Inhalation of carbon monoxide reduces skeletal muscle injury after hind limb ischemia-reperfusion injury in mice

Carbon Monoxide Alleviates Post-ischemia-reperfusion Skeletal Muscle Injury and Systemic Inflammation

Restoration of blood flow in skeletal muscle after a prolonged period of ischemia induces muscular ischemia-reperfusion injury, leading to local injury/dysfunction in muscles followed by systemic inflammatory responses. However, preventive/curative agents for skeletal muscle ischemia injury are unavailable in clinics to date. Increasing evidence has validated that carbon monoxide (CO) prevents the progression of ischemia-reperfusion injury in various organs owing to its versatile bioactivity. Previously, we developed a bioinspired CO donor, CO-bound red blood cells (CO-RBC), which mimics the dynamics of RBC-associated CO in the body. In the present study, we have tested the therapeutic potential of CO-RBC in muscular injury/dysfunction and secondary systemic inflammation induced by skeletal muscle ischemia-reperfusion. The results indicate that CO-RBC rather than RBC alone suppressed elevation of plasma creatine phosphokinase, a marker of muscular injury, in rats subjected to both hind limbs ischemia-reperfusion. In addition, the results of the treadmill walking test revealed a significantly decreased muscular motor function in RBC-treated rats subjected to both hind limbs ischemia-reperfusion than that in healthy rats, however, CO-RBC treatment facilitated sustained muscular motor functions after hind limbs ischemia-reperfusion. Furthermore, CO-RBC rather than RBC suppressed the production of tumour necrosis factor (TNF)-α and interleukin (IL)-6, which were upregulated by muscular ischemia-reperfusion. Interestingly, CO-RBC treatment induced higher levels of IL-10 compared to saline or RBC treatments. Based on these findings, we suggest that CO-RBC exhibits a suppressive effect against skeletal muscle injury/dysfunction and systemic inflammatory responses after skeletal muscle ischemia-reperfusion.

Hmox1 (Heme Oxygenase-1) Protects Against Ischemia-Mediated Injury via Stabilization of HIF-1α (Hypoxia-Inducible Factor-1α)

OBJECTIVE

Hmox1 (heme oxygenase-1) is a stress-induced enzyme that catalyzes the degradation of heme to carbon monoxide, iron, and biliverdin. Induction of Hmox1 and its products protect against cardiovascular disease, including ischemic injury. Hmox1 is also a downstream target of the transcription factor HIF-1α (hypoxia-inducible factor-1α), a key regulator of the body's response to hypoxia. However, the mechanisms by which Hmox1 confers protection against ischemia-mediated injury remain to be fully understood. Approach and Results: Hmox1 deficient (Hmox1-/-) mice had impaired blood flow recovery with severe tissue necrosis and autoamputation following unilateral hindlimb ischemia. Autoamputation preceded the return of blood flow, and bone marrow transfer from littermate wild-type mice failed to prevent tissue injury and autoamputation. In wild-type mice, ischemia-induced expression of Hmox1 in skeletal muscle occurred before stabilization of HIF-1α. Moreover, HIF-1α stabilization and glucose utilization were impaired in Hmox1-/- mice compared with wild-type mice. Experiments exposing dermal fibroblasts to hypoxia (1% O2) recapitulated these key findings. Metabolomics analyses indicated a failure of Hmox1-/- mice to adapt cellular energy reprogramming in response to ischemia. Prolyl-4-hydroxylase inhibition stabilized HIF-1α in Hmox1-/- fibroblasts and ischemic skeletal muscle, decreased tissue necrosis and autoamputation, and restored cellular metabolism to that of wild-type mice. Mechanistic studies showed that carbon monoxide stabilized HIF-1α in Hmox1-/- fibroblasts in response to hypoxia.

CONCLUSIONS

Our findings suggest that Hmox1 acts both downstream and upstream of HIF-1α, and that stabilization of HIF-1α contributes to Hmox1's protection against ischemic injury independent of neovascularization.

An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation

Inflammation is a key driver in many pathological conditions such as allergy, cancer, Alzheimer’s disease, and many others, and the current state of available drugs prompted researchers to explore new therapeutic targets. In this context, accumulating evidence indicates that the transcription factor Nrf2 plays a pivotal role controlling the expression of antioxidant genes that ultimately exert anti-inflammatory functions. Nrf2 and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH- associated protein 1 (Keap1), play a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Interestingly, Nrf2 is proved to contribute to the regulation of the heme oxygenase-1 (HO-1) axis, which is a potent anti-inflammatory target. Recent studies showed a connection between the Nrf2/antioxidant response element (ARE) system and the expression of inflammatory mediators, NF-κB pathway and macrophage metabolism. This suggests a new strategy for designing chemical agents as modulators of Nrf2 dependent pathways to target the immune response. Therefore, the present review will examine the relationship between Nrf2 signaling and the inflammation as well as possible approaches for the therapeutic modulation of this pathway.

The role of neutrophil extracellular traps and TLR signaling in skeletal muscle ischemia reperfusion injury

Ischemia reperfusion (IR) injury results in devastating skeletal muscle fibrosis. Here, we recapitulate this injury with a mouse model of hindlimb IR injury which leads to skeletal muscle fibrosis. Injury resulted in extensive immune infiltration with robust neutrophil extracellular trap (NET) formation in the skeletal muscle, however, direct targeting of NETs via the peptidylarginine deiminase 4 (PAD4) mechanism was insufficient to reduce muscle fibrosis. Circulating levels of IL-10 and TNFα were significantly elevated post injury, indicating toll-like receptor (TLR) signaling may be involved in muscle injury. Administration of hydroxychloroquine (HCQ), a small molecule inhibitor of TLR7/8/9, following injury reduced NET formation, IL-10, and TNFα levels and ultimately mitigated muscle fibrosis and improved myofiber regeneration following IR injury. HCQ treatment decreased fibroadipogenic progenitor cell proliferation and partially inhibited ERK1/2 phosphorylation in the injured tissue, suggesting it may act through a combination of TLR7/8/9 and ERK signaling mechanisms. We demonstrate that treatment with FDA-approved HCQ leads to decreased muscle fibrosis and increased myofiber regeneration following IR injury, suggesting short-term HCQ treatment may be a viable treatment to prevent muscle fibrosis in ischemia reperfusion and traumatic extremity injury.

Hydrogen-rich saline attenuates ischemia-reperfusion injury in skeletal muscle

BACKGROUND

To investigate the potential beneficial effect of hydrogen-rich saline (HRS) in ischemia-reperfusion (IR) injury of skeletal muscle.

METHODS

Three experimental groups were established in male Sprague-Dawley rats: (1) sham group, (2) IR with normal saline group, (3) and IR with HRS group. A rat model of skeletal muscle IR injury was induced by 3-h tourniquet occlusion on its left hind limb and 4-h reperfusion. Normal saline and HRS (1.0 mL/100 g) were administered intraperitoneally at 10 min before reperfusion, respectively. Muscle and serum samples were analyzed for detecting the levels of myeloperoxidase (MPO), superoxide dismutase (SOD), malondialdehyde (MDA), and hydroxyl radical (•OH). Muscle samples were assessed by wet/dry rate, hematoxylin and eosin histologic assessment, Bcl2, Bax, cytochrome C, LC3B, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, and electron microscopy.

RESULTS

The wet/dry ratio increased significantly in the IR group (P < 0.01 compared with that in the sham group) and decreased significantly in IR with HRS groups (4.12 ± 0.14 versus 4.12 ± 0.14, P < 0.01 compared with that in the IR group). Muscle tissues and serum of the IR group had significantly increased levels of MPO, MDA, •OH content, and decreased SOD activities compared with the sham group (P < 0.01). The activity of SOD in the IR with HRS group was greatly elevated compared with that in the IR group (295.028 ± 9.288 versus 249.190 ± 5.450 in muscle tissues; 91.627 ± 2.604 versus 73.4045 ± 6.487 in serum; P < 0.01), whereas the levels of MPO, MDA, and •OH content were clearly reduced (MPO: 0.5649 ± 0.0724 versus 1.0984 ± 0.0824 in muscle tissues; 0.7257 ± 0.1232 versus 1.3147 ± 0.0531 in serum. MDA: 4.457 ± 0.650 versus 7.107 ± 0.597 in muscle tissues; 2.531 ± 0.434 versus 4.626 ± 0.237 in serum. •OH: 16.451 ± 0.806 versus 19.871 ± 0.594 in muscle tissues; 500.212 ± 7.387 versus 621.352 ± 7.591 in serum, P < 0.01). The integrated optical density of positive amethyst staining increased significantly in the IR group (P < 0.01 compared with that in the sham group) and decreased significantly in IR with HRS group (928.79 ± 234.537 versus 3005.972 ± 83.567, P < 0.01 compared with that in the IR group). Muscle tissues of the IR group had significantly increased levels of Bax, cytochrome C, LC3B content, and decreased Bcl2 activities compared with those in the sham group (P < 0.01). The activity of Bcl2 in the IR with HRS group was greatly elevated compared with that in the IR group (0.2635 ± 0.0704 versus 0.1242 ± 0.0662; P < 0.01), whereas the levels of Bax, cytochrome C, and LC3B content were clearly reduced (Bax: 0.3103 ± 0.0506 versus 0.5122 ± 0.0148; cytochrome C: 0.4194 ± 0.1116 versus 0.8127 ± 0.0166; LC3B: 0.5884 ± 0.0604 versus 1.3758 ± 0.0319; respectively, P < 0.01).

CONCLUSIONS

HRS seems to be effective in attenuating IR injury in skeletal muscle via its antioxidant, anti-apoptosis, and anti-autophagy effect.

Can gas replace protein function? CO abrogates the oxidative toxicity of myoglobin

Outside their cellular environments, hemoglobin (Hb) and myoglobin (Mb) are known to wreak oxidative damage. Using haptoglobin (Hp) and hemopexin (Hx) the body defends itself against cell-free Hb, yet mechanisms of protection against oxidative harm from Mb are unclear. Mb may be implicated in oxidative damage both within the myocyte and in circulation following rhabdomyolysis. Data from the literature correlate rhabdomyolysis with the induction of Heme Oxygenase-1 (HO-1), suggesting that either the enzyme or its reaction products are involved in oxidative protection. We hypothesized that carbon monoxide (CO), a product, might attenuate Mb damage, especially since CO is a specific ligand for heme iron. Low density lipoprotein (LDL) was chosen as a substrate in circulation and myosin (My) as a myocyte component. Using oxidation targets, LDL and My, the study compared the antioxidant potential of CO in Mb-mediated oxidation with the antioxidant potential of Hp in Hb-mediated oxidation. The main cause of LDL oxidation by Hb was found to be hemin which readily transfers from Hb to LDL. Hp prevented heme transfer by sequestering hemin within the Hp-Hb complex. Hemin barely transferred from Mb to LDL, and oxidation appeared to stem from heme iron redox in the intact Mb. My underwent oxidative crosslinking by Mb both in air and under N₂. These reactions were fully arrested by CO. The data are interpreted to suit several circumstances, some physiological, such as high muscle activity, and some pathological, such as rhabdomyolysis, ischemia/reperfusion and skeletal muscle disuse atrophy. It appear that CO from HO-1 attenuates damage by temporarily binding to deoxy-Mb, until free oxygen exchanges with CO to restore the equilibrium.

Interaction of the carbon monoxide-releasing molecule Ru(CO)3Cl(glycinate) (CORM-3) with Salmonella enterica serovar Typhimurium: in situ measurements of carbon monoxide binding by integrating cavity dual-beam spectrophotometry

Carbon monoxide (CO) is a toxic gas that binds to haems, but also plays critical signalling and cytoprotective roles in mammalian systems; despite problems associated with systemic delivery by inhalation of the gas, it may be employed therapeutically. CO delivered to cells and tissues by CO-releasing molecules (CO-RMs) has beneficial and toxic effects not mimicked by CO gas; CO-RMs are also attractive candidates as novel antimicrobial agents. Salmonella enterica serovar Typhimurium is an enteropathogen causing gastroenteritis in humans. Recent studies have implicated haem oxygenase-1 (HO-1), the protein that catalyses the degradation of haem into biliverdin, free iron and CO, in the host immune response to Salmonella infection. In several studies, CO administration via CO-RMs elicited many of the protective roles of HO-1 induction and so we investigated the effects of a well-characterized water-soluble CO-RM, Ru(CO)3Cl(glycinate) (CORM-3), on Salmonella. CORM-3 exhibits toxic effects at concentrations significantly lower than those reported to cause toxicity to RAW 264.7 macrophages. We demonstrated here, through oxyhaemoglobin assays, that CORM-3 did not release CO spontaneously in phosphate buffer, buffered minimal medium or very rich medium. CORM-3 was, however, accumulated to high levels intracellularly (as shown by inductively coupled plasma MS) and released CO inside cells. Using growing Salmonella cultures without prior concentration, we showed for the first time that sensitive dual-beam integrating cavity absorption spectrophotometry can detect directly the CO released from CORM-3 binding in real-time to haems of the bacterial electron transport chain. The toxic effects of CO-RMs suggested potential applications as adjuvants to antibiotics in antimicrobial therapy.

Inhaled carbon monoxide accelerates resolution of inflammation via unique proresolving mediator-heme oxygenase-1 circuits

Resolution of acute inflammation is an active event accompanied by biosynthesis of specialized proresolving mediators (SPM). We employed a systems approach to determine the impact of CO in resolution active programs during self-limited inflammation in mice. Compared with ambient air, inhaled CO gas (250 ppm) significantly limited PMN infiltration (∼44%, 6 h) into peritoneum and shortened resolution interval from 4 to 2 h. We profiled exudate lipid mediators (LM) via metabololipidomics, CO reduced leukotriene B4 (21 ± 11 versus 59 ± 24 pg/mouse, 6 h), and elevated SPM including resolvin (Rv) D1 (27 ± 4 versus 16 ± 5 pg/mouse) and maresin 1 (26 ± 9 versus 15 ± 3 pg/mouse). With human macrophages, SPM (10 pM-10 nM) elevated heme oxygenase (HO)-1 (∼50%, 8 h). CO also enhanced HO-1 expression and accumulation of RvD1 and RvD5, an action reversed by blockage of a key SPM biosynthesis enzyme 15-lipoxygenase type 1. Compared with normoxia, CO increased ∼30% phagocytosis of opsonized zymosan with human macrophage, which was further enhanced by SPM (∼100%). This CO increased phagocytosis was blocked by 15-lipoxygenase inhibition, and SPM stimulated phagocytosis was diminished by HO-1 inhibition. In murine peritonitis, both pre- and posttreatment with CO inhalation significantly increased macrophages carrying ingested apoptotic PMN in exudates and enhanced PMN apoptosis. Taken together, these results indicate that CO accelerates resolution of acute inflammation, shortens resolution intervals, enhances macrophage efferocytosis, and temporally regulates local levels of lipid mediator/SPM. Moreover, they provide proresolving mechanisms for HO-1/CO, which is part of the SPM-initiated resolution circuit.