The addition of blood flow restriction during resistance exercise does not increase prolonged low-frequency force depression.

At a given exercise intensity, blood flow restriction (BFR) reduces the volume of exercise required to impair post-exercise neuromuscular function. Compared to traditional exercise, the time course of recovery is less clear. After strenuous exercise, force output assessed with electrical muscle stimulation is impaired to a greater extent at low versus high stimulation frequencies, a condition known as prolonged low-frequency force depression (PLFFD). It is unclear if BFR increases PLFFD after exercise. This study tested if BFR during exercise increases PLFFD and slows recovery of neuromuscular function compared to regular exercise. Fifteen physically active participants performed six low-load sets of knee-extensions across four conditions: resistance exercise to task failure (RETF), resistance exercise to task failure with BFR applied continuously (BFRCONT) or intermittently (BFRINT), and resistance exercise matched to the lowest exercise volume condition (REVM). Maximal voluntary contraction (MVC) force output, voluntary activation and a force-frequency (1-100 Hz) curve were measured before and 0, 1, 2, 3, 4 and 24 h after exercise. Exercise to task failure caused similar reductions at 0 h for voluntary activation (RETF = 81.0 ± 14.2%, BFRINT = 80.9 ± 12.4% and BFRCONT = 78.6 ± 10.7%) and MVC force output (RETF = 482 ± 168 N, BFRINT = 432 ± 174 N, and BFRCONT = 443 ± 196 N), which recovered to baseline values between 4 and 24 h. PLFFD occurred only after RETF at 1 h supported by a higher frequency to evoke 50% of the force production at 100 Hz (1 h: 17.5 ± 4.4 vs. baseline: 15 ± 4.1 Hz, P = 0.0023), BFRINT (15.5 ± 4.0 Hz; P = 0.03), and REVM (14.9 ± 3.1 Hz; P = 0.002), with a trend versus BFRCONT (15.7 ± 3.5 Hz; P = 0.063). These findings indicate that, in physically active individuals, using BFR during exercise does not impair the recovery of neuromuscular function by 24 h post-exercise.

Effect of blood flow restriction and electrical muscle stimulation on human glycemic response to a glucose challenge.

PURPOSE: To determine whether reduced tissue oxygen availability through blood flow restriction (BFR) alone, or in combination with electrically induced muscle contractions, can improve glucose clearance after an acute glucose challenge. METHODS: In a randomized crossover design, 21 young participants (females: 12) were allocated to perform 1) electrical muscle stimulation (EMS), 2) BFR, 3) EMS + BFR or 4) no treatment (control). Participants completed each condition immediately preceding a 2 h oral glucose tolerance test (100 g). Primary analyses were performed on the glucose area under the curve (AUC) at time points 0-30, 30-120, and 0-120 min. Secondary analyses were performed on glycemic responses based on biological sex and estimated muscle phenotype. RESULTS: Compared to the control (322±25 mM∙min), the 0-30 min AUC was reduced following EMS (293±22 mM∙min, p = 0.0004), and EMS + BFR (298±36 mM∙min., p = 0.006), whereas BFR in isolation did not differ (306±30 mM∙min, p = 0.1). The 30-120 and 0-120 min glucose AUCs were similar across conditions. Based on effect size from the control conditions, our secondary analysis suggests different 0-30 min glycemic responses after EMS + BFR between females (dz = 0.206) vs. males (dz = 1.461) and/or slow (dz = 0.426) vs. fast (dz = 1.075) muscle phenotype. CONCLUSION: Reducing tissue oxygen availability with BFR did not augment the effects of EMS in the overall group; however, we provide preliminary data to suggest possible sex and/or muscle phenotypic responses in glycemic regulation with these modalities.

Investigating the Relevance of Maximal Speed and Acceleration in Varsity-Level Female Ice Hockey Players.

PURPOSE: To characterize and compare female ice hockey players' peak skating speed and acceleration ability during linear sprints and gameplay. We also sought to quantify the time spent at various speeds and the frequency of accelerations at different thresholds during games. METHODS: Seventeen varsity-level female ice hockey players (20 [1.4] y, 68.9 [4.9] kg, 167.6 [4.7] cm) participated in an on-ice practice session (performing 3 × 40-m linear sprints) and 4 regular-season games while being monitored using a local positioning system. Speed and acceleration were recorded from the sprint and within-game monitoring. Time on ice spent in relative skating speed zones and the frequency of accelerations at different intensities were recorded. RESULTS: Players' greatest peak speeds (29.5 [1.3] vs 28.3 [1.1] km/h) and accelerations (4.39 [0.48] vs 3.34 [0.36] m/s2) reached during gameplay were higher than those reached in linear sprinting (both P < .01). Peak in-game values were moderately predicted by linear sprint values for speed (r = .69, P < .01) but not for acceleration (r < .01, P = .95). Players spent little time at near-peak linear sprint speeds (≥80% [22.7 km/h], ∼3% time on ice; ≥90% [25.5 km/h], <1% of time on ice) during gameplay. However, 26% to 35% of accelerations recorded during the 4 games were ≥90% of linear sprint acceleration. CONCLUSIONS: Although skating speed may be advantageous in specific game situations, our results suggest that players spend little time at near-maximal speeds while accelerating frequently during games. This warrants further investigation of direction changes, skating transitions, repeated sprints, and other determinant variables potentially related to on-ice success and the implementation of training strategies to improve repeated acceleration or qualities beyond maximal skating speed.

Altered carbohydrate oxidation during exercise in overreached endurance athletes is applicable to training monitoring with continuous glucose monitors.

PURPOSE: The purpose of the study was to investigate whether carbohydrate utilization is altered during exercise in overreached endurance athletes and examine the utility of continuous glucose monitors (CGM) to detect overreaching status. METHODS: Eleven endurance athletes (M:8, F:3) completed a 5-week training block consisting of 1 week of reduced training (PRE), 3 weeks of high-intensity overload training (POST), and 1 week of recovery training (REC). Participants completed a Lamberts and Lambert Submaximal Cycling Test (LSCT) and 5 km time-trial at PRE, POST, and REC time points, 15 min following the ingestion of a 50 g glucose beverage with glucose recorded each minute via CGM. RESULTS: Performance in the 5 km time-trial was reduced at POST (∆-7 ± 10 W, p = 0.04, η p 2 = 0.35) and improved at REC (∆12 ± 9 W from PRE, p = 0.01, η p 2 = 0.66), with reductions in peak lactate (∆-3.0 ± 2.0 mmol/L, p = 0.001, η p 2 = 0.71), peak HR (∆-6 ± 3 bpm, p < 0.001, η p 2 = 0.86), and Hooper-Mackinnon well-being scores (∆10 ± 5 a.u., p < 0.001, η p 2 = 0.79), indicating athletes were functionally overreached. The respiratory exchange ratio was suppressed at POST relative to REC during the 60% (POST: 0.80 ± 0.05, REC: 0.87 ± 0.05, p < 0.001, η p 2 = 0.74), and 80% (POST: 0.93 ± 0.05, REC: 1.00 ± 0.05, p = 0.003, η p 2 = 0.68) of HR-matched submaximal stages of the LSCT. CGM glucose was reduced during HR-matched submaximal exercise in the LSCT at POST (p = 0.047, η p 2 = 0.36), but not the 5 km time-trial (p = 0.07, η p 2 = 0.28) in overreached athletes. CONCLUSION: This preliminary investigation demonstrates a reduction in CGM-derived glucose and carbohydrate oxidation during submaximal exercise in overreached athletes. The use of CGM during submaximal exercise following standardized nutrition could be employed as a monitoring tool to detect overreaching in endurance athletes.

Blood flow restriction does not alter the early hypertrophic signaling and short-term adaptive response to resistance exercise when performed to task failure.

Previous research supports that low-load resistance exercise with blood flow restriction (LL-BFR) acutely increases physiological responses and muscle mass accrual compared with low-load resistance exercise (LL-RE) alone. However, most studies have work-matched LL-BFR and LL-RE. Completing sets to similar perceived efforts, thereby allowing for a variable amount of work, may provide a more ecologically valid approach to compare LL-BFR and LL-RE. This study aimed to examine acute signaling and training responses following LL-RE or LL-BFR performed to task failure. Ten participants had each leg randomly assigned to perform LL-RE or LL-BFR. Muscle biopsies were obtained before and 2-h after the first exercise bout and after 6-wk of training for Western blot and immunohistochemistry analyses. Repeated measure ANOVA and intraclass coefficients (ICCs) were used to compare responses of each condition. After exercise, AKT(T308) phosphorylation increased after LL-RE and LL-BFR (both ∼145% of baseline, P < 0.05) and trended for p70 S6K(T389) (LL-RE: ∼158% and LL-BFR: ∼137%, P = 0.06). BFR did not alter these responses, resulting in fair-excellent ICCs for signaling proteins involved in anabolism (ICCAKT(T308) = 0.889, P = 0.001; ICCAKT(S473) = 0.519, P = 0.074; ICCp70 S6K(T389) = 0.514, P = 0.105). After training, muscle fiber cross-sectional area and vastus lateralis whole muscle thickness were similar between conditions (ICC ≥ 0.637, P ≤ 0.031). Similar acute and chronic responses between conditions and high ICC values between legs suggest that both LL-BFR and LL-RE performed by the same person result in similar adaptations. These data support the concept that sufficient muscular exertion is a key factor for training-induced muscle hypertrophy with low-load resistance exercise independent of total work and blood flow.NEW & NOTEWORTHY The addition of blood flow restriction during low-load resistance exercise is considered to increase the signaling events and muscle growth responses to a greater extent than low-load resistance exercise alone. It remains unclear whether blood flow restriction accelerates or increases these adaptive responses, as most studies have each condition perform the same amount of work. Despite different amounts of work performed, we show similar signaling and muscle growth responses occur after low-load resistance exercise with and without blood flow restriction. Our work supports that blood flow restriction accelerates fatigue but does not increase the signaling events and muscle growth responses during low-load resistance exercise.

Reliability and validity of an indoor local positioning system for measuring external load in ice hockey players.

This study determined the reliability and validity of a Kinexon local positioning system (LPS) for measuring external load in ice hockey players during an on-ice session. Fourteen ice hockey players (25.1 y, 78.6 kg, 176.9 cm) wore two LPS sensors to examine the inter-sensor reliability of the LPS during an on-ice session, and LPS speed and acceleration were measured during 40 m linear on-ice sprints and compared to a previously validated robotic sprint device to examine LPS accuracy. The coefficient of variation (CV), standard error of measurement (SEM), and intra-class correlation coefficient (ICC) were calculated for each LPS measure. Pearson's correlations, simple linear regressions, and Bland-Altman plots were used to test the agreement and relationship between the two systems. Statistical significance was determined at p < 0.05. The majority of LPS measures were reliable (CV < 10% and ICC > 0.9) when comparing the two sensors worn by each player. Peak speed, speed at 5 m, and 0-5 m acceleration were all comparable to those reported by the robotic sprint device, with nearly perfect (peak speed and 0-5 m acceleration) and very large (speed at 5 m) magnitudes of correlation and mean biases <0.5 km/hr for speed measures and <0.01 m/s2 for acceleration. The present results demonstrate that the Kinexon LPS is reliable and accurate for investigating on-ice external load in ice hockey players when sensors are consistently secured on the back of the players' shoulder pads.

Nitrate consumption preserves HFD-induced skeletal muscle mitochondrial ADP sensitivity and lysine acetylation: A potential role for SIRT1.

Dietary nitrate supplementation, and the subsequent serial reduction to nitric oxide, has been shown to improve glucose homeostasis in several pre-clinical models of obesity and insulin resistance. While the mechanisms remain poorly defined, the beneficial effects of nitrate appear to be partially dependent on AMPK-mediated signaling events, a central regulator of metabolism and mitochondrial bioenergetics. Since AMPK can activate SIRT1, we aimed to determine if nitrate supplementation (4 mM sodium nitrate via drinking water) improved skeletal muscle mitochondrial bioenergetics and acetylation status in mice fed a high-fat diet (HFD: 60% fat). Consumption of HFD induced whole-body glucose intolerance, and within muscle attenuated insulin-induced Akt phosphorylation, mitochondrial ADP sensitivity (higher apparent Km), submaximal ADP-supported respiration, mitochondrial hydrogen peroxide (mtH2O2) production in the presence of ADP and increased cellular protein carbonylation alongside mitochondrial-specific acetylation. Consumption of nitrate partially preserved glucose tolerance and, within skeletal muscle, normalized insulin-induced Akt phosphorylation, mitochondrial ADP sensitivity, mtH2O2, protein carbonylation and global mitochondrial acetylation status. Nitrate also prevented the HFD-mediated reduction in SIRT1 protein, and interestingly, the positive effects of nitrate ingestion on glucose homeostasis and mitochondrial acetylation levels were abolished in SIRT1 inducible knock-out mice, suggesting SIRT1 is required for the beneficial effects of dietary nitrate. Altogether, dietary nitrate preserves mitochondrial ADP sensitivity and global lysine acetylation in HFD-fed mice, while in the absence of SIRT1, the effects of nitrate on glucose tolerance and mitochondrial acetylation were abrogated.

Blood flow restriction training and the high-performance athlete: science to application.

The manipulation of blood flow in conjunction with skeletal muscle contraction has greatly informed the physiological understanding of muscle fatigue, blood pressure reflexes, and metabolism in humans. Recent interest in using intentional blood flow restriction (BFR) has focused on elucidating how exercise during periods of reduced blood flow affects typical training adaptations. A large initial appeal for BFR training was driven by studies demonstrating rapid increases in muscle size, strength, and endurance capacity, even when notably low intensities and resistances, which would typically be incapable of stimulating change in healthy populations, were used. The incorporation of BFR exercise into the training of strength- and endurance-trained athletes has recently been shown to provide additive training effects that augment skeletal muscle and cardiovascular adaptations. Recent observations suggest BFR exercise alters acute physiological stressors such as local muscle oxygen availability and vascular shear stress, which may lead to adaptations that are not easily attained with conventional training. This review explores these concepts and summarizes both the evidence base and knowledge gaps regarding the application of BFR training for athletes.

Endurance and Sprint Training Improve Glycemia and V˙O2peak but only Frequent Endurance Benefits Blood Pressure and Lipidemia.

PURPOSE: Sprint interval training (SIT) has gained popularity as a time-effective alternative to moderate-intensity endurance training (END). However, whether SIT is equally effective for decreasing cardiometabolic risk factors remains debatable, as many beneficial effects of exercise are thought to be transient, and unlike END, SIT is not recommended daily. Therefore, in line with current exercise recommendations, we examined the ability of SIT and END to improve cardiometabolic health in overweight/obese males. METHODS: Twenty-three participants were randomized to perform 6 wk of constant workload SIT (3 d·wk-1, 4-6 × 30 s ~170% Wpeak, 2 min recovery, n = 12) or END (5 d·wk-1, 30-40 min, ~60% Wpeak, n = 11) on cycle ergometers. Aerobic capacity (V˙O2peak), body composition, blood pressure (BP), arterial stiffness, endothelial function, glucose and lipid tolerance, and free-living glycemic regulation were assessed pre- and posttraining. RESULTS: Both END and SIT increased V˙O2peak (END ~15%, SIT ~5%) and glucose tolerance (~20%). However, only END decreased diastolic BP, abdominal fat, and improved postprandial lipid tolerance, representing improvements in cardiovascular risk factors that did not occur after SIT. Although SIT, but not END, increased endothelial function, arterial stiffness was not altered in either group. Indices of free-living glycemic regulation were improved after END and trended toward an improvement after SIT (P = 0.06-0.09). However, glycemic control was better on exercise compared with rest days, highlighting the importance of exercise frequency. Furthermore, in an exploratory nature, favorable individual responses (V˙O2peak, BP, glucose tolerance, lipidemia, and body fat) were more prevalent after END than low-frequency SIT. CONCLUSION: As only high-frequency END improved BP and lipid tolerance, free-living glycemic regulation was better on days that participants exercised, and favorable individual responses were consistent after END, high-frequency END may favorably improve cardiometabolic health.

Blood Flow Restriction Combined with Electrical Stimulation Attenuates Thigh Muscle Disuse Atrophy.

PURPOSE: This study aimed to investigate the effects of blood flow restriction (BFR) combined with electrical muscle stimulation (EMS) on skeletal muscle mass and strength during a period of limb disuse. METHODS: Thirty healthy participants (22 ± 3 yr; 23 ± 3 kg·m-2) were randomly assigned to control (CON; n = 10), BFR alone (BFR; n = 10), or BFR combined with EMS (BFR + EMS; n = 10). All participants completed unloading of a single leg for 14 d, with no treatment (CON), or while treated with either BFR or BFR + EMS (twice daily, 5 d·wk-1). BFR treatment involved arterial three cycles of 5-min occlusion using suprasystolic pressure, each separated by 5 min of reperfusion. EMS (6 s on, 15 s off; 200 µs; 60 Hz; 15% maximal voluntary contraction [MVC]) was applied continuously throughout the three BFR cycles. Quadriceps muscle mass (whole-thigh lean mass via dual-energy x-ray absorptiometry and vastus lateralis [VL] muscle thickness via ultrasound) and strength (via knee extension MVC) were assessed before and after the 14-d unloading period. RESULTS: After limb unloading, whole-thigh lean mass decreased in the control group (-4% ± 1%, P < 0.001) and BFR group (-3% ± 2%, P = 0.001), but not in the BFR + EMS group (-0.3% ± 3%, P = 0.8). VL muscle thickness decreased in the control group (-4% ± 4%, P = 0.005) and was trending toward a decrease in the BFR group (-8% ± 11%, P = 0.07) and increase in the BFR + EMS group (+5% ± 10%, P = 0.07). Knee extension MVC decreased over time (P < 0.005) in the control group (-18% ± 15%), BFR group (-10% ± 13%), and BFR + EMS group (-18% ± 15%), with no difference between groups (P > 0.5). CONCLUSION: Unlike BFR performed in isolation, BFR + EMS represents an effective interventional strategy to attenuate the loss of muscle mass during limb disuse, but it does not demonstrate preservation of strength.

Vascular Function Is Differentially Altered by Distance after Prolonged Running.

PURPOSE: Ultraendurance exercise is steadily growing in popularity; however, the effect of increasingly prolonged durations of exercise on the vascular endothelium is unknown. The aim of this study was to characterize the effect of various ultramarathon running distances on vascular form and function. METHODS: We evaluated vascular endothelial function via flow-mediated dilation (FMD) in the superficial femoral artery, as well as microvascular function, inflammatory factors, and central artery stiffness, before and after participants completed 25-km (7M:2F), 50-km (11M:10F), 80-km (9M:4F), or 160-km (9M:2F) trail races all run on the same day and course. RESULTS: Completion required 149 ± 20, 386 ± 111, 704 ± 130, and 1470 ± 235 min, with corresponding average paces of 6.0 ± 0.8, 7.7 ± 2.2, 8.6 ± 1.3, and 9.6 ± 1.3 min·km-1, respectively. At baseline, there were no differences in participant characteristics across race distance groups. Shear rate stimulus trended toward an increase after the race (P = 0.07), but resting postrace artery diameter (P < 0.001) was elevated to a similar extent in all conditions. There was a reduction in FMD after the 50-km race (Δ -1.9% ± 2.2%, P < 0.01), but not the 25-km (Δ +0.3% ± 2.9%, P = 0.8), the 80-km (Δ -1.5% ± 3.2%, P = 0.1), or the 160-km (Δ +0.5% ± 2.5%, P = 0.5) race. Inflammatory markers increased most after 160 km, but arterial stiffness and microvascular function were not differently affected by race distance. CONCLUSIONS: Although the superficial femoral artery baseline diameter was larger postexercise regardless of race distance, only the 50-km race reduced FMD, whereas a short-duration higher-intensity race (25 km) and longer-duration lower-intensity races (160 km) did not. Therefore, a 50-km ultramarathon may represent the intersection between higher-intensity exercise over a prolonged duration, causing reduced endothelial function not seen in shorter or longer distances.

Alterations in Cardiac Function Following Endurance Exercise Are Not Duration Dependent.

Cardiac function has been shown to transiently decrease following prolonged exercise, with greater durations related to increased impairment. However, the prospective assessment of exercise duration on cardiac performance is rare, and the influence of relative exercise intensity is typically not assessed in relation to these changes. The aim of this study was to determine whether progressively longer running distances over the same course would elicit greater cardiac impairment. The present investigation examined cardiac alterations in 49 athletes, following trail-running races of 25, 50, 80, and 160 km, performed on the same course on the same day. Echocardiography, including conventional and speckle tracking imaging, was performed with legs-raised to 60° to mitigate alterations in preload both pre- and post-race. Race-intensities were monitored via heart rate (HR). Following the races, mean arterial pressure (Δ-11 ± 7 mmHg, P < 0.0001), and HR (Δ19 ± 14 bpm, P < 0.0001) were altered independent of race distance. Both left and right ventricular (LV and RV) diastolic function were reduced (ΔLV E/A -0.54 ± 0.49, P < 0.0001; ΔRV A' + 0.02 ± 0.04 m/s, P = 0.01) and RV systolic function decreased (ΔTAPSE -0.25 ± 0.9 cm, P = 0.01), independent of race distance. Cardiac impairment was not apparent using speckle tracking analysis with cubic spline interpolation. While race duration was unrelated to cardiac alterations, increased racing HR was related to greater RV base dilation (r = -0.37, P = 0.03). Increased time spent at higher exercise intensities was related to reduced LV ejection fraction following 25 km (r = -0.81, P = 0.03), LV systolic strain rate following 50 km (r = 0.59, P = 0.04), and TAPSE (r = -0.81, P = 0.03) following 80 km races. Increased running duration did not affect the extent of exercise-induced cardiac fatigue, however, intensity may be a greater driver of cardiac alterations.

The Effect of Body Position on Measures of Arterial Stiffness in Humans.

BACKGROUND: The dynamics ofpulsatile waveforms travelling the central aorta are governed by pressures and arterial compliance. Arterial stiffness, the inverse of compliance, is an independent risk factor for cardiovascular disease and has been suggested as a superior risk index compared to brachial blood pressure (BP). Arterial stiffness is typically measured via carotid-femoral pulse wave velocity (cfPWV) in the supine position; however, different body positions alter orthostatic column height, impacting heart rate and BP. The purpose of this investigation was to examine different body positions and associated measures of cfPWV. METHODS: Measures of resting cfPWV were acquired simultaneously with BP during supine, head-up tilt (HUT), head-down tilt (HDT), and Fowler's position, all at 45 degrees from vertical. RESULTS: Relative to supine, cfPWV was increased 1.1 ± 1.0 and 1.5 ± 1.1 m/s (both p ≤ 0.001) in HUT and Fowler's positions, respectively. Supine to HDT cfPWV was unaltered (p = 0.1), despite an increase in mean arterial pressure (MAP) (10 ± 9 mm Hg). When cfPWV was normalized to MAP, the same effects persisted (p ≤ 0.001). CONCLUSION: Increasing orthostatic column height by changing posture independently increases resting cfPWV, concurrent with increases in BP. This data demonstrates the impact of body position on measures of central artery stiffness, which may have clinical relevance.

Low-load resistance training to task failure with and without blood flow restriction: muscular functional and structural adaptations.

The application of blood flow restriction (BFR) during resistance exercise is increasingly recognized for its ability to improve rehabilitation and for its effectiveness in increasing muscle hypertrophy and strength among healthy populations. However, direct comparison of the skeletal muscle adaptations to low-load resistance exercise (LL-RE) and low-load BFR resistance exercise (LL-BFR) performed to task failure is lacking. Using a within-subject design, we examined whole muscle group and skeletal muscle adaptations to 6 wk of LL-RE and LL-BFR training to repetition failure. Muscle strength and size outcomes were similar for both types of training, despite ~33% lower total exercise volume (load × repetition) with LL-BFR than LL-RE (28,544 ± 1,771 vs. 18,949 ± 1,541 kg, P = 0.004). After training, only LL-BFR improved the average power output throughout the midportion of a voluntary muscle endurance task. Specifically, LL-BFR training sustained an 18% greater power output from baseline and resulted in a greater change from baseline than LL-RE (19 ± 3 vs. 3 ± 4 W, P = 0.008). This improvement occurred despite histological analysis revealing similar increases in capillary content of type I muscle fibers following LL-RE and LL-BFR training, which was primarily driven by increased capillary contacts (4.53 ± 0.23 before training vs. 5.33 ± 0.27 and 5.17 ± 0.25 after LL-RE and LL-BFR, respectively, both P < 0.05). Moreover, maximally supported mitochondrial respiratory capacity increased only in the LL-RE leg by 30% from baseline (P = 0.006). Overall, low-load resistance training increased indexes of muscle oxidative capacity and strength, which were not further augmented with the application of BFR. However, performance on a muscle endurance test was improved following BFR training.

Evaluating the Anti-cancer Efficacy of a Synthetic Curcumin Analog on Human Melanoma Cells and Its Interaction with Standard Chemotherapeutics.

Melanoma is the leading cause of skin-cancer related deaths in North America. Metastatic melanoma is difficult to treat and chemotherapies have limited success. Furthermore, chemotherapies lead to toxic side effects due to nonselective targeting of normal cells. Curcumin is a natural product of Curcuma longa (turmeric) and has been shown to possess anti-cancer activity. However, due to its poor bioavailability and stability, natural curcumin is not an effective cancer treatment. We tested synthetic analogs of curcumin that are more stable. One of these derivatives, Compound A, has shown significant anti-cancer efficacy in colon, leukemia, and triple-negative inflammatory breast cancer cells. However, the effects of Compound A against melanoma cells have not been studied before. In this study, for the first time, we demonstrated the efficacy of Compound A for the selective induction of apoptosis in melanoma cells and its interaction with tamoxifen, taxol, and cisplatin. We found that Compound A induced apoptosis selectively in human melanoma cells by increasing oxidative stress. The anti-cancer activity of Compound A was enhanced when combined with tamoxifen and the combination treatment did not result in significant toxicity to noncancerous cells. Additionally, Compound A did not interact negatively with the anti-cancer activity of taxol and cisplatin. These results indicate that Compound A could be developed as a selective and effective melanoma treatment either alone or in combination with other non-toxic agents like tamoxifen.

Blood flow restricted resistance exercise and reductions in oxygen tension attenuate mitochondrial H2 O2 emission rates in human skeletal muscle.

KEY POINTS: Blood flow restricted resistance exercise (BFR-RE) is capable of inducing comparable adaptations to traditional resistance exercise (RE), despite a lower total exercise volume. It has been suggested that an increase in reactive oxygen species (ROS) production may be involved in this response; however, oxygen partial pressure ( PO2 ) is reduced during BFR-RE, and the influence of PO2 on mitochondrial redox balance remains poorly understood. In human skeletal muscle tissue, we demonstrate that both maximal and submaximal mitochondrial ROS emission rates are acutely decreased 2 h following BFR-RE, but not RE, occurring along with a reduction in tissue oxygenation during BFR-RE. We further suggest that PO2 is involved in this response because an in vitro analysis revealed that reducing PO2 dramatically decreased mitochondrial ROS emissions and electron leak to ROS. Altogether, these data indicate that mitochondrial ROS emission rates are attenuated following BFR-RE, and such a response is likely influenced by reductions in PO2 . ABSTRACT: Low-load blood flow restricted resistance exercise (BFR-RE) training has been proposed to induce comparable adaptations to traditional resistance exercise (RE) training, however, the acute signalling events remain unknown. Although a suggested mechanism of BFR-RE is an increase in reactive oxygen species (ROS) production, oxygen partial pressure ( PO2 ) is reduced during BFR-RE, and the influence of O2 tension on mitochondrial redox balance remains ambiguous. We therefore aimed to determine whether skeletal muscle mitochondrial bioenergetics were altered following an acute bout of BFR-RE or RE, and to further examine the role of PO2 in this response. Accordingly, muscle biopsies were obtained from 10 males at rest and 2 h after performing three sets of single-leg squats (RE or BFR-RE) to failure at 30% one-repetition maximum. We determined that mitochondrial respiratory capacity and ADP sensitivity were not altered in response to RE or BFR-RE. Although maximal (succinate) and submaximal (non-saturating ADP) mitochondrial ROS emission rates were unchanged following RE, BFR-RE attenuated these responses by ∼30% compared to pre-exercise, occurring along with a reduction in skeletal muscle tissue oxygenation during BFR-RE (P < 0.01 vs. RE). In a separate cohort of participants, evaluation of mitochondrial bioenergetics in vitro revealed that mild O2 restriction (50 µm) dramatically attenuated maximal (∼4-fold) and submaximal (∼50-fold) mitochondrial ROS emission rates and the fraction of electron leak to ROS compared to room air (200 µm). Combined, these data demonstrate that mitochondrial ROS emissions are attenuated following BFR-RE, a response which may be mediated by a reduction in skeletal muscle PO2 .

Corrigendum: Cancer Cell Mitochondria Targeting by Pancratistatin Analogs is Dependent on Functional Complex II and III.

This corrects the article DOI: 10.1038/srep42957.

Exploiting mitochondrial and oxidative vulnerabilities with a synthetic analog of pancratistatin in combination with piperlongumine for cancer therapy.

Harsh adverse effects as a result of nonspecific targeting of chemotherapeutics currently pose obstacles in cancer therapy; thus, it would be invaluable to devise novel approaches to specifically target cancer cells. The natural compound pancratistatin (PST) has been shown to preferentially induce apoptosis in a variety of cancer cell types. Recently, several analogs of PST were shown to be efficacious in inducing apoptosis in a variety of aggressive cancer cell types via cancer cell mitochondrial targeting; it caused dissipation of mitochondrial membrane potential and decreased oxygen consumption, and with isolated mitochondria, it induced the release of apoptogenic factors. The natural compound piperlongumine has been shown to target the stress response to reactive oxygen species in cancer cells. We explored the combinatorial potential of two small molecules (SVTH-6 and piperlongumine) that target these vulnerabilities in cancer cells. Interestingly, when combined with the PST analog, SVTH-6, an increase in mitochondrial dysfunction was observed, leading to an enhanced cytotoxic effect against several human cancer cell types. Additionally, this combination treatment was effective in reducing cancer cell growth in physiologically more relevant 3-dimensional spheroid cell cultures. This enhanced effect was found to be dependent on reactive oxygen species generation because an antioxidant could rescue cancer cells from this combination treatment. Importantly, noncancerous cells were markedly less sensitive to this combination treatment. Thus, targeting mitochondrial and oxidative stress vulnerabilities of cancer cells could be an effective strategy for cancer therapy.-Ma, D., Gilbert, T., Pignanelli, C., Tarade, D., Noel, M., Mansour, F., Gupta, M., Ma, S., Ropat, J., Curran, C., Vshyvenko, S., Hudlicky, T., Pandey. S. Exploiting mitochondrial and oxidative vulnerabilities with a synthetic analog of pancratistatin in combination with piperlongumine for cancer therapy.

Selective Targeting of Cancer Cells by Oxidative Vulnerabilities with Novel Curcumin Analogs.

Recently, research has focused on targeting the oxidative and metabolic vulnerabilities in cancer cells. Natural compounds like curcumin that target such susceptibilities have failed further clinical advancements due to the poor stability and bioavailability as well as the need of high effective doses. We have synthesized and evaluated the anti-cancer activity of several monocarbonyl analogs of curcumin. Interestingly, two novel analogs (Compound A and I) in comparison to curcumin, have increased chemical stability and have greater anti-cancer activity in a variety of human cancer cells, including triple-negative, inflammatory breast cancer cells. In particular, the generation of reactive oxygen species was selective to cancer cells and occurred upstream of mitochondrial collapse and execution of apoptosis. Furthermore, Compound A in combination with another cancer-selective/pro-oxidant, piperlongumine, caused an enhanced anti-cancer effect. Most importantly, Compound A was well tolerated by mice and was effective in inhibiting the growth of human triple-negative breast cancer and leukemia xenografts in vivo when administered intraperitoneally. Thus, exploiting oxidative vulnerabilities in cancer cells could be a selective and efficacious means to eradicate malignant cells as demonstrated by the curcumin analogs presented in this report with high therapeutic potential.

Structurally simplified biphenyl combretastatin A4 derivatives retain in vitro anti-cancer activity dependent on mitotic arrest.

The cis-stilbene, combretastatin A4 (CA4), is a potent microtubule targeting and vascular damaging agent. Despite promising results at the pre-clinical level and extensive clinical evaluation, CA4 has yet to be approved for therapeutic use. One impediment to the development of CA4 is an inherent conformational instability about the ethylene linker, which joins two aromatic rings. We have previously published preliminary data regarding structurally simplified biphenyl derivatives of CA4, lacking an ethylene linker, which retain anti-proliferative and pro-apoptotic activity, albeit at higher doses. Our current study provides a more comprehensive evaluation regarding the anti-proliferative and pro-apoptotic properties of biphenyl CA4 derivatives in both 2D and 3D cancerous and non-cancerous cell models. Computational analysis has revealed that cytotoxicity of CA4 and biphenyl analogues correlates with predicted tubulin affinity. Additional mechanistic evaluation of the biphenyl derivatives found that their anti-cancer activity is dependent on prolonged mitotic arrest, in a similar manner to CA4. Lastly, we have shown that cancer cells deficient in the extrinsic pathway of apoptosis experience delayed cell death following treatment with CA4 or analogues. Biphenyl derivatives of CA4 represent structurally simplified analogues of CA4, which retain a similar mechanism of action. The biphenyl analogues warrant in vivo examination to evaluate their potential as vascular damaging agents.