Ethyl 3,4-dihydroxy benzoate, a unique preconditioning agent for alleviating hypoxia-mediated oxidative damage in L6 myoblasts cells

Modular Toolbox as Snap Jewelry for Biomimetic Synthesis of Multifunctional Amino Acid Surfactants Inspired by Melanin

Amino acid surfactants have gained significant importance in overcoming the limitations of conventional surfactants, notably, their low biocompatibility and biodegradability. However, the current amino acid surfactants lack multifunctional properties due to the nonreactivity of their aliphatic chains, necessitating the development of a new type of amino acid surfactant. A novel melanin-like amino acid surfactant and a biomimetic synthesis route were devised by mimicking the biosynthesis of melanin. Renewable natural polyphenol compounds with catechol moieties were utilized as building blocks for the hydrophobic group. In a proof-of-concept experiment, ethyl protocatechuate was oxidized to o-quinone and subsequently covalently linked to the amino group of lysine via Michael addition. The chemical structure was verified using liquid chromatography-tandem mass spectroscopy. The melanin-like amino acid surfactant exhibited excellent surface-active properties, with a critical micelle concentration of 1.59 mN m-1. Furthermore, it demonstrated remarkable emulsifying, foaming, solubilizing, dispersing, and wetting capabilities. Notably, it also possessed multifunctionality, including antibacterial activity, antioxidant activity, robustness, and mildness. These outstanding properties indicate significant potential for various applications. This strategy offers innovative insights and a versatile, modular toolbox for synthesizing multifunctional amino acid surfactants that mimic melanin. The approach allows for the easy interchange of o-quinone building blocks, which is akin to snap jewelry.

The effects of prolyl hydroxylase inhibition during and post, hypoxia, oxygen glucose deprivation and oxidative stress, in isolated rat hippocampal slices

The contributions of hypoxia and oxidative stress to the pathophysiology of acute ischemic stroke are well established and can lead to disruptions in synaptic signaling. Hypoxia and oxidative stress lead to the neurotoxic overproduction of reactive oxygen species (ROS) and the stabilization of hypoxia inducible factors (HIF). Compounds such as prolyl-4-hydroxylase domain enzyme inhibitors (PHDIs) have been shown to have a preconditioning and neuroprotective effect against ischemic insults such as hypoxia, anoxia, oxygen glucose deprivation (OGD) or H2O2. Therefore, this study explored the effects of two PHDIs, JNJ-42041935 (10 µM) and roxadustat (100 µM) on cell viability using organotypic hippocampal slice cultures. We also assessed the effects of these compounds on synaptic transmission during and post hypoxia, OGD and H2O2 application in isolated rat hippocampal slices using field recording electrophysiological techniques and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit trafficking using immunohistochemistry. Our organotypic data demonstrated a protective role for both inhibitors, where slices had significantly less cell death post anoxia and OGD compared to controls. We also report a distinct modulatory role for both JNJ-42041935 and roxadustat on fEPSP slope post hypoxia and OGD but not H2O2. In addition, we report that application of roxadustat impaired long-term potentiation, but only when applied post-hypoxia. This inhibitory effect was not reversed with co-application of the cyclin-dependent kinase 5 (CDK-5) inhibitor, roscovitine (10 µM), suggesting a CDK-5 independent synaptic AMPAR trafficking mechanism. Both hypoxia and OGD induced a reduction in synaptic AMPA GluA2 subunits, the OGD effect being reversed by prior treatment with both JNJ-42041935 and roxadustat. These results suggest an important role for PHDs in synaptic signaling and plasticity during episodes of ischemic stress.

Prolyl Hydroxylase Inhibition Mitigates Allograft Injury During Liver Transplantation

BACKGROUND

Ischemia and reperfusion injury (IRI) determines primary allograft function after liver transplantation (LT). Primary graft dysfunction (PGD) is associated with increased morbidity and impaired graft survival and can eventually progress to graft failure requiring retransplantation. Hypoxia-inducible transcription factor-prolyl hydroxylase containing enzymes (PHD1, PHD2, and PHD3) are molecular oxygen sensors, which control the adaptive hypoxia response through the hypoxia-inducible factor (HIF). In this study, we have investigated pharmacological activation of the HIF pathway through inhibition of PHDs as a strategy to reduce PGD after LT.

METHODS

Primary rat hepatocytes were isolated and the impact of the pan-PHD small-molecule inhibitor ethyl-3,4-dihydroxybenzoate (EDHB) on HIF-1 and its downstream target gene expression assessed. Subsequently, various rodent models of segmental warm liver ischemia and reperfusion and orthotopic LT were applied to study the impact of EDHB on normothermic or combined cold and warm liver IRI. Liver enzyme levels and histology were analyzed to quantify hepatic IRI.

RESULTS

In vitro, EDHB induced HIF-1 signaling and significantly upregulated its downstream target heme-oxygenase 1 in primary rat hepatocytes. In vivo, after establishment of the optimal EDHB pretreatment conditions in a murine IRI model, EDHB pretreatment significantly mitigated hepatic IRI after warm segmental liver ischemia and reperfusion and allograft injury after orthotopic LT in rats. Mechanistically, EDHB stabilized HIF-1 in the liver and subsequently increased hepatoprotective heme-oxygenase 1 levels, which correlated with reduced hepatic IRI in these models.

CONCLUSIONS

This proof-of-concept study establishes a strong therapeutic rationale for targeting PHDs with small-molecule inhibitors to mitigate PGD after LT.

The Array of Antibacterial Action of Protocatechuic Acid Ethyl Ester and Erythromycin on Staphylococcal Strains

The spread of antibiotic resistance among bacteria has become one of the major health problems worldwide. Methicillin-resistant staphylococcal strains are especially dangerous because they are often resistant to other antibiotics. The increasing insensitivity to macrolides, lincosamides and streptogramin B antibiotics of methicillin-resistant staphylococcal isolates has limited the use of these drugs in therapy. The combination of natural compounds and antibiotics can be considered as an alternative tool to fight multi-drug-resistant pathogen infections. The aim of the presented study was to examine the antibacterial activity of protocatechuic acid ethyl ester–erythromycin combination towards Staphylococcus aureus and Staphylococcus epidermidis strains with various resistance profiles to methicillin and macrolides, lincosamides and streptogramin B (MLS_B) antibiotics. The in-vitro antibacterial potential of the above combination was investigated by minimum inhibitory concentration assays and checkerboard testing. The observed effects were strain dependent, with 8 of 12 tested staphylococcal strains showing an indifferent effect on the natural compound and erythromycin; for 2 strains, the tested combination had an additive effect, while for another 2, the effect was synergistic. Interestingly, the multi-drug-resistant strains were more sensitive to the cooperative action of the protocatechuic acid ethyl ester and the antibiotic.

Prolyl hydroxylase domain inhibitors: can multiple mechanisms be an opportunity for ischemic stroke?

Stroke and cerebrovascular disease are now the fifth most common cause of death behind other diseases such as heart, cancer and respiratory disease and accounts for approximately 40-50 fatalities per 100,000 people each year in the United States. Currently the only therapy for acute stroke, is intravenous administration of tissue plasminogen activator which was approved in 1996 by the FDA. Surprisingly no new treatments have come on the market since, although endovascular mechanical thrombectomy is showing promising results in trials. Recently focus has shifted towards a preventative therapy rather than trying to reverse or limit the amount of damage occurring following stroke onset. During one of the components of ischemia, hypoxia, a number of physiological changes occur within neurons which include the stabilization of hypoxia-inducible factors. The activity of these proteins is regulated by O₂, Fe²⁺, 2-OG and ascorbate-dependant hydroxylases which contain prolyl-4-hydroxylase domains (PHDs). PHD inhibitors are capable of pharmacologically activating the body's own endogenous adaptive response to low levels of oxygen and have therefore become an attractive therapeutic target for treating ischemia. They have been widely used in the periphery and have been shown to have a preconditioning and protective effect against a later and more severe ischemic insult. Currently there are a number of these agents in phase 1, 2 and 3 clinical trials for the treatment of anemia. In this review we assess the neuroprotective effects of PHD inhibitors, including dimethyloxalylglycine and deferoxamine and suggest that not all of their effects in the CNS are HIF-dependent. Unravelling new roles and a better understanding of the function of PHD inhibitors in the CNS may be of great benefit especially when investigating their use in the treatment of stroke and other ischemic diseases.

Sphingosine-1-phosphate pretreatment amends hypoxia-induced metabolic dysfunction and impairment of myogenic potential in differentiating C2C12 myoblasts by stimulating viability, calcium homeostasis and energy generation

Sphingosine-1-phosphate (S1P) has a role in transpiration in patho-physiological signaling in skeletal muscles. The present study evaluated the pre-conditioning efficacy of S1P in facilitating differentiation of C2C12 myoblasts under a normoxic/hypoxic cell culture environment. Under normoxia, exogenous S1P significantly promoted C2C12 differentiation as evident from morphometric descriptors and differentiation markers of the mature myotubes, but it could facilitate only partial recovery from hypoxia-induced compromised differentiation. Pretreatment of S1P optimized the myokine secretion, intracellular calcium release and energy generation by boosting the aerobic/anaerobic metabolism and mitochondrial mass. In the hypoxia-exposed cells, there was derangement of the S1PR1-3 expression patterns, while the same could be largely restored with S1P pretreatment. This is being proposed as a plausible underlying mechanism for the observed pro-myogenic efficacy of exogenous S1P preconditioning. The present findings are an invaluable addition to the existing knowledge on the pro-myogenic potential of S1P and may prove beneficial in the field of hypoxia-related myo-pathologies.

The roles of AKR1C1 and AKR1C2 in ethyl-3,4-dihydroxybenzoate induced esophageal squamous cell carcinoma cell death

The aldo-keto reductase (AKR) superfamily of enzymes is critical for the detoxification of drugs and toxins in the human body; these enzymes are involved not only in the development of drug resistance in cancer cells but also in the metabolism of polycyclic aromatic hydrocarbons. Here, we demonstrated that AKR1C1/C2 increased the metabolism of ethyl-3,4-dihydroxybenzoate (EDHB) in esophageal squamous cell carcinoma (ESCC) cells. Previous studies have shown that EDHB can effectively induce esophageal cancer cell autophagy and apoptosis, and the AKR1C family represents one set of highly expressed genes after EDHB treatment. To explore the cytotoxic effects of EDHB, esophageal cancer cells with higher (KYSE180) or lower (KYSE510) AKR1C expression levels were evaluated in this study. The proliferation of KYSE180 cells was inhibited more effectively than that of KYSE510 cells by EDHB treatment. Furthermore, the effective subunits of the AKR superfamily, AKR1C1/C2, were quantitatively identified using multiple reaction monitoring (MRM) assays. The sensitivity of esophageal cancer cells to EDHB was significantly attenuated by the siRNA knockdown of AKR1C1/C2. Moreover, the expression of autophagy inducers (Beclin, LC3II and BNIP3) and NDRG1 was significantly elevated in KYSE180 cells, but not in KYSE510 cells, after EDHB treatment. When autophagy was inhibited by 3-methyladenine, KYSE180 cells exhibited an increased sensitivity to EDHB, which may be a metabolic substrate of AKR1C1/C2. These results indicated that ESCC patients with high AKR1C1/C2 expression may be more sensitive to EDHB, and AKR1C1/C2 may facilitate EDHB-induced autophagy and apoptosis, thus providing potential guidance for the chemoprevention of ESCC.

Nijmegen Breakage Syndrome fibroblasts and iPSCs: cellular models for uncovering disease-associated signaling pathways and establishing a screening platform for anti-oxidants

Nijmegen Breakage Syndrome (NBS) is associated with cancer predisposition, premature aging, immune deficiency, microcephaly and is caused by mutations in the gene coding for NIBRIN (NBN) which is involved in DNA damage repair. Dermal-derived fibroblasts from NBS patients were reprogrammed into induced pluripotent stem cells (iPSCs) in order to bypass premature senescence. The influence of antioxidants on intracellular levels of ROS and DNA damage were screened and it was found that EDHB-an activator of the hypoxia pathway, decreased DNA damage in the presence of high oxidative stress. Furthermore, NBS fibroblasts but not NBS-iPSCs were found to be more susceptible to the induction of DNA damage than their healthy counterparts. Global transcriptome analysis comparing NBS to healthy fibroblasts and NBS-iPSCs to embryonic stem cells revealed regulation of P53 in NBS fibroblasts and NBS-iPSCs. Cell cycle related genes were down-regulated in NBS fibroblasts. Furthermore, oxidative phosphorylation was down-regulated and glycolysis up-regulated specifically in NBS-iPSCs compared to embryonic stem cells. Our study demonstrates the utility of NBS-iPSCs as a screening platform for anti-oxidants capable of suppressing DNA damage and a cellular model for studying NBN de-regulation in cancer and microcephaly.

Double Knockdown of PHD1 and Keap1 Attenuated Hypoxia-Induced Injuries in Hepatocytes

Background and Aims: Hypoxia and oxidative stress contribute toward liver fibrosis. In this experiment, we used small hairpin RNA (shRNA) to interfere with the intracellular oxygen sensor—prolyl hydroxylase 1 (PHD1) and the intracellular oxidative stress sensor—kelch-like ECH associated protein 1 (Keap1) in the hypoxic hepatocytes in order to investigate the function of PHD1and Keap1.

Methods: We first established the CCl₄-induced liver fibrosis model, subsequently, the levels of the PHD1, hypoxia-inducible factor-1α (HIF-1α), hypoxia-inducible factor-2α (HIF-2α), Keap1, and nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) were detected in liver tissues. Simultaneously, AML12 cells co-transfected with PHD1 and Keap1shRNAs were constructed in vitro, then the intracellular oxidative stress, the proportion of cells undergoing apoptosis, and cell viability were measured. The expression of pro-fibrogenic molecules were analyzed via quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The level of alpha-1 type I collagen (COL1A1) was determined using an enzyme-linked immunosorbent assay (ELISA). Finally, serum-free “conditioned medium” (CM) from the supernatant of hypoxic AML12 hepatocytes was used to culture rat hepatic stellate cells (HSC-T6), and the levels of fibrosis-related molecules, apoptosis, and cell proliferation were determined.

Results: The marker of hypoxia—HIF-1α and HIF-2α in the livers with fibrosis were upregulated, however, the increase in PHD1 expression was not statistically significant in comparison to the control group. Sign of oxidative stress—Keap1 was increased, while the expression of Nrf2, one of the Keap1 main downstream molecules, was reduced in the hepatocytes. And in vitro, the double-knockdown of PHD1 and Keap1 in AML12 hepatocytes presented with decreased hypoxia-induced oxidative stress and apoptosis, furthermore, these hypoxic AML12 cells showed the increased cell viability and the doweregulated expression of pro-fibrogenic molecules. In addition, HSC-T6 cells cultured in the hypoxic double-knockdown CM demonstrated the downregulation of fibrosis-related molecules, diminished cell proliferation, and enhanced apoptosis.

Conclusions: Our study demonstrated that double-knockdown of PHD1 and Keap1 attenuated hypoxia and oxidative stress induced injury in the hepatocytes, and subsequently inhibited HSC activation, which offers a novel therapeutic strategy in the prophylaxis and treatment of liver fibrosis.

MicroRNA-17-5p mediates hypoxia-induced autophagy and inhibits apoptosis by targeting signal transducer and activator of transcription 3 in vascular smooth muscle cells

The aim of the present study was to investigate hypoxia-induced apoptosis and autophagy in vascular smooth muscle cells (VSMCs) and the underlying molecular mechanisms of microRNA (miR)-17-5p responses in an anaerobic environment. The results revealed that miR-17-5p expression was significantly upregulated in VSMCs subjected to hypoxic conditions (P<0.05) and lower miR-17-5p levels were observed in ethyl 3,4-dihydroxybenzoate-treated and hypoxia inducible factor-1 loss-of-function cells. Additionally, it was demonstrated that miR-17-5p is associated with hypoxia-induced autophagy, which was confirmed by upregulating the light chain 3-II/LC3-I ratio and downregulating nucleoporin p62. Cell apoptosis was inhibited in response to hypoxia, and levels of pro-apoptotic proteins B-cell lymphoma 2-associated X protein and p-caspase were markedly decreased when VSMCs were subjected to hypoxic conditions. Furthermore, expression of signal transducer and activator of transcription 3 (STAT3) decreased when cells were transfected with overexpressing miR-17-5p and subjected to hypoxic conditions, and the combination of miR-17-5p loss-of-function and hypoxia induced greater upregulation in the protein expression of STAT3 compared with a single treatment for hypoxia in VSMCs. In conclusion, miR-17-5p may be a novel hypoxia-responsive miR and hypoxia may induce protective autophagy and anti-apoptosis in VSMCs by targeting STAT3.

Ethyl 3,4-dihydroxybenzoate (EDHB): a prolyl hydroxylase inhibitor attenuates acute hypobaric hypoxia mediated vascular leakage in brain

Sudden exposure to altitude hypoxia is responsible for acute mountain sickness (AMS) in un-acclimatized persons. If not treated in time, AMS can worsen and leads to high altitude cerebral edema, which can be fatal. Present study explores the efficacy of ethyl 3,4-dihydroxybenzoate (EDHB), a prolyl hydroxylase enzyme inhibitor, in modulating adaptive responses to hypobaric hypoxia (HH) in rat brain. Male Sprague-Dawley rats treated with EDHB (75 mg/kg for 3 days), were subjected to acute HH exposure at 9144 m (30,000 ft) for 5 h. Animals were assessed for transvascular leakage and edema formation in brain and role of key inflammatory markers along with hypoxia responsive genes. HH stress increased transvascular permeability and edema formation in conjunction with upregulation of nuclear factor-κB (NF-κB) and its regulated proteins. There was surge in pro-inflammatory cytokines tumor necrosis factor-α, interleukin-6, interferon-γ, monocyte chemoattractant protein-1 and decrement in anti-inflammatory cytokine interleukin-10. Further, upregulation of vascular endothelial growth factor (VEGF), a vascular permeability marker and down-regulation of antioxidant and anti-inflammatory proteins hemoxygenase (HO-1) and metallothionein (MT-1) was also observed under hypoxia. EDHB supplementation effectively scaled down HH induced cerebral edema with concomitant downregulation of brain NF-κB expression. There was significant curtailment of pro-inflammatory cytokines and cell adhesion molecules. There was significant downregulation of permeability factor VEGF by EDHB with concomitant increment in hypoxia inducible factor (HIF1α) and anti-inflammatory proteins HO-1 and MT-1 compared to HH control thus accentuating the potential of EDHB as effective hypoxic preconditioning agent in ameliorating HH mediated injury in brain.

Preconditioning with ethyl 3,4-dihydroxybenzoate augments aerobic respiration in rat skeletal muscle

Muscle respiratory capacity decides the amount of exertion one's skeletal muscle can undergo, and endurance exercise is believed to increase it. There are also certain preconditioning methods by which muscle respiratory and exercise performance can be enhanced. In this study, preconditioning with ethyl 3,4-dihydroxybenzoate (EDHB), a prolyl hydroxylase domain enzyme inhibitor, has been investigated to determine its effect on aerobic metabolism and bioenergetics in skeletal muscle, thus facilitating boost in physical performance in a rat model. We observed that EDHB supplementation increases aerobic metabolism via upregulation of HIF-mediated GLUT1 and GLUT4, thus enhancing glucose uptake in muscles. There was also a twofold rise in the activity of enzymes of tricarboxylic acid (TCA) cycle and glycolysis, ie, hexokinase and phosphofructokinase. There was an increase in citrate synthase and succinate dehydrogenase activity, resulting in the rise in the levels of ATP due to enhanced Krebs cycle activity as substantiated by enhanced acetyl-CoA levels in EDHB-treated rats as compared to control group. Increased lactate dehydrogenase activity, reduced expression of monocarboxylate transporter 1, and increase in monocarboxylate transporter 4 suggest transport of lactate from muscle to blood. There was a concomitant decrease in plasma lactate, which might be due to enhanced transport of lactate from blood to the liver. This was further supported by the rise in liver pyruvate levels and liver glycogen levels in EDHB-supplemented rats as compared to control rats. These results suggest that EDHB supplementation leads to improved physical performance due to the escalation of aerobic respiration quotient, ie, enhanced muscle respiratory capacity.

HIF-1-driven skeletal muscle adaptations to chronic hypoxia: molecular insights into muscle physiology

Skeletal muscle is a metabolically active tissue and the major body protein reservoir. Drop in ambient oxygen pressure likely results in a decrease in muscle cells oxygenation, reactive oxygen species (ROS) overproduction and stabilization of the oxygen-sensitive hypoxia-inducible factor (HIF)-1α. However, skeletal muscle seems to be quite resistant to hypoxia compared to other organs, probably because it is accustomed to hypoxic episodes during physical exercise. Few studies have observed HIF-1α accumulation in skeletal muscle during ambient hypoxia probably because of its transient stabilization. Nevertheless, skeletal muscle presents adaptations to hypoxia that fit with HIF-1 activation, although the exact contribution of HIF-2, I kappa B kinase and activating transcription factors, all potentially activated by hypoxia, needs to be determined. Metabolic alterations result in the inhibition of fatty acid oxidation, while activation of anaerobic glycolysis is less evident. Hypoxia causes mitochondrial remodeling and enhanced mitophagy that ultimately lead to a decrease in ROS production, and this acclimatization in turn contributes to HIF-1α destabilization. Likewise, hypoxia has structural consequences with muscle fiber atrophy due to mTOR-dependent inhibition of protein synthesis and transient activation of proteolysis. The decrease in muscle fiber area improves oxygen diffusion into muscle cells, while inhibition of protein synthesis, an ATP-consuming process, and reduction in muscle mass decreases energy demand. Amino acids released from muscle cells may also have protective and metabolic effects. Collectively, these results demonstrate that skeletal muscle copes with the energetic challenge imposed by O2 rarefaction via metabolic optimization.