Angiotensin II promotes iron accumulation and depresses PGI₂ and NO synthesis in endothelial cells: effects of losartan and propranolol analogs

COVID-19, ferrosenescence and neurodegeneration, a mini-review

Exacerbation of cognitive, motor and nonmotor symptoms have been described in critically ill COVID-19 patients, indicating that, like prior pandemics, neurodegenerative sequelae may mark the aftermath of this viral infection. Moreover, SARS-CoV-2, the causative agent of COVID-19 disease, was associated with hyperferritinemia and unfavorable prognosis in older individuals, suggesting virus-induced ferrosenescence. We have previously defined ferrosenescence as an iron-associated disruption of both the human genome and its repair mechanisms, leading to premature cellular senescence and neurodegeneration. As viruses replicate more efficiently in iron-rich senescent cells, they may have developed the ability to induce this phenotype in host tissues, predisposing to both immune dysfunction and neurodegenerative disorders. In this mini-review, we summarize what is known about the SARS-CoV-2-induced cellular senescence and iron dysmetabolism. We also take a closer look at immunotherapy with natural killer cells, angiotensin II receptor blockers ("sartans"), iron chelators and dipeptidyl peptidase 4 inhibitors ("gliptins") as adjunct treatments for both COVID-19 and its neurodegenerative complications.

Iron Overload Damages the Endothelial Mitochondria via the ROS/ADMA/DDAHII/eNOS/NO Pathway

It has been recognized that iron overload may harm the body's health. Vascular endothelial cells (VECs) are one of the main targets of iron overload injury, and the mechanism involved was thought to be related to the excessive generation of reactive oxygen species (ROS). However, the subcellular and temporal characteristics of ROS generation, potential downstream mechanisms, and target organelles in VECs injured by iron overload have not been expounded yet. In this study, we elucidated the abovementioned issues through both in vivo and in vitro experiments. Mice were fed pellet diets that were supplemented with iron for 4 consecutive months. Results showed that the thoracic aortic strips' endothelium-dependent dilation was significantly impaired and associated with inflammatory changes, noticeable under brown TUNEL-positive staining in microscopy analysis. In addition, the serum content of asymmetric dimethylarginine (ADMA) increased, whereas nitric oxide (NO) levels decreased. Furthermore, the dimethylarginine dimethylaminohydrolase II (DDAHII) expression and activity, as well as the phosphorylation of endothelial nitric oxide synthase (eNOS) in aortic tissue, were inhibited. Human umbilical vein endothelial cells were treated with 50 μM iron dextran for 48 hours, after which the cell viability, NO content, DDAHII expression and activity, and phosphorylation of eNOS decreased and lactate dehydrogenase and caspase-3 activity, ADMA content, and apoptotic cells significantly increased. After the addition of L-arginine (L-Arg) or pAD/DDAHII, the abovementioned changes were reversed. By dynamically detecting the changes of ROS generation in the cytoplasm and mitochondria and interfering with different aspects of signaling pathways, we have confirmed for the first time that excessive ROS originates from the cytoplasm and activates the ROS-induced ROS release (RIRR) mechanism, leading to mitochondrial dysfunction. Together, our data suggested that excessive free iron ions produced excess ROS in the cytoplasm. Thus, excess ROS create one vicious circle by activating the ADMA/eNOS/DDAHII/NO pathway and another vicious circle by activation of the RIRR mechanism, which, when combined, induce a ROS burst, resulting in mitochondrial dysfunction and damaged VECs.

Macro- and Microelement Status in Animal and Human Hypertension: the Role of the ACE Gene I/D Polymorphism

Genetic factors that predispose to hypertension may contribute to element disturbances observed in hypertensive patients. We tested the hypothesis that the deletion allele of the angiotensin-converting enzyme (ACE) gene is associated with element imbalances in hypertension. The concentrations of elements in genetically predisposed to hypertension rats (SHRs) and their controls (WKY rats) were also examined. ICP-MS was used for elemental analysis of human hair and animal fur. Genotyping was performed by PCR. We also measured micronuclei frequency and distribution of peripheral blood leukocytes in cell cycle phases by flow cytometry and studied the correlations of these parameters with element contents. In general, the tendency for higher levels of toxic and lower levels of essential elements is observed in hypertension, specifically in patients carrying the D allele. Hypertensive men had significantly higher Be, V, Cr, As, Mo, Ag, Sb, and Na levels and lower Ca, Zn, Ba, and U levels compared with control subjects; the differences were not significant for Mg, Al, K, Mn, Fe, Co, Ni, Cu, Se, Cd, Tl, Pb, and Th. The D allele was associated with higher Be, Mo, and Th levels and lower Zn, Se, and Tl levels. The concentrations of Ca, Co, Mo and U were higher in SHR than those in the WKY rats. Mo, an antagonist of Cu, positively correlated with the S-phase cells, and Cu positively correlated with micronuclei frequency. The results suggest an involvement of the ACE I/D polymorphism in element imbalances in hypertension and attract attention to the possible significant role of genetic factors in Mo accumulation.

Clinical Significance of Endothelial Dysfunction in Essential Hypertension

The endothelium is recognized as a major determinant of vascular physiology and pathophysiology. Over the last few decades, a plethora of studies have implicated endothelial dysfunction in the progression of atherosclerosis and the subclinical target organ damage observed in essential hypertension. However, the clinical significance of diagnosing endothelial dysfunction in patients with essential hypertension remains under investigation. Although a number of vascular and non-vascular markers of endothelial dysfunction have been proposed, there is an ongoing quest for a marker in the clinical setting that is optimal, inexpensive, and reproducible. In addition, endothelial dysfunction emerges as a promising therapeutic target of agents that are readily available in clinical practice. In this context, a better understanding of its role in essential hypertension becomes of great importance. Here, we aim to investigate the clinical significance of endothelial dysfunction in essential hypertension by accumulating novel data on (a) early diagnosis using robust markers with prognostic value in cardiovascular risk prediction, (b) the association of endothelial dysfunction with subclinical vascular organ damage, and (c) potential therapeutic targets.

The Protective Effect of Bafilomycin A1 Against Cobalt Nanoparticle-Induced Cytotoxicity and Aseptic Inflammation in Macrophages In Vitro

Co ions released due to corrosion of Co nanoparticles (CoNPs) in the lysosomes of macrophages may be a factor in the particle-induced cytotoxicity and aseptic inflammation accompanying metal-on-metal (MOM) hip prosthesis failure. Here, we show that CoNPs are easily dissolved under a low pH, simulating the acidic lysosomal environment. We then used bafilomycin A1 to change the pH inside the lysosome to inhibit intracellular corrosion of CoNPs and then investigated its protective effects against CoNP-induced cytotoxicity and aseptic inflammation on murine macrophage RAW264.7 cells. XTT {2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide} assays revealed that bafilomycin A1 can significantly decrease CoNP-induced cytotoxicity in RAW264.7 cells. Enzyme-linked immunosorbent assays showed that bafilomycin A1 can significantly decrease the subtoxic concentration of CoNP-induced levels of pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), but has no effect on anti-inflammatory cytokines (transforming growth factor-β and interleukin-10) in RAW264.7 cells. We studied the protective mechanism of bafilomycin A1 against CoNP-induced effects in RAW264.7 cells by measuring glutathione/oxidized glutathione (GSH/GSSG), superoxide dismutase, catalase, and glutathione peroxidase levels and employed scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer assays to observe the ultrastructural cellular changes. The changes associated with apoptosis were assessed by examining the pAKT and cleaved caspase-3 levels using Western blotting. These data strongly suggested that bafilomycin A1 can potentially suppress CoNP-induced cytotoxicity and aseptic inflammation by inhibiting intracellular corrosion of CoNPs and that the reduction in Co ions released from CoNPs may play an important role in downregulating oxidative stress in RAW264.7 cells.

Angiotensin II inhibits uptake of transferrin-bound iron but not non-transferrin-bound iron by cultured astrocytes

The existence of all components of the renin-angiotensin system (RAS) and the iron metabolism system, and the recent findings on the functions of angiotensin II (ANGII) in peripheral iron metabolism imply that ANGII might play a role in iron homeostasis by regulating expression of iron transport proteins in the brain. Here, we investigated effects of ANGII on uptake and release of iron as well as expression of cell iron transport proteins in cultured astrocytes. We demonstrated that ANGII could significantly inhibit transferrin-bound iron (Tf-Fe) uptake and iron release as well as the expression of transferrin receptor 1 (TfR1) and the iron exporter ferroportin 1 (Fpn1) in cultured astrocytes. This indicated that the inhibitory role of ANGII on Tf-Fe uptake and iron release is mediated by its negative effect on the expression of TfR1 and Fpn1. We also provided evidence that ANGII had no effect on divalent metal transporter 1 (DMT1) expression as well as non-transferrin-bound iron (NTBI) uptake in the cells. Our findings showed that ANGII has a role to affect expression of iron transport proteins in astrocytes in vitro and also suggested that ANGII might have a physiological function in brain iron homeostasis.

Mg supplementation protects against ritonavir-mediated endothelial oxidative stress and hepatic eNOS downregulation

Ritonavir (RTV), a prototypical protease inhibitor currently used as a key component of anti-HIV therapy, is known for its endothelial and hepatic toxicity. The effects of RTV and magnesium supplementation on cultured bovine endothelial cell (EC) and rat hepatic endothelial nitric oxide synthase (eNOS) status were investigated. RTV dose-dependently (5-30 µM) decreased EC viability after 48 h; high Mg (2mM) significantly attenuated the lost viability. ECs incubated with 15 µM RTV for 6 to 24h resulted in two- to fourfold elevation of oxidized glutathione and a 25% loss of total glutathione. At 24h, EC superoxide production due to RTV was detected by dihydroethidium staining and increased 41% when quantified by flow cytometry; altered glutathione status and superoxide levels were both substantially reversed by 2mM Mg. RTV reduced eNOS mRNA (-25% at 24 h) and led to decreased eNOS dimer/monomer ratios; nitric oxide-derived products decreased 40%; both changes were attenuated by Mg supplementation. In male Lewis-Brown Norway rats, RTV administration (75 mg/kg/day, 5 weeks) resulted in an 85% increase in plasma 8-isoprostane and a 23% decrease in hepatic eNOS mRNA; concomitantly, eNOS protein decreased 75%, whereas plasma nitrite level was reduced 48%. Dietary Mg supplementation (sixfold higher than control) prevented the eNOS mRNA decrease along with lowering 8-isoprostane and restored the eNOS protein and plasma nitrite levels comparable to controls. In conclusion, Mg attenuates RTV-mediated EC oxidative eNOS dysfunction and downregulation of hepatic eNOS expression; we suggest that Mg can serve as a beneficial adjunct therapeutic against RTV-mediated eNOS toxicity.

Angiotensin II inhibits iron uptake and release in cultured neurons

Based on the well-confirmed roles of angiotensin II (ANGII) in iron transport of peripheral organs and cells, the causative link of excess brain iron with and the involvement of ANGII in neurodegenerative disorders, we speculated that ANGII might also have an effect on expression of iron transport proteins in the brain. In the present study, we investigated effects of ANGII on iron uptake and release using the radio-isotope methods as well as expression of cell iron transport proteins by Western blot analysis in cultured neurons. Our findings demonstrated for the first time that ANGII significantly reduced transferrin-bound iron and non-transferrin bound iron uptake and iron release as well as expression of two major iron uptake proteins transferrin receptor 1 and divalent metal transporter 1 and the key iron exporter ferroportin 1 in cultured neurons. The findings suggested that endogenous ANGII might have a physiological significance in brain iron metabolism.