Acetaminophen influences musculoskeletal signaling but not adaptations to endurance exercise training

Acetaminophen (ACE) is a widely used analgesic and antipyretic drug with various applications, from pain relief to fever reduction. Recent studies have reported equivocal effects of habitual ACE intake on exercise performance, muscle growth, and risks to bone health. Thus, this study aimed to assess the impact of a 6-week, low-dose ACE regimen on muscle and bone adaptations in exercising and non-exercising rats. Nine-week-old Wistar rats (n = 40) were randomized to an exercise or control (no exercise) condition with ACE or without (placebo). For the exercise condition, rats ran 5 days per week for 6 weeks at a 5% incline for 2 min at 15 cm/s, 2 min at 20 cm/s, and 26 min at 25 cm/s. A human equivalent dose of ACE was administered (379 mg/kg body weight) in drinking water and adjusted each week based on body weight. Food, water intake, and body weight were measured daily. At the beginning of week 6, animals in the exercise group completed a maximal treadmill test. At the end of week 6, rats were euthanized, and muscle cross-sectional area (CSA), fiber type, and signaling pathways were measured. Additionally, three-point bending and microcomputer tomography were measured in the femur. Follow-up experiments in human primary muscle cells were used to explore supra-physiological effects of ACE. Data were analyzed using a two-way ANOVA for treatment (ACE or placebo) and condition (exercise or non-exercise) for all animal outcomes. Data for cell culture experiments were analyzed via ANOVA. If omnibus significance was found in either ANOVA, a post hoc analysis was completed, and a Tukey's adjustment was used. ACE did not alter body weight, water intake, food intake, or treadmill performance (p > .05). There was a treatment-by-condition effect for Young's Modulus where placebo exercise was significantly lower than placebo control (p < .05). There was no treatment by condition effects for microCT measures, muscle CSA, fiber type, or mRNA expression. Phosphorylated-AMPK was significantly increased with exercise (p < .05) and this was attenuated with ACE treatment. Furthermore, phospho-4EBP1 was depressed in the exercise group compared to the control (p < .05) and increased in the ACE control and ACE exercise group compared to placebo exercise (p < .05). A low dose of ACE did not influence chronic musculoskeletal adaptations in exercising rodents but acutely attenuated AMPK phosphorylation and 4EBP1 dephosphorylation post-exercise.

MyD88 and not TRIF knockout is sufficient to abolish LPS-induced inflammatory responses in bone-derived macrophages

Macrophages play an important role in the response to infection and/or repair of injury in tissues. To examine the NF-κB pathway in response to an inflammatory stimulus, we used wild-type bone-marrow-derived macrophages (BMDMs) or BMDMs with knockout (KO) of myeloid differentiation primary response 88 (MyD88) and/or Toll/interleukin-1 receptor domain-containing adapter-inducing interferon-β (TRIF) via CRISPR/Cas9. Following treatment of BMDMs with lipopolysaccharide (LPS) to induce an inflammatory response, translational signalling of NF-κB was quantified via immunoblot and cytokines were measured. Our findings reveal that MyD88 KO, but not TRIF KO, decreased LPS-induced NF-κB signalling, and 10% expression of basal MyD88 expression was sufficient to partially rescue the abolished inflammatory cytokine secretion observed upon MyD88 KO.

The dose-response effects of arachidonic acid on primary human skeletal myoblasts and myotubes

Background

Cellular inflammatory response, mediated by arachidonic acid (AA) and cyclooxygenase, is a highly regulated process that leads to the repair of damaged tissue. Recent studies on murine C2C12 cells have demonstrated that AA supplementation leads to myotube hypertrophy. However, AA has not been tested on primary human muscle cells. Therefore, the purpose of this study was to determine whether AA supplementation has similar effects on human muscle cells.

Methods

Proliferating and differentiating human myoblasts were exposed to AA in a dose-dependent manner (50-0.80 µM) for 48 (myoblasts) or 72 (myotubes) hours. Cell viability was tested using a 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay and cell counting; myotube area was determined by immunocytochemistry and confocal microscopy; and anabolic signaling pathways were evaluated by western blot and RT-PCR.

Results

Our data show that the treatment of primary human myoblasts treated with 50 µM and 25 µM of AA led to the release of PGE₂ and PGF_2α at levels higher than those of control-treated cells (p < 0.001 for all concentrations). Additionally, 50 µM and 25 µM of AA suppressed myoblast proliferation, myotube area, and myotube fusion. Anabolic signaling indicated reductions in total and phosphorylated TSC2, AKT, S6, and 4EBP1 in myoblasts at 50 µM of AA (p < 0.01 for all), but not in myotubes. These changes were not affected by COX-2 inhibition with celecoxib.

Conclusion

Together, our data demonstrate that high concentrations of AA inhibit myoblast proliferation, myotube fusion, and myotube hypertrophy, thus revealing potential deleterious effects of AA on human skeletal muscle cell health and viability.

Celecoxib impairs primary human myoblast proliferation and differentiation independent of cyclooxygenase 2 inhibition

The use of non-steroidal anti-inflammatory drugs (NSAIDs) for treatment of musculoskeletal injuries is commonplace in the general, athletic, and military populations. While NSAIDs have been studied in a variety of tissues, the effects of NSAIDs on skeletal muscle have not been fully defined. To address this, we investigated the degree to which the cyclooxygenase (COX)-2-selective NSAID celecoxib affects muscle cell proliferation, differentiation, anabolic signaling, and mitochondrial function in primary human skeletal myoblasts and myotubes. Primary muscle cells were treated with celecoxib or NS-398 (a pharmacological inhibitor of COX-2) as a control. Celecoxib administration significantly reduced myoblast proliferation, viability, fusion, and myotube area in a dose-dependent manner, whereas NS-398 had no effect on any of these outcomes. Celecoxib treatment was also associated with reduced phosphorylation of ribosomal protein S6 in myoblasts, and reduced phosphorylation of AKT, p70S6K, S6, and ERK in myotubes. In contrast, NS-398 did not alter phosphorylation of these molecules in myoblasts or myotubes. In myoblasts, celecoxib significantly reduced mitochondrial membrane potential and respiration, as evidenced by the decreased citric acid cycle (CAC) intermediates cis-aconitic acid, alpha-keto-glutarate acid, succinate acid, and malic acid. Similar results were observed in myotubes, although celecoxib also reduced pyruvic acid, citric acid, and fumaric acid. NS-398 did not affect CAC intermediates in myoblasts or myotubes. Together, these data reveal that celecoxib inhibits proliferation, differentiation, intracellular signaling, and mitochondrial function in primary human myoblasts and myotubes independent of its function as a COX-2 inhibitor.

Comparison of CRISPR and adenovirus-mediated Myd88 knockdown in RAW 264.7 cells and responses to lipopolysaccharide stimulation

Genomic manipulation offers the possibility for novel therapies in lieu of medical interventions in use today. The ability to genetically restore missing inflammatory genes will have a monumental impact on our current immunotherapy treatments. This study compared the efficacy of two different genetic manipulation techniques: clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) transfection to adenoviral transduction to determine which method would provide the most transient and stable knockdown of myeloid differentiation primary response 88 (MyD88). MyD88 is a major regulator of nuclear factor kappa light chain enhancer of activated B cells (NFκB) pathway in Raw 264.7 macrophages. Following genetic manipulation, cells were treated for 24 h with Lipopolysaccharide (LPS) to stimulate the inflammatory pathway. Confirmation of knockdown was determined by western immunoblotting and quantification of band density. Both CRISPR/Cas9 and adenoviral transduction produced similar knockdown efficiency (~64% and 60%, respectively) in MyD88 protein 48 h post adenoviral transduction. NFκB phosphorylation was increased in CRISPR/Cas9-mediated MyD88 knockdown and control cells, but not in adenovirus-mediated MyD88 knockdown cells, following LPS administration. CRISPR/Cas9-mediated MyD88 knockdown macrophages treated with LPS for 24 h showed a 65% reduction in tumor necrosis factor alpha (TNFα) secretion, and a 67% reduction in interleukin-10 (IL-10) secretion when compared to LPS-stimulated control cells (P ≤ 0.01 for both). LPS did not stimulate TNFα or IL-10 secretion in adenovirus-mediated control or MyD88 knockdown cells. These data demonstrate that Raw 264.7 macrophages maintain responsiveness to inflammatory stimuli following CRISPR/Cas9-mediated reductions in MyD88, but not following adenovirus-mediated MyD88 knockdown.

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.

Exogenous Gene Transmission of Isocitrate Dehydrogenase 2 Mimics Ischemic Preconditioning Protection

Ischemic preconditioning confers organ-wide protection against subsequent ischemic stress. A substantial body of evidence underscores the importance of mitochondria adaptation as a critical component of cell protection from ischemia. To identify changes in mitochondria protein expression in response to ischemic preconditioning, we isolated mitochondria from ischemic preconditioned kidneys and sham-treated kidneys as a basis for comparison. The proteomic screen identified highly upregulated proteins, including NADP+-dependent isocitrate dehydrogenase 2 (IDH2), and we confirmed the ability of this protein to confer cellular protection from injury in murine S3 proximal tubule cells subjected to hypoxia. To further evaluate the role of IDH2 in cell protection, we performed detailed analysis of the effects of Idh2 gene delivery on kidney susceptibility to ischemia-reperfusion injury. Gene delivery of IDH2 before injury attenuated the injury-induced rise in serum creatinine (P<0.05) observed in controls and increased the mitochondria membrane potential (P<0.05), maximal respiratory capacity (P<0.05), and intracellular ATP levels (P<0.05) above those in controls. This communication shows that gene delivery of Idh2 can confer organ-wide protection against subsequent ischemia-reperfusion injury and mimics ischemic preconditioning.

Hydrodynamic Isotonic Fluid Delivery Ameliorates Moderate-to-Severe Ischemia-Reperfusion Injury in Rat Kidneys

Highly aerobic organs like the kidney are innately susceptible to ischemia-reperfusion (I/R) injury, which can originate from sources including myocardial infarction, renal trauma, and transplant. Therapy is mainly supportive and depends on the cause(s) of damage. In the absence of hypervolemia, intravenous fluid delivery is frequently the first course of treatment but does not reverse established AKI. Evidence suggests that disrupting leukocyte adhesion may prevent the impairment of renal microvascular perfusion and the heightened inflammatory response that exacerbate ischemic renal injury. We investigated the therapeutic potential of hydrodynamic isotonic fluid delivery (HIFD) to the left renal vein 24 hours after inducing moderate-to-severe unilateral IRI in rats. HIFD significantly increased hydrostatic pressure within the renal vein. When conducted after established AKI, 24 hours after I/R injury, HIFD produced substantial and statistically significant decreases in serum creatinine levels compared with levels in animals given an equivalent volume of saline via peripheral infusion (P<0.05). Intravital confocal microscopy performed immediately after HIFD showed improved microvascular perfusion. Notably, HIFD also resulted in immediate enhancement of parenchymal labeling with the fluorescent dye Hoechst 33342. HIFD also associated with a significant reduction in the accumulation of renal leukocytes, including proinflammatory T cells. Additionally, HIFD significantly reduced peritubular capillary erythrocyte congestion and improved histologic scores of tubular injury 4 days after IRI. Taken together, these results indicate that HIFD performed after establishment of AKI rapidly restores microvascular perfusion and small molecule accessibility, with improvement in overall renal function.