Reduction in hypoxia-reoxygenation-induced myocardial mitochondrial damage with exogenous methane

Radical-Driven Methane Formation in Humans Evidenced by Exogenous Isotope-Labeled DMSO and Methionine

Methane (CH₄), which is produced endogenously in animals and plants, was recently suggested to play a role in cellular physiology, potentially influencing the signaling pathways and regulatory mechanisms involved in nitrosative and oxidative stress responses. In addition, it was proposed that the supplementation of CH₄ to organisms may be beneficial for the treatment of several diseases, including ischemia, reperfusion injury, and inflammation. However, it is still unclear whether and how CH₄ is produced in mammalian cells without the help of microorganisms, and how CH₄ might be involved in physiological processes in humans. In this study, we produced the first evidence of the principle that CH₄ is formed non-microbially in the human body by applying isotopically labeled methylated sulfur compounds, such as dimethyl sulfoxide (DMSO) and methionine, as carbon precursors to confirm cellular CH₄ formation. A volunteer applied isotopically labeled (²H and ¹³C) DMSO on the skin, orally, and to blood samples. The monitoring of stable isotope values of CH₄ convincingly showed the conversion of the methyl groups, as isotopically labeled CH₄ was formed during all experiments. Based on these results, we considered several hypotheses about endogenously formed CH₄ in humans, including physiological aspects and stress responses involving reactive oxygen species (ROS). While further and broader validation studies are needed, the results may unambiguously serve as a proof of concept for the endogenous formation of CH₄ in humans via a radical-driven process. Furthermore, these results might encourage follow-up studies to decipher the potential physiological role of CH₄ and its bioactivity in humans in more detail. Of particular importance is the potential to monitor CH₄ as an oxidative stress biomarker if the observed large variability of CH₄ in breath air is an indicator of physiological stress responses and immune reactions. Finally, the potential role of DMSO as a radical scavenger to counteract oxidative stress caused by ROS might be considered in the health sciences. DMSO has already been investigated for many years, but its potential positive role in medical use remains highly uncertain.

Methane Admixture Protects Liver Mitochondria and Improves Graft Function after Static Cold Storage and Reperfusion

Mitochondria are targets of cold ischemia-reperfusion (IR), the major cause of cell damage during static cold preservation of liver allografts. The bioactivity of methane (CH₄) has recently been recognized in various hypoxic and IR conditions as having influence on many aspects of mitochondrial biology. We therefore hypothesized that cold storage of liver grafts in CH₄-enriched preservation solution can provide an increased defence against organ dysfunction in a preclinical rat model of liver transplantation. Livers were preserved for 24 h in cold histidine-tryptophan-ketoglutarate (HTK) or CH₄-enriched HTK solution (HTK-CH₄) (n = 24 each); then, viability parameters were monitored for 60 min during normothermic isolated reperfusion and perfusate and liver tissue were collected. The oxidative phosphorylation capacity and extramitochondrial Ca²⁺ movement were measured by high resolution respirometry. Oxygen and glucose consumption increased significantly while hepatocellular damage was decreased in the HTK-CH₄ grafts compared to the HTK group. Mitochondrial oxidative phosphorylation capacity was more preserved (128.8 ± 31.5 pmol/s/mL vs 201.3 ± 54.8 pmol/s/mL) and a significantly higher Ca²⁺ flux was detected in HTK-CH₄ storage (2.9 ± 0.1 mV/s) compared to HTK (2.3 ± 0.09 mV/s). These results demonstrate the direct effect of CH₄ on hepatic mitochondrial function and extramitochondrial Ca²⁺ fluxes, which may have contributed to improved graft functions and a preserved histomorphology after cold IR.

Ginsenoside Rg1 Ameliorates Acute Renal Ischemia/Reperfusion Injury via Upregulating AMPKα1 Expression

Acute renal ischemia/reperfusion (I/R) injury often occurs during kidney transplantation and other kidney surgeries, and the molecular mechanism involves oxidative stress. We hypothesized that ginsenoside Rg1 (Rg1), a saponin derived from ginseng, would protect the renal tissue against acute renal I/R injury by upregulating 5' adenosine monophosphate-activated protein kinase α1 (AMPKα1) expression and inhibiting oxidative stress. The models of acute anoxia/reoxygenation (A/R) damage in normal rat kidney epithelial cell lines (NRK-52E) and acute renal I/R injury in mice were constructed. The results revealed that pretreatment with 25 μM Rg1 significantly increased NRK-52E viability, decreased lactate dehydrogenase (LDH) activity and apoptosis, suppressed reactive oxygen species generation and oxidative stress, stabilized mitochondrial membrane potential and reduced mitochondria permeability transition pore openness, decreased adenosine monophosphate/adenosine triphosphate ratio, and upregulated the expression of AMPKα1, cytochrome b-c1 complex subunit 2, NADH dehydrogenase (ubiquinone) 1 beta subcomplex subunit 8, and B-cell lymphoma 2, while downregulating BCL2-associated X protein expression. The effects of Rg1 pretreatment were similar to those of pAD/Flag-AMPKα1. After acute renal I/R injury, serum creatinine, blood urea nitrogen, LDH activity, and oxidative stress in renal tissue significantly increased. Rg1 pretreatment upregulated AMPKα1 expression, which protects against acute renal I/R injury by maintaining renal function homeostasis, inhibiting oxidative stress, and reducing apoptosis. Compound C, a specific inhibitor of AMPK, reversed the effects of Rg1. In summary, Rg1 pretreatment upregulated AMPKα1 expression, inhibited oxidative stress, maintained mitochondrial function, improved energy metabolism, reduced apoptosis, and ultimately protected renal tissue against acute renal I/R injury.

Methane-rich saline protects against sepsis-associated cognitive deficits in mice

Sepsis is associated with multiple organ dysfunction, and the brain is particularly vulnerable. Sepsis-associated encephalopathy (SAE) increases the mortality of patients with sepsis; however, the pathogenesis of SAE remains unclear. Methane, the simplest aliphatic hydrocarbon, has been reported to have anti-inflammatory and organ-protective effects. This study aimed to investigate the effects of methane on the cognitive deficits in mice with experimental sepsis. We randomly divided C57BL/6 male mice into sham, cecal ligation and puncture (CLP), and CLP + methane-rich saline (MS) groups. Twenty-four hours after surgery, behavioral tests were conducted on surviving mice and the hippocampus were collected for biochemical analysis. We found that CLP resulted in cognitive deficits in septic mice. A physiological mechanistic investigation revealed that microglia in the hippocampus are largely activated, coupled with the production of inflammatory cytokines and reactive oxygen species (ROS). Notably, methane inhibited the activation of microglia in the hippocampus, reduced the severity of inflammation, diminished the generation of ROS, and ultimately alleviated behavioral impairment in septic mice. Together, these show that treatment with methane ameliorated cognitive deficits in septic mice, which is partly related to the anti-inflammatory and antioxidative effects in the hippocampus.

Bioactivity of Inhaled Methane and Interactions With Other Biological Gases

A number of studies have demonstrated explicit bioactivity for exogenous methane (CH₄), even though it is conventionally considered as physiologically inert. Other reports cited in this review have demonstrated that inhaled, normoxic air-CH₄ mixtures can modulate the in vivo pathways involved in oxidative and nitrosative stress responses and key events of mitochondrial respiration and apoptosis. The overview is divided into two parts, the first being devoted to a brief review of the effects of biologically important gases in the context of hypoxia, while the second part deals with CH₄ bioactivity. Finally, the consequence of exogenous, normoxic CH₄ administration is discussed under experimental hypoxia- or ischaemia-linked conditions and in interactions between CH₄ and other biological gases, with a special emphasis on its versatile effects demonstrated in pulmonary pathologies.

Propofol via Antioxidant Property Attenuated Hypoxia-Mediated Mitochondrial Dynamic Imbalance and Malfunction in Primary Rat Hippocampal Neurons

BACKGROUND

Hypoxia may induce mitochondrial abnormality, which is associated with a variety of clinical phenotypes in the central nervous system. Propofol is an anesthetic agent with neuroprotective property. We examined whether and how propofol protected hypoxia-induced mitochondrial abnormality in neurons.

METHODS

Primary rat hippocampal neurons were exposed to propofol followed by hypoxia treatment. Neuron viability, mitochondrial morphology, mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (MMP), and adenosine triphosphate (ATP) production were measured. Mechanisms including reactive oxygen species (ROS), extracellular regulated protein kinase (ERK), protein kinase A (PKA), HIF-1α, Drp1, Fis1, Mfn1, Mfn2, and Opa1 were investigated.

RESULTS

Hypoxia increased intracellular ROS production and induced mPTP opening, while reducing ATP production, MMP values, and neuron viability. Hypoxia impaired mitochondrial dynamic balance by increasing mitochondrial fragmentation. Further, hypoxia induced the translocation of HIF-1α and increased the expression of Drp1, while having no effect on Fis1 expression. In addition, hypoxia induced the phosphorylation of ERK and Drp1ser616, while reducing the phosphorylation of PKA and Drp1ser637. Importantly, we demonstrated all these effects were attenuated by pretreatment of neurons with 50 μM propofol, antioxidant α-tocopherol, and ROS scavenger ebselen. Besides, hypoxia, propofol, α-tocopherol, or ebselen had no effect on the expression of Mfn1, Mfn2, and Opa1.

CONCLUSIONS

In rat hippocampal neurons, hypoxia induced oxidative stress, caused mitochondrial dynamic imbalance and malfunction, and reduced neuron viability. Propofol protected mitochondrial abnormality and neuron viability via antioxidant property, and the molecular mechanisms involved HIF-1α-mediated Drp1 expression and ERK/PKA-mediated Drp1 phosphorylation.

Reduction in hypoxia-reoxygenation-induced myocardial mitochondrial damage with exogenous methane

Albeit previous experiments suggest potential anti‐inflammatory effect of exogenous methane (CH₄) in various organs, the mechanism of its bioactivity is not entirely understood. We aimed to investigate the potential mitochondrial effects and the underlying mechanisms of CH₄ in rat cardiomyocytes and mitochondria under simulated ischaemia/reperfusion (sI/R) conditions. Three‐day‐old cultured cardiomyocytes were treated with 2.2% CH₄‐artificial air mixture during 2‐hour‐long reoxygenation following 4‐hour‐long anoxia (sI/R and sI/R + CH₄, n = 6‐6), with normoxic groups serving as controls (SH and SH + CH₄; n = 6‐6). Mitochondrial functions were investigated with high‐resolution respirometry, and mitochondrial membrane injury was detected by cytochrome c release and apoptotic characteristics by using TUNEL staining. CH₄ admixture had no effect on complex II (CII)‐linked respiration under normoxia but significantly decreased the complex I (CI)‐linked oxygen consumption. Nevertheless, addition of CH₄ in the sI/R + CH4 group significantly reduced the respiratory activity of CII in contrast to CI and the CH₄ treatment diminished mitochondrial H₂O₂ production. Substrate‐induced changes to membrane potential were partially preserved by CH₄, and additionally, cytochrome c release and apoptosis of cardiomyocytes were reduced in the CH₄‐treated group. In conclusion, the addition of CH₄ decreases mitochondrial ROS generation via blockade of electron transport at CI and reduces anoxia‐reoxygenation‐induced mitochondrial dysfunction and cardiomyocyte injury in vitro.