A small-molecule allosteric inhibitor of BAX protects against doxorubicin-induced cardiomyopathy

Doxorubicin remains an essential component of many cancer regimens, but its use is limited by lethal cardiomyopathy, which has been difficult to target, owing to pleiotropic mechanisms leading to apoptotic and necrotic cardiac cell death. Here we show that BAX is rate-limiting in doxorubicin-induced cardiomyopathy and identify a small-molecule BAX inhibitor that blocks both apoptosis and necrosis to prevent this syndrome. By allosterically inhibiting BAX conformational activation, this compound blocks BAX translocation to mitochondria, thereby abrogating both forms of cell death. When co-administered with doxorubicin, this BAX inhibitor prevents cardiomyopathy in zebrafish and mice. Notably, cardioprotection does not compromise the efficacy of doxorubicin in reducing leukemia or breast cancer burden in vivo, primarily due to increased priming of mitochondrial death mechanisms and higher BAX levels in cancer cells. This study identifies BAX as an actionable target for doxorubicin-induced cardiomyopathy and provides a prototype small-molecule therapeutic.

Myocardial apoptosis in heart disease: does the emperor have clothes?

Since the discovery of a novel mechanism of cell death that differs from traditional necrosis, i.e., apoptosis, there have been numerous studies concluding that increased apoptosis augments myocardial infarction and heart failure and that limiting apoptosis protects the heart. Importantly, the vast majority of cells in the heart are non-myocytes with only roughly 30 % myocytes, yet almost the entire field studying apoptosis in the heart has disregarded non-myocyte apoptosis, e.g., only 4.7 % of 423 studies on myocardial apoptosis in the past 3 years quantified non-myocyte apoptosis. Accordingly, we reviewed the history of apoptosis in the heart focusing first on myocyte apoptosis, followed by the history of non-myocyte apoptosis in myocardial infarction and heart failure. Apoptosis of several of the major non-myocyte cell types in the heart (cardiac fibroblasts, endothelial cells, vascular smooth muscle cells, macrophages and leukocytes) may actually be responsible for affecting the severity of myocardial infarction and heart failure. In summary, even though it is now known that the majority of apoptosis in the heart occurs in non-myocytes, very little work has been done to elucidate the mechanisms by which non-myocyte apoptosis might be responsible for the adverse effects of apoptosis in myocardial infarction and heart failure. The goal of this review is to provide an impetus for future work in this field on non-myocyte apoptosis that will be required for a better understanding of the role of apoptosis in the heart.

Atorvastatin enhanced nitric oxide release and reduced blood pressure, nitroxidative stress and rantes levels in hypertensive rats with diabetes

Clinical trials have shown that atorvastatin benefits patients with diabetes even with normal baseline LDL levels. We hypothesized that atorvastatin improves endothelial cell (EC) function and reduces inflammation in hypertensive rats with diabetes. Non-diabetic and streptozotocin-induced type 2 diabetic male spontaneously hypertensive rats (SHR) were treated with atorvastatin at 20 mg/kg/day. After five weeks, nitric oxide (NO) and peroxynitrite (ONOO(-)) were measured in aortic and glomerular endothelial cells. A tandem of nanosensors was used to simultaneously measure NO and ONOO(-) concentration and their ratio [NO]/[ONOO(-)] was monitored with a time resolution better than 10 μs and detection limit 1 nM. [NO]/[ONOO(-)] was applied as a marker of endothelial NO synthase (eNOS) uncoupling, endothelial dysfunction and nitroxidative stress. Glucose, cholesterol, blood pressure (BP), and the cytokine RANTES were also measured. Diabetic SHR rats had elevated glucose (355 ± 38 mg/dL), mean BP (172 ± 15 mmHg), and plasma RANTES (38.4 ± 2.7 ng/mL), low endothelial NO bioavailability and high ONOO(-). Maximal NO release measured 267 ± 29 nM in aortic endothelium of SHR rats and 214 ± 20 nM for diabetic SHR rats; [NO]/[ONOO(-)] was 0.88 ± 12 and 0.61 ± 0.08, respectively. [NO]/[ONOO(-)] ratios below one indicate a high uncoupling of eNOS, endothelial dysfunction and high nitroxidative stress. Atorvastatin treatment partially restored endothelial function by increasing NO level by 98%, reducing ONOO(-) by 40% and favorably elevating [NO]/[ONOO(-)] to 1.1 ± 0.2 for diabetic SHR rats and 1.6 ± 0.3 for SHR rats. The effects of atorvastatin were similar in glomerular endothelial cells and were partially reproduced by modulators of eNOS or NADPH oxidase. Atorvastatin had no significant effect on fasting glucose or total cholesterol levels but reduced mean BP by 21% and 11% in diabetic and non-diabetic animals, respectively. Atorvastatin also reduced RANTES levels by 50%. Atorvastatin favorably increased the [NO]/[ONOO(-)] balance, enhanced endothelial cytoprotective NO, decreased cytotoxic ONOO(-) and reduced BP, inflammation and RANTES levels in diabetic, hypertensive rats without altering cholesterol levels. These findings provide insights into mechanisms of restoration of endothelial function and vascular protection by atorvastatin in diabetes and hypertension.

Pegylation increases platelet biocompatibility of gold nanoparticles

The increasing use of gold nanoparticles in medical diagnosis and treatment has raised the concern over their blood compatibility. The interactions of nanoparticles with blood components may lead to platelet aggregation and endothelial dysfunction. Therefore, medical applications of gold nanoparticles call for increased nanoparticle stability and biocompatibility. Functionalisation of nanoparticles with polythelene glycol (PEGylation) is known to modulate cell-particle interactions. Therefore, the aim of the current study was to investigate the effects of PEGylated-gold nanoparticles on human platelet function and endothelial cells in vitro. Gold nanoparticles, 15 nm in diameter, were synthesised in water using sodium citrate as a reducing and stabilising agent. Functionalised polyethylene glycol-based thiol polymers were used to coat and stabilise pre-synthesised gold nanoparticles. The interaction of gold nanoparticles-citrate and PEGylated-gold nanoparticles with human platelets was measured by Quartz Crystal Microbalance with Dissipation. Platelet-nanoparticles interaction was imaged using phase-contrast, scanning and transmission electron microscopy. The inflammatory effects of gold nanoparticles-citrate and PEGylated-gold nanoparticles in endothelial cells were measured by quantitative real time polymerase chain reaction. PEGylated-gold nanoparticles were stable under physiological conditions and PEGylated-gold nanoparticles-5400 and PEGylated-gold nanoparticles-10800 did not affect platelet aggregation as measured by Quartz Crystal Microbalance with Dissipation. In addition, PEGylated-gold nanoparticles did not induce an inflammatory response when incubated with endothelial cells. Therefore, this study shows that PEGylated-gold nanoparticles with a higher molecular weight of the polymer chain are both platelet- and endothelium-compatible making them attractive candidates for biomedical applications.

Amlodipine increased endothelial nitric oxide and decreased nitroxidative stress disproportionately to blood pressure changes

BACKGROUND

Clinical trials have shown that amlodipine reduces cardiovascular events at a rate that is not predicted by changes in brachial arterial pressure alone. These findings may be explained, in part, by the pleiotropic effects of amlodipine on endothelial cell (EC) function. In this study, we elucidated the effect of amlodipine on nitric oxide (NO) bioavailability and cytotoxic peroxynitrite (ONOO(-)) and blood pressure (BP).

METHODS

Spontaneously hypertensive rats (SHRs) were treated with vehicle or amlodipine (5 mg/kg/day) for 8 weeks and compared with untreated, baseline rats. NO and ONOO(-) release from aortic and glomerular ECs were measured ex vivo using amperometric nanosensors following maximal stimulation with calcium ionophore. BP was measured using the tail-cuff method.

RESULTS

As compared with baseline, vehicle treatment had reduced aortic endothelial NO release from 157 ± 11 nM to 55 ± 6 nM and increased ONOO(-) from 69 ± 7 nM to 156 ± 19 nM. The NO/ONOO(-) ratio, a comprehensive measurement of eNOS function, decreased from 2.3 ± 0.3 to 0.3 ± 0.1. Compared with vehicle, amlodipine treatment restored NO to 101 ± 3 nM, decreased ONOO(-) to 50 ± 4 nM, and increased the NO/ONOO(-) ratio to 2.0 ± 0.2, a level similar to baseline. Similar changes were observed for glomerular ECs. Mean arterial blood pressure increased from 149 ± 3 mm Hg (baseline) to 174 ± 1 mm Hg (vehicle). Amlodipine slightly, but significantly, decreased mean arterial blood pressure to 167 ± 3 mm Hg vs. vehicle treatment.

CONCLUSIONS

Amlodipine increased NO bioavailability and decreased nitroxidative stress in SHRs with EC dysfunction disproportionately to BP changes. These direct, vascular effects of amlodipine on EC function may contribute to reduced risk for atherothrombotic events as observed in clinical trials.

The favorable kinetics and balance of nebivolol-stimulated nitric oxide and peroxynitrite release in human endothelial cells

Background

Nebivolol is a third-generation beta-blocker used to treat hypertension. The vasodilation properties of nebivolol have been attributed to nitric oxide (NO) release. However, the kinetics and mechanism of nebivolol-stimulated bioavailable NO are not fully understood.

Methods

Using amperometric NO and peroxynitrite (ONOO^-) nanosensors, β₃-receptor (agonist: L-755,507; antagonists: SR59230A and L-748,337), ATP efflux (the mechanosensitive ATP channel blocker, gadolinium) and P2Y-receptor (agonists: ATP and 2-MeSATP; antagonist: suramin) modulators, superoxide dismutase and a NADPH oxidase inhibitor (VAS2870), we evaluated the kinetics and balance of NO and ONOO^- stimulated by nebivolol in human umbilical vein endothelial cells (HUVECs). NO and ONOO^- were measured with nanosensors (diameter ~ 300 nm) placed 5 ± 2 μm from the cell membrane and ATP levels were determined with a bioluminescent method. The kinetics and balance of nebivolol-stimulated NO and ONOO^- were compared with those of ATP, 2-MeSATP, and L-755,507.

Results

Nebivolol stimulates endothelial NO release through β₃-receptor and ATP-dependent, P2Y-receptor activation with relatively slow kinetics (75 ± 5 nM/s) as compared to the kinetics of ATP (194 ± 10 nM/s), L-755,507 (108 ± 6 nM/s), and 2-MeSATP (105 ± 5 nM/s). The balance between cytoprotective NO and cytotoxic ONOO^- was expressed as the ratio of [NO]/[ONOO^-] concentrations. This ratio for nebivolol was 1.80 ± 0.10 and significantly higher than that for ATP (0.80 ± 0.08), L-755,507 (1.08 ± 0.08), and 2-MeSATP (1.09 ± 0.09). Nebivolol induced ATP release in a concentration-dependent manner.

Conclusion

The two major pathways (ATP efflux/P2Y receptors and β₃ receptors) and several steps of nebivolol-induced NO and ONOO^- stimulation are mainly responsible for the slow kinetics of NO release and low ONOO^-. The net effect of this slow kinetics of NO is reflected by a favorable high ratio of [NO]/[ONOO^-] which may explain the beneficial effects of nebivolol in the treatment of endothelial dysfunction, hypertension, heart failure, and angiogenesis.

Effects of angiotensin receptor blockers on endothelial nitric oxide release: the role of eNOS variants

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Angiotensin II receptor blockers improve endothelial cell-dependent vasodilation in patients with hypertension through suppression of angiotensin II type 1 receptors but may have additional and differential effects on endothelial nitric oxide synthase (eNOS) function.

WHAT THIS STUDY ADDS

• The key finding from this study is that angiotensin II receptor blockers (ARBs) differentially enhanced nitric oxide (NO) release in a manner influenced by certain genetic variants of eNOS. This finding provides new insights into the effects of ARBs on endothelial cell-dependent vasodilation and eNOS function that are of high importance in vascular medicine and clinical pharmacology. AIM Angiotensin II receptor blockers (ARBs) improve endothelial cell (EC)-dependent vasodilation in patients with hypertension through suppression of angiotensin II type 1 receptors but may have additional and differential effects on endothelial nitric oxide (NO) synthase (eNOS) function. To investigate this question, we tested the effects of various ARBs on NO release in ECs from multiple donors, including those with eNOS genetic variants linked to higher cardiovascular risk.

METHODS

The effects of ARBs (losartan, olmesartan, telmisartan, valsartan), at 1 µm, on NO release were measured with nanosensors in human umbilical vein ECs obtained from 18 donors. NO release was stimulated with calcium ionophore (1 µm) and its maximal concentration was correlated with eNOS variants. The eNOS variants were determined by a single nucleotide polymorphism in the promoter region (T-786C) and in the exon 7 (G894T), linked to changes in NO metabolism. RESULTS All of the ARBs caused an increase in NO release as compared with untreated samples (P < 0.01, n= 4-5 in all eNOS variants). However, maximal NO production was differentially influenced by eNOS genotype. Olmesartan increased maximal NO release by 30%, which was significantly greater (P < 0.01, n= 4-5 in all eNOS variants) than increases observed with other ARBs.

CONCLUSIONS

The ARBs differentially enhanced NO release in ECs in a manner influenced by eNOS single nucleotide polymorphisms. These findings provide new insights into the effects of ARBs on EC-dependent vasodilation and eNOS function.

Mechanisms of toxicity of amorphous silica nanoparticles on human lung submucosal cells in vitro: protective effects of fisetin

There is growing evidence that amorphous silica nanoparticles (SiO₂-NP) can cause an inflammatory response in the lung. We studied in vitro the effects of exposing human lung submucosal cells to SiO₂-NP of various sizes (10, 150, and 500 nm) for 2-24 h. Cell survival, reactive oxygen species (ROS), malondialdehyde (MDA) levels, cytokine production, inflammatory gene expression, and genotoxicity were measured after exposure of Calu-3 cells to 10SiO₂-NP in the presence or absence of the flavanoid fisetin and an antioxidant enzyme catalase. The exposure of Calu-3 cells to 10SiO₂-NP resulted in (1) increased cytotoxicity and cell death in a time- and concentration-dependent manner, with a lethal concentration (LC₅₀) of 9.7 μg/mL after 24 h; (2) enhanced gene expression of interleukin (IL)-6, IL-8, and matrix metalloproteinase-9; (3) a significant correlation between increases in MDA and cytotoxicity at 18 h; (4) ROS production; (5) IL-6 and IL-8 release; and (6) up-regulation of the pro-apoptotic genes, p53 and caspase-3. Cell death and inflammatory reactions were attenuated by fisetin and catalase. We observed that 150- and 500SiO₂-NP exerted no toxic effects on Calu-3 cells. In conclusion, the nanotoxicity of amorphous 10SiO₂-NP on submucosal cells is associated with inflammation, the release of ROS leading to apoptosis, and decreased cell survival. The nanotoxic effects of 10SiO₂-NP can be decreased by fisetin and catalase treatment, implicating oxidative stress in this injury.

Amorphous silica nanoparticles aggregate human platelets: potential implications for vascular homeostasis

Background

Amorphous silica nanoparticles (SiNP) can be used in medical technologies and other industries leading to human exposure. However, an increased number of studies indicate that this exposure may result in cardiovascular inflammation and damage. A high ratio of nitric oxide to peroxynitrite concentrations ([NO]/[ONOO⁻]) is crucial for cardiovascular homeostasis and platelet hemostasis. Therefore, we studied the influence of SiNP on the platelet [NO]/[ONOO⁻] balance and platelet aggregation.

Methods

Nanoparticle–platelet interaction was examined using transmission electron microscopy. Electrochemical nanosensors were used to measure the levels of NO and ONOO⁻ released by platelets upon nanoparticle stimulation. Platelet aggregation was studied using light aggregometry, flow cytometry, and phase contrast microscopy.

Results

Amorphous SiNP induced NO release from platelets followed by a massive stimulation of ONOO⁻ leading to an unfavorably low [NO]/[ONOO⁻] ratio. In addition, SiNP induced an upregulation of selectin P expression and glycoprotein IIb/IIIa activation on the platelet surface membrane, and led to platelet aggregation via adenosine diphosphate and matrix metalloproteinase 2-dependent mechanisms. Importantly, all the effects on platelet aggregation were inversely proportional to nanoparticle size.

Conclusions

The exposure of platelets to amorphous SiNP induces a critically low [NO]/[ONOO⁻] ratio leading to platelet aggregation. These findings provide new insights into the pharmacological profile of SiNP in platelets.

Amorphous silica nanoparticles trigger nitric oxide/peroxynitrite imbalance in human endothelial cells: inflammatory and cytotoxic effects

Background

The purpose of this study was to investigate the mechanism of noxious effects of amorphous silica nanoparticles on human endothelial cells.

Methods

Nanoparticle uptake was examined by transmission electron microscopy. Electrochemical nanosensors were used to measure the nitric oxide (NO) and peroxynitrite (ONOO⁻) released by a single cell upon nanoparticle stimulation. The downstream inflammatory effects were measured by an enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and flow cytometry, and cytotoxicity was measured by lactate dehydrogenase assay.

Results

We found that the silica nanoparticles penetrated the plasma membrane and rapidly stimulated release of cytoprotective NO and, to a greater extent, production of cytotoxic ONOO⁻. The low [NO]/[ONOO⁻] ratio indicated increased nitroxidative/oxidative stress and correlated closely with endothelial inflammation and necrosis. This imbalance was associated with nuclear factor κB activation, upregulation of key inflammatory factors, and cell death. These effects were observed in a nanoparticle size-dependent and concentration-dependent manner.

Conclusion

The [NO]/[ONOO⁻] imbalance induced by amorphous silica nanoparticles indicates a potentially deleterious effect of silica nanoparticles on vascular endothelium.