Effect of metformin on exercise capacity: A meta-analysis

Type 2 diabetes is linked to higher physiologic markers of effort during exercise

Background

People with type 2 diabetes (T2D) have lower rates of physical activity (PA) than the general population. This is significant because insufficient PA is linked to cardiovascular morbidity and mortality, particularly in individuals with T2D. Previously, we identified a novel barrier to physical activity: greater perceived effort during exercise in women. Specifically, women with T2D experienced exercise at low-intensity as greater effort than women without T2D at the same low-intensity - based on self-report and objective lactate measurements. A gap in the literature is whether T2D confers greater exercise effort in both sexes and across a range of work rates.

Objectives

Our overarching objective was to address these gaps regarding the influence of T2D and relative work intensity on exercise effort. We hypothesized that T2D status would confer greater effort during exercise across a range of work rates below the aerobic threshold.

Methods

This cross-sectional study enrolled males and post-menopausal females aged 50-75 years. Measures of exercise effort included: 1) heart rate, 2) lactate and 3) self-report of Rating of Perceived Exertion (RPE); each assessment was during the final minute of a 5-minute bout of treadmill exercise. Treadmill exercise was performed at 3 work rates: 1.5 mph, 2.0 mph, and 2.5 mph, respectively. To determine factors influencing effort, separate linear mixed effect models assessed the influence of T2D on each outcome of exercise effort, controlling for work rate intensity relative to peak oxygen consumption (%VO2peak). Models were adjusted for any significant demographic associations between effort and age (years), sex (male/female), baseline physical activity, or average blood glucose levels.

Results

We enrolled n=19 people with T2D (47.4% female) and n=18 people (55.6% female) with no T2D. In the models adjusted for %VO2peak, T2D status was significantly associated with higher heart rate (p = 0.02) and lactate (p = 0.01), without a significant association with RPE (p = 0.58).

Discussions

Across a range of low-to-moderate intensity work rates in older, sedentary males and females, a diagnosis of T2D conferred higher objective markers of effort but did not affect RPE. Greater objective effort cannot be fully attributed to impaired fitness, as it persisted despite adjustment for %VO2peak. In order to promote regular exercise and reduce cardiovascular risk for people with T2D, 1) further efforts to understand the mechanistic targets that influence physiologic exercise effort should be sought, and 2) comparison of the effort and tolerability of alternative exercise training prescriptions is warranted.

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

A multimodal precision-prevention approach combining lifestyle intervention with metformin repurposing to prevent cognitive impairment and disability: the MET-FINGER randomised controlled trial protocol

BACKGROUND

Combining multimodal lifestyle interventions and disease-modifying drugs (novel or repurposed) could provide novel precision approaches to prevent cognitive impairment. Metformin is a promising candidate in view of the well-established link between type 2 diabetes (T2D) and Alzheimer's Disease and emerging evidence of its potential neuro-protective effects (e.g. vascular, metabolic, anti-senescence). MET-FINGER aims to test a FINGER 2.0 multimodal intervention, combining an updated FINGER multidomain lifestyle intervention with metformin, where appropriate, in an APOE ε4-enriched population of older adults (60-79 years) at increased risk of dementia.

METHODS

MET-FINGER is an international randomised, controlled, parallel-group, phase-IIb proof-of-concept clinical trial, where metformin is included through a trial-within-trial design. 600 participants will be recruited at three sites (UK, Finland, Sweden). Participants at increased risk of dementia based on vascular risk factors and cognitive screening, will be first randomised to the FINGER 2.0 intervention (lifestyle + metformin if eligible; active arm) or to receive regular health advice (control arm). Participants allocated to the FINGER 2.0 intervention group at risk indicators of T2D will be additionally randomised to receive metformin (2000 mg/day or 1000 mg/day) or placebo. The study duration is 2 years. The changes in global cognition (primary outcome, using a Neuropsychological Test Battery), memory, executive function, and processing speed cognitive domains; functional status; lifestyle, vascular, metabolic, and other dementia-related risk factors (secondary outcomes), will be compared between the FINGER 2.0 intervention and the control arm. The feasibility, potential interaction (between-groups differences in healthy lifestyle changes), and disease-modifying effects of the lifestyle-metformin combination will be exploratory outcomes. The lifestyle intervention is adapted from the original FINGER trial (diet, physical activity, cognitive training, monitoring of cardiovascular/metabolic risk factors, social interaction) to be consistently delivered in three countries. Metformin is administered as Glucophage®XR/SR 500, (500 mg oral tablets). The metformin/placebo treatment will be double blinded.

CONCLUSION

MET-FINGER is the first trial combining a multimodal lifestyle intervention with a putative repurposed disease-modifying drug for cognitive impairment prevention. Although preliminary, its findings will provide crucial information for innovative precision prevention strategies and form the basis for a larger phase-III trial design and future research in this field.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT05109169).

Is there a different rating of perceived exertion in men with type 2 diabetes mellitus?

Objective

Studies show that patients with type 2 diabetes mellitus (T2DM) do not engage in regular exercise as often as individuals without T2DM. In addition to numerous barriers to engaging in regular exercise, a different rating of perceived exertion (RPE) during physical activity has been hypothesized to play a role. Therefore, this study investigates whether T2DM affects RPE.

Methods

RPE values (BORG scale ratings) and heart rate (HR) data were analyzed during an endurance step test (25 W + 25 W every 2 min) at different workloads relative to the individual maximum load (50%, 70% and 90% of peak workload (Wpeak)) in patients with T2DM and in non-diabetic control (CON) subjects (n = 12 in each group). Furthermore, in a larger group of overweight patients with T2DM (n = 81), it was investigated whether glycated hemoglobin (HbA1c) levels correlate with RPE values at the different relative loads.

Results

Neither RPE nor HR values significantly differed between T2DM and CON subjects at 50%, 70% or 90% of Wpeak. No significant correlations were identified between HbA1c levels and RPE values.

Conclusion

There is no evidence in our study that T2DM leads to a different perception of physical exertion. Other causes must therefore be responsible for the increased lack of motivation of T2DM patients to engage in regular exercise.

The effect of metformin treatment on volumes of free-living physical activity and sedentary behaviour: A post-hoc analysis of the PRE-D trial

Perceived physical exertion is increased when exercise is performed on metformin treatment, but the clinical relevance of this is unknown. In this post hoc analysis of a randomized, controlled trial, we investigated whether metformin treatment was associated with lower levels of free-living physical activity.   Ninety individuals with overweight/obesity (BMI>25 m2/kg) and HbA1c-defined prediabetes (39-47 mmol/mol) were randomized to treatment with dapagliflozin (SGLT2-inhibitor; 10 mg once daily, n=30), metformin (850 mg twice daily, n=30) or no treatment (control, n=30) for 13 weeks in a parallel-group, open-label trial. Before (baseline), during (6 weeks) and immediately after (13 weeks) cessation of treatment, a 6-day assessment of physical activity and sedentary behaviour was performed using accelerometer-based physical activity monitors. Intention-to-treat analyses revealed no within-group changes or differences in change between the groups for any measures of physical activity or sedentary behaviour at neither 6 nor 13 weeks. Short-term metformin treatment does not reduce free-living physical activity level in individuals with overweight/obesity and HbA1c-defined prediabetes.

The effect of SGLT-2 inhibitors on cardiorespiratory fitness capacity: A systematic review and meta-analysis

Objective: The study aimed to evaluate the effect of sodium-glucose transporter 2 (SGLT-2) inhibitors on various parameters of exercise capacity and provide an evidence-based basis for type 2 diabetes mellitus (T2DM) combined with heart failure (HF) patients or HF patients without T2DM who use SGLT-2 inhibitors to improve cardiorespiratory fitness (CRF). Methods: According to the participant, intervention, comparison, and outcome (PICO) elements, the effects of SGLT-2 inhibitor administration on VO₂ or VO₂peak were researched in this study. Weighted mean difference (WMD) and 95% confidence intervals (CIs) were calculated (random-effects model). Heterogeneity was assessed by the I² test. Results: Six studies were included according to the eligibility criteria: four were RCTs, and two were non-RCTs. Compared with the control group, the merge results of RCTs showed that SGLT-2 inhibitors could significantly increase the VO₂peak (WMD, 2.02 ml kg^-1 min^-1, 95% CI: 0.68-3.37, and p = 0.03; I² = 0% and p = 0.40) and VAT (WMD, 1.57 ml kg^-1 min^-1, 95% CI: 0.06-3.07, and p = 0.04; I² = 0% and p = 0.52) of the obese population, patients with T2DM, and chronic HF patients with or without T2DM. Subgroup analysis showed that SGLT-2 inhibitors improved the VO₂peak in non-HF patients (WMD, 3.57 ml kg^-1 min^-1, 95% CI: 0.87-6.26, and p = 0.009; I² = 4% and p = 0.31) more than in HF patients (WMD, 1.46 ml kg^-1 min^-1, 95% CI: -0.13-3.04, and p = 0.07; I² = 0% and p = 0.81). Moreover, the merge of single-arm studies also indicated that empagliflozin could improve VO₂peak (MD, 1.11 ml kg^-1 min^-1, 95% CI: 0.93-1.30, and p = 0.827, Δ p = 0.000 and I² = 0%) of T2DM patients with chronic HF. Conclusion: Despite the limited number of studies and samples involved, the meta-analysis preliminarily demonstrated that SGLT-2 inhibitors could improve some parameters of exercise capacity (VO₂peak, VAT) in chronic HF patients with or without T2DM and obese individuals, which had a positive effect on promoting cardiopulmonary fitness to help these populations improve their prognosis. Systematic Review Registration: [https://www.crd.york.ac.uk/prospero/#recordDetails], identifier [CRD42020202788].

The GDF15-GFRAL pathway is dispensable for the effects of metformin on energy balance

Metformin is a blood-glucose-lowering medication with physiological effects that extend beyond its anti-diabetic indication. Recently, it was reported that metformin lowers body weight via induction of growth differentiation factor 15 (GDF15), which suppresses food intake by binding to the GDNF family receptor α-like (GFRAL) in the hindbrain. Here, we corroborate that metformin increases circulating GDF15 in mice and humans, but we fail to confirm previous reports that the GDF15-GFRAL pathway is necessary for the weight-lowering effects of metformin. Instead, our studies in wild-type, GDF15 knockout, and GFRAL knockout mice suggest that the GDF15-GFRAL pathway is dispensable for the effects of metformin on energy balance. The data presented here question whether metformin is a sufficiently strong stimulator of GDF15 to drive anorexia and weight loss and emphasize that additional work is needed to untangle the relationship among metformin, GDF15, and energy balance.

Voluntary wheel running behaviour as a tool to assess the severity in a mouse pancreatic cancer model

Laboratory animals frequently undergo routine experimental procedures such as handling, restraining and injections. However, as a known source of stress, these procedures potentially impact study outcome and data quality. In the present study, we, therefore, performed an evidence-based severity assessment of experimental procedures used in a pancreatic cancer model including surgical tumour induction and subsequent chemotherapeutic treatment via repeated intraperitoneal injections. Cancer cell injection into the pancreas was performed during a laparotomy under general anaesthesia. After a four-day recovery phase, mice received either drug treatment (galloflavin and metformin) or the respective vehicle substances via daily intraperitoneal injections. In addition to clinical scoring, an automated home-cage monitoring system was used to assess voluntary wheel running (VWR) behaviour as an indicator of impaired well-being. After surgery, slightly elevated clinical scores and minimal body weight reductions, but significantly decreased VWR behaviour were observed. During therapy, body weight declined in response to chemotherapy, but not after vehicle substance injection, while VWR activity was decreased in both cases. VWR behaviour differed between treatment groups and revealed altered nightly activity patterns. In summary, by monitoring VWR a high impact of repeated injections on the well-being of mice was revealed and substance effects on well-being were distinguishable. However, no differences in tumour growth between treatment groups were observed. This might be due to the severity of the procedures uncovered in this study, as exaggerated stress responses are potentially confounding factors in preclinical studies. Finally, VWR was a more sensitive indicator of impairment than clinical scoring in this model.

Metformin anticipates peak of lactate during high-intensity interval training but no changes performance or neuromuscular response in amateur swimmers

BACKGROUND & AIMS

Metformin demonstrated potential to improve metabolic efficiency in short-intense and prolonged-continuous efforts. The present study investigates the acute effects of metformin intake on performance, rating of perceived exertion (RPE), blood lactate, blood glucose and neuromuscular parameters related to swimming high-intensity interval series.

METHODS

A double-blind, crossover, randomized and placebo-controlled study was carried out. Seven healthy swimmers ingested metformin (500 mg) or placebo capsules on different days and performed a typical high-intensity training series (10 bouts of 50 m with a 3-min interval). Performance, RPE, neuromuscular parameters (lower and upper limbs), blood lactate and glucose were analyzed by the Wilcoxon Signed-Rank and Friedman's tests between supplementation situations and moments, respectively (p > 0.05), the moment where glucose and blood lactate peak were found were analyzed by a Student t-test (p > 0.05) and a Bayesian repeated-measures ANOVA for effects analysis (BF_incl).

RESULTS

The anticipation of blood glucose and peak lactate was signaling by the interaction effect (metformin increased and placebo decreased) between the eighth and the last bout (BF_incl: 4.230 and 5.188 respectively). The second interaction effect of blood glucose and lactate (metformin maintained and placebo increased) during recoveries between 5 min and 7 min (BF_incl: 3.825 and 3.806 respectively) also signaling the anticipatory behavior of both physiological parameters. The anticipation of blood lactate peak concentration after metformin intake confirms the anticipatory behavior of blood lactate (p: 0.015).

CONCLUSIONS

The anticipatory behavior of glucose was not confirmed. Although the anticipatory peak of blood lactate, metformin does not affect neuromuscular responses, RPE and performance.

REGISTRATION OF CLINICAL TRIAL

RBR-67wxdw8 Effects of metformin during swimmer training performance.

Exercise-Pharmacology Interactions: Metformin, Statins, and Healthspan

There is an increased focus on treatments to extend the healthspan. There is solid evidence that exercise extends the healthspan, but other treatments, such as metformin and statins, are also gaining traction. If metformin and statins will be used to prolong healthspan, we must understand their effects in those free of disease and in combination with exercise.

The genetic association of the transcription factor NPAT with glycemic response to metformin involves regulation of fuel selection

The biguanide, metformin, is the first-choice therapeutic agent for type-2 diabetes, although the mechanisms that underpin metformin clinical efficacy remain the subject of much debate, partly due to the considerable variation in patient response to metformin. Identification of poor responders by genotype could avoid unnecessary treatment and provide clues to the underlying mechanism of action. GWAS identified SNPs associated with metformin treatment success at a locus containing the NPAT (nuclear protein, ataxia-telangiectasia locus) and ATM (ataxia-telangiectasia mutated) genes. This implies that gene sequence dictates a subsequent biological function to influence metformin action. Hence, we modified expression of NPAT in immortalized cell lines, primary mouse hepatocytes and mouse tissues, and analysed the outcomes on metformin action using confocal microscopy, immunoblotting and immunocytochemistry. In addition, we characterised the metabolic phenotype of npat heterozygous knockout mice and established the metformin response following development of insulin resistance. NPAT protein was localised in the nucleus at discrete loci in several cell types, but over-expression or depletion of NPAT in immortalised cell models did not change cellular responses to biguanides. In contrast, metformin regulation of respiratory exchange ratio (RER) was completely lost in animals lacking one allele of npat. There was also a reduction in metformin correction of impaired glucose tolerance, however no other metabolic abnormalities, or response to metformin, were found in the npat heterozygous mice. In summary, we provide methodological advancements for the detection of NPAT, demonstrate that minor reductions in NPAT mRNA levels (20–40%) influence metformin regulation of RER, and propose that the association between NPAT SNPs and metformin response observed in GWAS, could be due to loss of metformin modification of cellular fuel usage.

Combination of Metformin and Exercise in Management of Metabolic Abnormalities Observed in Type 2 Diabetes Mellitus

Excess nutrient intake and lack of exercise characterize the problem of obesity and are common factors in insulin resistance (IR). With an increasing number of prediabetic, and type 2 diabetic populations, metformin is still the most prescribed glucose-lowering drug and is often accompanied by recommendations for regular physical exercise. Metformin, by the inhibition of complex 1 of the electron transport chain, and exercise, by increasing energy expenditure, both elicit a low cellular energy state that leads to improvements in glucose control via activation of adenosine 5' monophosphate-activated protein kinase (AMPK). An augmented stimulation of the energy-sensing enzyme AMPK by either of the two modalities leads to an increase in glycogenolysis, glucose uptake, fat oxidation, a decrease in glycogen and protein synthesis, and gluconeogenesis in muscle and the liver, which are remarked as having positive effects on metabolic pathophysiology observed in IR and type 2 diabetes mellitus (T2DM). While both modalities exploit the energy-sensing enzyme AMPK to attain glucose homeostasis, the synergistic effect of these two treatments is not distinctly supported by the literature. Further, an antagonistic dynamic has been observed in cases where metformin and exercise were combined. Reduction of insulin-sensitizing effects of exercise and an overall hindrance of exercise performance and adaptations have been reported and could suggest the possible incongruity of these two modalities. The aim of this review is to elucidate the effect that metformin and exercise have on the management of the metabolic abnormalities observed in T2DM and to provide an insight into the interaction of these two modalities.

The Effect of Metformin on Self-Selected Exercise Intensity in Healthy, Lean Males: A Randomized, Crossover, Counterbalanced Trial

INTRODUCTION

In general, patients with type 2 diabetes have lower cardiorespiratory fitness levels and perform exercise at lower intensities compared to healthy controls. Since metformin (MET) has been shown to increase the rate of perceived exertion (RPE) during exercise with a fixed intensity, MET per se may reduce self-selected exercise intensity. The aim of this study was to assess the effect of MET on self-selected exercise intensity.

METHODS

Healthy males were eligible for this crossover, counterbalanced study with two treatment periods: MET and placebo (PLA), each lasting 17 days. Treatment dose was gradually increased and reached 2 g/day on treatment day 9, and continued at that level for the rest of the treatment period. The two periods were performed in randomized order. Two experimental days (A+B) were conducted on Day 15 (A) and Day 17 (B) of each period, respectively. Day A consisted of an exercise bout with self-selected exercise intensity (equal to RPE = 14-15 on the Borg Scale). Day B consisted of an exercise bout with fixed intensity (70% of VO₂peak). Oxygen consumption rate was assessed continuously during both exercise bouts.

RESULTS

Fifteen males (age 23.7 ± 0.6 years, BMI 22.3 ± 2.0, VO_2peak 3.5 ± 0.6 L/min) were included in the study. On Day B, RPE was higher in MET compared to PLA (14.8 ± 0.4 vs. 14.0 ± 0.3, P = 0.045). On Day A, no difference in self-selected exercise intensity measured by oxygen consumption rate (PLA 2.33 ± 0.09 L O₂/min, MET 2.42 ± 0.10 L O₂/min, P = 0.09) was seen between treatment periods.

CONCLUSIONS

Self-selected exercise intensity was not reduced by MET in healthy males, despite the fact that MET increased RPE during an exercise bout with fixed intensity.

Effect of long-term moderate-exercise combined with metformin-treatment on antioxidant enzymes activity and expression in the gastrocnemius of old female Wistar rats

Oxidative stress is known to be involved in the etiology of sarcopenia, a progressive loss of muscle mass and force related to elderly incapacity. A successful intervention to prevent this condition has been exercise-based therapy. Metformin (MTF), an anti-diabetic drug with pleiotropic effects, is known to retain redox homeostasis. However, the combined use of MTF with exercise has shown controversial experimental results. Our research group has shown that MTF-treatment does not limit the benefits provided by exercise, probably by inducing a hormetic response. Hence, our aim was to evaluate the effect of exercise in combination with MTF-treatment on the redox state of old female Wistar rats. Animals were divided into six groups; three groups preformed exercise on a treadmill for 5 days/week for 20 months and the other three were sedentary. Also, two groups of each, exercised and sedentary animals were treated with MTF for 6 or 12 months correspondingly, beside the untreated groups. Rats were euthanized at 24 months. Muscular functionality was analyzed as the relation between the lean mass free of bone with respect to the grip strength. Superoxide dismutase, catalase, and glutathione peroxidase content, enzymatic activity and redox state were determined in the gastrocnemius muscle. Our results showed that the exercised group treated with MTF for 12 months presented higher GSH/GSSG rate and high antioxidant scavenging power in contrast to the MTF-treatment for 6 months, where the beneficial effect was less noticeable.

The Effect of Metformin on Thyroid-Associated Serum Hormone Levels and Physiological Indexes: A Meta-Analysis

BACKGROUND

Many diseases can be treated with metformin. People with serum thyrotropin (TSH) levels higher than 10 mIU/L are at a risk of cardiovascular events. Some studies have suggested that metformin can lower serum TSH levels to a subnormal level in patients with hyperthyrotropinaemia or hypothyroidism.

OBJECTIVE

The objective of this analysis is to evaluate the effect of metformin treatment on serum TSH, free triiodothyronine (FT3), and free thyroxine (FT4) levels and other associated physiological indices.

METHODS

A comprehensive search using the PubMed, EMBASE, Web of Science and Cochrane Central databases was undertaken for controlled trials on the effect of metformin on serum TSH, FT3, and FT4 levels and associated physiological indices. The primary outcome measures were serum TSH, FT3 and FT4 levels, thyroid size, thyroid nodule size, blood pressure, heart rate, body weight, and body mass index (BMI). The final search was conducted in April 2019.

RESULTS

Six RCTs were included. A total of 494 patients met the inclusion criteria. Metformin treatment did not significantly lower the serum TSH levels at 3 or 6 months but did at 12 months. Moreover, forest plots also suggested that metformin can significantly lower the serum TSH levels in patients with normal thyroid function but cannot statistically change the serum TSH levels in patients with abnormal thyroid function. In addition, metformin treatment clearly lowered the serum FT3 levels and had no significant effect on serum FT4 levels. Lastly, metformin cannot significantly change the systolic blood pressure (SBP) or BMI but can clearly increase the diastolic blood pressure (DBP).

CONCLUSION

Metformin treatment can significantly lower the serum TSH levels, and this effect was much clearer after a 12-month treatment duration and in people with normal thyroid function. However, metformin cannot significantly change the serum FT4 levels or lower serum FT3 levels in people with non-thyroid cancer diseases. In addition, metformin can significantly increase DBP, but it has no clear effect on SBP or BMI.

Atomoxetine Does Not Improve Complex Attention in Idiopathic Parkinson's Disease Patients with Cognitive Deficits: A Meta-Analysis

Objectives

To evaluate the effects of atomoxetine on complex attention and other neurocognitive domains in idiopathic Parkinson's disease (PD).

Methods

Interventional trials reporting changes in complex attention and other neurocognitive functions (Diagnostic and Statistical Manual of Mental Disorders-5) following administration of atomoxetine for at least 8 weeks in adults with idiopathic PD were included. Effect sizes (Cohen's d), the standardized mean difference in the scores of each cognitive domain, were compared using a random-effects model (MetaXL version 5.3).

Results

Three studies were included in the final analysis. For a change in complex attention in PD with mild cognitive impairment (MCI), the estimated effect size was small and nonsignificant (0.16 (95% CI: −0.09, 0.42), n = 42). For changes in executive function, perceptual-motor function, language, social cognition, and learning and memory, the estimated effect sizes were small and medium, but nonsignificant. A deteriorative trend in executive function was observed after atomoxetine treatment in PD with MCI. For a change in global cognitive function in PD without MCI, the estimated effect size was large and significant.

Conclusion

In idiopathic PD with MCI, atomoxetine does not improve complex attention. Also, a deteriorative trend in the executive function was noted.

Glucose Uptake and Insulin Response in Tissue-engineered Human Skeletal Muscle

BACKGROUND

Tissue-engineered muscles ("myobundles") offer a promising platform for developing a human in vitro model of healthy and diseased muscle for drug development and testing. Compared to traditional monolayer cultures, myobundles better model the three-dimensional structure of native skeletal muscle and are amenable to diverse functional measures to monitor the muscle health and drug response. Characterizing the metabolic function of human myobundles is of particular interest to enable their utilization in mechanistic studies of human metabolic diseases, identification of related drug targets, and systematic studies of drug safety and efficacy.

METHODS

To this end, we studied glucose uptake and insulin responsiveness in human tissue-engineered skeletal muscle myobundles in the basal state and in response to drug treatments.

RESULTS

In the human skeletal muscle myobundle system, insulin stimulates a 50% increase in 2-deoxyglucose (2-DG) uptake with a compiled EC₅₀ of 0.27 ± 0.03 nM. Treatment of myobundles with 400 µM metformin increased basal 2-DG uptake 1.7-fold and caused a significant drop in twitch and tetanus contractile force along with decreased fatigue resistance. Treatment with the histone deacetylase inhibitor 4-phenylbutyrate (4-PBA) increased the magnitude of insulin response from a 1.2-fold increase in glucose uptake in the untreated state to a 1.4-fold increase after 4-PBA treatment. 4-PBA treated myobundles also exhibited increased fatigue resistance and increased twitch half-relaxation time.

CONCLUSION

Although tissue-engineered human myobundles exhibit a modest increase in glucose uptake in response to insulin, they recapitulate key features of in vivo insulin sensitivity and exhibit relevant drug-mediated perturbations in contractile function and glucose metabolism.

Chronic metformin intake improves anaerobic but not aerobic capacity in healthy rats

The effect of chronic metformin intake on aerobic and anaerobic capacity was examined in healthy rats. Twenty rats completed 10 days of metformin (MET) ingestion (250 mg). After this period, the animals performed four high-intensity bouts until exhaustion at 9%, 11%, 13%, and 15% of body mass (BM) in swimming, separated by 24 h, with prior metformin (250 mg) or placebo (PL). The critical load (CL) and anaerobic work capacity (AWC – W′) were calculated and considered aerobic and anaerobic capacity, respectively. There was no difference in CL between the MET and PL groups (p > 0.05). The AWC – W′ was higher in the MET group than in the PL group (p = 0.004). Time until exhaustion (seconds) at all bouts were higher (p < 0.004) in the MET group (9% of BM = 434.5 ± 267.3, 11% of BM = 269.6 ± 214.2, 13% of BM = 174.0 ± 40.9, 15% of BM = 146.6 ± 15.9) compared to the PL group (9% of BM = 96.4 ± 22.3, 11% of BM = 65.5 ± 13.4, 13% of BM = 51.1 ± 5.5, 15% of BM = 40.8 ± 7.5). Glucose concentration was higher at 90 and 120 min than at 0 and 30 min for the MET group (intragroup) during the oral glucose test tolerance; there was no difference between the MET and PL groups for area under curve. MET ingestion enhances AWC – W′ and times to exhaustion but not aerobic capacity.

Long-Term Moderate Exercise Combined with Metformin Treatment Induces an Hormetic Response That Prevents Strength and Muscle Mass Loss in Old Female Wistar Rats

Sarcopenia is a syndrome characterized by a progressive and generalized skeletal muscle mass and strength loss, as well as a poor physical performance, which as strongly been associated with aging. Sedentary lifestyle in the elderly contributes to this condition; however, physical activity improves health, reducing morbidity and mortality. Recent studies have shown that metformin (MTF) can also prevent muscle damage promoting muscular performance. To date, there is great controversy if MTF treatment combined with exercise training improves or nullifies the benefits provided by physical activity. This study is aimed at evaluating the effect of long-term moderate exercise combined with MTF treatment on body composition, strength, redox state, and survival rate during the life of female Wistar rats. In this study, rats performed moderate exercise during 20 of their 24 months of life and were treated with MTF for one year or for 6 months, i.e., from 12 to 24 months old and 18 to 24 months old. The body composition (percentage of fat, bone, and lean mass) was determined using a dual-energy X-ray absorption scanner (DXA), and grip strength was determined using a dynamometer. Likewise, medial and tibial nerve somatosensory evoked potentials were evaluated and the redox state was measured by HPLC, calculating the GSH/GSSG ratio in the gastrocnemius muscle. Our results suggest- that the MTF administration, both in the sedentary and the exercise groups, might activate a mechanism that is directly related to the induction of the hormetic response through the redox state modulation. MTF treatment does not eliminate the beneficial effects of exercise throughout life, and although MTF does not increase muscle mass, it increases longevity.

Sitagliptin improves diastolic cardiac function but not cardiorespiratory fitness in adults with type 2 diabetes

BACKGROUND

People with type 2 diabetes mellitus (T2D) have preclinical cardiac and vascular dysfunction associated with low cardiorespiratory fitness (CRF). This is especially concerning because CRF is a powerful predictor of cardiovascular mortality, a primary issue in T2D management. Glucagon-like pepetide-1 (GLP-1) augments cardiovascular function and our previous data in rodents demonstrate that potentiating the GLP-1 signal with a dipeptidyl peptidase-4 (DPP4) inhibitor augments CRF. Lacking are pharmacological treatments which can target T2D-specific physiological barriers to exercise to potentially permit adaptations necessary to improve CRF and thereby health outcomes in people with T2D. We therefore hypothesized that administration of a DPP4-inhibitor (sitagliptin) would improve CRF in adults with T2D.

METHODS AND RESULTS

Thirty-eight participants (64 ± 1 years; mean ± SE) with T2D were randomized in a double-blinded study to receive 100 mg/day sitagliptin, 2 mg/day glimepiride, or placebo for 3 months after baseline measurements. Fasting glucose decreased with both glimepiride and sitagliptin compared with placebo (P = 0.002). CRF did not change in any group (Placebo: Pre: 15.4 ± 0.9 vs. Post: 16.1 ± 1.1 ml/kg/min vs. Glimepiride: 18.5 ± 1.0 vs. 17.7 ± 1.2 ml/kg/min vs. Sitagliptin: 19.1 ± 1.2 vs. 18.3 ± 1.1 ml/kg/min; P = 0.3). Sitagliptin improved measures of cardiac diastolic function, however, measures of vascular function did not change with any treatment.

CONCLUSIONS

Three months of sitagliptin improved diastolic cardiac function, however, CRF did not change. These data suggest that targeting the physiological contributors to CRF with sitagliptin alone is not an adequate strategy to improve CRF in people with T2D.

CLINICAL TRIALS REGISTRATION

www.clinicaltrials.gov NCT01951339.