential Link between Glycine Metabolism, Glutathione and Diabetes

Type 2 diabetes (T2D) is accompanied by alterations in amino acid metabolism. Interestingly, in both humans and rodents, circulating glycine levels are significantly reduced in obesity, glucose intolerance and T2D identifying glycine as a biomarker of T2D and raising the possibility that altered glycine metabolism plays an active role in the etiology of the disease. The goals of our study are to determine if altered glycine metabolism plays a functional role in the development of diabetes. The glycine cleavage system (GCS) is the only biochemical route that degrades glycine in humans and loss‐of‐function mutations of GCS cause hyperglycinemia. Here, we show that the expression of the rate‐limiting enzyme of GCS, Glycine Decarboxylase (GLDC), is upregulated in livers of hyperinsulinemic mouse models of diabetes, and in hepatoma cell lines insulin stimulates transcription of the GLDC gene. We identified the insulin responsive transcription factor Sterol regulatory element binding protein 1c (SREBP‐1c) as the primary mediator of this insulin stimulatory effect. We also observed that altering GLDC expression levels strongly affected intracellular glutathione levels and levels of reactive oxygen species (ROS). Our findings suggest a working model in which Srebp1c‐mediated regulation of GLDC is responsible for the reduction of glycine levels seen in insulin resistant states and may play function as a compensatory mechanism to increase glutathione production as a defense against diabetes‐induced oxidative stress.Support or Funding InformationThis work is supported by NIH R21AG050741, and the Michigan Diabetes Research and Training Center.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Excess androgen production in subcutaneous adipose tissue of women with polycystic ovarian syndrome is not related to insulin or LH.

The purpose of this study was to investigate androgen production and the role of insulin and LH in its regulation in subcutaneous adipose tissue (SAT) of women with polycystic ovarian syndrome (PCOS). Protein and mRNA expression of androgen synthesis enzymes (Cytochrome P450 17A1 [CYP17A1] and Aldo-keto reductase 1C3 [AKR1C3]) were measured in SAT biopsies from women with PCOS, diagnosed according to the Rotterdam criteria (n=15) and healthy controls (n=15). Cultured mature adipocytes (differentiated from SAT biopsies) were treated with insulin ± phosphoinositol-3-kinase inhibitor (LY294002) or LH ± insulin. CYP17A1 and AKR1C3 mRNA expression and testosterone concentrations were measured in treated and untreated adipocyte cultures. AKR1C3 mRNA was significantly (P<0.001) greater in PCOS versus non-PCOS SAT, but CYP17A1 was not significantly different between the two groups. AKR1C3 and CYP17A1 protein expression was not significantly different in PCOS versus non-PCOS SAT. In untreated adipocyte cultures, CYP17A1, AKR1C3 and testosterone levels were significantly higher in the PCOS versus the non-PCOS groups. Addition of insulin increased AKR1C3 mRNA and testosterone levels, but not CYP17A1 mRNA in non-PCOS with no effect on PCOS adipocytes. The stimulatory effects of insulin were not inhibited by LY294002. Addition of LH increased CYP17A1, AKR1C3 and testosterone in non-PCOS adipocytes with no effect in PCOS adipocytes. In conclusion, SAT of women with PCOS produces excess androgen, which may contribute to PCOS-related hyperandrogenaemia. This SAT androgen excess is independent of obesity and is not directly stimulated by insulin or LH.

The relationship of arterial hypertension with the disturbance of glucose tolerance

Arterial hypertension and impaired glucose tolerance are in many ways interdependent and often precede a more pronounced pathology, the metabolic syndrome. In this regard, it is an actual problem of modern medicine, as the timely diagnosis and treatment of this combination can reduce the disability and mortality in this cohort of patients, prolonging their life and preserving their working capacity. Clinical features of hypertension with concomitant metabolic disorders are: frequent formation of refractory hypertension, early damage to target organs-development of LVH (left ventricular hypertrophy), quickly leading to myocardial dysfunction, renal hyper filtration and MAU, reduction of aortic and arteries elasticity. It has been established that impairment of insulin's ability to suppress glucose production in the liver and/or stimulate glucose uptake by peripheral tissues can underlie a decrease in insulin sensitivity. Since in healthy people 75–80% of glucose is utilized by skeletal muscles, it is more likely that its main cause of IR is impaired insulin stimulated glucose utilization [8]. A certain value in the development of hypertrophy and proliferation of smooth muscle cells and fibroblasts of the vascular wall in hypertension has a stimulating effect of insulin on collagen synthesis. It has been established that the thickness of the intima media complex of the carotid artery and the number of desquamated endotheliocytes circulating in the blood of patients with hypertension with IGT closely correlate with elevated insulin levels [5]. Thus, hypertension and IGT are largely interdependent conditions, significantly affect health and often precede a more pronounced pathology-the metabolic syndrome. Timely diagnosis and correction of this combination can reduce disability and premature death, prolong and improve their quality of life, and maintain their efficiency.

Inositols in Insulin Signaling and Glucose Metabolism.

In the past decades, both the importance of inositol for human health and the complex interaction between glucose and inositol have been the subject of increasing consideration. Glucose has been shown to interfere with cellular transmembrane transport of inositol, inhibiting, among others, its intestinal absorption. Moreover, intracellular glucose is required for de novo biosynthesis of inositol through the inositol-3-phosphate synthase 1 pathway, while a few glucose-related metabolites, like sorbitol, reduce intracellular levels of inositol. Furthermore, inositol, via its major isomers myo-inositol and D-chiro-inositol, and probably some of its phosphate intermediate metabolites and correlated enzymes (like inositol hexakisphosphate kinase) participate in both insulin signaling and glucose metabolism by influencing distinct pathways. Indeed, clinical data support the beneficial effects exerted by inositol by reducing glycaemia levels and hyperinsulinemia and buffering negative effects of sustained insulin stimulation upon the adipose tissue and the endocrine system. Due to these multiple effects, myoIns has become a reliable treatment option, as opposed to hormonal stimulation, for insulin-resistant PCOS patients.

The mechanistic links between insulin and human organic anion transporter 4

Human organic anion transporter 4 (hOAT4) belongs to a class of organic anion transporters that exert critical function in the secretion, absorption, and distribution of numerous drugs in the body, such as anti-viral drugs, anti-cancer therapeutics, antibiotics, antihypertensive medicine, and anti-inflammatory drugs. hOAT4 is richly existent in the kidney and placenta. We previously established that serum- and glucocorticoid-inducible kinases (sgk) stimulate hOAT4 expression and transport activity by abrogating the inhibitory effect of a ubiquitin ligase Nedd4-2. Insulin is one of the upstream signaling molecules for sgk. We therefore investigated the effect of insulin on hOAT4 function. We showed that insulin stimulated hOAT4 expression and transport activity, and the action of insulin was abolished in cells overexpressing Nedd4-2-specific siRNA to knockdown the endogenous Nedd4-2. We further showed that insulin phosphorylated serine 327 on Nedd4-2 and weakened the interaction between hOAT4 and Nedd4-2. Interestingly, in cells overexpressing sgk2, the stimulatory effect of insulin on hOAT4 was diminished. In addition, the stimulatory effect of insulin on hOAT4 was blocked by wortmannin and buparlisib, two PI3K inhibitors. In conclusion, our study demonstrated that insulin stimulates hOAT4 expression and transport activity by abrogating the inhibition effect of Nedd4-2 on the transporter. Moreover, insulin regulates hOAT4 by competing with sgk2 rather than through sgk2.

Metabolomic Signatures of Insulin Resistance in Human Skeletal Muscle Are Exacerbated with Insulin Stimulation

Metabolomic profiling has identified signatures of insulin resistance in skeletal muscle; however, the direct effect of insulin stimulation on these metabolite signatures in humans remains largely unresolved. To address this, we investigated the effect of insulin stimulation on skeletal muscle metabolites in a well characterized cohort of humans spanning the spectrum of insulin sensitivity. Vastus lateralis muscle samples were obtained from endurance athletes, sedentary lean and obese adults, and individuals with type 2 diabetes (n=16,15,15,12, respectively) under basal conditions and 1-hour into a hyperinsulinemic-euglycemic clamp. Metabolomic analysis was performed using UPLC-MS/MS. Basal concentrations of TCA cycle intermediates, including citrate, alpha-ketoglutarate, succinate, fumarate, malate and oxaloacetate, were positively related to insulin sensitivity (steady-state clamp Rd glucose in mg/kg/min; all P&amp;lt;0.01). Most of these relationships strengthened during insulin stimulation, with the strongest relationships observed for malate (r2 = 0.453, P&amp;lt;0.01) and fumarate (r2 = 0.501, P&amp;lt;0.01) that reflected a blunted increase in TCA intermediates during insulin stimulation with insulin resistance. Insulin stimulation lowered most medium- and long-chain acyl-carnitines compared with basal levels; however, this effect was also attenuated as a function of insulin resistance, signaling impaired metabolic flexibility. Notably, basal levels of several acyl-carnitines, including C12:0, C14:0, C16:0 and C18:1, were increased in endurance athletes compared with other groups (all P&amp;lt;0.05). Several amino acids, including leucine, isoleucine and lysine, were negatively related to insulin sensitivity in the basal and insulin stimulated state (all P&amp;lt;0.01). Together these findings indicate that physiologic insulin stimulation exacerbates metabolic signatures of skeletal muscle insulin resistance in humans. Disclosure S.A. Newsom: None. L. Perreault: Advisory Panel; Self; Novo Nordisk A/S. Speaker's Bureau; Self; Novo Nordisk A/S. Advisory Panel; Self; Merck &amp; Co., Inc.. Speaker's Bureau; Self; Merck &amp; Co., Inc., AstraZeneca, Janssen Pharmaceuticals, Inc., Boehringer Ingelheim Pharmaceuticals, Inc.. Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc.. Advisory Panel; Self; Sanofi. Speaker's Bureau; Self; Sanofi. A. Kerege: None. K.A. Harrison: None. D.E. Kahn: None. T. Nemkov: None. A. D’Alessandro: None. B. Bergman: Research Support; Self; Eli Lilly and Company. Advisory Panel; Spouse/Partner; Novo Nordisk Inc., Merck &amp; Co., Inc., AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company.