Tamoxifen and oestrogen both protect the rat muscle against physiological damage

Safety and efficacy of tamoxifen in boys with Duchenne muscular dystrophy (TAMDMD): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

Drug repurposing could provide novel treatment options for Duchenne muscular dystrophy. Because tamoxifen-an oestrogen receptor regulator-reduced signs of muscular pathology in a Duchenne muscular dystrophy mouse model, we aimed to assess the safety and efficacy of tamoxifen in humans as an adjunct to corticosteroid therapy over a period of 48 weeks.

METHODS

We did a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 12 study centres in seven European countries. We enrolled ambulant boys aged 6·5-12·0 years with a genetically confirmed diagnosis of Duchenne muscular dystrophy and who were on stable corticosteroid treatment for more than 6 months. Exclusion criteria included ophthalmological disorders, including cataracts, and haematological disorders. We randomly assigned (1:1) participants using an online randomisation tool to either 20 mg tamoxifen orally per day or matched placebo, stratified by centre and corticosteroid intake. Participants, caregivers, and clinical investigators were masked to treatment assignments. Tamoxifen was taken in addition to standard care with corticosteroids, and participants attended study visits for examinations every 12 weeks. The primary efficacy outcome was the change from baseline to week 48 in scores on the D1 domain of the Motor Function Measure in the intention-to-treat population (defined as all patients who fulfilled the inclusion criteria and began treatment). This study is registered with ClinicalTrials.gov (NCT03354039) and is completed.

FINDINGS

Between May 24, 2018, and Oct 14, 2020, 95 boys were screened for inclusion, and 82 met inclusion criteria and were initially enrolled into the study. Three boys were excluded after initial screening due to cataract diagnosis or revoked consent directly after screening, but before randomisation. A further boy assigned to the placebo group did not begin treatment. Therefore, 40 individuals assigned tamoxifen and 38 allocated placebo were included in the intention-to-treat population. The primary efficacy outcome did not differ significantly between tamoxifen (-3·05%, 95% CI -7·02 to 0·91) and placebo (-6·15%, -9·19 to -3·11; 2·90% difference, -3·02 to 8·82, p=0·33). Severe adverse events occurred in two participants: one participant who received tamoxifen had a fall, and one who received placebo suffered a panic attack. No deaths or life-threatening serious adverse events occurred. Viral infections were the most common adverse events.

INTERPRETATION

Tamoxifen was safe and well tolerated, but no difference between groups was reported for the primary efficacy endpoint. Slower disease progression, defined by loss of motor function over time, was indicated in the tamoxifen group compared with the placebo group, but differences in outcome measures were neither clinically nor statistically significant. Currently, we cannot recommend the use of tamoxifen in daily clinical practice as a treatment option for boys with Duchenne muscular dystrophy due to insufficient clinical evidence.

FUNDING

Thomi Hopf Foundation, ERA-Net, Swiss National Science Foundation, Duchenne UK, Joining Jack, Duchenne Parent Project, Duchenne Parent Project Spain, Fondation Suisse de Recherche sur les Maladies Musculaires, Association Monegasque contre les Myopathies.

A state-of-the-art review of tamoxifen as a potential therapeutic for duchenne muscular dystrophy

Introduction: This systematic review analyzes the state-of-art repurposing of the drug tamoxifen (TAM) in the treatment of Duchenne Muscular Dystrophy (DMD), including its mechanism of action, toxicological findings, and past and ongoing clinical trials. A parallel aim of this work was to explore whether evidence exists to support further funding of investigation on TAM treatment for DMD patients with a pivotal trial in young patients. Bringing evidence and answering the scientific question of whether this treatment could improve the quality-of-life of DMD patients is needed to establish guidelines and accelerate access to promising therapies for DMD patients. Methods: The search was conducted in January 2022 utilizing PubMed. All MeSH terms for "Duchenne Muscular Dystrophy" and "tamoxifen" were used. The inclusion and exclusion criteria were defined according to the PICOS framework. Results: The included publications all explored the use of TAM with promising outcomes in muscular strength recovery and a decrease in pathology biomarkers. Two reviews recognize TAM as a potential treatment for DMD patients and state that drug repurposing plays a crucial role in the quest for a drug candidate to treat this rare disease. Conclusion: According to available data, TAM shows promise as a treatment for DMD, both pharmacologically and clinically. However, published data to date are insufficient to definitively conclude the beneficial effect of TAM on quality-of-life and ultimately survival, particularly in the youngest patients diagnosed with DMD.

Tamoxifen treatment ameliorates contractile dysfunction of Duchenne muscular dystrophy stem cell-derived cardiomyocytes on bioengineered substrates

Duchenne muscular dystrophy (DMD) is a progressive genetic myopathy that leads to heart failure from dilated cardiomyopathy by early adulthood. Recent evidence suggests that tamoxifen, a selective estrogen receptor modulator widely used to treat breast cancer, ameliorates DMD cardiomyopathy. However, the mechanism of action of 4-hydroxytamoxifen, the active metabolite of tamoxifen, on cardiomyocyte function remains unclear. To examine the effects of chronic 4-hydroxytamoxifen treatment, we used state-of-the-art human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and a bioengineered platform to model DMD. We assessed the beating rate and beating velocity of iPSC-CMs in monolayers and as single cells on micropatterns that promote a physiological cardiomyocyte morphology. We found that 4-hydroxytamoxifen treatment of DMD iPSC-CMs decreased beating rate, increased beating velocity, and ameliorated calcium-handling deficits, leading to prolonged viability. Our study highlights the utility of a bioengineered iPSC-CM platform for drug testing and underscores the potential of repurposing tamoxifen as a therapy for DMD cardiomyopathy.

Melatonin reverses mitochondria dysfunction and oxidative stress-induced apoptosis of Sudan I-exposed mouse oocytes

Sudan I is one of the industry dyes and widely used in cosmetics, wax agent, solvent and textile. Sudan I has multiple toxicity such as carcinogenicity, mutagenicity, genotoxicity and oxidative damage. However, Sudan I has been illegally used as colorant in food products, triggering worldwide attention about food safety. Nevertheless, the toxicity of Sudan I on reproduction, particularly on oocyte maturation is still unclear. In the present study, using mouse in vivo models, we report the toxicity effects of Sudan I on mouse oocyte. The results reflect that Sudan I exposure disrupts spindle organization and chromosomes alignment as well as cortical actin distribution, thus leading to the failure of polar body extrusion. Based on the transcriptome results, it is found that the exposure of Sudan I leads to the change in expression of 764 genes. Moreover, it's further reflected that the damaging effects of Sudan I are mediated by the destruction of mitochondrial functions, which induces the accumulated ROS to stimulate oxidative stress-induced apoptosis. As an endogenous hormone, melatonin within the ovarian follicle plays function on improving oocyte quality and female reproduction by efficiently suppressing oxidative stress. Moreover, melatonin supplementation also improves oocyte quality and increases fertilization rate during in vitro culture. Consistent with these, we find that in vivo supplementation of melatonin efficaciously suppresses mitochondrial dysfunction and the accompanying apoptosis, thus reverses oocyte meiotic deteriorations. Collectively, our results prove the reproduction toxicity of Sudan I for the exposure of Sudan I reduces the oocyte quality, and demonstrate the protective effects of melatonin against Sudan I-induced meiotic deteriorations.

Effects of Creatine Supplementation on Muscle Fatigue in Rats Receiving Doxorubicin Treatment

The purpose of this study was to investigate the effects of in vivo creatine monohydrate (Cr) supplementation on doxorubicin (Dox)-induced muscle dysfunction. Male rats were fed a diet supplemented with 3% Cr or a standard chow for 2 wk. After 2 wk of feeding, animals received Dox or saline as a placebo. Five days post-injection, grip strength was measured, and muscle fatigue was analyzed ex vivo. When compared with controls, a significantly lower grip strength was observed with Dox treatment, but no significant handgrip difference was observed with Cr feeding prior to Dox treatment when compared to controls. In the isolated muscle fatigue experiments, solei (primarily type I muscle) from controls produced significantly less force than baseline at 60 s and solei from Dox treated rats produced significantly less force than baseline at 30 s; however, Cr feeding prior to Dox produced significantly less force than baseline at 60 s. In the primarily type II EDL, a decline in force production from baseline was observed at 50 s in controls and Cr + Dox and at 20 s in standard chow + Dox. Cr attenuated the increase in fatigue that accompanies Dox treatment suggesting that Cr supplementation may have use in managing Dox myotoxicity.

Time Course of Oxidative Stress, Inflammation, and Muscle Damage Markers for 5 Days After a Soccer Match: Effects of Sex and Playing Position

Souglis, A, Bogdanis, GC, Chryssanthopoulos, C, Apostolidis, N, and Geladas, ND. Time course of oxidative stress, inflammation and muscle damage markers for 5 days after a soccer match: Effects of sex and playing position. J Strength Cond Res 32(7): 2045-2054, 2018-This study examined the influence of sex and playing position on the time course of selected oxidative stress, inflammation, and muscle damage markers after an official soccer match. Sixty professional soccer players (30 men and 30 women) were divided into 3 groups, according to their playing position: defenders, midfielders, and attackers. Each group consisted of 10 male and 10 female players. Sixty healthy volunteers (30 men and 30 women) served as control. Blood samples were taken before and after the match and daily for 5 days after the match. Analysis of variance revealed different responses over time between sex and playing positions, as shown by the 3-way interaction, for creatine kinase (CK), protein carbonyls (PCs), catalase, fibrinogen, uric acid (UA), lactate dehydrogenase, reduced glutathione, C-reactive protein, and interleukin 6 (p < 0.01). Male players had higher values compared with women of the same playing position, for all oxidative, inflammatory, and muscle damage indices (p < 0.01). Also, in both sexes, midfielders had higher peaks in all indices compared with defenders (p < 0.05). Five days after the game CK and UA concentrations had not returned to pregame levels in any exercise group, whereas PCs were still elevated in male midfielders and attackers (p < 0.05). These results show that sex and playing position influence the time course of selected oxidative stress, inflammation, and muscle damage markers after an official soccer game. This information should be taken into account by practitioners for the design of training programs after match play.

The effects of a multi-ingredient supplement on markers of muscle damage and inflammation following downhill running in females

BACKGROUND

The effects of a multi-ingredient performance supplement (MIPS) on markers of inflammation and muscle damage, perceived soreness and lower limb performance are unknown in endurance-trained female athletes. The purpose of this study was to determine the impact of MIPS (NO-Shotgun®) pre-loaded 4 weeks prior to a single-bout of downhill running (DHR) on hsC-Reactive Protein (hsCRP), interleukin (IL)-6, creatine kinase (CK), muscle soreness, lower limb circumferences and performance.

METHOD

Trained female runners (n = 8; 29 ± 5.9 years) (VO_2max: ≥ 50 ml^-1.kg^-1.min^-1, midfollicular phase (7-11 days post-menses) were randomly assigned in a double-blind manner into two groups: MIPS (n = 4) ingested one serving of NO Shotgun daily for 28 days prior to DHR and 30 min prior to all post-testing visits; Control (CON) (n = 4) consumed an isocaloric maltodextrin placebo in an identical manner to MIPS. hsCRP, IL-6, CK, perceived soreness, limb circumferences, and performance measures (flexibility, squat jump peak power) were tested on 5 occasions; immediately before (PRE), immediately post-DHR, 24, 48 and 72 h post-DHR.

RESULTS

There were main effects of time for CK (p = 0.05), pain pressure threshold (right tibialis anterior (p = 0.010), right biceps femoris (p = 0.01), and left iliotibial band (ITB) (p = 0.05) across all time points), and maximum squat jump power (p = 0.04). Compared with 24 h post-DHR, maximum squat jump power was significantly lower at 48 h post-DHR (p = 0.05). Lower body perceived soreness was significantly increased at 24 h (p = 0.02) and baseline to 48 h (p = 0.02) post DHR. IL-6 peaked immediately post-DHR (p = 0.03) and hsCRP peaked at 24 h post-DHR (p = 0.06). Calculation of effect sizes indicated a moderate attenuation of hsCRP in MIPS at 72 h post-DHR.

CONCLUSIONS

Consumption of MIPS for 4 weeks prior to a single bout of DHR attenuated inflammation three days post, but did not affect perceived soreness and muscle damage markers in endurance trained female runners following a single bout of DHR.

Supplementation Strategies to Reduce Muscle Damage and Improve Recovery Following Exercise in Females: A Systematic Review

Exercise-induced muscle damage (EIMD) caused by unaccustomed or strenuous exercise can result in reduced muscle force, increased muscle soreness, increased intramuscular proteins in the blood, and reduced performance. Pre- and post-exercise optimal nutritional intake is important to assist with muscle-damage repair and reconditioning to allow for an accelerated recovery. The increased demand for training and competing on consecutive days has led to a variety of intervention strategies being used to reduce the negative effects of EIMD. Nutritional intervention strategies are largely tested on male participants, and few report on sex-related differences relating to the effects of the interventions employed. This review focuses on nutritional intervention strategies employed to negate the effects of EIMD, focussing solely on females.

Influence of ovarian hormones on strength loss in healthy and dystrophic female mice

PURPOSE

The primary objective of this study was to determine whether strength loss and recovery after eccentric contractions are impaired in healthy and dystrophic female mice with low levels of ovarian hormones.

METHODS

Female C57BL/6 (wild-type) or mdx mice were randomly assigned to ovarian-intact (Sham) and ovariectomized (Ovx) groups. Anterior crural muscles were tested for susceptibility to injury from 150 or 50 eccentric contractions in wild-type and mdx mice, respectively. An additional experiment challenged mdx mice with a 2-wk treadmill running protocol followed by an eccentric contraction injury to posterior crural muscles. Functional recovery from injury was evaluated in wild-type mice by measuring isometric torque 3, 7, 14, or 21 d after injury.

RESULTS

Ovarian hormone deficiency in wild-type mice did not affect susceptibility to injury because the ∼50% isometric torque loss after eccentric contractions did not differ between Sham and Ovx mice (P = 0.121). Similarly, in mdx mice, hormone deficiency did not affect the percent of preinjury isometric torque lost by anterior crural muscles after eccentric contractions (P = 0.952), but the percent of preinjury torque in posterior crural muscles was lower in Ovx than in Sham mice (P = 0.014). Recovery from injury in wild-type mice was affected by hormone deficiency. Sham mice recovered preinjury isometric strength by 14 d (96% ± 2%), whereas Ovx mice maintained deficits at 14 and 21 d after injury (80% ± 3% and 84% ± 2%, P < 0.001).

CONCLUSIONS

Ovarian hormone status did not affect the vulnerability of skeletal muscle to strength loss after eccentric contractions. However, ovarian hormone deficiency did impair the recovery of muscle strength in female mice.

Effect of tamoxifen on fatty degeneration and atrophy of rotator cuff muscles in chronic rotator cuff tear: An animal model study

Fatty degeneration of the rotator cuff muscles is an irreversible change resulting from chronic rotator cuff tear and is associated with poor clinical outcomes following rotator cuff repair. We evaluated the effect of Tamoxifen, a competitive estrogen receptor inhibitor, on fatty degeneration using a mouse model for chronic rotator cuff tear. Sixteen adult mice were divided into two diet groups (Tamoxifen vs. Regular) and subjected to surgical creation of a large rotator cuff tear and suprascapular nerve transection in their left shoulder with the right shoulder serving as a control. The rotator cuff muscles were harvested at 16 weeks and subjected to histology and RT-PCR for adipogenic and myogenic markers. Histology showed substantially decreased atrophy and endomysial inflammation in Tamoxifen group, but no significant differences in the amount of intramuscular adipocytes and lipid droplets compared to the Regular group. With RT-PCR, the operated shoulders showed significant upregulation of myogenin and PPAR-γ, and downregulation of myostatin compared to the nonsurgical shoulder. No significant differences of gene expression were found between the two diet groups. Our study demonstrated that tamoxifen diet leads to decreased muscle atrophy and inflammatory changes following chronic rotator cuff tear, but has no apparent effect on adipogenesis.

Hepatoprotective effect of 17β-estradiol as antioxidant modulators against stress damage

BACKGROUND

Liver is one of the most important organs affected by exercise. According to the literature a few study to date has investigated the effects of estrogen supplementation on exercise-induced oxidative stress in liver tissue of rats.

OBJECTIVES

We aimed to investigate the effects of estrogen supplementation on oxidative stress markers in liver tissue of exercised rats.

MATERIALS AND METHODS

Male rats (n = 35) were divided as estrogen supplemented (n = 18) and non-supplemented groups (n = 17); these groups were further divided as rest and eccentric exercised groups. Eccentric exercise groups were further divided as rats killed after 1 hour and 48 hours of eccentric exercise. Estrogen (10 mg/kg) was administered subcutaneously for 30 days. Eccentric exercise was applied as treadmill run (15° downhill, 20 m/min) consisting of periods of "5 min" run and 2 min rest repeated 18 times. The rat liver was examined biochemically and histologically. Activities of GST, GSH-Px, CAT, SOD and MDA concentration were also measured spectrophotometrically.

RESULTS

Some disruptions were detected in experimental groups compared with the control group. Additionally, exercise training caused an increase in SOD and decrease in GSH-Px activities in some experimental groups. SOD activities increased significantly in group 3 (Estrogen (-), eccentric exercise (+) killed (after 1 h), compared with group 5 (Estrogen (-), eccentric exercise (+) killed (after 48 h). On the other hand, GSH-Px activities were also significantly decreased in groups 3, 4 and 5 compared with the control group. Leukocyte infiltration in liver increased after 48 hours compared with after 1 hour and estrogen supplementation was not able to prevent this infiltration.

CONCLUSIONS

Estrogen seemed to be not very effective to prevent eccentric exercise-induced liver damage.

The anticancer drug tamoxifen counteracts the pathology in a mouse model of duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe disorder characterized by progressive muscle wasting,respiratory and cardiac impairments, and premature death. No treatment exists so far, and the identification of active substances to fight DMD is urgently needed. We found that tamoxifen, a drug used to treat estrogen-dependent breast cancer, caused remarkable improvements of muscle force and of diaphragm and cardiac structure in the mdx(5Cv) mouse model of DMD. Oral tamoxifen treatment from 3 weeks of age for 15 months at a dose of 10 mg/kg/day stabilized myofiber membranes, normalized whole body force, and increased force production and resistance to repeated contractions of the triceps muscle above normal values. Tamoxifen improved the structure of leg muscles and diminished cardiac fibrosis by~ 50%. Tamoxifen also reduced fibrosis in the diaphragm, while increasing its thickness,myofiber count, and myofiber diameter, thereby augmenting by 72% the amount of contractile tissue available for respiratory function. Tamoxifen conferred a markedly slower phenotype to the muscles.Tamoxifen and its metabolites were present in nanomolar concentrations in plasma and muscles,suggesting signaling through high-affinity targets. Interestingly, the estrogen receptors ERa and ERb were several times more abundant in dystrophic than in normal muscles, and tamoxifen normalized the relative abundance of ERb isoforms. Our findings suggest that tamoxifen might be a useful therapy for DMD.

Selective estrogen receptor-β activation stimulates skeletal muscle growth and regeneration

There is increasing evidence suggesting that estrogens augment skeletal muscle regeneration processes after injury. To study the contribution of estrogen receptors α and β (ERα and ERβ) during muscle regeneration, skeletal muscles of ovariectomized (OVX) rats, as well as ERα- and ERβ-knockout (αErko and βErko) mice, were injured with a myotoxin (notexin). OVX rats were simultaneously treated with the ER-selective ligands genistein, ERα agonist 16α-LE2 (alpha), ERβ agonist 8β-VE2 (beta), or 17β-estradiol (E(2)). OVX rats showed significantly elevated serum creatine kinase (CK) activity after muscle injury compared to intact sham-treated animals. Treatment with ER ligands significantly reduced CK activity. TNF-α, IL-10, and MCP-1 expression served to characterize immune responses. Treatment with all ER ligands, but particularly E(2) and beta, reduced TNF-α, but elevated MCP-1 and IL-10 expression. PCNA and MyoD expression served to define satellite cell activation and proliferation and were found to be up-regulated by beta and E(2). To further study muscle regeneration responses, expression of the embryonic myosin heavy chain (MHC) was analyzed. Beta and E(2) but not alpha increased embryonic MHC expression compared to OVX. The absence of ERβ in βErko mice negatively affected CK activity levels and expression of satellite cell and muscle regeneration markers (MHC embryonic, MyoD, Pax7) compared with αErko and wild-type mice. In a classic Hershberger assay using male rats, beta stimulated muscle growth, accompanied by a strong induction of IGF-1 expression. Our data provide evidence that ERβ signaling is involved in the regulation of skeletal muscle growth and regeneration by stimulating anabolic pathways, activating satellite cells and modulating immune responses.

A rehabilitation exercise program to remediate skeletal muscle atrophy in an estrogen-deficient organism may be ineffective

To determine rehabilitation exercise program effects under hormone deficient (ovariectomy or OVX) and hormone supplemented [OVX + 17-beta estradiol (E2)] conditions. Mature female rats (n = 123) were assigned to OVX or OVX + E2-supplemented groups. OVX and OVX + E2 groups were allocated to one of four conditions: (1) control, (2) hindlimb unweighted (HLU) for 4 weeks to induce muscle atrophy, (3) cage Recovery for 2 weeks after HLU, and (4) Recovery with 2 weeks of rehabilitation exercise program after 4 weeks of HLU. Atrophy following HLU was comparable for OVX and OVX + E2-supplemented rats and was significant in all muscles examined (soleus, tibialis anterior, plantaris, gastrocnemius, quadriceps). Also significant with HLU was the decline in muscle force (P < 0.05) in soleus, plantaris, gastrocnemius and tibialis anterior (quadriceps not tested). There were trends toward return of muscle mass in Recovery OVX and Recovery OVX + E2 groups but only the E2 supplemented OVX rats had return of muscle mass (4/5 muscles studied) with exercise. Peak tetanic tension (Po) returned to control values in the E2 supplemented Exercise rats but not in the unsupplemented Exercise group. For example, gastrocnemius Po for OVX HLU, OVX Recovery and OVX-Exercise groups was 82%*, 82%* and 76%* of control. Gastrocnemius Po for E2 supplemented HLU, Recovery and Exercise groups was 72%*, 95% and 106% of control (*P < 0.05 compared to control). H&E cross-sections from OVX-Exercise rats showed central nuclei. In conclusion, a rehabilitation exercise program to remediate acute atrophy in females appears more effective if E2 is present.

Oestrogen receptor-alpha activation augments post-exercise myoblast proliferation

AIM

Our laboratory has shown that oestrogen acts to augment myoblast (satellite cell) activation, proliferation and total number and that this may occur through an oestrogen receptor (OR)-mediated mechanism. The purpose of this study was to further investigate the mechanism of oestrogen influence on augmentation of post-exercise myoblast numbers through use of a specific OR-alpha agonist, propyl pyrazole triol (PPT).

METHODS

Ovariectomized rats were used (n = 64) and separated into four groups: sham, oestrogen supplemented, agonist supplemented, and a combined oestrogen and agonist supplemented group. These groups were further subdivided into control (unexercised) and exercise groups. Surgical removal of white vastus and soleus muscles was performed 72 h post-exercise. Muscle samples were immunostained for the myoblast markers Pax7 and MyoD.

RESULTS

A significant increase in total (Pax7-positive) and activated (MyoD-positive) myoblasts was found in all groups post-exercise. A further significant augmentation of total and activated myoblasts occurred in oestrogen supplemented, agonist supplemented and the combined oestrogen and agonist supplemented groups post-exercise in white vastus and soleus muscles relative to unsupplemented animals.

CONCLUSION

These results demonstrate that both oestrogen and the specific OR-alpha receptor agonist, PPT, can significantly and to similar degrees augment myoblast number and activation following exercise-induced muscle damage. This suggests that oestrogen acts through an OR-mediated mechanism to stimulate myoblast proliferation following exercise, with OR-alpha playing a primary role.

Estrogen receptor-alpha and -beta and aromatase knockout effects on lower limb muscle mass and contractile function in female mice

Estrogen (E2) is reported to regulate skeletal muscle mass and contractile function; whether E2 exerts its effects through estrogen receptor-alpha (ERalpha) or -beta (ERbeta) is unclear. We determined the effect of ERalpha or ERbeta elimination on muscle mass and contractile function in multiple muscles of the lower limb, muscles with different locomotor tasks and proportions of fiber types I and II: soleus (Sol), plantaris (Plan), tibialis anterior (TA), and gastrocnemius (Gast) in mature female mice. To determine E2 elimination effects on muscle, we also used aromatase (Ar) knockout (KO) and wild-type (WT) mice. ERalpha and ArKO body weights were approximately 10 and 20% higher than WT. Although muscle mass tended to show a commensurate increase in both groups, only the TA was significantly larger in ERalpha (P<0.05). Ratios of muscle mass to body mass revealed significantly lower values for Gast and TA in ArKO mice (P<0.05). Tetanic tension (Po) per calculated anatomical cross-sectional area (aCSA) in ERalpha KO was lower in TA and Gast than in WT. Lower Po/aCSA in ERalpha KO Gast and TA was also supported histologically by significantly less Po/fiber areas (P<0.05). ArKO mice also had lower Po/aCSA in Gast and TA compared with WT. ERbeta KO and WT mice were comparable in all measures. Our results support the hypothesis that E2 effects on skeletal muscle are mediated in part via the ERalpha but that E2 effects may be mediated via more than one mechanism or receptor.

Exercise improves postischemic cardiac function in males but not females: consequences of a novel sex-specific heat shock protein 70 response

Exercise is a physiological inducer of the cardioprotective heat shock protein, Hsp70. The putative biological events involved in signaling this response exhibit sexual dimorphism. Thus, it was hypothesized that exercise-mediated induction of Hsp70 would demonstrate sex specificity. After treadmill running, male rats exhibited 2-fold greater levels of cardiac Hsp70 relative to the levels in gonadally intact female rats (P<0.001). Ovariectomized female rats exhibited exercise-mediated induction of Hsp70 similar to that observed for male rats, and estrogen treatment in these female rats reversed this effect (P<0.001). Attenuation of Hsp70 signaling by estrogen was non-receptor-mediated, possibly involving a cellular membrane-stabilizing mechanism of action. The physiological importance of this sex-specific hormone-mediated stress response is underscored by the disparity in functional adaptation in response to exercise between male rats and female rats. Exercise markedly improved postischemic left ventricular developed pressure, the maximal rate of contraction, and maximal rate of relaxation, and it reduced left ventricular end-diastolic pressure in male rats (P<0.001). No such benefit of exercise was observed in intact female rats. A causal role for Hsp70 in this sex-specific cardioprotective adaptation was indicated, inasmuch as ablation of Hsp70 induction with antisense oligonucleotides designed against Hsp70 transcripts attenuated improvement in the recovery of cardiac function in exercised male rats (P<0.05). Thus, the sex-specific hormone-mediated Hsp70 response to exercise results in cardioprotective adaptation, preferentially in male rats relative to female rats. These findings suggest that exercise may be more important for males than for females in defending against the effects of heart disease and offer a novel manner by which males may reduce the sex gap in susceptibility to adverse cardiac events.

Estrogen attenuates postexercise HSP70 expression in skeletal muscle

Exercise has been demonstrated as a physiological inducer of heat shock protein (HSP)70. Many of the proposed signals of this response exhibit sexual dimorphism. Thus the present objectives were to determine whether HSP70 induction after exercise exhibits gender specificity and to elucidate the mechanisms underlying such a phenomenon. Postexercise HSP70 induction in skeletal muscle was greater in male than female rats at the level of protein and mRNA (P = 0.005). Moreover, placebo-treated ovariectomized animals demonstrated a greater HSP70 response to exercise than those treated with estrogen (P = 0.015 and 0.019 for protein and mRNA, respectively). These findings indicate that the gender-specific HSP70 response to exercise is mediated by the female-specific hormone estrogen. Compounds structurally related to 17beta-estradiol, the major endogenous estrogen, but which do not activate the estrogen receptor, also attenuated HSP70 induction with exercise (P < 0.01), indicating a nongenomic hormonal mechanism. These findings highlight a specific example of the biological differences between males and females and reiterate the physiological effects of sex hormones extending beyond their roles in reproductive function.

Oestrogen and sex influence on muscle damage and inflammation: evidence from animal models

Recent evidence suggests that oestrogen and sex may influence the degree of disruption and post-damage inflammatory response seen in skeletal muscle. Evidence primarily from animal models suggests that oestrogen may be able to attenuate muscle disruption and attenuate or delay muscle leukocyte infiltration after contraction-induced and ischaemia-reperfusion-induced damage. Several potential mechanisms for this effect are discussed, along with the potential for oestrogen to influence the ultimate rate of skeletal muscle recovery from damage.

Effects of prior exercise on eccentric exercise-induced neutrophilia and enzyme release

PURPOSE

The purpose of this study was to determine the effects of prior exercise on changes in circulating neutrophils, neutrophil activation, and myocellular enzymes following a standardized bout of eccentric exercise.

METHODS

Twenty-four male volunteers were randomized into three groups (N = 8). Group C performed 10 sets of 10 eccentric contractions of the quadriceps muscles with both legs (100% of the concentric IRM). Group D and Group F exercised for 2 h at 56%VO2max on a cycle ergometer followed by a similar bout of eccentric contractions. Group F also received 7.5 mL x kg(-1) of a carbohydrate-electrolyte beverage every 30 min during the submaximal exercise, whereas group D received no fluid.

RESULTS

Body weight remained unchanged in groups C and F and decreased in group D by 1.56 +/- 0.34 kg. Ultrastructural Z-Band damage increased three-fold following exercise and remained elevated 3 d after exercise but was not different among groups. Circulating neutrophils were elevated more in group D compared with those in group C immediately after the exercise or rest period, and this difference persisted 3 h after the eccentric exercise. Serum lactoferrin concentrations increased 3.3-fold after exercise in all groups (P < 0.01). Creatine kinase levels (CK) rose in all subjects, with subjects in Group F and D having a significantly greater rise in CK after exercise compared with those in group C.

CONCLUSIONS

These data indicate that submaximal exercise followed by a bout of eccentric exercise results in similar amounts of myofibrillar injury with a larger neutrophil response and CK release.

The effects of oral contraceptives on delayed onset muscle soreness following exercise

Several authors have suggested that estrogen may serve to protect skeletal muscle from exercise-induced damage. The present study examined the effects of regularly ingesting estrogen, in the form of oral contraceptives, on postexercise muscle damage following a bench-stepping regimen. Women currently ingesting oral contraceptives (OC) were compared with eumennorheic controls (CG). All subjects performed a 50-min stepping exercise during the midluteal phase of their menstrual cycle. Muscle damage was evaluated on 2, 3, and 5 days postexercise using several established indirect indicators: perceived soreness, strength and range of motion changes, girth measurements, and creatine kinase (CK) activity. Subjects on OC reported significantly lower quadriceps soreness (p < 0.05) relative to the CG (peak soreness = 4.0 and 7.8, respectively, on a scale of 1-10 where 1 is normal and 10 is very, very sore). These results indicate that oral contraceptive use attenuates soreness following an exhaustive stepping activity but cannot support a relationship between estrogen ingestion and other indices of exercise-induced muscle damage.

Can estrogens diminish exercise induced muscle damage?

Estrogens are female sex hormones that may also protect against peroxidative damage of membrane lipids and low density lipoproteins (LDL). Studies have reported that female rats have greater protection against free radical induced lipid peroxidation and muscle damage consequent to exercise than do male rats. It has been suggested that the lower susceptibility to exercise induced oxidative stress and muscle membrane disruption of female rats may be due primarily to the antioxidant and membrane stabilizing properties of estrogens. Studies on humans have indicated that the lower incidence of atherosclerosis seen in premenopausal females in comparison to males is due at least in part to the ability of estrogens to diminish LDL peroxidation. However, there is little evidence as to the potential of estrogens to protect human females from free radical induced peroxidation and muscle damage due to exercise. This paper reviews the evidence for membrane stabilization potential of estrogens and their possible mechanisms, and speculates as to the potential significance of this for human exercise.