Enhancement of satellite cell differentiation and functional recovery in injured skeletal muscle by hyperbaric oxygen treatment

Effects of Hyperbaric Oxygen Therapy on Long COVID: A Systematic Review

The coronavirus disease (COVID-19) pandemic has resulted in an increasing population that is experiencing a wide range of long-lasting symptoms after recovery from the acute infection. Long COVID refers to this specific condition and is associated with diverse symptoms, such as fatigue, myalgias, dyspnea, headache, cognitive impairment, neurodegenerative symptoms, anxiety, depression, and a sense of despair. The potential of hyperbaric oxygen therapy (HBOT) to improve chronic fatigue, cognitive impairments, and neurological disorders has been established; therefore, the use of HBOT to treat long COVID has also been studied. We conducted a literature search between 1 January 2019 and 30 October 2023, focusing on the clinical efficacy and utility of HBOT for treating long COVID and found ten clinical studies that fit the review topic, including one case report, five one-group pretest-posttest design studies, one safety report from a randomized controlled trial (RCT), and three complete reports of RCTs. Most studies found that HBOT can improve quality of life, fatigue, cognition, neuropsychiatric symptoms, and cardiopulmonary function. Although HBOT has shown some benefits for long COVID symptoms, further rigorous large-scale RCTs are required to establish precise indications, protocols, and post-treatment evaluations.

Traumatic muscle injury

Traumatic muscle injury represents a collection of skeletal muscle pathologies caused by trauma to the muscle tissue and is defined as damage to the muscle tissue that can result in a functional deficit. Traumatic muscle injury can affect people across the lifespan and can result from high stresses and strains to skeletal muscle tissue, often due to muscle activation while the muscle is lengthening, resulting in indirect and non-contact muscle injuries (strains or ruptures), or from external impact, resulting in direct muscle injuries (contusion or laceration). At a microscopic level, muscle fibres can repair focal damage but must be completely regenerated after full myofibre necrosis. The diagnosis of muscle injury is based on patient history and physical examination. Imaging may be indicated to eliminate differential diagnoses. The management of muscle injury has changed within the past 5 years from initial rest, immobilization and (over)protection to early activation and progressive loading using an active approach. One challenge of muscle injury management is that numerous medical treatment options, such as medications and injections, are often used or proposed to try to accelerate muscle recovery despite very limited efficacy evidence. Another challenge is the prevention of muscle injury owing to the multifactorial and complex nature of this injury.

Effects of hyperbaric oxygen therapy on human psychomotor performance: A review

Psychomotor performance is the coordination of a sensory or ideational (cognitive) process and a motor activity. All sensorimotor processes involved in planning and execution of voluntary movements need oxygen supply and seem to be significantly disrupted in states of hypoxia. Hyperbaric oxygen therapy has become a widely used treatment in routine medicine and sport medicine due to its beneficial effects on different aspects of human physiology and performance. This paper presents state-of-the-art data on the effects of hyperbaric oxygen therapy on different aspects of human psychomotor function. The therapy's influence on musculoskeletal properties and motor abilities as well as the effects of hyperbaric oxygenation on cognitive, myocardial and pulmonary functions are presented. In this review the molecular and physiological processes related to human psychomotor performance in response to hyperbaric oxygen are discussed to contribute to this fast-growing field of research in integrative medicine. Please cite this article as: Olex-Zarychta D. Effects of hyperbaric oxygen therapy on human psychomotor performance: A review. J Integr Med. 2023; 21(5): 430-440.

Hyperbaric oxygen treatment for long coronavirus disease-19: a case report

BACKGROUND

The coronavirus disease 2019 pandemic has resulted in a growing population of individuals who experience a wide range of persistent symptoms referred to as "long COVID." Symptoms include neurocognitive impairment and fatigue. Two potential mechanisms could be responsible for these long-term unremitting symptoms: hypercoagulability, which increases the risk of blood vessel occlusion, and an uncontrolled continuous inflammatory response. Currently, no known treatment is available for long COVID. One of the options to reverse hypoxia, reduce neuroinflammation, and induce neuroplasticity is hyperbaric oxygen therapy. In this article, we present the first case report of a previously healthy athletic individual who suffered from long COVID syndrome treated successfully with hyperbaric oxygen therapy.

CASE PRESENTATION

A previously healthy 55-year-old Caucasian man presented 3 months after severe coronavirus disease 2019 infection with long COVID syndrome. His symptoms included a decline in memory, multitasking abilities, energy, breathing, and physical fitness. After evaluation that included brain perfusion magnetic resonance imaging, diffusion tensor imaging, computerized cognitive tests, and cardiopulmonary test, he was treated with hyperbaric oxygen therapy. Each session included exposure to 90 minutes of 100% oxygen at 2 atmosphere absolute pressure with 5-minute air breaks every 20 minutes for 60 sessions, 5 days per week. Evaluation after completing the treatment showed significant improvements in brain perfusion and microstructure by magnetic resonance imaging and significant improvement in memory with the most dominant effect being on nonverbal memory, executive functions, attention, information procession speed, cognitive flexibility, and multitasking. The improved cognitive functions correlated with the increased cerebral blood flow in brain regions as measured by perfusion magnetic resonance imaging. With regard to physical capacity, there was a 34% increase in the maximum rate of oxygen consumed during exercise and a 44% improvement in forced vital capacity. The improved physical measurements correlated with the regain of his pre-COVID physical capacity.

CONCLUSIONS

We report the first case of successfully treated long COVID symptoms with hyperbaric oxygen therapy with improvements in cognition and cardiopulmonary function. The beneficial effects of hyperbaric oxygen shed additional light on the pathophysiology of long COVID. As this is a single case report, further prospective randomized control studies are needed.

Effects of hyperoxia and hypoxia on the proliferation of C2C12 myoblasts

Hyperoxic conditions are known to accelerate skeletal muscle regeneration after injuries. In the early phase of regeneration, macrophages invade the injured area and subsequently secrete various growth factors, which regulate myoblast proliferation and differentiation. Although hyperoxic conditions accelerate muscle regeneration, it is unknown whether this effect is indirectly mediated by macrophages. Here, using C2C12 cells, we show that not only hyperoxia but also hypoxia enhance myoblast proliferation directly, without accelerating differentiation into myotubes. Under hyperoxic conditions (95% O₂ + 5% CO₂), the cell membrane was damaged because of lipid oxidization, and a disrupted cytoskeletal structure, resulting in suppressed cell proliferation. However, a culture medium containing vitamin C (VC), an antioxidant, prevented this lipid oxidization and cytoskeletal disruption, resulting in enhanced proliferation in response to hyperoxia exposure of ≤4 h/day. In contrast, exposure to hypoxic conditions (95% N₂ + 5% CO₂) for ≤8 h/day enhanced cell proliferation. Hyperoxia did not promote cell differentiation into myotubes, regardless of whether the culture medium contained VC. Similarly, hypoxia did not accelerate cell differentiation. These results suggest that regardless of hyperoxia or hypoxia, changes in oxygen tension can enhance cell proliferation directly, but do not influence differentiation efficiency in C2C12 cells. Moreover, excess oxidative stress abrogated the enhancement of myoblast proliferation induced by hyperoxia. This research will contribute to basic data for applying the effects of hyperoxia or hypoxia to muscle regeneration therapy.

Expression profiles of SLC39A/ZIP7, ZIP8 and ZIP14 in response to exercise-induced skeletal muscle damage

BACKGROUND

Zinc transporters are thought to facilitate the mobilization of zinc (Zn) and the role of Zn as a signaling mediator during cellular events. Little is known about the response of Zn movement and zinc transporters during muscle proliferation and differentiation processes after damage.

METHODS

After rats were subjected to one 90-min session of downhill running to cause muscle damage, the gastrocnemius muscles were harvested to assess the expression of zinc transporters SLC39A/ZIP7, ZIP8, ZIP14 and myogenic regulatory factors at the 0 h, 6 h, 12 h, 1 d, 2 d, 3 d, 1 w and 2 w time points after exercise.

RESULTS

SLC39A/ZIP7, ZIP8 and ZIP14 had translocated to different compartments of the cell following damage, and they exhibited differential expression profiles after eccentric exercise. The results regarding the myogenetic regulators showed that nf-κb was upregulated 2 d after exercise, and STAT3 and Akt1 mRNA levels were mostly expressed 2 w after exercise. The upregulation of phosphatidylinositol 3-kinase, catalytic subunit gamma (pik3cg), erk1 and erk2 mostly occurred at the early stage (6 h or 12 h) after exercise. In addition, we found that zip7, zip8 and zip14 expression was moderately correlated with certain markers of muscle regeneration.

CONCLUSION

The zinc transporters SLC39A/ZIP7, ZIP8 and ZIP14 have differential expression profiles upon eccentric exercise, and they might regulate muscle proliferation or differentiation processes through different cellular pathways after exercise-induced muscle damage.

Hemodynamic response during hyperbaric treatment on skeletal muscle in a type 2 diabetes rat model

Mild hyperbaric treatment prevents type 2 diabetes progression due to increased oxygen concentration and blood flow in skeletal muscle. However, it remains unknown whether this treatment is effective during all stages of type 2 diabetes. This study aimed to investigate the influences of hyperbaric treatment at 1.3 atmospheres absolute (ATA) on hemodynamic response in various stages of type 2 diabetes. Otsuka Long-Evans Tokushima fatty (OLETF) and Long-Evans Tokushima Otsuka (LETO) rats were used as models of type 2 diabetes and healthy controls, respectively. Glucose levels were significantly higher in OLETF rats than in LETO rats at all ages. Glucose intolerance gradually increased with age in OLETF rats. Insulin levels in OLETF rats were significantly higher at 20-week-old, however, were significantly lower at 60-week-old than in LETO rats. Oxy-Hb, total Hb, and StO₂ in skeletal muscle were increased during hyperbaric treatment in both rats. The hemodynamic changes were significantly higher in OLETF rats than LETO rats, and those changes were also pronounced at 8-week-old compared with other age in OLETF rats. These results suggest that hyperbaric treatment at 1.3 ATA acts on pathophysiological factors and the efficacy could be found only in the early stage of type 2 diabetes.

Disease-associated metabolic alterations that impact satellite cells and muscle regeneration: perspectives and therapeutic outlook

Many chronic disease patients experience a concurrent loss of lean muscle mass. Skeletal muscle is a dynamic tissue maintained by continuous protein turnover and progenitor cell activity. Muscle stem cells, or satellite cells, differentiate (by a process called myogenesis) and fuse to repair and regenerate muscle. During myogenesis, satellite cells undergo extensive metabolic alterations; therefore, pathologies characterized by metabolic derangements have the potential to impair myogenesis, and consequently exacerbate skeletal muscle wasting. How disease-associated metabolic disruptions in satellite cells might be contributing to wasting is an important question that is largely neglected. With this review we highlight the impact of various metabolic disruptions in disease on myogenesis and skeletal muscle regeneration. We also discuss metabolic therapies with the potential to improve myogenesis, skeletal muscle regeneration, and ultimately muscle mass.

Hyperbaric Oxygen Therapy Attenuates Burn-Induced Denervated Muscle Atrophy

Background: Neuronal apoptosis and inflammation in the ventral horn of the spinal cord contribute to denervated muscle atrophy post-burn. Hyperbaric oxygen therapy (HBOT) exerts anti-inflammation and neuroprotection. Furthermore, hypoxia-inducible factor (HIF)-1α has been reported to promote inflammation and apoptosis. We investigated the therapeutic potential of HBOT and the role of HIF-1α post-burn. Methods: Sprague-Dawley rats were divided into three groups: a control group, an untreated burn group receiving burn and sham treatment, and a HBOT group receiving burn injury and HBOT. The burn injury was induced with 75ºC ± 5ºC at the right hindpaw. HBOT (100% oxygen at 2.5 atmosphere, 90 min/day) and sham HBOT (21% oxygen at 1 atmosphere, 90 min/day) was started on day 28 after burn injury and continued for 14 treatments (days 28-41). Incapacitance (hind limb weight bearing) testing was conducted before burn and weekly after burn. At day 42 post-burn, the gastrocnemius muscle and the spinal cord ventral horn were analyzed. Results: HBOT improved burn-induced weight bearing imbalance. At day 42 post-burn, less gastrocnemius muscle atrophy and fibrosis were noted in the HBOT group than in the untreated burn group. In the ventral horn, HBOT attenuated the neuronal apoptosis and glial activation post-burn. The increases in phosphorylated AKT/mTOR post-burn were reduced after HBOT. HBOT also inhibited HIF-1α signaling, as determined by immunofluorescence and western blot. Conclusions: HBOT reduces burn-induced neuronal apoptosis in the ventral horn, possibly through HIF-1α signaling.

A novel PAI-1 inhibitor prevents ageing-related muscle fiber atrophy

Sarcopenia is among the most common medical problems of the aging population worldwide and a major social concern. Here, we explored the therapeutic potential of TM5484, a novel orally available PAI-1 inhibitor, to prevent sarcopenia. The sarcopenic phenotypes of the calf muscle of 12- and 6-month-old middle-aged mice were compared. Although significant decline of isometric gastrocnemius muscle force was detected in the older untreated mice, those administered TM5484 had significantly greater calf muscle force, as determined using isometric measurements by electrical stimulation. Histological analysis indicated that cross-sectional gastrocnemius muscle fibers in untreated older mice were thinner than those in younger mice; however, TM5484-treated group showed thicker fibers than younger mice. Treatment with TM5484 for 6 months enhanced Igf1, Atrogin-1, Mt-Co1, and Chrna1 mRNA expression in the mice gastrocnemius muscle, with increased serum IGF-1 concentration. TM5484 induced dose-dependent Igf1, Atrogin-1, and Chrna1 expression in C2C12 myoblastic cells, confirming cell autonomous effect. Further, the presence of plasmin for 72 h caused significantly increased Igf1 expression in C2C12 cells. These findings suggest that oral PAI-1 inhibitors represent a promising therapeutic candidate for preventing sarcopenia progression in humans.

Comparison of the efficacy of topical hyperbaric oxygen therapy alone vs a combination of physical methods including topical hyperbaric oxygen therapy, magnetotherapy, and low-energy light therapy in the treatment of venous leg ulcers

The aim of the study was to compare the therapeutic efficacy of topical hyperbaric oxygen therapy alone vs a combination of physical methods including topical hyperbaric oxygen therapy, magnetotherapy and low-energy light therapy in the treatment of venous leg ulcers. Thirty-six patients were treated with topical oxygen hyperbaria and 29 patients were treated with a combination of physical methods. The assessment of ulcer surface area with use of a planimetric method, pain intensity with use of Laitinen scale and quality of life by means of EuroQol scale were performed. In both groups a statistically significant (P < .05) reduction of ulcer surface area has been obtained, but in patients treated with combined physical therapy average percentage reduction of ulcer surface area (36.44% ± 11.04%) was statistically significantly (P = .00001) bigger as compared to other group (13.65% ± 8.32%). In both groups of patients statistically significant (P < .05) reduction of frequency and intensity of pain, reduced intake of analgesic drugs and reduction of limitations of physical activity, as well as statistically significant improvement of quality of life have been observed, but in patients treated with combined physical therapy an average increase in the score in EuroQoL scale (61.03 ± 7.14) was statistically significantly (P = .00001) bigger as compared to other group (25.27 ± 8.16). It was concluded that topical hyperbaric oxygen therapy alone and a combination of physical methods cause significant reduction of ulcer surface area, reduction of pain intensity, as well as improvement of the quality of life, but a combination of physical methods is more efficient.

Hyperbaric Oxygen Therapy in Sports Musculoskeletal Injuries

Hyperbaric oxygen therapy (HBOT) is a well-established treatment for a variety of conditions. Hyperbaric oxygen therapy is the administration of 100% oxygen breathing in a pressure vessel at higher than atmospheric pressure (1 atmosphere absolute = 101 kPa). Typically, treatment is given daily for between 1 and 2 h at pressures of 2.0 to 2.8 ATA, depending on the indication. Sporting injuries are often treated over 3 to 10 sessions. Hyperbaric oxygen therapy has been documented to be effective and is approved in 14 medical indications by the Undersea and Hyperbaric Medical Society, including, but not limited to, carbon monoxide poisoning, compromised skin grafts and flaps, crush injuries, necrotizing soft tissue infections, and nonhealing ulcers with arterial insufficiencies. Recently, HBOT for sports musculoskeletal injuries is receiving increased attention. Hyperbaric oxygen therapy may allow injured athletes to recover faster than normal rehabilitation methods. Any reduction in collegiate and professional athletes' rehabilitation period can be financially significant for top-level sports teams; however, further research is required to confirm HBOT's benefits on sports musculoskeletal injuries. The purpose of this review to discuss the current understanding of HBOT as a treatment modality for common musculoskeletal injuries in sport medicine. Moreover, we will highlight the advantages and disadvantages of this modality, as well as relevant clinical and research applications.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

VEGF and bFGF induction by nitric oxide is associated with hyperbaric oxygen-induced angiogenesis and muscle regeneration

Hyperbaric oxygen (HBO) treatment promotes early recovery from muscle injury. Reactive oxygen species (ROS) upregulation is a key mechanism of HBO, which produces high O₂ content in tissues through increased dissolution of oxygen at high pressure. Nitric oxide (NO), a type of ROS, generally stabilizes hypoxia-inducible factor (HIF) 1α and stimulates secretion of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) from endothelial cells and macrophages, which then induces angiogenesis. The purpose of the present study was to investigate whether HBO could promote angiogenesis via induction of NO and induce muscle regeneration in contused rat skeletal muscles. The HBO protocol consisted of 2.5 atmospheres absolute (ATA) 100% oxygen for 120 minutes, once a day for 5 consecutive days. We also evaluated the effects of a ROS inhibitor (NAC) or NOS-specific inhibitor (L-NAME) on HBO. HBO significantly increased NO₃⁻, VEGF, and bFGF levels and stabilized HIF1α within 1 day. HBO promoted blood vessel formation at 3–7 days and muscle healing at 5–7 days after contusion. Administration of both NAC and L-NAME before HBO suppressed angiogenesis and muscle regeneration even after HBO. HBO thus promoted angiogenesis and muscle regeneration mainly through generation of NO in the early phase after muscle contusion injury.

The Effect of Hyperbaric Oxygen Treatment on Myoblasts and Muscles After Contusion Injury

The recommended treatment varies depending on the severity of muscle injuries. The aim of this study was to evaluate the in vitro myoblast proliferation and the in vivo histologic and physiologic effects of hyperbaric oxygen treatment on muscle healing after contusion. Cells from the C2C12 myoblast cell line were exposed to 100% O₂ for 25 min then to air for 5 min at 2.5 atmospheres absolute in a hyperbaric chamber for a total treatment duration of 90 min per 48 h at intervals of 2, 4, 6 and 8 days. Cell growth measurements and western blot analysis of myogenin and actin were performed. Then, 18 mice aged 8-10 weeks were used in the muscle contusion model. The histologic and physiologic effects and muscle regeneration after hyperbaric oxygen treatment were evaluated. The myoblast growth rate was significantly higher (p < 0.05) after hyperbaric oxygen treatment. Densitometric evaluation demonstrated a 39% (p < 0.05) and 25% (p < 0.05) increase in myogenin and actin protein levels, respectively, in the cells treated with 1 dose of hyperbaric oxygen. Similarly, the myogenin and actin protein levels increased for samples receiving multiple hyperbaric oxygen treatments when compared with the control. Physiologic evaluation of fast twitch and tetanus strength revealed a significant difference between the control group and the 14-day hyperbaric oxygen group. In conclusion, hyperbaric oxygen treatment increases the myoblast growth rate and myogenin and actin production. Better histologic and physiologic performance were found after hyperbaric oxygen treatment in animal contusion model. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:329-335, 2020.

The effect of hyperbaric oxygenation therapy on myocardial function

Hyperbaric oxygenation therapy is successfully implemented for the treatment of several disorders. Data on the effect of hyperbaric oxygenation on echocardiographic parameters in asymptomatic patients is limited. The current study sought to evaluate the effect of hyperbaric oxygenation therapy on echocardiographic parameters in asymptomatic patients. Thirty-one consecutive patients underwent a 60-sessions course of hyperbaric oxygenation therapy in an attempt to improve cognitive impairment. In all subjects, echocardiography examination was performed before and after a course of hyperbaric oxygenation therapy. Conventional and speckle tracking imaging parameters were calculated and analyzed. The mean age was 70 ± 9.5 years, 28 [90%] were males. History of coronary artery disease was present in 12 [39%]. 94% suffered from hypertension, 42% had diabetes mellitus. Baseline wall motion abnormalities were found in eight patients, however, global ejection fraction was within normal limits. During the study, ejection fraction [EF], increased from 60.71 ± 6.02 to 62.29 ± 5.19%, p = 0.02. Left ventricular end systolic volume [LVESV], decreased from 38.08 ± 13.30 to 35.39 ± 13.32 ml, p = 0.01. Myocardial performance index [MPi] improved, from 0.29 ± 0.07 to 0.26 ± 0.08, p = 0.03. Left ventricular [LV] global longitudinal strain increased from - 19.31 ± 3.17% to - 20.16 ± 3.34%, p = 0.036 due to improvement in regional strain in the apical and antero-septal segments. Twist increased from 18.32 ± 6.61° to 23.12 ± 6.35° p = 0.01, due to improvement in the apical rotation, from 11.76 ± 4.40° to 16.10 ± 5.56°, p = 0.004. Hyperbaric oxygen therapy appears to improve left ventricular function, especially in the apical segments, and is associated with better cardiac performance. If our results are confirmed in further studies, HBOT can be used in many patients with heart failure and systolic dysfunction.

Biotoxins in muscle regeneration research

Skeletal muscles are characterized by their unique regenerative capacity following injury due to the presence of muscle precursor cells, satellite cells. This characteristic allows researchers to study muscle regeneration using experimental injury models. These injury models should be stable and reproducible. Variety of injury models have been used, among which the intramuscular injection of myotoxic biotoxins is considered the most common and widespread method in muscle regeneration research. By using isolated biotoxins, researchers could induce acute muscle damage and regeneration in a controlled and reproducible manner. Therefore, it is considered an easy method for inducing muscle injury in order to understand the different mechanisms involved in muscle injuries and tissue response following injury. However, different toxins and venoms have different compositions and subsequently the possible effects of these toxins on skeletal muscle vary according to their composition. Moreover, regeneration of injured muscle by venoms and toxins varies according to the target of toxin or venom. Therefore, it is essential for researcher to be aware of the mechanism and possible target of toxin-induced injury. The current paper provides an overview of the biotoxins used in skeletal muscle research.

Early Recovery of Exercise-Related Muscular Injury by HBOT

Early recovery from muscular injury is crucial for elite athletes. Hyperbaric oxygen therapy (HBOT) has been reported to be beneficial in terms of accelerating cell recovery and tissue repair, which are considered to be helpful for eliminating fatigue and recovering stamina. This study was performed to evaluate the efficacy of HBOT for exercise-related muscular injury. Forty-one athletes with exercise-related muscular injuries were recruited and randomized into an HBOT group and a control group. All participants received 10 sessions of either HBOT or placebo treatment. The brief pain inventory (BPI) was completed, and serum samples were analyzed. Data were collected before treatment (T1), at the end of the fifth treatment session (T2), at the end of the tenth treatment session (T3), and two weeks after T3 (T4). At T3, the HBOT group showed prominent reductions in the levels of creatine phosphokinase (CK), glutamic oxaloacetate transaminase (GOT), and myoglobin (MB), which lasted until T4. However, the control group did not present any statistical differences in levels from T1 to T4. In terms of pain intensity and interference, the HBOT group showed significant improvements at T3, while no improvements were observed in the control group. In conclusion, HBOT facilitates the early recovery of exercise-related muscular injury. This trial is registered with ISRCTN17817041.

Lactate Promotes Myoblast Differentiation and Myotube Hypertrophy via a Pathway Involving MyoD In Vitro and Enhances Muscle Regeneration In Vivo

Lactate is a metabolic substrate mainly produced in muscles, especially during exercise. Recently, it was reported that lactate affects myoblast differentiation; however, the obtained results are inconsistent and the in vivo effect of lactate remains unclear. Our study thus aimed to evaluate the effects of lactate on myogenic differentiation and its underlying mechanism. The differentiation of C2C12 murine myogenic cells was accelerated in the presence of lactate and, consequently, myotube hypertrophy was achieved. Gene expression analysis of myogenic regulatory factors showed significantly increased myogenic determination protein (MyoD) gene expression in lactate-treated cells compared with that in untreated ones. Moreover, lactate enhanced gene and protein expression of myosin heavy chain (MHC). In particular, lactate increased gene expression of specific MHC isotypes, MHCIIb and IId/x, in a dose-dependent manner. Using a reporter assay, we showed that lactate increased promoter activity of the MHCIIb gene and that a MyoD binding site in the promoter region was necessary for the lactate-induced increase in activity. Finally, peritoneal injection of lactate in mice resulted in enhanced regeneration and fiber hypertrophy in glycerol-induced regenerating muscles. In conclusion, physiologically high lactate concentrations modulated muscle differentiation by regulating MyoD-associated networks, thereby enhancing MHC expression and myotube hypertrophy in vitro and, potentially, in vivo.

Hyperbaric oxygen reduces inflammation, oxygenates injured muscle, and regenerates skeletal muscle via macrophage and satellite cell activation

Hyperbaric oxygen treatment (HBO) promotes rapid recovery from soft tissue injuries. However, the healing mechanism is unclear. Here we assessed the effects of HBO on contused calf muscles in a rat skeletal muscle injury model. An experimental HBO chamber was developed and rats were treated with 100% oxygen, 2.5 atmospheres absolute for 2 h/day after injury. HBO reduced early lower limb volume and muscle wet weight in contused muscles, and promoted muscle isometric strength 7 days after injury. HBO suppressed the elevation of circulating macrophages in the acute phase and then accelerated macrophage invasion into the contused muscle. This environment also increased the number of proliferating and differentiating satellite cells and the amount of regenerated muscle fibers. In the early phase after injury, HBO stimulated the IL-6/STAT3 pathway in contused muscles. Our results demonstrate that HBO has a dual role in decreasing inflammation and accelerating myogenesis in muscle contusion injuries.

Extracorporeal Shock Wave Therapy Accelerates Regeneration After Acute Skeletal Muscle Injury

BACKGROUND

Muscle injuries are among the most common sports-related lesions in athletes; however, optimal treatment remains obscure. Extracorporeal shock wave therapy (ESWT) may be a promising approach in this context, because it has gained increasing importance in tissue regeneration in various medical fields.

HYPOTHESIS

ESWT stimulates and accelerates regenerative processes of acute muscle injuries.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adult Sprague-Dawley rats were divided into 4 experimental groups (2 ESWT+ groups and 2 ESWT- groups) as well as an uninjured control group (n ≥ 6 in each group). An acute cardiotoxin-induced injury was set into the quadriceps femoris muscle of rats in the experimental groups. A single ESWT session was administered to injured muscles of the ESWT+ groups 1 day after injury, whereas ESWT- groups received no further treatment. At 4 and 7 days after injury, 1 each of the ESWT+ and ESWT- groups was euthanized. Regenerating lesions were excised and analyzed by histomorphometry and immunohistochemistry to assess fiber size, myonuclear content, and recruitment of satellite cells.

RESULTS

The size and myonuclear content of regenerating fibers in ESWT+ muscle was significantly increased compared with ESWT- muscle fibers at both 4 and 7 days after injury. Similarly, at both time points, ESWT+ muscles exhibited significantly higher contents of pax7-positive satellite cells, mitotically active H3P⁺ cells, and, of cells expressing the myogenic regulatory factors, myoD and myogenin, indicating enhanced proliferation and differentiation rates of satellite cells after ESWT. Mitotic activity at 4 days after injury was doubled in ESWT+ compared with ESWT- muscles.

CONCLUSION

ESWT stimulates regeneration of skeletal muscle tissue and accelerates repair processes.

CLINICAL RELEVANCE

We provide evidence for accelerated regeneration of damaged skeletal muscle after ESWT. Although further studies are necessary, our findings support the view that ESWT is an effective method to improve muscle healing, with special relevance to sports injuries.

Achieving Acetylcholine Receptor Clustering in Tissue-Engineered Skeletal Muscle Constructs In vitro through a Materials-Directed Agrin Delivery Approach

Volumetric muscle loss (VML) can result from trauma, infection, congenital anomalies, or surgery, and produce permanent functional and cosmetic deficits. There are no effective treatment options for VML injuries, and recent advances toward development of muscle constructs lack the ability to achieve innervation necessary for long-term function. We sought to develop a proof-of-concept biomaterial construct that could achieve acetylcholine receptor (AChR) clustering on muscle-derived cells (MDCs) in vitro. The approach consisted of the presentation of neural (Z+) agrin from the surface of microspheres embedded with a fibrin hydrogel to muscle cells (C2C12 cell line or primary rat MDCs). AChR clustering was spatially restricted to areas of cell (C2C12)-microsphere contact when the microspheres were delivered in suspension or when they were incorporated into a thin (2D) fibrin hydrogel. AChR clusters were observed from 16 to 72 h after treatment when Z+ agrin was adsorbed to the microspheres, and for greater than 120 h when agrin was covalently coupled to the microspheres. Little to no AChR clustering was observed when agrin-coated microspheres were delivered from specially designed 3D fibrin constructs. However, cyclic stretch in combination with agrin-presenting microspheres led to dramatic enhancement of AChR clustering in cells cultured on these 3D fibrin constructs, suggesting a synergistic effect between mechanical strain and agrin stimulation of AChR clustering in vitro. These studies highlight a strategy for maintaining a physiological phenotype characterized by motor endplates of muscle cells used in tissue engineering strategies for muscle regeneration. As such, these observations may provide an important first step toward improving function of tissue-engineered constructs for treatment of VML injuries.

Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity

Reduced oxygen (O₂) levels (hypoxia) are present during embryogenesis and exposure to altitude and in pathologic conditions. During embryogenesis, myogenic progenitor cells reside in a hypoxic microenvironment, which may regulate their activity. Satellite cells are myogenic progenitor cells localized in a local environment, suggesting that the O₂ level could affect their activity during muscle regeneration. In this review, we present the idea that O₂ levels regulate myogenesis and muscle regeneration, we elucidate the molecular mechanisms underlying myogenesis and muscle regeneration in hypoxia and depict therapeutic strategies using changes in O₂ levels to promote muscle regeneration. Severe hypoxia (≤1% O₂) appears detrimental for myogenic differentiation in vitro, whereas a 3-6% O₂ level could promote myogenesis. Hypoxia impairs the regenerative capacity of injured muscles. Although it remains to be explored, hypoxia may contribute to the muscle damage observed in patients with pathologies associated with hypoxia (chronic obstructive pulmonary disease, and peripheral arterial disease). Hypoxia affects satellite cell activity and myogenesis through mechanisms dependent and independent of hypoxia-inducible factor-1α. Finally, hyperbaric oxygen therapy and transplantation of hypoxia-conditioned myoblasts are beneficial procedures to enhance muscle regeneration in animals. These therapies may be clinically relevant to treatment of patients with severe muscle damage.-Chaillou, T. Lanner, J. T. Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity.

Alternative treatments for muscle injury: massage, cryotherapy, and hyperbaric oxygen

Current evidence suggests that popular alternative therapies such as massage, cryotherapy, and hyperbaric oxygen exposure as currently practiced on humans have little effect on recovery from minor muscle damage such as induced by exercise. While further research is still needed, hyperbaric oxygen exposure shows clear promise for potentially being a successful adjunct treatment for enhancing muscle repair and recovery from more severe crush on contusion injury in humans. Cryotherapy or icing, as currently practiced, will not likely be successful in cooling muscle sufficiently to have any significant influence on muscle repair regardless of the degree of injury. However, based on studies in animal models, it may be that if sufficient muscle cooling could be achieved in humans, it could actually delay recovery and increase muscle scarring following significant muscle damage. Conclusions about the effectiveness of massage on influencing muscle recovery from more severe injury cannot yet be made due to a lack of experimental evidence with a more significant muscle damage model.

P21 deficiency delays regeneration of skeletal muscular tissue

The potential relationship between cell cycle checkpoint control and tissue regeneration has been indicated. Despite considerable research being focused on the relationship between p21 and myogenesis, p21 function in skeletal muscle regeneration remains unclear. To clarify this, muscle injury model was recreated by intramuscular injection of bupivacaine hydrochloride in the soleus of p21 knockout (KO) mice and wild type (WT) mice. The mice were sacrificed at 3, 14, and 28 days post-operation. The results of hematoxylin-eosin staining and immunofluorescence of muscle membrane indicated that muscle regeneration was delayed in p21 KO mice. Cyclin D1 mRNA expression and both Ki-67 and PCNA immunohistochemistry suggested that p21 deficiency increased cell cycle and muscle cell proliferation. F4/80 immunohistochemistry also suggested the increase of immune response in p21 KO mice. On the other hand, both the mRNA expression and western blot analysis of MyoD, myogenin, and Pax7 indicated that muscular differentiation was delayed in p21KO mice. Considering these results, we confirmed that muscle injury causes an increase in cell proliferation. However, muscle differentiation in p21 KO mice was inhibited due to the low expression of muscular synthesis genes, leading to a delay in the muscular regeneration. Thus, we conclude that p21 plays an important role in the in vivo healing process in muscular injury.