Insulin stimulation of glucose uptake in skeletal muscles and adipose tissues in vivo is NO dependent

The genetic and dietary landscape of the muscle insulin signalling network

Metabolic disease is caused by a combination of genetic and environmental factors, yet few studies have examined how these factors influence signal transduction, a key mediator of metabolism. Using mass spectrometry-based phosphoproteomics, we quantified 23,126 phosphosites in skeletal muscle of five genetically distinct mouse strains in two dietary environments, with and without acute in vivo insulin stimulation. Almost half of the insulin-regulated phosphoproteome was modified by genetic background on an ordinary diet, and high-fat high-sugar feeding affected insulin signalling in a strain-dependent manner. Our data revealed coregulated subnetworks within the insulin signalling pathway, expanding our understanding of the pathway's organisation. Furthermore, associating diverse signalling responses with insulin-stimulated glucose uptake uncovered regulators of muscle insulin responsiveness, including the regulatory phosphosite S469 on Pfkfb2, a key activator of glycolysis. Finally, we confirmed the role of glycolysis in modulating insulin action in insulin resistance. Our results underscore the significance of genetics in shaping global signalling responses and their adaptability to environmental changes, emphasising the utility of studying biological diversity with phosphoproteomics to discover key regulatory mechanisms of complex traits.

Associations of early pregnancy serum uric acid levels with risk of gestational diabetes and birth outcomes: a retrospective cohort study

BACKGROUND

Previous evidence suggests that higher blood uric acid (UA) levels are associated with adverse cardiovascular outcomes during pregnancy and subsequent birth outcomes. However, it has been relatively unclear whether these associations persist in normotensive pregnant women.

METHODS

The study was based on a retrospective analysis of 18,250 mother-infant pairs in a large obstetric center in China. Serum UA concentrations in early pregnancy (median: 17.6, IQR: 16.3, 18.6 gestational weeks) were assessed. Hyperuricemia was defined as ≥ one standard deviation (SD) of the reference value for the corresponding gestational age. Outcomes of gestational diabetes mellitus (GDM), preterm birth (PB), low birth weight (LBW), macrosomia, small for gestational age (SGA) and large for gestational age (LGA) were extracted from the medical records.

RESULTS

The mean maternal UA level was 0.22 ± 0.05 mmol/L, and 2,896 (15.9%) subjects had hyperuricemia. After adjustment for several covariates, UA was associated with several adverse outcomes. The ORs (95%CI) per one SD increase in serum UA concentration were 1.250 (1.136, 1.277) for GDM, 1.137 (1.060, 1.221) for PB, 1.134 (1.051, 1.223) for LBW, and 1.077 (1.020, 1.137) for SGA, respectively. Similar adverse associations were found between hyperuricemia and GDM, PB (ORs: 1.394 and 1.385, P < 0.001), but not for LBW, macrosomia, SGA, and LGA. Adverse associations tended to be more pronounced in subjects with higher BMI for outcomes including PB, LBW, and SGA (P interaction = 0.001-0.028).

CONCLUSION

Higher UA levels in early pregnancy were associated with higher risk of GDM, PB, LBW, and SGA in normotensive Chinese women.

Elevated levels of renal function tests conferred increased risks of developing various pregnancy complications and adverse perinatal outcomes: insights from a population-based cohort study

OBJECTIVES

Physiological changes during pregnancy can affect the results of renal function tests (RFTs). In this population-based cohort study, we aimed to establish trimester-specific reference intervals (RIs) of RFTs in singleton and twin pregnancies and systematically investigate the relationship between RFTs and adverse pregnancy outcomes.

METHODS

The laboratory results of the first- and third-trimester RFTs, including blood urea nitrogen (BUN), serum uric acid (UA), creatinine (Crea) and cystatin C (Cys C), and the relevant medical records, were retrieved from 29,328 singleton and 840 twin pregnant women who underwent antenatal examinations from November 20, 2017 to January 31, 2021. The trimester-specific RIs of RFTs were estimated with both of the direct observational and the indirect Hoffmann methods. The associations between RTFs and pregnancy complications as well as perinatal outcomes were assessed by logistic regression analysis.

RESULTS

Maternal RFTs showed no significant difference between the direct RIs established with healthy pregnant women and the calculated RIs derived from the Hoffmann method. In addition, elevated levels of RFTs were associated with increased risks of developing various pregnancy complications and adverse perinatal outcomes. Notably, elevated third-trimester RFTs posed strong risks of preterm birth (PTB) and fetal growth restriction (FGR).

CONCLUSIONS

We established the trimester-specific RIs of RFTs in both singleton and twin pregnancies. Our risk analysis findings underscored the importance of RFTs in identifying women at high risks of developing adverse complications or outcomes during pregnancy.

Maternal uric acid levels and risk of gestational diabetes mellitus: A systematic review and dose-response meta-analysis of cohort studies including 105,380 participants

AIMS/INTRODUCTION

Although the association between uric acid levels and adverse pregnancy outcomes has been investigated, the effects of higher uric acid levels on the risk of gestational diabetes mellitus (GDM) have yet to be established. Therefore, this systematic review and meta-analysis aimed to investigate the relationship between uric acid levels during pregnancy and the risk of GDM.

MATERIALS AND METHODS

PubMed/Medline, Scopus and Web of Science databases were searched up to April 2022 for relevant observational studies. A random effects model was used to estimate pooled odds ratios (OR) and 95% confidence intervals (95% CI). To assess the heterogeneity of included studies, the I2 index was used.

RESULTS

Among the initial 262 studies that were recognized from the databases search, 23 studies including 105,380 participants were eligible. Pooled analysis showed that higher uric acid levels significantly affected the risk of GDM (OR 2.58, 95% CI 1.89-3.52, I2  = 90.8%, P < 0.001). Subgroup analyses based on the gestational week showed that higher uric acid levels before the 20th week of gestation were significantly associated with the risk of GDM (OR 3.26, 95% CI 2.26-4.71, I2  = 89.3%, P < 0.001). Based on the meta-regression analysis, uric acid levels and odds of GDM were significantly correlated with the participants' age, and it was more significant in younger pregnant women.

CONCLUSIONS

This study showed a positive association between uric acid levels and the risk of GDM. Also, our results indicate that measuring uric acid levels before 20 weeks of gestation can potentially predict GDM, especially in younger women.

Repurposing Drugs for Diabetes Mellitus as Potential Pharmacological Treatments for Sarcopenia - A Narrative Review

Sarcopenia, the age-related loss of muscle strength and mass or quality, is a common condition with major adverse consequences. Although the pathophysiology is incompletely understood, there are common mechanisms between sarcopenia and the phenomenon of accelerated ageing seen in diabetes mellitus. Drugs currently used to treat type 2 diabetes mellitus may have mechanisms of action that are relevant to the prevention and treatment of sarcopenia, for those with type 2 diabetes and those without diabetes. This review summarises shared pathophysiology between sarcopenia and diabetes mellitus, including the effects of advanced glycation end products, mitochondrial dysfunction, chronic inflammation and changes to the insulin signalling pathway. Cellular and animal models have generated intriguing, albeit mixed, evidence that supports possible beneficial effects on skeletal muscle function for some classes of drugs used to treat diabetes, including metformin and SGLT2 inhibitors. Most human observational and intervention evidence for the effects of these drugs has been derived from populations with type 2 diabetes mellitus, and there is a need for intervention studies for older people with, and at risk of, sarcopenia to further investigate the balance of benefit and risk in these target populations. Not all diabetes treatments will be safe to use in those without diabetes because of variable side effects across classes. However, some agents [including glucagon-like peptide (GLP)-1 receptor agonists and SGLT2 inhibitors] have already demonstrated benefits in populations without diabetes, and it is these agents, along with metformin, that hold out the most promise for further investigation in sarcopenia.

Serum uric acid and the risk of gestational diabetes mellitus: a systematic review and meta-analysis

AIMS

Serum uric acid (SUA) is considered as a risk factor for gestational diabetes mellitus (GDM). However, current studies showed inconsistent results. This study aimed to explore the relationship between SUA levels and GDM risk.

METHODS

Eligible studies were retrieved from PubMed, Web of Science, Embase, China National Knowledge Infrastructure, and Wanfang databases up to November 1, 2022. The pooled standardized mean difference (SMD) and 95% confidence interval (CI) were used to represent the difference in SUA levels between GDM women and controls. The combined odds ratios (OR) and 95% CI were applied to assess association between SUA levels and GDM risk. Subgroup analyses were conducted on study continents, design, and quality, detection time of SUA, and GDM diagnostic criteria.

RESULTS

Totally 11 studies including five case-control and six cohort studies, in which 80,387 pregnant women with 9815 GDM were included. The overall meta-analysis showed that the mean SUA level in GDM group was significantly higher than in controls (SMD = 0.423, 95%CI = 0.019-0.826, p = .040, I² = 93%). Notably, pregnant women with elevated levels of SUA had a significantly increased risk of GDM (OR = 1.670, 95%CI = 1.184-2.356, p = .0035, I² = 95%). Furthermore, subgroup analysis performed on the detection time of SUA showed a significant difference in the association between SUA and GDM risk within different trimesters (1st trimester: OR = 3.978, 95%CI = 2.177-7.268; 1st to 2nd trimester: OR = 1.340, 95%CI = 1.078-1.667; p between subgroups <.01).

CONCLUSIONS

Elevated SUA was positively associated with GDM risk, particularly in the 1st trimester of pregnancy. Further studies with high quality are required to validate the findings of this study.

Dysregulated insulin secretion is associated with pancreatic β-cell hyperplasia and direct acinar-β-cell trans-differentiation in partially eNOS-deficient mice

eNOS-deficient mice were previously shown to develop hypertension and metabolic alterations associated with insulin resistance either in standard dietary conditions (eNOS-/- homozygotes) or upon high-fat diet (HFD) (eNOS+/- heterozygotes). In the latter heterozygote model, the present study investigated the pancreatic morphological changes underlying the abnormal glycometabolic phenotype. C57BL6 wild type (WT) and eNOS+/- mice were fed with either chow or HFD for 16 weeks. After being longitudinally monitored for their metabolic state after 8 and 16 weeks of diet, mice were euthanized and fragments of pancreas were processed for histological, immuno-histochemical and ultrastructural analyses. HFD-fed WT and eNOS+/- mice developed progressive glucose intolerance and insulin resistance. Differently from WT animals, eNOS+/- mice showed a blunted insulin response to a glucose load, regardless of the diet regimen. Such dysregulation of insulin secretion was associated with pancreatic β-cell hyperplasia, as shown by larger islet fractional area and β-cell mass, and higher number of extra-islet β-cell clusters than in chow-fed WT animals. In addition, only in the pancreas of HFD-fed eNOS+/- mice, there was ultrastructural evidence of a number of hybrid acinar-β-cells, simultaneously containing zymogen and insulin granules, suggesting the occurrence of a direct exocrine-endocrine transdifferentiation process, plausibly triggered by metabolic stress associated to deficient endothelial NO production. As suggested by confocal immunofluorescence analysis of pancreatic histological sections, inhibition of Notch-1 signaling, likely due to a reduced NO availability, is proposed as a novel mechanism that could favor both β-cell hyperplasia and acinar-β-cell transdifferentiation in eNOS-deficient mice with impaired insulin response to a glucose load.

The Association Between Total Percent Fat and Serum Uric Acid in Adults

Background

Serum uric acid (SUA) has been proven to be closely associated with metabolic abnormalities, including obesity. This study aimed to investigate the detailed relationship between total percent fat (TPF) and SUA among adults.

Methods

Briefly, 23,715 adults aged 18–59 years in the National Health and Nutrition Examination Survey (NHANES) 1999–2018 were included in this study. Multivariable linear regression models were used to examine the association between TPF and SUA. Subgroup analyses stratified by sex and obesity status were also performed by multivariable linear regression. Then, fitted smoothing curves and generalized additive models were also applied to address the non-linear relationship between TPF and SUA. Finally, a recursive algorithm was used to calculate the inflection point in the non-linear relationship and a two-segment piecewise linear regression model was used to analyze the relationship between TPF and SUA on both sides of the inflection point.

Results

There were 15,808 (66.7%) obese individuals in all 23,715 participants. In the fully adjusted model, there was a positive association between TPF and SUA (β = 0.99, 95% CI: 0.73–1.26). Besides, this positive association remained statistically significant in subgroup analyses stratified by sex and obesity status. Interestingly, in males, the association of TPF and SUA was an inverted U-shaped curve (inflection point: 34.3%).

Conclusion

Our study revealed a significant positive relationship between TPF and SUA among adults and this association remained statistically significant when stratified by sex and obesity status, but the shape of the smoothing curve in males differed from that in females.

Nitric oxide modulates bone anabolism through regulation of osteoblast glycolysis and differentiation

Previous studies have shown that nitric oxide (NO) supplements may prevent bone loss and fractures in preclinical models of estrogen deficiency. However, the mechanisms by which NO modulates bone anabolism remain largely unclear. Argininosuccinate lyase (ASL) is the only mammalian enzyme capable of synthesizing arginine, the sole precursor for nitric oxide synthase-dependent (NOS-dependent) NO synthesis. Moreover, ASL is also required for channeling extracellular arginine to NOS for NO production. ASL deficiency (ASLD) is thus a model to study cell-autonomous, NOS-dependent NO deficiency. Here, we report that loss of ASL led to decreased NO production and impairment of osteoblast differentiation. Mechanistically, the bone phenotype was at least in part driven by the loss of NO-mediated activation of the glycolysis pathway in osteoblasts that led to decreased osteoblast differentiation and function. Heterozygous deletion of caveolin 1, a negative regulator of NO synthesis, restored NO production, osteoblast differentiation, glycolysis, and bone mass in a hypomorphic mouse model of ASLD. The translational significance of these preclinical studies was further reiterated by studies conducted in induced pluripotent stem cells from an individual with ASLD. Taken together, our findings suggest that ASLD is a unique genetic model for studying NO-dependent osteoblast function and that the NO/glycolysis pathway may be a new target to modulate bone anabolism.

Mesenteric lymphatic dysfunction promotes insulin resistance and represents a potential treatment target in obesity

Visceral adipose tissue (VAT) encases mesenteric lymphatic vessels and lymph nodes through which lymph is transported from the intestine and mesentery. Whether mesenteric lymphatics contribute to adipose tissue inflammation and metabolism and insulin resistance is unclear. Here we show that obesity is associated with profound and progressive dysfunction of the mesenteric lymphatic system in mice and humans. We find that lymph from mice and humans consuming a high-fat diet (HFD) stimulates lymphatic vessel growth, leading to the formation of highly branched mesenteric lymphatic vessels that 'leak' HFD-lymph into VAT and, thereby, promote insulin resistance. Mesenteric lymphatic dysfunction is regulated by cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF)-C-VEGF receptor (R)3 signalling. Lymph-targeted inhibition of COX-2 using a glyceride prodrug approach reverses mesenteric lymphatic dysfunction, visceral obesity and inflammation and restores glycaemic control in mice. Targeting obesity-associated mesenteric lymphatic dysfunction thus represents a potential therapeutic option to treat metabolic disease.

D-ribose-L-cysteine prevents oxidative stress and cardiometabolic syndrome in high fructose high fat diet fed rats

Cardiometabolic syndrome has been linked with dietary modification. Therefore, we investigated the effects of D-ribose-L-cysteine (DRLC) in rats fed with high fructose high fat (HFHF) diet. Twenty rats (n = 5), divided into 4 groups were concurrently exposed to HFHF and/or DRLC (250 mg/kg, p.o) during the 8 weeks study. The result showed that compared to control group, HFHF group had significant impairment in lipid and glucose homeostasis, increased cardiac xanthine oxidase, systolic blood pressure, heart rate, %body weight change and fluid intake. Also, there were significant reductions in HDL-C, cardiac (GPX, NO&GGT), feed intake and relative heart weight in the latter, relative to the former. However, there were no significant differences in most of the observed physical and biochemical changes in HFHF + DRLC group compared to control. DRLC alone did not disrupt the level of biomarkers. Conclusively, DRLC prevented the manifestation of oxidative stress and cardiometabolic syndrome in HFHF-diet fed rats.

Defective Allele of the Neuronal Nitric Oxide Synthase Gene Increases Insulin Resistance During Acute Phase of Myocardial Infarction

Background

Glycemic disorders are strong predictors of mortality in ST-elevation myocardial infarction (STEMI) patients, and disruption in nitric oxide (NO) production is associated with insulin-resistant states. We evaluated whether a defective allele of the neuronal nitric oxide synthase (nNOS) gene (NOS1) might influence insulin response and blood-glucose balance during the acute phase of STEMI and if post-infarction total plasma-NO levels and vasodilation scores varied across nNOS genotypes.

Methods

Consecutive patients with STEMI (n=354) underwent clinical evaluations and genotyping for the promoter variation rs41279104. In-hospital clinical and blood evaluations were performed at admission and five days after STEMI, with glycemic, insulinemic, and disposition indices assessed at the same times. Flow-mediated dilation (FMD) was assessed by reactive hyperemia on the 30th day.

Results

Homozygotes for the defective allele (A) showed lower glycemia and insulin sensitivity on day 1 while showing the highest β-cell function and no changes in the circulating NO pool, which is compatible with hyperresponsive β cells counteracting the inherent glucose-resistant state of AA patients. At day 5, glycemic scores had shifted to indicate greater insulin sensitivity among A homozygotes, paralleled by a significant yet poor increase in NO bioavailability compared to that among G carriers. All in all, defective homozygotes showed greater insulin resistance at admission that had reversed by 5 days after STEMI. Even so, A carriers developed lower FMD scores compared to G homozygotes after the acute phase.

Conclusion

A defective nNOS allele (and due decline in NO production) seemed to elicit a hyperinsulinemia response to compensate for an insulin-resistant state during the acute phase of STEMI and to be associated with poor endothelial function after the acute phase.

Potential of Beetroot and Blackcurrant Compounds to Improve Metabolic Syndrome Risk Factors

Metabolic syndrome (MetS) is a group of metabolic abnormalities, which together lead to increased risk of coronary heart disease (CHD) and type 2 diabetes mellitus (T2DM), as well as reduced quality of life. Dietary nitrate, betalains and anthocyanins may improve risk factors for MetS and reduce the risk of development of CHD and T2DM. Beetroot is a rich source of dietary nitrate, and anthocyanins are present in high concentrations in blackcurrants. This narrative review considers the efficacy of beetroot and blackcurrant compounds as potential agents to improve MetS risk factors, which could lead to decreased risk of CHD and T2DM. Further research is needed to establish the mechanisms through which these outcomes may occur, and chronic supplementation studies in humans may corroborate promising findings from animal models and acute human trials.

Exogenous carbohydrate and regulation of muscle carbohydrate utilisation during exercise

PURPOSE

Carbohydrates (CHO) are one of the fundamental energy sources during prolonged steady state and intermittent exercise. The consumption of exogenous CHO during exercise is common place, with the aim to enhance sporting performance. Despite the popularity around exogenous CHO use, the process by which CHO is regulated from intake to its use in the working muscle is still not fully appreciated. Recent studies utilizing the hyperglycaemic glucose clamp technique have shed light on some of the potential barriers to CHO utilisation during exercise. The present review addresses the role of exogenous CHO utilisation during exercise, with a focus on potential mechanisms involved, from glucose uptake to glucose delivery and oxidation at the different stages of regulation.

METHODS

Narrative review.

RESULTS

A number of potential barriers were identified, including gastric emptying, intestinal absorption, blood flow (splanchnic and muscle), muscle uptake and oxidation. The relocation of glucose transporters plays a key role in the regulation of CHO, particularly in epithelial cells and subsequent transport into the blood. Limitations are also apparent when CHO is infused, particularly with regards to blood flow and uptake within the muscle.

CONCLUSION

We highlight a number of potential barriers involved with the regulation of both ingested and infused CHO during exercise. Future work on the influence of longitudinal training within the regulation processes (such as the gut) is warranted to further understand the optimal type, dose and method of CHO delivery to enhance sporting performance.

Association between serum uric acid and metabolic syndrome: a cross-sectional study in Bangladeshi adults

Elevated levels of serum uric acid (SUA) have been suggested to associate with cardiovascular disease, diabetes and metabolic syndrome (MetS). However, information is limited on the association between SUA and MetS in general adults. This study aimed to assess the relationship of SUA with MetS and its components in general adults in Bangladesh. A total of 420 participants were enrolled in this study and biochemical parameters including SUA, fasting blood glucose (FBG) and lipid profile were analyzed using standard methods. The NECP criteria were applied to define MetS. The association of SUA with MetS and its components were evaluated by multinomial logistic regression models. The overall prevalence of MetS was 22% with 21.9% in males and 22.1% in female participants. Male subjects had a high prevalence of elevated components of MetS than in the female subjects (p < 0.05 for all cases). The mean concentration of SUA was significantly higher in subjects of the MetS group compared to the non-MetS group (p < 0.05). The components of MetS were raised with the increasing concentrations of SUA across the quartiles. In regression analysis, SUA was significantly associated with the prevalence of MetS in Bangladeshi adults. In conclusion, elevated SUA was significantly associated with the prevalence of MetS and its components.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Association of Serum Uric Acid, Urea Nitrogen, and Urine Specific Gravity Levels at 16-18 Weeks of Gestation with the Risk of Gestational Diabetes Mellitus

OBJECTIVE

To evaluate the associations of serum uric acid (UA), urea nitrogen (UN), and urine specific gravity (USG) levels in the first trimester of pregnancy with the risk of gestational diabetes mellitus (GDM).

PATIENTS AND METHODS

A retrospective cohort study was conducted in 1,769 pregnant women aged 31.55 ± 3.91 years. UA, UN, and USG levels were measured during the 16-18th week of gestation. GDM was diagnosed by an oral 75 g glucose tolerance test during the 24-28th week of gestation.

RESULTS

A multivariate adjusted logistic regression analysis showed that UA levels in the highest quartile increased the risk of GDM by 55.7% (odds ratio [OR]: 1.557, 95% confidence interval [CI]: 1.055-2.298; p = 0.026) compared to those in the lowest quartile. USG levels in the second, third, and fourth quartiles increased the risk of GDM by 67.6% (95% CI: 1.090-2.421), 112.4% (95% CI: 1.446-3.119), and 94.5% (95% CI: 1.314-2.880), respectively, compared to those in the first quartile (p trend = 0.001). No significant association between UN levels and the GDM risk was observed. When the extreme composite biomarker score quartiles were compared, the adjusted OR (95% CI) for GDM was 1.909 (95% CI: 1.332-2.736). Age-stratified analyses revealed similar results in women aged ≤35 years only, but not in those aged >35 years.

CONCLUSION

Higher levels of UA and USG and a higher composite kidney function biomarker score during the 16-18th week of gestation were positively and independently associated with an increased risk of GDM.

Converging Relationships of Obesity and Hyperuricemia with Special Reference to Metabolic Disorders and Plausible Therapeutic Implications

BACKGROUND

Obesity and hyperuricemia mutually influence metabolic syndrome. This study discusses the metabolic relationships between obesity and hyperuricemia in terms of pathophysiology, complications, and treatments.

METHODS

We searched for preclinical or clinical studies on the pathophysiology, complications, and therapy of obesity and hyperuricemia on the PubMed database.

RESULTS

In this systemic review, we summarized our searching results on topics of pathophysiology, complications and therapeutic strategy. In pathophysiology, we firstly introduce genetic variations for obesity, hyperuricemia and their relationships by genetic studies. Secondly, we talk about the epigenetic influences on obesity and hyperuricemia. Thirdly, we describe the central metabolic regulation and the role of hyperuricemia. Then, we refer to the character of adipose tissue inflammation and oxidative stress in the obesity and hyperuricemia. In the last part of this topic, we reviewed the critical links of gut microbiota in the obesity and hyperuricemia. In the following part, we review the pathophysiology of major complications in obesity and hyperuricemia including insulin resistance and type 2 diabetes mellitus, chronic kidney disease, cardiovascular diseases, and cancers. Finally, we recapitulate the therapeutic strategies especially the novel pharmaceutic interventions for obesity and hyperuricemia, which concurrently show the mutual metabolic influences between two diseases.

CONCLUSION

The data reviewed here delineate the metabolic relationships between obesity and hyperuricemia, and provide a comprehensive overview of the therapeutic targets for the management of metabolic syndromes.

Intestinal Fructose and Glucose Metabolism in Health and Disease

The worldwide epidemics of obesity and diabetes have been linked to increased sugar consumption in humans. Here, we review fructose and glucose metabolism, as well as potential molecular mechanisms by which excessive sugar consumption is associated to metabolic diseases and insulin resistance in humans. To this end, we focus on understanding molecular and cellular mechanisms of fructose and glucose transport and sensing in the intestine, the intracellular signaling effects of dietary sugar metabolism, and its impact on glucose homeostasis in health and disease. Finally, the peripheral and central effects of dietary sugars on the gut–brain axis will be reviewed.

The effects of dietary nitrate on plasma glucose and insulin sensitivity in sheep

Nitrate (NO₃ ^¯ ) is an effective non-protein nitrogen source for gut microbes and reduces enteric methane (CH₄ ) production in ruminants. Nitrate is reduced to ammonia by rumen bacteria with nitrite (NO₂ ^¯ ) produced as an intermediate. The absorption of NO₂ ^¯ can cause methaemoglobinaemia in ruminants. Metabolism of NO₃ ^¯ and NO₂ ^¯ in blood and animal tissues forms nitric oxide (NO) which has profound physiological effects in ruminants and has been shown to increase glucose uptake and insulin secretion in rodents and humans. We hypothesized that absorption of small quantities of NO₂ ^¯ resulting from a low-risk dose of dietary NO₃ ^¯ will increase insulin sensitivity (S_I ) and glucose uptake in sheep. We evaluated the effect of feeding sheep with a diet supplemented with 18 g NO₃ ^¯ /kg DM or urea (Ur) isonitrogenously to NO₃ ^¯ , on insulin and glucose dynamics. A glucose tolerance test using an intravenous bolus of 1 ml/kg LW of 24% (w/v) glucose was conducted in twenty sheep, with 10 sheep receiving 1.8% supplementary NO₃ ^¯ and 10 receiving supplementary urea isonitrogenously to NO₃ ^¯ . The MINMOD model used plasma glucose and insulin concentrations to estimate basal plasma insulin (I_b ) and basal glucose concentration (G_b ), insulin sensitivity (S_I ), glucose effectiveness (S_G ), acute insulin response (AIRg) and disposition index (DI). Nitrate supplementation had no effect on I_b (p > .05). The decrease in blood glucose occurred at the same rate in both dietary treatments (S_G ; p = .60), and there was no effect of NO₃ ^¯ on either G_b , S_I , AIRg or DI. This experiment found that the insulin dynamics assessed using the MINMOD model were not affected by NO₃ ^¯ administered to fasted sheep at a low dose of 1.8% NO₃ ^¯ in the diet.

Procyanidin C1, a Component of Cinnamon Extracts, Is a Potential Insulin Sensitizer That Targets Adipocytes

Natural products are one of the main sources for discovering new lead compounds. We previously reported that cinnamon extract has a promising effect in regulating lipid tissue volume and insulin sensitivity in vivo. However, its effective component and the underlying mechanism are not known. In the present study, we analyzed the effect of different components of cinnamon on regulating insulin sensitivity in 3T3-L1 adipocytes. Functional assay revealed that, of the six major components of cinnamon extracts, the B-type procyanidin, procyanidin C1, improves the differentiation of 3T3-L1 cells (TG content: 1.10 ± 0.09 mM at a dosage of 25 μM vs 0.67 ± 0.02 mM in vehicle group, p < 0.001) and promotes insulin-induced glucose uptake (8.58 ± 1.43 at a dosage of 25 μM vs 3.05 ± 1.24 in vehicle group, p < 0.001). Mechanism studies further suggested that procyanidin C1 activates the AKT-eNOS pathway, thus up-regulating glucose uptake and enhancing insulin sensitivity in mature adipocytes. Taken together, our study identified B-type procyanidin C1, a component of cinnamon extract, that stimulates preadipocyte differentiation and acts as a potential insulin action enhancer through the AKT-eNOS pathway in mature adipocytes.

Dystrophin R16/17 protein therapy restores sarcolemmal nNOS in trans and improves muscle perfusion and function

Background

Delocalization of neuronal nitric oxide synthase (nNOS) from the sarcolemma leads to functional muscle ischemia. This contributes to the pathogenesis in cachexia, aging and muscular dystrophy. Mutations in the gene encoding dystrophin result in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). In many BMD patients and DMD patients that have been converted to BMD by gene therapy, sarcolemmal nNOS is missing due to the lack of dystrophin nNOS-binding domain.

Methods

Dystrophin spectrin-like repeats 16 and 17 (R16/17) is the sarcolemmal nNOS localization domain. Here we explored whether R16/17 protein therapy can restore nNOS to the sarcolemma and prevent functional ischemia in transgenic mice which expressed an R16/17-deleted human micro-dystrophin gene in the dystrophic muscle. The palmitoylated R16/17.GFP fusion protein was conjugated to various cell-penetrating peptides and produced in the baculovirus-insect cell system. The best fusion protein was delivered to the transgenic mice and functional muscle ischemia was quantified.

Results

Among five candidate cell-penetrating peptides, the mutant HIV trans-acting activator of transcription (TAT) protein transduction domain (mTAT) was the best in transferring the R16/17.GFP protein to the muscle. Systemic delivery of the mTAT.R16/17.GFP protein to micro-dystrophin transgenic mice successfully restored sarcolemmal nNOS without inducing T cell infiltration. More importantly, R16/17 protein therapy effectively prevented treadmill challenge-induced force loss and improved muscle perfusion during contraction.

Conclusions

Our results suggest that R16/17 protein delivery is a highly promising therapy for muscle diseases involving sarcolemmal nNOS delocalizaton.

Electronic supplementary material

The online version of this article (10.1186/s10020-019-0101-6) contains supplementary material, which is available to authorized users.

An in vivo pharmacological study: Variation in tissue-accumulation for the drug probucol as the result of targeted microtechnology and matrix-acrylic acid optimization and stabilization techniques

Type 2 diabetes (T2D) is characterised by β-cell damage and hyperglycaemia. The lipophilic drug, probucol, has shown significant β-cell protective and potential antidiabetic effects, which were enhanced by hydrophilic bile acid incorporation using taurocholic acid and chenodeoxycholic acid. However, probucol has severe cardiotoxicity and a variable absorption profile, which limit its potential applications in T2D. Accordingly, this study aimed to design multiple formulations to optimise probucol oral delivery in T2D and test their effects on probucol absorption and accumulation in the heart. Adult male mice were given a high fat diet (HFD), and a week later, injected with a single dose of alloxan to accelerate T2D development, and once diabetes confirmed, divided into three groups (six to seven mice each). The groups were gavaged a daily dose of probucol powder, probucol microcapsules, or probucol-bile acid microcapsules for three months, and euthanized; and blood, tissues, and feces collected for blood glucose and probucol concentration analyses. Probucol concentrations in plasma were similar among all the groups. Groups given probucol microcapsules and probucol-bile acid microcapsules showed significant reduction in probucol accumulation in the heart compared with the group given probucol powder (p<0.05). Probucol microencapsulation with or without bile acids reduced its accumulation in heart tissues, without changing plasma concentrations, which may be beneficial in reducing its cardiotoxicity and optimise its potential applications in T2D.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Dystrophin R16/17-syntrophin PDZ fusion protein restores sarcolemmal nNOSμ

Background

Loss of sarcolemmal nNOSμ is a common manifestation in a wide variety of muscle diseases and contributes to the dysregulation of multiple muscle activities. Given the critical role sarcolemmal nNOSμ plays in muscle, restoration of sarcolemmal nNOSμ should be considered as an important therapeutic goal.

Methods

nNOSμ is anchored to the sarcolemma by dystrophin spectrin-like repeats 16 and 17 (R16/17) and the syntrophin PDZ domain (Syn PDZ). To develop a strategy that can independently restore sarcolemmal nNOSμ, we engineered an R16/17-Syn PDZ fusion construct and tested whether this construct alone is sufficient to anchor nNOSμ to the sarcolemma in three different mouse models of Duchenne muscular dystrophy (DMD).

Results

Membrane-associated nNOSμ is completely lost in DMD. Adeno-associated virus (AAV)-mediated delivery of the R16/17-Syn PDZ fusion construct successfully restored sarcolemmal nNOSμ in all three models. Further, nNOS restoration was independent of the dystrophin-associated protein complex.

Conclusions

Our results suggest that the R16/17-Syn PDZ fusion construct is sufficient to restore sarcolemmal nNOSμ in the dystrophin-null muscle.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0182-x) contains supplementary material, which is available to authorized users.

The Immunomodulatory and Anti-Inflammatory Role of Polyphenols

This review offers a systematic understanding about how polyphenols target multiple inflammatory components and lead to anti-inflammatory mechanisms. It provides a clear understanding of the molecular mechanisms of action of phenolic compounds. Polyphenols regulate immunity by interfering with immune cell regulation, proinflammatory cytokines' synthesis, and gene expression. They inactivate NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and modulate mitogen-activated protein Kinase (MAPk) and arachidonic acids pathways. Polyphenolic compounds inhibit phosphatidylinositide 3-kinases/protein kinase B (PI3K/AkT), inhibitor of kappa kinase/c-Jun amino-terminal kinases (IKK/JNK), mammalian target of rapamycin complex 1 (mTORC1) which is a protein complex that controls protein synthesis, and JAK/STAT. They can suppress toll-like receptor (TLR) and pro-inflammatory genes' expression. Their antioxidant activity and ability to inhibit enzymes involved in the production of eicosanoids contribute as well to their anti-inflammation properties. They inhibit certain enzymes involved in reactive oxygen species ROS production like xanthine oxidase and NADPH oxidase (NOX) while they upregulate other endogenous antioxidant enzymes like superoxide dismutase (SOD), catalase, and glutathione (GSH) peroxidase (Px). Furthermore, they inhibit phospholipase A2 (PLA2), cyclooxygenase (COX) and lipoxygenase (LOX) leading to a reduction in the production of prostaglandins (PGs) and leukotrienes (LTs) and inflammation antagonism. The effects of these biologically active compounds on the immune system are associated with extended health benefits for different chronic inflammatory diseases. Studies of plant extracts and compounds show that polyphenols can play a beneficial role in the prevention and the progress of chronic diseases related to inflammation such as diabetes, obesity, neurodegeneration, cancers, and cardiovascular diseases, among other conditions.

The pectin-insulin patch application prevents the onset of peripheral neuropathy-like symptoms in streptozotocin-induced diabetic rats

Peripheral neuropathic condition is amongst the classical symptoms of progressed diabetes. An intensive glycemic control with insulin injections has been shown to delay the onset and the progression of this condition in diabetes. In this study, we investigated the effect of pectin-insulin patch application on peripheral neuropathic symptoms in streptozotocin-induced diabetic rats. Pectin-insulin patches (20.0, 40.8, and 82.9 μg/kg) were daily applied thrice in streptozotocin-induced diabetic rats for 45 days. The diabetic animals sham treated with insulin-free patch served as negative control, while diabetic animals receiving subcutaneous insulin served as positive controls. The locomotor activity, gripping strength, and thermal perception were assessed at day 36, day 40, and day 44, respectively. On the 45th day, the animals were sacrificed, after which the plasma insulin, nitric oxide, C-reactive protein, tumor necrosis factor alpha, and malondialdehyde were measured. The patch application attenuated hyperglycemia with an improvement in the locomotor activity, thermal perception, and gripping strength in diabetic animals. Furthermore, the application of the patch augmented plasma nitric oxide while attenuating plasma malondialdehyde and tumor necrosis factor alpha. The application of pectin-insulin patch delays the onset of peripheral neuropathic-like symptoms in diabetic animals.

Acute Nitric Oxide Synthase Inhibition Accelerates Transendothelial Insulin Efflux In Vivo

Before insulin can stimulate glucose uptake in muscle, it must be delivered to skeletal muscle (SkM) through the microvasculature. Insulin delivery is determined by SkM perfusion and the rate of movement of insulin across the capillary endothelium. The endothelium therefore plays a central role in regulating insulin access to SkM. Nitric oxide (NO) is a key regulator of endothelial function and stimulates arterial vasodilation, which increases SkM perfusion and the capillary surface area available for insulin exchange. The effects of NO on transendothelial insulin efflux (TIE), however, are unknown. We hypothesized that acute reduction of endothelial NO would reduce TIE. However, intravital imaging of TIE in mice revealed that reduction of NO by l-N^G-nitro-l-arginine methyl ester (l-NAME) enhanced the rate of TIE by ∼30% and increased total extravascular insulin delivery. This accelerated TIE was associated with more rapid insulin-stimulated glucose lowering. Sodium nitroprusside, an NO donor, had no effect on TIE in mice. The effects of l-NAME on TIE were not due to changes in blood pressure alone, as a direct-acting vasoconstrictor (phenylephrine) did not affect TIE. These results demonstrate that acute NO synthase inhibition increases the permeability of capillaries to insulin, leading to an increase in delivery of insulin to SkM.

Passive stretch regulates skeletal muscle glucose uptake independent of nitric oxide synthase

Skeletal muscle contraction increases glucose uptake via an insulin-independent mechanism. Signaling pathways arising from mechanical strain are activated during muscle contractions, and mechanical strain in the form of passive stretching stimulates glucose uptake. However, the exact mechanisms regulating stretch-stimulated glucose uptake are not known. Since nitric oxide synthase (NOS) has been implicated in the regulation of glucose uptake during ex vivo and in situ muscle contractions and during exercise, and NO is increased with stretch, we examined whether the increase in muscle glucose uptake during stretching involves NOS. We passively stretched isolated extensor digitorum longus muscles (15 min at ~100-130 mN) from control mice and mice lacking either neuronal NOSµ (nNOSµ) or endothelial NOS (eNOS) isoforms, as well as used pharmacological inhibitors of NOS. Stretch significantly increased muscle glucose uptake appoximately twofold ( P < 0.05), and this was unaffected by the presence of the NOS inhibitors N^G-monomethyl-l-arginine (100 µM) or N^G-nitro-l-arginine methyl ester (100 µM). Similarly, stretch-stimulated glucose uptake was not attenuated by deletion of either eNOS or nNOSµ isoforms. Furthermore, stretching failed to increase skeletal muscle NOS enzymatic activity above resting levels. These data clearly demonstrate that stretch-stimulated skeletal muscle glucose uptake is not dependent on NOS. NEW & NOTEWORTHY Passive stretching is known to activate muscle glucose uptake through mechanisms that partially overlap with contraction. We report that genetic knockout of endothelial nitric oxide synthase (NOS) or neuronal NOS or pharmacological NOS inhibition does not affect stretch-stimulated glucose uptake. Passive stretch failed to increase NOS activity above resting levels. This information is important for the study of signaling pathways that regulate stretch-stimulated glucose uptake and indicate that NOS should be excluded as a potential signaling factor in this regard.

Effects of Body Mass Index, Glycemic Control, and Hypoglycemic Drugs on Serum Uric Acid Levels in Type 2 Diabetic Patients

Background

Plasma uric acid has been shown to be associated with an increased risk of hypertension, cardiovascular disease, chronic kidney disease, insulin resistance, and metabolic syndrome. Conflicting data regarding plasma uric acid levels in type 2 diabetes mellitus and their role in the development and progression of diabetic complications have been observed by many studies. The present study aimed to evaluate plasma uric acid levels in type 2 diabetic patients and to determine the effects of hypoglycemic drugs and pharmacologic insulin on plasma uric acid concentration.

Subjects and methods

The study included 162 type 2 diabetic patients divided into three groups (insulin taking group (N=58), glibenclamide taking group (N=40), and metformin taking group (N=64), and 47 normal healthy controls. A questionnaire that included variables such as age, sex, duration of disease, and body mass index (BMI) were answered by all the participants. Blood samples were collected and estimated for serum uric acid (SUA), fasting blood sugar (FBS), and glycated hemoglobin (HbA1c) using standard methods and the data were statistically analyzed.

Results

Diabetic patients showed a significant increase in serum uric acid, fasting blood sugar, glycated hemoglobin, and body mass index when compared to control subjects. The serum uric acid levels of metformin and glibenclamide taking groups were significantly higher than the control group. The difference of serum uric concentration between the insulin taking group and both the control and metformin groups was statistically non-significant. On the other hand, obese diabetics showed a significantly higher serum uric acid than overweight and lean diabetics. Furthermore, serum uric acid had a significant strong positive correlation with body mass index.

Conclusion

Type 2 diabetes mellitus (T2DM) is associated with high serum uric acid levels. Hypoglycemic drugs and pharmacologic insulin do not have a large impact on SUA concentration, but obesity seems to be the primary determinant of SUA levels in T2DM patients. The condition of diabetes may have a direct effect on the oxidation of the purine nucleotides resulting in the increased uric acid (UA) levels. In addition, hyperinsulinemia could lead to hyperuricemia by increasing the rate of xanthine oxidase synthesis. There is a strong relationship between T2DM and obesity with high uric acid levels.

Association Between Uric Acid and Metabolic Syndrome in Elderly Women

Objective

To investigate the relationship between uric acid and metabolic syndrome (MetS) in elderly women.

Methods

A total of 468 women aged ≥60 years participating in a health examination were enrolled. The association between uric acid and MetS and its individual variables was evaluated by univariate and multivariate logistic regression models.

Results

A dose-response relationship was observed for the prevalence of MetS and uric acid quartiles. Subjects in the second, third and fourth quartile of uric acid had a 2.23-fold, 2.25-fold and 4.41-fold increased risk, respectively, of MetS than those in the first uric acid quartile (p for trend <0.001). Furthermore, each 1 mg/dl increment of serum uric acid level had a 1.38-fold increased risk of MetS (OR 1.38; 95% CI, 1.14-1.69; p=0.001).

Conclusions

Our present study demonstrated that elevated uric acid was positively associated with the prevalence of MetS in elderly women. Further random control trials are needed to elucidate the effectiveness of treatment of hyperuricaemia in reducing the incidence of MetS in elderly women.

Potential benefits of dietary nitrate ingestion in healthy and clinical populations: A brief review

This article provides an overview of the current literature relating to the efficacy of dietary nitrate (NO₃^-) ingestion in altering aspects of cardiovascular and metabolic health and exercise capacity in healthy and diseased individuals. The consumption of NO₃^--rich vegetables, such as spinach and beetroot, have been variously shown to promote nitric oxide bioavailability, reduce systemic blood pressure, enhance tissue blood flow, modulate muscle O₂ utilisation and improve exercise tolerance both in normoxia and in hypoxia, as is commonly observed in a number of disease states. NO₃^- ingestion may, therefore, act as a natural means for augmenting performance and attenuating complications associated with limited O₂ availability or transport, hypertension and the metabolic syndrome. Recent studies indicate that dietary NO₃^- might also augment intrinsic skeletal muscle contractility and improve the speed and power of muscle contraction. Moreover, several investigations suggest that NO₃^- supplementation may improve aspects of cognitive performance both at rest and during exercise. Collectively, these observations position NO₃^- as more than a putative ergogenic aid and suggest that increasing natural dietary NO₃^- intake may act as a prophylactic in countering the predations of senescence and certain cardiovascular-metabolic diseases.

Effects of sildenafil treatment on thermogenesis and glucose homeostasis in diet-induced obese mice

Stimulation of thermogenic pathways appears to be a promising approach to find new ways of tackling metabolic diseases like obesity and diabetes mellitus type 2. Thermogenic, weight reducing and insulin sensitizing effects of phosphodiesterase 5 (PDE 5) inhibitors have recently been postulated, suggesting that modulators of endogenous cGMP signaling have the therapeutic potential to treat metabolic disorders. However, most studies have been performed in vitro or in animals that were not glucose intolerant. We, thus, aimed to test the metabolic effects of the PDE 5 inhibitor sildenafil by treating diet-induced obese (DIO) mice orally for 8 days. Surprisingly, our results revealed no changes in body temperature, brown adipose tissue (BAT) thermogenesis and gene expression in BAT and inguinal white adipose tissue (iWAT), thus excluding a thermogenic or 'browning' effect of sildenafil in preexisting obesity. In contrast, sildenafil-treated DIO mice displayed changes in liver metabolism and glucose homeostasis resulting in impaired glucose tolerance (P < 0.05), demonstrating for the first time an unfavorable metabolic effect of increased hepatic cGMP signaling in obesity. As sildenafil is commonly prescribed to treat pulmonary arterial hypertension and erectile dysfunction in diabetic and/or obese patients, follow up studies are urgently required to re-evaluate the drug safety.

Uric acid in the pathogenesis of metabolic, renal, and cardiovascular diseases: A review

The association between uric acid (UA) on one side and systemic hypertension (Htn), dyslipidemia, glucose intolerance, overweight, fatty liver, renal disease and cardiovascular disease (CVD) on the other side is well recognized. However, the causal relationship between UA and these different clinical problems is still debatable. The recent years have witnessed hundreds of experimental and clinical trials that favored the opinion that UA is a probable player in the pathogenesis of these disease entities. These studies disclosed the strong association between hyperuricemia and metabolic syndrome (MS), obesity, Htn, type 2 diabetes mellitus (DM), non-alcoholic fatty liver disease, hypertriglyceridemia, acute kidney injury, chronic kidney disease (CKD), coronary heart disease (CHD), heart failure and increased mortality among cardiac and CKD patients. The association between UA and nephrolithiasis or preeclampsia is a non-debatable association. Recent experimental trials have disclosed different changes in enzyme activities induced by UA. Nitric oxide (NO) synthase, adenosine monophosphate kinase (AMPK), adenosine monophosphate dehydrogenase (AMPD), and nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase are affected by UA. These changes in enzymatic activities can lead to the observed biochemical and pathological changes associated with UA. The recent experimental, clinical, interventional, and epidemiologic trials favor the concept of a causative role of UA in the pathogenesis of MS, renal, and CVDs.

Targeting the NO/superoxide ratio in adipose tissue: relevance to obesity and diabetes management

Insulin sensitivity and metabolic homeostasis depend on the capacity of adipose tissue to take up and utilize excess glucose and fatty acids. The key aspects that determine the fuel-buffering capacity of adipose tissue depend on the physiological levels of the small redox molecule, nitric oxide (NO). In addition to impairment of NO synthesis, excessive formation of the superoxide anion (О2•- ) in adipose tissue may be an important interfering factor diverting the signalling of NO and other reactive oxygen and nitrogen species in obesity, resulting in metabolic dysfunction of adipose tissue over time. Besides its role in relief from superoxide burst, enhanced NO signalling may be responsible for the therapeutic benefits of different superoxide dismutase mimetics, in obesity and experimental diabetes models. This review summarizes the role of NO in adipose tissue and highlights the effects of NO/О2•- ratio 'teetering' as a promising pharmacological target in the metabolic syndrome.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Concurrent Beet Juice and Carbohydrate Ingestion: Influence on Glucose Tolerance in Obese and Nonobese Adults

Insulin resistance and obesity are characterized by low nitric oxide (NO) bioavailability. Insulin sensitivity is improved with stimulation of NO generating pathways. Consumption of dietary nitrate (NO₃⁻) increases NO formation, via NO₃⁻ reduction to nitrite (NO₂⁻) by oral bacteria. We hypothesized that acute dietary nitrate (beet juice) ingestion improves insulin sensitivity in obese but not in nonobese adults. 12 nonobese (body mass index: 26.3 ± 0.8 kg/m² (mean ± SE)) and 10 obese adults (34.0 ± 0.8 kg/m²) ingested beet juice, supplemented with 25 g of glucose (carbohydrate load: 75 g), with and without prior use of antibacterial mouthwash to inhibit NO₃⁻ reduction to NO₂⁻. Blood glucose concentrations after beet juice and glucose ingestion were greater in obese compared with nonobese adults at 60 and 90 minutes (P = 0.004). Insulin sensitivity, as represented by the Matsuda Index (where higher values reflect greater insulin sensitivity), was lower in obese compared with nonobese adults (P = 0.009). Antibacterial mouthwash rinsing decreased insulin sensitivity in obese (5.7 ± 0.7 versus 4.9 ± 0.6) but not in nonobese (8.1 ± 1.0 versus 8.9 ± 0.9) adults (P = 0.048). In conclusion, insulin sensitivity was improved in obese but not in nonobese adults following coingestion of beet juice and glucose when oral bacteria nitrate reduction was not inhibited. Obese adults may benefit from ingestion of healthy nitrate-rich foods during meals.

S-nitrosylation of endogenous protein tyrosine phosphatases in endothelial insulin signaling

Nitric oxide (NO) exerts its biological function through S-nitrosylation of cellular proteins. Due to the labile nature of this modification under physiological condition, identification of S-nitrosylated residue in enzymes involved in signaling regulation remains technically challenging. The present study investigated whether intrinsic NO produced in endothelium-derived MS-1 cells response to insulin stimulation might target endogenous protein tyrosine phosphatases (PTPs). For this, we have developed an approach using a synthetic reagent that introduces a phenylacetamidyl moiety on S-nitrosylated Cys, followed by detection with anti-phenylacetamidyl Cys (PAC) antibody. Coupling with sequential blocking of free thiols with multiple iodoacetyl-based Cys-reactive chemicals, we employed this PAC-switch method to show that endogenous SHP-2 and PTP1B were S-nitrosylated in MS-1 cells exposed to insulin. The mass spectrometry detected a phenylacetamidyl moiety specifically present on the active-site Cys463 of SHP-2. Focusing on the regulatory role of PTP1B, we showed S-nitrosylation to be the principal Cys reversible redox modification in endothelial insulin signaling. The PAC-switch method in an imaging format illustrated that a pool of S-nitrosylated PTP1B was colocalized with activated insulin receptor to the cell periphery, and that such event was endothelial NO synthase (eNOS)-dependent. Moreover, ectopic expression of the C215S mutant of PTP1B that mimics the active-site Cys215 S-nitrosylated form restored insulin responsiveness in eNOS-ablated cells, which was otherwise insensitive to insulin stimulation. This work not only introduces a new method that explores the role of physiological NO in regulating signal transduction, but also highlights a positive NO effect on promoting insulin responsiveness through S-nitrosylation of PTP1B's active-site Cys215.

Association of Serum Uric Acid with Cardiovascular Disease in Taiwanese Patients with Primary Hypertension

BACKGROUND

Hyperuricemia is closely linked to hypertension and may be a marker of susceptibility or an intermediate step in the development of metabolic syndrome. However, recently, there have been conflicting conclusions regarding the independent role of uric acid as a risk factor of cardiovascular disease (CVD). The specific role of serum uric acid (SUA) in relation to CVD remains controversial, and there are limited reports utilizing Asian data available on this issue. Therefore, this study investigated the association between SUA and cardiovascular disease in Taiwanese patients with essential hypertension.

METHODS

There were 3472 participants from 55-80 years of age (1763 males, 1709 females) from 38 sites across Taiwan in this hospital-based cross-sectional study, covering the period November 2005 to December 2006. The CVD included diagnosed angina pectoris, myocardial infarction, congestive heart failure, and stroke.

RESULTS

Hyperuricemia is positively associated with CVD in both sexes when a unified cut-off SUA level of 7 mg/dl was used. However, the odds ratios (ORs) for all CVD were greater in magnitude in hypertensive women than in men when there was co-morbidity of diabetes. The ORs of all CVD in the diabetes subgroup were statistically significantly (p = 0.01 for women, p = 0.07 for men). By multivariate analysis, hyperuricemia did not confer an increased risk of CVD.

CONCLUSIONS

Hyperuricemia may be associated with increased risk of CVD, but is not an independent risk factor of CVD in essential hypertensive Taiwanese patients.

KEY WORDS

Cardiovascular disease; Hypertension; Hyperuricemia; Uric acid.

Glucose Transporters in Cardiac Metabolism and Hypertrophy

The heart is adapted to utilize all classes of substrates to meet the high-energy demand, and it tightly regulates its substrate utilization in response to environmental changes. Although fatty acids are known as the predominant fuel for the adult heart at resting stage, the heart switches its substrate preference toward glucose during stress conditions such as ischemia and pathological hypertrophy. Notably, increasing evidence suggests that the loss of metabolic flexibility associated with increased reliance on glucose utilization contribute to the development of cardiac dysfunction. The changes in glucose metabolism in hypertrophied hearts include altered glucose transport and increased glycolysis. Despite the role of glucose as an energy source, changes in other nonenergy producing pathways related to glucose metabolism, such as hexosamine biosynthetic pathway and pentose phosphate pathway, are also observed in the diseased hearts. This article summarizes the current knowledge regarding the regulation of glucose transporter expression and translocation in the heart during physiological and pathological conditions. It also discusses the signaling mechanisms governing glucose uptake in cardiomyocytes, as well as the changes of cardiac glucose metabolism under disease conditions.

Modulating DDAH/NOS Pathway to Discover Vasoprotective Insulin Sensitizers

Insulin resistance syndrome (IRS) is a configuration of cardiovascular risk factors involved in the development of metabolic disorders including type 2 diabetes mellitus. In addition to diet, age, socioeconomic, and environmental factors, genetic factors that impair insulin signaling are centrally involved in the development and exacerbation of IRS. Genetic and pharmacological studies have demonstrated that the nitric oxide (NO) synthase (NOS) genes are critically involved in the regulation of insulin-mediated glucose disposal. The generation of NO by the NOS enzymes is known to contribute to vascular homeostasis including insulin-mediated skeletal muscle vasodilation and insulin sensitivity. By contrast, excessive inhibition of NOS enzymes by exogenous or endogenous factors is associated with insulin resistance (IR). Asymmetric dimethylarginine (ADMA) is an endogenous molecule that competitively inhibits all the NOS enzymes and contributes to metabolic perturbations including IR. The concentration of ADMA in plasma and tissue is enzymatically regulated by dimethylarginine dimethylaminohydrolase (DDAH), a widely expressed enzyme in the cardiovascular system. In preclinical studies, overexpression of DDAH has been shown to reduce ADMA levels, improve vascular compliance, and increase insulin sensitivity. This review discusses the feasibility of the NOS/DDAH pathway as a novel target to develop vasoprotective insulin sensitizers.

Redox implications in adipose tissue (dys)function--A new look at old acquaintances

Obesity is an energy balance disorder associated with dyslipidemia, insulin resistance and diabetes type 2, also summarized with the term metabolic syndrome or syndrome X. Increasing evidence points to “adipocyte dysfunction”, rather than fat mass accretion per se, as the key pathophysiological factor for metabolic complications in obesity. The dysfunctional fat tissue in obesity characterizes a failure to safely store metabolic substrates into existing hypertrophied adipocytes and/or into new preadipocytes recruited for differentiation. In this review we briefly summarize the potential of redox imbalance in fat tissue as an instigator of adipocyte dysfunction in obesity. We reveal the challenge of the adipose redox changes, insights in the regulation of healthy expansion of adipose tissue and its reduction, leading to glucose and lipids overflow.

•

Adipose tissue (AT) buffers nutrient excess determining overall metabolic health.

•

Redox insight in lipid storage and adipogenesis of AT is reviewed.

•

Redox modulation of AT as therapeutic target in obesity/syndrome X is considered.

Apelin and energy metabolism

A wide range of adipokines identified over the past years has allowed considering the white adipose tissue as a secretory organ closely integrated into overall physiological and metabolic control. Apelin, a ubiquitously expressed peptide was known to exert different physiological effects mainly on the cardiovascular system and the regulation of fluid homeostasis prior to its characterization as an adipokine. This has broadened its range of action and apelin now appears clearly as a new player in energy metabolism in addition to leptin and adiponectin. Apelin has been shown to act on glucose and lipid metabolism but also to modulate insulin secretion. Moreover, different studies in both animals and humans have shown that plasma apelin concentrations are usually increased during obesity and type 2 diabetes. This mini-review will focus on the various systemic apelin effects on energy metabolism by addressing its mechanisms of action. The advances concerning the role of apelin in metabolic diseases in relation with the recent reports on apelin concentrations in obese and/or diabetic subjects will also be discussed.

Common variants related to serum uric acid concentrations are associated with glucose metabolism and insulin secretion in a Chinese population

Background

Elevated serum uric acid concentration is an independent risk factor and predictor of type 2 diabetes (T2D). Whether the uric acid-associated genes have an impact on T2D remains unclear. We aimed to investigate the effects of the uric acid-associated genes on the risk of T2D as well as glucose metabolism and insulin secretion.

Method

We recruited 2,199 normal glucose tolerance subjects from the Shanghai Diabetes Study I and II and 2,999 T2D patients from the inpatient database of Shanghai Diabetes Institute. Fifteen single nucleotide polymorphisms (SNPs) mapped in or near 11 loci (PDZK1, GCKR, LRP2, SLC2A9, ABCG2, LRRC16A, SLC17A1, SLC17A3, SLC22A11, SLC22A12 and SF1) were genotyped and serum biochemical parameters related to uric acid and T2D were determined.

Results

SF1 rs606458 showed strong association to T2D in both males and females (p = 0.034 and 0.0008). In the males, LRRC16A was associated with 2-h insulin and insulin secretion (p = 0.009 and 0.009). SLC22A11 was correlated with HOMA-B and insulin secretion (p = 0.048 and 0.029). SLC2A9 rs3775948 was associated with 2-h glucose (p = 0.043). In the females, LRP2 rs2544390 and rs1333049 showed correlations with fasting insulin, HOMA-IR and insulin secretion (p = 0.028, 0.033 and 0.052 and p = 0.034, 0.047 and 0.038, respectively). SLC2A9 rs11722228 was correlated with 2-h glucose, 2-h insulin and insulin secretion (p = 0.024, 0.049 and 0.049, respectively).

Conclusions

Our results indicated that the uric acid-associated genes have an impact on the risk of T2D, glucose metabolism and insulin secretion in a Chinese population.

Hyperuricemia is a risk factor for the onset of impaired fasting glucose in men with a high plasma glucose level: a community-based study

Background

It is not clear whether elevated uric acid is a risk factor for the onset of impaired fasting glucose after stratifying by baseline fasting plasma glucose levels. We conducted a community-based retrospective longitudinal cohort study to clarify the relationship between uric acid levels and the onset of impaired fasting glucose, according to baseline fasting plasma glucose levels.

Methods

We enrolled 6,403 persons (3,194 men and 3,209 women), each of whom was 18–80 years old and had >2 annual check-ups during 2003–2010. After excluding persons who had fasting plasma glucose levels ≥6.11 mM and/or were currently taking anti-diabetic agents, the remaining 5,924 subjects were classified into quartiles according to baseline fasting plasma glucose levels. The onset of impaired fasting glucose was defined as fasting plasma glucose ≥6.11 mM during the observation period.

Results

In the quartile groups, 0.9%, 2.1%, 3.4%, and 20.2% of the men developed impaired fasting glucose, respectively, and 0.1%, 0.3%, 0.5%, and 5.6% of the women developed impaired fasting glucose, respectively (P trend <0.001). After adjusting for age, body mass index, systolic blood pressure, triacylglycerols, high density lipoprotein-cholesterol, creatinine, fatty liver, family history of diabetes, alcohol consumption, and current smoking, uric acid levels were positively associated with onset of impaired fasting glucose in men with highest-quartile fasting plasma glucose levels (adjusted hazard ratio, 1.003; 95% confidence interval, 1.0001–1.005, P = 0.041).

Conclusions

Among men with high fasting plasma glucose, hyperuricemia may be independently associated with an elevated risk of developing impaired fasting glucose.

Ursodeoxycholic acid ameliorates fructose-induced metabolic syndrome in rats

The metabolic syndrome (MS) is characterized by insulin resistance, dyslipidemia and hypertension. It is associated with increased risk of cardiovascular diseases and type-2 diabetes. Consumption of fructose is linked to increased prevalence of MS. Ursodeoxycholic acid (UDCA) is a steroid bile acid with antioxidant, anti-inflammatory activities and has been shown to improve insulin resistance. The current study aims to investigate the effect of UDCA (150 mg/kg) on MS induced in rats by fructose administration (10%) in drinking water for 12 weeks. The effects of UDCA were compared to fenofibrate (100 mg/kg), an agonist of PPAR-α receptors. Treatment with UDCA or fenofibrate started from the 6^th week after fructose administration once daily. Fructose administration resulted in significant increase in body weight, elevations of blood glucose, serum insulin, cholesterol, triglycerides, advanced glycation end products (AGEs), uric acid levels, insulin resistance index and blood pressure compared to control rats. Moreover, fructose increased oxidative stress in aortic tissues indicated by significant increases of malondialdehyde (MDA), expression of iNOS and reduction of reduced glutathione (GSH) content. These disturbances were associated with decreased eNOS expression, increased infiltration of leukocytes and loss of aortic vascular elasticity. Treatment with UDCA successfully ameliorated the deleterious effects of fructose. The protective effect of UDCA could be attributed to its ability to decrease uric acid level, improve insulin resistance and diminish oxidative stress in vascular tissues. These results might support possible clinical application of UDCA in MS patients especially those present with liver diseases, taking into account its tolerability and safety. However, further investigations on human subjects are needed before the clinical application of UDCA for this indication.

Prior exercise and postprandial incretin responses in lean and obese individuals

PURPOSE

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) help regulate postprandial triacylglycerol (TAG) and insulin concentrations, but the effects of acute aerobic exercise on GLP-1 or GIP responses are unclear. The purpose of this study was to determine whether reductions in postprandial TAG and insulin with exercise are associated with GLP-1 and GIP responses.

METHODS

Thirteen normal-weight (NW) and 13 obese (Ob) individuals participated in two, 4-d trials in random order including an exercise (EX) and a no exercise (NoEX) trial. Diet was controlled during both trials. The EX trial consisted of 1 h of treadmill walking (55%-60% of V˙O2peak) during the evening of day 3 of the trial, 12 h before a 4-h mixed meal test on day 4, during which frequent blood samples were collected to assess postprandial lipemia, glycemia, insulin, C-peptide, GIP, and GLP-1 responses. Insulin secretion was estimated using the insulinogenic index, and insulin clearance was estimated using the ratio of insulin to C-peptide.

RESULTS

Postprandial TAG were 29% lower after EX in Ob individuals (P < 0.05) but were not significantly altered in NW individuals (P > 0.05). The drop in postprandial HDL cholesterol was attenuated with EX in Ob individuals (P < 0.05). Insulin responses were 14% lower after EX in Ob individuals (P < 0.05), and this was associated with reduced insulin secretion (P < 0.05), with no change in insulin clearance (P > 0.05). Glucose, C-peptide, GIP, and GLP-1 were not different between trials.

CONCLUSION

A 1-h bout of moderate-intensity aerobic exercise the night before a mixed meal attenuates TAG and insulin responses in Ob but not NW individuals, an effect not associated with altered GLP-1 or GIP responses.

Comorbidities in patients with crystal diseases and hyperuricemia

Crystal arthropathies are among the most common causes of painful inflammatory arthritis. Gout, the most common example, has been associated with cardiovascular and renal disease. In recent years, evidence for these associations and those involving other comorbidities, such as the metabolic syndrome, have emerged, and the importance of asymptomatic hyperuricemia has been established. In this review, an update on evidence, both experimental and clinical, is presented, and associations between hyperuricemia, gout, and several comorbidities are described. Causality regarding calcium pyrophosphate arthropathy and associated comorbidities is also reviewed.