Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats

The abnormalities of adrenomedullary hormonal system in genetic hypertension: Their contribution to altered regulation of blood pressure

It is widely accepted that sympathetic nervous system plays a crucial role in the development of hypertension. On the other hand, the role of adrenal medulla (the adrenomedullary component of the sympathoadrenal system) in the development and maintenance of high blood pressure in man as well as in experimental models of hypertension is still controversial. Spontaneously hypertensive rats (SHR) are the most widely used animal model of human essential hypertension characterized by sympathetic hyperactivity. However, the persistence of moderately elevated blood pressure in SHR subjected to sympathectomy neonatally as well as the resistance of adult SHR to the treatment by sympatholytic drugs suggests that other factors (including enhanced activity of the adrenomedullary hormonal system) are involved in the pathogenesis of hypertension of SHR. This review describes abnormalities in adrenomedullary hormonal system of SHR rats starting with the hyperactivity of brain centers regulating sympathetic outflow, through the exaggerated activation of sympathoadrenal preganglionic neurons, to the local changes in chromaffin cells of adrenal medulla. All the above alterations might contribute to the enhanced release of epinephrine and/or norepinephrine from adrenal medulla. Special attention is paid to the alterations in the expression of genes involved in catecholamine biosynthesis, storage, release, reuptake, degradation and adrenergic receptors in chromaffin cells of SHR. The contribution of the adrenomedullary hormonal system to the development and maintenance of hypertension as well as its importance during stressful conditions is also discussed.

Effects and Mechanisms of Radiofrequency Ablation of Renal Sympathetic Nerve on Anti-Hypertension in Canine

Background

Radiofrequency ablation of renal sympathetic nerve (RDN) shows effective BP reduction in hypertensive patients while the specific mechanisms remain unclear.

Objective

We hypothesized that abnormal levels of norepinephrine (NE) and changes in NE-related enzymes and angiotensinconverting enzyme 2 (ACE2), angiotensin (Ang)-(1-7) and Mas receptor mediate the anti-hypertensive effects of RDN.

Methods

Mean values of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were assessed at baseline and follow-up. Plasma and renal norepinephrine (NE) concentrations were determined using highperformance liquid chromatography with electrochemical detection, and levels of NE-related enzyme and ACE2-Ang(1-7)- Mas were measured using real time PCR, Western blot and immunohistochemistry or Elisa in a hypertensive canine model fed with high-fat diet and treated with RDN. The parameters were also determined in a sham group treated with renal arteriography and a control group fed with normal diet.

Results

RDN decreased SBP, DBP, MAP, plasma and renal NE. Compared with the sham group, renal tyrosine hydroxylase (TH) expression was lower and renalase expression was higher in the RDN group. Compared with the control group, renal TH and catechol-o-methyl transferase (COMT) were higher and renalase was lower in the sham group. Moreover, renal ACE2, Ang-(1-7) and Mas levels of the RDN group were higher than those of the sham group, which were lower than those of the control group.

Conclusion

RDN shows anti-hypertensive effect with reduced NE and activation of ACE2-Ang(1-7)-Mas, indicating that it may contribute to the anti-hypertensive effect of RDN.

Urocortin 2 lowers blood pressure and reduces plasma catecholamine levels in mice with hyperadrenergic activity

Exaggerated adrenergic activity is associated with human hypertension. The peptide urocortin 2 (Ucn 2) inhibits catecholamine synthesis and secretion from adrenal chromaffin cells in vitro and administration to mammals lowers blood pressure (BP). The chromogranin A-null mouse (Chga-/-) manifests systemic hypertension because of excessive catecholamine secretion from the adrenal and decreased catecholamine storage. In the present study, we investigated whether systemic administration of Ucn 2 could reduce BP and adrenal and plasma levels of catecholamines in vivo. Ucn 2 peptide was administered to freely moving, conscious Chga-/- and wild-type control mice. Telemetry and HPLC measured changes in BP and catecholamine levels, respectively. In both groups of mice, Ucn 2 dose-dependently decreased BP, and this effect was mediated by corticotropin factor-receptor type 2. However, in Chga-/- mice, the maximal percentage decrease of systolic BP from basal systolic BP was 37% compared with only a 23% reduction in wild-type mice (P=0.04). In Chga-/- mice only, Ucn 2 decreased adrenal and plasma levels of catecholamines as well as adrenal levels of tyrosine hydroxylase protein and phosphorylation. In vitro mechanistic studies demonstrated that Ucn 2 reduces both catecholamine secretion and tyrosine hydroxylase promoter activity, suggesting that the exaggerated action of Ucn 2 to reduce BP in the Chga-/- mouse is mediated through inhibition of both catecholamine synthesis and secretion. The data suggest that Ucn 2 may be therapeutically useful in regulating the exaggerated sympathoadrenal function of hyperadrenergic hypertension.

Delivery of sry1, but not sry2, to the kidney increases blood pressure and sns indices in normotensive wky rats

BACKGROUND

Our laboratory has shown that a locus on the SHR Y chromosome increases blood pressure (BP) in the SHR rat and in WKY rats with the SHR Y chromosome (SHR/y rat). A candidate for this Y chromosome hypertension locus is Sry, a gene that encodes a transcription factor responsible for testes determination. The SHR Y chromosome has six divergent Sry loci. The following study examined if exogenous Sry1 or Sry2 delivered to the kidney would elevate renal tyrosine hydroxylase, renal catecholamines, plasma catecholamines and telemetered BP over a 28 day period. We delivered 50 mug of either the expression construct Sry1/pcDNA 3.1, Sry2/pcDNA 3.1, or control vector into the medulla of the left kidney of normotensive WKY rats by electroporation. Weekly air stress was performed to determine BP responsiveness. Separate groups of animals were tested for renal function and plasma hormone patterns and pharmacological intervention using alpha adrenergic receptor blockade. Pre-surgery baseline and weekly blood samples were taken from Sry1 electroporated and control vector males for plasma renin, aldosterone, and corticosterone. BP was measured by telemetry and tyrosine hydroxylase and catecholamines by HPLC with electrochemical detection.

RESULTS

In the animals receiving the Sry1 plasmid there were significant increases after 21 days in resting plasma norepinephrine (NE, 27%) and renal tyrosine hydroxylase content (41%, p < .05) compared to controls. BP was higher in animals electroporated with Sry1 (143 mmHg, p < .05) compared to controls (125 mmHg) between 2-4 weeks. Also the pressor response to air stress was significantly elevated in males electroporated with Sry1 (41 mmHg) compared to controls (28 mmHg, p < .001). Sry2 did not elevate BP or SNS indices and further tests were not done. The hormone profiles for plasma renin, aldosterone, and corticosterone between electroporated Sry1 and control vector males showed no significant differences over the 28 day period. Alpha adrenergic receptor blockade prevented the air stress pressor response in both strains. Urinary dopamine significantly increased after 7 days post Sry electroporation.

CONCLUSION

These results are consistent with a role for Sry1 in increasing BP by directly or indirectly activating renal sympathetic nervous system activity.

Fasudil attenuates sympathetic nervous activity in the adrenal medulla of spontaneously hypertensive rats

We investigated the effects of fasudil, a Rho kinase inhibitor, on hypertension in spontaneously hypertensive rats and on the catecholamine synthetic pathway. Ten-week-old male SHR and Wistar-Kyoto rats were administered fasudil (10 mg/kg/day s.c.) for 4 days. Systolic blood pressure was measured using the tail-cuff method. Catecholamine levels were measured with high-performance liquid chromatography-ECD methods. Tyrosine hydroxylase protein levels were measured in Western blot analysis. The tyrosine hydroxylase mRNA level was measured using real-time PCR methods. Fasudil significantly decreased systolic blood pressure in spontaneously hypertensive rats, but not in Wistar-Kyoto rats. Fasudil also significantly decreased catecholamine, tyrosine hydroxylase protein, and tyrosine hydroxylase mRNA levels in the adrenal medulla of spontaneously hypertensive rats. These results suggest that the depressor effects of fasudil on hypertension in spontaneously hypertensive rats may be related to inhibition of the catecholamine synthetic pathway.

The Future of Antihypertensive Treatment

Despite progress in recent years in the prevention, detection, and treatment of high blood pressure (BP), hypertension remains an important public health challenge. Hypertension affects approximately 1 billion individuals worldwide. High BP is associated with an increased risk of mortality and morbidity from stroke, coronary heart disease, congestive heart failure, and end-stage renal disease; it also has a negative impact on the quality of life. Hypertension cannot be eliminated because there are no vaccines to prevent the development of hypertension, but, its incidence can be decreased by reducing the risk factors for its development, which include obesity, high dietary intake of fat and sodium and low intake of potassium, physical inactivity, smoking, and excessive alcohol intake. For established hypertension, efforts are to be directed to control BP by lifestyle modification (LSM). However, if BP cannot be adequately controlled with LSM, then pharmacotherapy can be instituted along with LSM. Normalization of BP reduces cardiovascular risk (for cardiovascular death, myocardial infarction, and cardiac arrest), provides renoprotection (prevention of the onset or slowing of proteinuria and progression of renal dysfunction to end-stage renal disease in patients with hypertension, diabetes mellitus types 1 and 2, and chronic renal disease), and decreases the risk of cerebrovascular events (stroke and cognition impairment), as has been amply demonstrated by a large number of randomized clinical trials. In spite of the availability of more than 75 antihypertensive agents in 9 classes, BP control in the general population is at best inadequate. Therefore, antihypertensive therapy in the future or near future should be directed toward improving BP control in treated hypertensive patients with the available drugs by using the right combinations at optimum doses, individually tailored gene-polymorphism directed therapy, or development of new modalities such as gene therapy and vaccines. Several studies have shown that BP can be reduced by lifestyle/behavior modification. Although, the reductions appear to be trivial, even small reductions in systolic BP (for example, 3-5 mm Hg) produce dramatic reduction in adverse cardiac events and stroke. On the basis of the results of clinical and clinical/observational studies, it has been recommended that more emphasis be placed on lifestyle/behavior modification (obesity, high dietary intake of fat and sodium, physical inactivity, smoking, excessive alcohol intake, low dietary potassium intake) to control BP and also to improve the efficacy of pharmacologic treatment of high BP. New classes of antihypertensive drugs and new compounds in the established drug classes are likely to widen the armamentarium available to combat hypertension. These include the aldosterone receptor blockers, vasodilator beta-blockers, renin inhibitors, endothelin receptor antagonists, and dual endopeptidase inhibitors. The use of fixed-dose combination drug therapy is likely to increase. There is a conceptual possibility that gene therapy may yield long-lasting antihypertensive effects by influencing the genes associated with hypertension. But, the treatment of human essential hypertension requires sustained over-expression of genes. Some of the challenging tasks for successful gene therapy that need to be mastered include identification of target genes, ideal gene transfer vector, precise delivery of genes into the required site (target), efficient transfer of genes into the cells of the target, and prompt assessment of gene expression over time. Targeting the RAS by antisense gene therapy appears to be a viable strategy for the long-term control of hypertension. Several problems that are encountered in the delivery of gene therapy include 1) low efficiency for gene transfer into vascular cells; 2) a lack of selectivity; 3) problem in determining how to prolong and control transgene expression or antisense inhibition; and 4) difficulty in minimizing the adverse effects of viral or nonviral vectors. In spite of the hurdles that face gene therapy administration in humans, studies in animals indicate that gene therapy may be feasible in treating human hypertension, albeit not in the near future. DNA testing for genetic polymorphism and determining the genotype of a patient may predict response to a certain class of antihypertensive agent and thus optimize therapy in individual patients. In this regard, there are some studies that report the effectiveness of antihypertensive therapy based upon the genotype of selected patients. Treatment of human hypertension with vaccines is feasible but is not likely to be available in the near future.

Sry delivery to the adrenal medulla increases blood pressure and adrenal medullary tyrosine hydroxylase of normotensive WKY rats

Background

Our laboratory has shown that a locus on the SHR Y chromosome increases blood pressure (BP) in the SHR rat and in WKY rats that had the SHR Y chromosome locus crossed into their genome (SHR/y rat). A potential candidate for this Y chromosome hypertension locus is Sry, a gene that encodes a transcription factor that is responsible for testes development and the Sry protein may affect other target genes.

Methods

The following study examined if exogenous Sry would elevate adrenal Th, adrenal catecholamines, plasma catecholamines and blood pressure. We delivered 10 μg of either the expression construct, Sry1/pcDNA 3.1, or control vector into the adrenal medulla of WKY rats by electroporation. Blood pressure was measured by the tail cuff technique and Th and catecholamines by HPLC with electrochemical detection.

Results

In the animals receiving Sry there were significant increases after 3 weeks in resting plasma NE (57%) and adrenal Th content (49%) compared to vector controls. BP was 30 mmHg higher in Sry injected animals (160 mmHg, p < .05) compared to vector controls (130 mmHg) after 2–3 weeks. Histological analysis showed that the electroporation procedure did not produce morphological damage.

Conclusion

These results provide continued support that Sry is a candidate gene for hypertension. Also, these results are consistent with a role for Sry in increasing BP by directly or indirectly activating sympathetic nervous system activity.

Orange juice increased the bioavailability of pravastatin, 3-hydroxy-3-methylglutaryl CoA reductase inhibitor, in rats and healthy human subjects

Our objective was to investigate the effects of orange juice on the pharmacokinetics of pravastatin in rats and healthy volunteers. The pharmacokinetics of pravastatin (100 mg/kg p.o.) were assessed with water, orange juice, and carbohydrates (12.5 ml/kg over 30 min) and with acetic acid (0.1 M, pH 3.44). The pharmacokinetics of simvastatin (100 mg/kg p.o.) were assessed with water and orange juice. In addition, the pharmacokinetics (based on plasma levels) of pravastatin 80 mg/kg i.v. were assessed with water and orange juice (5 ml/kg) in rats. The pharmacokinetics of oral pravastatin (10 mg) were assessed when administered with water and orange juice (800 ml over 3 h) in a two-way crossover study in 14 healthy volunteers. Orange juice significantly increased the area under the curve (0-150 min) of pravastatin in rats. Orange juice had no effects on the pharmacokinetic parameters of intravenously administered pravastatin in rats. Carbohydrates and acetic acid with pH and concentration equivalent to those of orange juice also resulted in no statistically significant differences in pravastatin pharmacokinetic parameters in rats. Orange juice did not result in any significant differences in the pharmacokinetic parameters of simvastatin in rats. Orange juice significantly increased oatp1 and oatp2 mRNA and protein in the intestine of rats. Orange juice significantly increased the area under the curve (0-240 min) of pravastatin in healthy volunteers. In conclusion, orange juice increases the bioavailability of pravastatin administered orally. Oatp1 and oatp2 may be related to increases of pharmacokinetics of pravastatin by orange juice.

Midkine is a potent regulator of the catecholamine biosynthesis pathway in mouse aorta

To discover regulatory pathways dependent on midkine (Mk the gene, MK the protein) signaling, we compared the transcriptional profiles of aortae obtained from Mk -/- and wild type (WT, +/+) mice; the comparison demonstrated an extraordinary high level expression of tyrosine hydroxylase (12-fold), the rate-limiting enzyme in catecholamine biosynthesis, DOPA decarboxylase (73-fold), and dopamine beta-hydroxylase (75-fold) in aortae of Mk -/- mice compared with aortae of WT (+/+) mice. Phenylethanolamine-N-methyltransferase, the enzyme catalyzing the conversion of norepinephrine into epinephrine, was not detected in either Mk -/- and WT (+/+) mouse aorta. The protein levels of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase confirmed the analysis of the transcriptional profiles. Surprisingly, MK failed to regulate the enzymes of the catecholamine biosynthesis pathway in 10 other tissues studied. Furthermore, the expression levels of the enzymes of catecholamine biosynthesis in aortae of Mk -/- mice were effectively the same as those in aortae of Pleiotrophin (Ptn the gene, PTN the protein) genetically deficient (Ptn -/-) mice when compared with WT (+/+) mice. The remarkable increases in levels of expression of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase suggest that MK together with PTN are very important regulators of the catecholamine pathway in mouse aorta and may critically regulate catecholamine biosynthesis and function in inflammatory and the other pathological conditions in which Mk or Ptn are upregulated. The data also establish that norepinephrine is effectively the only catecholamine synthesized in mouse aorta.

Decreased tyrosine hydroxylase activity in the adrenals of spontaneously hypertensive rats

Higher activity of the peripheral sympathetic nervous system, accompanied by higher tyrosine hydroxylase activity is frequently and consistently reported in human essential hypertension as well as in animal models of hypertension. However, results obtained in the adrenals, particularly in young animals before the development of hypertension, are scarce and controversial. In the present study tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats and of age-matched control Wistar Kyoto rats were evaluated before, during and after the development of hypertension (5, 12 and 22-week-old animals). Results show that both tyrosine hydroxylase activity and total amine content in the adrenals of spontaneously hypertensive rats were significantly reduced (35% reduction) at all studied ages. Determination of the kinetic parameters for tyrosine hydroxylase in the adrenals of 5 week-old spontaneously hypertensive rats revealed a 38% reduction in V(max) values (13.4 versus 21.3 nmol L-DOPA/mg prot/h in age-matched controls) accompanied by lower levels of expression of both tyrosine hydroxylase total protein and phosphoSer40 observed by Western-Blot. In contrast, norepinephrine content in both plasma and tail artery were significantly higher in the spontaneously hypertensive strain. In conclusion, contrary to the higher peripheral sympathetic activity, tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats are markedly reduced before, during and after the development of hypertension. End product, long-term feedback inhibition by the high norepinephrine plasma levels could be responsible for this reduction, establishing yet another regulatory mechanism of tyrosine hydroxylase operating in adrenal cromaffin cells.

Pleiotrophin is a major regulator of the catecholamine biosynthesis pathway in mouse aorta

To better understand the phenotype of pleiotrophin (PTN the protein, Ptn the gene) genetically deficient mice (Ptn -/-), we compared the transcriptional profiles of aortae obtained from Ptn -/- and wild type (WT, Ptn +/+) mice using a 14,400 gene microarray chip (Affymetrix) and confirmed the analysis of relevant genes by real time RT-PCR. We identified a dramatic upregulation of expression of tyrosine hydroxylase (TH), DOPA decarboxylase, and dopamine beta-hydroxylase in aortae of Ptn -/- mice in comparison with WT (Ptn +/+) mice. In contrast, transcripts of phenylethanolamine-N-methyltransferase, the enzyme catalyzing the conversion of norepinephrine into epinephrine, were not detected in aortae in either mouse strain. These findings suggest that Ptn gene expression has a critical role in determining the levels of expression of the enzymes of catecholamine biosynthesis in aorta and through this mechanism, PTN may regulate levels of endogenous catecholamine synthesis and potentially the vascular tone of aorta.

Potential of gene therapy for pediatric neurotransmitter diseases: lessons from Parkinson's disease

Gene therapy methods have continued to develop rapidly, and many initial limitations that hampered clinical application have been overcome. Thus serious consideration of clinical application of gene therapy is warranted for selected disorders in which the pathogenesis is well defined. Parkinson's disease has been the most extensively studied target of gene therapy for central nervous system disorders and shares many features with pediatric neurotransmitter diseases. Neurotransmitter replacement therapy using catecholamine-synthesizing genes and delivery of neurotrophic factors such as glial cell line-derived neurotrophic factors has been successful in animal models of Parkinson's disease. Application of gene therapy for pediatric neurotransmitter diseases will require delineating the optimal set of genes to correct the consequences of the deficiencies. The optimal anatomical targets and proper timing of the gene replacement must be understood. Safety of gene therapy vehicles and the ability to regulate gene expression will be essential for eventual clinical application.

Gene therapy for gastric cancer: A review

Gastric cancer is common in China, and its early diagnosis and treatment are difficult. In recent years great progress has been achieved in gene therapy, and a wide array of gene therapy systems for gastric cancer has been investigated. The present article deals with the general principles of gene therapy and then focuses on how these principles may be applied to gastric cancer.

Tyrosine hydroxylase gene expression in ventrolateral medulla oblongata of WKY and SHR: a quantitative real-time polymerase chain reaction study

The aims of this study were, first, to determine quantitatively the levels of tyrosine hydroxylase (TH) gene expression in both peripheral and central sites related to blood pressure regulation, and to compare the level of expression in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Second, to see if any relationship exists between TH gene expression and systolic arterial blood pressure. Total RNA was isolated from adrenal glands and from tissue punches taken from the C1 and A1 cell groups in the rostral and caudal ventrolateral medulla oblongata of the brainstem, respectively. Total RNA was reverse-transcribed into cDNA followed by quantitative fluorescence detection polymerase chain reaction for TH cDNA. The levels of TH gene expression measured as a percentage of the house-keeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in SHR, were significantly higher ( approximately 2.5-fold) compared to WKY in all sites examined (P<0.01). There was a positive and significant relationship between systolic blood pressure and TH gene expression in the C1 area of the brainstem in both WKY (n = 5, P<0.05) and SHR (n=6, P<0.05). Taken together, these results suggest that elevated gene expression of the TH gene is associated with the phenotypic characteristic of SHR.