Angiotensin AT1-receptor blockers and cerebrovascular protection: do they actually have a cutting edge over angiotensin-converting enzyme inhibitors?

First, an update of the vascular systemic and tissue renin-angiotensin-aldosterone system is provided to explain how it is regulated at the systemic and tissue levels, and how many angiotensin peptides and receptors can be modulated by the various antihypertensive drugs. Second, experimental data is presented to support the hypothesis that antihypertensive drugs that increase angiotensin II formation, such as diuretics, AT1-receptor blockers and dihydropyridines, may have greater brain anti-ischemic effects than antihypertensive drugs that decrease angiotensin II formation, such as beta-blockers and angiotensin-converting enzyme inhibitors, because they increase activation of angiotensin AT2 and AT4 receptors. Indeed, these trigger brain anti-ischemic mechanisms by favouring cerebral blood flow (angiogenesis and recruitment of pre-existing collateral circulation, specifically in the ischemic brain where AT2 receptors are overexpressed) or by directly increasing neuronal resistance to anoxia. Third, we review most of the large primary and secondary stroke prevention trials as well as the ACCESS acute stroke trial in which antihypertensive drugs were evaluated. With the exception of the secondary stroke prevention trial PRoFESS, most trials support the hypothesis that angiotensin II-increasing drugs confer specific blood pressure-independent brain ischemia protection when compared with angiotensin II-decreasing drugs or placebo. A careful analysis of the PRoFESS trial, however, reveals study design limitations, the main one being that diastolic BP (<80 mmHg) in the first month post-stroke may have been too low in at least one third of the population with baseline systolic blood pressure less than 130 mmHg, because a high dose of telmisartan was given after a very short post-stroke delay (median 15 days) without discontinuation of the baseline antihypertensive treatment.

Prevention of dementia by antihypertensive drugs: how AT1-receptor-blockers and dihydropyridines better prevent dementia in hypertensive patients than thiazides and ACE-inhibitors.

Our review of cohort studies and clinical trials evaluating antihypertensive drugs in the prevention of cognition decline and all dementia in patients with hypertension indicates that two antihypertensive drug classes have greater protective effects, independent of blood pressure decrease: dihydropyridine calcium-channel blockers as shown in the Syst-Eur trial and angiotensin-AT1 receptor blockers as found in the MOSES and ONTARGET trials. By contrast, diuretics and angiotensin-converting enzyme-inhibitors (ACEIs) prevent dementia only in patients with a stroke history, provided they are combined, and prevent stroke recurrence. A Japanese cohort study and a small trial in patients already suffering from Alzheimer's disease (AD) suggest, however, that the BBB-penetrating ACEI may slow down cognitive decline. Only cohort studies support the hypothesis that diuretics, (especially potassium-sparing diuretics), may decrease the risk of AD. beta-blockers worsen cognition decline, or are neutral, according to whether or not they cross the BBB. Centrally-acting sympatholytic agent have a negative impact on cognition as BBB-penetrating beta-blockers, probably by blunting the adrenergic pathways. The AD protective effect of DHP appears related to the blockade of neuronal calcium channels. The ambiguous effect of ACEI on cognitive decline and dementia prevention may be explained by the fact that brain ACE is not specific for angiotensin-I. Brain ACE also catabolizes cognition-enhancing brain peptides, amyloid peptides and converts toxic Abeta(42) into less toxic Abeta(40). Therefore, ACEIs may have short-term cognition-enhancing properties and may increase in the long term Abeta(42) brain burden and cognitive decline. The clinical relevance of this scenario, mainly observed in animals, cannot be excluded in man, since the ACE gene has been associated with AD via the human whole genome analysis. To support the hypothesized deleterious effect of ACEI on human AD, confirmation that the ACE gene polymorphism DD is associated with protection against AD is necessary, since this polymorphism increases ACE activity. Independently of their preventive impact on beta-amyloid degenerative neuropathological process by overexpressing insulin degrading enzyme which catabolyses amyloid, the angiotensin AT1-receptor-blockers may have greater cognition protective effects than ACEI (observed in the ONTARGET trial), as they share with ACEI cognition-enhancing effects directly linked with a common AT1-blunting effect. In addition, they increase angiotensin II and IV formation and therefore stimulate non-opposed AT2 and AT4 receptors, whose activation in cognitive processes is well established.