Chronic one-kidney hypertension in rabbits. I. Treatment with kidney extracts

Development of DNA vaccines as an anti-hypertensive therapy or for anti-angiogenesis

INTRODUCTION

Vaccines are used as preventive medicine for infectious diseases worldwide; however, several recent studies have indicated the potential of therapeutic vaccines for managing Alzheimer's disease or hypertension.

AREAS COVERED

The concept and history of therapeutic vaccines for hypertension are introduced. The improvement of drug compliance associated with vaccines in hypertensive patients may assist in better control of blood pressure, leading to reduced complications. Recently, groups have attempted to develop a therapeutic vaccine against hypertension. The vaccine-induced anti-angiotensin II antibodies can efficiently ameliorate high blood pressure. DNA vaccines have also been designed via a similar strategy using a plasmid vector encoding a hepatitis B core (HBc)-angiotensin II fusion protein. The immunogenic molecule (i.e., HBc) is used to provide an antigen that supports the activation of T cells in this DNA vaccine system. The platform technology can also be applied to generate a VEGF vaccine for cancer.

EXPERT OPINION

To date, several clinical studies of DNA vaccines have been conducted, but their effectiveness has not been determined. We hope that the novel concept of DNA vaccines will contribute to promoting health and medicine in the future.

Peptide Vaccines for Hypertension and Diabetes Mellitus

Vaccines are commonly used as a preventive medicine for infectious diseases worldwide; however, the trial for an amyloid beta vaccine against Alzheimer’s disease will open a new concept in vaccination. In case of therapeutic vaccines for cancer, their targets are usually specific antigens in cancer cells, allowing activated cytotoxic T cells (CTLs) to attach and remove the antigen-presenting cancer cells. In our therapeutic vaccines against hypertension, the target is angiotensin II (Ang II) and induced anti-Ang II antibodies could efficiently ameliorate high blood pressure. Similarly, we developed the therapeutic vaccine against DPP4 for diabetes mellitus. However, because Ang II or DPP4 is an endogenous hormone, we must avoid autoimmune disease induced by these vaccines. Therefore, our system was used to design a therapeutic vaccine that elicits anti-Ang II or DPP4 antibodies without CTL activation against Ang II or DPP4. In this review, we will describe our concept of therapeutic vaccines for hypertension and diabetes mellitus.

Decrease in blood pressure and regression of cardiovascular complications by angiotensin II vaccine in mice

Vaccines have been recently developed to treat various diseases such as cancer, rheumatoid arthritis and Alzheimer’s disease in addition to infectious diseases. However, before use in the clinical setting, vaccines targeting self-antigens must be demonstrated to be effective and safe, evoking an adequate humoral immune response from B cells while avoiding T cell activation in response to self. Although the vaccine targeting angiotensin II (Ang II) is efficient in rodents and humans, little is known regarding the immunological activation and safety of the vaccine. In this study, we evaluated the efficiency and safety of an Ang II peptide vaccine in mice. Immunization with Ang II conjugated to keyhole limpet hemocyanin (KLH) successfully induced the production of anti-Ang II antibody, which blocked Ang II signaling in human aortic smooth muscle cells. However, Ang II itself did not activate T cells, as assessed by the proliferation and lymphokine production of T cells in immunized mice, whereas KLH activated T cells. In an Ang II-infused model, the non-immunized mice showed high blood pressure (BP), whereas the immunized mice (Ang II-KLH) showed a significant decrease in systolic BP, accompanied by significant reductions in cardiac hypertrophy and fibrosis. Importantly, anti-Ang II antibody titer was not elevated even after the administration of large amounts of Ang II, indicating that Ang II itself boosted antibody production, most likely due to less activation of T cells. In addition, no accumulation of inflammatory cells was observed in immunized mice, because endogenous Ang II would not activate T cells after immunization with Ang II-KLH. Taken together, these data indicate that vaccines targeting Ang II might be effective to decrease high BP and prevent cardiovascular complications without severe side effects.

Vaccines in the management of hypertension

IMPORTANCE OF THE FIELD

In the USA only 35% of patients with hypertension achieve adequate blood pressure control. Non-compliance is one of the main barriers to treatment. Vaccine against hypertension is an innovative treatment, injected every 4 - 6 months, to combat non-compliance.

AREAS COVERED IN THIS REVIEW

Pathogenesis of hypertension and progress towards developing a hypertension vaccine, including the virus-like-particle-based approach, new adjuvant molecules and the potential toxicity of hypertension vaccine.

WHAT THE READER WILL GAIN

The pathogenesis of hypertension is multifactorial. The most common cause is disruption of the Renin-angiotensin-aldosterone system (RAAS), and the first vaccine study was carried out against renin. While the vaccine reduced blood pressure in animal models, it also caused autoimmune disease. In the last decade, vaccines against angiotensin I, angiotensin II, and angiotensin II-type 1 receptors have demonstrated acceptable safety profiles in animal and human studies.

TAKE HOME MESSAGE

Reduction in blood pressure can be achieved by inducing immunity against targets in the RAAS. The target antigen and selection of adjuvant are crucial factors determining effectiveness and safety of the vaccine. CYT006-AngQb (angiotensin II vaccine) reduced blood pressure in humans but the results were not reproducible with more frequent dosing. Vaccines for hypertension are still in the early phase. We hope for an effective vaccine for hypertension in the years to come.

Contrasting regression of blood pressure and cardiovascular structure in declipped renovascular hypertensive rats

We investigated the time relationship between changes in blood pressure and changes in the structure of the resistance vasculature. Blood pressure, heart/body weight ratio, and morphology and function of mesenteric resistance arteries from 1-kidney, 1-clip renovascular hypertensive rats were followed before and after declipping at age 14 weeks. The rats were divided into 5 groups, which were investigated 6 hours, 24 hours, 1 week, 4 weeks, and 8 weeks after declipping and compared with 2 normotensive and 2 renovascular hypertensive control groups at 14 weeks and 18 weeks. Systolic blood pressure was elevated 2 weeks after application of the clip and stabilized after 6 weeks. Declipping induced a prompt fall in blood pressure within 6 hours, and blood pressure was normalized within 1 week. Heart/body weight ratio was increased in renovascular hypertensive rats, and declipping induced a gradual decrease in the ratio, which was normalized within 4 weeks. Media/lumen ratio and media area of mesenteric resistance arteries were increased in renovascular hypertensive rats, and declipping did not affect media/lumen ratio and media area within 8 weeks, although there was a tendency for some regression of media/lumen ratio. There were no differences in response to high potassium, noradrenaline, or acetylcholine. Thus, these findings show definitively that declipping causes rapid reversal of renovascular hypertension in rats accompanied by gradual reduction of the heart/body weight ratio but lack of normalization in the mesenteric resistance vessels. This provides clear evidence that neither vascular nor cardiac structural changes are capable of keeping rats hypertensive.

Immunologic approaches to blockade of the renin-angiotensin system: a review

Several immunologic approaches to blockade of the renin-angiotensin system (RAS) have been reported, involving most of the proteins and peptides of the biochemical cascade: renin, substrate, angiotensins, and converting enzyme. None as yet has involved blockade of angiotensin II receptors. Earlier and more recent studies used passive transfer of heterologous antibodies or active immunization against RAS proteins and peptides. Passive transfers have been performed with both polyclonal antibodies and now with specific monoclonal immunoglobulins. The latter are better defined in affinity, quantity, and capacity to bind and thus inhibit the biologic activity of the antigen. Active immunization produced long-term blockade of part or all of the biologic activity of the system. The immunopathologic consequences of the use of antibodies raised against a self-antigen could be of interest in defining the predominant site of storage and secretion of the relevant protein and hence the respective roles of different tissues in the production of specific proteins in, for example, the vascular pulmonary bed for converting enzyme and renal arterial tree for renin. In all cases immunologic methods offer in vivo experimental models of short- or long-term RAS blockade that could be compared with pharmacologic methods, such as converting-enzyme inhibition, angiotensin II antagonists, and renin inhibitors.

The role of renin in the control of the circulation and in hypertensive disease

Renin is a hormone secreted by the juxtaglomerular cells of the kidney; it interacts with a plasma protein substrate to produce a decapeptide prohormone angiotensin I. Converting hormone located on vascular endothelium converts the decapeptide to an octapeptide, angiotensin II, which effects vasoconstriction, the secretion of aldosterone by the adrenal cortex, and retention of sodium by the kidney. The biosynthesis and control of renin secretion are not well understood, and the question as to whether renin is synthesized and stored in a larger precursor form is as yet unresolved. Whether or not higher molecular weight or inactive forms of renin in plasma have a role in controlling renin activity or whether they simply represent a degradative pathway for renin is as yet uncertain. The availability of several inhibitors of the renin-angiotensin system has served to define the role of renin both in normal cardiovascular homeostasis and in renovascular hypertension. It appears that renin plays an important role in maintaining blood pressure in the salt- or volume-depleted state and that it is responsible for the initial phases of renovascular hypertension in any model of this disease process. Renin's part in chronic renovascular hypertension depends on whether or not sodium is permitted to accumulate. If sodium intake is restricted or if sodium excretion is unimpaired (such as in two-kidney renovascular hypertension models), renin continues to play a significant role during the chronic phase.

Angiotensin and sodium balance: their role in chronic two-kidney Goldblatt hypertension

The purpose of this study was twofold: 1) to determine whether the failure of rats with chronic renovascular hypertension to respond to the angiotensin II antagonist (AIIA) with a decrease in mean blood pressure (BP) was dur to the agonistic effect of the antagonist; and, 2) if this was not the case, to examine whether a positive sodium balance impaired the reversal of the hypertension, after unclamping, in the rats that did not respond to angiotensin inhibitors. For this purpose, rats with chronic, two-kidney Goldblatt hypertension (one renal artery clamped and contralateral untouched) were tested for their BP response to the AIIA (1-Sar-8-Ala-angiotensin II) and to the converting enzyme inhibitor (CEI) SQ20,881, which is devoid of agonistic effect. Approximately 50% of the rats responded to both inhibitors either with no change or with a decrease in BP of less than 20 mm Hg (nonresponders). The other 50% had a decrease in BP of 20 mm Hg or greater (responders). The decrease in BP produced by the AIIA and the CEI correlated significantly (r = 0.76). Nonresponders to both inhibitors were unclamped or sham unclamped. A positive sodium balance was produced before surgery by injecting either 400 or 1000 microEq of sodium and was maintained for 12 hours. Direct BP significantly decreased 12 hours after surgery in the unclamped rats despite a continuous positive sodium balance. In the sham unclamped rats, BP did not change. These data indicate that the failure to respond to the AIIA is not due to the agonistic effect of this peptide. Furthermore, these data suggest that a positive sodium balance is not a major pathogenetic factor in maintaining the high BP in the nonresponder rats, since a positive sodium balance failed to maintain the hypertension after unclamping.

Chronic one-kidney hypertension in rabbits. III. Renopressin, a new hypertensive substance

The blood pressure of rabbits with chronic one-kidney hypertension can be lowered to normal by immunization with hog kidney cortex preparations that do not contain renin, thus providing evidence for a new factor essential for the maintenance of an elevated blood pressure. A search for the new factor has led to the discovery of a hypertensive substance which we have named renopressin. Subcutaneous injection of the new substance into normal rabbits produces a delayed, slow increase in blood pressure, and after a few days the development of a moderate hypertension which persists indefinitely. The response of the blood pressure to renopressin is totally unlike that to renin. While the pressor action of renin can be blocked by an angiotensin II antagonist, the hypertension caused by renopressin cannot. Renin can increase the blood pressure of hypertensive rabbits; renopressin has no effect. The blood pressure of hypertensive rabbits and of normal rabbits made hypertensive by injection of renopressin can be lowered to normal by passive immunization with the same antibody preparation. The evidence is consistent with the possibility that renopressin and the agent causing the elevation of blood pressure in hypertensive rabbits are similar or identical.

Chronic one-kidney hypertension in rabbits. II. Evidence for a new factor

The arterial pressure of rabbits with chronic one-kidney hypertension can be lowered to normotensive levels by direct immunization with preparations made from the cortex of hog kidneys. Hypertensive rabbits that are immunized with large amounts of renin may develop high plasma antirenin titers without affecting their blood pressure. Removal of renin by chromatography on columns of immobilized antirenin yields preparations with little or no renin. Such preparations may be effective in lowering blood pressure although they do not elicit the formation of plasma antirenin and the rabbits remain sensitive to challenging doses of rabbit renin. The evidence suggests that an unknown substance is responsible for the development of a cross-reacting antibody that neutralizes an unknown factor that is essential for the maintence of an elevated blood pressure level in rabbits with chronic one-kidney hypertension.

The biochemistry of the renin-angiotensin system and its role in hypertension

The renin-angiotensin system has an important role in maintaining elevated blood pressure levels in certain forms of experimental and human hypertension. Renin, an enzyme produced by the juxtaglomerular cells of the kidney, acts on a protein substrate found in the alpha 2-globulin fraction of the plasma to produce a decapeptide, angiotensin I. This decapeptide is not directly pressor, but on passage through the pulmonary circulation is converted to an octapeptide, angiotensin II, a very potent pressor substance which acts by causing constriction of arteriolar smooth muscle. In addition to its direct action which increases blood pressure, angiotensin II acts on the adrenal cortex to cause the release of the sodium-retaining hormone aldosterone. Recent evidence suggests that this action may be mediated by the heptapeptide, angiotensin III. Both renin and its protein substrate exist in multiple forms and renin may also exist as a high molecular-weight "pro-hormone," although the physiologic significance of these forms is not clear. The elucidation of the biochemistry of the renin-angiotensin system has provided us with inhibitors which allow the system to be blocked effectively in vivo. Thus, angiotensin antagonists such as Sar 1, IIe 8-angiotensin II and converting enzyme inhibitors such as BPP 9a (SQ 20881) have proved useful in the study of experimental and human hypertension.