Redox Signaling Important for Inflammatory Response and Repair Capability in Muscle

A new study1 reports how the regulation of skeletal muscle adaptation to exercise depends critically on signaling via ROS (reactive oxygen species). This leads to the conclusion that excessive antioxidant activity can interfere with important beneficial regulatory pathways during exercise.

We have mentioned in earlier newsletters that it is important to be cautious in using very powerful antioxidants such as N-acetylcysteine because, under certain conditions, it can inhibit signaling via free radicals (reactive oxygen species) that may be important for regulating beneficial pathways. Exercise is a good example of the need to balance antioxidant and oxidant activity so as to avoid muscle injury by oxidative stress, while not inhibiting ROS signaling to the extent that it no longer induces beneficial adaptive responses to exercise in muscle. On the other hand, as we have also explained in our earlier articles on hydrogen, hydrogen is a selective antioxidant that scavenges the toxic hydroxyl radicals and the potent oxidant peroxynitrite that are not thought to be involved in cellular signaling, but do not interfere with the radicals that ARE important for physiological cellular signaling, such as superoxide and nitric oxide. [See “Hydrogen Therapy” in the June 2012 issue of Life Enhancement.]

This study involved 10 healthy male human subjects that were recreationally trained, as assessed by their maximal oxygen consumption, by exercising 3 times or more a week for 12 months or more. These subjects received either NAC (N-acetylcysteine) or placebo immediately after an acute bout of eccentric exercise on an isokinetic dynamometer (after, not before or during) and daily for 8 days after exercise in a double-blind, crossover, repeated measures design. Those receiving NAC were given 20 mg NAC/kg per day orally in a drink containing water, a sugar-free cordial, and a low calorie glucose/dextrose powder (to improve flavor and to prevent detection by subjects of when they had received placebo). Various techniques, including muscle biopsy, were used to analyze for muscle damage.

The study participants suffered severe muscle damage and inflammatory responses as a result of the eccentric exercise, as assessed by DOMS, CK (creatine kinase), CRP (C-reactive protein), proinflammatory cytokines, oxidative stress markers, and leukocytosis as well as a substantial decrease in muscle function.

Discussion of these effects included the explanation by the authors that “[a]dequate removal of cellular debris by neutrophils or macrophages may be critical for complete recovery of injured muscle, whereas molecules released by these cells (cytokines, prostaglandins, and chemokines) may regulate muscle repair and growth. [] NAC treatment resulted in a 30% drop in neutrophil count and macrophage infiltration 48 h after exercise. Whereas not statistically significant, it is of physiological interest. [] The NAC-enhanced GSH [glutathione] availability may have induced redox perturbations, downregulating pathways mediating immune cell mobilization. This may result in incomplete clearing of debris, which may be a prerequisite for full recovery of muscle performance.” Thus, the authors propose that their results point to amelioration of oxidative damage by an antioxidant (NAC) and enhanced muscle performance shortly after aseptic muscle damage, but that NAC may paradoxically delay long-term recovery by interfering with intracellular redox signaling pathways.

As it is made clear in the careful wording of the interpretation and conclusions, the understanding by the authors of why the effects of NAC were in some respects beneficial and in other respects harmful are based upon generally accepted (but not conclusively proven) scientific hypotheses concerning redox processes that are not fully understood. Still, the fact that redox pathways can induce both beneficial and harmful outcomes of ROS signaling, depending on the situation, the tissue, the quantities of oxidants and antioxidants, and other factors has become generally recognized.

On the basis of this and other work, we suggest that taking NAC immediately after eccentric exercise is probably not advisable.

An earlier study reported on the effects of a 4 week intervention of antioxidants on physical exercise in 20 healthy young men.2 The researchers also found that antioxidants interfered with beneficial adaptations to exercise. The scientists were specifically looking for what differences would occur when the subjects took (or did not take) antioxidants during exercise. In that study, the researchers found that exercise increased parameters of insulin sensitivity (as indicated by glucose infusion rate and plasma adiponectin), but only in those not taking antioxidants (1000 mg of vitamin C and 400 iu vitamin E per day). The study also involved taking muscle biopsies to detect gene expression changes. Results showed that there was increased expression of ROS [reactive oxygen species]-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, as well as PPARgamma coactivators PGC1alpha and PGC1beta—but only in the absence of antioxidants. The PPARgamma coactivators are part of a mitochondrial biogenesis system. Molecular mediators of ROS defenses, such as superoxide dismutases 1 and 2 and glutathione peroxidase were also increased during exercise but only when antioxidants were not being taken.

The scientists2 interpreted the results to be a consequence of hormesis—that is, these beneficial effects of exercise were the result of adaptive changes induced by ROS, which were prevented when adequate amounts of antioxidants were present. “Consistent with the concept of mitohormesis, exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.”2

Whether antioxidants interfere with the beneficial effects of exercise, then, is a matter largely of dose and timing. Thus, we recommend that when exercising, avoid taking large amounts of antioxidants or highly potent antioxidants (such as N-acetylcysteine)for 3 hours or so before the exercise, and for another couple of hours afterward.

Hydrogen, a Selective Antioxidant, May Not Interfere with Exercise Adaptations

It is possible (we speculate) that hydrogen, as a highly specific antioxidant, which scavenges mostly hydroxyl radicals and peroxynitrite, may not interfere with these effects of exercise which involved, as an example, increased oxidative defensive enzymes to protect against superoxide radicals, while hydrogen does not appear to interfere with physiological superoxide signaling. As reported in an early paper3 on hydrogen’s antioxidant properties, researchers said, “H2 selectively reduced the hydroxyl radical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H2 did not react with other ROS, which possess physiological roles.” We hope to see research on hydrogen and exercise published soon.


  1. Michailidis et al. Thiol-based antioxidant supplementation alters human skeletal muscle signaling and attenuates its inflammatory response and recovery after intense eccentric exercise. Am J Clin Nutr. 98:233-45 (2013).
  2. Ristow et al. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci USA. 106(21):8665-70 (2009).
  3. Ohsawa et al. Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. Nat Med. 13(6):688-94 (2007).