Insulin resistance, adipokines, and oxidative stress in nondiabetic, hypercholesterolemic patients: leptin as an 8-epi-prostaglandin F2alpha determinant

Effect of lemon peel flavonoids on UVB-induced skin damage in mice

By establishing an effective ultraviolet B (UVB) radiation model of skin damage in mice, the effect of lemon peel flavonoids (LPF) on skin damage was explored. UVB skin damage in UV-irradiated mice was simulated, and animal models were established. Serum parameters were measured using kits, skin sections were stained with hematoxylin-eosin (H&E) and Masson, and quantitative polymerase chain reaction (qPCR) was used to detect the expression of skin tissue-related mRNA. The experimental results showed that LPF increased the activity of catalase (CAT) and superoxide dismutase (SOD) oxidases in serum of mice with UVB-induced skin damage and decreased MDA, interleukin-1β (IL-1β), IL-6, IL-10, and tumor necrosis factor-alpha (TNF-α) levels. Pathological observation indicated that LPF alleviated the skin tissue lesions caused by UVB. LPF upregulated the mRNA expression of SOD1, SOD2, CAT, nuclear factor erythroid-2 related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and inhibitor of NF-κB alpha (IκB-α) and downregulated the expression of nuclear factor kappa B (NF-κB), p38 MAPK, and cyclooxygenase-2 (COX-2) in the skin tissue of skin-damaged mice. There was a greater protective effect of LPF on the skin as compared to vitamin C (VC) at the same application concentration, and the effect of LPF was positively correlated with the concentration. High performance liquid chromatography (HPLC) analysis showed that LPF contained five flavonoid compounds, namely isomangiferin, rutin, astragalin, naringin, and quercetin. We demonstrated that flavonoids from LPF exhibit an excellent skin protection effect with satisfactory application value.

The relationship between glucose variability and insulin sensitivity and oxidative stress in subjects with prediabetes

AIM

The present study assessed the relationship between glucose variability (GV) and insulin levels, insulin resistance and oxidative stress at early stages of glucose intolerance.

MATERIAL AND METHODS

A total of 50 subjects - 12 males and 38 females, mean age 55.6 ± 9.7 years, mean BMI 28.4 ± 6.4 kg/m², divided into 2 groups according to glucose tolerance: 32 with prediabetes and 18 with normal glucose tolerance were included. Glucose tolerance was assessed by OGTT according to WHO 2006 criteria. Plasma glucose and serum insulin were measured at fasting, 120-minute and 180-minute during the test; and oxLDL and 3-Nitrotyrosine - at fasting and 120-minute. HOMA-IR and OGIS indexes were calculated. HbA1c and lipid levels was assessed. Continuous glucose monitoring was performed with a blind sensor (FreeStyle Libre Pro) for a mean period of 13.6 ± 2.3 days.

RESULTS

Our results demonstrate significantly increased insulin resistance in subjects with prediabetes, whereas there is no difference in oxidative stress markers between the two groups. OxLDL and 3-NT correlate positively with insulin levels and HOMA-IR and negatively with OGIS in both groups. There is a positive association between oxidative stress markers and 120-minute glucose in the prediabetes group. Insulin levels and HOMA-IR are positively related to plasma glucose and reciprocally to CV and M-Value in prediabetes, since the latter association is with borderline significance after adjustment for hypertension and smoking.

CONCLUSIONS

Our results demonstrate a significant correlation between oxidative stress and insulin resistance at early stages of glucose intolerance. Both chronic hyperglycemia and GV seem to be related to insulin levels and insulin resistance, and just postload glycaemia to oxidative stress in prediabetes.

Carnosine Supplementation Improves Serum Resistin Concentrations in Overweight or Obese Otherwise Healthy Adults: A Pilot Randomized Trial

Adipokines play an important role in the regulation of glucose metabolism. We have previously shown that carnosine supplementation in overweight or obese non-diabetic individuals improves glucose metabolism but does not change adiponectin concentrations. However, its effect on other adipokines has not been investigated. Herein we further determined the effect of carnosine supplementation on serum adipsin, resistin and leptin. Twenty-two overweight or obese otherwise healthy adults were randomly assigned to receive either 2 g of carnosine (n = 13) or identically looking placebo (n = 9) for 12 weeks. Serum adipsin, leptin and resistin were analyzed using a bead-based multiplex assay. Carnosine supplementation decreased serum resistin concentrations compared to placebo (mean change from baseline: −35 ± 83 carnosine vs. 35 ± 55 ng/mL placebo, p = 0.04). There was a trend for a reduction in serum leptin concentrations after carnosine supplementation (−76 ± 165 ng/mL carnosine vs. 20 ± 28 ng/mL placebo, p = 0.06). The changes in leptin and resistin concentrations were inversely related to the change in concentration for urinary carnosine (r = −0.72, p = 0.0002; r = −0.67, p = 0.0009, respectively), carnosine-propanal (r = −0.56, p = 0.005; r = −0.63, p = 0.001, respectively) and carnosine-propanol (r = −0.61, p = 0.002; r = −0.60, p = 0.002, respectively). There were no differences between groups in change in adipsin concentrations. Our findings show carnosine supplementation may normalize some, but not all, of the serum adipokine concentrations involved in glucose metabolism, in overweight and obese individuals. Further clinical trials with larger samples are needed to confirm these results.

In utero exposure to germinated brown rice and its oryzanol-rich extract attenuated high fat diet-induced insulin resistance in F1 generation of rats

Background

The development of insulin resistance is multifactorial, with maternal pre- and postnatal nutrition having significant influences. In this regard, high fat diet (HFD) feeding in pregnancy has been shown to increase risks of metabolic diseases. Thus, we investigated the effects of supplementation of HFD with germinated brown rice (GBR) and GBR-derived gamma oryzanol-rich extract (OE) on insulin resistance and its epigenetic implications in pregnant rats and their offsprings.

Methods

Pregnant female Sprague dawley rats were fed with HFD alone, HFD + GBR or HFD + OE (100 or 200 mg/kg/day) throughout pregnancy and lactation. Their offsprings were weaned at 4 weeks post-delivery and were followed up until 8 weeks. Serum levels of adipokines were measured in dams and their offsprings, and global DNA methylation and histone acetylation patterns were estimated from the liver.

Results

The dams and offsprings of the GBR and OE groups had lower weight gain, glycemic response, 8-Iso prostaglandin, retinol binding protein 4 and fasting insulin, and elevated adiponectin levels compared with the HFD group. Fasting leptin levels were lower only in the GBR groups. Hepatic global DNA methylation was lower in the GBR groups while hepatic H4 acetylation was lower in both GBR and OE dams. In the offsprings, DNA methylation and H4 acetylation were only lower in the OE group. However, dams and offsprings of the GBR and OE groups had higher hepatic H3 acetylation.

Conclusions

GBR and OE can be used as functional ingredients for the amelioration of HFD-induced epigeneticallymediated insulin resistance.

Urine 8-isoprostane in relation to adiposity and insulin resistance in individuals at high cardiometabolic risk

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of many conditions, including insulin resistance and obesity. However, in vivo data concerning these relationships are scarce and conflicting. Therefore, the aim of this study was to investigate the association of oxidative stress with abdominal adiposity and insulin resistance in individuals at high cardiometabolic risk.

METHODS

A total of 116 overweight/obese individuals participating in the HealthGrain and Etherpaths European Projects, having waist circumference (WC) and any other component of the metabolic syndrome, were included in this cross-sectional evaluation. 8-Isoprostane concentrations in 24-hr urine were measured as marker of oxidative stress in vivo. Baseline anthropometric and metabolic parameters were analyzed according to quartiles of 8-isoprostanes. Linear regression (LR) analysis was used to assess clinical correlates of oxidative stress.

RESULTS

Urinary 8-isoprostane levels were 52% higher in men than in women (P<0.001). Across the isoprostanes quartiles, there was a significant increase in WC and body weight [P for trend<0.001; analysis of variance (ANOVA) P<0.001] and fasting triglycerides (P for trend<0.05; ANOVA P<0.05), and a significant decrease in high-density lipoprotein cholesterol (P for trend<0.001; ANOVA P=0.001). No significant association between urinary isoprostane concentrations and insulin resistance [homeostasis model assessment of insulin resistance (HOMA-IR)] was found. WC circumference and body weight remained significant after adjustment for age and gender (P=0.023 and P=0.014, respectively) and independently associated with isoprostanes at LR (P<0.005 for both).

CONCLUSIONS

Central obesity was independently associated with oxidative stress even in a population homogeneous for adiposity and cardiometabolic risk, whereas no relationship was observed between oxidative stress and insulin resistance.

Lipid peroxidation, nitric oxide metabolites, and their ratio in a group of subjects with metabolic syndrome

Our aim was to evaluate lipid peroxidation, expressed as thiobarbituric acid-reactive substances (TBARS), nitric oxide metabolites (nitrite + nitrate) expressed as NOx, and TBARS/NOx ratio in a group of subjects with metabolic syndrome (MS). In this regard we enrolled 106 subjects with MS defined according to the IDF criteria, subsequently subdivided into diabetic (DMS) and nondiabetic (NDMS) and also into subjects with a low triglycerides/HDL-cholesterol (TG/HDL-C) index or with a high TG/HDL-C index. In the entire group and in the four subgroups of MS subjects we found an increase in TBARS and NOx levels and a decrease in TBARS/NOx ratio in comparison with normal controls. Regarding all these parameters no statistical difference between DMS and NDMS was evident, but a significant increase in NOx was present in subjects with a high TG/HDL-C index in comparison with those with a low index. In MS subjects we also found a negative correlation between TBARS/NO x ratio and TG/HDL-C index. Considering the hyperactivity of the inducible NO synthase in MS, these data confirm the altered redox and inflammatory status that characterizes the MS and suggest a link between lipid peroxidation, inflammation, and insulin resistance, evaluated as TG/HDL-C index.

Oxidative stress and inflammatory markers in relation to circulating levels of adiponectin

OBJECTIVE

Previous epidemiological studies together with animal studies have suggested an association between adiponectin and oxidative stress and inflammation, but community-based studies are lacking. Our objective was to investigate the relative importance of oxidative stress and inflammatory markers, representing different pathways in relation to adiponectin.

DESIGN AND METHODS

In a cross-sectional sample of 929 70-year-old individuals (50% women) of the Prospective Investigation of the Vasculature in Uppsala Seniors study, relations between serum adiponectin and oxidative stress [conjugated dienes (CD), homocysteine, total antioxidant capacity, oxidized low-density lipoprotein (OxLDL), OxLDL antibodies, baseline CD of LDL, glutathione (GSH), total glutathione (TGSH), glutathione disulfide], circulation interleukins (IL-6, IL-8), other cytokines [tumor necrosis factor α, monocyte chemotactic protein-1 (MCP-1), epidermal growth factor (EGF), vascular endothelial growth factor], cell adhesion molecules (vascular cell adhesion molecule-1, intercellular adhesion molecule-1, E-selectin, P-selectin, L-selectin), and systemic inflammatory markers [C-reactive protein (CRP), leukocyte count] in separate models were investigated.

RESULTS

In age- and sex-adjusted, as well as multivariable-adjusted models, adiponectin was significantly and positively associated with GSH, log TGSH, whereas an inverse association was observed for CD and log EGF. An inverse association between adiponectin and MCP-1, log E-selectin, and log CRP was significant in age- and sex-adjusted models, but not in multivariable-adjusted models.

CONCLUSIONS

Our results imply that higher levels of adiponectin are associated with a more beneficial oxidative stress profile, with higher levels of principal anti-oxidative GSH and total GSH together with lower levels of lipid peroxidation, possibly through shared pathways. Further studies are needed to investigate whether changes in the oxidative stress profile may be a mechanism linking adiponectin with type 2 diabetes and/or cardiovascular disease.

Relationship between obesity and serum reactive oxygen metabolites in adolescents

OBJECTIVES

Various cross-sectional studies have revealed a significant positive relationship between systemic oxidative stress and obesity-related indices such as body mass index (BMI, kg/m²). However, little is known of the role of oxidative stress during adolescence. The aim of this study was to determine the association between obesity and serum reactive oxygen metabolites (ROM) in adolescents.

METHOD

A total of 595 healthy junior high school students from northern Japan were enrolled in the study. Oxidative stress was evaluated by measuring serum levels of ROM. Obesity indices included BMI and percentage body fat (PBF). The analyses were stratified by sex and controlled for age and menarche. Partial correlation coefficients and analysis of covariance were also analyzed.

RESULTS

In female students, ROM levels increased with increasing BMI and PBF. Therefore, ROM levels were significantly higher in the underweight group than in the BMI-classified overweight-obese (P < 0.001) and normal weight groups (P < 0.05). ROM levels were significantly higher in the high PBF group than in the underweight (P < 0.05) and normal groups (P < 0.001).

CONCLUSION

The results of this study show that, regardless of menarche, obesity indicators such as BMI and PBF are correlated with the level of oxidative stress in female adolescents.

Eicosanoids and adipokines in breast cancer: from molecular mechanisms to clinical considerations

Chronic inflammation is one of the foremost risk factors for different types of malignancies, including breast cancer. Additional risk factors of this pathology in postmenopausal women are weight gain, obesity, estrogen secretion, and an imbalance in the production of adipokines, such as leptin and adiponectin. Various signaling products of transcription factor, nuclear factor-kappaB, in particular inflammatory eicosanoids, reactive oxygen species (ROS), and cytokines, are thought to be involved in chronic inflammation-induced cancer. Together, these key components have an influence on inflammatory reactions in malignant tissue damage when their levels are deregulated endogenously. Prostaglandins (PGs) are well recognized in inflammation and cancer, and they are solely biosynthesized through cyclooxygenases (COXs) from arachidonic acid. Concurrently, ROS give rise to bioactive isoprostanes from arachidonic acid precursors that are also involved in acute and chronic inflammation, but their specific characteristics in breast cancer are less demonstrated. Higher aromatase activity, a cytochrome P-450 enzyme, is intimately connected to tumor growth in the breast through estrogen synthesis, and is interrelated to COXs that catalyze the formation of both inflammatory and anti-inflammatory PGs such as PGE(2), PGF(2α), PGD(2), and PGJ(2) synchronously under the influence of specific mediators and downstream enzymes. Some of the latter compounds upsurge the intracellular cyclic adenosine monophosphate concentration and appear to be associated with estrogen synthesis. This review discusses the role of COX- and ROS-catalyzed eicosanoids and adipokines in breast cancer, and therefore ranges from their molecular mechanisms to clinical aspects to understand the impact of inflammation.

Obesity and breast cancer: a clinical biochemistry perspective

OBJECTIVES

To evaluate the laboratory diagnosis aspects of obesity-related health problems with special reference to postmenopausal breast cancer.

DESIGN AND METHODS

We conducted a systemic search of the literature primarily from the PubMed to obtain the relevant data.

RESULTS

Obesity is associated with the dysregulations of a number of body components such as blood constituents, extracellular matrix, and hormones/growth factors axes, which could be utilized for early diagnosis.

CONCLUSIONS

Obesity-related disorders including breast cancer have emerged as major health problems in almost all the nations. There is a need to elucidate different biochemical markers that are being used in the clinics or have the potential for such use. A precise understanding of the complex pathologies related with obesity is useful in prevention, early diagnosis and overall clinical management.

F2-isoprostanes and adiposity in older adults

We examined whether a systemic marker of oxidative stress, F(2)-isoprostanes (F(2)-IPs), was associated with total and regional adiposity, adipocytokines, and change in adiposity. Using data from 726 participants enrolled in the Health, Aging, and Body Composition (Health ABC) study, F(2)-IPs and adipocytokines were measured from baseline plasma samples. Total adiposity was measured by whole-body dual-energy X-ray absorptiometry and regional adiposity by abdominal and thigh computed tomography scans at baseline and 5-year follow-up. ANOVA models were estimated to examine associations between F(2)-IP tertiles and baseline adiposity and changes in body composition. Median F(2)-IPs was 54.3 pg/ml; women had significantly higher levels than men (61.5 vs. 48.9 pg/ml, P < 0.001). F(2)-IPs were associated with higher levels of adiponectin, leptin, and tumor necrosis factor-α (TNF-α). Positive associations were found between F(2)-IPs and all measures of total and regional adiposity among women. In linear regression models, adipocytokines mediated associations among women. Over 5 years of follow-up, women in the highest vs. lowest F(2)-IP tertile exhibited significant loss of weight (lowest tertile: -1.1 kg, highest tertile: -2.7 kg, P < 0.05). In conclusion, F(2)-IPs were associated with measures of total and regional adiposity in women alone and these associations were partially explained by adipocytokines. F(2)-IPs predicted loss of total adiposity over time among women.

Relationships of systemic oxidative stress to body fat distribution, adipokines and inflammatory markers in healthy middle-aged women

Obesity and systemic oxidative stress are closely related. However data concerning the relationships between oxidative stress and body fat mass distribution are sparse. Anthropometric and metabolic profile was evaluated in 148 clinically healthy middle-aged women to assess the correlations between oxidative stress, fat mass distribution, adipokines, and inflammatory markers. Systemic oxidative stress was assessed by urinary creatinine-indexed 8-epi-prostaglandin F-(2alpha) (8-epi-PGF(2alpha)). Body fat mass distribution was examined by dual-energy X-ray absorptiometry (DXA). Lipid profile, adipokines and inflammatory markers including leptin, adiponectin, high sensitive C-reactive protein (hsCRP), plasminogen activator inhibitor-1 (PAI-1), tumor necrosis factor-alpha (TNF-alpha) were determined. We found body mass index (BMI), waist circumference (WC), both central and peripheral DXA-derived regional fat mass (FM) accumulations were positively correlated with 8-epi-PGF(2alpha). Leptin, hsCRP and PAI-1also positively associated with 8-epi-PGF(2alpha). After adjustment for BMI and WC, lower-body FM, total FM and PAI-1 retained significant association with 8-epi-PGF(2alpha). Mutliple linear regression analyses indicated lower-body FM and PAI-1 were the two important predicators of 8-epi-PGF(2alpha). These results suggest that DXA-derived regional FM indices, especially low extremity adiposity, are more closely associated with systemic oxidative stress than indirect anthropometric indices. Positive associations between 8-epi-PGF(2alpha) and PAI-1, hsCRP, leptin support the notion that oxidative-stress-induced dysregulation of inflammation and adipokines may mediate the obesity-related metabolic derangement.

Expanding role for the apelin/APJ system in physiopathology

Apelin is a bioactive peptide known as the ligand of the G protein-coupled receptor APJ. Diverse active apelin peptides exist under the form of 13, 17 or 36 amino acids, originated from a common 77-amino-acid precursor. Both apelin and APJ mRNA are widely expressed in several rodent and human tissues and have functional effects in both the central nervous system and peripheral tissues. Apelin has been shown to be involved in the regulation of cardiovascular functions, fluid homeostasis, vessel formation and cell proliferation. More recently, apelin has been described as an adipocyte-secreted factor (adipokine), up-regulated in obesity. By acting as circulating hormone or paracrine factor, adipokines are involved in physiological regulations (fat depot development, energy storage, metabolism or eating behavior) or in the promotion of obesity-associated disorders (type 2 diabetes and cardiovascular dysfunctions). In this regard, expression of apelin gene in adipose tissue is increased by insulin and TNFα. This review will consider the main roles of apelin in physiopathology with particular attention on its role in energy balance regulation and in obesity-associated disorders.

Association of oxidative stress, insulin resistance, and diabetes risk phenotypes: the Framingham Offspring Study

OBJECTIVE

Systemic oxidative stress causes insulin resistance in rodents. We tested the hypothesis that oxidative stress and insulin resistance are associated in humans.

RESEARCH DESIGN AND METHODS

We used cross-sectional data from 2,002 nondiabetic subjects of the community-based Framingham Offspring Study. We measured insulin resistance with the homeostasis model and defined categorical insulin resistance as homeostasis model assessment of insulin resistance (HOMA-IR) > 75th percentile. We measured oxidative stress using the ratio of urine 8-epi-prostaglandin F2alpha (8-epi-PGF2alpha) to creatinine and used age- and sex-adjusted regression models to test the association of oxidative stress with insulin resistance in individuals without diabetes and among subgroups at elevated risk of diabetes.

RESULTS

Across 8-epi-PGF2alpha/creatinine tertiles, the prevalence of insulin resistance increased (18.0, 27.5, and 29.4% for the first, second, and third tertiles, respectively; P < 0.0001), as did mean levels of HOMA-IR (3.28, 3.83, and 4.06 units; P < 0.0001). The insulin resistance-oxidative stress association was attenuated by additional adjustment for BMI (P = 0.06 across tertiles for insulin resistance prevalence; P = 0.004 for mean HOMA-IR). Twenty-six percent of participants were obese (BMI > or = 30 kg/m2), 39% had metabolic syndrome (according to the Adult Treatment Panel III definition), and 37% had impaired fasting glucose (IFG) (fasting glucose 5.6-6.9 mmol/l). Among 528 obese participants, respectively, insulin resistance prevalence was 41.3, 60.6, and 54.2% across 8-epi-PGF2alpha/creatinine tertiles (P = 0.005); among 781 subjects with metabolic syndrome, insulin resistance prevalence was 41.3, 56.7, and 51.7% (P = 0.0025); and among 749 subjects with IFG, insulin resistance prevalence was 39.6, 47.2, and 51.6% (P = 0.04).

CONCLUSIONS

Systemic oxidative stress is associated with insulin resistance in individuals at average or elevated risk of diabetes even after accounting for BMI.

Impact of the high-molecular-weight form of adiponectin on endothelial function in healthy young men

OBJECTIVE

Adiponectin is an adipocyte-derived, antiatherogenic protein that is present in plasma as a large multimeric structure of high molecular weight (HMW) and in a trimer or hexamer form (non-HMW). The biological activities of these isoforms have not yet been elucidated. We therefore examined the effect of these isoforms on endothelial function in healthy young men.

DESIGN

One hundred apparently healthy young men without overt cardiovascular disease (mean age 30 years) were recruited in this cross-sectional study based on voluntary enrollment.

MEASUREMENTS

We evaluated endothelial function estimated by flow-mediated dilatation (FMD) of the brachial artery during reactive hyperaemia, and measured total and HMW adiponectin levels.

RESULTS

Both HMW and non-HMW adiponectin levels showed a significant, inverse correlation with body mass index (BMI). FMD was significantly correlated with fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), malondialdehyde-modified low density lipoprotein (MDA-LDL), LDL particle size, and HMW adiponectin (r = 0.320, P = 0.001), but not non-HMW adiponectin (r = 0.125, P = 0.22). In multivariate analysis, HMW adiponectin and MDA-LDL were selected as independent factors capable of influencing FMD. No variables determined nitroglycerin-induced dilatation.

CONCLUSIONS

These results suggest that even in young men, plasma adiponectin levels can predict endothelial dysfunction before any overt vascular disease has occurred. HMW adiponectin may be more useful as a marker of endothelial dysfunction than total adiponectin.