Masayuki Tanaka

Background: Type 2 diabetes mellitus (T2DM) is associated with impaired skeletal muscle mass and function; however, respiratory muscle involvement has not been fully investigated, particularly in Japanese patients. This study aimed to evaluate respiratory muscle strength and identify its associated factors in Japanese patients with T2DM. Methods: This cross-sectional study included 55 patients with T2DM without respiratory disease. Maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax) were measured and expressed as percentages of the predicted values (PImax %pred and PEmax %pred). Clinical variables, including age, sex, body mass index (BMI), diabetic polyneuropathy (DPN), skeletal muscle index (SMI), handgrip strength, and 6-min walk distance (6MWD), were assessed. Correlation and multiple regression analyses were performed to identify factors associated with PImax %pred. Results: PImax %pred was significantly lower than the predicted value (69.5% [95% CI: 63.1–75.9], p < 0.001), whereas PEmax %pred did not differ significantly from the predicted value (95.6% [95% CI: 86.8–104.3]). PImax %pred was significantly associated with age, BMI, SMI, handgrip strength, and 6MWD. In multiple regression analysis, age, sex, BMI, and handgrip strength were independently associated with PImax %pred, whereas DPN was not. These findings remained unchanged after adjusting for smoking habits. Conclusions: Inspiratory muscle strength was selectively reduced in Japanese patients with T2DM and was independently associated with general physical characteristics and overall muscle strength. Inspiratory muscle weakness may reflect generalized skeletal muscle dysfunction rather than solely a neuropathic impairment. This assessment of respiratory muscle strength may provide additional insights into the physical function of patients with T2DM.

Objective: Diabetes is associated with microvascular complications in multiple tissues. Nailfold capillaries (NFCs) provide a noninvasive window for assessing microvascular alterations; however, their temporal association with skeletal muscle microvascular changes during diabetes progression remains unclear. This study aimed to determine whether NFC structural changes reflect skeletal muscle microvascular alterations and muscle‐type‐specific vulnerability in a non‐obese type 2 diabetes model. Methods: Spontaneously Diabetic Torii (SDT) rats, a non‐obese type 2 diabetes model, and age‐matched Sprague–Dawley rats were studied. NFC morphology was evaluated by capillaroscopy at 12, 18, and 28 weeks of age. Soleus and plantaris muscles were collected for histological and gene expression analyses, and glucose tolerance was evaluated by oral glucose tolerance testing at each time point. Results: At 12 weeks of age, SDT rats exhibited mild glucose intolerance without significant abnormalities in NFC morphology or skeletal muscle capillary indices. At 18 weeks, when glucose intolerance became evident in the absence of persistent hyperglycemia, NFC narrowing and reduced density were observed, accompanied by capillary rarefaction in the predominantly fast‐twitch plantaris muscle, whereas the slow‐twitch soleus muscle remained relatively preserved. By 28 weeks, persistent hyperglycemia was present, and overt muscle atrophy was observed exclusively in the plantaris muscle. Conclusion: NFC structural alterations emerge alongside skeletal muscle microvascular rarefaction at the stage of glucose intolerance and precede overt muscle atrophy in fast‐twitch muscle. NFC assessment may serve as a noninvasive indicator of early microvascular alterations relevant to diabetes‐associated skeletal muscle deterioration.

Diabetes induces skeletal muscle atrophy and capillary regression, especially in oxidative muscles, such as the soleus (SOL). Capillary regression impairs oxygen and substrates delivery, and contributes to metabolic dysfunction and vascular complications. Although protective effects of antioxidants have been demonstrated in disuse models, their role in diabetes-induced capillary regression remains unclear. We examined whether dietary astaxanthin supplementation attenuates capillary regression in the SOL muscles of rats with streptozotocin-induced diabetes. Twenty-four male Wistar rats (6 weeks old) were randomly divided into three groups: control (CON), streptozotocin-induced diabetes (STZ), and STZ with astaxanthin supplementation (STZ + AST). Diabetes was induced by a single tail vein injection of streptozotocin (STZ; 50 mg/kg). Astaxanthin (100 mg/kg/day) was orally administered to the STZ + AST group for 6 weeks. The SOL muscles were analyzed for the capillary-to-fiber (C/F) ratio, oxidative stress (dihydroethidium [DHE] staining), and expression of angiogenesis- and AGEs-related proteins by western blotting. Rats in the STZ group exhibited decreased muscle C/F ratio, increased DHE fluorescence, and elevated FOXO1 and TSP-1. Astaxanthin supplementation significantly improved the C/F ratio and reduced excessively generated ROS and anti-angiogenic protein expression. In addition, the VEGF-A/TSP-1 ratio improved in the STZ + AST group rats. Although the RAGE levels remained elevated, a downward trend was observed following astaxanthin treatment. Astaxanthin supplementation attenuated diabetes-induced capillary regression in the SOL muscles by suppressing oxidative stress and modulating angiogenic signaling. These findings suggest a therapeutic potential for protecting the skeletal muscle microvasculature under diabetic conditions.

This study aimed to investigate the effects of Brazilian propolis on body fat mass and levels of adiponectin and reactive oxygen species among community-dwelling elderly females. This was a double-blind randomized placebo-controlled trial. Altogether, 78 females aged 66–84 years were randomly assigned to the propolis (PRO; n = 39) or placebo (PLA; n = 39) group. For 12 weeks, the PRO group were given three capsules containing 227 mg of propolis twice a day. Meanwhile, the PLA group were given daily placebo capsules. Of 78 participants, 53 (PLA group: n = 28, PRO group: n = 25) completed the study. Although no changes were observed in absolute or relative fat mass in the PLA group, they showed a significant decline in the PRO group. The level of serum adiponectin in the PLA group did not change, although that of the PRO group significantly increased. The level of d-ROMs in the PLA group significantly increased, whereas that of the PRO group significantly decreased. The serum SOD activity in the PLA group significantly decreased, whereas that of the PRO group tended to increase. These results suggest that propolis supplementation may decrease body fat mass and oxidative stress among community-dwelling elderly females.