Involvement of inflammation and adverse vascular remodelling in the blood pressure raising effect of repeatedly heated palm oil in rats

Abstract

Oil thermoxidation during deep frying generates harmful oxidative free radicals that induce inflammation and increase the risk of hypertension. This study aimed to investigate the effect of repeatedly heated palm oil on blood pressure, aortic morphometry, and vascular cell adhesion molecule-1 (VCAM-1) expression in rats. Male Sprague-Dawley rats were divided into five groups: control, fresh palm oil (FPO), one-time-heated palm oil (1HPO), five-time-heated palm oil (5HPO), or ten-time-heated palm oil (10HPO). Feeding duration was six months. Blood pressure was measured at baseline and monthly using tail-cuff method. After six months, the rats were sacrificed and the aortic arches were dissected for morphometric and immunohistochemical analyses. FPO group showed significantly lower blood pressure than all other groups. Blood pressure was increased significantly in 5HPO and 10HPO groups. The aortae of 5HPO and 10HPO groups showed significantly increased thickness and area of intima-media, circumferential wall tension, and VCAM-1 than other groups. Elastic lamellae were disorganised and fragmented in 5HPO- and 10HPO-treated rats. VCAM-1 expression showed a significant positive correlation with blood pressure. In conclusion, prolonged consumption of repeatedly heated palm oil causes blood pressure elevation, adverse remodelling, and increased VCAM-1, which suggests a possible involvement of inflammation.

Figure 1

Blood pressure in all groups during the study period. Data are expressed as mean ± SEM. FPO, fresh palm oil: 1HPO, one-times-heated palm oil: 5HPO five-time-heated palm oil; 10HPO ten-time-heated palm oil. *P < 0.05 between pre- and posttreatment values for the same group; ^# P < 0.05 versus control; ^† P < 0.05 versus FPO; ^‡ P < 0.05 versus 1HPO.

Figure 2

Photomicrographs of aortic sections stained with Verhoeff-Van Gieson. Groups are as follows: (a) control rats; rats fed, (b) fresh (FPO), (c) one-time-heated (1HPO), (d) five-time-heated (5HPO), or (e) ten-time-heated palm oil (10HPO). Thickened tunica media is observed in 5HPO and 10HPO groups [(d) and (e)], with an increased interlamellar space when compared to the control and FPO groups [(a) and (b)]. Disorganisation and fragmentation of the elastic lamellae were also observed in 5HPO and 10HPO (arrow, (d) and (e)). L: lumen; TI: tunica intima; TM: tunica media; TA: tunica adventitia. Same magnification is applied to all pictures (×200). Calibration bar = 50 μm.

Figure 3

Endothelial VCAM-1 expression in rats. Data are expressed as mean ± SEM. FPO, fresh palm oil; 1HPO, one-time-heated palm oil; 5HPO, five-time-heated palm oil; 10HPO, ten-time-heated palm oil. *P < 0.05 versus control, FPO, and 1HPO.

Figure 4

Photomicrographs of aortic sections showing immunostaining for VCAM-1. Groups are as follows: (a) control rats; rats fed (b) fresh (FPO), (c) one-time-heated (1HPO), (d) five-time-heated (5HPO), or (e) ten-time-heated palm oil (10HPO). Aortic sections from rats fed 5HPO and 10HPO showed an intense staining of VCAM-1 on the tunica intima [(d) and (e)]. In contrast, aortic sections from rats fed FPO and 1HPO showed relatively little staining of VCAM-1 [(b) and (c)] compared to control (a). TI: tunica intima; TM: tunica media. Same magnification is applied to all pictures (×400). Calibration bar = 50 μm.

Figure 5

Correlation between blood pressure and endothelial VCAM-1 expression in rats.