Associations between dietary diversity and high sensitive C-reactive protein among Japanese workers: findings of a cross-sectional and longitudinal study.

PURPOSE: To clarify the association between dietary diversity and inflammatory status in Japanese workers. METHODS: Of 1,460 men and women aged 20-64 years in 2010 (baseline), those who were followed-up at least once between 2011 and 2018 were included in this study; 1,433 participants and 745 participants were included in the cross-sectional and longitudinal analyses, respectively. Dietary intake was assessed using a food frequency questionnaire at baseline, and the dietary diversity score was determined using the Quantitative Index for Dietary Diversity (QUANTIDD). High-sensitivity C-reactive protein (hs-CRP) was taken to indicate inflammatory status at the baseline and follow-up surveys. In the cross-sectional analysis using baseline data, a generalized linear model was used to calculate adjusted means and 95% confidence intervals (CIs) for hs-CRP according to the QUANTIDD score. In the longitudinal analysis, generalized estimating equations were used to calculate the adjusted mean (95% CI) for hs-CRP in follow-up according to the QUANTIDD score at baseline. RESULTS: In the cross-sectional analysis, the hs-CRP concentration in male participants was significantly lower in those who had a high QUANTIDD score (adjusted mean [95% CI]: 0.074 [0.009-0.140] mg/dL in the lower group vs. 0.038 [-0.029-0.105] mg/dL in the higher group, p-value = 0.034). In the longitudinal analysis, the hs-CRP concentration of male participants also tended to be lower in those with higher QUANTIDD scores (p-value = 0.103). In both the cross-sectional and longitudinal analyses in women, there was no significant difference between the lower and higher QUANTIDD score groups. CONCLUSION: These findings suggest that, in male Japanese workers, higher dietary diversity might be important for maintaining a low inflammatory status.

Associations between dietary diversity and dyslipidemia among Japanese workers: cross-sectional study and longitudinal study findings.

OBJECTIVE: The aim of this study was to determine the associations between dietary diversity and risk of dyslipidemia in Japanese workers. METHODS: The cross-sectional study included 1399 participants aged 20-63 years and the longitudinal study included 751 participants aged 20-60 years in 2012-2013 (baseline) who participated at least once from 2013 to 2017 with cumulative participation times of 4.9 times. Dietary intake was assessed using a food frequency questionnaire, and dietary diversity score (DDS) was determined using the Quantitative Index for Dietary Diversity. Dyslipidemia was diagnosed when at least one of the following conditions was met: hypertriglyceridemia, high LDL-cholesterol, low HDL-cholesterol, high non-HDL-cholesterol, and a history of dyslipidemia. Multivariable logistic regression was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for dyslipidemia with control of confounding factors in cross-sectional analysis. Generalized estimating equations were used for calculating the ORs (95% CI) for dyslipidemia in the follow-up period according to the DDS at baseline with control of confounding factors in longitudinal analysis. RESULTS: Cross-sectional analysis showed that the highest DDS reduced the odds of dyslipidemia in men (OR [95% CI] in Tertile 3: 0.67 [0.48-0.95], p value = 0.023). In longitudinal analysis, a moderate DDS reduced the risk of dyslipidemia (OR [95% CI] in Tertile 2: 0.21 [0.07-0.60], p value = 0.003) in women. CONCLUSIONS: The results of cross-sectional analysis in this study suggest that the higher diversity of diet might reduce the presence of dyslipidemia in men and the results of longitudinal analysis suggest that a moderate DDS might reduce the risk of dyslipidemia in women. Further studies are needed since the results of cross-sectional and longitudinal analyses in this study were inconsistent.

Associations of dietary diversity with allergic diseases in Japanese workers: a cross-sectional study.

BACKGROUND AND OBJECTIVES: The aim of this study was to determine the associations of dietary diversity with prevalences of allergic diseases. METHODS AND STUDY DESIGN: The participants were 1,317 men and women aged 20 to 63 years who were living in Tokushima Prefecture, Japan during the period 2012-2013. We obtained anthropometric data and information on lifestyle characteristics and current medical histories of allergic diseases using a self-administered questionnaire. Dietary intake was assessed using a food frequency questionnaire, and dietary diversity was determined using the Quantitative Index for Dietary Diversity (QUANTIDD). The ORs and 95% CIs for each of the allergic diseases with a 1 standard deviation (SD) increase in the QUANTIDD score were estimated, controlling for age, family history of allergic diseases, education, smoking, drinking, physical activity, energy intake and BMI. RESULTS: Higher dietary diversity showed significant inverse dose-response relationships with allergic diseases and allergic rhinitis in women. Multivariate-adjusted ORs (95% CI) for allergic diseases and allergic rhinitis with 1 SD increase in the QUANTIDD score were 0.77 (95% CI: 0.60-0.98, p=0.037) and 0.69 (95% CI: 0.53-0.90, p=0.007), respectively, in women. There were no significant associations between dietary diversity and allergic diseases in men. CONCLUSIONS: The results indicate that there is an inverse association between higher dietary diversity and allergic rhinitis in Japanese female workers.

Potential Role of Free Fatty Acids in the Pathogenesis of Periodontitis and Primary Sjögren's Syndrome.

Clinical studies have shown that metabolic disorders such as type 2 diabetes and dyslipidemia are associated with increased risk of oral-related diseases, such as periodontitis and Sjögren's syndrome. Although changes in the immune system are critical in both of these metabolic disorders and oral-related diseases, the mechanism underlying the interaction between these diseases remains largely unknown. Obesity and type 2 diabetes are known to be associated with higher concentrations of free fatty acids in blood. Among free fatty acids, saturated fatty acids such as palmitic acid have been demonstrated to induce inflammatory responses mainly via the innate immune systems, and to be involved in the pathogenesis of type 2 diabetes in tissues such as adipose tissue, liver, pancreas, and skeletal muscle. Here, we highlight recent advances in evidence for the potential involvement of palmitic acid in the pathogenesis of periodontitis and Sjögren's syndrome, and discuss the possibility that improvement of the lipid profile could be a new strategy for the treatment of these diseases.

Possible Involvement of Palmitate in Pathogenesis of Periodontitis.

Type 2 diabetes (T2D) is characterized by decreased insulin sensitivity and higher concentrations of free fatty acids (FFAs) in plasma. Among FFAs, saturated fatty acids (SFAs), such as palmitate, have been suggested to promote inflammatory responses. Although many epidemiological studies have shown a link between periodontitis and T2D, little is known about the clinical significance of SFAs in periodontitis. In this study, we showed that gingival fibroblasts have cell-surface expression of CD36, which is also known as FAT/fatty acid translocase. Moreover, CD36 expression was increased in gingival fibroblasts of high-fat diet-induced T2D model mice, compared with gingival fibroblasts of mice fed a normal diet. DNA microarray analysis revealed that palmitate increased mRNA expression of pro-inflammatory cytokines and chemokines in human gingival fibroblasts (HGF). Consistent with these results, we confirmed that palmitate-induced interleukin (IL)-6, IL-8, and CXCL1 secretion in HGF, using a cytokine array and ELISA. SFAs, but not an unsaturated fatty acid, oleate, induced IL-8 production. Docosahexaenoic acid (DHA), which is one of the omega-3 polyunsaturated fatty acids, significantly suppressed palmitate-induced IL-6 and IL-8 production. Treatment of HGF with a CD36 inhibitor also inhibited palmitate-induced pro-inflammatory responses. Finally, we demonstrated that Porphyromonas gingivalis (P.g.) lipopolysaccharide and heat-killed P.g. augmented palmitate-induced chemokine secretion in HGF. These results suggest a potential link between SFAs in plasma and the pathogenesis of periodontitis.

Palmitate-stimulated monocytes induce adhesion molecule expression in endothelial cells via IL-1 signaling pathway.

Increased intake of saturated fatty acids (SFAs), such as palmitate (Pal), is linked to a higher risk of type 2 diabetes and cardiovascular disease. Although recent studies have investigated the direct effects of SFAs on inflammatory responses in vascular endothelial cells, it remains unknown whether SFAs also induce these responses mediated by circulating cells. In this study, especially focused on adhesion molecules and monocytes, we investigated the indirect effects of Pal on expression and release of ICAM-1 and E-selectin in vascular endothelial cells. Phorbol 12-myristate 13-acetate (PMA)-treated THP-1 (pTHP-1) cells and human monocytes were stimulated with various free fatty acids (FFAs). SFAs, but not unsaturated fatty acids (UFAs), increased interleukin (IL)-1ß secretion and decreased IL-1 receptor antagonist (IL-1Ra) secretion, resulting in an increase in the IL-1ß/IL-1Ra secretion ratio. UFAs dose-dependently inhibited the increase in IL-1ß secretion and decrease in IL-1Ra secretion induced by Pal. Moreover, in human aortic and vein endothelial cells, expression and release of ICAM-1 and E-selectin were induced by treatment with conditioned medium collected from Pal-stimulated pTHP-1 cells and human monocytes, but not by Pal itself. The up-regulated expression and release of adhesion molecules by the conditioned medium were mostly abolished by recombinant human IL-1Ra supplementation. These results suggest that the Pal-induced increase in the ratio of IL-1ß/IL-1Ra secretion in monocytes up-regulates endothelial adhesion molecules, which could enhance leukocyte adhesion to endothelium. This study provides further evidence that IL-1ß neutralization through receptor antagonism may be useful for preventing the onset and development of cardiovascular disease.

Roles of mitochondrial fragmentation and reactive oxygen species in mitochondrial dysfunction and myocardial insulin resistance.

PURPOSE: Evidence suggests an association between aberrant mitochondrial dynamics and cardiac diseases. Because myocardial metabolic deficiency caused by insulin resistance plays a crucial role in heart disease, we investigated the role of dynamin-related protein-1 (DRP1; a mitochondrial fission protein) in the pathogenesis of myocardial insulin resistance. METHODS AND RESULTS: DRP1-expressing H9c2 myocytes, which had fragmented mitochondria with mitochondrial membrane potential (ΔΨm) depolarization, exhibited attenuated insulin signaling and 2-deoxy-d-glucose (2-DG) uptake, indicating insulin resistance. Treatment of the DRP1-expressing myocytes with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP) significantly improved insulin resistance and mitochondrial dysfunction. When myocytes were exposed to hydrogen peroxide (H2O2), they increased DRP1 expression and mitochondrial fragmentation, resulting in ΔΨm depolarization and insulin resistance. When DRP1 was suppressed by siRNA, H2O2-induced mitochondrial dysfunction and insulin resistance were restored. Our results suggest that a mutual enhancement between DRP1 and reactive oxygen species could induce mitochondrial dysfunction and myocardial insulin resistance. In palmitate-induced insulin-resistant myocytes, neither DRP1-suppression nor TMPyP restored the ΔΨm depolarization and impaired 2-DG uptake, however they improved insulin signaling. CONCLUSIONS: A mutual enhancement between DRP1 and ROS could promote mitochondrial dysfunction and inhibition of insulin signal transduction. However, other mechanisms, including lipid metabolite-induced mitochondrial dysfunction, may be involved in palmitate-induced insulin resistance.

Mitochondrial dysfunction caused by saturated fatty acid loading induces myocardial insulin-resistance in differentiated H9c2 myocytes: a novel ex vivo myocardial insulin-resistance model.

Heart failure (HF) is often accompanied with metabolic disorders and insufficient energy production. Some previous studies have suggested an elevated serum free fatty acid (FA) due to chronic adrenergic stimulation induces myocardial insulin-resistance, which further impairs myocardial energy production. Because little is known about the pathogenesis of FA-induced cardiac insulin-resistance, we established an ex vivo cardiac insulin-resistant model and investigated the relationship between insulin-resistance and mitochondrial dysfunction. The ex vivo insulin-resistant myocytes, which was produced by treating differentiated H9c2 myocytes with palmitate (saturated FA; 0.2mM) for 24h, exhibited insulin-signaling deficiency and attenuated 2-deoxy-d-glucose (2-DG) uptake. When myocytes were pretreated with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP, a ROS scavenger; 200 µM), the insulin-signaling deficiency by palmitate was restored, whereas the attenuated 2-DG uptake was remained. In contrast to TMPyP, the pretreatment with perhexiline (a mitochondrial FA uptake inhibitor; 2 µM) restored the insulin-signaling deficiency and the attenuated 2-DG uptake by palmitate. Perhexiline restored the depolarized mitochondrial membrane potential (ΔΨm) and the reduced intracellular ATP by palmitate, and thereby improved the impaired GLUT4 recruitment to plasma membrane after insulin, whereas TMPyP failed to do so. These results suggested that the mitochondrial dysfunction by saturated FA loading and consequent intracellular energy shortage induced myocardial insulin-resistance in our ex vivo insulin-resistant model.

Long-term impact of COVID-19 pandemic on secular changes in metabolic parameters in Japanese workers : Tokushima Cohort Study.

OBJECTIVE: The coronavirus disease 2019 (COVID-19) pandemic has caused unprecedented changes in people's lifestyles. Since then, our lifestyle has remained different from what it used to be in the pre-pandemic era. This study investigated the long-term impact of the COVID-19 pandemic on secular changes in metabolic parameters in Japanese workers. METHODS: A total of 519 eligible subjects completed fiscal year (FY) 2017, FY2019 and FY2021 surveys. Comparison between pre-COVID-19 (Δpre-covid19 : FY2019-2017) and during COVID-19 (Δcovid19 : FY2021-2019) was performed in each sex. RESULTS: Increment of diastolic blood pressure (DBP) in Δcovid19 was significantly greater than that in Δpre-covid19 (Δpre-covid19 to Δcovid19 : 0.22 ± 6.17 to 2.59 ± 6.69 mmHg, p = 0.0002 in males, -0.18 ± 6.26 to 2.16 ± 6.60 mmHg, p = 0.01 in females). In females, increments of waist circumference and fasting plasma glucose in Δcovid19 were also significantly greater than those in Δpre-covid19 (both p < 0.05). Conversely, increments of BMI and body fat in Δcovid19 were significantly smaller than those in Δpre-covid19 in males (both p < 0.05). CONCLUSION: Our findings suggest that there was an apparent metabolic impact of the COVID-19 pandemic on DBP increment in Japanese workers. In addition, COVID-19 may have influenced males and females differently in relation to glucose metabolism and anthropometric measurements related to obesity / adiposity. J. Med. Invest. 71 : 47-53, February, 2024.

Myosin IIA participates in docking of Glut4 storage vesicles with the plasma membrane in 3T3-L1 adipocytes.

In adipocytes and myocytes, insulin stimulation translocates glucose transporter 4 (Glut4) storage vesicles (GSVs) from their intracellular storage sites to the plasma membrane (PM) where they dock with the PM. Then, Glut4 is inserted into the PM and initiates glucose uptake into these cells. Previous studies using chemical inhibitors demonstrated that myosin II participates in fusion of GSVs and the PM and increase in the intrinsic activity of Glut4. In this study, the effect of myosin IIA on GSV trafficking was examined by knocking down myosin IIA expression. Myosin IIA knockdown decreased both glucose uptake and exposures of myc-tagged Glut4 to the cell surface in insulin-stimulated cells, but did not affect insulin signal transduction. Interestingly, myosin IIA knockdown failed to decrease insulin-dependent trafficking of Glut4 to the PM. Moreover, in myosin IIA knockdown cells, insulin-stimulated binding of GSV SNARE protein, vesicle-associated membrane protein 2 (VAMP2) to PM SNARE protein, syntaxin 4 was inhibited. These data suggest that myosin IIA plays a role in insulin-stimulated docking of GSVs to the PM in 3T3-L1 adipocytes through SNARE complex formation.

Development of fully automated and ultrasensitive assays for urinary adiponectin and their application as novel biomarkers for diabetic kidney disease.

Glomerular filtration rate (GFR) and urinary albumin excretion rate (UAER) are used to diagnose and classify the severity of chronic kidney disease. Total adiponectin (T-AN) and high molecular weight adiponectin (H-AN) assays were developed using the fully automated immunoassay system, HI-1000 and their significance over conventional biomarkers were investigated. The T-AN and H-AN assays had high reproducibility, good linearity, and sufficient sensitivity to detect trace amounts of adiponectin in the urine. Urine samples after gel filtration were analyzed for the presence of different molecular isoforms. Low molecular weight (LMW) forms and monomers were the major components (93%) of adiponectin in the urine from a diabetic patient with normoalbuminuria. Urine from a microalbuminuria patient contained both high molecular weight (HMW) (11%) and middle molecular weight (MMW) (28%) adiponectin, although the LMW level was still high (52%). The amount of HMW (32%) and MMW (42%) were more abundant than that of LMW (24%) in a diabetic patient with macroalbuminuria. T-AN (r = - 0.43) and H-AN (r = - 0.38) levels showed higher correlation with estimated GFR (eGFR) than UAER (r = - 0.23). Urinary levels of both T-AN and H-AN negatively correlated with renal function in diabetic patients and they may serve as new biomarkers for diabetic kidney disease.

Dietary diversity and characteristics of lifestyle and awareness of health in Japanese workers†:†a cross-sectional study.

The aim of this study was to clarify the characteristics of lifestyle and health awareness according to dietary diversity in a Japanese worksite population. The participants were 1,312 men and women aged 20 to 63 years who were living in Tokushima Prefecture, Japan during the period 2012-2013. We obtained anthropometric data and information on lifestyle characteristics using a self-administered questionnaire. Dietary intake was assessed using a food frequency questionnaire, and dietary diversity was determined using the Quantitative Index for Dietary Diversity (QUANTIDD). The characteristics of lifestyle and health awareness according to quartiles of the QUANTIDD score were assessed using the chi-square test and a general linear model. The higher the QUANTIDD score was, the larger were the proportions of participants who knew the appropriate amount of dietary intake and participants who referred to nutritional component information when choosing and / or buying food. Among participants with higher QUANTIDD scores, the proportion of participants who considered their current diet was good was high in women, whereas the proportion of participants who wanted to improve their diet in the future was high in men. Those results indicate that higher dietary diversity was related to better characteristics of lifestyle and awareness of health. J. Med. Invest. 67 : 255-264, August, 2020.

Association of accumulated advanced glycation end-products with a high prevalence of sarcopenia and dynapenia in patients with type 2 diabetes.

AIMS/INTRODUCTION: Advanced glycation end-products (AGEs), which are a major cause of diabetic vascular complications, accumulate in various tissues under chronic hyperglycemic conditions, as well as with aging in patients with diabetes. The loss of muscle mass and strength, so-called sarcopenia and dynapenia, has recently been recognized as a diabetic complication. However, the influence of accumulated AGEs on muscle mass and strength remains unclear. The present study aimed to evaluate the association of sarcopenia and dynapenia with accumulated AGEs in patients with type 2 diabetes. MATERIALS AND METHODS: We recruited 166 patients with type 2 diabetes aged ≥30 years (mean age 63.2 ± 12.3 years; body mass index 26.3 ± 4.9 kg/m2 ; glycated hemoglobin 7.1 ± 1.1%). Skin autofluorescence as a marker of AGEs, limb skeletal muscle mass index, grip strength, knee extension strength and gait speed were assessed. RESULTS: Sarcopenia and dynapenia were observed in 7.2 and 13.9% of participants, respectively. Skin autofluorescence was significantly higher in patients with sarcopenia and dynapenia. Skin autofluorescence was the independent determinant for skeletal muscle mass index, grip strength, knee extension strength, sarcopenia and dynapenia. CONCLUSIONS: Accumulated AGEs could contribute to reduced muscle mass and strength, leading to sarcopenia and dynapenia in patients with type 2 diabetes.

Cardiomyocytes cultured on mechanically compliant substrates, but not on conventional culture devices, exhibit prominent mitochondrial dysfunction due to reactive oxygen species and insulin resistance under high glucose.

RATIONALE: Diabetes causes cardiac dysfunction, and understanding of its mechanism is still incomplete. One reason could be limitations in modeling disease conditions by current in vitro cardiomyocyte culture. Emerging evidence suggests that the mechanical properties of the microenvironment affect cardiomyocyte function. Nevertheless, the impact of high glucose on cardiomyocytes cultured on substrates whose stiffness matches that of the heart (approximately 15 kPa) is untested. OBJECTIVE: To test the hypothesis that cardiomyocytes cultured in microenvironments that mimic the mechanical properties of those for cardiomyocytes in vivo may reproduce the pathophysiology characteristics of diabetic cardiomyocytes ex vivo, such as the morphological appearance, ROS accumulation, mitochondrial dysfunction, apoptosis and insulin-stimulated glucose uptake. METHODS AND RESULTS: Isolated neonatal rat cardiomyocytes were seeded on 15 kPa polyacrylamide (PAA) gels, whose stiffness mimics that of heart tissues, or on glass coverslips, which represent conventional culture devices but are unphysiologically stiff. Cells were then cultured at 5 mM glucose, corresponding to the normal blood glucose level, or at high glucose levels (10 to 25 mM). Cytoskeletal disorganization, ROS accumulation, attenuated mitochondrial membrane potential and attenuated ATP level caused by high glucose and their reversal by a ROS scavenger were prominent in cells on gels, but not in cells on coverslips. The lack of response to ROS scavenging could be attributable to enhanced apoptosis in cells on glass, shown by enhanced DNA fragmentation and higher caspase 3/7 activity in cells on glass coverslips. High-glucose treatment also downregulated GLUT4 expression and attenuated insulin-stimulated glucose uptake only in cells on 15 kPa gels. CONCLUSION: Our data suggest that a mechanically compliant microenvironment increases the susceptibility of primary cardiomyocytes to elevated glucose levels, which enables these cells to serve as an innovative model for diabetic heart research.

Soy product and isoflavone intake associations with allergic diseases in Japanese workers: rhinitis, dermatitis and asthma.

BACKGROUND AND OBJECTIVES: The aim of this study was to determine the associations of intake of soy products and isoflavones with allergic diseases. METHODS AND STUDY DESIGN: We conducted a cross-sectional study in 1437 participants (aged 20-64 years) who were living in Tokushima Prefecture, Japan during the period 2010- 2011. We obtained anthropometric data and information on life style characteristics including dietary intake and current medical histories of allergic diseases using a structural self-administered questionnaire. Multiple logistic regression models were used to assess the associations of soy products and isoflavones with allergic diseases after controlling for age, family history of allergic diseases, smoking, drinking, physical activity, energy intake, BMI and dietary factors. RESULTS: Intake of soy products showed significant inverse dose-response relationships with allergic rhinitis. The third quartile for soy products had an adjusted OR of 0.56 (95% CI: 0.35-0.91) compared to the reference group (first quartile), though intake of soy products showed no dose-response relationship with atopic dermatitis. Intake of soy isoflavones showed a significant inverse dose-response relationship with atopic dermatitis, though the association between intake of soy isoflavones and atopic dermatitis was U-shaped after adjustments for potential confounders. On the other hand, the associations between intake of soy isoflavones and other allergic diseases were not significant. CONCLUSIONS: The results indicate that higher intake of soy products is associated with reduced risk of allergic rhinitis in Japanese workers. Furthermore, moderate intake amounts of soy products and soy isoflavones are associated with inverse risk of atopic dermatitis.

Associations between intake of dietary fermented soy food and concentrations of inflammatory markers: a cross-sectional study in Japanese workers.

Epidemiological investigations have shown that consumption of soybeans or soy foods reduces the risk of the development of cardiovascular disease, cancer and osteoporosis. The aim of this study was to determine the associations between different soy foods and inflammatory markers, including high-sensitivity C-reactive protein (hs-CRP), interleukin (IL)-6, and IL-18, in Japanese workers. The cross-sectional study included 1,426 Japanese workers (1,053 men and 373 women) aged 20 to 64 years. Intake of 12 soy foods was estimated by a validated food frequency questionnaire. Associations of total soy foods, fermented soy food, non-fermented soy food, soy isoflavone with hs-CRP, IL-6, and IL-18 levels were examined by general linear model regression analysis. We found that total fermented soy food intake was inversely associated with multivariable-adjusted geometric concentration of IL-6 in men (Q1:1.03 pg/mL, Q5:0.94 pg /mL;P for trend = 0.031). Furthermore, it was shown that IL-6 concentrations were inversely associated with miso intake (ß = -0.068;p = 0.034) and soy sauce intake in men (ß = -0.074;p = 0.018). This study suggests that intake of total fermented soy food, miso and soy sauce be associated with IL-6 concentrations in Japanese men. J. Med. Invest. 65:74-80, February, 2018.

PI 4,5-P2 stimulates glucose transport activity of GLUT4 in the plasma membrane of 3T3-L1 adipocytes.

Insulin-stimulated glucose uptake through GLUT4 plays a pivotal role in maintaining normal blood glucose levels. Glucose transport through GLUT4 requires both GLUT4 translocation to the plasma membrane and GLUT4 activation at the plasma membrane. Here we report that a cell-permeable phosphoinositide-binding peptide, which induces GLUT4 translocation without activation, sequestered PI 4,5-P2 in the plasma membrane from its binding partners. Restoring PI 4,5-P2 to the plasma membrane after the peptide treatment increased glucose uptake. No additional glucose transporters were recruited to the plasma membrane, suggesting that the increased glucose uptake was attributable to GLUT4 activation. Cells overexpressing phosphatidylinositol-4-phosphate 5-kinase treated with the peptide followed by its removal exhibited a higher level of glucose transport than cells stimulated with a submaximal level of insulin. However, only cells treated with submaximal insulin exhibited translocation of the PH-domains of the general receptor for phosphoinositides (GRP1) to the plasma membrane. Thus, PI 4,5-P2, but not PI 3,4,5-P3 converted from PI 4,5-P2, induced GLUT4 activation. Inhibiting F-actin remodeling after the peptide treatment significantly impaired GLUT4 activation induced either by PI 4,5-P2 or by insulin. These results suggest that PI 4,5-P2 in the plasma membrane acts as a second messenger to activate GLUT4, possibly through F-actin remodeling.

Separation of insulin signaling into distinct GLUT4 translocation and activation steps.

GLUT4 (glucose transporter 4) plays a pivotal role in insulin-induced glucose uptake to maintain normal blood glucose levels. Here, we report that a cell-permeable phosphoinositide-binding peptide induced GLUT4 translocation to the plasma membrane without inhibiting IRAP (insulin-responsive aminopeptidase) endocytosis. However, unlike insulin treatment, the peptide treatment did not increase glucose uptake in 3T3-L1 adipocytes, indicating that GLUT4 translocation and activation are separate events. GLUT4 activation can occur at the plasma membrane, since insulin was able to increase glucose uptake with a shorter time lag when inactive GLUT4 was first translocated to the plasma membrane by pretreating the cells with this peptide. Inhibition of phosphatidylinositol (PI) 3-kinase activity failed to inhibit GLUT4 translocation by the peptide but did inhibit glucose uptake when insulin was added following peptide treatment. Insulin, but not the peptide, stimulated GLUT1 translocation. Surprisingly, the peptide pretreatment inhibited insulin-induced GLUT1 translocation, suggesting that the peptide treatment has both a stimulatory effect on GLUT4 translocation and an inhibitory effect on insulin-induced GLUT1 translocation. These results suggest that GLUT4 requires translocation to the plasma membrane, as well as activation at the plasma membrane, to initiate glucose uptake, and both of these steps normally require PI 3-kinase activation.

Cut-off value of total adiponectin for managing risk of developing metabolic syndrome in male Japanese workers.

AIM: To determine the optimal cut-off value of serum total adiponectin for managing the risk of developing metabolic syndrome (MetS) in male Japanese workers. METHODS: A total of 365 subjects without MetS aged 20-60 years were followed up prospectively for a mean of 3.1 years. The accelerated failure-time model was used to estimate time ratio (TR) and cut-off value for developing MetS. RESULTS: During follow-up, 45 subjects developed MetS. Age-adjusted TR significantly declined with decreasing total adiponectin level (≤ 4.9, 5.0-6.6, 6.7-8.8 and ≥ 8.9 µg/ml, P for trend = 0.003). In multivariate analyses, TR of MetS was 0.12 (95% CI 0.02-0.78; P = 0.03) in subjects with total adiponectin level of 5.0-6.6 µg/ml, and 0.15 (95% CI 0.02-0.97; P = 0.047) in subjects with total adiponectin level ≤ 4.9 µg/ml compared with those with total adiponectin level ≥ 8.9 µg/ml. The accelerated failure-time model showed that the optimal cut-off value of total adiponectin for managing the risk of developing MetS was 6.2 µg/ml. In the multivariate-adjusted model, the mean time to the development of MetS was 78% shorter for total adiponectin level ≤ 6.2 µg/ml compared with > 6.2 µg/ml (TR 0.22, 95% CI: 0.08-0.64, P = 0.005). CONCLUSION: Our findings suggest that the cut-off value for managing the risk of developing MetS is 6.2 µg/ml in male Japanese workers. Subjects with total adiponectin level ≤ 6.2 µg/ml developed MetS more rapidly than did those with total adiponectin level > 6.2 µg/ml.

Correlation of fibroblast growth factor 21 serum levels with metabolic parameters in Japanese subjects.

OBJECTS: Since serum level of fibroblast growth factor 21 (FGF21) has been implicated as a potential biomarker for the early detection of the metabolic syndrome and type 2 diabetes, we examined how FGF21 serum levels are correlated with metabolic parameters in Japanese subjects. METHODS: FGF21 levels were analyzed by enzyme-linked immunosorbent assays. Spearman's correlation and multiple stepwise regression analyses were used to examine the relationship between serum FGF21 and other factors. A Mann-Whitney U test was performed between the normal and high groups for triglycerides and systolic blood pressure (BP) respectively. RESULTS: By univariate correlation analysis, serum FGF21 levels were significantly associated with triglyceride levels, systolic BP, diastolic BP, pulse pressure, body mass index (BMI), age, fasting plasma glucose (FPG) levels, and total cholesterol levels. Multiple regression analysis (adjusted for age, gender, and BMI) showed that serum FGF21 levels were independently and significantly associated with triglyceride levels and systolic BP. Serum FGF21 levels were significantly higher in subjects with high triglyceride levels and high systolic BP compared with those who had normal triglyceride levels and normal systolic BP respectively. CONCLUSIONS: This study found that FGF21 levels might be a biomarker for some metabolic disorders associated with metabolic syndrome.