Hypertension is a health public problem. Inhibitors of angiotensin converting enzyme (ACE) are widely used for treatment of hypertension. These effects may be due to decreasing the activation of the renin angiotensin aldosterone system (RAAS). Evidences have shown that ACE inhibitors (ACEi) are antioxidant through of the reduction in the formation of angiotensin II. This peptide may promote increased formation of reactive oxygen species (ROS) mainly by activate b-nicotinamide adenine dinucleotide phosphate (NADPH) oxidase pathways. In addition, there are other effects induced by ACEi, as inhibition of extracellular matrix metalloproteinases (MMPs), which seems to be associated with benefits effects in the antihypertensive therapies. In this regard, non-specific inhibitors of MMPs, such as doxycycline, have been suggested as important pharmacological tools for cardiovascular diseases treatment. Studies have indicated that doxycycline attenuated the hypertension-induced cardiac and vascular alterations or other disorders such as like myocardial infarction. Besides inhibiting MMPs, doxycycline has antioxidant effects which may to contribute to the beneficial effects shown in several studies. Based on the importance and the benefits of doxycycline treatment in cardiovascular disease more studies are required to elucidate this antioxidant mechanism that remain totally unclear. At this sense, some evidences have shown biochemical similarities between doxycycline and ACEi suggesting a possible ACE inhibition mediated by doxycycline. For example, ACEi may inhibit MMPs by direct interaction with these proteases, like doxycycline. Moreover, and more sustained in the literature, doxycycline is a chelating of divalent metals, such as calcium and zinc, which are essential for the activity of ACE. Because of these similarities and due to doxycycline-induced antioxidant in hypertensive rats, we hypothesized that doxycycline is able to inhibit ACE, decreasing the activity of NADPH oxidase (induced by activation of the RAAS), promoting the reduction in ROS formation that was evidenced in previous studies. To examine this hypothesis, plasma and aorta samples will be collected from 2-kidney and 1-clip (2K1C) hypertensive rats treated with doxycycline or with vehicle for 4 weeks. In these samples will be evaluated: (1) ACE activity vascular and systemic, and (2) NADPH oxidase activity. Furthermore, the plasma of hypertensive rats treated with vehicle will be used to assess the possible doxycycline propriety in inhibit ACE in vitro assay (incubating directly in the plasma of these animals, suggests that it could inhibit ACE due to its ability to chelate zinc).
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