Abstract P423: Chronic Doxycycline Administration Inhibits Angiotensin Converting Enzyme Activity and Exerts Antioxidants Effects in Renovascular Hypertensive Rats

Abstract

Doxycycline (Dox), an established matrix metalloproteinase (MMP) inhibitor, and angiotensin-converting enzyme inhibitors (ACEi) present beneficial cardiovascular effects which could be consequence of their antioxidants properties. Furthermore, some evidences have shown other biochemical similarities between Dox and ACEi suggesting that Dox could also inhibit ACE and ACEi directly interact with MMPs and inhibit these proteases. Supporting this idea, Dox is able to chelate divalent metals, such as calcium and zinc, which are essential for the ACE activity. In this regard, we hypothesized that Dox inhibits ACE activity in hypertensive rats which leads to a reduction in ROS production and decrease hypertension. Sham-operated or 2K1C hypertensive rats were treated with Dox (30 mg/Kg/day) or water for 4 weeks. Systolic blood pressure (SBP) was monitored weekly. Dox treatment reduced SBP in 2K1C rats from 200±12 mmHg to 158±8 mmHg (P<0.05). In addition, Dox treatment attenuated reactive oxygen species (ROS) levels in hypertensive animals measured by lucigenin chemiluminescense (in RLU/mg of aorta: from 711±1.0 to 377±93; P<0.05). ACE activity in aorta was increased in untreated 2K1C rats (22±0.8 nmols/min/g) when compared with the Sham group (12±1.0 nmols/min/g; P<0.05) and Dox treatment was able to reduce ACE activity in 2K1C rats (15±2.0 nmols/min/g; P<0.05). To evaluate whether Dox inhibits ACE activity in vitro , aortic tissues from 2K1C rats were incubated with Dox or Captopril (a known ACEi ). Dox in vitro did not affect ACE activity while captopril inhibited 80% of its activity. To verify whether Dox could inhibit ACE activity in vivo , an acute assay was performed with different doses of angiotensin I (in μg/Kg: 0.03, 0.3 and 3), after the single administration of Dox or saline (i.p.). Angiotensin I infusion increased mean arterial pressure dose-dependently and Dox pretreatment did not attenuated these increases significantly (P>0.05) as Captopril.Taken together, these results show that chronic treatment with Dox inhibits ACE activity in aorta of 2K1C rats, which contribute to ROS reduction and SBP attenuation. However, the mechanism by which Dox inhibits ACE activity needs further investigation.