Synergistic vascular protective effects of combined low doses of PPARalpha and PPARgamma activators in angiotensin II-induced hypertension in rats

Abstract

Background and purpose: Protective cardiovascular effects of peroxisome proliferator activated receptor (PPAR)alpha and PPARgamma activators have been demonstrated. If used as vasoprotective agents in high risk vascular patients rather than for their metabolic benefits, these agents could be associated with unwanted side effects. As a proof of concept to support the use of combined low doses of PPARalpha and PPARgamma as vascular protective agents in high risk vascular patients, we tested the hypothesis that combined low doses of PPARalpha (fenofibrate) and PPARgamma (rosiglitazone) activators would provide vascular protective benefits similar to full individual doses of these PPAR agonists.

Experimental approach: Male Sprague-Dawley rats infused with Ang II (120 ng kg(-1) min(-1)) were treated with rosiglitazone (1 or 2 mg kg(-1) day(-1)) alone or concomitantly with fenofibrate (30 mg kg(-1) day(-1)) for 7 days. Thereafter, vessels was assessed on a pressurized myograph, while NAD(P)H oxidase activity was determined by lucigenin chemiluminescence. Inflammation was evaluated using ELISA for NFkappaB and Western blotting for adhesion molecules.

Key results: Ang II-induced blood pressure increase, impaired acetylcholine-induced vasorelaxation, altered vascular structure, and enhanced vascular NAD(P)H oxidase activity and inflammation were significantly reduced by low dose rosiglitazone+fenofibrate.

Conclusions and implications: Combined low doses of PPARalpha and PPARgamma activators attenuated development of hypertension, corrected vascular structural abnormalities, improved endothelial function, oxidative stress, and vascular inflammation. These agents used in low-dose combination have synergistic vascular protective effects. The clinical effects of combined low-dose PPARalpha and PPARgamma activators as vascular protective therapy, potentially with reduced side-effects and drug interactions, should be assessed.

Figure 1

Radio-telemetry analysis of mean BP over 7 days. Values are means±s.e.m., n=6 animals per group. Mean BP shown in (a) are from rats treated with saline (Ctrl), Ang II, fenofibrate (Feno) and different combinations of 2 mg kg⁻¹ day⁻¹ of rosiglitazone (Rosi-2). Mean BP shown in (b) are from rats treated with saline (Ctrl), Ang II, Feno and different combinations of 1 mg kg⁻¹ day⁻¹ of rosiglitazone (Rosi-1). ^*P<0.05 Ang II vs CTRL, Rosi-2+Feno and Ang+ Rosi-2+ Feno on day 7; ^†P<0.05 Ang II vs. CTRL and Rosi-1+Feno on day 7 (one-way ANOVA followed by Newman–Keuls test).

Figure 2

Endothelial function in mesenteric resistance arteries. Concentration–response curves to acetylcholine (ACh). Relaxation responses are % increase in lumen after noradrenaline precontraction. Values are means±s.e.m., n=5–6 animals/group. Concentration response curves shown in (a) are from rats treated with saline, Ang II, fenofibrate (Feno) and different combinations of 2 mg kg⁻¹ day⁻¹ of rosiglitazone (Rosi-2). Concentration response curves shown in (b) are from rats treated with saline, Ang II, fenofibrate (Feno) and different combinations of 1 mg kg⁻¹ day⁻¹ of rosiglitazone (Rosi-1). ^*P<0.05 vs Ang+Feno, Ang +Rosi-1, Rosi-2+Feno and Rosi-1+Feno; ^†P<0.01 vs CTRL (one-way repeated-measures ANOVA followed by Newman–Keuls test).

Figure 3

Role of oxidative stress in ACh-induced relaxation. Inhibition exerted by L-NAME on maximal relaxing response of mesenteric resistance arteries to ACh in the absence (saline, white bars) and in the presence of vitamin C (black bars). Values are means±s.e.m., n=6–7 animals per group. ^*P<0.05 vs saline of all other groups; ^†P<0.05 vs saline Ang II (two-way ANOVA followed by Newman–Keuls test).

Figure 4

NAD(P)H oxidase activity in mesenteric resistance arteries of all groups. Values are means±s.e.m., n=6–8 animals per group. ^*P<0.001 vs controls; ^†P<0.05 vs Ang II (one-way ANOVA followed by Newman–Keuls test).

Figure 5

NFκB activity (a and b) and VCAM-1 expression (c and d) in mesenteric arteries and aorta, respectively, of all groups. Top panels are representative blots, whereasile bottom panels are values represented as means±s.e.m., n=6–8 animals per group. ^*P<0.01 vs controls, Rosi-1+Feno and Rosi-2+Feno; ^†P<0.05 vs. Ang II; ^‡P<0.05 vs controls (one-way ANOVA followed by Newman–Keuls test).