Redefining the major contributors to superoxide production in contracting skeletal muscle. The role of NAD(P)H oxidases

Abstract

The production of reactive oxygen and nitrogen species (RONS) by skeletal muscle is important as it (i) underlies oxidative damage in many degenerative muscle pathologies and (ii) plays multiple regulatory roles by fulfilling important cellular functions. Superoxide and nitric oxide (NO) are the primary radical species produced by skeletal muscle and studies in the early 1980s demonstrated that their generation is augmented during contractile activity. Over the past 30 years considerable research has been undertaken to identify the major sites that contribute to the increased rate of RONS generation in response to contractions. It is widely accepted that NO is regulated by the nitric oxide synthases, however the sites that modulate changes in superoxide during exercise remain unclear. Despite the initial indications that the mitochondrial electron transport chain was the predominant source of superoxide during activity, with the development of analytical methods a number of alternative potential sites have been identified including the NAD(P)H oxidases, xanthine oxidase, cyclooxygenases, and lipoxygenases linked to the activity of the phospholipase A2 enzymes. In the present review we outline the subcellular sites that modulate intracellular changes in superoxide in skeletal muscle and based on the available experimental evidence in the literature we conclude that the NAD(P)H oxidases are likely to be the major superoxide generating sources in contracting skeletal muscle.

Redox homeostasis and age‐related deficits in neuromuscular integrity and function

“…Aerobic organisms including humans have adapted well to the atmosphere, using atmospheric O 2 by respiration and to obtain energy efficiency 46. Although O 2 plays a key role in aerobic cellular metabolism, studies in the 1950s showed that O 2 could cause cellular damage47 by the generation of reactive species (Figure 2), derivatives of O 2 48.…”

“…Briefly, superoxide is generated by the mitochondrial electron transport chain including complex I, complex III76, 77 and, recently, complex II78, 79, 80; the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzymes including NOX2, NOX4, DUOX1 and DUOX255, 56, 59, 81; xanthine oxidase82, 83; and the lipoxygenases (LOXs),84 which are linked to arachidonic acid released by the phospholipase A 2 enzymes85, 86 (for a detailed review, see Ref. [46]. …”

“…NO is a weak reducing agent, with a relatively long half‐life70 and reacts with O 2 to form nitric dioxide and superoxide to produce peroxynitrite 110. There are three different isoforms of NOS expressed in skeletal muscle; the neuronal NOS (nNOS or type I), the inducible NOS (iNOS or type II) and the endothelial NOS isoenzyme (eNOS or type III) 46, 111. nNOS, originally discovered in neuronal tissue, is expressed along the sarcolemma of skeletal muscle fibres and interacts with the dystrophin–glycoprotein complex via a linkage to α1‐syntrophin 112.…”

“…This study instigated intensive research in the field or redox biology, and the first article to demonstrate that skeletal muscle augmented reactive species in response to contractile activity appeared in 1982 50. These studies cited the mitochondrial organelle as the major source of reactive species in muscle cells,50, 178 but over the past 35 years, the development of analytical approaches has been instrumental in the discovery of additional redox sites in various subcellular compartments of skeletal myofibres 46, 55. RONS produced by skeletal muscle were initially considered as ‘toxic’ by‐products of metabolic processes inducing cellular damage and since these initial reports, a substantial amount of evidence suggests that redox homeostasis plays an underlying role in various human myopathies, neurodegenerative and metabolic diseases including muscular dystrophies, amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease and diabetes; for detailed reviews, see Refs [112, 179, 180, 181].…”

Sites of Superoxide and Hydrogen Peroxide Production by Muscle Mitochondria Assessed ex Vivo under Conditions Mimicking Rest and Exercise

“…However, excess production is detrimental for skeletal muscle performance (30,31). Mitochondria are leading candidates for the increased production of these reactive species during exercise (30,32), although others argue for non-mitochondrial sources (26,32).…”