Angiotensinogen gene knockout delays and attenuates cold-induced hypertension

Prolonged attenuation of cold-induced hypertension by adenoviral delivery of renin antisense

BACKGROUND

Renin has been linked to the pathogenesis of some forms of hypertension, including cold-induced hypertension (CIH). Although several antihypertensive drugs that inhibit angiotensin-converting enzyme (ACE) and angiotensin II (Ang II) type 1 (AT(1)) receptors are available, they are short-lasting and have side effects. Inhibition of renin [the first and rate-limiting step of the renin-angiotensin system (RAS)] would provide an inhibition of the entire RAS. Thus, we developed an antisense approach for specific inhibition of renin based on the genetic design. The objective of this study was to test our hypothesis that adenoviral delivery of renin antisense inhibits renin and attenuates CIH.

METHODS

Recombinant adenoviruses carrying rat renin antisense (rAdv.RRA) and LacZ reporter gene (rAdv.LacZ) were constructed and used for in vivo gene transfer via intravenous injection. Four groups of rats were used (six rats/group). Blood pressure did not differ among the four groups during the control period at room temperature (25 degrees C). Two groups of rats received rAdv.RRA (2.5 x 10(9) pfu/rat, intravenously), while the other two groups received the same dose of rAdv.LacZ and served as controls. After gene delivery, one rAdv.LacZ-treated and one rAdv.RRA-treated group were exposed to cold (5 degrees C), while the remaining groups were kept at 25 degrees C. Blood pressure was monitored weekly during cold exposure. A 24-hour urine sample was collected during weeks 1, 3, and 5 for measuring urinary aldosterone excretion. At the end of week 5, all animals were killed and blood was collected for measurement of plasma renin activity (PRA), total plasma renin, plasma active renin, and plasma aldosterone. Vascular Ang II contents were measured in all rats.

RESULTS

Blood pressure of the rAdv.LacZ-treated group rose significantly within 2 weeks of exposure to cold and reached 158.2 +/- 6.4 mm Hg by week 5. In contrast, blood pressure (117.1 +/- 5.3 mm Hg) of the cold-exposed group treated with rAdv.RRA did not increase until 5 weeks after exposure to cold. Thus, a single dose of rAdv.RRA prevented CIH for at least 5 weeks. rAdv.RRA abolished the cold-induced increases in PRA, total plasma renin, plasma active renin, vascular Ang II, and plasma and urine aldosterone, indicating effective inhibition of the entire RAS.

CONCLUSION

rAdv.RRA effectively inhibited the entire RAS and produced prolonged attenuation of CIH. Antisense inhibition of renin may be a novel and ideal approach for long-term control of hypertension.

Human eNOS gene delivery attenuates cold-induced elevation of blood pressure in rats

We previously showed that chronic cold exposure inhibits endothelial nitric oxide synthase (eNOS) expression and decreases nitric oxide (NO) production. The aim of the present study was to evaluate the possible role of the NO system in the development of cold-induced hypertension (CIH) by testing the hypothesis that adenoviral delivery of human eNOS gene increases NO production and attenuates CIH in rats. The effect of in vivo delivery of adenovirus carrying human eNOS full-length cDNA (rAdv.heNOS) on CIH was tested using four groups of Sprague-Dawley rats (6 rats/group). Blood pressure (BP) did not differ among the four groups during the control period at room temperature (24 degrees C). Two groups of rats received intravenous injection of rAdv.heNOS (1 x 10(9) plaque-forming units/rat), and the other two groups received the same dose of rAdv.LacZ to serve as controls. After gene delivery, one rAdv.heNOS-treated group and one rAdv.LacZ-treated group were exposed to cold (6 degrees C) while the remaining groups were kept at 24 degrees C. We found that the BP of the rAdv.LacZ group increased significantly within 1 wk of exposure to cold and reached a peak level at week 5 (152.2 +/- 6.4 mmHg). In contrast, BP (118.7 +/- 8.4 mmHg) of the cold-exposed rAdv.heNOS group did not increase until 5 wk after exposure to cold. The rAdv.heNOS increased plasma and urine levels of NO significantly in cold-exposed rats, which indicates that eNOS gene transfer increased NO production. Notably, rAdv.heNOS decreased plasma levels of norepinephrine and plasma renin activity in cold-exposed rats, which suggests that eNOS gene transfer may decrease the activities of the sympathetic nervous system and the renin-angiotensin system. Immunohistochemical analysis showed that the transferred human eNOS was expressed in both endothelium and adventitia of mesenteric arteries. We conclude that 1) eNOS gene transfer attenuates CIH by increasing NO production and inhibiting the sympathetic nervous system and the renin-angiotensin system; and 2) the NO system appears to mediate this nongenetic, nonpharmacological, nonsurgical model of hypertension.

Historic perspectives and recent advances in major animal models of hypertension

Hypertension and related cardiovascular diseases are the leading causes of death in many countries. The etiology of human essential hypertension is largely unknown. It is highly likely that hypertension is a complex and multifactorial disease resulting from the interaction of multiple genetic and environmental factors. Animal models of hypertension have been proved to be useful to study the pathogenesis of, and to find a new therapy for, hypertension. The aim of this article is to briefly review the most widely used rodent models of experimental hypertension, including history and recent advances. These models are classified as genetically-induced, environmentally-induced, pharmacologically-induced, and renal-induced hypertension according to the way of induction; the typical representatives of each of these major types of experimental hypertension are spontaneous hypertension, cold-induced hypertension, DOCA-salt-induced hypertension, and renal-induced hypertension, respectively. The processes of induction of hypertension, possible pathogenesis, characteristics, advantages, and limitations of these animal models are reviewed. In addition, the clinical implications of the above experimental models of hypertension are addressed.

Genetic AT1Areceptor deficiency attenuates cold-induced hypertension

The aim of this study was to test our hypotheses that AT1Areceptors play a role in the pathogenesis of cold-induced hypertension (CIH) and in the cold-induced increase in drinking responses to ANG II. Two groups of wild-type (WT) and two groups of AT1Areceptor gene knockout (AT1A-KO) mice were used (6/group). Blood pressures (BP) of the four groups were similar during the control period at room temperature (25°C). After the control period, one group of WT and one group of AT1A-KO mice were exposed to cold (5°C), while the remaining groups were kept at 25°C. BP of the cold-exposed WT group elevated significantly within 1 wk of exposure to cold and increased gradually to a maximum level by week 5. However, there was only a slight increase in BP of the cold-exposed AT1A-KO group. The maximal cold-induced increase in BP (ΔBP) is significantly less in AT1A-KO group (11 ± 3 mmHg) than in WT group (49 ± 6 mmHg), indicating that AT1Areceptor deficiency attenuates cold-induced elevation of BP. Interestingly, both WT and AT1A-KO mice developed cardiac and renal hypertrophy to the same extent. AT1A-KO caused a significant increase in urine and plasma levels of nitric oxide (NO), indicating that the renin-angiotensin system inhibits NO formation probably via AT1Areceptors. Cold exposure inhibited endothelial NO synthase protein expressions and decreased urine and plasma levels of NO, which may be mediated partially by AT1Areceptors. AT1A-KO completely abolished the cold-induced increase in drinking responses to ANG II. We conclude that 1) AT1Areceptors play an essential role in the pathogenesis of CIH but not cardiac hypertrophy; 2) the role of AT1Areceptors in CIH may be mediated partially by its inhibitory effect on the NO system; and 3) cold-induced increase in drinking response to ANG II is mediated by AT1Areceptors.

Expression of human eNOS in cardiac and endothelial cells

In this chapter we provide a detailed technique-focused protocol for expression of human endothelial nitric oxide synthase (eNOS) gene delivered by replication-deficient adenovirus. It includes construction of recombinant plasmid with human eNOS gene full-length cDNA (heNOS), packaging of adenovirus with heNOS (Adv-heNOS) in 293 cells, confirmation of Adv-heNOS, amplification of high-titer stockAdv-heNOS, determination of the Adv-heNOS titer, expression of Adv-heNOS in the human abdominal aorta endothelial (HAAE1) cell line and rat heart myoblast cell line (H9C2), and measurement of human eNOS activity and NO production.

Effect of ambient temperature on cardiovascular parameters in rats and mice: a comparative approach

Ambient air temperatures (T(a)) of <6 degrees C or >29 degrees C have been shown to induce large changes in arterial blood pressure and heart rate in homeotherms. The present study was designed to investigate whether small incremental changes in T(a), such as those found in typical laboratory settings, would have an impact on blood pressure and other cardiovascular parameters in mice and rats. We predicted that small decreases in T(a) would impact the cardiovascular parameters of mice more than rats due to the increased thermogenic demands resulting from a greater surface area-to-volume ratio in mice relative to rats. Cardiovascular parameters were measured with radiotelemetry in mice and rats that were housed in temperature-controlled environments. The animals were exposed to different T(a) every 72 h, beginning at 30 degrees C and incrementally decreasing by 4 degrees C at each time interval to 18 degrees C and then incrementally increasing back up to 30 degrees C. As T(a) decreased, mean blood pressure, heart rate, and pulse pressure increased significantly for both mice (1.6 mmHg/ degrees C, 14.4 beats.min(-1). degrees C(-1), and 0.8 mmHg/ degrees C, respectively) and rats (1.2 mmHg/ degrees C, 8.1 beats.min(-1). degrees C(-1), and 0.8 mmHg/ degrees C, respectively). Thus small changes in T(a) significantly impact the cardiovascular parameters of both rats and mice, with mice demonstrating a greater sensitivity to these T(a) changes.