Effect of androgen deprivation therapy on the contractile properties of type I and type II skeletal muscle fibres in men with non-metastatic prostate cancer

Skeletal Muscle Function Is Altered in Male Mice on Low-Dose Androgen Receptor Antagonist or Estrogen Receptor Agonist

In males, skeletal muscle function may be altered by shifts in either circulating testosterone or estrogen. We examined the effect of acute (2-week) exposures to 17α-ethinyl estradiol (EE2), an estrogen receptor (ER) agonist, or flutamide, an androgen receptor (AR) antagonist, on the contractile function of individual skeletal muscle fibers from slow-contracting soleus and fast-contracting extensor digitorum longus muscles from adult male mice. Single fiber specific tension (force divided by cross-sectional area) was decreased with flutamide treatment in all myosin heavy chain (MHC) fiber types examined (I, IIA, and IIB); similar effects were observed with EE2 treatment but only in the fastest-contracting MHC IIB fibers. The decreases in maximally Ca2+-activated specific tension were primarily a result of fewer strongly bound myosin-actin cross-bridges, with flutamide treatment also showing lower myofilament lattice stiffness. Myosin-actin cross-bridge kinetics were slower in MHC IIA fibers in flutamide-treated mice, but faster in EE2-treated mice, indicating that contractile velocity may be affected differently in this fiber type, which is commonly expressed in human skeletal muscle. Importantly, these effects were observed in the absence of outcomes previously used to evaluate ER agonists or AR antagonists in rodents including weight of reproductive organs or mammary gland morphology. Our findings indicate that substantial shifts in skeletal muscle function occur in male mice following acute exposures to low doses of a pharmacological ER agonist and an AR antagonist. These results suggest that countermeasures to maintain physical function may be needed early in situations that induce similar ER agonist and AR antagonist conditions.

Effects of Androgen Deprivation Therapy on Extraocular Muscles, Retrobulbar Orbital Fat, and the Optic Nerve in Patients with Prostate Cancer

INTRODUCTION

The aim of this study was to evaluate radiologically the effects of long-term luteinizing hormone-releasing hormone (LHRH) agonist therapy on extraocular muscle thickness, retrobulbar orbital fat (ROF), and the optic nerve (ON) in prostate cancer (PCa) patients.

METHODS

The retrospective study included patients with primary or recurrent PCa who received androgen deprivation therapy (ADT) for at least 12 months. Each patient underwent gallium-68 prostate-specific membrane antigen positron emission tomography-computed tomography both before and at the end of the 12-month treatment. Thickness of the ON, lateral rectus muscle, medial rectus muscle, superior rectus muscle, and inferior rectus muscle were measured by using the coronal CT sections in soft tissue window. ROF, ocular protrusion, and ON length were measured in sagittal and coronal planes. Changes in these anatomical structures induced by LHRH analogs were investigated by comparing pre- and post-treatment measurements.

RESULTS

A total of 57 patients were included in the study. Median PSA and TT values ​​of the patients before treatment were 36.5 (range, 19.6-51.2) ng/mL and 614.0 (range, 472.0-743.0) ng/dL, respectively, and these values ​​decreased significantly after the treatment (10.6 [range, 5.2-14.2] ng/mL and 36.5 [range, 19.6-51.2] ng/dL, respectively, p < 0.001 for both). After the treatment, there was a statistically significant decrease in the areas of inferior rectus muscle, superior rectus muscle, lateral rectus muscle, and medial rectus muscle (p < 0.001 for all), while significant increases were observed in ROF (11.9%, p < 0.001) and ON thickness (14.3%, p = 0.004). The amount of ocular protrusion also showed a significant increase of approximately 14% after the treatment (14.0 [range, 12.0-16.0] mm vs. 16.0 [range, 14.0-17.2] mm, p < 0.001).

DISCUSSION/CONCLUSION

Our findings, for the first time in the literature, indicated that ADT causes a decrease in extraocular muscle mass and an increase in ROF with ocular protrusion. It can be asserted that these changes are similar to the changes in skeletal muscle and fat mass in other body parts. Further studies with a higher level of evidence are needed to clinically evaluate the increase in ocular protrusion and ON enlargement, which are likely to be caused by the increase in ROF.

Effect of Periodized Resistance Training on Skeletal Muscle During Androgen Deprivation Therapy for Prostate Cancer: A Pilot Randomized Trial

PURPOSE

Prostate cancer survivors (PCS) receive androgen deprivation therapy (ADT) as treatment for recurrent cancer, yet ADT is associated with loss of skeletal muscle and physical function. Resistance training can counter both muscle and physical function loss; however, an understanding of the molecular responses of skeletal muscle to resistance training during ADT is still undefined. This sub-analysis of the original randomized, controlled pilot trial investigated effects of 12 weeks of periodized resistance training on mRNA expression of the anabolic genes IGF-1, myogenin, PGC-1α4 and the catabolic genes myostatin and MuRF-1 in skeletal muscle of PCS on ADT. Secondary aims investigated if changes in lean mass and physical function correlated with changes in mRNA expression.

METHODS

PCS on ADT (n = 17) were randomized to 12 weeks of supervised resistance training (EXE, n = 9) or home-based stretching (STRETCH, n = 8) 3 days per week. Outcomes were assessed at baseline and post-intervention. Muscle biopsies were analyzed by RT-PCR for mRNA expression. Body composition was assessed through dual-energy X-ray absorptiometry, and physical function through muscular strength, timed up and go, stair climb, and 400 m walk.

RESULTS

MuRF-1 mRNA expression was significantly greater in EXE compared to STRETCH post-intervention (P = .005). Change in MuRF-1 mRNA expression significantly correlated with improvements in strength and physical function (P < .05), while change in IGF-1 expression correlated with change in lean mass (P = .015).

CONCLUSION

Twelve weeks of resistance training increased mRNA expression of MuRF-1 in skeletal muscle of PCS on ADT. Elevations in resting mRNA expression of IGF-1, myogenin and PGC-1α4, and reduction in mRNA expression of myostatin that are typically expected following resistance training were not observed.

Type-2 muscle fiber atrophy is associated with sarcopenia in elderly men with hip fracture

Sarcopenia is a common geriatric syndrome and can lead to falls and fragility fractures. It is associated with a decline of muscle fiber numbers and size. Muscle biopsies of the vastus lateralis muscle were taken from thirty-two patients with hip fracture (18 women and 14 men; mean age: 82.2 ± 6.2 years). Serial cross sections of skeletal muscle were labeled with myosin heavy chain slow (fiber type-1) and fast (fiber type-2) antibodies in order to measure the size, ratio and percentage of mixed fiber types. The presence of sarcopenia was defined according to the EWGSOP2 criteria by using BIA and handgrip strength measurement. Sarcopenia was identified in 5 patients (3 women and 2 men), probable-sarcopenia in 11 patients (4 women and 7 men). Significant differences in fiber diameter were found for fiber type-2 in men but not in women. Only 1-3% mixed fiber types were found in sarcopenic patients, indicating a final stage where reinnervation is not possible to occur anymore. Muscle fiber type-2 atrophy seems to be a histological marker for sarcopenia in men.

Muscle hypertrophy and muscle strength: dependent or independent variables? A provocative review

The question whether the muscle hypertrophy induced by resistance training, hormone administration or genetic manipulation is accompanied by a proportional increase in muscle strength is still open. This review summarizes and analyses data obtained in human and rodent muscles in studies that have monitored in parallel changes in muscle size and changes in muscle force, measured in isometric contractions in vivo, in isolated muscles ex vivo (in rodents) and in single muscle fibers. Although a general positive relation exists among the two variables, a number of studies show a clear dissociation with increase of muscle size with no change or even decrease in strength and, vice versa, increase in strength without increase in size. The possible mechanisms of such dissociation, which involves neural motor control and/or cellular and molecular adaptations of muscle fibers, are briefly discussed.

Testosterone suppression does not exacerbate disuse atrophy and impairs muscle recovery that is not rescued by high protein

Androgen deprivation therapy (ADT) decreases muscle mass, force, and physical activity levels, but it is unclear whether disuse atrophy and testosterone suppression are additive. Additionally, conflicting reports exist on load-mediated hypertrophy during ADT and if protein supplementation offsets these deficits. This study sought to determine the role of testosterone suppression and a high-protein diet on 1) immobilization-induced atrophy and 2) muscle regrowth during reloading. Eight-week-old male Fischer 344 rats underwent sham surgery (Sham), castration surgery (ORX), or ORX and a high-casein diet supplemented with branched-chain amino acids (BCAA) (ORX+CAS/AA) followed by 10 days of unilateral immobilization (IMM) and 0, 6, or 14 days of reloading. With IMM, body mass gains were ~8% greater than ORX and ORX+CAS/AA that increased to 15% during reloading (both P < 0.01). IMM reduced muscle mass by 11-34% (all P < 0.01) and extensor digitorum longus and soleus (SOL) force by 21% and 49% (both P < 0.01), respectively, with no group differences. During reloading, castration reduced gastrocnemius mass (~12%) at 6 days and SOL mass (~20%) and SOL force recovery (~46%) at 14 days relative to Sham (all P < 0.05). Specific force reduced castration deficits, indicating that muscle atrophy was a key contributor. IMM decreased SOL cross-sectional area by 30.3% (P < 0.001), with a trend for reduced regrowth in ORX and ORX+CAS/AA following reloading (P = 0.083). Castration did not exacerbate disuse atrophy but may impair recovery of muscle function, with no benefit from a CAS/AA diet during reloading. Examining functional outcomes in addition to muscle mass during dietary interventions provides novel insights into muscle regrowth during ADT.NEW & NOTEWORTHY Low testosterone levels during skeletal muscle disuse did not worsen declines in muscle mass and function, although hypogonadism may attenuate recovery during subsequent reloading. Diets high in casein did not improve outcomes during immobilization or reloading. Practical strategies are needed that do not compromise caloric intake yet provide effective protein doses to augment these adverse effects.

Effects of high-intensity intermittent exercise on the contractile properties of human type I and type II skeletal muscle fibers

In vitro studies have shown that alterations in redox state can cause a range of opposing effects on the properties of the contractile apparatus in skeletal muscle fibers. To test whether and how redox changes occurring in vivo affect the contractile properties, vastus lateralis muscle fibers from seven healthy young adults were examined at rest (PRE) and following (POST) high-intensity intermittent cycling exercise. Individual mechanically skinned muscle fibers were exposed to heavily buffered solutions at progressively higher free [Ca²⁺] to determine their force-Ca²⁺ relationship. Following acute exercise, Ca²⁺ sensitivity was significantly decreased in type I fibers (by 0.06 pCa unit) but not in type II fibers (0.01 pCa unit). Specific force decreased after the exercise in type II fibers (-18%) but was unchanged in type I fibers. Treatment with the reducing agent dithiothreitol (DTT) caused a small decrease in Ca²⁺-sensitivity in type II fibers at PRE (by ∼0.014 pCa units) and a significantly larger decrease at POST (∼0.035 pCa units), indicating that the exercise had increased S-glutathionylation of fast troponin I. DTT treatment also increased specific force (by ∼4%), but only at POST. In contrast, DTT treatment had no effect on either parameter in type I fibers at either PRE or POST. In type I fibers, the decreased Ca²⁺ sensitivity was not due to reversible oxidative changes and may have contributed to a decrease in power production during vigorous exercises. In type II fibers, exercise-induced redox changes help counter the decline in Ca²⁺-sensitivity while causing a small decline in maximum force.NEW & NOTEWORTHY This study identified important cellular changes occurring in human skeletal muscle fibers following high-intensity intermittent exercise: 1) a decrease in contractile apparatus Ca²⁺ sensitivity in type I but not type II fibers, 2) a decrease in specific force only in type II muscle fibers, and 3) a redox-dependent increase in Ca²⁺ sensitivity occurring only in type II fibers, which would help maintain muscle performance by countering the normal metabolite-induced decline in Ca²⁺ sensitivity.

Equivalent L-type channel (CaV1.1) function in adult female and male mouse skeletal muscle fibers

Loss of total muscle force during aging has both atrophic and non-atrophic components. The former deficit is a direct consequence of reduced muscle mass while the latter has been attributed to a depression of excitation-contraction (EC) coupling. It is well established that age-onset reductions in sex hormone production regulate the atrophic component in both males and females. However, it is unknown whether the non-atrophic component is influenced by sex hormones. Since the non-atrophic component has been linked mechanistically to reduced expression of the skeletal muscle L-type Ca²⁺ channel (Ca_V1.1), we recorded L-type Ca²⁺ currents, gating charge movements and depolarization-induced changes in myoplasmic Ca²⁺ from flexor digitorum brevis (FDB) fibers of naïve and gonadectomized mice of both sexes. Our first set of experiments sought to identify any basal differences in EC coupling or L-type Ca²⁺ flux between the sexes; no detectable differences in any of the aforementioned parameters were observed between FDB harvested from either naïve males or females. In the latter segments of the study, ovariectomy (OVX) and orchiectomy (ORX) models were used to assess the possible influence of sex hormones on EC coupling and/or L-type Ca²⁺ flux. In these experiments, FDB fibers harvested from OVX and ORX mice both showed no differences in L-type Ca²⁺ current, gating charge movement or depolarization-induced changes in Ca²⁺ release from the sarcoplasmic reticulum. Taken together, our results indicate L-type Ca²⁺ channel function and EC coupling are: 1) equivalent between the sexes, and 2) not significantly regulated by sex hormones. Since recent NIH review guidelines mandate the consideration of sex differences as a criterion for review, our work indicates the suitability of either sex for the study of the fundamental mechanisms of EC coupling. Thus, our findings may accelerate the research process by conserving animals, labor and financial resources.