Attenuation of the development of hypercholesterolemic atherosclerosis by thymoquinone

Abstract

Thymoquinone (TQ), derived from Nigella sativa seed, is an antioxidant. The present study investigated whether TQ attenuates the development of atherosclerosis, and/or reduces the serum lipid levels and oxidative stress in rabbits. New Zealand white female rabbits were assigned to four groups of six animals each: group I, control; group II, 1% cholesterol diet; group III, 1% cholesterol plus TQ (10 mg/kg/day; through a nasogastric tube) diet; and group IV, 1% cholesterol plus TQ (20 mg/kg/day; through a nasogastric tube) diet. Blood samples were collected at baseline and after four and eight weeks on the experimental diets for measurement of serum lipids, total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), TC/HDL-C ratio and oxidative stress biomarkers (malondialdehyde [MDA] and protein carbonyls). At the end of the eight weeks, the aorta was removed for the assessment of atherosclerotic changes, MDA and protein carbonyls. Group II animals developed atherosclerosis (45%±11% of the intimal surface of aorta was covered with atherosclerotic plaques), which was associated with an increase in the serum TC, TG, LDL-C, HDL-C, TC/HDL-C, MDA and protein carbonyls. In group III, TQ decreased serum TC, LDL-C, MDA and protein carbonyls by 26%, 29%, 85% and 62%, respectively, and aortic MDA by 73%, which was associated with a 40% reduction of the development of aortic atherosclerosis. The higher dose of TQ in group IV had effects similar to the lower dose (group III), except that this dose further decreased serum TG. It is concluded that TQ attenuates hypercholesterolemic atherosclerosis and this effect is associated with a decrease in serum lipids and oxidative stress.

Figures

Figure 1)

Sequential changes in serum total cholesterol (TC) and triglycerides (TG) in the four groups. Results are expressed as mean ± SD. Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day. aP<0.05, zero time versus four and eight weeks in the respective groups; bP<0.05, group I versus other groups; cP<0.05, group II versus groups III or IV; dP<0.05, group III versus group IV

Figure 2)

Sequential changes in serum low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) in the four experimental groups. Results are expressed as mean ± SD. Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day. aP<0.05, zero time versus four and eight weeks in the respective groups; bP<0.05, group I versus other groups; cP<0.05, group II versus groups III or IV

Figure 3)

Sequential changes in total cholesterol (TC)/high-density lipoprotein cholesterol (HDL-C) ratio and serum malondialdehyde (MDA) in the four experimental groups. Results are expressed as mean ± SD. Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day. aP<0.05, zero time versus four and eight weeks in the respective groups; bP<0.05, group I versus other groups; cP<0.05, group II versus groups III or IV; eP<0.05, group IV versus other groups

Figure 4)

Representative photographs of the intimal surfaces of aortas from the four experimental groups showing Sudan IV-stained lipid deposits (dark staining in groups II, III and IV). Note the difference between the extent of atherosclerosis between group II and groups III and IV. Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day

Figure 5)

Representative photographs of the microscopic changes from the four groups stained with hematoxylin and eosin. Note the normal arterial wall structure in group I (original magnification ×10), the increased intimal thickness in group II that involves most of the aortic circumference and the lesser thickness that involves much smaller portions of the aortic circumference in groups III and IV (original magnification ×4). Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day

Figure 6)

Representative photographs of the microscopic changes from the four groups stained with elastic fibre stain. Note the black-stained elastic fibres, the relatively well-defined internal elastic lamina (IEL) and the poorly defined external elastic lamina (EEL) (original magnification ×4). Group I: normal diet; group II: 1% cholesterol diet; group III: 1% cholesterol diet plus thymoquinone 10 mg/kg/day; group IV: 1% cholesterol diet plus thymoquinone 20 mg/kg/day