Reduced skeletal muscle phosphocreatine concentration in type 2 diabetic patients: a quantitative image-based phosphorus-31 MR spectroscopy study

Multiparametric Aging Study Across Adulthood in the Leg Through Quantitative MR Imaging, 1H Spectroscopy, and 31P Spectroscopy at 3T

BACKGROUND

Improved characterization of healthy muscle aging is needed to establish early biomarkers in age-related diseases.

PURPOSE

To quantify age-related changes on multiple MRI and clinical variables evaluated in the same cohort and identify correlations among them.

STUDY TYPE

Prospective.

POPULATION

70 healthy subjects (30 men) from 20 to 81 years old.

FIELD STRENGTH/SEQUENCE

3T/water T2 (multiecho SE, multi-TE STEAM), water T1 (GRE MR Fingerprinting), fat-fraction (multiecho GRE, multi-TE STEAM), carnosine (PRESS), multicomponent water T2 (ISIS-CPMG SE train), and 31P pulse-acquire spectroscopy.

ASSESSMENT

Age- and sex-related changes on: Imaging: fat-fraction (FFMRI), water T1 (T1-H2O), and T2 (T2-H2O-MRI) and their heterogeneities ΔT1-H2O and ΔT2-H2O-MRI in the posterior compartment (PC) and anterior compartment (AC) of the leg. 1H spectroscopy: Carnosine concentration, pH, water T2 components (T2-H2O-CPMG), fat-fraction (FFMRS), and water T2 (T2-H2O-MRS) in the gastrocnemius medialis. 31P spectroscopy: Phosphodiesters (PDE), phosphomonoesters, inorganic phosphates (Pi), and phosphocreatine (PCr) normalized to adenosine triphosphate (ATP) and pH in the calf. Clinical evaluation: Body-mass index (BMI), gait speed (GS), plantar flexion strength, handgrip strength (HS), HS normalized to wrist circumference (HSnorm), physical activity assessment.

STATISTICAL TESTS

Multilinear regressions with sex and age as fixed factors. Spearman correlations calculated between variables. Benjamini-Hochberg procedure for false positives reduction (5% rate). A P < 0.05 significance level was used.

RESULTS

Significant age-related increases were found for BMI (ρAge = 0.04), HSnorm (ρAge = -0.01), PDE/ATP (ρAge = 2.8 × 10-3), Pi/ATP (ρAge = 2.0 × 10-3), Pi/PCr (ρAge = 0.3 × 10-3), T2-H2O-MRS (ρAge = 0.051 msec), FFMRS (ρAge = 0.036) the intermediate T2-H2O-CPMG component time (ρAge = 0.112 msec), and fraction (ρAge = -0.3 × 10-3); and in both compartments for FFMRI (ρAge = 0.06, PC; ρAge = 0.06, AC), T2-H2O-MRI (ρAge = 0.05, PC; ρAge = 0.05, AC; msec), ΔT2-H2O-MRI (ρAge = 0.02, PC; ρAge = 0.02, AC; msec), T1-H2O (ρAge = 1.08, PC; ρAge = 1.06, AC; msec), and ΔT1-H2O (ρAge = 0.22, PC; ρAge = 0.37, AC; msec). The best age predictors, accounting for sex-related differences, were HSnorm (R2 = 0.52) and PDE/ATP (R2 = 0.44). In both leg compartments, the imaging measures and HSnorm were intercorrelated. In PC, T2-H2O-MRS and FFMRS also showed numerous correlations to the imaging measures. PDE/ATP correlated to T1-H2O, T2-H2O-MRI, ΔT2-H2O-MRI, FFMRI, FFMRS, the intermediate T2-H2O-CPMG, BMI, Pi/PCr, and HSnorm.

DATA CONCLUSION

Our multiparametric MRI approach provided an integrative view of age-related changes in the leg and revealed multiple correlations between these parameters and the normalized HS.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 3.

Nonequilibrium thermodynamics and mitochondrial protein content predict insulin sensitivity and fuel selection during exercise in human skeletal muscle

Introduction: Many investigators have attempted to define the molecular nature of changes responsible for insulin resistance in muscle, but a molecular approach may not consider the overall physiological context of muscle. Because the energetic state of ATP (ΔGATP) could affect the rate of insulin-stimulated, energy-consuming processes, the present study was undertaken to determine whether the thermodynamic state of skeletal muscle can partially explain insulin sensitivity and fuel selection independently of molecular changes. Methods: 31P-MRS was used with glucose clamps, exercise studies, muscle biopsies and proteomics to measure insulin sensitivity, thermodynamic variables, mitochondrial protein content, and aerobic capacity in 16 volunteers. Results: After showing calibrated 31P-MRS measurements conformed to a linear electrical circuit model of muscle nonequilibrium thermodynamics, we used these measurements in multiple stepwise regression against rates of insulin-stimulated glucose disposal and fuel oxidation. Multiple linear regression analyses showed 53% of the variance in insulin sensitivity was explained by 1) VO2max (p = 0.001) and the 2) slope of the relationship of ΔGATP with the rate of oxidative phosphorylation (p = 0.007). This slope represents conductance in the linear model (functional content of mitochondria). Mitochondrial protein content from proteomics was an independent predictor of fractional fat oxidation during mild exercise (R2 = 0.55, p = 0.001). Conclusion: Higher mitochondrial functional content is related to the ability of skeletal muscle to maintain a greater ΔGATP, which may lead to faster rates of insulin-stimulated processes. Mitochondrial protein content per se can explain fractional fat oxidation during mild exercise.

Sarcopenia - Definition, Radiological Diagnosis, Clinical Significance

BACKGROUND

 Sarcopenia is an age-related syndrome characterized by a loss of muscle mass and strength. As a result, the independence of the elderly is reduced and the hospitalization rate and mortality increase. The onset of sarcopenia often begins in middle age due to an unbalanced diet or malnutrition in association with a lack of physical activity. This effect is intensified by concomitant diseases such as obesity or metabolic diseases including diabetes mellitus.

METHOD

 With effective preventative diagnostic procedures and specific therapeutic treatment of sarcopenia, the negative effects on the individual can be reduced and the negative impact on health as well as socioeconomic effects can be prevented. Various diagnostic options are available for this purpose. In addition to basic clinical methods such as measuring muscle strength, sarcopenia can also be detected using imaging techniques like dual X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI), and sonography. DXA, as a simple and cost-effective method, offers a low-dose option for assessing body composition. With cross-sectional imaging techniques such as CT and MRI, further diagnostic possibilities are available, including MR spectroscopy (MRS) for noninvasive molecular analysis of muscle tissue. CT can also be used in the context of examinations performed for other indications to acquire additional parameters of the skeletal muscles (opportunistic secondary use of CT data), such as abdominal muscle mass (total abdominal muscle area - TAMA) or the psoas as well as the pectoralis muscle index. The importance of sarcopenia is already well studied for patients with various tumor entities and also infections such as SARS-COV2.

RESULTS AND CONCLUSION

 Sarcopenia will become increasingly important, not least due to demographic changes in the population. In this review, the possibilities for the diagnosis of sarcopenia, the clinical significance, and therapeutic options are described. In particular, CT examinations, which are repeatedly performed on tumor patients, can be used for diagnostics. This opportunistic use can be supported by the use of artificial intelligence.

KEY POINTS

· Sarcopenia is an age-related syndrome with loss of muscle mass and strength.. · Early detection and therapy can prevent negative effects of sarcopenia.. · In addition to DEXA, cross-sectional imaging techniques (CT, MRI) are available for diagnostic purposes.. · The use of artificial intelligence (AI) offers further possibilities in sarcopenia diagnostics..

CITATION FORMAT

· Vogele D, Otto S, Sollmann N et al. Sarcopenia - Definition, Radiological Diagnosis, Clinical Significance. Fortschr Röntgenstr 2023; DOI: 10.1055/a-1990-0201.

Exercise and Creatine Supplementation to Augment the Adaptation of Exercise Training Among Breast Cancer Survivors Completing Chemotherapy: Protocol for an Open-label Randomized Controlled Trial (the THRIVE Study)

BACKGROUND

In breast cancer survivors, chemotherapy-induced muscle loss has been shown to be attenuated with structured resistance exercise. Creatine supplementation can increase bioenergetics in skeletal muscle, which helps to improve overall strength and endurance and reduce muscular fatigue. Therefore, we hypothesize that adding creatinine supplementation to exercise training will accelerate improvements in strength, endurance, and bioenergetics in breast cancer survivors.

OBJECTIVE

The primary objective is to determine the effects of combining creatine supplementation with exercise on modulating strength and physical function in breast cancer survivors by comparing these effects to those of exercise alone. The secondary objectives are to determine if creatine supplementation and exercise can increase the intramuscular storage of creatine and improve body composition by comparing this intervention to exercise alone.

METHODS

We aim to test our hypothesis by conducting an open-label randomized controlled trial of 30 breast cancer survivors who have completed chemotherapy within 6 months of enrollment. Eligible participants will be equally randomized (1:1) to either a creatine and exercise group or an exercise-only group for this 12-week intervention. Individuals who are randomized to receive creatine will be initially dosed at 20 g per day for 7 days to boost the availability of creatine systemically. Thereafter, the dose will be reduced to 5 g per day for maintenance throughout the duration of the 12-week protocol. All participants will engage in 3 center-based exercise sessions, which will involve completing 3 sets of 8 to 12 repetitions on chest press, leg press, seated row, shoulder press, leg extension, and leg curl machines. The primary outcomes will include changes in strength, body composition, and physical function in breast cancer survivors. The secondary outcomes will be intramuscular concentrations of creatine and adenosine triphosphate in the vastus lateralis, midthigh cross-sectional area, and quality of life.

RESULTS

As of October 2021, a total of 9 patients have been enrolled into the study. No unexpected adverse events have been reported.

CONCLUSIONS

Creatine is being studied as a potential agent for improving strength, endurance, and bioenergetics in breast cancer survivors following chemotherapy. The findings from our trial may have future implications for supporting breast cancer survivors in reversing the muscle loss experienced during chemotherapy and improving their physical function and quality of life.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04207359; https://clinicaltrials.gov/ct2/show/NCT04207359.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/26827.

Muscular carnosine is a marker for cardiorespiratory fitness and cardiometabolic risk factors in men with type 1 diabetes

PURPOSE

Muscle is an essential organ for glucose metabolism and can be influenced by metabolic disorders and physical activity. Elevated muscle carnosine levels have been associated with insulin resistance and cardiometabolic risk factors. Little is known about muscle carnosine in type 1 diabetes (T1D) and how it is influenced by physical activity. The aim of this study was to characterize muscle carnosine in vivo by proton magnetic resonance spectroscopy (¹H MRS) and evaluate the relationship with physical activity, clinical characteristics and lipoprotein subfractions.

METHODS

16 men with T1D (10 athletes/6 sedentary) and 14 controls without diabetes (9/5) were included. Body composition by DXA, cardiorespiratory capacity (VO₂peak) and serum lipoprotein profile by proton nuclear magnetic resonance (¹H NMR) were obtained. Muscle carnosine scaled to water (carnosine_W) and to creatine (carnosine_CR), creatine and intramyocellular lipids (IMCL) were quantified in vivo using ¹H MRS in a 3T MR scanner in soleus muscle.

RESULTS

Subjects with T1D presented higher carnosine CR levels compared to controls. T1D patients with a lower VO₂peak presented higher carnosine_CR levels compared to sedentary controls, but both T1D and control groups presented similar levels of carnosine_CR at high VO₂peak levels. Carnosine_W followed the same trend. Integrated correlation networks in T1D demonstrated that carnosine_W and carnosine_CR were associated with cardiometabolic risk factors including total and abdominal fat, pro-atherogenic lipoproteins (very low-density lipoprotein subfractions), low VO₂peak, and IMCL.

CONCLUSIONS

Elevated muscle carnosine levels in persons with T1D and their effect on atherogenic lipoproteins can be modulated by physical activity.

Posttranscriptional Regulation of Insulin Resistance: Implications for Metabolic Diseases

Insulin resistance defines an impairment in the biologic response to insulin action in target tissues, primarily the liver, muscle, adipose tissue, and brain. Insulin resistance affects physiology in many ways, causing hyperglycemia, hypertension, dyslipidemia, visceral adiposity, hyperinsulinemia, elevated inflammatory markers, and endothelial dysfunction, and its persistence leads to the development metabolic disease, including diabetes, obesity, cardiovascular disease, or nonalcoholic fatty liver disease (NAFLD), as well as neurological disorders such as Alzheimer’s disease. In addition to classical transcriptional factors, posttranscriptional control of gene expression exerted by microRNAs and RNA-binding proteins constitutes a new level of regulation with important implications in metabolic homeostasis. In this review, we describe miRNAs and RBPs that control key genes involved in the insulin signaling pathway and related regulatory networks, and their impact on human metabolic diseases at the molecular level, as well as their potential use for diagnosis and future therapeutics.

Cardiovascular benefits from SGLT2 inhibition in type 2 diabetes mellitus patients is not impaired with phosphate flux related to pharmacotherapy

The beneficial cardiorenal outcomes of sodium-glucose cotransporter 2 inhibitors (SGLT2i) in patients with type 2 diabetes mellitus (T2DM) have been substantiated by multiple clinical trials, resulting in increased interest in the multifarious pathways by which their mechanisms act. The principal effect of SGLT2i (-flozin drugs) can be appreciated in their ability to block the SGLT2 protein within the kidneys, inhibiting glucose reabsorption, and causing an associated osmotic diuresis. This ameliorates plasma glucose elevations and the negative cardiorenal sequelae associated with the latter. These include aberrant mitochondrial metabolism and oxidative stress burden, endothelial cell dysfunction, pernicious neurohormonal activation, and the development of inimical hemodynamics. Positive outcomes within these domains have been validated with SGLT2i administration. However, by modulating the sodium-glucose cotransporter in the proximal tubule (PT), SGLT2i consequently promotes sodium-phosphate cotransporter activity with phosphate retention. Phosphatemia, even at physiologic levels, poses a risk in cardiovascular disease burden, more so in patients with type 2 diabetes mellitus (T2DM). There also exists an association between phosphatemia and renal impairment, the latter hampering cardiovascular function through an array of physiologic roles, such as fluid regulation, hormonal tone, and neuromodulation. Moreover, increased phosphate flux is associated with an associated increase in fibroblast growth factor 23 levels, also detrimental to homeostatic cardiometabolic function. A contemporary commentary concerning this notion unifying cardiovascular outcome trial data with the translational biology of phosphate is scant within the literature. Given the apparent beneficial outcomes associated with SGLT2i administration notwithstanding negative effects of phosphatemia, we discuss in this review the effects of phosphate on the cardiometabolic status in patients with T2DM and cardiorenal disease, as well as the mechanisms by which SGLT2i counteract or overcome them to achieve their net effects. Content drawn to develop this conversation begins with proceedings in the basic sciences and works towards clinical trial data.

The Role of Mitochondrial Adaptation and Metabolic Flexibility in the Pathophysiology of Obesity and Insulin Resistance: an Updated Overview

PURPOSE OF REVIEW

The term "metabolic flexibility" denotes the dynamic responses of the cellular oxidative machinery in order to adapt to changes in energy substrate availability. A progressive loss of this adaptive capacity has been implicated in the development of obesity-related comorbidities. Mitochondria are dynamic intracellular organelles which play a fundamental role in energy metabolism, and the mitochondrial adaptation to environmental challenges may be viewed as the functional component of metabolic flexibility. Herein, we attempt to comprehensively review the available evidence regarding the role of mitochondrial adaptation and metabolic flexibility in the pathogenesis of obesity and related morbidities, namely insulin resistance states and non-alcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

Overall, there is a concrete body of evidence to support the presence of impaired mitochondrial adaptation as a principal component of systemic metabolic inflexibility in conditions related to obesity. There are still many unresolved questions regarding the relationship between the gradual loss of mitochondrial adaptability and the progression of obesity-related complications, such as causality issues, the timely appearance and reversibility of the described disturbances, and the generalizability of the findings to the mitochondrial content of every affected tissue or organ. The evidence regarding the causality between the observed associations remains inconclusive, although most of the available data points towards a bidirectional, potentially mutually amplifying relationship. The spectrum of NAFLD is of particular interest, since functional and pathological changes in the course of its development closely mirror the progression of dysmetabolism, if not constituting a dynamic component of the latter.

Greater fatigability and motor unit discharge variability in human type 2 diabetes

This study determined the discharge characteristics of motor units from two lower limb muscles before and after fatiguing exercise in people with type 2 diabetes (T2D) with no symptoms of polyneuropathy and activity‐matched controls. Seventeen people with T2D (65.0 ± 5.6 years; 8 women) and 17 controls (63.6 ± 4.5 years; 8 women) performed: (a) intermittent, isometric contractions at 50% maximal voluntary isometric contraction (MVIC) sustained to failure with the ankle dorsiflexors, and (b) a dynamic fatiguing task (30% MVIC load) for 6 min with the knee extensors. Before and after the fatiguing tasks, motor unit characteristics (including coefficient of variation (CV) of interspike intervals (ISI)) were quantified from high‐density electromyography and muscle contractile properties were assessed via electrical stimulation. Fatigability was ~50% greater for people with T2D than controls for the dorsiflexors (time‐to‐failure: 7.3 ± 4.1 vs. 14.3 ± 9.1 min, p = .010) and knee extensors (power reduction: 56.7 ± 11.9 vs. 31.5 ± 25.5%, p < .001). The CV of ISI was greater for the T2D than control group for the tibialis anterior (23.1 ± 11.0 vs. 21.3 ± 10.7%, p < .001) and vastus lateralis (27.8 ± 20.2 vs. 24.5 ± 16.1%, p = .011), but these differences did not change after the fatiguing exercises. People with T2D had greater reductions in the electrically evoked twitch amplitude of the dorsiflexors (8.5 ± 5.1 vs. 4.0 ± 3.4%·min^‐1, p = .013) and knee extensors (49.1 ± 10.0 vs. 31.8 ± 15.9%, p = .004) than controls. Although motor unit activity was more variable in people with T2D than controls, the greater fatigability of the T2D group for lower limb muscles was due to mechanisms involving disruption of contractile function of the exercising muscles rather than motor unit behavior.

Beyond the myocardium? SGLT2 inhibitors target peripheral components of reduced oxygen flux in the diabetic patient with heart failure with preserved ejection fraction

Recent cardiovascular outcome trials have highlighted the propensity of the antidiabetic agents, SGLT2 inhibitors (SGLT2is or -flozin drugs), to exert positive clinical outcomes in patients with cardiovascular disease at risk for major adverse cardiovascular events (MACEs). Of interest in cardiac diabetology is the physiological status of the patient with T2DM and heart failure with preserved ejection fraction (HFpEF), a well-examined association. Underlying this pathologic tandem are the effects that long-standing hyperglycemia has on the ability of the HFpEF heart to adequately deliver oxygen. It is believed that shortcomings in oxygen diffusion or utilization and the resulting hypoxia thereafter may play a role in underlying the clinical sequelae of patients with T2DM and HFpEF, with implications in the long-term decline of extra-cardiac tissue. Oxygen consumption is one of the most critical factors in indexing heart failure disease burden, warranting a probe into the role of SGLT2i on oxygen utility in HFpEF and T2DM. We investigated the role of oxygen flux in the patient with T2DM and HFpEF extending beyond the heart with focuses on cellular metabolism, perivascular fibrosis with endothelial dysfunction, hematologic changes, and renal effects with neurohormonal considerations in the patient with HFpEF and T2DM. Moreover, we give a commentary on potential therapeutic targets of these components with SGLT2i to gain insight into disease burden amelioration in patients with HFpEF and T2DM.

Older adults with sarcopenia have distinct skeletal muscle phosphodiester, phosphocreatine, and phospholipid profiles

The loss of skeletal muscle mass and function with age (sarcopenia) is a critical healthcare challenge for older adults. 31‐phosphorus magnetic resonance spectroscopy (³¹P‐MRS) is a powerful tool used to evaluate phosphorus metabolite levels in muscle. Here, we sought to determine which phosphorus metabolites were linked with reduced muscle mass and function in older adults. This investigation was conducted across two separate studies. Resting phosphorus metabolites in skeletal muscle were examined by ³¹P‐MRS. In the first study, fifty‐five older adults with obesity were enrolled and we found that resting phosphocreatine (PCr) was positively associated with muscle volume and knee extensor peak power, while a phosphodiester peak (PDE2) was negatively related to these variables. In the second study, we examined well‐phenotyped older adults that were classified as nonsarcopenic or sarcopenic based on sex‐specific criteria described by the European Working Group on Sarcopenia in Older People. PCr content was lower in muscle from older adults with sarcopenia compared to controls, while PDE2 was elevated. Percutaneous biopsy specimens of the vastus lateralis were obtained for metabolomic and lipidomic analyses. Lower PCr was related to higher muscle creatine. PDE2 was associated with glycerol‐phosphoethanolamine levels, a putative marker of phospholipid membrane damage. Lipidomic analyses revealed that the major phospholipids, (phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol) were elevated in sarcopenic muscle and were inversely related to muscle volume and peak power. These data suggest phosphorus metabolites and phospholipids are associated with the loss of skeletal muscle mass and function in older adults.

Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy

Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy.

Molecular imaging of diabetes and diabetic complications: Beyond pancreatic β-cell targeting

Diabetes is a chronic non-communicable disease affecting over 400 million people worldwide. Diabetic patients are at a high risk of various complications, such as cardiovascular, renal, and other diseases. The pathogenesis of diabetes (both type 1 and type 2 diabetes) is associated with a functional impairment of pancreatic β-cells. Consequently, most efforts to manage and prevent diabetes have focused on preserving β-cells and their function. Advances in imaging techniques, such as magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography, and single-photon-emission computed tomography, have enabled noninvasive and quantitative detection and characterization of the population and function of β-cells in vivo. These advantages aid in defining and monitoring the progress of diabetes and determining the efficacy of anti-diabetic therapies. Beyond β-cell targeting, molecular imaging of biomarkers associated with the development of diabetes, e.g., lymphocyte infiltration, insulitis, and metabolic changes, may also be a promising strategy for early detection of diabetes, monitoring its progression, and occurrence of complications, as well as facilitating exploration of new therapeutic interventions. Moreover, molecular imaging of glucose uptake, production and excretion in specified tissues is critical for understanding the pathogenesis of diabetes. In the current review, we summarize and discuss recent advances in noninvasive imaging technologies for imaging of biomarkers beyond β-cells for early diagnosis of diabetes, investigation of glucose metabolism, and precise diagnosis and monitoring of diabetic complications for better management of diabetic patients.