New approach for measurement of sympathetic nervous abnormality in conscious, spontaneously hypertensive rats

Recent Progress in FD-LC-MS/MS Proteomics Method

Through the course of our bio-analytical chemistry studies, we developed a novel proteomics analysis method, FD-LC-MS/MS (fluorogenic derivatization-liquid chromatography-tandem mass spectrometry). This method consists of fluorogenic derivatization (FD), LC separation, and detection/quantification of the derivatized proteins, followed by isolation, tryptic digestion of the isolated proteins, and final identification of the isolated proteins using electrospray ionization nano-LC-MS/MS of the generated peptide mixtures with a probability-based protein identification algorithm. In this review, we will present various examples where this method has been used successfully to identify expressed proteins in individual human cells. FD-LC-MS/MS is also suitable for differential proteomics analysis. Here, two biological samples are treated by the same steps mentioned above, and the two chromatograms obtained are compared to identify peaks with different intensities (variation in protein levels). Associated peak fractions are then isolated, and the differentially expressed proteins between the two samples are identified by LC-MS/MS. Several biomarkers for cancers have been identified by FD-LC-MS/MS. For more efficient separation, nano-flow LC with a phenyl-bonded monolithic silica-based capillary column was adopted for cell-expressed intact protein analysis. The derivatized human cell proteins (K562) and yeast cell (Saccharomyces cerevisiae) proteins as model intact cell proteins were analyzed by nano-flow LC with fluorescence detection. More than 1,300 protein peaks were separated/detected from both cells. For straightforward comparison of multiple peak separation profiles, a novel type of chromatogram display, termed the “spiderweb” chromatogram, was developed. A nano-LC-FD-LC-mass spectrometry trial for molecular weight estimation of FD proteins has also been conducted.

Daily Ingestion of Eggplant Powder Improves Blood Pressure and Psychological State in Stressed Individuals: A Randomized Placebo-Controlled Study

Eggplant (Solanum melongena) is a globally popular vegetable and its significant health effect has not been reported in randomized controlled trials. Recently, we reported that eggplant was rich in choline esters, including acetylcholine (ACh), and had an antihypertensive effect in spontaneously hypertensive rats. Here, we evaluated the effects of a continuous intake of eggplant powder on blood pressure (BP), stress, and psychological state (PS) in 100 stressed participants with normal-high BP or grade 1 hypertension in a randomized, double-blind, placebo-controlled, parallel-group comparative study. The participants were randomly assigned to the eggplant or placebo group. Participants in the eggplant group ingested capsules containing eggplant powder (1.2 g/day; 2.3 mg of ACh/day) for 12 weeks, whereas participants in the placebo group ingested placebo capsules. The primary outcome assessed was hospital BP. Secondary outcomes were stress and PS. Eggplant powder intake significantly decreased the hospital diastolic blood pressure (DBP) at week 8 overall and in the normal-high BP group, and the systolic blood pressure (SBP) and DBP at week 12 overall and in the grade 1 hypertension group, compared to those of the placebo group. It also improved negative PSs at week 8 or 12 in the normal-high BP group. This is the first evidence of the BP- and PS-improving effects of eggplant intake in humans. The functional substance responsible for the effects was estimated to be eggplant-derived choline ester, namely ACh.

Divergent profile between hypothalamic and plasmatic aminopeptidase activities in WKY and SHR. Influence of beta-adrenergic blockade

AIMS

Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) differ in their renin-angiotensin system function and sympathetic tone. The metabolism of angiotensins and vasopressin depends on the action of certain aminopeptidases whose activity may be influenced by the autonomic nervous system. Their regulation may differ between WKY and SHR in hypothalamus and plasma according to the sympathetic tone. We analyzed aminopeptidases responsible for the hydrolysis of certain angiotensins, vasopressin, cholecystokinin or enkephalins in hypothalamus and plasma of WKY and SHR in untreated controls rats and under beta-adrenoceptor blockade. Systolic blood pressure, food intake, water intake and diuresis were measured as parameters modulated by the autonomic nervous system and the above mentioned peptides.

MAIN METHODS

Glutamyl-, aspartyl-, cystinyl- and alanyl-aminopeptidase activities were analyzed fluorimetrically in plasma and hypothalamus of control and propranolol-treated (100mg/kg/day administered in drinking water for 1month) WKY and SHR, using arylamide derivatives as substrates.

KEY FINDINGS

An opposite response of aminopeptidases to propranolol treatment between plasma and hypothalamus was observed in either WKY and SHR. Furthermore, the behavior of aminopeptidases was inversed between WKY and SHR either in hypothalamus and plasma: while the activity increased in hypothalamus and decreased in plasma of WKY, it decreased in hypothalamus and increased in plasma of SHR.

SIGNIFICANCE

These results revealed an inverse response of aminopeptidases between hypothalamus and plasma and also an opposite behavior of these enzymes between WKY and SHR in hypothalamus and plasma. These observations support the involvement of the sympathetic system in the modulation of aminopeptidase activities.

Central vagal activation by alpha(2) -adrenergic stimulation is impaired in spontaneously hypertensive rats

AIM

To elucidate the abnormality of vagal control in spontaneously hypertensive rats (SHR) by measuring left ventricular myocardial interstitial acetylcholine (ACh) release in response to α(2) -adrenergic stimulation as an index of in vivo vagal nerve activity.

METHODS

A cardiac microdialysis technique was applied to the rat left ventricle in vivo, and the effect of α(2) -adrenergic stimulation by medetomidine or electrical vagal nerve stimulation on myocardial interstitial ACh levels was examined in normotensive Wistar-Kyoto rats (WKY) and SHR under anaesthetized conditions.

RESULTS

Intravenous medetomidine (0.1 mg kg(-1) ) significantly increased the ACh levels in WKY (from 2.4 ± 0.6 to 4.2 ± 1.3 nmol L(-1) , P < 0.05, n = 7) but not in SHR (from 2.5 ± 0.7 to 2.7 ± 0.7 nmol L(-1) , n = 7). In contrast, electrical vagal nerve stimulation increased the ACh levels in both WKY (from 1.0 ± 0.4 to 2.9 ± 0.9 nmol L(-1) , P < 0.001, n = 6) and SHR (from 0.9 ± 0.2 to 2.2 ± 0.4 nmol L(-1) , P < 0.001, n = 6). Intravenous administration of medetomidine (0.1 mg kg(-1) ) did not affect the vagal nerve stimulation-induced ACh release in either WKY or SHR.

CONCLUSION

Medetomidine-induced central vagal activation was impaired in SHR, whereas peripheral vagal control of ACh release was preserved. In addition to abnormal sympathetic control, vagal control by the central nervous system may be impaired in SHR.

Discrepant regulation of QT (QTc) interval duration by calcium channel blockade and angiotensin converting enzyme inhibition in experimental hypertension

Antihypertensive treatment may reduce prolonged QT duration in hypertension. Generally, the reductions of blood pressure and/or of cardiac mass are believed to be the responsible factors. However, drugs are not equivalent in QT modulation despite similar antihypertensive and antihypertrophic action. We investigated the effect of a calcium channel blocker, lacidipine and an angiotensin-converting enzyme inhibitor, enalapril on QT duration in rats. Normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were treated with lacidipine (at the dose of 1.5 mg/kg per day for WKY and 3 mg/kg per day for SHR) or enalapril (5 mg/kg per day for WKY and 10 mg/kg per day for SHR) during 8 weeks. Tail-cuff systolic blood pressure (sBP), left ventricular weight (LVW), vascular function of isolated aorta and mesenteric artery and duration of QT (and QTc) interval on Frank electrocardiograms were evaluated. As expected, untreated SHR showed elevated sBP, impaired vascular reactivity, increased LVW and prolonged QT when compared with WKY (p < 0.05). After treatment, both agents markedly improved vascular reactivity and reduced sBP in SHR (p < 0.05). Additionally, enalapril reduced LVW in both hypertensive (by 17%; p < 0.05) and normotensive rats (by 13%; p < 0.05) and, consequently, corrected QT duration in SHR. Interestingly, lacidipine also reduced LVW in SHR (by 9%; p < 0.05), but without influence on prolonged QT. Moreover, lacidipine had no effect on LVW in WKYs but prolonged their QT interval (by 10%; p < 0.05). In conclusion, lacidipine did not reverse a progressive prolongation of QT in SHR, despite sBP lowering and LVW reduction. Thus, the lowering of blood pressure and/or reduction of LVW are not sufficient per se to normalize ventricular repolarization in hypertensive cardiac disease. More likely, modulation of QT prolongation by antihypertensive drugs is a function of their complex action on blood pressure, vascular function, cardiac mass and on reflex neurohumoral activation.

The Renin-Angiotensin System in the Development of Salt-Sensitive Hypertension in Animal Models and Humans

Hypertension is still one of the major causes of death from cardiovascular failure. Increased salt intake may aggravate the rise in blood pressure and the development of consequential damage of the heart, the vessels and other organs. The general necessity of restricted salt intake regardless of blood pressure or salt sensitivity has been a matter of debate over the past decades. This review summarizes the main pathogenic mechanisms of hypertension and salt sensitivity in rat models, particularly in the spontaneously hypertensive rat (SHR), and in patients with essential hypertension (EH). Although SHRs are commonly considered to be salt-resistant, there is much evidence that salt loading may deteriorate blood pressure and cardiovascular function even in these animals. Similarly, EH is not a homogenous disorder - some patients, but not all, exhibit pronounced salt sensitivity. The renin-angiotensin system (RAS) plays a key role in the regulation of blood pressure and salt and fluid homeostasis and thus is one of the main targets of antihypertensive therapy. This review focuses on the contribution of the RAS to the pathogenesis of salt-sensitive hypertension in SHRs and patients with EH.

Targeting cardiac sympatho-vagal imbalance using gene transfer of nitric oxide synthase

Heightened sympathetic excitation and diminished parasympathetic suppression of heart rate, cardiac contractility and vascular tone are all associated with cardiovascular diseases such as hypertension and ischemic heart disease. This phenotype often exists before these disease states have been established and is a strong correlate of mortality in the population. However, the causal role of the autonomic phenotype in the development and maintenance of hypertension and myocardial ischemia remains a subject of debate, as are the mechanisms responsible for regulating sympathovagal balance. Emerging evidence suggests oxidative stress and reactive oxygen species (such as nitric oxide (NO) and superoxide) play important roles in the modulation of autonomic balance, but so far the most important sites of action of these ubiquitous signaling molecules are unclear. In many cases, these mediators have opposing effects in separate tissues rendering conventional pharmacological approaches non-efficacious. Novel techniques have recently been used to augment these signaling pathways experimentally in a targeted fashion to central autonomic nuclei, cardiac neurons, and myocytes using gene transfer of NO synthase. This review article discusses these recent advances in the understanding of the roles of NO and its oxidative metabolites on autonomic imbalance in models of cardiovascular disease.

Changes in the in vitro pharmacodynamic properties of metoprolol in atria isolated from spontaneously hypertensive rats

1. The present study addressed possible changes in the dissociation constant of metoprolol and its inverse agonist activity in spontaneously hypertensive rats (SHR). In addition, a possible correlation between cardiac hypertrophy and the inverse agonist activity of metoprolol was explored. 2. In order to determine the dissociation constant (expressed as the pKb) of metoprolol, a cumulative concentration-response curve to noradrenaline was constructed in the absence or presence of metoprolol (0.1, 1 or 10 micromol/L). In a second experiment, a cumulative concentration-response curve to metoprolol was constructed to determine its inverse agonist activity. 3. The ventricular weight of SHR was significantly greater compared with Wistar-Kyoto (WKY) rats. A rightward shift of the concentration-response curve to noradrenaline was observed in SHR compared with WKY rats. The pKb of metoprolol was smaller in SHR compared with WKY rats (6.35 +/- 0.14 vs 6.99 +/- 0.12, respectively; P < 0.05). No difference was observed in the maximal response (Emax) of the concentration-time effect of metoprolol in WKY rats and SHR (-29.1 +/- 7.1 vs-28.2 +/- 8.5%, respectively; n = 6 for both). However, the concentration of metoprolol eliciting a half-maximal effect (expressed as the pEC50) was significantly smaller in SHR compared with WKY rats (4.82 +/- 0.07 vs 5.29 +/- 0.13, respectively; n = 6; P < 0.05). Although a significant correlation (r = -0.876) between the ventricular weight/bodyweight (VW/BW) ratio and the pEC50 of the chronotropic effect of metoprolol was found, no relationship (r = -0.257) was found between the VW/BW ratio and Emax. 4. In summary, the present study provides the first evidence of a change in the in vitro pharmacodynamic properties of metoprolol in SHR. The sympathetic overactivity present in SHR not only reduces the positive chronotropic effect of noradrenaline, but also diminishes the constant dissociation of metoprolol from atrial beta1-adrenoceptors and its inverse agonist activity. A significant correlation between the VW/BW ratio and the inverse agonist potency of metoprolol was found, suggesting a possible link between cardiac hypertrophy and the reduction of the inverse agonist activity of metoprolol.

Recent advances in methods for the analysis of catecholamines and their metabolites

Catecholamines, for example epinephrine, norepinephrine, and dopamine, are widely distributed and are important neurotransmitters and hormones in mammalian species. Several methods have been developed for analysis of catecholamines and related compounds. Determination of catecholamines in biological fluids has enabled us to clarify the physiological role played by these amines. Catecholamine levels in plasma and/or urine are also useful for diagnosis of several diseases, for example hypertension, pheochromocytoma, and neuroblastoma. This review covers reports from 2000 to the present of methods for the analysis of catecholamines and their metabolites.

Effects of salt loading and various therapies on cardiac hypertrophy and fibrosis in young spontaneously hypertensive rats

We investigated the effects of salt loading on blood pressure, cardiac hypertrophy and fibrosis as well as on the effectiveness of various antihypertensive therapies in young spontaneously hypertensive rats (SHR). Twenty-five male SHR were salt-stimulated by drinking 1% NaCl from 3 to 6 months of age. Eighteen of them were treated for the last 2 weeks of salt loading with either the angiotensin-converting enzyme inhibitor captopril, the beta-adrenergic receptor blocker propranolol or the calcium-channel antagonist verapamil. Age-matched male Wistar-Kyoto (WKY) rats and SHR drinking only water served as controls. At the age of 6 months, SHR had significantly elevated blood pressure that was unchanged by salt loading. Relative heart weight was increased in SHR without (3.3) and even more so with salt intake (3.6 vs. 2.4 in WKY). Left ventricular (LV) hypertrophy was accompanied by a 17-fold increase in the expression of mRNA for atrial natriuretic factor (ANF) both in untreated and salt-loaded SHR compared to WKY (p<0.001). Collagen I and III mRNA increased 1.7-1.8-fold in SHR without and with additional salt intake (p<0.01). None of the therapies significantly reduced blood pressure or hypertrophy. Although captopril had no antihypertensive effect, it reduced ANF, collagen I and III mRNA in LV to control level. Less pronounced effects were achieved with verapamil. These findings emphasize the cardioprotective role of captopril which may not be fully expressed in the presence of elevated salt intake.

Reduced Membrane-Bound Catechol-O-Methyltransferase in the Liver of Spontaneously Hypertensive Rats

We have previously reported that methylation of catecholamines by catechol-O-methyltransferase (COMT) was attenuated in spontaneously hypertensive rats (SHR) with acute hypotension as compared with that of Wistar-Kyoto (WKY) rats. Here we examined the soluble (S-) and membrane-bound (MB-) COMT activities and COMT protein in the liver, kidney, and erythrocytes in both strains. Both the activities and the amounts of MB-COMT in the liver were lower in SHR than in WKY rats, but no such trend was found in the kidney or erythrocytes. Nor was such a trend observed in any of these three tissues for S-COMT. These results indicate that liver MB-COMT may be a relevant factor in blood pressure regulation in rats.

Analytical Chemical Studies on High-Performance Recognition and Detection of Bio-molecules in Life

In order to understand the mechanism for maintaining life of animals based on the search of dynamics of biomolecules, I have developed several sensitive and selective methods for their quantification. Using the methods of derivatization with the developed benzofurazan fluorogenic reagents (4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), ammonium 7-fluoro-2,1,3-benzoxadiazole 4-sulfonate (SBD-F) and etc.) followed by high-performance liquid chromatography (HPLC)--fluorescence detection, a certain kind of biological and clinical importance was demonstrated of chiral bio-molecules (D-amino acids, D-lactic acid and so on), peptides and proteins. The proposed method (derivatization with SBD-F, isolation of the fluorescent proteins by two-dimensional HPLC, enzymatic digestion and identification of the altered proteins by HPLC-mass spectrometry (MS)/MS with database-searching algorithm) for proteomics studies revealed the changed proteins in the islets of Langerhans of the dexamethazone-induced diabetic rats. An importance of catecholamine metabolism on the blood pressure regulation was also suggested by the method of HPLC-chemiluminescence detection of catecholamines and their 3-O-methylmetabolites. A new field of Analytical Chemistry, i.e., Bio-Analytical Chemistry, was also proposed.

Assay of catechol-O-methyltransferase activity in human erythrocytes using norepinephrine as a natural substrate

BACKGROUND

Catechol-O-methyltransferase (COMT) catalyses the inactivation of catecholamines. It is widely distnbuted in most tissues in soluble (S-COMT) and membrane-bound (MB-COMT) forms. Recently, we used a new assay for COMT activity and demonstrated that COMT plays an important role in blood pressure regulation in spontaneously hypertensive rats. In order to investigate whether this is true for human hypertension, we have evaluated the erythrocyte COMT assay in humans.

METHOD

The assay procedure included the use of norepinephrine (NE) as a natural substrate and the quantification of the reaction product, normetanephrine, followed by high-performance liquid chromatography separation and fluorescence or chemiluminescence detection.

RESULTS

After evaluation of the method, the optimum conditions were obtained for the assay of human erythrocyte COMT. The S- and MB-COMT activities obtained were 50.6 (24.5) and 329.8 (179.4) fmol/min/mg protein, respectively [mean (standard deviation); n = 54]. The Km values for NE were 91.3 (14.1) and 11.7 (1.1) micromol/L for S- and MB-COMT, respectively (n = 6).

CONCLUSION

The established assay method used to assess S- and MB-COMT activities in human erythrocytes could be useful to elucidate catecholamine metabolism in the normal physiological state as well as in the pathology of certain diseases.

Effects of fragrance inhalation on sympathetic activity in normal adults

We investigated the effects of fragrance inhalation on sympathetic activity in normal adult subjects using both power spectral analysis of blood pressure fluctuations and measurement of plasma catecholamine levels. Fragrance inhalation of essential oils, such as pepper oil, estragon oil, fennel oil or grapefruit oil, resulted in 1.5- to 2.5-fold increase in relative sympathetic activity, representing low frequency amplitude of systolic blood pressure (SBP-LF amplitude), compared with inhalation of an odorless solvent, triethyl citrate (P<0.05, each). In contrast, fragrance inhalation of rose oil or patchouli oil caused a 40% decrease in relative sympathetic activity (P<0.01, each). Fragrance inhalation of pepper oil induced a 1.7-fold increase in plasma adrenaline concentration compared with the resting state (P = 0.06), while fragrance inhalation of rose oil caused a 30% decrease in adrenaline concentration (P<0.01). Our results indicate that fragrance inhalation of essential oils may modulate sympathetic activity in normal adults.

Effects of ACE inhibitor and beta-adrenergic blocker on plasma NPY and NPY receptors in aortic vascular smooth muscle cells from SHR and WKY rats

To investigate the effects of the angiotensin-converting enzyme (ACE) inhibitor, peridopril, and the beta-adrenergic blocker, metoprolol, on plasma neuropeptide Y (NPY), and NPY receptors in aortic vascular smooth muscle cells (VSMCs) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), both strains of rats were fed with different doses of the drugs (peridopril or metoprolol) for 7 days to get the optimal dosages. After that, 18 male SHR and 18 male age-matched WKY rats were divided into three groups: control, peridopril (2mg/kg/day) and metoprolol (2mg/kg/day). After two months of treatment, VSMCs were isolated from the media layer of the aortic wall. Results showed that the SHRs had higher plasma concentrations and binding sites/affinity for NPY as compared to WKY rats. Peridopril dose-dependently decreased plasma NPY concentrations in WKY rats, and the absolute changes of plasma NPY were greater in SHRs than in WKY rats. Metoprolol showed none of these changes. Metoprolol decreased while peridopril increased NPY binding sites/affinity in SHRs. This indicated that lowered plasma NPY concentration and decreased NPY receptor in VSMCs, might play some roles in the anti-hypertensive mechanisms mediated by ACE inhibitor and beta-adrenergic blockers.

Simultaneous determination of 3,4-dihydroxyphenylacetic acid and homovanillic acid using high performance liquid chromatography-fluorescence detection and application to rat kidney microdialysate

We established a sensitive and simultaneous determination method of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) using HPLC-fluorescence detection. This method adopted the column-switching system, which included an on-line extraction of carboxylic acids by a strong anion-exchange column followed by separation on an ODS column, coulometric oxidation, fluorogenic reaction with ethylenediamine, and fluorescence detection. The detection limits were 50 and 100 fmol/injection for DOPAC and HVA, respectively (a signal-to-noise ratio of 3). The method was applicable to 50 microl of rat kidney microdialysate with a sufficient accuracy and precision. The concentrations of DOPAC and HVA in rat kidney microdialysate were 131+/-29 and 404+/-44 nM, respectively (n=5). This is the first report of DOPAC and HVA quantified in rat kidney microdialysate.

Determination of catecholamines and their 3-O-methyl metabolites in mouse plasma

The determination of catecholamines and their 3-O-methyl metabolites in a single mouse plasma is necessary to understand the role of the sympathetic nervous activity, while the inactivation of catecholamines by catechol-O-methyltransferase indicates the activity of blood pressure regulation in animals. Here we report the basal catecholamines and their 3-O-methyl metabolite concentrations obtained from 15 microL of mouse plasma utilizing semi-microcolumn high-performance liquid chromatography (HPLC)-peroxyoxalate chemiluminescence detection system. The concentrations were 6.63 +/- 1.37 pmol/mL plasma, 0.49 +/- 0.10 pmol/mL plasma, 5.25 +/- 2.30 pmol/mL plasma, 3.23 +/- 0.84 pmol/mL plasma, 0.44 +/- 0.11 pmol/mL plasma, and 3.39 +/- 1.67 pmol/mL plasma for norepinephrine, epinephrine, dopamine, normetanephrine, metanephrine and 3-methoxytyramine, respectively (n = 5-7). Further, when blood pressure was reduced by minoxidil, plasma catecholamines were found to be significantly increased by the baroreflex-mediated response in mouse.