Inflammation-associated intramyocellular lipid alterations in human pancreatic cancer cachexia.

BACKGROUND: Cancer cachexia is a multifactorial metabolic syndrome characterized by systemic inflammation and ongoing skeletal muscle loss resulting in weakness, poor quality of life, and decreased survival. Whereas lipid accumulation in skeletal muscle is associated with cancer cachexia as well as the prognosis of cancer patients, surprisingly little is known about the nature of the lipids that accumulate in the muscle during cachexia, and whether this is related to inflammation. We aimed to identify the types and distributions of intramyocellular lipids in patients with and without cancer cachexia. METHODS: Rectus abdominis muscle biopsies were collected during surgery of patients with pancreatic ductal adenocarcinoma (n = 10 without cachexia, n = 20 cachectic without inflammation (CRP < 10 mg/L), n = 10 cachectic with inflammation (CRP ≥ 10 mg/L). L3-CT scans were analysed to assess body composition based on validated thresholds in Hounsfield units (HU). Muscle sections were stained with Oil-Red O and H&E to assess general lipid accumulation and atrophy. Untargeted lipidomic analyses were performed on laser-microdissected myotubes using LC-MS/MS. The spatial distribution of intramyocellular lipids with differential abundance between groups was visualized by mass-spectrometry imaging. Genes coding for inflammation markers and enzymes involved in de novo ceramide synthesis were studied by qPCR. RESULTS: Muscle radiation attenuation was lower in cachectic patients with inflammation (median 24.3 [18.6-30.8] HU) as compared with those without inflammation (34.2 [29.3-38.7] HU, P = 0.033) or no cachexia (37.4 [33.9-42.9] HU, P = 0.012). Accordingly, intramyocellular lipid content was lower in non-cachectic patients (1.9 [1.6-2.1]%) as compared with those with cachexia with inflammation (5.5 [4.5-7.3]%, P = 0.002) or without inflammation (4.8 [2.6-6.0]%, P = 0.017). Intramyocellular lipid accumulation was associated with both local IL-6 mRNA levels (rs = 0.57, P = 0.015) and systemic CRP levels (rs = 0.49, P = 0.024). Compared with non-cachectic subjects, cachectic patients had a higher relative abundance of intramyocellular glycerophospholipids and a lower relative abundance of glycerolipids. Furthermore, increases in several intramyocellular lipids such as SM(d36:1), PC(34:1), and TG(48:1) were found in cachectic patients with inflammation and correlated with specific cachexia features. Altered intramyocellular lipid species such as PC(34:1), LPC(18:2), and TG(48:1) showed an uneven distribution in muscle sections of cachectic and non-cachectic patients, with areas featuring abundance of these lipids next to areas almost devoid of them. CONCLUSIONS: Intramyocellular lipid accumulation in patients with cachexia is associated with both local and systemic inflammation, and characterized by changes in defined lipid species such as glycerolipids and glycerophospholipids.

Association of insulin resistance with the accumulation of saturated intramyocellular lipid: A comparison with other fat stores.

It has been shown using proton magnetic resonance spectroscopy (1H MRS) that, in a group of females, whole-body insulin resistance was more closely related to accumulation of saturated intramyocellular lipid (IMCL) than to IMCL concentration alone. This has not been investigated in males. We investigated whether age- and body mass index-matched healthy males differ from the previously reported females in IMCL composition (measured as CH2:CH3) and IMCL concentration (measured as CH3), and in their associations with insulin resistance. We ask whether saturated IMCL accumulation is more strongly associated with insulin resistance than other ectopic and adipose tissue lipid pools and remains a significant predictor when these other pools are taken into account. In this group of males, who had similar overall insulin sensitivity to the females, IMCL was similar between sexes. The males demonstrated similar and even stronger associations of IMCL with insulin resistance, supporting the idea that a marker reflecting the accumulation of saturated IMCL is more strongly associated with whole-body insulin resistance than IMCL concentration alone. However, this marker ceased to be a significant predictor of whole-body insulin resistance after consideration of other lipid pools, which implies that this measure carries no more information in practice than the other predictors we found, such as intrahepatic lipid and visceral adipose tissue. As the marker of saturated IMCL accumulation appears to be related to these two predictors and has a much smaller dynamic range, this finding does not rule out a role for it in the pathogenesis of insulin resistance.

Importance of skeletal muscle lipid levels for muscle function and physical function in older individuals.

The skeletal muscle contains lipids inside (intramyocellular lipids, IMCL) or outside (extramyocellular lipids, EMCL) its cells. The muscle lipid content increases with age; however, the characteristics of IMCL and EMCL in older individuals are not well known. We aimed to examine the characteristics of skeletal muscle lipids by investigating their relationship with muscle function and physical functions. Seven elderly men and 16 elderly women participated. The skeletal muscle lipid content, including IMCL and EMCL, was measured in the vastus lateralis by proton magnetic resonance spectroscopy. Isometric knee extension with maximal voluntary contraction (MVC) and time-to-task failure for knee extension with 50% MVC were measured as muscle functions. The participants performed six physical function tests: preferred gait speed, maximal gait speed, Timed Up and Go, chair sit-to-stand, handgrip strength, and stand from the floor. The time to knee extension task failure had a significant relationship with the IMCL (rs = -0.43, P < 0.05), but not with the EMCL content. Significant relationships were confirmed in the EMCL content with the sit-to-stand (rs = -0.48, P < 0.05) and stand-from-the-floor (rs = 0.53, P < 0.05) tests. These findings indicated that muscle lipids are associated with muscle and physical functional performances in older individuals. Novelty: No relationship was confirmed between IMCL and EMCL in older individuals. Muscle endurance performance had a relationship with IMCL, but not with EMCL. Relationships between EMCL and physical functional tests (e.g., sit-to-stand and stand from the floor) were confirmed.

A novel phenolic formulation for treating hepatic and peripheral insulin resistance by regulating GLUT4-mediated glucose uptake.

Chronic insulin resistance suppresses muscle and liver response to insulin, which is partially due to impaired vesicle trafficking. We report here that a formula consisting of resveratrol, ferulic acid and epigallocatechin-3-O-gallate is more effective in ameliorating muscle and hepatic insulin resistance than the anti-diabetic drugs, metformin and AICAR. The formula enhanced glucose transporter-4 (GLUT4) translocation to the plasma membrane in the insulin-resistant muscle cells by regulating both insulin-independent (calcium and AMPK) and insulin-dependent (PI3K) signaling molecules. Particularly, it regulated the subcellular location of GLUT4 through endosomes to increase glucose uptake under insulin-resistant condition. Meanwhile, this phytochemicals combination increased glycogen synthesis and decreased glucose production in the insulin-resistant liver cells. On the other hand, this formula also showed anti-diabetic potential by the reduction of lipid content in the myotubes, hepatocytes, and adipocytes. This study demonstrated that the three phenolic compounds in the formula could work in distinct mechanisms and enhance both insulin-dependent and independent vesicles trafficking and glucose transport mechanisms to improve carbohydrate and lipid metabolism.

Contribution of skeletal muscle and serum lipids to muscle contraction induced by neuromuscular electrical stimulation in older individuals.

Intramyocellular lipids (IMCL) stored in droplets in muscle cells and free fatty acids (FFA) from fat cells in the blood are the main substrates of adenosine triphosphate during continuous muscle contractions of relatively lower intensity. Although it is known that the lipid oxidative capacity decreases with aging, the effect of IMCL and FFA on muscle contraction in older individuals remains unclear. The purpose of this study was to investigate the contribution of skeletal muscle lipids and blood lipids as energy sources for muscle contraction in older individuals. Eighteen older individuals (mean age: 70.4 ± 3.5 years) underwent muscle contraction intervention induced by intermittent neuromuscular electrical stimulation (NMES) to the vastus lateralis for 30 min. Fasting blood samples were obtained and proton magnetic resonance spectroscopy (1 H-MRS) was performed before and after NMES, and the parameters (including IMCL and extramyocellular lipid [EMCL]) from 1 H-MRS, along with FFA and adiponectin levels, were analyzed using the blood samples of all participants. Levels of IMCL and EMCL did not change (p > 0.05); however, FFA and adiponectin levels decreased from 1.1 ± 0.5 mEq/L to 0.8 ± 0.2 mEq/L and 12.0 ± 5.3 µg/ml to 11.4 ± 5.0 µg/ml, after NMES (p < 0.05), respectively. These findings indicate that serum lipids, but not skeletal muscle lipids, are the energy substrate utilized during involuntary muscle contraction in older individuals.

Ectopic fat deposition in populations of black African ancestry: A systematic review and meta-analysis.

AIMS: In populations of black African ancestry (BA), a paradox exists whereby lower visceral adipose tissue is found despite their high risk for type 2 diabetes (T2D). This systematic review investigates ethnic differences in other ectopic fat depots (intrahepatic lipid: IHL; intramyocellular lipid: IMCL and intrapancreatic lipid; IPL) to help contextualise their potential contribution to T2D risk. METHODS: A systematic literature search was performed in December 2020 to identify studies reporting at least one ectopic fat comparison between BA and one/more other ethnicity. For IHL, a meta-analysis was carried out with studies considered comparable based on the method of measurement. RESULTS: Twenty-eight studies were included (IHL: n = 20; IMCL: n = 8; IPL: n = 4). Meta-analysis of 11 studies investigating IHL revealed that it was lower in BA populations vs pooled ethnic comparators (MD -1.35%, 95% CI -1.55 to -1.16, I2 = 85%, P < 0.00001), white European ancestry (MD -0.94%, 95% CI -1.17 to -0.70, I2 = 79%, P < 0.00001), Hispanic ancestry (MD -2.06%, 95% CI -2.49 to -1.63, I2 = 81%, P < 0.00001) and South Asian ancestry comparators (MD -1.92%, 95% CI -3.26 to -0.57, I2 = 78%, P = 0.005). However, heterogeneity was high in all analyses. Most studies found no significant differences in IMCL between BA and WE. Few studies investigated IPL, however, indicated that IPL is lower in BA compared to WE and HIS. CONCLUSION: The discordance between ectopic fat and greater risk for T2D in BA populations raises questions around its contribution to T2D pathophysiology in BA.

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 ß (IRß) 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.

Increasing skeletal muscle carnitine content in older individuals increases whole-body fat oxidation during moderate-intensity exercise.

Intramyocellular lipid (IMCL) utilization is impaired in older individuals, and IMCL accumulation is associated with insulin resistance. We hypothesized that increasing muscle total carnitine content in older men would increase fat oxidation and IMCL utilization during exercise, and improve insulin sensitivity. Fourteen healthy older men (69 ± 1 year, BMI 26.5 ± 0.8 kg/m2 ) performed 1 h of cycling at 50% VO2 max and, on a separate occasion, underwent a 60 mU/m2 /min euglycaemic hyperinsulinaemic clamp before and after 25 weeks of daily ingestion of a 220 ml insulinogenic beverage (44.4 g carbohydrate, 13.8 g protein) containing 4.5 g placebo (n = 7) or L-carnitine L-tartrate (n = 7). During supplementation, participants performed twice-weekly cycling for 1 h at 50% VO2 max. Placebo ingestion had no effect on muscle carnitine content or total fat oxidation during exercise at 50% VO2 max. L-carnitine supplementation resulted in a 20% increase in muscle total carnitine content (20.1 ± 1.2 to 23.9 ± 1.7 mmol/kg/dm; p < 0.01) and a 20% increase in total fat oxidation (181.1 ± 15.0 to 220.4 ± 19.6 J/kg lbm/min; p < 0.01), predominantly due to increased IMCL utilization. These changes were associated with increased expression of genes involved in fat metabolism (ACAT1, DGKD & PLIN2; p < 0.05). There was no change in resting insulin-stimulated whole-body or skeletal muscle glucose disposal after supplementation. This is the first study to demonstrate that a carnitine-mediated increase in fat oxidation is achievable in older individuals. This warrants further investigation given reduced lipid turnover is associated with poor metabolic health in older adults.

Endurance Runners with Intramyocellular Lipid Accumulation and High Insulin Sensitivity Have Enhanced Expression of Genes Related to Lipid Metabolism in Muscle.

CONTEXT: Endurance-trained athletes have high oxidative capacities, enhanced insulin sensitivities, and high intracellular lipid accumulation in muscle. These characteristics are likely due to altered gene expression levels in muscle. DESIGN AND SETTING: We compared intramyocellular lipid (IMCL), insulin sensitivity, and gene expression levels of the muscle in eight nonobese healthy men (control group) and seven male endurance athletes (athlete group). Their IMCL levels were measured by proton-magnetic resonance spectroscopy, and their insulin sensitivity was evaluated by glucose infusion rate (GIR) during a euglycemic-hyperinsulinemic clamp. Gene expression levels in the vastus lateralis were evaluated by quantitative RT-PCR (qRT-PCR) and microarray analysis. RESULTS: IMCL levels in the tibialis anterior muscle were approximately 2.5 times higher in the athlete group compared to the control group, while the IMCL levels in the soleus muscle and GIR were comparable. In the microarray hierarchical clustering analysis, gene expression patterns were not clearly divided into control and athlete groups. In a gene set enrichment analysis with Gene Ontology gene sets, "RESPONSE TO LIPID" was significantly upregulated in the athlete group compared with the control group. Indeed, qRT-PCR analysis revealed that, compared to the control group, the athlete group had 2-3 times higher expressions of proliferator-activated receptor gamma coactivator-1 alpha (PGC1A), adiponectin receptors (AdipoRs), and fatty acid transporters including fatty acid transporter-1, plasma membrane-associated fatty acid binding protein, and lipoprotein lipase. CONCLUSIONS: Endurance runners with higher IMCL levels have higher expression levels of genes related to lipid metabolism such as PGC1A, AdipoRs, and fatty acid transporters in muscle.

Label-free CARS microscopy reveals similar triacylglycerol acyl chain length and saturation in myocellular lipid droplets of athletes and individuals with type 2 diabetes.

AIMS/HYPOTHESIS: Intramyocellular lipid (IMCL) content associates with development of insulin resistance, albeit not in insulin-sensitive endurance-trained athletes (trained). Qualitative and spatial differences in muscle lipid composition may underlie this so-called athlete's paradox. Here we studied triacylglycerol (TAG) composition of individual myocellular lipid droplets (LDs) in trained individuals and individuals with type 2 diabetes mellitus. METHODS: Trained ([Formula: see text] 71.0 ± 1.6 ml O2 [kg lean body mass (LBM)]-1 min-1), normoglycaemic (fasting glucose 5.1 ± 0.1 mmol/l) individuals and untrained ([Formula: see text] 36.8 ± 1.5 ml O2 [kg LBM]-1 min-1) individuals with type 2 diabetes (fasting glucose 7.4 ± 0.5 mmol/l), with similar IMCL content (3.5 ± 0.7% vs 2.5 ± 0.3%, p = 0.241), but at opposite ends of the insulin sensitivity spectrum (glucose infusion rate 93.8 ± 6.6 vs 25.7 ± 5.3 µmol [kg LBM]-1 min-1 for trained individuals and those with type 2 diabetes, respectively) were included from our database in the present study. We applied in situ label-free broadband coherent anti-Stokes Raman scattering (CARS) microscopy to sections from skeletal muscle biopsies to measure TAG acyl chain length and saturation of myocellular LDs. This approach uniquely permits examination of individual LDs in their native environment, in a fibre-type-specific manner, taking into account LD size and subcellular location. RESULTS: Despite a significant difference in insulin sensitivity, we observed remarkably similar acyl chain length and saturation in trained and type 2 diabetic individuals (chain length: 18.12 ± 0.61 vs 18.36 ± 0.43 number of carbons; saturation: 0.37 ± 0.05 vs 0.38 ± 0.06 number of C=C bonds). Longer acyl chains or higher saturation (lower C=C number) could be detected in subpopulations of LDs, i.e. large LDs (chain length: 18.11 ± 0.48 vs 18.63 ± 0.57 carbon number) and subsarcolemmal LDs (saturation: 0.34 ± 0.02 vs 0.36 ± 0.04 C=C number), which are more abundant in individuals with type 2 diabetes. CONCLUSIONS/INTERPRETATION: In contrast to reports of profound differences in the lipid composition of lipids extracted from skeletal muscle from trained and type 2 diabetic individuals, our in situ, LD-specific approach detected only modest differences in TAG composition in LD subpopulations, which were dependent on LD size and subcellular location. If, and to what extent, these modest differences can impact insulin sensitivity remains to be elucidated. Graphical abstract.

Changes in skeletal muscle diffusion parameters owing to intramyocellular lipid.

INTRODUCTION: Several studies investigated the changes in diffusion of water molecules in skeletal muscle cells of lifestyle-related-disease patients who performed a hybrid training (HYBT) for six months. They reported that the apparent diffusion coefficient (ADC) and all diffusion eigenvalues (λ1, λ2, and λ3) increased after the HYBT, owing to the enlargement of the intramyocellular diffusion space (intracellular space) caused by the muscular hypertrophy. We assumed that the HYBT promoted metabolism of the whole skeletal muscle including lipids, which reduced the amount of intramyocellular lipid (IMCL), and led to a secondary enlargement of the diffusion space in the skeletal muscle cells. However, the IMCL has to be a diffusion limiting factor in order to verify this hypothesis. Until now, there is no report on whether IMCL is a diffusion limiting factor for water molecules. The objective of this study was to examine whether the IMCL is a diffusion limiting factor in skeletal muscle cells. MATERIALS AND METHODS: We performed a three-dimensional quantification of the IMCL in triceps surae muscles of lifestyle-related-disease patients and healthy volunteers. In addition, we measured the ADC in the volume of interest (VOI), diffusion anisotropy (FA), and diffusion eigenvalues (λ1, λ2, and λ3), and evaluated the correlations between these diffusion parameters and IMCL. RESULTS: The results showed that the amount of IMCL was positively and negatively correlated with the FA and λ3, respectively, in lifestyle-related-disease patients. In addition, there was a weak negative correlation between IMCL and ADC, λ1, and λ2. There was no correlation between the amount of IMCL and diffusion parameters of healthy volunteers. DISCUSSION: Above a certain amount, the IMCL correlates with the diffusion parameters. A higher amount of IMCL leads to smaller diffusion eigenvalues. This result suggested that IMCL possibility of influencing diffusion of water molecules in skeletal muscle cells. However, in order for the influence of IMCL to be reflected in the diffusion eigenvalues, it was needed large amount of IMCL existed, and we thought that the influence was smaller than the influence by the already reported cell membrane.

Exercising your fat (metabolism) into shape: a muscle-centred view.

Fatty acids are an important energy source during exercise. Training status and substrate availability are determinants of the relative and absolute contribution of fatty acids and glucose to total energy expenditure. Endurance-trained athletes have a high oxidative capacity, while, in insulin-resistant individuals, fat oxidation is compromised. Fatty acids that are oxidised during exercise originate from the circulation (white adipose tissue lipolysis), as well as from lipolysis of intramyocellular lipid droplets. Moreover, hepatic fat may contribute to fat oxidation during exercise. Nowadays, it is clear that myocellular lipid droplets are dynamic organelles and that number, size, subcellular distribution, lipid droplet coat proteins and mitochondrial tethering of lipid droplets are determinants of fat oxidation during exercise. This review summarises recent insights into exercise-mediated changes in lipid metabolism and insulin sensitivity in relation to lipid droplet characteristics in human liver and muscle. Graphical abstract.

One-leg inactivity induces a reduction in mitochondrial oxidative capacity, intramyocellular lipid accumulation and reduced insulin signalling upon lipid infusion: a human study with unilateral limb suspension.

AIMS/HYPOTHESIS: Physical inactivity, low mitochondrial function, increased intramyocellular lipid (IMCL) deposition and reduced insulin sensitivity are common denominators of chronic metabolic disorders, like obesity and type 2 diabetes. Yet, whether low mitochondrial function predisposes to insulin resistance in humans is still unknown. METHODS: Here we investigated, in an intervention study, whether muscle with low mitochondrial oxidative capacity, induced by one-legged physical inactivity, would feature stronger signs of lipid-induced insulin resistance. To this end, ten male participants (age 22.4 ± 4.2 years, BMI 21.3 ± 2.0 kg/m2) underwent a 12 day unilateral lower-limb suspension with the contralateral leg serving as an active internal control. RESULTS: In vivo, mitochondrial oxidative capacity, assessed by phosphocreatine (PCr)-recovery half-time, was lower in the inactive vs active leg. Ex vivo, palmitate oxidation to 14CO2 was lower in the suspended leg vs the active leg; however, this did not result in significantly higher [14C]palmitate incorporation into triacylglycerol. The reduced mitochondrial function in the suspended leg was, however, paralleled by augmented IMCL content in both musculus tibialis anterior and musculus vastus lateralis, and by increased membrane bound protein kinase C (PKC) θ. Finally, upon lipid infusion, insulin signalling was lower in the suspended vs active leg. CONCLUSIONS/INTERPRETATION: Together, these results demonstrate, in a unique human in vivo model, that a low mitochondrial oxidative capacity due to physical inactivity directly impacts IMCL accumulation and PKCθ translocation, resulting in impaired insulin signalling upon lipid infusion. This demonstrates the importance of mitochondrial oxidative capacity and muscle fat accumulation in the development of insulin resistance in humans. TRIAL REGISTRATION: ClinicalTrial.gov NCT01576250. FUNDING: PS was supported by a 'VICI' Research Grant for innovative research from the Netherlands Organization for Scientific Research (Grant 918.96.618).

The impact of a high-fat diet in mice is dependent on duration and age, and differs between muscles.

Prolonged high-fat diets (HFDs) can cause intramyocellular lipid (IMCL) accumulation that may negatively affect muscle function. We investigated the duration of a HFD required to instigate these changes, and whether the effects are muscle specific and aggravated in older age. Muscle morphology was determined in the soleus, extensor digitorum longus (EDL) and diaphragm muscles of female CD-1 mice from 5 groups: young fed a HFD for 8 weeks (YS-HFD, n=16), young fed a HFD for 16 weeks (YL-HFD, n=28) and young control (Y-Con, n=28). The young animals were 20 weeks old at the end of the experiment. Old (70 weeks) female CD-1 mice received either a normal diet (O-Con, n=30) or a HFD for 9 weeks (OS-HFD, n=30). Body mass, body mass index and intramyocellular lipid (IMCL) content increased in OS-HFD (P≤0.003). In the young mice, this increase was seen in YL-HFD and not YS-HFD (P≤0.006). The soleus and diaphragm fibre cross-sectional area (FCSA) in YL-HFD was larger than that in Y-Con (P≤0.004) while OS-HFD had a larger soleus FCSA compared with that of O-Con after only 9 weeks on a HFD (P<0.001). The FCSA of the EDL muscle did not differ significantly between groups. The oxidative capacity of fibres increased in young mice only, irrespective of HFD duration (P<0.001). High-fat diet-induced morphological changes occurred earlier in the old animals than in the young, and adaptations to HFD were muscle specific, with the EDL being least responsive.

Skeletal muscle lipid droplets are resynthesized before being coated with perilipin proteins following prolonged exercise in elite male triathletes.

Intramuscular triglycerides (IMTG) are a key substrate during prolonged exercise, but little is known about the rate of IMTG resynthesis in the postexercise period. We investigated the hypothesis that the distribution of the lipid droplet (LD)-associated perilipin (PLIN) proteins is linked to IMTG storage following exercise. Fourteen elite male triathletes (27 ± 1 yr, 66.5 ± 1.3 mL·kg-1·min-1) completed 4 h of moderate-intensity cycling. During the first 4 h of recovery, subjects received either carbohydrate or H2O, after which both groups received carbohydrate. Muscle biopsies collected pre- and postexercise and 4 and 24 h postexercise were analyzed using confocal immunofluorescence microscopy for fiber type-specific IMTG content and PLIN distribution with LDs. Exercise reduced IMTG content in type I fibers (-53%, P = 0.002), with no change in type IIa fibers. During the first 4 h of recovery, IMTG content increased in type I fibers (P = 0.014), but was not increased more after 24 h, where it was similar to baseline levels in both conditions. During recovery the number of LDs labeled with PLIN2 (70%), PLIN3 (63%), and PLIN5 (62%; all P < 0.05) all increased in type I fibers. Importantly, the increase in LDs labeled with PLIN proteins only occurred at 24 h postexercise. In conclusion, IMTG resynthesis occurs rapidly in type I fibers following prolonged exercise in highly trained individuals. Furthermore, increases in IMTG content following exercise preceded an increase in the number of LDs labeled with PLIN proteins. These data, therefore, suggest that the PLIN proteins do not play a key role in postexercise IMTG resynthesis.

Effects of aerobic exercise training on the arterial stiffness and intramyocellular or extramyocellular lipid in overweight and obese men.

Intramyocellular lipid (IMCL) and extramyocellular lipid (EMCL) of ectopic fat in muscles are associated with arterial stiffness in normal-weight individuals. Furthermore, aerobic exercise training-induced changes in IMCL or EMCL content are related to a decrease in arterial stiffness in elderly people. Though arterial stiffness is strongly related with obesity, but the effects of aerobic exercise training on IMCL or EMCL content, with a particular focus on arterial stiffness, in obese individuals remains unclear. Here, we investigated the effects of aerobic exercise training on IMCL or EMCL content and arterial stiffness in obese individuals. First, in a cross-sectional study, we examined the relationship between arterial stiffness and IMCL or EMCL content in 24 overweight and obese men. Secondly, we investigated the effects of aerobic exercise intervention on arterial stiffness and IMCL or EMCL content in 21 overweight and obese men. In the cross-sectional study, EMCL content was positively correlated with baPWV and ß-stiffness index, whereas IMCL content was negatively correlated with baPWV. In the intervention study, there were no significant changes in baPWV, ß-stiffness index, and IMCL and EMCL contents after aerobic exercise training. However, exercise-induced change in baPWV and ß-stiffness index were positively correlated with changes in EMCL content. Moreover, the group of improvements in baPWV was only correlated significantly with reduced EMCL content. These results suggest that IMCL and EMCL contents may affect arterial stiffness in overweight and obese men.

Redundancy in regulation of lipid accumulation in skeletal muscle during prolonged fasting in obese men.

Fasting in human subjects shifts skeletal muscle metabolism toward lipid utilization and accumulation, including intramyocellular lipid (IMCL) deposition. Growth hormone (GH) secretion amplifies during fasting and promotes lipolysis and lipid oxidation, but it is unknown to which degree lipid deposition and metabolism in skeletal muscle during fasting depends on GH action. To test this, we studied nine obese but otherwise healthy men thrice: (a) in the postabsorptive state ("CTRL"), (b) during 72-hr fasting ("FAST"), and (c) during 72-hr fasting and treatment with a GH antagonist (GHA) ("FAST + GHA"). IMCL was assessed by magnetic resonance spectroscopy (MRS) and blood samples were drawn for plasma metabolomics assessment while muscle biopsies were obtained for measurements of regulators of substrate metabolism. Prolonged fasting was associated with elevated GH levels and a pronounced GHA-independent increase in circulating medium- and long-chain fatty acids, glycerol, and ketone bodies indicating increased supply of lipid intermediates to skeletal muscle. Additionally, fasting was associated with a release of short-, medium-, and long-chain acylcarnitines to the circulation from an increased ß-oxidation. This was consistent with a ≈55%-60% decrease in pyruvate dehydrogenase (PDHa) activity. Opposite, IMCL content increased ≈75% with prolonged fasting without an effect of GHA. We suggest that prolonged fasting increases lipid uptake in skeletal muscle and saturates lipid oxidation, both favoring IMCL deposition. This occurs without a detectable effect of GHA on skeletal muscle lipid metabolism.

Ectopic fat, insulin resistance and metabolic disease in non-obese Asians: investigating metabolic gradation.

Although metabolic abnormalities commonly occur in non-obese Asians, their pathogenesis is not fully understood. Proton magnetic resonance spectroscopy has been used to analyze intracellular lipids in humans, and results suggest that ectopic fat accumulation in muscle and liver may induce insulin resistance in each tissue independently of obesity. Thus, measurement of ectopic fat currently plays an important role in the study of insulin resistance in non-obese Asians. In addition, studies using 2-step hyperinsulinemic euglycemic clamp with a glucose tracer may clarify how tissue-specific insulin resistance in muscle, liver, and adipose tissue contributes to the development of metabolic disease in non-obese Japanese. Although numerous studies have elucidated the pathophysiology of insulin resistance in obese subjects, research on "metabolic gradation," defined as the gradual transition from an insulin-sensitive to an insulin-resistant state, is less common, especially in terms of early metabolic changes. This review addresses a simple question: when and how is insulin resistance induced in non-obese East Asians? Several studies revealed that impaired insulin clearance and hyperinsulinemia not only compensated for insulin resistance, but also secondarily facilitated insulin resistance and weight gain. In this regard, we recently found that impaired insulin clearance and hyperinsulinemia could occur in apparently healthy subjects without significant insulin resistance, suggesting that this change may be an initial trigger that drives subsequent insulin resistance and weight gain. Further research is required to clarify the pathogenesis of metabolic gradation in non-obese Asians.

Exercise as 'precision medicine' for insulin resistance and its progression to type 2 diabetes: a research review.

Type 2 diabetes and obesity epidemics are in effect in the United States and the two pathologies are linked. In accordance with the growing appreciation that 'exercise is medicine,' it is intuitive to suggest that exercise can play an important role in the prevention and/or treatment of these conditions. However, if exercise is to truly be considered as a viable alternative to conventional healthcare prevention/treatment strategies involving pharmaceuticals, it must be prescribed with similar scrutiny. Indeed, it seems reasonable to posit that the recent initiative calling for 'precision medicine' in the US standard healthcare system should also be applied in the exercise setting. In this narrative review, we consider a number of explanations that have been forwarded regarding the pathological progression to type 2 diabetes both with and without the concurrent influence of overweight/obesity. Our goal is to provide insight regarding exercise strategies that might be useful as 'precision medicine' to prevent/treat this disease. Although the etiology of type 2 diabetes is complex and cause/consequence characteristics of associated dysfunctions have been debated, it is well established that impaired insulin action plays a critical early role. Consequently, an exercise strategy to prevent/treat this disease should be geared toward improving insulin sensitivity both from an acute and chronic standpoint. However, research suggests that a chronic improvement in insulin sensitivity only manifests when weight loss accompanies an exercise intervention. This has resonance because ectopic fat accumulation appears to represent a central component of disease progression regardless of whether obesity is also part of the equation. The cause/consequence characteristics of the relationship between insulin resistance, pathological fat deposition and/or mobilsation, elevated and/or poorly-distributed lipid within myocytes and an impaired capacity to use lipid as fuel remains to be clarified as does the role of muscle mitochondria in the metabolic decline. Until these issues are resolved, a multidimensional exercise strategy (e.g., aerobic exercise at a range of intensities and resistance training for muscular hypertrophy) could provide the best alternative for prevention/treatment.