Severe Acute Respiratory Syndrome Coronavirus 2, COVID-19, and the Renin-Angiotensin System: Pressing Needs and Best Research Practices

The coronavirus disease 2019 (COVID-19) pandemic is associated with significant morbidity and mortality throughout the world, predominantly due to lung and cardiovascular injury. The virus responsible for COVID-19-severe acute respiratory syndrome coronavirus 2-gains entry into host cells via ACE2 (angiotensin-converting enzyme 2). ACE2 is a primary enzyme within the key counter-regulatory pathway of the renin-angiotensin system (RAS), which acts to oppose the actions of Ang (angiotensin) II by generating Ang-(1-7) to reduce inflammation and fibrosis and mitigate end organ damage. As COVID-19 spans multiple organ systems linked to the cardiovascular system, it is imperative to understand clearly how severe acute respiratory syndrome coronavirus 2 may affect the multifaceted RAS. In addition, recognition of the role of ACE2 and the RAS in COVID-19 has renewed interest in its role in the pathophysiology of cardiovascular disease in general. We provide researchers with a framework of best practices in basic and clinical research to interrogate the RAS using appropriate methodology, especially those who are relatively new to the field. This is crucial, as there are many limitations inherent in investigating the RAS in experimental models and in humans. We discuss sound methodological approaches to quantifying enzyme content and activity (ACE, ACE2), peptides (Ang II, Ang-[1-7]), and receptors (types 1 and 2 Ang II receptors, Mas receptor). Our goal is to ensure appropriate research methodology for investigations of the RAS in patients with severe acute respiratory syndrome coronavirus 2 and COVID-19 to ensure optimal rigor and reproducibility and appropriate interpretation of results from these investigations.

Abstract 051: High Salt Enhances ROS and Ang II Contractions of Glomerular Afferent Arterioles From Mice With Reduced Renal Mass

High salt intake, angiotensin II (Ang II), and reactive oxygen species (ROS) enhance progression of chronic kidney disease (CKD). We reported that myogenic contractions of renal afferent arterioles (RAAs) were enhanced by superoxide (O 2 ·- ) generated from p47 phox /NOX2 but inhibited by H 2 O 2 generated from POLDIP2/NOX4. We tested the hypothesis that feeding a high salt diet to mice with the reduced renal mass (RRM) model of CKD generates specific ROS in their RAAs that enhances Ang II contractions.

Methods and Results: C57BL/6 mice received surgical RRM or sham operations and 6% or 0.4% NaCl salt for 3 months. Ang II contractions were measured in RAAs perfused at 45 mmHg and superoxide (O 2 ·- ) and H 2 O 2 by fluorescence microscopy. RRM enhanced the gene expression in RAAs for p47 phox and NOX2 and high salt intake in mice with RRM enhanced the gene expression for AT1Rs, POLDIP2 and NOX4 and reduced the gene expression for catalase. Mice with RRM fed a normal salt diet had contractions to 10 -6 mol·l -1 Ang II similar to sham (-56 ± 5 vs -52 ± 5 %; NS). However, RRM mice fed a high salt diet had an enhanced O 2 ·- and H 2 O 2 generation (P<0.005) with Ang II in RAAs and enhanced Ang II maximal contractions (-72 ± 2 vs -45 ± 2%; P<0.005) that were dependent on O 2 ·- from NOX2 since they were prevented in p47 phox -/- mice and on H 2 O 2 from NOX4 since they were prevented in mice with transgenic smooth muscle cell expression of catalase (tg CAT-SMC ), and in POLDIP2 +/- mice. However, RAA contractions to lower concentrations of Ang II (10 -8 to 10 -11 mol·l -1 ) were paradoxically enhanced in tg CAT-SMC vs Wt mice (-17 ± 2 vs -1 ± 1%; P<0.01) and in POLDIP2 +/- vs +/+ mice (-22 ± 3 vs -5 ± 3; P<0.01). Tempol normalized the ROS and Ang II contractions in RAAs from mice with RRM. In conclusion, both O 2 ·- from p47 phox /NOX2 and H 2 O 2 from NOX4/POLDIP2 enhance maximal Ang II contractions of RAAs from mice with RRM fed a high salt diet but H 2 O 2 from NOX4/POLDIP2 reduces the sensitivity to lower concentrations of Ang II by >100-fold and tempol prevents all of these changes Thus, although a high salt intake reduces circulating Ang II, blockade of angiotensin receptors or ROS may prove beneficial for patients with CKD unable to restrict salt.

FGF Suppresses Poldip2 Expression in Osteoblasts

Osteoporosis is one of the most prevalent ageing-associated diseases that are soaring in the modern world. Although various aspects of the disease have been investigated to understand the bases of osteoporosis, the pathophysiological mechanisms underlying bone loss is still incompletely understood. Poldip2 is a molecule that has been shown to be involved in cell migration of vascular cells and angiogenesis. However, expression of Poldip2 and its regulation in bone cells were not known. Therefore, we examined the Poldip2 mRNA expression and the effects of bone regulators on the Poldip2 expression in osteoblasts. We found that Poldip2 mRNA is expressed in osteoblastic MC3T3-E1 cells. As FGF controls osteoblasts and angiogenesis, FGF regulation was investigated in these cells. FGF suppressed the expression of Poldip2 in MC3T3-E1 cells in a time dependent manner. Protein synthesis inhibitor but not transcription inhibitor reduced the FGF effects on Poldip2 gene expression in MC3T3-E1 cells. As for bone-related hormones, dexamethasone was found to enhance the expression of Poldip2 in osteoblastic MC3T3-E1 cells whereas FGF still suppressed such dexamethasone effects. With respect to function, knockdown of Poldip2 by siRNA suppressed the migration of MC3T3-E1 cells. Poldip2 was also expressed in the primary cultures of osteoblast-enriched cells and FGF also suppressed its expression. Finally, Poldip2 was expressed in femoral bone in vivo and its levels were increased in aged mice compared to young adult mice. These data indicate that Poldip2 is expressed in osteoblastic cells and is one of the targets of FGF. J. Cell. Biochem. 118: 1670-1677, 2017. © 2016 Wiley Periodicals, Inc.

Abstract TP110: Polymerase δ-Interacting Protein 2 Regulates Astrocyte Activation in Ischemic Stroke

Introduction: Polymerase δ-Interacting Protein 2 (Poldip2) is a binding partner of Nox4 NADPH oxidase and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). Nox4 and CEACAM1 have been implicated in stroke, but with different outcomes: both contribute to neurodegeneration but only CEACAM1 contributes to blood brain barrier (BBB) dysfunction. However, the underlying mechanisms are still obscure.

Hypothesis: Poldip2+/- mice may be protected from the consequences of transient middle cerebral artery occlusion (tMCAO).

Methods: tMCAO was induced in wild type (WT) and Poldip2+/- mice. The volume of the ischemic lesion was measured in TTC-stained sections. BBB breakdown was evaluated by Evans blue dye extravasation. Poldip2 protein expression was evaluated by immunofluorescence and western blotting. RT-PCR was used to measure mRNA levels of cytokines, MMPs and TIMPs. Astrocytes were transfected with Poldip2 siRNA in culture and mRNA levels of cytokines were evaluated.

Results: Poldip2+/- and WT mice displayed comparable infarct sizes following tMCAO (n=6). A decrease in Evans blue dye extravasation was observed in Poldip2+/- mice (25±3 vs 6±2uM/g) (n=7). Upregulation of cytokine mRNA following tMCAO was also attenuated in Poldip2+/- mice (n=5): MCP-1(253±34 vs 83±23AU), IL-6 (134±38 vs 38±10AU), TNFα (39±12 vs 12±3AU), MMP-2 (19±3 vs 10±1AU), MMP-9 (253±12 vs 13±3AU) and TIMP-1 (286±110 vs 61±15AU). Poldip2 protein expression increased in the ischemic brain of WT mice after tMCAO (69±4 vs 20±5AU) and was predominantly located in astrocytes (n=4). Poldip2 protein expression was also increased in astrocytes following oxygen and glucose deprivation (79±15 vs 27±5AU) (n=6), and Poldip2 siRNA prevented cytokine induction under these conditions.

Conclusions: In conclusion, Poldip2 contributes to stroke-induced BBB breakdown via its ability to inhibit a pro- inflammatory response in perivascular astrocytes.

Abstract 279: Vascular Aging In Aldosterone Associated Hypertension: Role Of NADPH Oxidase 1

In hypertension, vascular aging is accelerated leading to heart failure, stroke and renal dysfunction. Cellular and molecular mechanisms of age-associated vascular changes are unclear, but enhanced ROS generation by NADPH oxidases (Nox) and aldosterone (aldo) have been suggested. Nox1 is of particular interest due to increased levels in hypertension. Here, we postulated that aldo plays an important role in vascular aging through Nox1-dependent mechanisms. We examined signalling molecules associated with aging in arteries from 2 experimental models: stroke-prone spontaneously hypertensive rats (SHRSP) rats and Nox1 knockout mice infused with aldo (300 ug/Kg/day). Gene expression was assessed by qPCR and protein levels by immunoblotting. Aldo was measured by ELISA. In SHRSP rats, aging-associated mRNA inflammatory markers, such as RANTES (5- fold), MCP-1 (6-fold) and IL-6 (2-fold); as well as aldo levels (6-fold) and H2AX (marker of aging-associated DNA damage - 1.5-fold) were increased compared with control rats, p<0.05. In mice treated with aldo, JNK (pro-inflammatory - 69%) and p66SHC (pro-senescence - 92%) activation were increased in mesenteric arteries (p<0.05); an effect blunted in vessels from Nox1 KO mice. In parallel studies, vascular smooth muscle cells (VSMCs) from adult and aged control mice, as well as, from adult Nox1 transgenic mice (Nox1 overexpression in VSMCs) were extracted and stimulated with H2O2 and aldo. Basal levels of p66SHC (39%) and OGG-1 (48%), markers of senescence, were increased in VSMCs from aged animals, p<0.05. H2O2 (64%) and aldo (84%) increased p66SHC activation in VSMCs from adult mice to similar levels observed in cells from aged animals (p<0.05). However, aldo effects on p66SHC activation were exacerbated in VSMCs from adult Nox1 transgenic mice. In conclusion, aldosterone may play an important role in the aging-like phenotype in vascular injury associated with hypertension. Such processes may involve Nox1 and redox-sensitive p66Shc signalling.

Abstract 553: Relaxin Attenuates Angiotensin II--Induced Proinflammatory Signaling in Vascular Smooth Muscle Cells

Relaxin 2 (RLX) was traditionally considered a reproductive hormone. However, recent studies indicate that it also has potent short-term vasodilatory and long-term arterial remodeling and anti-fibrotic effects. Based on these findings, a recombinant form of relaxin, Serelaxin, was successfully used in treatment of the acute heart failure. In the present study, we tested the hypothesis that RLX can attenuate the Angiotensin II (Ang II) mediated vascular inflammation. Ang II, the principal hormone of the renin-angiotensin system, can induce secretion of the Monocyte Chemoattractant Protein-1 (MCP-1) and Interleukin 6 (IL-6). Release of these proinflammatory mediators is an initial step in vascular inflammation, an important early component in the development of cardiovascular disease. Utilizing ELISA, we observed that RLX pretreatment inhibited Ang II-induced secretion of MCP-1 and IL-6 by 70 (p<0.05) and 87% (p<0.05), respectively, in human aortic smooth muscle cells. The same effect was achieved in isolated mouse aortas. We next studied the effect of RLX on Ang II-induced activation of the NFκB pathway and ROS signaling. RLX pretreatment inhibited Ang II-mediated induction of NADPH oxidase 5 expression and production of H2O2 as measured by the sensor HyPer. RLX also prevented P65 phosophorylation and nuclear translocation in response to Ang II. We conclude that RLX inhibits secretion of IL-6 and MCP-1 likely through interference with ROS-mediated NFκB activation. Via this mechanism, RLX may thus represent a therapeutic treatment of pro-inflammatory cardiovascular conditions such as acute heart failure, peripheral arterial disease, and aortic aneurysms.

Abstract 140: Anti-inflammatory and Anti-atherogenic Role of Bmp Receptor II In Endothelial Cells

Atherosclerosis is a multifactorial disease that arises from a combination of endothelial dysfunction and inflammation, occurring preferentially in arterial regions exposed to disturbed flow. Bone morphogenic protein-4 (BMP4) produced by disturbed flow induces inflammation, endothelial dysfunction and hypertension, suggesting the importance of BMPs in vascular biology and disease. BMPs bind to two different types of BMP receptors (BMPRI and II) to instigate intracellular signaling. Increasing evidences suggest a correlative role of BMP4 and atherosclerosis, but the role of BMP receptors especially BMPRII in atherosclerosis is still unclear and whether knockdown of BMPRII is the cause or the consequence of atherosclerosis is still not known. It is therefore, imperative to investigate the mechanisms by which BMPRII expression is modulated and its ramifications in atherosclerosis. Initially, we expected that knockdown of BMPRII will result in loss of pro-atherogenic BMP4 signaling and will thereby prevent atherosclerosis. Contrarily, we found that loss of BMPRII expression causes endothelial inflammation and atherosclerosis. Using BMPRII siRNA and BMPRII +/- mice, we found that BMPRII knockdown induces endothelial inflammation in a BMP-independent manner via mechanisms involving reactive oxygen species (ROS), NFκB, and NADPH oxidases. Further, BMPRII +/- ApoE -/- mice develop accelerated atherosclerosis compared to BMPRII +/+ ApoE -/- mice, suggesting loss of BMPRII may induce atherosclerosis. Interestingly, we found that multiple pro-atherogenic stimuli such as hypercholesterolemia, disturbed flow, pro-hypertensive angiotensin II, and pro-inflammatory cytokine, TNFα, downregulate BMPRII expression in endothelium, while anti-atherogenic stimuli such as stable flow and statin treatment upregulate its expression, both in vivo and in vitro . Moreover, we found that BMPRII expression is significantly diminished in human coronary advanced atherosclerotic lesions. These results suggest that BMPRII is a critical, anti-inflammatory and anti-atherogenic protein that is commonly targeted by multiple pro- and anti-atherogenic factors. BMPRII could be used as a novel diagnostic and therapeutic target in atherosclerosis.

Anti-inflammatory and antiatherogenic role of BMP receptor II in endothelial cells

OBJECTIVE

Atherosclerosis is an inflammatory disease with multiple underlying metabolic and physical risk factors. Bone morphogenic protein 4 (BMP4) expression is increased in endothelium in atherosclerosis-prone regions and is known to induce endothelial inflammation, endothelial dysfunction, and hypertension. BMP actions are mediated by 2 different types of BMP receptors (BMPRI and BMPRII). Here, we show a surprising finding that loss of BMPRII expression causes endothelial inflammation and atherosclerosis.

APPROACH AND RESULTS

Using BMPRII siRNA and BMPRII(+/-) mice, we found that specific knockdown of BMPRII, but not other BMP receptors (Alk1, Alk2, Alk3, Alk6, ActRIIa, and ActRIIb), induced endothelial inflammation in a ligand-independent manner by mechanisms mediated by reactive oxygen species, nuclear factor-KappaB, and reduced nicotinamide adenine dinucleotide phosphate oxidases. Further, BMPRII(+/-)ApoE(-/-) mice developed accelerated atherosclerosis compared with BMPRII(+/+)ApoE(-/-) mice. Interestingly, we found that multiple proatherogenic stimuli, such as hypercholesterolemia, disturbed flow, prohypertensive angiotensin II, and the proinflammatory cytokine (tumor necrosis factor-α), downregulated BMPRII expression in endothelium, whereas antiatherogenic stimuli, such as stable flow and statin treatment, upregulated its expression in vivo and in vitro. Moreover, BMPRII expression was significantly diminished in human coronary advanced atherosclerotic lesions. Also, we were able to rescue the endothelial inflammation induced by BMPRII knockdown by overexpressing the BMPRII wild type, but not by the BMPRII short form lacking the carboxyl-terminal tail region.

CONCLUSIONS

These results suggest that BMPRII is a critical, anti-inflammatory, and antiatherogenic protein that is commonly targeted by multiple pro- and antiatherogenic factors. BMPRII may be used as a novel diagnostic and therapeutic target in atherosclerosis.

Role of coronin 1B in PDGF-induced migration of vascular smooth muscle cells

RATIONALE

The type I subclass of coronins, a family of actin-binding proteins, regulates various actin-dependent cellular processes, including migration. However, the existence and role of coronins in vascular smooth muscle cell (VSMC) migration has yet to be determined.

OBJECTIVE

The goal of the present study was to define the mechanism by which coronins regulate platelet-derived growth factor (PDGF)-induced VSMC migration.

METHODS AND RESULTS

Coronin 1B (Coro1B) and 1C (Coro1C) were both found to be expressed in VSMCs at the mRNA and protein levels. Downregulation of Coro1B by siRNA increases PDGF-induced migration, while downregulation of Coro1C has no effect. We confirmed through kymograph analysis that the Coro1B-downregulation-mediated increase in migration is directly linked to increased lamellipodial protraction rate and protrusion distance in VSMC. In other cell types, coronins exert their effects on lamellipodia dynamics by an inhibitory interaction with the ARP2/3 complex, which is disrupted by the phosphorylation of Coro1B. We found that PDGF induces phosphorylation of Coro1B on serine-2 via PKCε, leading to a decrease in the interaction of Coro1B with the ARP2/3 complex. VSMCs transfected with a phosphodeficient S2A Coro1B mutant showed decreased migration in response to PDGF, suggesting that the phosphorylation of Coro1B is required for the promotion of migration by PDGF. In both the rat and mouse, Coro1B phosphorylation was increased in response to vessel injury in vivo.

CONCLUSIONS

Our data suggest that phosphorylation of Coro1B and the subsequent reduced interaction with ARP2/3 complex participate in PDGF-induced VSMC migration, an important step in vascular lesion formation.

Effects of the antioxidant drug tempol on renal oxygenation in mice with reduced renal mass

We tested the hypothesis that reactive oxygen species (ROS) contributed to renal hypoxia in C57BL/6 mice with &frac56; surgical reduction of renal mass (RRM). ROS can activate the mitochondrial uncoupling protein 2 (UCP-2) and increase O(2) usage. However, UCP-2 can be inactivated by glutathionylation. Mice were fed normal (NS)- or high-salt (HS) diets, and HS mice received the antioxidant drug tempol or vehicle for 3 mo. Since salt intake did not affect the tubular Na(+) transport per O(2) consumed (T(Na/)Q(O2)), further studies were confined to HS mice. RRM mice had increased excretion of 8-isoprostane F(2α) and H(2)O(2), renal expression of UCP-2 and renal O(2) extraction, and reduced T(Na/)Q(O2) (sham: 20 ± 2 vs. RRM: 10 ± 1 μmol/μmol; P < 0.05) and cortical Po(2) (sham: 43 ± 2, RRM: 29 ± 2 mmHg; P < 0.02). Tempol normalized all these parameters while further increasing compensatory renal growth and glomerular volume. RRM mice had preserved blood pressure, glomeruli, and patchy tubulointerstitial fibrosis. The patterns of protein expression in the renal cortex suggested that RRM kidneys had increased ROS from upregulated p22(phox), NOX-2, and -4 and that ROS-dependent increases in UCP-2 led to hypoxia that activated transforming growth factor-β whereas erythroid-related factor 2 (Nrf-2), glutathione peroxidase-1, and glutathione-S-transferase mu-1 were upregulated independently of ROS. We conclude that RRM activated distinct processes: a ROS-dependent activation of UCP-2 leading to inefficient renal O(2) usage and cortical hypoxia that was offset by Nrf-2-dependent glutathionylation. Thus hypoxia in RRM may be the outcome of NADPH oxidase-initiated ROS generation, leading to mitochondrial uncoupling counteracted by defense pathways coordinated by Nrf-2.

Angiotensin II and NADPH oxidase increase ADMA in vascular smooth muscle cells

Asymmetrical dimethylarginine inhibits nitric oxide synthase, cationic amino acid transport, and endothelial function. Patients with cardiovascular risk factors often have endothelial dysfunction associated with increased plasma asymmetrical dimethylarginine and markers of reactive oxygen species. We tested the hypothesis that reactive oxygen species, generated by nicotinamide adenine dinucleotide phosphate oxidase, enhance cellular asymmetrical dimethylarginine. Incubation of rat preglomerular vascular smooth muscle cells with angiotensin II doubled the activity of nicotinamide adenine dinucleotide phosphate oxidase but decreased the activities of dimethylarginine dimethylaminohydrolase by 35% and of cationic amino acid transport by 20% and doubled cellular (but not medium) asymmetrical dimethylarginine concentrations (P<0.01). This was blocked by tempol or candesartan. Cells stably transfected with p22(phox) had a 50% decreased protein expression and activity of dimethylarginine dimethylaminohydrolase despite increased promoter activity and mRNA. The decreased DDAH protein expression and the increased asymmetrical dimethylarginine concentration in p22(phox)-transfected cells were prevented by proteosomal inhibition. These cells had enhanced protein arginine methylation, a 2-fold increased expression of protein arginine methyltransferase-3 (P<0.05) and a 30% reduction in cationic amino acid transport activity (P<0.05). Asymmetrical dimethylarginine was increased from 6+/-1 to 16+/-3 micromol/L (P<0.005) in p22(phox)-transfected cells. Thus, angiotensin II increased cellular asymmetrical dimethylarginine via type 1 receptors and reactive oxygen species. Nicotinamide adenine dinucleotide phosphate oxidase increased cellular asymmetrical dimethylarginine by increasing enzymes that generate it, enhancing the degradation of enzymes that metabolize it, and reducing its cellular transport. This could underlie increases in cellular asymmetrical dimethylarginine during oxidative stress.

Overexpression of Akt converts radial growth melanoma to vertical growth melanoma

Melanoma is the cancer with the highest increase in incidence, and transformation of radial growth to vertical growth (i.e., noninvasive to invasive) melanoma is required for invasive disease and metastasis. We have previously shown that p42/p44 MAP kinase is activated in radial growth melanoma, suggesting that further signaling events are required for vertical growth melanoma. The molecular events that accompany this transformation are not well understood. Akt, a signaling molecule downstream of PI3K, was introduced into the radial growth WM35 melanoma in order to test whether Akt overexpression is sufficient to accomplish this transformation. Overexpression of Akt led to upregulation of VEGF, increased production of superoxide ROS, and the switch to a more pronounced glycolytic metabolism. Subcutaneous implantation of WM35 cells overexpressing Akt led to rapidly growing tumors in vivo, while vector control cells did not form tumors. We demonstrated that Akt was associated with malignant transformation of melanoma through at least 2 mechanisms. First, Akt may stabilize cells with extensive mitochondrial DNA mutation, which can generate ROS. Second, Akt can induce expression of the ROS-generating enzyme NOX4. Akt thus serves as a molecular switch that increases angiogenesis and the generation of superoxide, fostering more aggressive tumor behavior. Targeting Akt and ROS may be of therapeutic importance in treatment of advanced melanoma.

Vitamin E reduces glomerulosclerosis, restores renal neuronal NOS, and suppresses oxidative stress in the 5/6 nephrectomized rat

Chronic kidney disease is accompanied by nitric oxide (NO) deficiency and oxidative stress, which contribute to progression. We investigated whether the antioxidant vitamin E could preserve renal function and NO bioavailability and reduce oxidative stress in the 5/6th nephrectomy (NX) rat model. We studied the following three groups of male Sprague-Dawley rats: sham (n = 6), 5/6 NX control (n = 6), and 5/6 NX treated with vitamin E (5,000 IU/kg chow; n = 5). The 5/6 NX group showed increased severity of glomerulosclerosis vs. sham, and this was ameliorated by vitamin E therapy. Both 5/6 NX groups showed similar elevations in plasma creatinine and proteinuria and decreased 24-h creatinine clearance compared with sham. There was increased NADPH-dependent superoxide production in 5/6 NX rats vs. sham that was prevented by vitamin E. Total NO production was similarly reduced in both 5/6 NX groups. There was unchanged abundance of endothelial nitric oxide synthesis (NOS) in renal cortex and medulla and neuronal (n) NOS in medulla. However, in kidney cortex, 5/6 NX rats had lower nNOS abundance than sham, which was restored by vitamin E. An increased plasma asymmetric dimethylarginine occurred with 5/6 NX associated with decreased renal dimethylarginine dimethylaminohydrolase activity and increased type 1 protein arginine methyltransferase expression.

Lack of long-term protective effect of antioxidant/anti-inflammatory therapy in transplant-induced ischemia/reperfusion injury

BACKGROUND

Alloantigen-independent factors contribute to long-term damage in renal transplant recipients, likely due to ischemia/reperfusion (I/R) injury at transplantation (Tx). I/R injury promotes oxidative stress and inflammation resulting in endothelial injury.

METHODS

In this study we investigated the long-term efficacy (22 weeks) of short-term (10 day) endothelial protection therapy (EP) in 'optimal' donor kidneys using the male Fisher 344 rat isograft (ISO) model. ISO-EP kidneys were compared to untreated ISO (ISO-UN) kidneys. EP involved dexamethasone to donor, ex vivo treatment of the kidney with deferoxamine and tempol, and administration to the recipient of L-arginine and tempol for 10 days. Rats were sacrificed 22 weeks following Tx and compared to age-matched, normal controls.

RESULTS

Both groups of ISO Tx rats developed similar renal dysfunction and structural damage and renal NADPH-oxidase-dependent O2- production was similarly elevated in ISO-UN and ISO-EP groups vs. controls. In vitro renal cortex NO synthase (NOS) activity was also similar in ISO-UN and ISO-EP rats, despite lower nNOS and eNOS protein abundance in ISO-EP.

CONCLUSION

I/R injury-induced late graft dysfunction occurs even when optimal donors are used and when short-term EP treatment is given. Increased renal superoxide production is not prevented by short-term EP therapy.

Pulsatile versus oscillatory shear stress regulates NADPH oxidase subunit expression: implication for native LDL oxidation

Shear stress regulates endothelial nitric oxide and superoxide (O2-*) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 microg/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress (tau(ave)) of 25 dyne/cm2 and (2) oscillating flow at tau(ave) of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL- and LDL2-. In response to oscillatory shear stress, gp91phox mRNA expression was upregulated by 2.9+/-0.3-fold, and its homologue, Nox4, by 3.9+/-0.9-fold (P<0.05, n=4), with a corresponding increase in O2-* production rate. The proportion of LDL- and LDL2- relative to static conditions increased by 67+/-17% and 30+/-7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (P<0.05, n=5). In contrast, pulsatile flow downregulated both gp91phox and Nox4 mRNA expression (by 1.8+/-0.2-fold and 3.0+/-0.12-fold, respectively), with an accompanying reduction in O2-* production, reduction in the extent of LDL modification (51+/-12% for LDL- and 30+/-7% for LDL2-), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O2-* production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding.

Effects of angiotensin II infusion on the expression and function of NAD(P)H oxidase and components of nitric oxide/cGMP signaling

Angiotensin II infusion causes endothelial dysfunction by increasing NAD(P)H oxidase-mediated vascular superoxide production. However, it remains to be elucidated how in vivo angiotensin II treatment may alter the expression of the gp91(phox) isoforms and the endothelial nitric oxide synthase (NOS III) and subsequent signaling events and whether, in addition to the NAD(P)H oxidase, NOS III contributes to vascular superoxide formation. We therefore studied the influence of in vivo angiotensin II treatment (7 days) in rats on endothelial function and on the expression of the NAD(P)H oxidase subunits p22(phox), nox1, nox4, and gp91(phox) and NOS III. Further analysis included the expression of NO-downstream targets, the soluble guanylyl cyclase (sGC), the cGMP-dependent protein kinase I (cGK-I), and the expression and phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) at Ser239 (P-VASP). Angiotensin II caused endothelial dysfunction and increased vascular superoxide. Likewise, we found an increase in vascular protein kinase C (PKC) activity, in the expression of nox1 (6- to 7-fold), gp91(phox) (3-fold), p22(phox) (3-fold), NOS III mRNA, and protein. NOS-inhibition with N(G)-nitro-L-arginine decreased superoxide in vessels from angiotensin II-treated animals, compatible with NOS-uncoupling. Vascular NO assessed with electron paramagnetic resonance was markedly reduced. Likewise, a decrease in sGC-expression and P-VASP levels was found. In vivo PKC-inhibition with chelerythrine reduced angiotensin II-induced superoxide production and markedly inhibited upregulation of NAD(P)H oxidase subunits. We therefore conclude that angiotensin II-induced increases in the activity and the expression of NAD(P)H oxidase are at least in part PKC-dependent. NADPH oxidase-induced superoxide production may trigger NOS III uncoupling, leading to impaired NO/cGMP signaling and to endothelial dysfunction in this animal model. The full text of this article is available at http://www.circresaha.org.

Mechanisms underlying endothelial dysfunction in diabetes mellitus

Incubation of endothelial cells in vitro with high concentrations of glucose activates protein kinase C (PKC) and increases nitric oxide synthase (NOS III) gene expression as well as superoxide production. The underlying mechanisms remain unknown. To address this issue in an in vivo model, diabetes was induced with streptozotocin in rats. Streptozotocin treatment led to endothelial dysfunction and increased vascular superoxide production, as assessed by lucigenin- and coelenterazine-derived chemiluminescence. The bioavailability of vascular nitric oxide (as measured by electron spin resonance) was reduced in diabetic aortas, although expression of endothelial NOS III (mRNA and protein) was markedly increased. NOS inhibition with N:(G)-nitro-L-arginine increased superoxide levels in control vessels but reduced them in diabetic vessels, identifying NOS as a superoxide source. Similarly, we found an activation of the NADPH oxidase and a 7-fold increase in gp91(phox) mRNA in diabetic vessels. In vitro PKC inhibition with chelerythrine reduced vascular superoxide in diabetic vessels, whereas it had no effect on superoxide levels in normal vessels. In vivo PKC inhibition with N:-benzoyl-staurosporine did not affect glucose levels in diabetic rats but prevented NOS III gene upregulation and NOS-mediated superoxide production, thereby restoring vascular nitric oxide bioavailability and endothelial function. The reduction of superoxide in vitro by chelerythrine and the normalization of NOS III gene expression and reduction of superoxide in vivo by N:-benzoyl-staurosporine point to a decisive role of PKC in mediating these phenomena and suggest a therapeutic potential of PKC inhibitors in the prevention or treatment of vascular complications of diabetes mellitus. The full text of this article is available at http://www.circresaha.org.