L-glutamine in vitro regulates rat aortic glutamate content and modulates nitric oxide formation and contractility responses

Glutamine Deficiency Promotes Immune and Endothelial Cell Dysfunction in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has caused the death of almost 7 million people worldwide. While vaccinations and new antiviral drugs have greatly reduced the number of COVID-19 cases, there remains a need for additional therapeutic strategies to combat this deadly disease. Accumulating clinical data have discovered a deficiency of circulating glutamine in patients with COVID-19 that associates with disease severity. Glutamine is a semi-essential amino acid that is metabolized to a plethora of metabolites that serve as central modulators of immune and endothelial cell function. A majority of glutamine is metabolized to glutamate and ammonia by the mitochondrial enzyme glutaminase (GLS). Notably, GLS activity is upregulated in COVID-19, favoring the catabolism of glutamine. This disturbance in glutamine metabolism may provoke immune and endothelial cell dysfunction that contributes to the development of severe infection, inflammation, oxidative stress, vasospasm, and coagulopathy, which leads to vascular occlusion, multi-organ failure, and death. Strategies that restore the plasma concentration of glutamine, its metabolites, and/or its downstream effectors, in conjunction with antiviral drugs, represent a promising therapeutic approach that may restore immune and endothelial cell function and prevent the development of occlusive vascular disease in patients stricken with COVID-19.

Roles of Endothelial Motilin Receptor and Its Signal Transduction Pathway in Motilin-Induced Left Gastric Artery Relaxation in Dogs

Background: Motilin increases left gastric artery (LGA) blood flow in dogs via the endothelial motilin receptor (MLNR). This article investigates the signaling pathways of endothelial MLNR.

Methods: Motilin-induced relaxation of LGA rings was assessed using wire myography. Nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) levels were measured using an NO assay kit and cGMP ELISA kit, respectively.

Results: Motilin concentration-dependently (EC₅₀=9.1±1.2×10⁻⁸M) relaxed LGA rings precontracted with U46619 (thromboxane A₂ receptor agonist). GM-109 (MLNR antagonist) significantly inhibited motilin-induced LGA relaxation and the production of NO and cGMP. N-ethylmaleimide (NEM; G-protein antagonist), U73122 [phospholipase C (PLC) inhibitor], and 2-aminoethyl diphenylborinate [2-APB; inositol trisphosphate (IP₃) blocker] partially or completely blocked vasorelaxation. In contrast, chelerythrine [protein kinase C (PKC) inhibitor] and H89 [protein kinase A (PKA) inhibitor] had no such effect. Low-calcium or calcium-free Krebs solutions also reduced vasorelaxation. N-nitro-L-arginine methyl ester [L-NAME; nitric oxide synthase (NOS) inhibitor] and ODQ [soluble guanylyl cyclase (sGC) inhibitor] completely abolished vasodilation and synthesis of NO and cGMP. Indomethacin (cyclooxygenase inhibitor), 18α-glycyrrhetinic acid [18α-GA; myoendothelial gap junction (MEGJ) inhibitor], and K⁺ channel inhibition through high K⁺ concentrations or tetraethylammonium (TEA-Cl; K_Ca channel blocker) partially decreased vasorelaxation, whereas glibenclamide (K_ATP channel blocker) had no such effect.

Conclusion: The current study suggests that motilin-induced LGA relaxation is dependent on endothelial MLNR through the G protein-PLC-IP₃ pathway and Ca²⁺ influx. The NOS-NO-sGC-cGMP pathway, prostacyclin, MEGJ, and K⁺ channels (especially K_Ca) are involved in endothelial-dependent relaxation of vascular smooth muscle (VSM) cells.

A metabolomic approach to identify the link between sports activity and atheroprotection

AIMS

Physical activity (PA) is a mainstay of cardiovascular prevention. This study aimed to identify metabolic mediators of PA that protect against the development of atherosclerosis.

METHODS AND RESULTS

A total of 2160 participants in the LIFE heart study were analysed with data on PA and vascular phenotyping. In a targeted metabolomic approach, 61 metabolites (amino acids and acylcarnitines) were measured using liquid chromatography-tandem mass spectrometry. We investigated the interactions between PA, metabolites and markers of atherosclerosis in order to uncover possible mediation effects. Intended sports activity, but no daily PA, was associated with a lower degree of atherosclerosis, odds ratio (OR) for total atherosclerotic burden of 0.76 (95% confidence interval 0.62-0.94), carotid artery plaque OR 0.79 (0.66-0.96), and peripheral artery disease OR 0.74 (0.56-0.98). Twelve amino acids, free carnitine, five acylcarnitines were associated with sports activity. Of these, eight metabolites were also associated with the degree of atherosclerosis. In the mediation analyses, a cluster of amino acids (arginine, glutamine, pipecolic acid, taurine) were considered as possible mediators of atheroprotection. In contrast, a group of members of the carnitine metabolism (free carnitine, acetyl carnitine, octadecenoyl carnitine) were associated with inactivity and higher atherosclerotic burden.

CONCLUSION

Our metabolomic approach, which is integrated into a mediation model, provides transformative insights into the complex metabolic processes involved in atheroprotection. Metabolites with antioxidant and endothelial active properties are believed to be possible mediators of atheroprotection. The metabolomic mediation approach can support the understanding of complex diseases in order to identify targets for prevention and therapy.

Vasodilatory effect of formaldehyde via the NO/cGMP pathway and the regulation of expression of KATP, BKCa and L-type Ca2+ channels

Formaldehyde (FA), a well-known toxic gas molecule similar to nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), is widely produced endogenously via numerous biochemical pathways, and has a number of physiological roles in the biosystem. We attempted to investigate the vasorelaxant effects of FA and their underlying mechanisms. We found that FA induced vasorelaxant effects on rat aortic rings in a concentration-dependent manner. The NO/cyclic guanosine 5' monophosphate (cGMP) pathway was up-regulated when the rat aortas were treated with FA. The expression of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel subunits α and β of the rat aortas was increased by FA. Similarly, the levels of ATP-sensitive K⁺ (K_ATP) channel subunits K_ir6.1 and K_ir6.2 were also up-regulated when the rat aortas were incubated with FA. In contrast, levels of the L-type Ca²⁺ channel (LTCC) subunits, Ca_v1.2 and Ca_v1.3, decreased dramatically with increasing concentrations of FA. We demonstrated that the regulation of FA on vascular contractility may be via the up-regulation of the NO/cGMP pathway and the modulation of ion channels, including the upregulated expression of the K_ATP and BK_Ca channels and the inhibited expression of LTCCs. Further study is needed to explore the in-depth mechanisms of FA induced vasorelaxation.

Metabolomic Approach to Redox and Nitrosative Reactions in Cardiovascular Diseases

Metabolomics, also referred to as metabonomics, is one of the most recent innovative technologies in medicine. It offers a direct functional read-out of phenotypes by the detection, identification, and quantification of a large number of metabolites within a biological sample such as urine and blood. Metabolites (<1500 Da) represent the output of cellular metabolism, accounting for expression and activity of genes, transcripts, and proteins, and offering unique insights into small molecule regulation, which may uncover new biochemical patterns. Metabolomics research has considerable potential for translating the metabolic fingerprint into personalized therapeutic strategies. Within the field of interest, cardiovascular disease (CVD) is one of the most developed areas. However, CVD remains the leading cause of death worldwide with a marked increase in mortality rates over the past six decades. In this scenario, recent findings indicate the important role of redox and nitrosative (RN) reactions in CVD development and progression. RN reactions are generally involved in the homeostatic modulation of a wide number of cellular and organ functions. Conversely, the imbalance of these reactions may lead to a condition of allostasis that in turn can cause CVD. The aim of this review is to highlight how the use of metabolomics may be useful for the study of RN reactions related to CVD, providing a tool to understand the mechanisms underlying reactions that could lead to impaired ROS or RNS formation.

Distinctive metabolomic fingerprint in scleroderma patients with pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) in systemic sclerosis (SS) identifies a poor prognosis subset of patients. Recent studies suggested a "metabolic theory" on the development of pulmonary arterial hypertension. On this basis we performed a metabolomic study in order to evaluate whether differences in pulmonary arterial blood metabolites were identifiable in SS patients with increased pulmonary vascular resistance (PVR).

METHODS

We studied 18 SS patients (age 58.7±15.6years) free of pulmonary fibrosis who underwent a right heart catheterization (RHC). A blood sample was collected during the RHC in the distal peripheral circulation of the pulmonary arteries to perform the metabolomic analysis.

RESULTS

Based on PVR we divided the population into Group A (n=8; PVR=1.16±0.23WU) and Group B (n=10; PVR=2.67±0.67WU; p<0.001 vs Group A). No significant differences were identified in terms of anthropometric, clinical, echo and therapeutic characteristics. At RHC the 2 groups showed a difference in mean pulmonary pressure values (Group A: 20±4mmHg; Group B: 27±3.4mmHg; p=0.03), with mild PAH in Group B. We applied an OSC-PLS-DA with a clear clusterization; SSc patients with PAH showed an increase in acetate, alanine, lactate, and lipoprotein levels and a decrease in γ-aminobutyrate, arginine, betaine, choline, creatine, creatinine, glucose, glutamate, glutamine, glycine, histidine, phenylalanine, and tyrosine levels CONCLUSIONS: Our results suggest that, despite similar clinical and disease-related parameters, SSc patients who develop PAH have an unfavorable metabolic profile able to cause an impaired production of metabolites with protective effects on endothelial cells.

Glutamate formation via the leucine-to-glutamate pathway of rat pancreas

The leucine-to-glutamate (Leu→Glu) pathway, which metabolizes the carbon atoms of l-leucine to form l-glutamate, was studied by incubation of rat tissue segments with l-[U-(14)C]leucine and estimation of the [(14)C]glutamate formed. Metabolism of the leucine carbon chain occurs in most rat tissues, but maximal activity of the Leu→Glu pathway for glutamate formation is limited to the thoracic aorta and pancreas. In rat aorta, the Leu→Glu pathway functions to relax the underlying smooth muscle; its functions in the pancreas are unknown. This report characterizes the Leu→Glu pathway of rat pancreas and develops methods to examine its functions. Pancreatic segments effect net formation of glutamate on incubation with l-leucine, l-glutamine, or a mix of 18 other plasma amino acids at their concentrations in normal rat plasma. Glutamate formed from leucine remains mainly in the tissue, whereas that from glutamine enters the medium. The pancreatic Leu→Glu pathway uses the leucine carbons for net glutamate formation; the α-amino group is not used; the stoichiometry is as follows: 1 mol of leucine yields 2 mol of glutamate (2 leucine carbons per glutamate) plus 2 mol of CO2. Comparison of the Leu→Glu pathway in preparations of whole pancreatic segments, isolated acini, and islets of Langerhans localizes it in the acini; relatively high activity is found in cultures of the AR42J cell line and very little in the INS-1 832/13 cell line. Pancreatic tissue glutamate concentration is homeostatically regulated in the range of ∼1-3 μmol/g wet wt. l-Valine and leucine ethyl, benzyl, and tert-butyl esters inhibit the Leu→Glu pathway without decreasing tissue total glutamate.

Glutamine supplementation alleviates vasculopathy and corrects metabolic profile in an in vivo model of endothelial cell dysfunction

Endothelial Cell Dysfunction (ECD) is a recognized harbinger of a host of chronic cardiovascular diseases. Using a mouse model of ECD triggered by treatment with L-Nω-methylarginine (L-NMMA), we previously demonstrated that renal microvasculature displays a perturbed protein profile, including diminished expression of two key enzymes of the Krebs cycle associated with a Warburg-type suppression of mitochondrial metabolism. We hypothesized that supplementation with L-glutamine (GLN), that can enter the Krebs cycle downstream this enzymatic bottleneck, would normalize vascular function and alleviate mitochondrial dysfunction. To test this hypothesis, mice with chronic L-NMMA-induced ECD were co-treated with GLN at different concentrations for 2 months. Results confirmed that L-NMMA led to a defect in acetylcholine-induced relaxation of aortic rings that was dose-dependently prevented by GLN. In caveolin-1 transgenic mice characterized by eNOS inactivation, L-NMMA further impaired vasorelaxation which was partially rescued by GLN co-treatment. Pro-inflammatory profile induced by L-NMMA was blunted in mice co-treated with GLN. Using an LC/MS platform for metabolite profiling, we sought to identify metabolic perturbations associated with ECD and offset by GLN supplementation. 3453 plasma molecules could be detected with 100% frequency in mice from at least one treatment group. Among these, 37 were found to be differentially expressed in a 4-way comparison of control vs. LNMMA both with and without GLN. One of such molecules, hippuric acid, an “uremic toxin” was found to be elevated in our non-uremic mice receiving L-NMMA, but normalized by treatment with GLN. Ex vivo analysis of hippuric acid effects on vasomotion demonstrated that it significantly reduced acetylcholine-induced vasorelaxation of vascular rings. In conclusion, functional and metabolic profiling of animals with early ECD revealed macrovasculopathy and that supplementation GLN is capable of improving vascular function. Metabolomic analyses reveal elevation of hippuric acid, which may further exacerbate vasculopathy even before the development of uremia.

Sulfur dioxide upregulates the aortic nitric oxide pathway in rats

Sulfur dioxide (SO(2)) is a common gaseous pollutant. It is also, however, endogenously generated from sulfur-containing amino acids. Recent studies have demonstrated that rat blood pressure can be lowered by SO(2)-exposure in vivo and that vasodilation caused by SO(2) at low concentrations (<450 microM) is endothelium-dependent in rat aorta. However, effects of SO(2) on nitric oxide synthase (NOS) and nitric oxide (NO) production have not been previously studied in rat aorta. The objective of the present study is to assess the effects of acute (10 min) and prolonged (2h) stimulation with different concentrations of SO(2) on NO/cGMP pathway in isolated rat aorta. The results show that: (1) the acute and prolonged pretreatments with SO(2) produced an inhibition of vasoconstrictions induced by norepinephrine. (2) SO(2) potentiated activity of endothelial nitric oxide synthase (eNOS), but not of induced NOS (iNOS). (3) SO(2) could increase expression of eNOS gene on the transcription and translation levels in rat aorta. (4) SO(2) enhanced NO formation in aortic tissue. (5) The level of cGMP in rat aorta was increased by SO(2) and no change of cAMP. These findings led to the conclusion: there were acute and prolonged effects of SO(2) on the NO/cGMP signalling pathway; and SO(2) could upregulate the eNOS-NO-cGMP pathway and at least partly by which the SO(2) might cause vasodilation and inhibition to vasoconstriction.

Epoxyeicosatrienoic acids: formation, metabolism and potential role in tissue physiology and pathophysiology

BACKGROUND

CYP enzymes from the CYP2C and CYP2J subfamilies metabolize arachidonic acid in a regiospecific and stereoselective manner to eight epoxyeicosatrienoic acids (EETs). Various EETs have been detected in the liver, as well as in many extrahepatic tissues, and have been implicated in numerous physiological functions from cell signaling to vasodilation and angiogenesis.

OBJECTIVE

This report reviews the sites of expression and activity of arachidonic acid epoxygenase CYP isoforms, as well as the physiological role and metabolism of EETs in various extrahepatic tissues. Possible functions of EETs in tissue pathophysiology and implications as potential drug targets are also discussed.

METHODS

The most recent primary research literature on EET forming enzymes and the new physiological functions of EETs in various tissues were reviewed.

RESULTS/CONCLUSIONS

Epoxyeicosatrienoic acids are important in maintaining the homeostasis and in responding to stress in various extra hepatic tissues. It is not clear whether these effects are owing to EETs acting on a universal receptor or through a mechanism involving a second messenger. A better understanding of the regulation of EET levels and their mechanism of action on various receptors will accelerate research aiming at developing therapeutic agents that target EET formation or metabolism pathways.

Ingestion of bonito extract ameliorates peripheral blood flow in mice loaded from over crowding stress

Bonito extract (BE) has been shown to improve various fatigue-related symptoms. The possibility that the improvement of blood flow contributes to the improvement of fatigue-related symptoms has been reported. However, even though BE has been found to increase peripheral blood flow in humans, an understanding of its mechanisms has remained elusive. The purpose of the present study is to construct an animal model system with which the blood flow-increasing effects of BE can be examined. Using mice loaded with crowding stress, an attempt was made to reproduce the increases in peripheral blood flow observed in humans after a single administration of BE. In this study, the crowded-condition mice (20 mice/cage) showed significantly increased catecholamine levels (noradrenaline, adrenaline, and dopamine) in their circulating blood and a decreased rate of skin blood perfusion in comparison with the normal-condition mice (6 mice/cage). The rate of skin blood perfusion was significantly increased by BE in the crowded-condition mice in comparison with the controls, but not influenced by BE in the normal-condition mice. This suggests that BE expands the vascular diameter by affecting the constriction of vessels induced by catecholamines.