Hypercapnia accelerates wound healing in endothelial cell monolayers exposed to hypoxia

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

Local Mucosal CO2 but Not O2 Insufflation Improves Gastric and Oral Microcirculatory Oxygenation in a Canine Model of Mild Hemorrhagic Shock

Introduction

Acute hemorrhage results in perfusion deficit and regional hypoxia. Since failure of intestinal integrity seem to be the linking element between hemorrhage, delayed multi organ failure, and mortality, it is crucial to maintain intestinal microcirculation in acute hemorrhage. During critical bleeding physicians increase FiO₂ to raise total blood oxygen content. Likewise, a systemic hypercapnia was reported to maintain microvascular oxygenation (μHbO₂). Both, O₂ and CO₂, may have adverse effects when applied systemically that might be prevented by local application. Therefore, we investigated the effects of local hyperoxia and hypercapnia on the gastric and oral microcirculation.

Methods

Six female foxhounds were anaesthetized, randomized into eight groups and tested in a cross-over design. The dogs received a local CO₂-, O₂-, or N₂-administration to their oral and gastric mucosa. Hemorrhagic shock was induced through a withdrawal of 20% of estimated blood volume followed by retransfusion 60 min later. In control groups no shock was induced. Reflectance spectrophotometry and laser Doppler were performed at the gastric and oral surface. Oral microcirculation was visualized by incident dark field imaging. Systemic hemodynamic parameters were recorded continuously. Statistics were performed using a two-way-ANOVA for repeated measurements and post hoc analysis was conducted by Bonferroni testing (p < 0.05).

Results

The gastric μHbO₂ decreased from 76 ± 3% to 38 ± 4% during hemorrhage in normocapnic animals. Local hypercapnia ameliorated the decrease of μHbO₂ from 78 ± 4% to 51 ± 8%. Similarly, the oral μHbO₂ decreased from 81 ± 1% to 36 ± 4% under hemorrhagic conditions and was diminished by local hypercapnia (54 ± 4%). The oral microvascular flow quality but not the total microvascular blood flow was significantly improved by local hypercapnia. Local O₂-application failed to change microvascular oxygenation, perfusion or flow quality. Neither CO₂ nor O₂ changed microcirculatory parameters and macrocirculatory hemodynamics under physiological conditions.

Discussion

Local hypercapnia improved microvascular oxygenation and was associated with a continuous blood flow in hypercapnic individuals undergoing hemorrhagic shock. Local O₂ application did not change microvascular oxygenation, perfusion and blood flow profiles in hemorrhage. Local gas application and change of microcirculation has no side effects on macrocirculatory parameters.

Beneficial Effects of Hypercapnic Acidosis on the Inhibition of Transforming Growth Factor β-1-induced Corneal Fibrosis in Vitro

PURPOSE

Corneal scarring is a common poor outcome of corneal trauma. Transforming growth factor β-1 plays a vital role in corneal fibrosis, inducing keratocyte transformation to myofibroblasts. Other than corneal transplantation, no other curative treatment methods for corneal scarring are currently available. Hypercapnic acidosis exerts anti-inflammatory and anti-migratory effects on numerous organs; however, its effect on corneal fibroblasts remains unknown. Hence, this study aimed to evaluate the effect of hypercapnic acidosis on transforming growth factor β-1-induced fibrosis in corneal fibroblasts and to elucidate the underlying mechanisms.

MATERIALS AND METHODS

Corneal fibroblasts were obtained from human limbal tissue and cultured with or without transforming growth factor β-1 under hypercapnic acidosis or no-hypercapnic acidosis conditions, and subjected to scratch wound, cell migration, and collagen matrix contraction assays. Furthermore, immunocytochemistry was performed to evaluate the alpha-smooth muscle actin stress fiber. Finally, western blotting was performed to assess the expression of proteins in the NF-κB and Smad pathways.

RESULTS

Hypercapnic acidosis suppressed collagen gel contraction capacity in transforming growth factor β-1-treated corneal fibroblasts and inhibited transforming growth factor β-1-induced cell migration. Moreover, hypercapnic acidosis downregulated corneal fibrosis marker alpha-smooth muscle actin in transforming growth factor β-1-treated corneal fibroblasts. Furthermore, hypercapnic acidosis suppressed transforming growth factor β-1-induced fibrosis, at least partly, by inhibiting Smad2/3 phosphorylation and down-regulating p-IκB-dependent and RelB signaling transduction.

CONCLUSIONS

Hypercapnic acidosis inhibits transforming growth factor β-1-induced corneal fibroblast migration, collagen gel contraction capacity, and alpha smooth muscle actin expression, potentially through the Smad and NF-κB pathways. Therefore, hypercapnic acidosis may be a potentially useful anti-fibrotic therapy for corneal scarring.

Bioinorganics and Wound Healing

Wound dressings and the healing enhancement (increasing healing speed and quality) are two components of wound care that lead to a proper healing. Wound care today consists mostly of providing an optimal environment by removing waste and necrotic tissues from a wound, preventing infections, and keeping the wounds adequately moist. This is however often not enough to re-establish the healing process in chronic wounds; with the local disruption of vascularization, the local environment is lacking oxygen, nutrients, and has a modified ionic and molecular concentration which limits the healing process. This disruption may affect cellular ionic pumps, energy production, chemotaxis, etc., and will affect the healing process. Biomaterials for wound healing range from simple absorbents to sophisticated bioactive delivery vehicles. Often placing a material in or on a wound can change multiple parameters such as pH, ionic concentration, and osmolarity, and it can be challenging to pinpoint key mechanism of action. This article reviews the literature of several inorganic ions and molecules and their potential effects on the different wound healing phases and their use in new wound dressings.

Hypercapnic tumor microenvironment confers chemoresistance to lung cancer cells by reprogramming mitochondrial metabolism in vitro

The tumor microenvironment has previously been reported to be hypercapnic (as high as ~84 mmHg), although its effect on tumor cell behaviors is unknown. In this study, high CO₂ levels, ranging from 5% to 15%, protected lung cancer cells from anticancer agents, such as cisplatin, carboplatin and etoposide, by suppressing apoptosis. The cytoprotective effect of a high CO₂ level was independent of acidosis and was due to mitochondrial metabolic reprogramming that reduced mitochondrial respiration, as assessed by oxygen consumption, oxidative phosphorylation, mitochondrial membrane and oxidative potentials, eventually leading to reduced reactive oxidant species production. In contrast, high CO₂ levels did not affect cisplatin-mediated DNA damage responses or the expression of Bcl-2 family proteins. Although high CO₂ levels inhibited glycolysis, this inhibition was not mechanistically involved in high CO₂-mediated reductions in mitochondrial respiration, because a high CO₂ concentration inhibited isolated mitochondria. A cytoprotective effect of high CO₂ levels on mitochondria DNA-depleted cells was not noted, lending support to our conclusion that high CO₂ levels act on mitochondria to reduce the cytotoxicity of anticancer agents. High CO₂-mediated cytoprotection was also noted in a 3D culture system. In conclusion, the hypercapnic tumor microenvironment reprograms mitochondrial respiratory metabolism causing chemoresistance in lung cancer cells. Thus, tumor hypercapnia may represent a novel target to improve chemosensitivity.

Hypercapnic acidosis induces mitochondrial dysfunction and impairs the ability of mesenchymal stem cells to promote distal lung epithelial repair

Acute respiratory distress syndrome (ARDS) is a devastating disorder characterized by diffuse inflammation and edema formation. The main management strategy, low tidal volume ventilation, can be associated with the development of hypercapnic acidosis (HCA). Mesenchymal stem cells (MSCs) are a promising therapeutic candidate currently in early-phase clinical trials. The effects of HCA on the alveolar epithelium and capillary endothelium are not well established. The therapeutic efficacy of MSCs has never been reported in HCA. In the present study, we evaluated the effects of HCA on inflammatory response and reparative potential of the primary human small airway epithelial and lung microvasculature endothelial cells as well as on the capacity of bone marrow-derived MSCs to promote wound healing in vitro. We demonstrate that HCA attenuates the inflammatory response and reparative potential of primary human small airway epithelium and capillary endothelium and induces mitochondrial dysfunction. It was found that MSCs promote lung epithelial wound repair via the transfer of functional mitochondria; however, this proreparative effect of MSCs was lost in the setting of HCA. Therefore, HCA may adversely impact recovery from ARDS at the cellular level, whereas MSCs may not be therapeutically beneficial in patients with ARDS who develop HCA.-Fergie, N., Todd, N., McClements, L., McAuley, D., O'Kane, C., Krasnodembskaya, A. Hypercapnic acidosis induces mitochondrial dysfunction and impairs the ability of mesenchymal stem cells to promote distal lung epithelial repair.

Instructive microenvironments in skin wound healing: Biomaterials as signal releasing platforms

Skin wound healing aims to repair and restore tissue through a multistage process that involves different cells and signalling molecules that regulate the cellular response and the dynamic remodelling of the extracellular matrix. Nowadays, several therapies that combine biomolecule signals (growth factors and cytokines) and cells are being proposed. However, a lack of reliable evidence of their efficacy, together with associated issues such as high costs, a lack of standardization, no scalable processes, and storage and regulatory issues, are hampering their application. In situ tissue regeneration appears to be a feasible strategy that uses the body's own capacity for regeneration by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the wound site to promote repair and regeneration. The aim is to engineer instructive systems to regulate the spatio-temporal delivery of proper signalling based on the biological mechanisms of the different events that occur in the host microenvironment. This review describes the current state of the different signal cues used in wound healing and skin regeneration, and their combination with biomaterial supports to create instructive microenvironments for wound healing.

Hypercapnia Accelerates Adipogenesis: A Novel Role of High CO2 in Exacerbating Obesity

Obesity is a major risk factor for the development of obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS), which manifest as intermittent hypercapnia and sustained plus intermittent hypercapnia, respectively. In this study, we investigated whether CO₂ affects adipocyte differentiation (adipogenesis) and maturation (hypertrophy). Human visceral or subcutaneous preadipocytes were grown to confluence and then induced to differentiate to adipocytes under hypocapnia, normocapnia, and hypercapnia with or without hypoxia. Adipogenesis was also induced under intermittent or sustained hypercapnia. Differentiated adipocytes were maintained to maturity under normocapnia or hypercapnia. Our main findings are as follows: (1) hypercapnia accelerated adipogenesis in visceral and subcutaneous preadipocytes, whereas hypocapnia inhibited adipogenesis; (2) hypercapnia did not affect adipocyte hypertrophy; (3) hypercapnia-accelerated adipogenesis was independent of extracellular acidosis, oxygen concentration, or either intermittent or sustained exposure to high CO₂; and (4) the mechanisms underlying hypercapnia-accelerated adipogenesis involved increased production of cyclic adenosine monophosphate (cAMP) via soluble adenylyl cyclase, leading to the activation of protein kinase A and exchanger protein directly activated by cAMP, which, in turn, activated proadipogenic transcription factors, such as cAMP response element binding protein, CCAAT/enhancer binding protein β, and peroxisome proliferator-activated receptor γ. This study reveals a novel role of high CO₂ in promoting adipogenesis, which provides mechanistic clues to a pathoetiological interaction between OSA/OHS and obesity. Our data suggest a vicious cycle of disease progression via the following mechanism: OSA/OHS → hypoventilation → hypercapnia → increased adipogenesis → increased fat mass → exacerbated OSA/OHS.

Nicotine enhances hepatocyte growth factor-mediated lung cancer cell migration by activating the α7 nicotine acetylcholine receptor and phosphoinositide kinase-3-dependent pathway

Cigarette smoking not only promotes lung carcinogenesis, but it has also been demonstrated to promote the progression of lung cancer. Despite nicotine being a major component of cigarette smoke, it is not carcinogenic when acting alone. Instead, it is believed to function as a tumor promoter. Due to the fatal consequences of lung cancer being primarily associated with the processes of invasion and metastasis, the present study aimed to determine the effect of nicotine on the migratory activity of lung cancer cells. The effect of nicotine on the migration of lung cancer A549 cells was evaluated by a wound healing assay. Hepatocyte growth factor (HGF) was used as a pro-migratory stimulus. During several of the experiments, specific inhibitors of α7-nicotine acetylcholine receptor (α7-nAchR), phosphoinositide kinase-3 (PI3K) and extracellular signal-related kinase (ERK)1/2 were included. The phosphorylation levels of Akt and ERK1/2 were examined using a cell-based protein phosphorylation assay. It was observed that nicotine did not induce cell migration by itself, but that it instead promoted HGF-induced cell migration. The effects of nicotine were inhibited by the pretreatment of the cells with the α7-nAchR inhibitor, methyllycaconitine, and the PI3K inhibitor, LY294002. The mitogen-activated protein kinase/ERK kinase kinase inhibitor exerted modest, but non-significant inhibitory activity on the effect of nicotine. Nicotine did not induce Akt phosphorylation by itself, but instead promoted the HGF-induced phosphorylation of Akt. It was also observed that nicotine had no effect on ERK1/2 phosphorylation. The results from the present study indicate that nicotine, when alone, does not have a pro-migratory function, but instead enhances responsiveness to the pro-migratory stimulus emitted by HGF. The current study provides an insight into the mechanism of tumor promotion by demonstrating that nicotine and α7-nAchRs act in synergy with the HGF-induced PI3K/Akt signaling pathway, increasing the sensitivity of lung cancer cells to HGF, and thereby promoting cell migration, a vital step in invasion and metastasis.

The external microenvironment of healing skin wounds

The skin wound microenvironment can be divided into two main components that influence healing: the external wound microenvironment, which is outside the wound surface; and the internal wound microenvironment, underneath the surface, to which the cells within the wound are exposed. Treatment methods that directly alter the features of the external wound microenvironment indirectly affect the internal wound microenvironment due to the exchange between the two compartments. In this review, we focus on the effects of temperature, pressure (positive and negative), hydration, gases (oxygen and carbon dioxide), pH, and anti-microbial treatment on the wound. These factors are well described in the literature and can be modified with treatment methods available in the clinic. Understanding the roles of these factors in wound pathophysiology is of central importance in wound treatment.

Obstructive Sleep Apnea: A Risk Factor for Surgical Site Infection following Colectomy

BACKGROUND

Obstructive sleep apnea (OSA) is associated with increased systemic oxidative stress, endothelial dysfunction, and activation of pro-inflammatory cascades, which increase host susceptibility to infection. OSA has not been evaluated as a risk factor for surgical site infection (SSI) following colectomy. We hypothesized that OSA increases the risk for SSI after colectomy.

METHODS

We performed a retrospective review of 507 colectomies that took place between August 2011 and September 2013. Forty-two patients carried the diagnosis of OSA prior to surgery. These 42 patients were matched to 68 patients with no OSA for age, body mass index (BMI), diabetes mellitus (DM), reason for surgery and surgical approach.

RESULTS

The rate of SSI was 28.6% (12 of 42) in the patients with and 10.3% (7 of 68) in the patients without OSA (p=0.03). Using logistic regression, the predictors of SSI following colectomy were found to be OSA (odds ratio [OR] of 3.98, 95% confidence interval [CI]=1.29-12.27), and DM (OR of 7.16, 95% CI=2.36-21.96). The average hospital stay after colectomy for patients with OSA complicated with SSI was 16.7 d whereas patients with OSA without SSI stayed 7.4 d (p<0.001). The rate of organ space infections was 9.5% (4 of 42) in the patients with OSA compared with 0 (p=0.02) in patients without OSA.

CONCLUSIONS

OSA is an independent risk factor for SSI following colectomy. Patients with OSA have substantially greater rates of organ space SSI and longer hospital stay.