5. Discussion
The results of this study showed that NS oil supplementation at 1000 mg/day dosage had no significant effect on serum levels of leptin and adiponectin. Also our finding showed Nigella sativa oil supplementation no significant effect on systolic and diastolic blood pressure among patients with non-alcoholic fatty liver disease. In a study by Dehkordi et al on subjects with mild hypertension at a dose of 100 mg and 200 mg )twice daily( were conducted, a significant reduction in systolic blood pressure and diastolic blood pressure was shown [26]. Jarrin et al in an animal study in rats with induced hypertension NS oil daily at a dose of 2.5 mg / kg body weight Systolic and diastolic blood pressure levels were significantly reduced. This effect being reduced by stimulating nitric oxide synthesis and release from the vascular endothelium. The hypotensive effects may also be based on the diuretic activity [27] Also, in this study, the levels of angiotensin converting enzyme activity in the Nigella sativa oil group were reduced [28]. Bader et al in a study that was conducted in patients with type 2 diabetes, NS oil supplementation significantly reduced systolic and diastolic blood pressure in this patients[29].
Clinical trial studies on the effects of NS on adiponectin levels are limited. Our findings are in agreement with the findings of Datau et al, indicating that NS powder (3g/day) supplementation had no significant effect on adiponectin serum levels in men with abdominal obesity after 12 weeks [30]. In another study by Mahdavi et al, NS oil supplementation concurrent with a low low-calorie diet in obese women showed a significant increase in adiponectin levels [31]. In an animal study on rats with metabolic syndrome, the results showed that administration of NS oil increased adiponectin levels in these rats [32]. It has been shown that adiponectin regulate the interaction between obesity and insulin resistance, and a reduction in weight and body fat mass increases plasma levels of adiponectin [31]. The current study showed that NS oil supplementation for 8 weeks do not a significant effects on serum leptin levels, compared to the placebo group. In animal study by Güllü et al that evaluated the effects of TQ on leptin, a significant decrease in leptin plasma levels was observed [33]. No significant effect of NS oil was observed on SBP and DBP. Similar to the results of our study, Qidwai and Bin Sayeed showed that NS seed supplementation doese not significant effect on SBP and DBP[34, 35]. In addition, Amin et al in another study have been shown that supplementation with Black seeds (1.5g/day) had no effect on SBP and DBP[36].
Also In contrast with our study, there are some studies that found NS had a significant beneficial effect on blood pressure. In clinical trial study by Dehkordi in patients with mild hypertension, NS seed exctract (two capsules per day containing 100 and/or 200 mg) supplementation for 8 weeks significantly lowered SBP and DBP[26]. Also, Najimi et al in a trial study investigated the effect 500mg/days of NS Oil supplementation on 45 patients with metabolic syndrome. They results after 8 weeks supplementation with of NS Oil have been shown a significant reduction in SBP and DBP[37]. There are several reasons for the inconsistent results between our study and another previous studies. Firstly, lack of hypertension in patients in this study. Secondly, the dosage and duration were not the same. Perhaps a higher dose with longer duration supplementation of NS is needed to produce an effect on leptin, adiponectin and blood pressure in patient with NAFLD. Further studies are needed to investigate the possible effect of black seed on leptin and adiponectin. The feasible mechanisms involved in the improvements in patient with NAFLD have been explained in previous study[38]. This effects may be connected to some factors like diuretic effect and calcium channels blocking feature of NS that are likely related to several components of NS involved in this effect, including TQ, and fatty acids that contain remarkable quantities of linoleic, oleic, and arachidonic acids, nigellicine, flavonoids, transanethole, p-Cymene, a-Pinene, limonene, carvone, and soluble fiber[38, 39]. NS compounds are also reported to have endothelium independent relaxation effects that may be due to suppression of Ca2+ release from the sarcoplasmic reticulum across the smooth muscle cells membrane and decrease of Ca2+ sensitivity and influx.
This is the first clinical trial to evaluate the effect of NS oil on the patient with NAFLD. The main limitations of our study were: short duration of intervention and small sample size.