4 | DISCUSSION
In this systematic review and meta-analysis, we summarized published evidence from five RCTs that investigated effect of BBR–silymarin on liver enzymes (ALT and AST) levels. To the best of our knowledge, this systematic review and meta‐analysis is the first one that examined the effect of BBR–silymarin supplementation on liver enzyme levels. The results of the review showed that supplementation with BBR–silymarin had no significant effect of on ALT and AST, in supplementation group compared with placebo group in both sexes including men and women with liver complications.
In the previous studies the effect of BBR and silymarin investigated separately and observed beneficial effects to decrease liver enzymes with BBR [31, 32]. Also studies represented that BBR was effective to treat NAFLD [43]. The half-life of BBR in liver is longer than that in other tissues, and these results may explain that liver is the main target tissue of BBR [44]. BBR due to the presence of P-gp have low oral bioavailability and low oral bioavailability can be improve by P-gp inhibitors such as silymarin. recently trials are experimenting on the nutraceutical combination of  berberis aristata plus-silybum marianum  to treat NAFLD [45].
BBR has been previously shown that decreases transaminase levels, reducing liver necrosis in hepatitis C infection [31] and has an effectiveness in decreasing serum triglyceride and serum level of ALT and AST within 48 hours in patients with NAFLD [32]. In case of total cholesterol [9, 46, 47] it seems that the hypocholesterolemic potential of BBR supplementation intensifies when is combined with statin therapy [6, 48, 49].
There were also few studies that did not report the effectiveness of silymarin on liver enzymes. A clinical trial of silymarin treatment in patients with cirrhosis of the liver showed liver function tests, such as ALT, bilirubin and alkaline phosphatase had no difference between the two study groups [50]. But other studies have also reported different result; a double blind study in 60 female patients were treated with antipsychotics (phenothiazines or butyrophenones) drugs plus 800 mg/day silymarin represent serum levels of AST or ALT decreased at least twice the normal values after 90 days, in receiving silymarin versus the placebo group, and no significant change within the γGT levels [33]. Moreover, in another trial 140 mg, Livergol capsule per day for 30 days reported a statistically significant difference between the two groups in terms of AST and ALT enzymes as the level of liver enzymes in the intervention group was lower than that in the control one, at the end of the study [34]; and a review article which published in 2001 showed in person with chronic alcoholic liver, silymarin treatment, normalized serum bilirubin, AST , ALT values, and γ-GT activity levels decreased in the silymarin supplementation groups [35, 36].
Dosage and duration are two important factors which may affect final results of clinical trials. Included studies in this met-analysis used different doses for their intervention. Silymarin; berberine supplementation was used in a study [9] with a dose of 300 mg silymarin compare to other study which its participants used 210 mg/day. Studies have found that milk thistle, alone or in combination with vitamin E, may help reduce insulin resistance, inflammation and liver damage in people with NAFLD [4, 51-53] and the dosages of silymarin utilized in these studies was 140–800 mg/day, so increase in silymarin dosage may be helpful but further studies are needed to test to prove it.
BBR by regulation of hepatic lipids [19, 20], glucose metabolism [20], and anti-inflammatory effect [21-25] play a role in improving the NAFLD. BBR significantly decreased Hepatic Fat Content (HFC) in the rats with high fat diet induced NAFLD by decreasing methylation of the microsomal triglyceride transfer protein (MTTP) promoter (13). Regulation of AMP-activated protein kinase (AMPK) independent mechanism for BBR to suppress obesity-associated inflammation and alleviate hepatic steatosis [21-23] decrease Cyclooxygenase-2 (COX-2), and mRNA levels of proinflammatory cytokines, resulting in an anti-inflammation effect [24, 25]. BBR also reduced rates of glucose appearance (Raglu), gluconeogenesis (GNG) and hepatic lipogenesis [20] and alleviated insulin sensitivity via activation of AMPK. Silymarin is another component used along with BBR may increase SOD, GSH, and GPx activity. Silymarin is another component of berberol, increases Superoxide dismutase (SOD) glutathione and glutathione peroxidase (GPx) activity. Additionally Silymarin improved hepatic fibrosis [26], decreased the hepatic levels of hydroxyproline and connective tissue growth factor (CTGF) [28], and inhibition of the 5-lipoxygenase pathway particularly LTB4 are the major targets of Silymarin in the treatment of NAFLD [29].
Despite the present study was the first to investigate the effects of berberis aristate and Silybum marianum on liver enzymes, our meta-analysis has some limitations. First, there were only a few eligible RCTs in this meta-analysis, and most of them had a relatively small population, thus performing further studies with a bigger population is needed to determine whether BBR–silymarin is not effective on controlling/lowering ALT and AST levels. Second, studies that were included had heterogeneous patient characteristics. Ultimately, the included studies enrolled only on adult subjects, so we cannot directly infer our studies’ results to children and the elderly.