A previous study from this laboratory showed that elevation of endogenous angiotensin II (Ang II) and upregulation of the angiotensin II type 1 (AT1) receptor in the carotid body (CB) are involved in the enhanced peripheral chemoreceptor sensitivity in rabbits with chronic heart failure (CHF). NADPH oxidase-derived superoxide anion mediates the effects of Ang II in many organs. We investigated whether this signaling pathway may mediate the enhanced peripheral chemoreceptor sensitivity induced by Ang II in CHF rabbits.
Methods and results:
By recording single-unit activity from the carotid sinus nerve in isolated preparations, we found that phenylarsine oxide 2 μM (PAO, NADPH oxidase inhibitor) and TEMPOL 1 mM (superoxide dismutase mimetic) significantly decreased not only the Ang II-enhanced CB chemoreceptor responses to different levels of hypoxia in sham rabbits (Δ-12.5 ± 0.8 and Δ-12.8 ± 0.9 imp/s at 40.7 ± 2.3 mm Hg of PO2, and Δ-5.6 ± 0.5 and Δ-5.3 ± 0.4 imp/s at 60.2 ± 3.1 mm Hg of PO2, p<0.05, respectively) but also the CHF-induced elevation of CB chemoreceptor responses to different levels of hypoxia (Δ-13.6 ± 1.1 and Δ-13.7 ± 0.9 imp/s at 40.9 ± 3.1 mm Hg of PO2, and Δ-6.7 ± 1.2 and Δ-6.6 ± 0.8 imp/s at 59.8 ± 3.5 mm Hg of PO2, p<0.05). In addition, mRNA and protein expressions of NADPH oxidase components (gp91phox, p40phox and p47phox) were higher in the CB from CHF rabbits compared to sham rabbits. Furthermore, 100 pM Ang II induced an increase in superoxide production in CB homogenates from sham rabbits, which was similar to that in CB homogenate from CHF rabbits. PAO and Tempol inhibited the Ang II- and CHF-enhanced superoxide anion production.
These results suggest that the enhanced peripheral chemoreceptor sensitivity mediated by Ang II in CHF rabbits occurs via a NADPH oxidase-superoxide signaling pathway.
Angiotensin; Reactive oxygen species; autonomic nervous system; chemoreceptor; heart failure
In this review, we summarize the present state of knowledge of the functional characteristics of the carotid body (CB) chemoreflex with respect to control of sympathetic nerve activity (SNA) in chronic heart failure (CHF). Evidence from both CHF patients and animal models of CHF has clearly established that the CB chemoreflex is enhanced in CHF and contributes to the tonic elevation in SNA. This adaptive change derives from altered function at the level of both the afferent and central nervous system (CNS) pathways of the reflex arc. At the level of the CB, an elevation in basal afferent discharge occurs under normoxic conditions in CHF rabbits, and the discharge responsiveness to hypoxia is enhanced. Outward voltage-gated K+ currents (IK) are suppressed in CB glomus cells from CHF rabbits, and their sensitivity to hypoxic inhibition is enhanced. These changes in IK derive partly from downregulation of nitric oxide synthase (NOS) / NO signaling and upregulation of angiotensin II (Ang II) / Ang II receptor (AT1R) signaling in glomus cells. At the level of the CNS, interactions of the enhanced input from CB chemoreceptors with altered input from baroreceptor and cardiac afferent pathways and from central Ang II further enhance sympathetic drive. In addition, impaired function of NO in the paraventricular nucleus of the hypothalamus participates in the increased SNA response to CB chemoreceptor activation. These results underscore the principle that multiple mechanisms involving Ang II and NO at the level of both the CB and CNS represent complementary and perhaps redundant adaptive mechanisms to enhance CB chemoreflex function in CHF.
In chronic heart failure (CHF), arterial baroreflex function is impaired, in part, by activation of the central renin-angiotensin system. A metabolite of Angiotensin II (Ang II), Ang-(1–7), has been shown to exhibit cardiovascular effects that are in opposition to that of Ang II. However, the action of Ang-(1–7) on sympathetic outflow and baroreflex function is not well understood, especially in CHF. The aim of this study was to determine the effect of intracerebroventricular infusion of Ang-(1–7) on baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in conscious rabbits with CHF. We hypothesized that central Ang-(1–7) would improve baroreflex function in CHF. Ang-(1–7) (2 nmol/1 μl/hour) or artificial cerebrospinal fluid (1 μl/hour) was infused by an osmotic mini-pump for 4 days in sham and pacing-induced CHF rabbits (n=3–6/group). Ang-(1–7) treatment had no effects in sham rabbits but reduced HR and increased baroreflex gain (7.4±1.5 bpm/mm Hg vs. 2.5±0.4 bpm/mm Hg, P<0.05) in CHF rabbits. The Ang-(1–7) antagonist A779 (8 nmol/1 μl/hr) blocked the improvement in baroreflex gain in CHF. Baroreflex gain increased in CHF+Ang-(1–7) animals when only the vagus was allowed to modulate baroreflex control by acute treatment with the β-1 antagonist metoprolol, indicating increased vagal tone. Baseline RSNA was significantly lower and baroreflex control of RSNA was enhanced in CHF rabbits receiving Ang-(1–7). These data suggest that augmentation of central Ang-(1–7) inhibits sympathetic outflow and increases vagal outflow in CHF thus contributing to enhanced baroreflex gain in this disease state.
angiotensin-(1–7); heart failure; sympathetic nervous system; baroreflex; vagus nerve; blood pressure; heart rate
Adenoviral-mediated overexpression of the intracellular superoxide (O2•−) scavenging enzyme copper/zinc superoxide dismutase (CuZnSOD) in the brain attenuates central angiotensin II (AngII)-induced cardiovascular responses. However, the therapeutic potential for adenoviral vectors is weakened by toxicity and the inability of adenoviral vectors to target the brain following peripheral administration. Therefore, we developed a non-viral delivery system in which CuZnSOD protein is electrostatically bound to a synthetic poly(ethyleneimine)-poly(ethyleneglycol) (PEI-PEG) polymer to form a polyion complex (CuZnSOD nanozyme). We hypothesized that PEI-PEG polymer increases transport of functional CuZnSOD to neurons, which inhibits AngII intra-neuronal signaling. The AngII-induced increase in O2•−, as measured by dihydroethidium fluorescence and electron paramagnetic resonance spectroscopy, was significantly inhibited in CuZnSOD nanozyme-treated neurons compared to free CuZnSOD- and non-treated neurons. CuZnSOD nanozyme also attenuated the AngII-induced inhibition of K+ current in neurons. Intracarotid injection of CuZnSOD nanozyme into rabbits significantly inhibited the pressor response of intracerebroventricular-delivered AngII; however, intracarotid injection of free CuZnSOD or PEI-PEG polymer alone failed to inhibit this response. Importantly, neither the PEI-PEG polymer alone nor the CuZnSOD nanozyme induced neuronal toxicity. These findings indicate that CuZnSOD nanozyme inhibits AngII intra-neuronal signaling in vitro and in vivo.
brain; superoxide dismutase; nanotechnology; drug delivery; copolymer; potassium current
Background and Aim
Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) family together with adrenomedullin (AM) and amylin. It has a wide distribution in the central nervous system (CNS) especially in hypothalamic paraventricular nucleus (PVN). Cardiac sympathetic afferent reflex (CSAR) is enhanced in chronic heart failure (CHF) rats. The aim of this study is to determine the effect of IMD in the PVN on CSAR and its related mechanisms in CHF rats.
Rats were subjected to left descending coronary artery ligation to induce CHF or sham-operation (Sham). Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were recorded. CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Acute experiments were carried out 8 weeks after coronary ligation or sham surgery under anesthesia. IMD and angiotensin II (Ang II) levels in the PVN were up-regulated in CHF rats. Bilateral PVN microinjection of IMD caused greater decreases in CSAR and the baseline RSNA and MAP in CHF rats than those in Sham rats. The decrease of CSAR caused by IMD was prevented by pretreatment with AM receptor antagonist AM22-52, but not CGRP receptor antagonist CGRP8-37. Ang II in the PVN significantly enhanced CSAR and superoxide anions level, which was inhibited by PVN pretreatment with IMD or tempol (a superoxide anions scavenger) in Sham and CHF rats.
IMD in the PVN inhibits CSAR via AM receptor, and attenuates the effects of Ang II on CSAR and superoxide anions level in CHF rats. PVN superoxide anions involve in the effect of IMD on attenuating Ang II-induced CSAR response.
Interleukin-33 (IL-33) has been linked to chronic heart failure (CHF) in animal studies, but data on serum IL-33 levels in human CHF are not available. We analyzed levels of IL-33 in serum, and investigated the possible role of IL-33 in oxidative stress.
A total of 191 subjects with advanced systolic CHF (CHF group), 175 patients with pre-existing cardiac diseases but no CHF (non-CHF group), and 177 healthy controls (HC group) were enrolled. Serum levels of IL-33, soluble ST2 (sST2) and N-terminal-pro-brain natriuretic peptide (NT-proBNP), malondialdehyde (MDA) content, erythrocyte superoxide dismutase (eSOD) activity, as well as left ventricular ejection fraction (LVEF), were determined. The exact form of IL-33 in serum was identified. Effects of IL-33 and sST2 on MDA content and SOD activity in angiotensin (Ang II)-stimulated AC16 cells were assessed.
Serum levels of IL-33 and sST2 were elevated in CHF patients, whereas IL-33/sST2 ratios were decreased. In CHF patients, pre-existing cardiac diseases and medications used upon hospital admission did not affect IL-33 concentrations or the IL-33/sST2 ratio. Full-length IL-33, which could not be detected in serum from HC and barely detected in non-CHF patients, was significantly up-regulated in CHF patients. IL-33 levels were positively correlated with markers of CHF severity. IL-33/sST2 ratios were slightly and negatively related to MDA concentrations. IL-33 directly reduced MDA and enhanced SOD activity in Ang II-stimulated AC16 cells, which were greatly attenuated by sST2.
Serum levels of IL-33, especially the full-length form, were elevated in CHF patients whereas IL-33 bioactivity was reduced. In advanced CHF, IL-33 may exert anti-oxidation effects, which may be overwhelmed by concurrently elevated levels of sST2.
Chronic heart failure; Interleukin-33; Soluble ST2; Oxidative stress
Angiotensin II (AngII) is the main effector peptide of the renin–angiotensin system (RAS), and contributes to the pathogenesis of cardiovascular disease by exerting its effects on an array of different cell types, including central neurons. AngII intra-neuronal signaling is mediated, at least in part, by reactive oxygen species, particularly superoxide (O2•−). Recently, it has been discovered that mitochondria are a major subcellular source of AngII-induced O2•−. We have previously reported that over-expression of manganese superoxide dismutase (MnSOD), a mitochondrial matrix-localized O2•− scavenging enzyme, inhibits AngII intra-neuronal signaling. Interestingly, over-expression of copper/zinc superoxide dismutase (CuZnSOD), which is believed to be primarily localized to the cytoplasm, similarly inhibits AngII intra-neuronal signaling and provides protection against AngII-mediated neurogenic hypertension. Herein, we tested the hypothesis that CuZnSOD over-expression in central neurons localizes to mitochondria and inhibits AngII intra-neuronal signaling by scavenging mitochondrial O2•−. Using a neuronal cell culture model (CATH.a neurons), we demonstrate that both endogenous and adenovirus-mediated over-expressed CuZnSOD (AdCuZnSOD) are present in mitochondria. Furthermore, we show that over-expression of CuZnSOD attenuates the AngII-mediated increase in mitochondrial O2•− levels and the AngII-induced inhibition of neuronal potassium current. Taken together, these data clearly show that over-expressed CuZnSOD in neurons localizes in mitochondria, scavenges AngII-induced mitochondrial O2•−, and inhibits AngII intra-neuronal signaling.
•Endogenous CuZnSOD is localized to mitochondria of AngII-sensitive neurons.•Adenovirus-mediated over-expressed CuZnSOD is localized to neuron mitochondria.•AngII-induced mitochondrial O2•− flux is attenuated by CuZnSOD over-expression.•Over-expressed CuZnSOD reduces AngII-mediated inhibition of neuronal K+ current.
AngII, angiotensin II; RAS, renin–angiotensin system; MnSOD, manganese superoxide dismutase; CuZnSOD, copper/zinc superoxide dismutase; AT1R, angiotensin type 1 receptor; NOX, NADPH oxidase; MIMS, mitochondrial inter-membrane space; Ikv, neuronal potassium current; ROS, reactive oxygen species; Mitochondria; Angiotensin II; CuZnSOD; Superoxide; Neurons; Potassium current
Although widely found in the cytoplasm of eucaryotes, the copper-zinc form of superoxide dismutase (CuZnSOD) has been identified in only a small number of bacterial species. One species is the freshwater bacterium Caulobacter crescentus, which also contains an SOD with iron as the metal cofactor (FeSOD). To investigate the function of this CuZnSOD and its structural relationship to the eucaryotic CuZnSODs, the gene encoding CuZnSOD (sodC) of C. crescentus CB15 was cloned and sequenced. By hybridization to pulsed-field electrophoresis gels, sodC was mapped near cysE in the C. crescentus chromosome. Through analysis of spheroplasts, the two SODs of C. crescentus were shown to be differently localized, CuZnSOD in the periplasm and FeSOD in the cytoplasm. In its natural habitat, C. crescentus is frequently associated with blue-green algae (cyanobacteria). The oxygen evolved by these photosynthetic algae may create an extracellular oxidative stress against which the periplasmic CuZnSOD may defend more effectively than the cytoplasmic FeSOD. Amino acid sequence alignments of C. crescentus CuZnSOD with eucaryotic CuZnSODs and with CuZnSOD of Photobacterium leiognathi (the only other bacterium from which CuZnSOD has been isolated and sequenced) suggest similar supersecondary structures for bacterial and eucaryotic CuZnSODs but reveal four novel substitutions in C. crescentus CuZnSOD: a phenylalanine critical to intrasubunit hydrophobic bonding replaced by alanine, a histidine ligand of zinc replaced by aspartate, and substitutions of two other previously invariant residues that stabilize zinc or both copper and zinc. These amino acid substitutions in C. crescentus CuZnSOD may have implications for its catalysis and stability.
Angiotensin-converting enzyme 2 (ACE2) has been suggested to be involved in the central regulation of autonomic function. During chronic heart failure (CHF), elevated central angiotensin II signaling contributes to the sustained increase of sympathetic outflow. This is accompanied by a downregulation of ACE2 in the brain. We hypothesized that central overexpression of ACE2 decreases sympathetic outflow and enhances baroreflex function in CHF. Transgenic mice overexpressing human ACE2 selectively in the brain (SYN-hACE2) and wild type littermates (WT) were used. CHF was induced by permanent coronary artery ligation (CAL). Four weeks after CAL, both WT and SYN-hACE2 mice exhibited a significant decrease in left ventricular ejection fraction (<40%). A slight decrease in MAP was found only in SYN-hACE2 mice. Compared with WT mice with CHF, brain-selective ACE2 overexpression attenuated left ventricular end-diastolic pressure; decreased urinary norepinephrine excretion; baseline RSNA (WT CHF: 71.6±7.6% Max vs. SYN-hACE2 CHF: 49.3±6.1% Max); and enhanced baroreflex sensitivity (Maximum Slope: WT Sham: 1.61±0.16 vs. SYN-hACE2 CHF: 1.51±0.17%/mmHg). Chronic subcutaneous blockade of mas receptor increased RSNA in SYN-hACE2 mice with CHF (A779: 67.3±5.8% vs. vehicle: 46.4±3.6% of Max). An up-regulation in angiotensin II type 1 receptor (AT1R) expression was detected in medullary nuclei in WT CHF mice, which was significantly attenuated in SYN-hACE2 mice with CHF. These data suggest that central ACE2 overexpression exerts a potential protective effect in CHF through attenuating sympathetic outflow. The mechanism for this effect involves angiotensin (1-7) mas signaling as well as a decrease in AT1R signaling in the medulla.
heart failure; angiotensin converting enzyme 2; angiotensin II; angiotensin I (1-7); autonomic function; baroreflex
We have previously reported that the expression of Angiotensin II (Ang II) type 1 receptors (AT1R) was increased in the rostral ventrolateral medulla (RVLM) of rabbits with chronic heart failure (CHF) and in the RVLM of normal rabbits infused with intracerebroventricular (ICV) Ang II. The present study investigated if oxidant stress plays a role in Ang II induced AT1R up-regulation and its relationship to the transcription factor activator protein 1 (AP1) in CHF rabbits and in the CATHa neuronal cell line. In CATHa cells, Ang II significantly increased AT1R mRNA by 123 ± 11%, P<0.01; c-Jun mRNA by 90 ± 20%, P<0.01; c-fos mRNA by 148 ± 49%, P<0.01; NADPH oxidase activity by 126 ± 43%, P<0.01 versus untreated cells. Tempol and Apocynin reversed the increased expression of AT1R mRNA, c-Jun mRNA, c-fos mRNA, and superoxide production induced by Ang II. We also examined the effect of ICV Tempol on the RVLM of CHF rabbits. Compared to vehicle treated CHF rabbits, Tempol significantly decreased AT1R protein expression (1.6±0.29 vs 0.88±0.16, P<0.05), phosphorylated Jnk protein (0.4 ± 0.05 vs 0.2 ± 0.04, P<0.05), cytosolic phosphorylated c-Jun (0.56 ± 0.1 vs 0.36 ± 0.05, P<0.05), and nuclear phosphorylated c-Jun (0.67±0.1 vs 0.3±0.08, P<0.01). Tempol also significantly decreased the AP-1-DNA binding activity in the RVLM of CHF rabbits compared to the vehicle group (9.14 × 103 vs 41.95 × 103 grey level P<0.01). These data suggest that Ang II induces AT1R up-regulation at the transcriptional level by induction of oxidant stress and activation of AP1 in both cultured neuronal cells and in intact brain of rabbits. Antioxidant agents may be beneficial in CHF and other states where brain Ang II is elevated by decreasing AT1R expression through the Jnk and AP1 pathway.
Copper-zinc superoxide dismutases (CuZnSODs) are infrequently found in bacteria although widespread in eukaryotes. Legionella pneumophila, the causative organism of Legionnaires' disease, is one of a small number of bacterial species that contain a CuZnSOD, residing in the periplasm, in addition to an iron SOD (FeSOD) in their cytoplasm. To investigate CuZnSOD function, we purified the enzyme from wild-type L. pneumophila, obtained amino acid sequence data from isolated peptides, cloned and sequenced the gene from a L. pneumophila library, and then constructed and characterized a CuZnSOD null mutant. In contrast to the cytoplasmic FeSOD, the CuZnSOD of L. pneumophila is not essential for viability. However, CuZnSOD is critical for survival during the stationary phase of growth. The CuZnSOD null mutant survived 10(4)- to 10(6)-fold less than wild-type L. pneumophila. In wild-type L. pneumophila, the specific activity of CuZnSOD increased during the transition from exponential to stationary-phase growth while the FeSOD activity was constant. These data support a role of periplasmic CuZnSOD in survival of L. pneumophila during stationary phase. Since L. pneumophila survives extensive periods of dormancy between growth within hosts. CuZnSOD may contribute to the ability of this bacterium to be a pathogen. In exponential phase, wild-type and CuZnSOD null strains grew with comparable doubling times. In cultured HL-60 and THP-1 macrophage-like cell lines and in primary cultures of human monocytes, multiplication of the CuZnSOD null mutant was comparable to that of wild type. This indicated that CuZnSOD is not essential for intracellular growth within macrophages or for killing of macrophages in those systems.
Cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation and angiotensin II (Ang II) in paraventricular nucleus (PVN) augments the CSAR in vagotomized (VT) and baroreceptor denervated (BD) rats with chronic heart failure (CHF). This study was designed to determine whether it is true in intact (INT) rats with CHF and to determine the effects of cardiac and baroreceptor afferents on the CSAR and sympathetic activity in CHF.
Sham-operated (Sham) or coronary ligation-induced CHF rats were respectively subjected to BD+VT, VT, cardiac sympathetic denervation (CSD) or INT. Under anesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded, and the CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Either CSAR or the responses of RSNA, MAP and CSAR to Ang II in PVN were enhanced in CHF rats treated with BD+VT, VT or INT. Treatment with VT or BD+VT potentiated the CSAR and the CSAR responses to Ang II in both Sham and CHF rats. Treatment with CSD reversed the capsaicin-induced RSNA and MAP changes and the CSAR responses to Ang II in both Sham and CHF rats, and reduced the RSNA and MAP responses to Ang II only in CHF rats.
The CSAR and the CSAR responses to Ang II in PVN are enhanced in intact CHF rats. Baroreceptor and vagal afferent activities inhibit CSAR and the CSAR responses to Ang II in intact Sham and CHF rats.
Neurohumoral disturbances characterize chronic heart failure (CHF) and are reflected, in part, as impairment of baroreflex sensitivity (BRS) and sympathetic function. However the mechanisms that trigger these neurohumoral abnormalities in CHF are not clear. We hypothesized that the BRS is blunted early in CHF and that the humoral effects occur later and contribute to progressive loss of cardiovascular control in CHF. We assessed the BRS (bpm/mmHg) and recorded renal sympathetic nerve activity (RSNA) in four groups of conscious rabbits at varying time intervals; control, one week CHF, two week CHF and three week CHF. CHF was induced by ventricular pacing at 360 bpm and was assessed by echocardiography. Arterial blood pressure and heart rate were recorded by an implanted telemetric device and RSNA through an implanted electrode. A significant fall in the ejection fraction, fractional shortening and an increase in LVESD & LVEDD was observed in all CHF groups. The BRS was significantly reduced in all the CHF groups with no significant change in the basal RSNA(% of maximum) after 1 week of pacing, a small but insignificant rise in RSNA was seen at 2 weeks and a significant rise in RSNA was observed at 3 weeks. AT1 receptor protein (Western Blot) and mRNA (RT-PCR) expression in the rostral ventrolateral medulla (RVLM) exhibited a progressive increase with the duration of CHF, reaching significance after 3 weeks, the same time point in which RSNA was significantly elevated. These data are the first to examine early changes in central AT1 receptors in CHF and suggest that the fall in BRS and hemodynamic changes occur early in the development of CHF followed by sympatho-excitation and over-expression of AT1 receptors with the progression of CHF causing further impairment of cardiovascular control.
Baroreflex; heart failure; sympathetic activity; angiotensin II receptor
Null mutants for Cu/Zn superoxide dismutase (CuZnSOD) in Drosophila melanogaster are male sterile, have a greatly reduced adult life span, and are hypersensitive to paraquat. We have introduced a synthetic bovine CuZnSOD transgene under the transcriptional control of the D. melanogaster 5C actin promoter into a CuZnSOD-null mutant of D. melanogaster. This was carried out by P-element-mediated transformation of the Drosophila-bovine CuZnSOD transgene into a CuZnSOD+ recipient strain followed by genetic crossing of the transgene into a strain carrying the CuZnSOD-null mutation, cSODn108. The resulting transformants express bovine CuZnSOD exclusively to about 30% of normal Drosophila CuZnSOD levels. Expression of the Drosophila-bovine CuZnSOD transgene in the CuZnSOD-null mutant rescues male fertility and resistance to paraquat to apparently normal levels. However, adult life span is restored to only 30% of normal, and resistance to hyperoxia is 90% of that found in control flies. This striking differential restoration of pleiotropic phenotypes could be the result of a threshhold of CuZnSOD expression necessary for normal male fertility and resistance to the toxicity of paraquat or hyperoxia which is lower than the threshold required to sustain a normal adult life span. Alternatively, the differential rescue of fertility, resistance to active oxygen, and life span might indicate different cell-specific transcriptional requirements for these functions which are normally provided by the control elements of the native CuZnSOD gene but are only partly compensated for by the transcriptional control elements of the actin 5C promoter.
Up-regulation of Angiotensin type 1 receptors (AT1R) in the rostral ventrolateral medulla (RVLM) contributes to the sympatho-excitation in the chronic heart failure (CHF). However, the role of AT2R is not clear. In this study, we measured AT1R and AT2R protein expression in the RVLM and determined their effects on renal sympathetic nerve activity (RSNA), blood pressure (BP), and heart rate (HR) in anaesthetized sham and CHF rats. We found that: (1) while AT1R expression in the RVLM was up-regulated, the AT2R was significantly down-regulated (CHF: 0.06 ± 0.02 vs sham: 0.15 ± 0.02, P < 0.05); (2) simultaneously stimulating RVLM AT1R and AT2R by Ang II evoked sympatho-excitation, hypertension, and tachycardia in both sham and CHF rats, with greater responses in CHF; (3) stimulating RVLM AT1R with Ang II plus the specific AT2R antagonist PD123319 induced a larger sympatho-excitatory response than simultaneously stimulating AT1R and AT2R in sham rats, but not in CHF; (4) activating RVLM AT2R with CGP42112 induced a sympatho-inhibition, hypotension, and bradycardia only in sham rats (RSNA: 36.4 ± 5.1 % of baseline vs 102 ± 3.9 % of baseline in aCSF, P < 0.05); (5) pretreatment with ETYA, a general inhibitor of AA metabolism, into the RVLM attenuates the CGP42112 induced sympatho-inhibition. These results suggest that AT2R in the RVLM exhibits an inhibitory effect on sympathetic outflow, which is, at least partially, mediated by an AA metabolic pathway. These data implicate a down regulation in the AT2R as a contributory factor in the sympatho-excitation in CHF.
Angiotensin II type 2 receptor; Angiotensin II type 1 receptor; rostral ventrolateral medulla; sympathetic outflow
Intracerebroventricular infusion of NaHS, a hydrogen sulfide (H2S) donor, increased mean arterial pressure (MAP). This study was designed to determine the roles of H2S in the paraventricular nucleus (PVN) in modulating sympathetic activity and cardiac sympathetic afferent reflex (CSAR) in chronic heart failure (CHF).
CHF was induced by left descending coronary artery ligation in rats. Renal sympathetic nerve activity (RSNA) and MAP were recorded under anesthesia. CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. PVN microinjection of low doses of a H2S donor, GYY4137 (0.01 and 0.1 nmol), had no significant effects on RSNA, MAP and CSAR. High doses of GYY4137 (1, 2 and 4 nmol) increased baseline RSNA, MAP and heart rate (HR), and enhanced CSAR. The effects were greater in CHF rats than sham-operated rats. A cystathionine-β-synthase (CBS) inhibitor, hydroxylamine (HA) in PVN had no significant effect on the RSNA, MAP and CSAR. CBS activity and H2S level in the PVN were decreased in CHF rats. No significant difference in CBS level in PVN was found between sham-operated rats and CHF rats. Stimulation of cardiac sympathetic afferents with capsaicin decreased CBS activity and H2S level in the PVN in both sham-operated rats and CHF rats.
Exogenous H2S in PVN increases RSNA, MAP and HR, and enhances CSAR. The effects are greater in CHF rats than those in sham-operated rats. Endogenous H2S in PVN is not responsible for the sympathetic activation and enhanced CSAR in CHF rats.
Angiotensin II (Ang II) produces oxidative stress and endothelial dysfunction in blood vessels. The vasculature from females may be protected against deleterious effects of Ang II. We tested the hypothesis that manganese superoxide dismutase (MnSOD) protects against Ang II-induced endothelial dysfunction. Experiments were performed in C57Bl/6, wild-type (MnSOD+/+) and MnSOD deficient (MnSOD+/−) mice treated systemically with vehicle or Ang II. Basilar arteries were isolated from C57Bl/6 mice treated for one week with a non-pressor dose of Ang II (0.28 mg/kg × day). Ang II treatment produced superoxide-mediated impairment of responses to the endothelium-dependent vasodilator acetylcholine (Ach)(P<0.05). In male, but not female MnSOD+/+ mice, Ang II modestly inhibited responses to ACh (P<0.05). In contrast, Ang II selectively impaired these responses by up to 70% in male MnSOD+/− mice (P<0.05) and this effect was reversed by tempol (P<0.05). Ang II had no effect on ACh responses in MnSOD+/− female mice. Vascular superoxide levels following treatment with an inhibitor of CuZn- and extracellular-SOD, were higher in Ang II-treated vs vehicle-treated MnSOD+/− mice. Thus, a non-pressor dose of Ang II produces endothelial dysfunction in male mice only, suggesting that the female vasculature is protected from Ang II. In male, but not female mice, MnSOD deficiency enhanced endothelial dysfunction, suggesting that MnSOD normally protects the vasculature during disease states in which Ang II contributes to vascular dysfunction.
genetically-altered mice; cerebral arteries; mitochondria; oxidative stress
To study whether and how cells adapt to chronic cellular stress, we exposed PC12 cells to the proteasome inhibitor MG132 (0.1 μM) for 2 weeks and longer. This treatment reduced chymotrypsin-like proteasome activity by 47% and was associated with protection against both 6-hydroxydopamine (6-OHDA, 100 μM) and higher dose MG132 (40 μM). Protection developed slowly over the course of the first 2 weeks of exposure and was chronic thereafter. There was no change in total glutathione levels after MG132. Buthionine sulfoximine (100 μM) reduced glutathione levels by 60%, but exacerbated 6-OHDA toxicity to the same extent in both MG132-treated and control cells and failed to reduce MG132-induced protection. Chronic MG132 resulted in elevated antioxidant proteins CuZn superoxide dismutase (SOD, +55%), MnSOD (+21%), and catalase (+15%), as well as chaperone heat shock protein 70 (+42%). Examination of SOD enzyme activity revealed higher levels of CuZnSOD (+40%), with no change in MnSOD. We further assessed the mechanism of protection by reducing CuZnSOD levels with two independent siRNA sequences, both of which successfully attenuated protection against 6-OHDA. Previous reports suggested that artificial overexpression of CuZnSOD in dopaminergic cells is protective. Our data complement such observations, revealing that dopaminergic cells are also able to use endogenous CuZnSOD in self-defensive adaptations to chronic stress, and that they can even do so in the face of extensive glutathione loss.
6-hydroxydopamine; dopamine transporter; glutathione; Parkinson’s disease; proteasome
We have suggested that intestinal microflora reduces the activity of the
antioxidant enzyme superoxide dismutase (SOD) in the mouse cecal mucosa. In this study,
gnotobiotic mice were used to examine the species of intestinal microflora influencing SOD
activity in the cecal mucosa. The total SOD activity in the cecal mucosa of each germ-free
(GF), gnotobiotic mouse with Escherichia coli,
Lactobacillus and Bacteroides was significantly higher
than that in the cecal mucosa of gnotobiotic mice with chloroform-treated feces (CHF),
conventionalized (CVz) mice and conventional (CV) mice (P<0.05). In
addition, CuZnSOD mRNA expression showed similar tendencies. Our results suggest that the
antioxidant defense status in the cecal mucosa is influenced by CHF inoculation.
cecal mucosa; chloroform-treated feces; germ-free; superoxide dismutase
Renovascular hypertension (RVH) in mice is characterized by an elevation in hypothalamic angiotensin-II (Ang-II) levels. The paraventricular nucleus (PVN) is a major cardioregulatory site implicated in the neurogenic component of RVH. Increased superoxide (O2−·) production in the PVN is involved in Ang-II-dependent neuro-cardiovascular diseases such as hypertension and heart failure. Here we tested the hypothesis that excessive O2−· production and activation of the redox-regulated transcription factor activator protein-1 (AP-1) in PVN contributes to the development and maintenance of RVH. Male C57Bl/6 mice underwent implantation of radiotelemeters, bilateral PVN injections of an adenovirus (Ad) encoding superoxide dismutase (AdCuZnSOD) or a control gene (LacZ), and unilateral renal artery clipping (2K1C) or sham surgery. AP-1 activity was longitudinally monitored in vivo by bioluminescence imaging in 2K1C or sham mice that had undergone PVN-targeted microinjections of an Ad encoding the firefly luciferase (Luc) gene downstream of AP-1 response elements (AdAP-1Luc). 2K1C evoked chronic hypertension and an increase in O2−· production in the PVN. Viral delivery of CuZnSOD to the PVN not only prevented the elevation in O2−·, but also abolished RVH. 2K1C also caused a surge in AP-1 activity in the PVN, which paralleled the rise in O2−· production in this brain region, and this was prevented by treatment with AdCuZnSOD. Finally, Ad-mediated expression of a dominant-negative inhibitor of AP-1 activity in the PVN prevented 2K1C-evoked hypertension. These results implicate oxidant signaling and AP-1 transcriptional activity in the PVN as key mediators in the pathogenesis of RVH.
two-kidney; one-clip (2K1C); Goldblatt; CuZnSOD; superoxide; adenovirus-mediated gene transfer
Although cytosolic superoxide dismutases (SODs) are widely distributed among bacteria, only a small number of species contain a periplasmic SOD. One of these is Caulobacter crescentus, which has a copper-zinc SOD (CuZnSOD) in the periplasm and an iron SOD (FeSOD) in the cytosol. The function of periplasmic CuZnSOD was studied by characterizing a mutant of C. crescentus with an insertionally inactivated CuZnSOD gene. Wild-type and mutant strains showed identical tolerance to intracellular superoxide. However, in response to extracellular superoxide, the presence of periplasmic CuZnSOD increased survival by as much as 20-fold. This is the first demonstration that periplasmic SOD defends against external superoxide of environmental origin. This result has implications for those bacterial pathogens that contain a CuZnSOD. C. crescentus was shown to contain a single catalase/peroxidase which, like Escherichia coli KatG catalase/peroxidase, is present in both the periplasmic and cytoplasmic fractions. The growth stage dependence of C. crescentus catalase/peroxidase and SOD activity was studied. Although FeSOD activity was identical in exponential- and stationary-phase cultures, CuZnSOD was induced nearly 4-fold in stationary phase and the catalase/peroxidase was induced nearly 100-fold. Induction of antioxidant enzymes in the periplasm of C. crescentus appears to be an important attribute of the stationary-phase response and may be a useful tool for studying its regulation.
Our previous study demonstrated that oral treatment with simvastatin (SIM) suppressed renal sympathetic nerve activity (RSNA) in the rabbits with chronic heart failure (CHF). The purpose of this experiment was to determine the effects of direct application of SIM to the central nervous system on RSNA and its relevant mechanisms. Experiments were carried out on 21 male New Zealand White rabbits with pacing induced CHF. The CHF rabbits received infusion of vehicle, SIM, or SIM + L-NAME into the lateral cerebral ventricle via osmotic minipump for 7 days. We found that, (1) In CHF rabbits, icv infusion of SIM significantly suppressed basal RSNA (1st day 69.5 ± 8.9 % of Max; 7th day 26.0 ± 6.0 % of Max. P < 0.05, n = 7) and enhanced arterial baroreflex function starting from the 2nd day and lasting through the following 5 days; (2) Statin treatment significantly upregulated nNOS protein expression in the rostral ventrolateral medulla (RVLM) (Control, n = 6, 0.12 ± 0.04; SIM treated, n = 7, 0.31 ± 0.05. P < 0.05); (3) In CATH.a neurons, incubation with SIM significantly upregulated the nNOS mRNA expression, which was blocked by co-incubation with Mevalonate, farnesyl-pyrophosphate, or geranylgeranyl-pyrophosphate; (4) Incubation with Y-27632 significantly upregulated nNOS mRNA expression in these neurons. These results suggest that central treatment with SIM decreased sympathetic outflow in CHF rabbits via up regulation of nNOS expression in RVLM, which may be due to the inhibition of HMG-CoA reductase and a decrease in Rho Kinase by SIM.
Oxidants are believed to play a major role in the development of emphysema.
This study aimed to determine if the expression of human copper–zinc superoxide dismutase (CuZnSOD) within the lungs of mice protects against the development of emphysema.
Transgenic CuZnSOD and littermate mice were exposed to cigarette smoke (6 h/d, 5 d/wk, for 1 yr) and compared with nonexposed mice. A second group was treated with intratracheal elastase to induce emphysema.
Lung inflammation was measured by cell counts and myeloperoxidase levels. Oxidative damage was assessed by immunofluorescence for 3-nitrotyrosine and 8-hydroxydeoxyguanosine and lipid peroxidation levels. The development of emphysema was determined by measuring the mean linear intercept (Lm).
Smoke exposure caused a fourfold increase in neutrophilic inflammation and doubled lung myeloperoxidase activity. This inflammatory response did not occur in the smoke-exposed CuZnSOD mice. Similarly, CuZnSOD expression prevented the 58% increase in lung lipid peroxidation products that occurred after smoke exposure. Most important, CuZnSOD prevented the onset of emphysema in both the smoke-induced model (Lm, 68 exposed control vs. 58 exposed transgenic; p < 0.04) and elastase-generated model (Lm, 80 exposed control vs. 63 exposed transgenic; p < 0.03). These results demonstrate for the first time that antioxidants can prevent smoke-induced inflammation and can counteract the proteolytic cascade that leads to emphysema formation in two separate animal models of the disease.
These findings indicate that strategies aimed at enhancing or supplementing lung antioxidants could be effective for the prevention and treatment of this disease.
emphysema; inflammation; oxidants
Benov and Fridovich recently reported the existence of a copper- and zinc-containing superoxide dismutase (CuZnSOD) in Escherichia coli (L. T. Benov and I. Fridovich, J. Biol. Chem. 269:25310-25314,1994). We have used the N-terminal protein sequence to isolate the gene encoding this enzyme. The gene, denoted sodC, is located at 37.1 min on the chromosome, adjacent to lhr and sodB. A monocistronic transcript of sodC accumulates only in stationary phase. The presence of a conventional leader sequence is consistent with physical data indicating that the E. coli enzyme, like other bacterial CuZnSODs, is secreted into the periplasm. Because superoxide cannot cross membranes, this localization indicates that the enzyme has evolved to defend periplasmic biomolecules against an extracytoplasmic superoxide source. Neither the source nor the target of the superoxide is known. Although once considered an exclusively eukaryotic enzyme, CuZnSOD has now been found in species that span three subdivisions of the purple bacteria. The bacterial CuZnSODs are more homologous to one another than to the eukaryotic enzymes, but active-site residues and structural motifs are clearly shared by both families of enzymes. The use of copper and an invariant disulfide bond suggest that the ancestral gene of present-day CuZnSODs evolved in an aerobic environment, long after the evolutionary split between the eukaryotes and the eubacteria. If so, a CuZnSOD gene must have been transferred laterally between members of these domains. The eukaryotic SODs most closely resemble that of Caulobacter crescentus, a relatively close descendant of the mitochondrial ancestor, suggesting that sodC may have entered the eukaryotes during the establishment of mitochondria.
In plants, CuZn superoxide dismutase (CuZnSOD, EC l.15.1.1), ascorbate peroxidase (APX, EC 126.96.36.199), and catalase (CAT, EC l.11.1.6) are important scavengers of reactive oxygen species (ROS) to protect the cell from damage. In the present study, we isolated three homologous genes (GhSOD1, GhAPX1, and GhCAT1) from Gossypium hirsutum. Overexpressing cassettes containing chimeric GhSOD1, GhAPX1, or GhCAT1 were introduced into cotton plants by Agrobacterium transformation, and overexpressed products of these genes were transported into the chloroplasts by transit peptide, as expected. The five types of transgenic cotton plants that overexpressed GhSOD1, GhAPX1, GhCAT1, GhSOD1 and GhAPX1 stack (SAT), and GhSOD1 and GhCAT1 stack (SCT) were developed. Analyses in the greenhouse showed that the transgenic plants had higher tolerance to methyl viologen (MV) and salinity than WT plants. Interestingly, SCT plants suffered no damage under stress conditions. Based on analyses of enzyme activities, electrolyte leakage, chlorophyll content, photochemical yield (Fv/Fm), and biomass accumulation under stresses, the SCT plants that simultaneously overexpressed GhSOD1 and GhCAT1 appeared to benefit from synergistic effects of two genes and exhibited the highest tolerance to MV and salt stress among the transgenic lines, while the SAT plants simultaneously overexpressing GhSOD1 and GhAPX1 did not. In addition, transgenic plants overexpressing antioxidant enzymes in their chloroplasts had higher tolerance to salt stress than those expressing the genes in their cytoplasms, although overall enzyme activities were almost the same. Therefore, the synergistic effects of GhSOD1 and GhCAT1 in chloroplasts provide a new strategy for enhancing stress tolerance to avoid yield loss.