Sulforaphane-rich broccoli sprout extract improves hepatic abnormalities in male subjects

Abstract

Aim: To evaluate effects of dietary supplementation of sulforaphane (SF)-rich broccoli sprout (BS) extract on hepatic abnormalities in Japanese male participants.

Methods: In a randomized, placebo-controlled, double blind trial, male participants with fatty liver received either BS capsules containing glucoraphanin [GR; a precursor of SF (n = 24)] or placebo (n = 28) for 2 mo. Liver function markers, serum levels of aspartate and alanine aminotransferases (AST and ALT, respectively) and γ-glutamyl transpeptidase (γ-GTP) and an oxidative stress marker, urinary levels of 8-hydroxydeoxyguanosine (8-OHdG), were measured and compared in participants before and after the trial period. In an animal model, chronic liver failure was induced in Sprague-Dawley rats by successive intraperitoneal injection with N-nitrosodimethylamine (NDMA) for 4 wk. Concomitantly, rats received AIN-76 diets supplemented with or without BS extract. Thereafter, rats were sacrificed, and their sera and livers were collected to measure serum liver function markers and hepatic levels of thiobarbituric acid reactive substances (TBARS) levels and hepatic glutathione S-transferase (GST) activity, a prototypical phase 2 antioxidant enzyme.

Results: Dietary supplementation with BS extract containing SF precursor GR for 2 mo significantly decreased serum levels of liver function markers, ALT [median (interquartile range), before: 54.0 (34.5-79.0) vs after supplementation: 48.5 (33.3-65.3) IU/L, P < 0.05] and γ-GTP [before: 51.5 (40.8-91.3) vs after: 50.0 (37.8-85.3) IU/L, P < 0.05], as well as the alkali phosphatase activity. Placebo showed no significant effects on the markers. The urinary level of 8-OHdG, an established oxidative stress marker, was significantly reduced in participants who had received BS capsules but not the placebo [before: 6.66 (5.51-9.03) vs after: 5.49 (4.89-6.66) ng/mg-creatinine, P < 0.05]. The reduction of urinary 8-OHdG was significantly correlated with decreased levels of both ALT and γ-GTP [∆8-OHdG and ∆ALT: Spearman r (r) 0.514 and P = 0.012, ∆8-OHdG and ∆γ-GTP: r = 0.496 and P = 0.016]. Intake of BS extract prevented NDMA-induced chronic liver failure in rats, which was attributable to the suppression of the increase in TBARS through induction of hepatic phase 2 antioxidant enzymes including hepatic GST (86.6 ± 95.2 vs 107.8 ± 7.7 IU/g, P < 0.01).

Conclusion: Dietary supplementation with BS extract containing the SF precursor GR is likely to be highly effective in improving liver function through reduction of oxidative stress.

Keywords: Broccoli sprout; Glucoraphanin; Hepatic abnormality; Nrf2; Oxidative stress; Phase 2 enzymes; Sulforaphane.

Figure 1

Effect of supplementation with broccoli sprout extract containing the sulforaphane precursor glucoraphanin on liver function markers in male participants with hepatic abnormalities. A, B: Serum levels of alanine aminotransferase (ALT) and γ-glutamyl transpeptidase (γ-GTP) in sulforaphane (SF) and placebo group participants (n = 24 and 28, respectively) before and after 2 mo of intervention. Each line between the circle symbols represents individual change in serum levels of ALT and γ-GTP. P values were analyzed by using the Wilcoxon single rank test.

Figure 2

Parallel improvements of an oxidative stress marker and liver function markers in sulforaphane group participants. A, B: Change levels of liver function markers, alanine aminotransferase and γ-glutamyl transpeptidase (∆ALT and ∆γ-GTP) were respectively plotted against changes in levels of urinary 8-hydroxydeoxyguanosine (∆8-OHdG), an in vivo oxidative stress marker, in SF group participants (n = 24). Each circle represents individual data. Spearman r and P were determined; C, D: ∆ALT and ∆γ-GTP were compared between participants with ∆8-OHdG < 0 (n = 15) and ∆8-OHdG ≥ 0 (n = 9). Each circle symbol represents an individual data point. Bars in graphs represent median values. P values were obtained by using the Mann-Whitney U test.

Figure 3

Effects of intake of broccoli sprout extract on liver function markers in serum from N-nitrosodimethylamine-induced chronic liver failure model rats. A, B: Serum activities of aspartate-aminotransferases (AST) and alanine aminotransferase (ALT) in male Sprague-Dawley rats who had received an AIN-76 diet containing no (sham, n = 6 and control, n = 8) or different amounts of BS extract at glucoraphanin (GR) doses of 62.5, 125, and 250 mg per 100 g diet (BS-low, BS-middle, and BS-high, respectively, n = 8) for 4 wk. All rats, except for the sham group, were intraperitoneally injected with N-nitrosodimethylamine (5 mg per kg body weight) on 3 consecutive days of the week for 4 wk; C, D: Serum levels of albumin and bilirubin in the rats. Data are shown as boxplots representing the minimum (bottom of the bar), 25th percentile (bottom of the box), median (horizontal line), 75^th percentile (top of the box), and the maximum observations (top of the bar). ^aP < 0.05 vs sham; ^cP < 0.05, ^dP < 0.01 vs control (Steel-Dwass test). BS: Broccoli sprout.

Figure 4

Effects of intake of broccoli sprout extract on oxidative stress and enzyme activity of glutathione S-transferase in livers from N-nitrosodimethylamine-induced chronic liver failure model rats. A: Thiobarbituric acid reactive substances (TBARS) levels were determined in livers from serum activities of alanine aminotransferase (AST) and alanine aminotransferase (ALT) in male Sprague-Dawley rats who had received an AIN-76 diet containing no (sham, n = 6 and control, n = 8) or different amount of BS extract at glucoraphanin (GR) doses of 62.5, 125, and 250 mg per 100 g diet (BS-low, BS-middle, and BS-high, respectively, n = 8) for 4 wk. All rats, except for sham group, were intraperitoneally injected with NDMA (5 mg per kg body weight) in 3 consecutive days of the week for 4 wk; B: GST activities in rat livers were determined with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. Data are shown as mean ± SE. ^aP < 0.05, ^bP < 0.01 vs sham, ^dP < 0.01, ^fP < 0.001 vs control (A: Tukey Kramer; B: Dunnett test).