Current Pharmaceutical Design - Volume 13, Issue 12, 2007

About three years ago we discussed in this Journal the development of additional potential applications of angiotensin converting enzyme inhibitors and of Angiotensin II (ANG II) receptor blockers in therapy. The deployment of these drugs in the treatment of diverse vascular conditions has been, for many years, a well established medical practice and every year millions of individuals benefit from this treatment. This successful deployment underlines the relevance that the reninangiotensin- aldosterone system (RAAS) plays in the regulation of the control mechanisms of our blood pressure and, more in general, of our homeostasis. It emerged, however, from many articles of that publication that the RAAS system and ANG II in particular, play additional roles in the modulation of our homeostasis such as the regulation of apoptosis, the modulation of cellular growth, specifically of fibroblasts and endothelial cells, and the modulation of angiogenesis. Additional information has been added in the past two-three years to these data. More knowledge also became available about the RAAS system genetic regulation, its interaction with prostaglandins and with other substances also controlling blood pressure, and about the presence and physiological role of another converting enzyme: ACE II. The presence of the various components of the system at local level in several tissues has also become relevant, especially their action on the smooth muscle fibers of the wall of arteries and arterioles of several organs, kidneys, and lungs in particular, or for the apoptotic regulation of many tissues. All these observations open the possibility of the deployment of ACE inhibitors and of A2 receptors antagonists as pharmacological modulators of many diseases other than hypertension. This journal's issue reviews and revises some of the previous experiences with these drugs and deals with some novel applications and deployments of them. Drs. Hamdi and Castellon [1] discuss the role that ACE polymorphism plays with a large number of diseases including cardiovascular, metabolic, immune, cancer, aging, neurodegenerative and psychiatric disorders and they report and summarize these associations. These observations lead to the question why this ACE polylmorphism is associated with so many diseases and what its function is. In the past, much attention has been given to the role that ACE, especially somatic ACE, plays on the synthesis of Angiotensin II in different tissues and on the extensive role that this octapeptide plays in the general homeostasis regulation. ACE, however, has been found to convert many other peptides and the investigation of these functions is extended to test the association of this polymorphism with the levels of other ACE isoenzymes. The experience with various ACE isoforms and their effect on cell's survival may better explain the ACE/ID polymorphism associated with many diseases. Drs. Igic and Behnia [2] report the pharmacological, immunological and genetic targeting of the Renin-Angiotensin system for the treatment of cardiovascular diseases. The investigators present the various components of the Renin Angiotensin system (RAS), discuss the biological activities of angiotensin peptides and the role of the enzymes that generate and metabolize the various types of angiotensin. They devote special attention to the role of Renin, ACE, ACE 2, chymase and neprylysin. Subsequently, on the basis of the experience with ACE inhibitors and type 1 ANG II receptor blockers, they discuss the rationale to target the RAS in its control of general homeostasis. Finally, they present the investigational agents acting on the RAS, which posses a potential for clinical deployment and give the perspective of pharmacological immunological and genetic targeting of the RAS for the treatment of cardiovascular diseases. Dr. Heffelfinger [3] discusses the role of RAS in the regulation of angiogenesis. It is well established that ANGII and bradykinin are angiogenic agents and affect the microvascular circulation. That implies that the ACE inhibition would have an impact on angiogenesis in vivo depending upon which factors are present in the system. The author reviews several conditions such as peripheral ischemia, stroke, retinopathy and cancer in relation to ANGII and bradykinin activity and evaluates the impact that ACE inhibitors posses in all those clinical conditions. It appears that peripheral ischemia and stroke seem to be dependent for angiogenesis regulation by bradykinin signaling, while cancer and retinopathy are more dependent upon ANGII. Published data on in vitro cultures as well in animal models suggest interesting predictions about how the RAS and bradykinin may function in humans and many data are now accumulating in humans confirming the data derived from experimental work. Modulation of angiogenesis by ACE inhibitors and ANG II receptor blockers may become a new therapeutical property of these drugs.........

The angiotensin converting enzyme (ACE) I/D polymorphism has been one of the most studied genetic systems. It comprises hundreds of reports and a myriad of disease associations, including cardiovascular, metabolic, immune, cancer, aging, neurodegenerative and psychiatric diseases. Despite the wealth of information on the ACE polymorphism and the well-known functions of ACE, several questions arise. Why does the ACE polymorphism associate with so many diseases? What is its function? In this review, we summarize the current information on the ACE polymorphism and explain its function in the context of cell survival. We also provide a model to understand its role in biology and disease at the organism and population levels.

Effective blood pressure control with a large arsenal of conventional antihypertensive drugs, such as diuretics, beta-adrenergic blockers, and calcium channel blockers, significantly reduce the morbidity and mortality associated with cardiovascular disease. However, blood pressure control with these drugs does not reduce cardiovascular disease risks to the levels in normotensive persons. Only two drug classes that inhibit or antagonize portions of the renin-angiotensin system (RAS), angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor type-1 (AT1 receptor) blockers, have protective and beneficial effects unrelated to the degree of blood pressure reduction. These drugs may prevent the blood pressure related functional and structural abnormalities of the cardiovascular system and reduce the end organdamage. The first part of this review presents the components of the RAS, biological actions of angiotensin peptides, and the functions of the enzymes that generate and metabolize angiotensins, including the likely effect of manipulating them. Special attention is devoted to renin, ACE, ACE2, chymase, and neprilysin. The second part of this review presents the rationale for targeting the RAS, based on clinical studies of the ACE inhibitors and AT1 receptor blockers. Finally, we present the investigational agents acting on the RAS that have a potential for clinical usage, and give the perspective of pharmacological, immunological and gene targeting of the RAS for treatment of cardiovascular disease.

Decades of experimentation on angiotensin and bradykinin have focused on macrovascular systemic effects. However, angiotensin II and bradykinin are both angiogenic agents, highlighting their ability to also effect the microvascular circulation. Not surprisingly, inhibition of angiotensin converting enzyme, which inhibits angiotensin II synthesis and bradykinin degradation, would have different impacts on angiogenesis in vivo dependent upon what factors were present in the system. Several pathological states in which angiogenesis is important, including peripheral ischemia, stroke, retinopathy, and cancer are examined in this review with respect to activity of angiotensin II and bradykinin and the impact of angiotensin converting enzyme inhibition. Although generalizations are not without legitimate criticism, one can think about peripheral ischemia and stroke as being more dependent upon bradykinin signaling and retinopathy and cancer as more dependent upon angiotensin II signaling to drive angiogenesis. Many exceptions are found that are specific to individual animal model systems. Furthermore, cancer systems that have been examined at any depth are few. However, published data on in vitro cultures and animal models present interesting predictions about how the renin angiotensin and bradykinin systems may function in humans. Since angiotensin converting enzyme inhibitors have been widely utilized pharmaceuticals for many years, we are now accumulating epidemiological data that test our predictions. The importance of understanding which agent, angiotensin and/or bradykinin, appears to be the more important regulator of angiogenesis in a given pathology will become increasing evident as more specific angiotensin II and bradykinin receptor blocking drugs make their way into clinical use.

The implication of the renin-angiotensin system (RAS) in the regulation of the cardiovascular system has been well known for many years. Accordingly, many pharmaceutical inhibitors have been developed to treat several pathologies, like hypertension and heart failure, and angiotensin converting enzyme (ACE) became one of the major target in the treatment of these cardiovascular diseases. In the last decade however, it has become apparent that the classical view of the RAS was not quite accurate. For instance, ACE has been shown to work not only by generating angiotensin-II but also by interacting with receptors outside the renin-angiotensin system. Moreover, it has been shown that many local RAS are present in different tissues, such as the heart, brain, kidney and vasculature. However, in the past, it was impossible to determine the role of these local systems as they were pharmacologically indistinguishable from the systemic RAS. Hence, in recent years, the development of transgenic animals has allowed us to determine that these local systems are implicated in the roles that had been originally attributed exclusively to the systemic action of the RAS. However, with almost 30% of the medicated hypertensive patients harboring an uncontrolled blood pressure, a need for new drugs and new targets appears necessary. With the new century came the discovery of a new homolog of ACE, called ACE2, and early studies suggest that it may play a pivotal role in the RAS by controlling the balance between the vasoconstrictor effects of angiotensin- II and the vasodilatory properties of the angiotensin1-7 peptide. Like ACE, ACE2 appears to hydrolyze peptides not related with the RAS and the enzyme has also been identified as a receptor for the severe acute respiratory syndrome (SARS) coronavirus. Although the tissue localization of ACE2 was originally though to be very restricted, new studies have emerged showing a more widespread distribution. Therefore, the whole dynamics of the RAS has to be re-evaluated in light of this new information. In this review, we will compare the structures, distributions and properties of ACE and its new homologue in the context of cardiovascular function, focusing on the autocrine/paracrine cardiac and brain renin-angiotensin systems and we will present recent data from the literature and our laboratory offering a new perspective on this potential target for the treatment of cardiovascular diseases.

Angiotensin II (ANGII) has been identified as a proapoptotic and profibrotic factor in experimental lung fibrosis models, and patients with the ID/DD polymorphism of ANG converting enzyme (ACE), which confers higher levels of ACE, are predisposed to lung fibrosis (Hum. Pathol. 32:521-528, 2001). Previous work from this laboratory has shown that human lung myofibroblasts isolated from patients with Idiopathic Pulmonary Fibrosis (IPF) synthesize the ANGII precursor angiotensinogen (AGT) constitutively. In attempts to understand the mechanisms and consequences of constitutive AGT synthesis by myofibroblasts, we studied myofibroblast-rich primary cultures of lung fibroblasts from patients with IPF (HIPF isolates), primary fibroblasts from normal human lung (NLFs), the IMR90 and WI38 human lung fibroblasts cell lines, and paraffin sections of lung biopsies from patients with IPF. Compared to the normal NLF isolates, HIPF primary fibroblast isolates constitutively synthesized more AGT and TGF-β1 mRNA, and released more AGT protein, ANGII and active TGF-β1 protein into serum-free conditioned media (both p<0.01). Incubation of HIPF fibrotic isolates with the ANGII receptor antagonist saralasin reduced both TGF-β1 mRNA and active protein, suggesting that the constitutive expression of AGT drives the higher expression of TGF-β1 by the HIPF cells. Consistent with this premise, treatment of either the primary NLFs or the WI38 cell line with 10-7M ANGII increased both TGF-β1 mRNA and soluble active TGF-β1 protein. Moreover, induction of the myofibroblast transition in the IMR90 cell line with 2ng/ml TGF-??1 increased steady state AGT mRNA levels by realtime PCR (8-fold, p<0.01) and induced expression of an AGT promoterluciferase reporter construct by over 10-fold (p<0.001). Antisense oligonucleotides against TGF-β1 mRNA or TGF-β neutralizing antibodies, when applied to the fibrotic HIPF cells in serum-free medium, significantly reduced AGT expression. In lung sections from IPF patient biopsies, immunoreactive AGT/ANGI proteins were detected in myofibroblasts, epithelial cells and presumptive alveolar macrophages. Together, these data support the existence of an angiotensin/TGF- β1 “autocrine loop” in human lung myofibroblasts and also suggest ANG peptide expression by epithelia and macrophages in the IPF lung. These findings may explain the ability of ACE inhibitors and ANG receptor antagonists to block experimental lung fibrosis in animals, and support the need for evaluation of these agents for potential treatment of human IPF. This manuscript discusses the data described above and their implications regarding IPF pathogenesis.

Apoptosis of alveolar epithelial cells (AECs) is believed to be critical for the development of bleomycin (BLEO)-induced pulmonary fibrosis. Previous studies showed that apoptosis of alveolar epithelial cells in response to BLEO could be abrogated by antisense oligonucleotides against angiotensinogen (AGT) mRNA and requires angiotensin II (ANG II) synthesis de novo [17]. In this study we hypothesized that blockade of local pulmonary ANG II synthesis by intratracheal (I.T.) administration of antisense oligonucleotides against AGT mRNA might attenuate BLEO-induced apoptosis of AECs and prevent pulmonary fibrosis. In a BLEO-induced rat model of lung fibrosis, endogenous lung AGT was upregulated in vivo as early as 3 hours after BLEO instillation, as detected by RT-PCR, in situ hybridization and immunohistochemistry. AGT mRNA and angiotensin peptides were localized in type II alveolar epithelial cells and also colocalized with alpha-smooth muscle actin (β-SMA), a marker of myofibroblasts. Tagged antisense administered I.T. was specifically accumulated by the lung relative to liver and kidney, and localized primarily in the epithelium of airways and cells within alveolar walls. The intratracheal AGT antisense reduced BLEO-induced pulmonary fibrosis measured by lung hydroxyproline assay, decreased lung AGT and active caspase-3 proteins, and reduced the number of apoptotic epithelial cells but had no effect on the serum ANG II concentration. These data are consistent with the hypothesis that lung-derived AGT and local pulmonary ANG II are required for BLEO-induced pulmonary fibrosis, and suggest the possibility of antisense-based manipulation of the local angiotensin system as a potential treatment of fibrotic lung diseases.

Nicotine, the major psychoactive agent present in tobacco, acts as a potent addictive drug both in humans and laboratory animals, whose locomotor activity is also stimulated. A large body of evidence indicates that the locomotor activation and the reinforcing effects of nicotine may be related to its stimulatory effects on the mesolimbic dopaminergic function. Thus, it is now well established that nicotine can increase in vivo DA outflow in the nucleus accumbens and the corpus striatum. The stimulatory effect of nicotine on DA release most probably results from its ability to excite the neuronal firing rate and to increase the bursting activity of DA neurons in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), and from its stimulatory action on DA terminals in the corpus striatum and the nucleus accumbens. The neurochemical data are consistent with neuroanatomical findings showing the presence of nicotinic acetylcholine receptors (nAChRs) in the SNc, the VTA, and in projection areas of the central dopaminergic system such as the corpus striatum and the nucleus accumbens. Several lines of evidence indicate that the reinforcing properties of drugs of abuse, including nicotine, can be affected by a number of transmitter systems which may act by modulating central dopaminergic function. In this paper, the neurobiological mechanisms underlying nicotine addiction will be reviewed, and the possible strategies for new pharmacological treatments of nicotine dependence will be examined.

Human T-cell leukemia virus type-1 (HTLV-1) is associated with a number of human diseases. Although the mechanism by which the virus causes diseases is still not known, studies indicate that viral replication is critical for the development of HTLV-1 associated myelopathy, and initial studies suggested that blocking replication with reverse transcriptase inhibitors had a therapeutic effect. Therefore, based on the success of HIV-1 protease inhibitors, the HTLV-1 protease is also a potential target for chemotherapy. Furthermore, mutated residues in HIV-1 protease that confer drug resistance are frequently seen in equivalent positions of other retroviral proteases, like HTLV-1 protease. Therefore, comparison of HTLV-1 and HIV-1 proteases is expected to aid the rational design of broad spectrum inhibitors effective against various retroviral proteases, including the mutant HIV-1 enzymes appearing in drug resistance. This review describes the characteristics of HTLV-1 protease, makes comparison with HIV-1 protease, and discusses the status of inhibitor development for the HTLV-1 protease.