A genome-wide association study identifies a locus associated with knee extension strength in older Japanese individuals

Sarcopenia is a common skeletal muscle disease in older people. Lower limb muscle strength is a good predictive value for sarcopenia; however, little is known about its genetic components. Here, we conducted a genome-wide association study (GWAS) for knee extension strength in a total of 3452 Japanese aged 60 years or older from two independent cohorts. We identified a significant locus, rs10749438 which is an intronic variant in TACC2 (transforming acidic coiled-coil-containing 2) (P = 4.2 × 10-8). TACC2, encoding a cytoskeleton-related protein, is highly expressed in skeletal muscle, and is reported as a target of myotonic dystrophy 1-associated splicing alterations. These suggest that changes in TACC2 expression are associated with variations in muscle strength in older people. The association was consistently observed in young and middle-aged subjects. Our findings would shed light on genetic components of lower limb muscle strength and indicate TACC2 as a potential therapeutic target for sarcopenia.

Corrigendum: Playing basketball and volleyball during adolescence is associated with higher bone mineral density in old age: the Bunkyo Health Study

[This corrects the article DOI: 10.3389/fphys.2023.1227639.].

Assessing interstitial fluid dynamics in type 2 diabetes mellitus and prediabetes cases through diffusion tensor imaging analysis along the perivascular space

Background and purpose

Glymphatic system in type 2 diabetes mellitus (T2DM) but not in the prodrome, prediabetes (Pre-DM) was investigated using diffusion tensor image analysis along the perivascular space (DTI-ALPS). Association between glymphatic system and insulin resistance of prominent characteristic in T2DM and Pre-DM between is yet elucidated. Therefore, this study delves into the interstitial fluid dynamics using the DTI-ALPS in both Pre-DM and T2DM and association with insulin resistance.

Materials and methods

In our cross-sectional study, we assessed 70 elderly individuals from the Bunkyo Health Study, which included 22 with Pre-DM, 18 with T2DM, and 33 healthy controls with normal glucose metabolism (NGM). We utilized the general linear model (GLM) to evaluate the ALPS index based on DTI-ALPS across these groups, considering variables like sex, age, intracranial volume, years of education, anamnesis of hypertension and hyperlipidemia, and the total Fazekas scale. Furthermore, we have explored the relationship between the ALPS index and insulin resistance, as measured by the homeostasis model assessment of insulin resistance (HOMA-IR) using GLM and the same set of covariates.

Results

In the T2DM group, the ALPS index demonstrated a reduction compared with the NGM group [family-wise error (FWE)-corrected p < 0.001; Cohen's d = -1.32]. Similarly, the Pre-DM group had a lower ALPS index than the NGM group (FWE-corrected p < 0.001; Cohen's d = -1.04). However, there was no significant disparity between the T2DM and Pre-DM groups (FWE-corrected p = 1.00; Cohen's d = -0.63). A negative correlation was observed between the ALPS index and HOMA-IR in the combined T2DM and Pre-DM groups (partial correlation coefficient r = -0.35, p < 0.005).

Conclusion

The ALPS index significantly decreased in both the pre-DM and T2DM groups and showed a correlated with insulin resistance. This indicated that changes in interstitial fluid dynamics are associated with insulin resistance.

Low Handgrip Strength (Possible Sarcopenia) With Insulin Resistance Is Associated With Type 2 Diabetes Mellitus

Context

Older adults with sarcopenic obesity are at high risk for type 2 diabetes mellitus (T2DM). However, few East Asians have sarcopenic obesity. Since many East Asians have insulin resistance (IR) without obesity, it is possible that older East Asians with sarcopenia and IR might be at high risk for T2DM. However, this relationship has not been studied.

Methods

This cross-sectional study included 1629 older adults aged 65 to 84 years registered in the Bunkyo Health Study. All underwent a 75-g oral glucose tolerance test and handgrip strength measurement. Participants were classified into 4 groups by possible sarcopenia (handgrip strength <28 kg in men and <18 kg in women) and IR status (triglyceride glucose [TyG] index ≥8.79 for men and ≥8.62 for women [third quartile]). Modified Poisson regression was used to estimate relative risk (RR) and 95% CIs for T2DM with adjustment for confounding factors.

Results

The mean age was 73.1 ± 5.4 years. T2DM was diagnosed in 212 (13.0%) participants. After adjusting for age, sex, body mass index, use of lipid-lowering medications, hypertension, and cardiovascular disease, possible sarcopenia and IR were associated with T2DM, with their coexistence showing a notably stronger association (control: RR, 1.00 [Reference]; possible sarcopenia: RR, 1.55 [95% CI, 1.04-2.30]; IR: RR, 2.69 [95% CI, 1.99-3.65]; and IR possible sarcopenia: RR, 4.76 [95% CI, 3.34-6.79]).

Conclusion

Possible sarcopenia based on low handgrip strength and IR based on the TyG index are independently associated with T2DM in older Japanese individuals. Their coexistence shows a particularly strong association with T2DM.

Fat Accumulation and Elevated Free Fatty Acid Are Associated With Age-Related Glucose Intolerance: Bunkyo Health Study

Context

Older adults have a high prevalence of new-onset diabetes, often attributed to age-related decreases in insulin sensitivity and secretion. It remains unclear whether both insulin sensitivity and secretion continue to deteriorate after age 65.

Objective

To investigate the effects of aging on glucose metabolism after age 65 and to identify its determinants.

Methods

This cross-sectional study involved 1438 Japanese older adults without diabetes. All participants underwent a 75-g oral glucose tolerance test (OGTT). Body composition and fat distribution were measured with dual-energy X-ray absorptiometry and magnetic resonance imaging. Participants were divided into 4 groups by age (65-69, 70-74, 75-79, and 80-84 years) to compare differences in metabolic parameters.

Results

Mean age and body mass index were 73.0 ± 5.4 years and 22.7 ± 3.0 kg/m2. The prevalence of newly diagnosed diabetes increased with age. Fasting glucose, fasting insulin, the area under the curve (AUC)-insulin/AUC-glucose and insulinogenic index were comparable between groups. AUC-glucose and AUC-insulin during OGTT were significantly higher and Matsuda index and disposition index (Matsuda index · AUC-insulin/AUC-glucose) were significantly lower in the age 80-84 group than in the age 65-69 group. Age-related fat accumulation, particularly increased visceral fat area (VFA), and elevated free fatty acid (FFA) levels were observed. Multiple regression revealed strong correlations of both Matsuda index and disposition index with VFA and FFA.

Conclusion

Glucose tolerance declined with age in Japanese older adults, possibly due to age-related insulin resistance and β-cell deterioration associated with fat accumulation and elevated FFA levels.

Medial meniscus extrusion is invariably observed and consistent with tibial osteophyte width in elderly populations: The Bunkyo Health Study

We reported that the full-length width of medial tibial osteophytes comprising cartilage and bone parts correlates with medial meniscus extrusion (MME) in early-stage knee osteoarthritis (OA). However, no data exist on the prevalence of MME and its relationship with osteophytes in the elderly population. 1191 elderly individuals (females 57%; 72.9 years old on average) in the Bunkyo Health Study underwent standing plain radiograph and proton density-weighted MRI on knee joints. MRI-detected OA changes were evaluated according to the Whole-Organ Magnetic Resonance Imaging Score. A new method of assessing the cartilage and bone parts of osteophytes was developed using pseudo-coloring images of proton density-weighted fat-suppressed MRI. Most subjects showed Kellgren-Lawrence grade 1 or 2 radiographic medial knee OA (88.1%), MME (98.7%, 3.90 ± 2.01 mm), and medial tibial osteophytes (99.3%, 3.27 ± 1.50 mm). Regarding OA changes, MME was closely associated with the full-length width of medial tibial osteophytes (β = 1.114; 95% CI 1.069-1.159; p < 0.001) in line with osteophyte width (intraclass correlation coefficient, 0.804; 95% CI 0.783-0.823). Our data revealed that MME and medial tibial osteophytes are observed in the elderly and demonstrate that the degree of MME is consistent with the full-length width of medial tibial osteophytes, suggesting that osteophytes might be implicated in MME.

Reduced gray matter volume in the default-mode network associated with insulin resistance

Insulin resistance may lead to structural and functional abnormalities of the human brain. However, the mechanism by which insulin resistance impairs the brain remains elusive. In this study, we used two large neuroimaging databases to investigate the brain regions where insulin resistance was associated with the gray matter volume and to examine the resting-state functional connectivity between these brain regions and each hypothalamic nucleus. Insulin resistance was associated with reduced gray matter volume in the regions of the default-mode and limbic networks in the cerebral cortex in older adults. Resting-state functional connectivity was prominent between these networks and the paraventricular nucleus of the hypothalamus, a hypothalamic interface connecting functionally with the cerebral cortex. Furthermore, we found a significant correlation in these networks between insulin resistance-related gray matter volume reduction and network paraventricular nucleus of the hypothalamus resting-state functional connectivity. These results suggest that insulin resistance-related gray matter volume reduction in the default-mode and limbic networks emerged through metabolic homeostasis mechanisms in the hypothalamus.

Playing basketball and volleyball during adolescence is associated with higher bone mineral density in old age: the Bunkyo Health Study

Introduction: Exercise is beneficial for increasing areal bone mineral density (aBMD) in adolescence and maintaining it in old age. Moreover, high-impact sports are more effective than low-impact sports in increasing aBMD. This study aimed to determine the types of adolescent sports played in school-based sports clubs associated with aBMD in old age. Methods: In total, 1,596 older adults (681 men and 915 women, age: 65-84 years) living in an urban area of Japan were evaluated for the femoral neck and lumbar spine aBMD using dual-energy X-ray absorptiometry. The association between adolescent sports played in sports clubs and aBMD in old age was analyzed using multiple regression analysis, with femoral neck and lumbar spine aBMD as dependent variables, and sports type and participant characteristics such as age, body weight, and serum 25-hydroxyvitamin D [25(OH)D] level, as independent variables. Results: For the femoral neck, basketball was associated with aBMD in older men (β = 0.079, p < 0.05) and women (β = 0.08, p < 0.01), whereas current body weight and 25(OH)D level were associated with aBMD in both sexes. For the lumbar spine, volleyball (β = 0.08, p < 0.01) and swimming (β = 0.06, p < 0.05) was significantly associated with lumbar spine aBMD, whereas current body weight, 25(OH)D, and diabetes mellitus were associated with aBMD in older women. Conclusion: Both men and women who played basketball in adolescence had higher femoral neck aBMD in old age. Moreover, women who played volleyball in adolescence had higher lumbar spine aBMD in old age.

Anterior meniscus extrusion is associated with anterior tibial osteophyte width in knee osteoarthritis - The Bunkyo Health Study

Background

In knee osteoarthritis (OA), medial meniscus extrudes both medially and anteriorly. We reported that full-length width of medial tibial osteophyte, which comprises cartilage and bone parts, is directly associated with medial meniscus extrusion in early-stage knee OA and hypothesized that anterior tibial osteophyte (ATO) is also associated with anterior meniscus extrusion (AME). Thus, we aimed to examine their prevalence and relationship.

Methods

Elderly subjects (638 females and 507 males; average 72.9 years old) in the Bunkyo Health Study cohort were enrolled. MRI-detected OA changes were evaluated according to the Whole Organ Magnetic Resonance Imaging Score. ATO was evaluated using the method which can assess both cartilage and bone parts of osteophyte by pseudo-coloring images of proton density-weighted fat-suppressed MRI.

Results

Most subjects showed the Kellgren-Lawrence grade 1/2 of the medial knee OA (88.1%), AME (94.3%, 3.7 ​± ​2.2 ​mm), and ATO (99.6%, 4.2 ​± ​1.5 ​mm). Among the OA changes, AME was most closely associated with full-length width of ATO (multivariable β ​= ​0.877, p ​< ​0.001). The area under the receiver operating characteristic curve for determining the presence of AME as evaluated by ATO width was 0.75 (95% confidence interval 0.60-0.84, p ​< ​0.001). The odds ratio for the presence of AME as evaluated by ATO width at 2.9 ​mm was 7.16 (4.23-12.15, p ​< ​0.001, age, gender, BMI, and K-L adjusted).

Conclusions

AME and ATO were inevitably observed in the elderly subjects and AME was closely associated with full-length width of ATO. Our study provides the first evidence on the close relationship between AME and ATO in knee OA.

A chronic high-fat diet does not exacerbate muscle atrophy in fast-twitch skeletal muscle of aged mice

NEW FINDINGS

What is the central question of this study? Ageing leads to a loss of mass in skeletal muscle, but the effect of obesity on ageing-related muscle wasting is unclear. In this study, we aimed to demonstrate the specific effect of obesity on fast-twitch skeletal muscle in ageing. What is the main finding and its importance? Our findings show that the obesity induced by long-term ingestion of a high-fat diet does not aggravate muscle wasting in fast-twitch skeletal muscle of aged mice, indicating that the present study provides morphological characteristics for skeletal muscle of sarcopenic obesity.

ABSTRACT

Obesity and ageing reduce muscle mass and lead to deficits in muscle maintenance, but it is not known whether obesity accelerates muscle wasting additively in the setting of ageing. We investigated morphological characteristics in fast-twitch extensor digitorum longus (EDL) muscle of mice fed a low-fat diet (LFD) or a high-fat diet (HFD) for 4 or 20 months. The fast-twitch EDL muscle was harvested, and the muscle fibre-type composition, individual muscle cross-sectional area and myotube diameter were measured. We found an increase in the percentage of type IIa and IIx myosin heavy chain fibres in the whole EDL muscle, but a decrease in type IIB myosin heavy chain in both HFD protocols. The cross-sectional area and myofibre diameter were lower in both groups of aged mice (after 20 months of LFD or HFD) compared with young mice (after 4 months of the diets), but there were no differences between mice fed LFD or HFD for 20 months. These data suggest that long-term feeding of HFD does not aggravate muscle wasting in fast-twitch EDL muscle of male mice.

A Short-Term High-Fat Diet Worsens Insulin Sensitivity with Changes in Metabolic Parameters in Non-Obese Japanese Men

A short-term high-calorie high-fat diet (HCHFD) impairs insulin sensitivity in non-obese South Asian but not Caucasian men; however, the effect of short-term HCHFD on insulin sensitivity in East Asians is unknown. We recruited 21 healthy non-obese Japanese men to evaluate metabolic parameters and gut microbiota before and after 6-day HCHFD consisting of a regular diet plus a 45% energy excess with dairy fat supplementation. We evaluated tissue-specific insulin sensitivity and metabolic clearance rate of insulin (MCRI) using a two-step hyperinsulinemic euglycemic clamp, glucose tolerance using the glucose tolerance test, and measured ectopic fat in muscle and the liver using ¹H-magnetic resonance spectroscopy. The primary outcome of this study was insulin sensitivity measured by the clamp study. The secondary/exploratory outcomes were other metabolic changes. After HCHFD, levels of circulating lipopolysaccharide binding protein (LBP), a marker of endotoxemia, increased by 14%. In addition, intramyocellular lipid levels in the tibialis anterior and soleus and intrahepatic lipid levels increased by 47%, 31%, and 200%, respectively. Insulin sensitivity decreased by 4% in muscle and 8% in liver. However, even with reduced insulin sensitivity, glucose metabolism was maintained by increased serum insulin concentrations due to lower MCRI and higher endogenous insulin secretion during the clamp. Glucose levels during the meal tolerance test were comparable before and after HCHFD. In conclusion, short-term HCHFD impaired insulin sensitivity in the muscle and livers of non-obese Japanese men with increased LBP and ectopic fat accumulation. Elevated insulin levels from modulated insulin secretion and clearance might contribute to the maintenance of normal glucose metabolism during the clamp and meal tolerance test.

Physical inactivity induces insulin resistance in plantaris muscle through protein tyrosine phosphatase 1B activation in mice

Inactivity causes insulin resistance in skeletal muscle and exacerbates various lifestyle-related diseases. We previously found that 24-h hindlimb cast immobilization (HCI) of the predominantly slow-twitch soleus muscle increased intramyocellular diacylglycerol (IMDG) and insulin resistance by activation of lipin1, and HCI after a high-fat diet (HFD) further aggravated insulin resistance. Here, we investigated the effects of HCI on the fast-twitch-predominant plantaris muscle. HCI reduced the insulin sensitivity of plantaris muscle by approximately 30%, and HCI following HFD dramatically reduced insulin sensitivity by approximately 70% without significant changes in the amount of IMDG. Insulin-stimulated phosphorylation levels of insulin receptor (IR), IR substrate-1, and Akt were reduced in parallel with the decrease in insulin sensitivity. Furthermore, tyrosine phosphatase 1B (PTP1B), a protein known to inhibit insulin action by dephosphorylating IR, was activated, and PTP1B inhibition canceled HCI-induced insulin resistance. In conclusion, HCI causes insulin resistance in the fast-twitch-predominant plantaris muscle as well as in the slow-twitch-predominant soleus muscle, and HFD potentiates these effects in both muscle types. However, the mechanism differed between soleus and plantaris muscles, since insulin resistance was mediated by the PTP1B inhibition at IR in plantaris muscle.

Effects of exercise habits in adolescence and older age on sarcopenia risk in older adults: the Bunkyo Health Study

BACKGROUND

Sarcopenia, defined as an age-associated loss of skeletal muscle mass and function, is a major risk factor for requiring long-term care. Because physical activity in adolescence and older age enhances peak muscle function in youth and prevents muscle function decline in older age, older adults with exercise habits during both periods may be at a lower risk for sarcopenia. We investigated the relationship between exercise habits in adolescence and older age and sarcopenia and its components in community-dwelling older Japanese adults.

METHODS

This study included 1607 community-dwelling individuals (aged 65-84, medians 73 years, 679 men and 928 women) with complete health examinations, including measurements of skeletal muscle index, handgrip strength and gait speed, who were enrolled in the Bunkyo Health Study. We divided the participants into four groups according to exercise habits in adolescence and older age: no exercise in either period (none-none; NN), exercise only in adolescence (active-none; AN), exercise only in older age (none-active; NA) and exercise in both periods (active-active; AA). Multivariate-adjusted logistic regression models were used to estimate the odds ratios (ORs) and associated 95% confidence intervals (CIs) in each group for the prevalence of sarcopenia, defined as low muscle mass and low muscle performance, as compared with the NN group. Low muscle performance was defined as low muscle strength and/or low gait speed.

RESULTS

The total prevalence of sarcopenia was 6.6% (45/679) in men and 1.7% (16/928) in women, the total prevalence of low muscle mass was 14.3% (97/679) in men and 5.2% (48/928) in women, and the total prevalence of low muscle performance was 25.6% (174/679) in men and 19.6% (182/928) in women. In men, the ORs (95% CIs) for sarcopenia, low muscle mass and low muscle performance were significantly lower in the AA group (sarcopenia: 0.29 [0.09-0.95], P = 0.041; low muscle mass: 0.21 [0.09-0.52], P = 0.001; and low muscle performance: 0.52 [0.28-0.97], P = 0.038). In women, the OR (95% CI) for low muscle performance was significantly lower in the AA group than in the other groups (0.48 [0.27-0.84], P = 0.010), whereas none of the ORs for sarcopenia and low muscle mass were significant.

CONCLUSIONS

Older men with exercise habits in both adolescence and older age were at a lower risk of sarcopenia, low muscle mass and low muscle performance, whereas older women with exercise habits at both time periods were at a lower risk of low muscle performance.

Neuroimaging findings related to glymphatic system alterations in older adults with metabolic syndrome

OBJECTIVE

The glymphatic system is a glial-based perivascular network that promotes brain metabolic waste clearance. Reduced glymphatic flow has been observed in rat models of type 2 diabetes and hypertension, indicating the role of vascular risk factors in the glymphatic system. However, little is known about how vascular risk factors affect the human glymphatic system. The present study aims to assess the relationships between metabolic syndrome (MetS), a cluster of vascular risk factors, and the glymphatic system function using diffusion magnetic resonance imaging (MRI)-based measures of water diffusivity in the glymphatic compartments, including the brain interstitial space and perivascular spaces around the deep medullary vein. We hypothesized that vascular risk factors are associated with glymphatic dysfunction, leading to cognitive impairment in older adults.

METHODS

This cross-sectional study assessed 61 older adults (age range, 65-82 years) who had participated in the Bunkyo Health Study, including 15 healthy controls (mean age, 70.87 ± 4.90 years) and 46 individuals with MetS (mean age, 71.76 ± 4.61 years). Fractional volume of extracellular-free water (FW) and an index of diffusion tensor imaging along the perivascular space (DTI-ALPS) were used as indirect indicators of water diffusivity in the interstitial extracellular and perivenous spaces of white matter, respectively.

RESULTS

After adjusting for age, sex, years of education, total Fazekas scale, Pittsburgh sleep quality index (PSQI) score, and intracranial volume (ICV), a significantly (P = 0.030; Cohen's d = 1.01) higher FW was observed in individuals with MetS than in the healthy controls. Furthermore, individuals with MetS had a significantly (P = 0.031; Cohen's d = 0.86) lower ALPS index than the healthy controls, with age, sex, years of education, total Fazekas scale, PSQI score, ICV, fractional anisotropy, and mean diffusivity included as confounding factors. Higher FW was significantly associated with lower ALPS index (r = -0.37; P = 0.004). Multiple linear regression (MLR) with backward elimination analyses showed that higher diastolic blood pressure (BP; standardized β = 0.33, P = 0.005) was independently associated with higher FW, whereas higher fasting plasma glucose levels (standardized β = -0.63, P = 0.002) or higher Brinkman index of cigarette consumption cumulative amount (standardized β = -0.27, P = 0.022) were associated with lower ALPS index. The lower ALPS index (standardized β, 0.28; P = 0.040) was associated with poorer global cognitive performance, which was determined using the Japanese version of the Montreal Cognitive Assessment (MOCA-J) scores. Finally, partial correlation analyses showed a significant correlation between higher FW and lower MOCA-J scores (r = -0.35; P = 0.025) and between higher FW and higher diastolic BP (r = 0.32, P = 0.044).

CONCLUSION

The present study shows the changes in diffusion MRI-based measures reflected by the higher FW and lower ALPS index in older adults with MetS, possibly due to the adverse effect of vascular risk factors on the glymphatic system. Our findings also indicate the associations between the diffusion MRI-based measures and elevated diastolic BP, hyperglycemia, smoking habit, and poorer cognitive performance. However, owing to the limitations of this study, the results should be cautiously interpreted.

Glymphatic system impairment in nonathlete older male adults who played contact sports in their youth associated with cognitive decline: A diffusion tensor image analysis along the perivascular space study

Background and purpose

Exposure to contact sports in youth causes brain health problems later in life. For instance, the repetitive head impacts in contact sports might contribute to glymphatic clearance impairment and cognitive decline. This study aimed to assess the effect of contact sports participation in youth on glymphatic function in old age and the relationship between glymphatic function and cognitive status using the analysis along the perivascular space (ALPS) index.

Materials and methods

A total of 52 Japanese older male subjects were included in the study, including 12 who played heavy-contact sports (mean age, 71.2 years), 15 who played semicontact sports (mean age, 73.1 years), and 25 who played noncontact sports (mean age, 71.3 years) in their youth. All brain diffusion-weighted images (DWIs) of the subjects were acquired using a 3T MRI scanner. The ALPS indices were calculated using a validated semiautomated pipeline. The ALPS indices from the left and right hemispheres were compared between groups using a general linear model, including age and years of education. Furthermore, partial Spearman's rank correlation tests were performed to assess the correlation between the ALPS indices and cognitive scores (Mini-Mental State Examination and the Japanese version of the Montreal Cognitive Assessment [MoCA-J]) after adjusting for age years of education and HbA1c.

Results

The left ALPS index was significantly lower in the heavy-contact and semicontact groups than that in the noncontact group. Although no significant differences were observed in the left ALPS index between the heavy-contact and semicontact groups and in the right ALPS index among groups, a trend toward lower was found in the right ALPS index in individuals with semicontact and heavy-contact compared to the noncontact group. Both sides' ALPS indices were significantly positively correlated with the MoCA-J scores.

Conclusion

The findings indicated the potential adverse effect of contact sports experience in youth on the glymphatic system function in old age associated with cognitive decline.

Effects of Arterial Stiffness on Cerebral WM Integrity in Older Adults: A Neurite Orientation Dispersion and Density Imaging and Magnetization Transfer Saturation Imaging Study

BACKGROUND AND PURPOSE

Arterial stiffness is reported to be able to cause axonal demyelination or degeneration. The present study aimed to use advanced MR imaging techniques to examine the effect of arterial stiffness on the WM microstructure among older adults.

MATERIALS AND METHODS

Arterial stiffness was measured using the cardio-ankle vascular elasticity index (CAVI). The high-CAVI (mean CAVI ≥ 9 points) and the low-CAVI groups (mean CAVI < 9 points) were created. The neuronal fiber integrity of the WM was evaluated by neurite orientation dispersion and density imaging and magnetization transfer saturation imaging. Tract-Based Spatial Statistics and the tracts-of-interest analysis were performed. Specific WM regions (corpus callosum, internal capsule, anterior thalamic radiation, corona radiata, superior longitudinal fasciculus, forceps minor, and inferior fronto-occipital fasciculus) were selected in the tracts-of-interest analysis.

RESULTS

In Tract-Based Spatial Statistics, the high-CAVI group showed a significantly lower myelin volume fraction value in the broad WM and significantly higher radial diffusivity and isotropic volume fraction values in the corpus callosum, forceps minor, inferior fronto-occipital fasciculus, internal capsule, corona radiata, and anterior thalamic radiation than the low-CAVI group. In tracts-of-interest analysis using multivariate linear regression, significant associations were found between the mean CAVI and radial diffusivity in the anterior thalamic radiation and the corona radiata; isotropic volume fraction in the anterior thalamic radiation and the corona radiata; and myelin volume fraction in the superior longitudinal fasciculus (P < .05). Additionally, partial correlation coefficients were observed for the significant associations of executive function with radial diffusivity and myelin volume fraction (P < .05).

CONCLUSIONS

Arterial stiffness could be associated with demyelination rather than axonal degeneration.

Prediabetes is an independent risk factor for sarcopenia in older men, but not in older women: the Bunkyo Health Study

BACKGROUND

Sarcopenia is a major cause of disability in the elderly. Although type 2 diabetes is a risk factor for increased sarcopenia, the relationship between prediabetes and sarcopenia has not been elucidated. We aimed to examine the relationship between sarcopenia and prediabetes.

METHODS

The design of this study is a cross-sectional study. We evaluated glucose metabolism using the 75-g oral glucose tolerance test and glycated haemoglobin, appendicular skeletal muscle mass, and hand grip strength in 1629 older adults living in an urban area of Tokyo, Japan. We investigated the frequency of sarcopenia in participants with normal glucose tolerance (NGT), prediabetes and diabetes. A multivariable logistic regression model was used to analyse the association between glucose tolerance and the prevalence of sarcopenia.

RESULTS

The mean age of participants was 73.1 ± 5.4 years. In men, 44.3% had NGT, 26.6% had prediabetes, and 29.1% had diabetes. In women, the distribution was 56.1%, 28.8% and 15.2%. The prevalence of sarcopenia was 12.7% in men and 11.9% in women. Logistic regression revealed that prediabetes and diabetes are independent risk factors for sarcopenia in men (prediabetes, odds ratio [OR] = 2.081 [95% confidence interval {CI}: 1.031-4.199]; diabetes, OR = 2.614 [95% CI: 1.362-5.018]) and diabetes, but not prediabetes, is an independent risk factor for sarcopenia in women (prediabetes, OR = 1.036 [95% CI: 0.611-1.757]; diabetes, OR = 2.099 [95% CI: 1.146-3.844]). In both sexes, higher age (men, OR = 1.086 [95% CI: 1.028-1.146]; women, OR = 1.195 [95% CI: 1.142-1.251]), higher body fat percentage (men, OR = 1.346 [95% CI: 1.240-1.461]; women, OR = 1.218 [95% CI: 1.138-1.303]) and lower body mass index (men, OR = 0.371 [95% CI: 0.299-0.461]; women, OR = 0.498 [95% CI: 0.419-0.593]) were independent risk factors for sarcopenia.

CONCLUSIONS

Although we confirmed that diabetes mellitus is associated with sarcopenia in both sexes, prediabetes is associated with sarcopenia in men, but not in women.

Association of ALDH2 Genotypes and Alcohol Intake with Dietary Patterns: The Bunkyo Health Study

Dietary habits are associated with various diseases and assessed by dietary patterns (DPs). Since the ALDH2 genotype is correlated with alcohol and several food preferences, this genotype is probably associated with DPs. In this cross-sectional study of 1612 elderly adults, we investigated the effects of the ALDH2 genotype on DPs and the mediating role of alcohol intake. We identified the ALDH2 genotype and conducted a dietary history survey, then used principal component analysis to determine DPs for each gender. We performed multiple regression analysis to determine the independent contribution of the ALDH2 genotype and alcohol intake to DP scores. We identified three DPs: the "Japanese side dish type" (DP1), the "Japanese dish with alcohol type" (DP2), and the "Western dish with alcohol type" (DP3). In men, the single nucleotide polymorphism ALDH2 rs671 was significantly associated with all DP scores. When alcohol intake was added as a covariate, ALDH2 rs671 was still significantly correlated with the DP2 score but not with the DP1 or DP3 score, and alcohol intake was significantly correlated with all DP scores. In women, ALDH2 rs671 was significantly associated with the DP2 and DP3 scores; however, after adding alcohol intake as a covariate, these associations disappeared, and alcohol intake significantly correlated with all DP scores. In conclusion, the ALDH2 genotype was associated with several DPs in elderly adults, but most associations were mediated by alcohol intake.

Impaired fatigue resistance, sarcoplasmic reticulum function, and mitochondrial activity in soleus muscle of db/db mice

Type 2 diabetes mellitus (T2DM) is characterized by reduced exercise tolerance due to increased fatigability in skeletal muscle. In this study, we investigated muscle fatigue resistance of soleus (SOL) muscle in obese type 2 diabetic model mice (db/db). No differences in muscle volume, absolute force, or specific force in SOL muscle were observed between db/db mice and control mice (db/+), while fatigue resistance evaluated by repeated tetanic contractions was significantly lower in db/db mice (30th tetani, db/+: 63.7 ± 4.7%, db/db: 51.3 ± 4.8%). The protein abundance related to Ca2+ release from the sarcoplasmic reticulum (SR) in SOL muscle was not different between db/db mice and db/+ mice, while SR Ca2+ -ATPase (Ca2+ reuptake to SR) protein was decreased in db/db mice compared to db/+ mice (db/+: 1.00 ± 0.17, db/db: 0.60 ± 0.04, relative units). In addition, mitochondrial oxidative enzyme activity (succinate dehydrogenase) was decreased in the SOL muscle of db/db mice (p < 0.05). These data suggest that fatigue resistance in slow-twitch dominant muscle is impaired in mice with T2DM. Decreased mitochondrial oxidative enzyme activity and impairment of Ca2+ uptake to SR, or both might be involved in the mechanisms.

White matter fiber-specific degeneration in older adults with metabolic syndrome

OBJECTIVE

Metabolic syndrome (MetS) is defined as a complex of interrelated risk factors for type 2 diabetes and cardiovascular disease, including glucose intolerance, abdominal obesity, hypertension, and dyslipidemia. Studies using diffusion tensor imaging (DTI) have reported white matter (WM) microstructural abnormalities in MetS. However, interpretation of DTI metrics is limited primarily due to the challenges of modeling complex WM structures. The present study used fixel-based analysis (FBA) to assess the effect of MetS on the fiber tract-specific WM microstructure in older adults and its relationship with MetS-related measurements and cognitive and locomotor functions to better understand the pathophysiology of MetS.

METHODS

Fixel-based metrics, including microstructural fiber density (FD), macrostructural fiber-bundle cross-section (FC), and a combination of FD and FC (FDC), were evaluated in 16 healthy controls (no components of MetS; four men; mean age, 71.31 ± 5.06 years), 57 individuals with premetabolic syndrome (preMetS; one or two components of MetS; 29 men; mean age, 72.44 ± 5.82 years), and 46 individuals with MetS (three to five components of MetS; 27 men; mean age, 72.15 ± 4.97 years) using whole-brain exploratory FBA. Tract of interest (TOI) analysis was then performed using TractSeg across 14 selected WM tracts previously associated with MetS. The associations between fixel-based metrics and MetS-related measurements, neuropsychological, and locomotor function tests were also analyzed in individuals with preMetS and MetS combined. In addition, tensor-based metrics (i.e., fractional anisotropy [FA] and mean diffusivity [MD]) were compared among the groups using tract-based spatial statistics (TBSS) analysis.

RESULTS

In whole-brain FBA, individuals with MetS showed significantly lower FD, FC, and FDC compared with healthy controls in WM areas, such as the splenium of the corpus callosum (CC), corticospinal tract (CST), middle cerebellar peduncle (MCP), and superior cerebellar peduncle (SCP). Meanwhile, in fixel-based TOI, significantly reduced FD was observed in individuals with preMetS and MetS in the anterior thalamic radiation, CST, SCP, and splenium of the CC compared with healthy controls, with relatively greater effect sizes observed in individuals with MetS. Compared with healthy controls, significantly reduced FC and FDC were only demonstrated in individuals with MetS, including regions with loss of FD, inferior cerebellar peduncle, inferior fronto-occipital fasciculus, MCP, and superior longitudinal fasciculus part I. Furthermore, negative correlations were observed between FD and Brinkman index of cigarette consumption cumulative amount and between FC or FDC and the Trail Making Test (parts B-A), which is a measure of executive function, waist circumference, or low-density lipoprotein cholesterol. Finally, TBSS analysis revealed that FA and MD were not significantly different among all groups.

CONCLUSIONS

The FBA results demonstrate that substantial axonal loss and atrophy in individuals with MetS and early axonal loss without fiber-bundle morphological changes in those with preMetS within the WM tracts are crucial to cognitive and motor function. FBA also clarified the association between executive dysfunction, abdominal obesity, hyper-low-density lipoprotein cholesterolemia, smoking habit, and compromised WM neural tissue microstructure in MetS.

An Investigation of Water Diffusivity Changes along the Perivascular Space in Elderly Subjects with Hypertension

BACKGROUND AND PURPOSE

Hypertension may be related to alterations of the glymphatic system, a waste metabolite drainage system in the brain. We aimed to investigate analysis along the perivascular space index changes in elderly subjects with hypertension.

MATERIALS AND METHODS

Diffusion-weighted images were acquired from 126 subjects, including 63 subjects with hypertension (25 men and 38 women; mean age, 72.45 years) and 63 age- and sex-matched controls (25 men and 38 women; mean age, 72.16 years). We calculated the analysis along the perivascular space index as a ratio of the mean of x-axis diffusivities in the projection and association areas to the mean of y-axis diffusivity in the projection area and z-axis diffusivity in the association area. The left, right, and mean analysis along the perivascular space indices of both hemispheres were compared between the hypertension and control groups using a Mann-Whitney U test. The Spearman correlation coefficient was used to assess the correlation between the left, right, and mean ALPS indices and blood pressure and pulse pressure.

RESULTS

The left (P = .011) and mean (P = .024) analysis along the perivascular space indices of the hypertension group were significantly lower than that of the control group. The left, right, and mean analysis along the perivascular space indices of all subjects were significantly negatively correlated with blood pressure values (r = -0.200 to -0.278, P = .002-0.046) and pulse pressure values (r = -0.221 to -0.245, P = .006-0.013).

CONCLUSIONS

Our results are consistent with a model in which hypertension causes glymphatic dysfunction.

Short-term physical inactivity induces diacylglycerol accumulation and insulin resistance in muscle via lipin1 activation

Physical inactivity impairs muscle insulin sensitivity. However, its mechanism is unclear. To model physical inactivity, we applied 24-h hind-limb cast immobilization (HCI) to mice with normal or high-fat diet (HFD) and evaluated intramyocellular lipids and the insulin signaling pathway in the soleus muscle. Although 2-wk HFD alone did not alter intramyocellular diacylglycerol (IMDG) accumulation, HCI alone increased it by 1.9-fold and HCI after HFD further increased it by 3.3-fold. Parallel to this, we found increased protein kinase C ε (PKCε) activity, reduced insulin-induced 2-deoxyglucose (2-DOG) uptake, and reduced phosphorylation of insulin receptor β (IRβ) and Akt, key molecules for insulin signaling pathway. Lipin1, which converts phosphatidic acid to diacylglycerol, showed increase of its activity by HCI, and dominant-negative lipin1 expression in muscle prevented HCI-induced IMDG accumulation and impaired insulin-induced 2-DOG uptake. Furthermore, 24-h leg cast immobilization in human increased lipin1 expression. Thus, even short-term immobilization increases IMDG and impairs insulin sensitivity in muscle via enhanced lipin1 activity.NEW & NOTEWORTHY Physical inactivity impairs muscle insulin sensitivity. However, its mechanism is unclear. To model physical inactivity, we applied 24-h hind-limb cast immobilization to mice with normal or high-fat diet and evaluated intramyocellular lipids and the insulin signaling pathway in the soleus muscle. We found that even short-term immobilization increases intramyocellular diacylglycerol and impairs insulin sensitivity in muscle via enhanced lipin1 activity.

ALDH2 rs671 Is Associated With Elevated FPG, Reduced Glucose Clearance and Hepatic Insulin Resistance in Japanese Men

CONTEXT

A recent meta-analysis of genome-wide association studies data from East Asians identified aldehyde dehydrogenase 2 (ALDH2) rs671 as a susceptibility variant for type 2 diabetes in males.

OBJECTIVE

To investigate the association between ALDH2 rs671 and metabolic characteristics.

METHODS

We studied 94 nonobese, nondiabetic, Japanese men. Using a 2-step hyperinsulinemic-euglycemic clamp, we evaluated insulin sensitivity in muscle and liver. Intrahepatic lipid and fat distribution were measured using 1H-magnetic resonance spectroscopy and magnetic resonance imaging, respectively. We divided participants into a risk-carrying group with ALDH2 rs671 G/G (n = 53) and a nonrisk-carrying group with ALDH2 rs671 G/A or A/A (n = 41).

RESULTS

The risk-carrying group had significantly higher levels of alcohol consumption (18.4 [interquartile range, IQR, 10.4-48.9]) vs 12.1 (IQR, 1.3-29.0) g/day; P = .003), elevated fasting plasma glucose (FPG) (97.5 ± 7.9 vs 93.5 ± 6.2 mg/dL; P = .010), lower hepatic insulin sensitivity (61.7 ± 20.5% vs 73.1 ± 15.9%; P = .003), and lower fasting glucose clearance (0.84 ± 0.8 dL·m-2·min-1 vs 0.87 ± 0.09 dL·m-2·min-1; P = .047) than the nonrisk-carrying group, while insulin resistance in muscle and body fat distribution were similar. The single linear correlation analysis revealed significant correlations between alcohol consumption and hepatic insulin sensitivity (r = -0.262, P = .011), fasting glucose clearance (r = -0.370, P < .001), or FPG (r = 0.489, P < .001). The multiple regression analysis revealed that both ALDH2 rs671 G/G genotype and alcohol consumption were significant independent correlates for hepatic insulin sensitivity, whereas only alcohol consumption was a significant independent correlate for fasting glucose clearance.

CONCLUSION

Our data suggest that high-alcohol intake-dependent and independent hepatic insulin resistance and reduced fasting glucose clearance due to high alcohol intake could be a relatively upstream metabolic abnormality in ALDH2 rs671 G/G carriers.

Comparison of Brain Volume Measurements Made with 0.3- and 3-T MR Imaging

The volumes of intracranial tissues of 40 healthy volunteers acquired from 0.3- and 3-T scanners were compared using intraclass correlation coefficients, correlation analyses, and Bland-Altman analyses. We found high intraclass correlation coefficients, high Pearson’s correlation coefficients, and low percentage biases in all tissues and most of the brain regions, although small differences were observed in some areas. These findings may support the validity of brain volumetry with low-field magnetic resonance imaging.

Ingestion of an exogenous ketone monoester improves the glycemic response during oral glucose tolerance test in individuals with impaired glucose tolerance: A cross-over randomized trial

AIMS/INTRODUCTION

As a low-carbohydrate diet and the use of sodium-glucose transporter-2 inhibitors are both known to increase D-beta-hydroxybutyrate levels, the effect of these levels on glucose metabolism has attracted attention. We investigated the acute effects of ketone monoester (KM) ingestion on blood glucose levels during the 75-g oral glucose tolerance test (OGTT) in participants with impaired glucose tolerance.

MATERIALS AND METHODS

Nine Japanese adults aged 48-62 years (4 men, 5 women) with impaired glucose tolerance participated in this study. After participants fasted overnight, we carried out OGTT for 180 min with and without KM ingestion on two separate days in a randomized cross-over design. We compared the area under the curve (AUC) of D-beta-hydroxybutyrate, glucose, insulin, C-peptide, glucagon and free fatty acids during OGTT.

RESULTS

The AUC of D-beta-hydroxybutyrate during OGTT was significantly higher with KM than without KM (KM 5995.3 ± 1257.1 mmol/L·h; without KM 116.1 ± 33.9 mmol/L·h, P < 0.0001), and the AUC of glucose with KM was significantly lower than that without KM (KM 406.6 ± 70.6 mg/dL·h; without KM 483.2 ± 74.3 mg/dL·h, P < 0.0001). This improved glucose excursion was associated with enhanced AUC of insulin during the first half (0-90 min) of OGTT, even though the AUC of C-peptide during this period was unchanged. In contrast, the AUC of insulin, C-peptide, glucagon and free fatty acids during 180 min of OGTT were similar in both conditions.

CONCLUSION

The ingestion of KM decreased the AUC of glucose during 75-g OGTT in Japanese individuals with impaired glucose tolerance, and the mechanism might involve elevated levels of circulating early phase insulin.

A decrease in plasma glucose levels is required for increased endogenous glucose production with a single administration of a sodium-glucose co-transporter-2 inhibitor tofogliflozin

AIM

To investigate whether changes in endogenous glucose production (EGP) and insulin and glucagon levels are elicited by the decrease in plasma glucose (PG) levels induced by the sodium-glucose co-transporter-2 (SGLT2) inhibitor tofogliflozin.

MATERIALS AND METHODS

We evaluated EGP in 12 Japanese patients with type 2 diabetes under the conditions of no drugs administered (CON), single administration of the SGLT2 inhibitor tofogliflozin (TOF), and single administration of TOF with adjustment of PG levels with exogenous glucose infusion to mimic changes in PG levels observed with CON (TOF + G). We evaluated changes in EGP and levels of C-peptide and glucagon from baseline to 180 minutes after drug administration.

RESULTS

Endogenous glucose production decreased in the CON (-0.22 ± 0.11 mg/kg·min) and TOF + G experiments (-0.31 ± 0.24 mg/kg·min), but not in the TOF experiment (+0.08 ± 0.19 mg/kg·min). The decrease in C-peptide was significantly greater in the TOF experiment (-0.11 ± 0.06 nmol/L) than in the CON (-0.03 ± 0.06 nmol/L) and the TOF + G experiments (-0.01 ± 0.11 nmol/L), while the increase in glucagon was significantly greater in the TOF experiment (+11.1 ± 6.3 pmol/L), but not in the TOF + G experiment (+8.6 ± 7.6 pmol/L) compared to the CON experiment (+5.1 ± 4.3 pmol/L).

CONCLUSIONS

These results indicate that the decrease in PG levels induced by SGLT2 inhibitor administration is required for the increase in EGP and decrease in insulin secretion.

Prevalence and Features of Impaired Glucose Tolerance in Young Underweight Japanese Women

OBJECTIVE

In Japan, while it is known that underweight women over the age of 40 years have a high risk for type 2 diabetes, there is a lack of clarity on the association between glucose tolerance and underweight in younger women. Accordingly, we investigate the prevalence and features of impaired glucose tolerance (IGT) in young underweight Japanese women.

DESIGNS AND METHODS

In this cross-sectional study, we recruited 56 normal weight and 98 underweight young Japanese women and evaluated their glucose tolerance levels using an oral glucose tolerance test. Then, we compared the clinical characteristics associated with normal glucose tolerance (NGT) and IGT in the underweight women. Insulin secretion, whole-body insulin sensitivity, and adipose tissue insulin resistance values were measured using the insulinogenic index, whole-body insulin sensitivity index (Matsuda index), and adipose insulin resistance index (Adipo-IR), respectively. Fitness level (peak VO2) was measured using an ergometer.

RESULTS

The prevalence of IGT was higher in the underweight women than the normal weight women (13.3% vs 1.8%). The underweight women with IGT showed a lower insulinogenic index, lower peak VO2, and Matsuda index and a higher fasting free fatty acid level and Adipo-IR than those with NGT. The whole-body composition was comparable between the NGT and IGT groups.

CONCLUSIONS

The prevalence of IGT was higher in young Japanese women with underweight than those with a normal weight. The underweight women with IGT showed impaired early-phase insulin secretion, low fitness levels, and reduced whole-body and adipose tissue insulin sensitivity levels.

Adipose Insulin Resistance and Decreased Adiponectin Are Correlated With Metabolic Abnormalities in Nonobese Men

CONTEXT

Adipose tissue dysfunction is characterized by decreased adiponectin (AN) levels and impaired adipose tissue insulin sensitivity (ATIS) and is associated with metabolic disorders. While Asians readily develop metabolic disease without obesity, it remains unclear how decreased AN level and impaired ATIS affect metabolic abnormalities in nonobese Asians.

DESIGN AND SETTING

To investigate the relationships between decreased AN level, impaired ATIS, and metabolic abnormalities, we studied 94 Japanese men whose body mass index was less than 25 kg/m2. We divided the subjects into 4 groups based on their median AN level and ATIS, the latter calculated as the degree of insulin-mediated suppression of free fatty acids during hyperinsulinemic euglycemic clamp, and compared the metabolic parameters in the 4 groups.

RESULTS

The High-ATIS/High-AN group (n = 29) showed similar anthropometric data to the High-ATIS/Low-AN group (n = 18). In contrast, both the Low-ATIS/High-AN (n = 18) and Low-ATIS/Low-AN (n = 29) groups showed significantly lower muscle insulin sensitivity than the High-ATIS groups. The intrahepatic lipid level in the Low-ATIS/Low-AN group was significantly higher than that in the High-ATIS groups. In addition, the Low-ATIS/Low-AN group had a significantly higher fasting serum triglyceride level and significantly lower high-density lipoprotein cholesterol level than the other 3 groups.

CONCLUSIONS

In nonobese Japanese men with high ATIS, the AN level was not associated with metabolic characteristics. On the other hand, subjects with low ATIS showed reduced muscle insulin sensitivity, and those with a decreased AN level demonstrated multiple metabolic abnormalities, represented by fatty liver and dyslipidemia.

Age-Related Changes in Relaxation Times, Proton Density, Myelin, and Tissue Volumes in Adult Brain Analyzed by 2-Dimensional Quantitative Synthetic Magnetic Resonance Imaging

OBJECTIVES

Quantitative synthetic magnetic resonance imaging (MRI) enables the determination of fundamental tissue properties, namely, T1 and T2 relaxation times and proton density (PD), in a single scan. Myelin estimation and brain segmentation based on these quantitative values can also be performed automatically. This study aimed to reveal the changes in tissue characteristics and volumes of the brain according to age and provide age-specific reference values obtained by quantitative synthetic MRI.

MATERIALS AND METHODS

This was a prospective study of healthy subjects with no history of brain diseases scanned with a multidynamic multiecho sequence for simultaneous measurement of relaxometry of T1, T2, and PD. We performed myelin estimation and brain volumetry based on these values. We performed volume-of-interest analysis on both gray matter (GM) and white matter (WM) regions for T1, T2, PD, and myelin volume fraction maps. Tissue volumes were calculated in the whole brain, producing brain parenchymal volume, GM volume, WM volume, and myelin volume. These volumes were normalized by intracranial volume to a brain parenchymal fraction, GM fraction, WM fraction, and myelin fraction (MyF). We examined the changes in the mean regional quantitative values and segmented tissue volumes according to age.

RESULTS

We analyzed data of 114 adults (53 men and 61 women; median age, 66.5 years; range, 21-86 years). T1, T2, and PD values showed quadratic changes according to age and stayed stable or decreased until around 60 years of age and increased thereafter. Myelin volume fraction showed a reversed trend. Brain parenchymal fraction and GM fraction decreased throughout all ages. The approximation curves showed that WM fraction and MyF gradually increased until around the 40s to 50s and decreased thereafter. A significant decline in MyF was first noted in the 60s age group (Tukey test, P < 0.001).

CONCLUSIONS

Our study showed changes according to age in tissue characteristic values and brain volumes using quantitative synthetic MRI. The reference values for age demonstrated in this study may be useful to discriminate brain disorders from healthy brains.

Maintenance of contractile force and increased fatigue resistance in slow-twitch skeletal muscle of mice fed a high-fat diet

Consumption of a high-fat diet (HFD) significantly increases exercise endurance performance during treadmill running. However, whether HFD consumption increases endurance capacity via enhanced muscle fatigue resistance has not been clarified. In this study, we investigated the effects of HFDs on contractile force and fatigue resistance of slow-twitch dominant muscles. The soleus (SOL) muscle of male C57BL/6J mice fed an HFD (60% kcal from fat) or a low-fat diet (LFD) for 12 wk was analyzed. Muscle contractile force was measured under resting conditions and during fatigue induced by repeated tetanic contractions (100 Hz, 50 contractions, and 2-s intervals). Differences in muscle twitch or tetanic force were not evident between HFD and LFD groups, whereas fatigue resistance was higher in the HFD groups. The SOL muscle of HFD-fed mice showed increased levels of markers related to oxidative capacity such as succinate dehydrogenase (SDH) and citrate synthase (CS) activity. In addition, electron microscopy analyses indicated that the total number of mitochondria and mitochondrial volume density increased in the SOL muscle of the HFD groups. These findings suggest that HFD consumption induces increased muscle fatigue resistance in slow-twitch dominant muscle fibers. This effect of HFD may be related to elevated oxidative enzyme activity, high mitochondrial content, or both.NEW & NOTEWORTHY In this study, we examined the effects of HFDs on muscle contractile force and fatigue resistance of slow-twitch dominant muscles ex vivo. We found that contractile function was comparable between the HFD groups and the LFD group, whereas fatigue resistance was higher in the HFD groups. This effect of HFD may be related to elevated oxidative enzyme activity, high mitochondrial content, or both.

Decreased Muscle Strength of Knee Flexors is Associated with Impaired Muscle Insulin Sensitivity in Non-Diabetic Middle-Aged Japanese Male Subjects

INTRODUCTION

Reduced muscle strength is a high risk factor for type 2 diabetes mellitus, and this association is especially strong in non-obese male individuals. However, it remains unclear how reduced muscle strength affects susceptibility to diabetes. We have examined whether lower limb muscle strength is associated with insulin resistance in non-obese Japanese male subjects.

METHODS

Measurements from 64 non-diabetic, non-obese, middle-aged Japanese men were analyzed. Insulin sensitivity in muscle was measured using the hyperinsulinemic-euglycemic clamp. Isometric muscle strength of the knee extensor and flexor muscles was evaluated using a dynameter.

RESULTS

Lower muscle strength of knee flexors, but not knee extensors, was associated with impaired muscle insulin sensitivity (knee flexor muscles: low, medium, and high strength was 6.6 ± 2.2, 7.3 ± 2.0, and 8.8 ± 2.2 mg/kg per minute, respectively, p for trend < 0.05; knee extensor muscles: low, medium, and high strength was 7.3 ± 2.5, 7.5 ± 2.2, and 7.8 ± 2.3 mg/kg per minute, respectively, p for trend = 0.73). Knee flexor muscle strength was also identified as an independent determinant of insulin sensitivity in the multiple regression analysis (β = 0.274, p = 0.036).

CONCLUSIONS

Diminished strength of knee flexor muscles, but not knee extensor muscles, was associated with muscle insulin sensitivity in non-diabetic, non-obese Japanese male subjects.

Shape of the glucose response curve during an oral glucose tolerance test is associated with insulin clearance and muscle insulin sensitivity in healthy non-obese men

Individuals with a monophasic glucose response curve (GRC) during a 75-g oral glucose tolerance test have a higher risk for type 2 diabetes than those with a biphasic GRC. However, no studies have addressed the association between GRC type and insulin clearance. Thus, we studied 49 healthy non-obese Japanese men. We divided study participants into the monophasic or biphasic group based on the shape of their GRC. We evaluated tissue-specific insulin sensitivity and insulin clearance using a two-step hyperinsulinemic-euglycemic clamp. The monophasic group had more visceral fat, lower insulin clearance and lower muscle insulin sensitivity than the biphasic group, whereas liver and adipose tissue insulin sensitivity, and insulin secretion were comparable. In conclusion, healthy non-obese men with a monophasic GRC have lower insulin clearance and muscle insulin sensitivity.

Effects of blood flow restriction on muscle size and gene expression in muscle during immobilization: A pilot study

PURPOSE

Muscle mass is known to rapidly decrease with muscle disuse. Previous reports suggest that repetitive blood flow restriction (BFR) mitigates the reduction of muscle mass with disuse. However, the effects of BFR on muscle atrophy and gene expression levels in muscle during cast immobilization have not been clarified.

METHODS

To investigate the effect of BFR on muscle atrophy and gene expression levels during cast immobilization in humans, we recruited 10 healthy males who were randomly divided into the control and BFR treatment groups. All subjects were immobilized with a cast for 14 days. BFR treatment was conducted only in the BFR group. We evaluated cross sectional area (CSA) of thigh muscles by magnetic resonance imaging before and 14 days after cast immobilization. A percutaneous biopsy of the vastus lateralis muscle (VL) was performed before and 1, 7, and 14 days after cast immobilization. Expression of genes related to muscle atrophy and synthesis were evaluated using real-time PCR.

RESULTS

The CSA of the VL and the thigh flexor muscles were significantly decreased in both groups; however, percent decrease in CSA was significantly smaller in the BFR group compared with the control group. In two-way repeated ANOVA analysis, the time × treatment interaction in gene expression of the muscle-specific ubiquitin ligases muscle ring finger 1 (MuRF1) was significant, and elevated MURF1 expression level by cast immobilization was seemed to be suppressed by the BFR treatment.

CONCLUSION

BFR treatment may prevent reduced VL and thigh flexor muscles and increased MuRF1 expression level during cast immobilization. Further study is required to confirm these results.

A chronic high-fat diet exacerbates contractile dysfunction with impaired intracellular Ca2+ release capacity in the skeletal muscle of aged mice

Obesity and aging reduce skeletal muscle contractile function. However, it remains unclear whether obesity additively promotes muscle contractile dysfunction in the setting of aging. In this study, we investigated skeletal muscle contractile function ex vivo and intracellular Ca²⁺ release in male C57BL/6J mice fed a low-fat diet (LFD) or a high-fat diet (HFD) for 4 or 20 mo. Tetanic force production in the extensor digitorum longus muscle was decreased by aging or HFD feeding, and the further reduction was observed in aged HFD mice. The 20-mo HFD-fed mice, not the 20-mo LFD-fed mice or 4-mo HFD-fed mice, showed reduced intracellular Ca²⁺ peak levels by high concentration of caffeine (25 mM) compared with 4-mo LFD mice. Aging and HFD feeding additively increased intramyocellular lipid (IMCL) levels and were associated with the degree of impaired muscle contractile force and peak Ca²⁺ level. These data suggest that impairment in the contractile force in aged muscle is aggravated by HFD, which may be due, at least in part, to dysfunction in intracellular Ca²⁺ release. The IMCL level may be a marker for impaired muscle contractile force caused by aging and HFD.NEW & NOTEWORTHY The aim of this study was to examine the effect of high-fat diet (HFD)-induced obesity on contractile function and Ca²⁺ release capacity in aged skeletal muscle. Not only were the force production and peak Ca²⁺ levels decreased by aging and HFD feeding, respectively, but also, these interventions had an additive effect in aged HFD-fed mice. These data suggest that the impairment in the contractile force in aged muscle is aggravated by a HFD, which may be due to synergistic dysfunction in intracellular Ca²⁺ release.

Characteristics associated with elevated 1-h plasma glucose levels during a 75-g oral glucose tolerance test in non-obese Japanese men

Elevated 1-h plasma glucose (1h-PG; ≥155 mg/dL) during an oral glucose tolerance test is a risk factor for type 2 diabetes. However, the metabolic characteristics of non-obese Asians with elevated 1h-PG are unknown. Thus, we studied 59 non-obese Japanese men with normal glucose tolerance. We divided study participants into the Low 1h-PG group (<155 mg/dL) and the High 1h-PG group (≥155 mg/dL). We compared the metabolic characteristics of the groups, including tissue-specific insulin sensitivity measured using a two-step hyperinsulinemic-euglycemic clamp. Insulinogenic index and adiponectin levels were significantly lower in the High 1h-PG group than in the Low 1h-PG group. Other characteristics, including insulin sensitivity, adiposity and ectopic fat accumulation, were similar between the groups. In conclusion, non-obese Japanese men with high 1h-PG have impaired early-phase insulin secretion and lower adiponectin levels. Insulin resistance and abnormal fat distribution were not evident in this population.

Skeletal muscle function and need for long-term care of urban elderly people in Japan (the Bunkyo Health Study): a prospective cohort study

PURPOSE

The proportion of elderly individuals (age ≥65 years) in Japan reached 27.7% in 2017, the highest in the world. A serious social problem in a super-aged society is the rise in the number of elderly people who need long-term care (LTC), which is mainly due to cerebrovascular disease, dementia, age-related frailty, falls and fractures, and joint disease. We hypothesised that decreased muscle mass, muscle strength and insulin sensitivity are the common risk factors for these diseases related to needing LTC. We developed a prospective cohort study of elderly subjects in an urban community to test this hypothesis. The primary objective is to prospectively investigate associations between muscle mass, muscle strength, and insulin sensitivity and incidence of main disease and risk factors of needing LTC. The primary outcomes are the incidence of cerebrovascular disease and cognitive decline.

PARTICIPANTS

Participants were 1629 people aged 65-84 years living in 13 communities in an urban area (Bunkyo-ku, Tokyo, Japan). Average age was 73.1±5.4 years.

FINDINGS TO DATE

We obtained baseline data on cognitive function, cerebral small vessel disease (SVD) determined by brain MRI, body composition, bone mineral density, arteriosclerosis, physical function, muscle mass, muscle strength and insulin sensitivity. Mild cognitive impairment and dementia were observed in 18.1% and 3.3% of participants, respectively. The prevalence of cerebral SVD was 24.8%. These characteristics are similar to those previously reported in elderly Japanese subjects.

FUTURE PLANS

We will ask participants about their health status, including incidence of cerebrovascular disease, falls, fractures and other diseases every year by mail. We plan to re-evaluate cognitive function, brain MRI parameters and other parameters at 5 and 10 years after the baseline evaluation. We will evaluate whether low muscle function (muscle mass, muscle strength or insulin sensitivity) is a risk factor for cognitive decline or cerebrovascular disease.

Higher C-Peptide Level During Glucose Clamp Is Associated With Muscle Insulin Resistance in Nonobese Japanese Men

Context

Circulating C-peptide is generally suppressed by exogenous insulin infusion. However, steady-state serum C-peptide (SS_SC) levels during hyperinsulinemic-euglycemic clamp in obese subjects are higher than in healthy subjects, which may contribute to hyperinsulinemia to compensate for insulin resistance. Even in healthy subjects, interindividual variations in SS_SC levels are present; however, the characteristics of subjects with high SS_SC levels in those populations have not been fully elucidated.

Objective

To investigate the clinical parameters associated with interindividual variations in SS_SC levels in apparently healthy, nonobese Japanese men.

Design and Participants

We studied 49 nonobese (BMI < 25 kg/m²), healthy Japanese men. We evaluated SS_SC and insulin sensitivity using hyperinsulinemic-euglycemic clamp with tracer. Intrahepatic lipid (IHL) was measured using proton magnetic resonance spectroscopy.

Results

We divided subjects into high and low SS_SC groups based on the median SS_SC value and compared their clinical parameters. Compared with the low SS_SC group, the high SS_SC group had IHL accumulation, impaired muscle insulin sensitivity, reduced insulin clearance, and hyperinsulinemia during a 75-g oral glucose tolerance test (OGTT). All of these factors were significantly correlated with SS_SC.

Conclusions

In healthy, nonobese men, higher SS_SC was associated with impaired muscle insulin sensitivity, IHL accumulation, and hyperinsulinemia during OGTT. These findings suggest that higher endogenous insulin secretion during hyperinsulinemia, along with reduced insulin clearance, may be an early change to maintain metabolic status in the face of moderate muscle insulin resistance, even in healthy, nonobese men.

Clinical Features of Nonobese, Apparently Healthy, Japanese Men With Reduced Adipose Tissue Insulin Sensitivity

CONTEXT

Adipose tissue insulin resistance has been observed in obese subjects and is considered an early metabolic defect that precedes insulin resistance in muscle and liver. Although Asians can readily develop metabolic disease without obesity, the clinical features of nonobese, apparently healthy, Asians with reduced adipose tissue insulin sensitivity (ATIS) have not been elucidated.

OBJECTIVE

To investigate the clinical parameters associated with reduced ATIS in nonobese, apparently healthy (body mass index <25 kg/m2), Japanese men.

METHODS

We studied 52 nonobese Japanese men without cardiometabolic risk factors. Using a two-step hyperinsulinemic euglycemic clamp with a glucose tracer, we evaluated the insulin sensitivity in muscle, liver, and adipose tissue. ATIS was calculated as the percentage of free fatty acid (FFA) suppression/insulin concentration during the first step of the glucose clamp.

RESULTS

Using the median ATIS value, the subjects were divided into low- and high-FFA suppression groups. The low-FFA suppression group had moderate fat accumulation in the abdominal subcutaneous adipose tissue and liver. Compared with the high-FFA group, they also had a lower fitness level, decreased insulin clearance, impaired insulin sensitivity in muscle, moderately elevated triglycerides, and lowered high-density lipoprotein cholesterol levels. All these factors correlated significantly with ATIS. Hepatic insulin sensitivity was comparable between the two groups.

CONCLUSIONS

In nonobese, apparently healthy, Japanese men, reduced ATIS was associated with moderate fat accumulation in subcutaneous fat and liver, lower insulin clearance, muscle insulin resistance, and moderate lipedema. These data suggest that reduced ATIS can occur early in the development of the metabolic syndrome, even in nonobese, apparently healthy, men.

Fatty Liver Has Stronger Association With Insulin Resistance Than Visceral Fat Accumulation in Nonobese Japanese Men

Context

Asians have a high prevalence of insulin resistance, even in the nonobese state. Whereas both visceral fat accumulation (VFA) and fatty liver (FL) have been shown to be associated with insulin resistance, it is still unclear which is a better marker to predict insulin resistance in nonobese Asians.

Objective

The aim of this study was to investigate the relation between VFA or FL and insulin resistance in nondiabetic nonobese Japanese men who do not have diabetes.

Design and Participants

We studied 87 nonobese (body mass index <25 kg/m²) Japanese men without diabetes. Using a two-step hyperinsulinemic euglycemic clamp, we evaluated insulin sensitivity in adipose tissue, muscle, and liver. Intrahepatic lipid and abdominal visceral fat area were measured by ¹H-magnetic resonance spectroscopy and MRI, respectively. Subjects were divided into four groups based on the presence or absence of VFA (visceral fat area ≥100 cm²) and FL (intrahepatic lipid ≥ 5%): control (non-VFA, non-FL; n = 54), VFA only (n = 18), FL only (n = 7), and VFA plus FL (n = 8).

Results

Subjects in the FL only and VFA plus FL groups had insulin resistance in adipose tissue and muscle, as well as relatively lower hepatic insulin sensitivity. The specific insulin sensitivities in these organs were comparable in the VFA only and control groups.

Conclusions

In nonobese Japanese men without diabetes, subjects with FL only or VFA plus FL but not VFA only had insulin resistance, suggesting that FL may be a more useful clinical marker than VFA to predict insulin resistance in nonobese Japanese men without diabetes.

A variant within the FTO confers susceptibility to diabetic nephropathy in Japanese patients with type 2 diabetes

To explore novel genetic loci for diabetic nephropathy, we performed genome-wide association studies (GWAS) for diabetic nephropathy in Japanese patients with type 2 diabetes. We analyzed the association of 5,768,242 single nucleotide polymorphisms (SNPs) in Japanese patients with type 2 diabetes, 2,380 nephropathy cases and 5,234 controls. We further performed GWAS for diabetic nephropathy using independent Japanese patients with type 2 diabetes, 429 cases and 358 controls and the results of these two GWAS were combined with an inverse variance meta-analysis (stage-1), followed by a de novo genotyping for the candidate SNP loci (p < 1.0 × 10⁻⁴) in an independent case-control study (Stage-2; 1,213 cases and 1,298 controls). After integrating stage-1 and stage-2 data, we identified one SNP locus, significantly associated with diabetic nephropathy; rs56094641 in FTO, P = 7.74 × 10⁻¹⁰. We further examined the association of rs56094641 with diabetic nephropathy in independent Japanese patients with type 2 diabetes (902 cases and 1,221 controls), and found that the association of this locus with diabetic nephropathy remained significant after integrating all association data (P = 7.62 × 10⁻¹⁰). We have identified FTO locus as a novel locus for conferring susceptibility to diabetic nephropathy in Japanese patients with type 2 diabetes.

Dysfunction of muscle contraction with impaired intracellular Ca2+ handling in skeletal muscle and the effect of exercise training in male db/db mice

Type 2 diabetes is characterized by reduced contractile force production and increased fatigability of skeletal muscle. While the maintenance of Ca²⁺ homeostasis during muscle contraction is a requisite for optimal contractile function, the mechanisms underlying muscle contractile dysfunction in type 2 diabetes are unclear. Here, we investigated skeletal muscle contractile force and Ca²⁺ flux during contraction and pharmacological stimulation in type 2 diabetic model mice ( db/db mice). Furthermore, we investigated the effect of treadmill exercise training on muscle contractile function. In male db/db mice, muscle contractile force and peak Ca²⁺ levels were both lower during tetanic stimulation of the fast-twitch muscles, while Ca²⁺ accumulation was higher after stimulation compared with control mice. While 6 wk of exercise training did not improve glucose tolerance, exercise did improve muscle contractile dysfunction, peak Ca²⁺ levels, and Ca²⁺ accumulation following stimulation in male db/db mice. These data suggest that dysfunctional Ca²⁺ flux may contribute to skeletal muscle contractile dysfunction in type 2 diabetes and that exercise training may be a promising therapeutic approach for dysfunctional skeletal muscle contraction. NEW & NOTEWORTHY The purpose of this study was to examine muscle contractile function and Ca²⁺ regulation as well as the effect of exercise training in skeletal muscle in obese diabetic mice ( db/db). We observed impairment of muscle contractile force and Ca²⁺ regulation in a male type 2 diabetic animal model. These dysfunctions in muscle were improved by 6 wk of exercise training.

Empagliflozin as add-on to linagliptin in a fixed-dose combination in Japanese patients with type 2 diabetes: Glycaemic efficacy and safety profile in a 52-week, randomized, placebo-controlled trial

AIMS

This double-blind, randomized, placebo-controlled trial (ClinicalTrials.gov NCT02453555) evaluated the efficacy and safety of empagliflozin (Empa) 10 or 25 mg as add-on to linagliptin (Lina) 5 mg (fixed-dose combination, Empa/Lina 10/5 or 25/5) in insufficiently controlled Japanese type 2 diabetes patients.

METHODS

The trial (40 sites; May 2015-March 2017) involved screening 433 adults (≥20 years) who were treatment-naive or were using one oral antidiabetic drug for ≥12 weeks, which was discontinued at enrolment. Patients with HbA1c 7.5%-10.0% after ≥16 weeks of using Lina (pre-enrolment or during a 16-week, open-label period) and 2 weeks of using placebo (Plc) for Empa/Lina 10/5, plus Lina, were randomized (2:1) to once-daily Empa/Lina 10/5 (n = 182) or Plc/Lina 10/5 (n = 93) for 24 weeks. Patients with HbA1c ≥ 7.0% at Week 24 received Empa/Lina up-titrated to 25/5 (n = 126) or the corresponding placebo (n = 80), per randomization, from Week 28; 172 Empa/Lina and 84 Plc/Lina patients completed 52 weeks.

RESULTS

Change from baseline in HbA1c was greater (P < .0001) with Empa/Lina than with Plc/Lina at Week 24 (primary outcome, -0.93% vs 0.21%; adjusted mean difference, -1.14%) and Week 52 (-1.16% vs 0.06%; adjusted mean difference, -1.22%). More patients with HbA1c < 7.0% and greater decreases in fasting plasma glucose, body weight and systolic blood pressure were seen in the Empa/Lina group than in the Plc/Lina group. Empa/Lina was well tolerated. The adverse events that were more frequent with Empa/Lina were known empagliflozin-associated events (eg, increased urination, increased blood ketones). There were no adjudication-confirmed diabetic ketoacidosis events or lower limb amputations.

CONCLUSIONS

These results support the notion that empagliflozin-linagliptin in fixed-dose combination is a therapeutic option for Japanese patients with type 2 diabetes.

Association Between Visceral Fat Accumulation and Exercise Tolerance in Non-Obese Subjects Without Diabetes

Background

We examined the associations between visceral fat accumulation, presence of the components of metabolic syndrome (MetS), and exercise tolerance in non-obese subjects without diabetes.

Methods

Seventy-four non-obese, non-diabetic Japanese men were enrolled. The subjects were divided into the following two groups: non-obese subjects without any MetS risk factors (n = 38, Group A) and non-obese subjects with one or two MetS risk factors (n = 36, Group B). Anthropometric and metabolic parameters were measured. The response of heart rate (HR) and blood pressure (BP), and exercise tolerance were also evaluated with a cardiopulmonary exercise test using a bicycle ergometer.

Results

The body mass index, abdominal circumference, visceral fat area, and homeostasis model assessment-insulin resistance, were significantly higher, while levels of anaerobic threshold and maximal oxygen uptake were significantly lower in Group B than in Group A. The levels of resting HR, resting BP, and BP at maximal exercise were significantly higher in Group B than in Group A. There were no significant differences in the HR at maximal exercise as well as the HR and BP after exercise between the two groups. The visceral fat area was significantly and negatively correlated with exercise tolerance. Multivariate linear regression analyses demonstrated that visceral fat area, but not abdominal circumference, was significantly and independently associated with maximal oxygen uptake.

Conclusions

These data suggest that the visceral fat area is a significant determinant for exercise tolerance even in non-obese subjects without diabetes.

Characteristics of Glucose Metabolism in Underweight Japanese Women

Context

Japanese women have substantially lower body mass index (BMI) than women in other developed countries. The BMI of Japanese women has steadily decreased over time. However, glucose metabolism in underweight Japanese women has not been fully characterized.

Objective

The aim of this study was to investigate glucose metabolism and the physical characteristics of underweight Japanese women.

Design and Participants

We recruited 31 young (20 to 29 years of age) and 30 postmenopausal (50 to 65 years of age) underweight women. We also recruited young normal-weight women (n = 13) and postmenopausal normal-weight women (n = 10) to serve as references. We administered an oral glucose tolerance test (OGTT) and evaluated intramyocellular lipid (IMCL) levels and body composition using ¹H-magnetic resonance spectroscopy and dual-energy X-ray absorptiometry, respectively.

Results

Young underweight women had similar glucose tolerance as young normal-weight women. However, postmenopausal underweight women had a higher area under the curve (AUC) for glucose during OGTT than postmenopausal normal-weight women. In postmenopausal underweight women, 2-hour glucose levels during OGTT were negatively correlated with lean body mass (r = −0.55, P < 0.01) and insulinogenic index (r = −0.42, P = 0.02) and were positively correlated with IMCL levels (r = 0.40, P = 0.03). Compared with young underweight women, postmenopausal underweight women had a higher AUC for glucose during OGTT and a lower insulinogenic index and AUC for insulin during OGTT.

Conclusions

Postmenopausal underweight women had more impaired glucose tolerance than young underweight women. In postmenopausal underweight women, the degree of glucose tolerance impairment was associated with decreased lean body mass, increased IMCL accumulation, and impaired insulin secretion.