Decreased grip strength, muscle pain, and atrophy occur in rats following long-term exposure to excessive repetitive motion

Jakyak-gamcho-tang, a decoction of Paeoniae Radix and Glycyrrhizae Radix et Rhizoma, ameliorates dexamethasone-induced muscle atrophy and muscle dysfunction

BACKGROUND

Although chronic treatment with glucocorticoids, such as dexamethasone, is frequently associated with muscle atrophy, effective and safe therapeutics for treating muscle atrophy remain elusive. Jakyak-gamcho-tang (JGT), a decoction of Paeoniae Radix and Glycyrrhizae Radix et Rhizoma, has long been used to relieve muscle tension and control muscle cramp-related pain. However, the effects of JGT on glucocorticoid-induced muscle atrophy are yet to be comprehensively clarified.

PURPOSE

The objective of the current study was to validate the protective effect of JGT in dexamethasone-induced muscle atrophy models and elucidate its underlying mechanism through integrated in silico - in vitro - in vivo studies.

STUDY DESIGN AND METHODS

Differential gene expression was preliminarily analyzed using the RNA-seq data to determine the effects of JGT on C2C12 myotubes. The protective effects of JGT were further validated in dexamethasone-treated C2C12 myotubes by assessing cell viability, myotube integrity, and mitochondrial function or in C57BL/6 N male mice with dexamethasone-induced muscle atrophy by evaluating muscle mass and physical performance. Transcriptomic pathway analysis was also performed to elucidate the underlying mechanism.

RESULTS

Based on preliminary gene set enrichment analysis using the RNA-seq data, JGT regulated various pathways related to muscle differentiation and regeneration. Dexamethasone-treated C2C12 myotubes and muscle tissues of atrophic mice displayed substantial muscle protein degradation and muscle loss, respectively, which was efficiently alleviated by JGT treatment. Importantly, JGT-mediated protective effects were associated with observations such as preservation of mitochondrial function, upregulation of myogenic signaling pathways, including protein kinase B/mammalian target of rapamycin/forkhead box O3, inhibition of ubiquitin-mediated muscle protein breakdown, and downregulation of inflammatory and apoptotic pathways induced by dexamethasone.

CONCLUSION

To the best of our knowledge, this is the first report to demonstrate that JGT could be a potential pharmaceutical candidate to prevent muscle atrophy induced by chronic glucocorticoid treatment, highlighting its known effects for relieving muscle spasms and pain. Moreover, transcriptomic pathway analysis can be employed as an efficient in silico tool to predict novel pharmacological candidates and elucidate molecular mechanisms underlying the effects of herbal medications comprising diverse biologically active ingredients.

Reproducibility of the 6-minute walk test in lung transplant recipients

PURPOSE

There is reason to believe that the favorable measurement properties of the 6‑minute walk test (6MWT) reported for retest reliability and its capability to detect a true change in healthy individuals or persons with chronic respiratory disease may not apply to lung transplant recipients (LuTXr). We therefore investigated retest reliability of the 6MWT and, in addition, made an attempt to explore whether the 6MWT was sensitive enough to detect important changes that occur with postacute rehabilitation in LuTXr after first time LuTX.

METHODS

Immediately before postacute rehabilitation, 50 LuTXr completed 6MWT testing twice, separated by 1-2 workdays (retest reliability), and were reassessed after completion of rehabilitation 2 months later (sensitivity to changes). Body function measures and health-related quality of life (HRQoL) assessments were collected at baseline.

RESULTS

Baseline retest 6‑minute walk distance (6MWD) and the age-related predicted walking distance (6MWD%pred) scores significantly increased before postacute rehabilitation. The intraclass coefficient of correlation ICC of the 6MWD was 0.93 (95% confidence interval, CI: 0.88-0.96) and its smallest real difference (SRD) 79 m (95% CI: 52;107). Receiver operating curve analyses revealed the rehabilitation associated changes in 6MWD/6MWD%pred to exceed the SRD/SRD% values in a highly accurate way.

CONCLUSION

The 6MWT overall represents a reliable functional performance tool in LuTXr that is sensitive to detect changes in physical performance as a result of medical postacute rehabilitation.

Blocking CCN2 Reduces Established Palmar Neuromuscular Fibrosis and Improves Function Following Repetitive Overuse Injury

The matricellular protein cell communication factor 2/connective tissue growth factor (CCN2/CTGF) is critical to development of neuromuscular fibrosis. Here, we tested whether anti-CCN2 antibody treatment will reduce established forepaw fibro-degenerative changes and improve function in a rat model of overuse injury. Adult female rats performed a high repetition high force (HRHF) task for 18 weeks. Tissues were collected from one subset after 18 wks (HRHF-Untreated). Two subsets were provided 6 wks of rest with concurrent treatment with anti-CCN2 (HRHF-Rest/anti-CCN2) or IgG (HRHF-Rest/IgG). Results were compared to IgG-treated Controls. Forepaw muscle fibrosis, neural fibrosis and entheseal damage were increased in HRHF-Untreated rats, compared to Controls, and changes were ameliorated in HRHF-Rest/anti-CCN2 rats. Anti-CCN2 treatment also reduced phosphorylated-β-catenin (pro-fibrotic protein) in muscles and distal bone/entheses complex, and increased CCN3 (anti-fibrotic) in the same tissues, compared to HRHF-Untreated rats. Grip strength declines and mechanical sensitivity observed in HRHF-Untreated improved with rest; grip strength improved further in HRHF-Rest/anti-CCN2. Grip strength declines correlated with muscle fibrosis, entheseal damage, extraneural fibrosis, and decreased nerve conduction velocity, while enhanced mechanical sensitivity (a pain-related behavior) correlated with extraneural fibrosis. These studies demonstrate that blocking CCN2 signaling reduces established forepaw neuromuscular fibrosis and entheseal damage, which improves forepaw function, following overuse injury.

Effect of Tetragonia tetragonoides (Pall.) Kuntze Extract on Andropause Symptoms

Testosterone and free testosterone levels decrease in men as they age, consequently inducing andropause symptoms, such as weight gain, fatigue, and depression. Therefore, this study aimed to evaluate the reducing effect of New Zealand spinach (NZS) on these androgenic symptoms by orally administering its extract to 26-week-old rats for four weeks. Biochemical blood testing was conducted, and the andropause symptoms-related indicators and muscular endurance levels were examined. In the NZS extract-treated rats, the decrease in muscle mass was suppressed, and immobility time was reduced in the forced swim test. In addition, the grip force and muscular endurance of the forelimbs were significantly increased compared to the control group; therefore, NZS extract exhibits a positive effect on the maintenance of muscle mass and improves muscular endurance. The representative male hormones, testosterone and progesterone, in the NZS extract-treated group were 1.84 times and 2.48 times higher than those in the control groups, respectively. Moreover, cholesterol and low-density lipoprotein, which affect lipid metabolism, were significantly reduced in the NZS extract-treated group. Overall, NZS extract shows potential for further development as a functional food material for improving muscle strength and relieving andropause symptoms.

Metabolic footprint in young, middle-aged and elderly rats with melatonin deficit

The pineal gland is suggested to be an essential area involved in the programming of fertility, growth, aging, and death of mammals via the released hormone melatonin.The present study aimed to ascertain the effect of melatonin deficit on several physiological and metabolic parameters, closely associated with the aging process, at certain stages of ontogenesis. Sham and rats with pinealectomy, operated at ages 3, 14, and 18-months, respectively, were tested two months later. Sham rats demonstrated an age-related decline of muscle strength, exercise endurance, motor activity, food intake, calorimetric parameters, and impaired lipid profile. Pinealectomy reduced the maximal time to exhaustion and body weight gain while diminished motor activity, food intake, O₂ consumption, CO₂ production, and energy expenditure during the Dark phase in the youngest rat group. In addition, melatonin deficit elevated arterial blood pressure (systolic, diastolic, and mean arterial pressure) and increased serum glucose and triglyceride level in 3-month-old rats while decreased the liver enzyme activity in 14-month-old rats. In conclusion, the present study brought new insights confirming the complex impact of melatonin deficit on important physiological, metabolic and biochemical markers related to aging and demonstrated for the first time that the lack of melatonin hormone is harmful in young adult rats.

Association between Musculoskeletal Pain and Bone Turnover Markers in Long-Term Pb-Exposed Workers

BACKGROUND

On chronic exposure, Lead (Pb) deposits in the skeletal system, replaces calcium ions, and alters the normal physiological processes, which in turn, lead to stunting, delayed fracture healing, and high resorption of collagen molecules. The present study aimed to assess the association of musculoskeletal pain and discomfort with bone turnover markers (BTMs) among long-term Pb-exposed workers.

STUDY DESIGN

A cross-sectional study.

METHODS

The study recruited 176 male Pb-exposed workers and 80 control subjects who were matched for age, gender, and socio-economic status. Blood lead levels (BLLs), bone growth markers, such as serum osteocalcin (OC), alkaline phosphatase (ALP), bone alkaline phosphatase (BAP), and bone resorption markers: serum pyridinoline (Pry), deoxypyridinoline (DPry), tartrate-resistant acid phosphatase-5b(TRACP-5b), and hydroxyproline in urine (HyP-U) of participants were investigated. Pain and discomfort in the musculoskeletal system were assessed using Nordic Musculoskeletal Questionnaire.

RESULTS

Pb-exposure was significantly associated with musculoskeletal discomfort of the lower back (P<0.001), upper back (P<0.001), and ankle/foot (P=0.011). Among bone formation markers, serum OC was significantly lower in musculoskeletal discomfort of elbows (P=0.033) and ankle/foot (P=0.042). Among bone resorption markers, serum DPry was significantly lower in musculoskeletal discomfort of the neck (P=0.049) and shoulders (P=0.023). HyP-U was significantly higher in musculoskeletal discomfort of shoulders (P=0.035) and lower back (P=0.036).

CONCLUSION

As evidenced by the obtained results, Pb-exposure was associated with musculoskeletal discomfort of the lower back, upper back, and ankle/foot. Lower bone formation (serum OC) marker was noted with musculoskeletal discomfort of elbows and ankle/foot. Furthermore, bone resorption markers were associated with musculoskeletal discomfort of the neck, shoulders, and lower back. The findings of the present study suggested that long-term Pb-exposure and BTMs were associated with musculoskeletal discomfort.

Effects of Tyrosine and Tryptophan Supplements on the Vital Indicators in Mice Differently Prone to Diet-Induced Obesity

We studied the effects of the addition of large neutral amino acids, such as tyrosine (Tyr) and tryptophan (Trp), in mice DBA/2J and tetrahybrid mice DBCB receiving a high-fat, high-carbohydrate diet (HFCD) for 65 days. The locomotor activity, anxiety, muscle tone, mass of internal organs, liver morphology, adipokines, cytokines, and biochemical indices of animals were assessed. The Tyr supplementation potentiated increased anxiety in EPM and contributed to a muscle tone increase, a decrease in the AST/ALT ratio, and an increase in protein anabolism in both mice strains. Tyr contributed to a decrease in liver fatty degeneration and ALT reduction only in DBCB that were sensitive to the development of obesity. The addition of Trp caused an increase in muscle tone and potentiated an increase in anxiety with age in animals of both genotypes. Trp had toxic effects on the livers of mice, which was manifested in increased fatty degeneration in DBCB, edema, and the appearance of micronuclei in DBA/2J. The main identified effects of Tyr on mice are considered in the light of its modulating effect on the dopamine neurotransmitter metabolism, while for the Trp supplement, effects were presumably associated with the synthesis of its toxic metabolites by representatives of the intestinal microflora.

Key indicators of repetitive overuse-induced neuromuscular inflammation and fibrosis are prevented by manual therapy in a rat model

BACKGROUND

We examined the effectiveness of a manual therapy consisting of forearm skin rolling, muscle mobilization, and upper extremity traction as a preventive treatment for rats performing an intensive lever-pulling task. We hypothesized that this treatment would reduce task-induced neuromuscular and tendon inflammation, fibrosis, and sensorimotor declines.

METHODS

Sprague-Dawley rats performed a reaching and lever pulling task for a food reward, 2 h/day, 3 days/week, for 12 weeks, while simultaneously receiving the manual therapy treatment 3 times per week for 12 weeks to either the task-involved upper extremities (TASK-Tx), or the lower extremities as an active control group (TASK-Ac). Results were compared to similarly treated control rats (C-Tx and C-Ac).

RESULTS

Median nerves and forearm flexor muscles and tendons of TASK-Ac rats showed higher numbers of inflammatory CD68+ and fibrogenic CD206+ macrophages, particularly in epineurium, endomysium and epitendons than TASK-Tx rats. CD68+ and CD206+ macrophages numbers in TASK-Tx rats were comparable to the non-task control groups. TASK-Ac rats had more extraneural fibrosis in median nerves, pro-collagen type I levels and immunoexpression in flexor digitorum muscles, and fibrogenic changes in flexor digitorum epitendons, than TASK-Tx rats (which showed comparable responses as control groups). TASK-Ac rats showed cold temperature, lower reflexive grip strength, and task avoidance, responses not seen in TASK-Tx rats (which showed comparable responses as the control groups).

CONCLUSIONS

Manual therapy of forelimbs involved in performing the reaching and grasping task prevented the development of inflammatory and fibrogenic changes in forearm nerves, muscle, and tendons, and sensorimotor declines.

Carbon dots from Artemisiae Argyi Folium Carbonisata: strengthening the anti-frostbite ability

In this study, novel carbon dots (CDs) were discovered and separated from Artemisiae Argyi Folium Carbonisata (AAFC) aqueous extract. AAFC-CDs were characterised by a series of methods, mainly including electron microscopy, optical technology and X-ray photoelectron spectroscopy (XPS). Results displayed that AAFC-CDs with a quantum yield (QY) around 0.19% had a size distribution between 6.0 and 10.0 nm and possessed a nearly spherical shape, with a lattice spacing of 0.369 nm. In mice, AAFC-CDs reduced the tissue damage, ear frostbite, and body stiffness caused by cold, and provided energy by increasing the use of blood glucose. The mechanism may be by decreasing concentration of IL-1βk, TNF-α and reducing the rise in blood glucose levels caused by frostbite. This study is the first to indicate that CDs may be the active constituent of AAFC against frostbite, suggesting their potential for clinical applications.

Blocking substance P signaling reduces musculotendinous and dermal fibrosis and sensorimotor declines in a rat model of overuse injury

Purpose/Aim: Substance P-NK-1R signaling has been implicated in fibrotic tendinopathies and myositis. Blocking this signaling with a neurokinin 1 receptor antagonist (NK1RA) has been proposed as a therapeutic target for their treatment.Materials and Methods: Using a rodent model of overuse injury, we pharmacologically blocked Substance P using a specific NK1RA with the hopes of reducing forelimb tendon, muscle and dermal fibrogenic changes and associated pain-related behaviors. Young adult rats learned to pull at high force levels across a 5-week period, before performing a high repetition high force (HRHF) task for 3 weeks (2 h/day, 3 days/week). HRHF rats were untreated or treated in task weeks 2 and 3 with the NK1RA, i.p. Control rats received vehicle or NK1RA treatments.Results: Grip strength declined in untreated HRHF rats, and mechanical sensitivity and temperature aversion increased compared to controls; these changes were improved by NK1RA treatment (L-732,138). NK1RA treatment also reduced HRHF-induced thickening in flexor digitorum epitendons, and HRHF-induced increases of TGFbeta1, CCN2/CTGF, and collagen type 1 in flexor digitorum muscles. In the forepaw upper dermis, task-induced increases in collagen deposition were reduced by NK1RA treatment.Conclusions: Our findings indicate that Substance P plays a role in the development of fibrogenic responses and subsequent discomfort in forelimb tissues involved in performing a high demand repetitive forceful task.

Effect of resveratrol on behavioral, biochemical, and immunological parameters of DBA/2J and tetrahybrid DBCB mice receiving diet with excess fat and fructose

Polyphenolic biologically active substances (BAS) including resveratrol (R) can exert beneficial effects on fat accumulation, blood pressure, glycemia, insulin sensitivity, and plasma lipid profile in patients with obesity, and associated diseases. The study aimed to determine the effect of R at a dose of 25 mg/kg body weight on the DBA/2J and DBCB mice with diet-induced obesity followed by the consumption high-fat high-carbohydrate diet (HFCD). Behavioral reactions (elevated plus maze [EPM]) and muscle tone (the strength of the forepaw grip) were tested, and plasma biochemical and immunological parameters were assessed. In the repeated EPM test, anxiety increased only in DBCB mice during the second trial. In DBCB mice treated with HFCD, the muscle tone decreased with the second trial; however, this effect was not observed in the background of R consumption. R decreased the level of triglycerides, diminished the activities of alanine and asparagine aminotransferases, which were elevated upon HFCD consumption. Ghrelin level increased after R consumption in mice of both genotypes. The leptin to ghrelin ratio was reduced in DBCB mice receiving R. Consumption of R increased IL-3 and IL-10 levels in both DBA/2J and DBCB mice. IL-12p70 level increased in DBCB mice in response to R. R addition to HFCD reduced several symptoms of dyslipidemia in highly sensitive tetrahybrid mice. The results obtained indicate the importance of a personalized (depending on the genotype) approach when any R prescription, among other BAS and dietary factors, are used in diet therapy for patients with low, moderate and high-risk obesity.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Effects of quercetin on the neuromotor function and behavioral responses of Wistar and Zucker rats fed a high-fat and high-carbohydrate diet

Quercetin can affect some pathological manifestations in obesity. The mechanism underlying the presumed therapeutic effect of quercetin is probably related to the influence on the central processes regulating energy homeostasis. Thus, the purpose of this study was to examine the effect of quercetin on the neuromotor and behavioral functions in Zucker (Z) and Wistar (W) rats with genetically and/or diet-induced obesity. Rats of both strains received balanced or high fat and fructose diet (HFCD) in a 62-day experiment or the same diets supplemented with quercetin at the dose of 50 mg/kg body weight per day. The neuromotor function and behavioral responses were examined using the grip strength test, open field test, elevated plus maze test and conditioned passive avoidance response (CPAR) test. The quercetin potentiated a decrease in anxiety in W rats consumed HFCD and this effect was absent in Z rats with a defect in the leptin receptor gene. In contrast, quercetin increased locomotor activity and impaired short-term memory in the CPAR test only in Z rats with the absence of normal leptin reception. Against the background of the identified changes quercetin exerted significant effects on the lipid and nitrogen metabolism indices such as HDL cholesterol, AsAT/AlAT activities ratio, urea level as well as body and fat mass that were different in Z and W rats. The data obtained show that the effects of quercetin on behavior vary significantly between two strains of rat and consequently are mediated by processes of leptin reception.

Manual therapy prevents onset of nociceptor activity, sensorimotor dysfunction, and neural fibrosis induced by a volitional repetitive task

Painful and disabling musculoskeletal disorders remain prevalent. In rats trained to perform repetitive tasks leading to signs and dysfunction similar to those in humans, we tested whether manual therapy would prevent the development of the pathologies and symptoms. We collected behavioral, electrophysiological, and histological data from control rats, rats that trained for 5 weeks before performing a high-repetition high-force (HRHF) task for 3 weeks untreated, and trained rats that performed the task for 3 weeks while being treated 3x/week using modeled manual therapy (MMT) to the forearm (HRHF + MMT). The MMT included bilateral mobilization, skin rolling, and long axis stretching of the entire upper limb. High-repetition high-force rats showed decreased performance of the operant HRHF task and increased discomfort-related behaviors, starting after training. HRHF + MMT rats showed improved task performance and decreased discomfort-related behaviors compared with untreated HRHF rats. Subsets of rats were assayed for presence or absence of ongoing activity in C neurons and slow Aδ neurons in their median nerves. Neurons from HRHF rats had a heightened proportion of ongoing activity and altered conduction velocities compared with control and MMT-treated rats. Median nerve branches in HRHF rats contained increased numbers of CD68 macrophages and degraded myelin basic protein, and showed increased extraneural collagen deposition, compared with the other groups. We conclude that the performance of the task for 3 weeks leads to increased ongoing activity in nociceptors, in parallel with behavioral and histological signs of neuritis and nerve injury, and that these pathophysiologies are largely prevented by MMT.

Comparative analysis of the influence of a high-fat/high-carbohydrate diet on the level of anxiety and neuromotor and cognitive functions in Wistar and DAT-KO rats

We compared anxiety, neuromotor, and cognitive functions in mutant rats with different allelic variants of dopamine transporter DAT knockout receiving balanced or excess in fat and fructose diet. The experiments were performed in DAT-/- homozygotes, DAT+/- heterozygotes, and DAT+/+ wild type rats. The genotype of DAT-KO rats was confirmed by restriction analysis of DAT gene compared to behavioral responses in the open field test (OF). Animals in the first groups of each strain were fed a balanced AIN93M diet; and those in the second groups with a high-fat/high-fructose diet. Neuromotor function was studied as grip strength, and behavioral responses were assessed in the elevated plus maze and conditioned passive avoidance response tests. The mass of the internal organs and white and brown fat, as well as selected lipid and nitrogen metabolism parameters in blood plasma were determined at the end of the experiment. DAT-/- had the highest specific grip strength, and showed an increase in initial exploratory activity in comparison with DAT+/- and DAT +/+. The exploratory activity was significantly reduced in the second test compared to the first one in DAT-/- and DAT+/- of first but not second group. Anxiety decreased with age in the second groups of DAT+/- and DAT+/+ (but not in DAT-/-) and was higher in DAT+/+ than in DAT+/- and DAT-/-. Excess fat and fructose resulted in the deterioration of short-term memory in DAT+/+. Lipidomic indices of blood plasma were less responsive to diet in DAT-/- and DAT-/+ in comparison to DAT+/+. The increased AsAT/AlAT activity ratio in DAT-/- compared with those in DAT+/+ suggests the activation of catabolism activity in the mutants. The consumption of excess fat and fructose significantly modified the effects produced by DAT gene allelic variants presumably due to the influence on the processes of dopamine metabolism.