Effects of dietary anticarcinogens on rat gastrointestinal glutathione S-transferase theta 1-1 levels.

Several naturally occurring food components or non-steroidal anti-inflammatory drugs (NSAIDs) may reduce gastrointestinal cancer rates. Recently we have shown that dietary administration of such compounds enhanced the glutathione S-transferase (GST) enzyme activity and class alpha, mu and pi isoenzyme levels in the rat gastrointestinal tract. Elevation of the levels of GSTs, a family of biotransformation enzymes with many functions such as detoxification of carcinogens, might be one of the mechanisms that lead to cancer prevention. We therefore investigated whether the anticarcinogens alpha-angelicalactone, alpha-tocopherol, beta-carotene, coumarin, ellagic acid, flavone, indole-3-carbinol, d-limonene, oltipraz, phenethylisothiocyanate (PEITC) and the sulphoraphane analogue compound-30 affect gastrointestinal rGSTT1-1 protein levels in male Wistar rats. rGSTT1-1 protein levels were determined in cytosolic fractions of liver and oesophageal-, gastric-, small intestinal- and colonic mucosa by densitometrical analyses of western blots after immunodetection with an anti human GSTT1-1 monoclonal antibody, that cross-reacts with rGSTT1-1. In control Wistar rats, gastrointestinal rGSTT1-1 protein levels were highest in the liver and decreased in the order liver > stomach > colon > oesophagus > small intestine. Gastric rGSTT1-1 protein levels were enhanced by alpha-angelicalactone, alpha-tocopherol, coumarin, ellagic acid, oltipraz, PEITC and the sulphoraphane analogue compound-30. Oesophageal rGSTT1-1 protein levels were elevated by a-angelicalactone and coumarin, whereas colonic rGSTT1-1 protein levels were elevated by coumarin. Ellagic acid, on the other hand, reduced hepatic rGSTT1-1 protein levels to 53% of the control. In conclusion, dietary anticarcinogens are capable of inducing rGSTT1-1 protein levels in the rat gastrointestinal tract, and are most pronounced in the stomach. Enhanced rGSTT1-1 protein levels might lead to an increase of enzyme activity and to a more efficient detoxification of carcinogens and thus could contribute to prevention of carcinogenesis.

Effects of dietary anticarcinogens on rat gastrointestinal glutathione peroxidase activity.

Several naturally occurring and synthetic food components reduce gastrointestinal cancer. Many of these compounds are scavengers of free radicals, formed during oxidative stress. Glutathione peroxidases (GPxs) protect against free radicals by catalysing their inactivation, thereby consuming glutathione (GSH). This might be one of the mechanisms leading to cancer prevention. We studied the effect of several dietary anticarcinogens on gastrointestinal GPx enzyme activities in male Wistar rats. Total as well as selenium-dependent and non-selenium-dependent GPx (t-GPx, Se-GPx and nSe-GPx) enzyme activities were determined in cytosolic fractions of oesophagus, gastric and colonic mucosa and liver. d-Limonene induced all three types of GPx activities in the oesophagus. d-Limonene and PEITC induced colonic t-GPX and nSe-GPx activity. beta-Carotene induced all three colonic GPx activities and hepatic t-GPx and Se-GPx activity. Coumarin and alpha-tocopherol induced gastric t-GPx and colonic nSe-GPx activity. Oltipraz enhanced oesophageal and gastric t-GPx and oesophageal, gastric and colonic Se-GPx. All other anticarcinogens induced one type of GPx activity at one site. In conclusion, the specific enhancement of GPx enzyme activities by dietary anticarcinogens might lead to a more efficient reduction of organic hydroperoxides and hydrogen peroxide and thus add to prevention of carcinogenesis in these organs.

Effect of Brussels sprouts on oxidative DNA-damage in man.

The effect of consumption of Brussels sprouts on the excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) into human urine was investigated. Ten non-smoking volunteers (five males and five females) were randomly assigned to two groups. Five volunteers started on a diet of 300 g of glucosinolate-free vegetables whereas the other five consumed 300 g of Brussels sprouts per day. After 1 week dietary regimes were reversed. Levels of 8-oxodG in 24-h urine samples were measured by high-performance liquid chromatography. In four of five males a reduction in 8-oxodG was found, whereas in the fifth male the 8-oxodG excretion was high in the control period and was even much higher in the sprouts period. In females no effect of consumption of Brussels sprouts on excretion of 8-oxodG was found. Our previous and present findings support the results of epidemiologic studies that consumption of brassica vegetables may diminish cancer risk.

Effects of consumption of Brussels sprouts on intestinal and lymphocytic glutathione S-transferases in humans.

A high intake of glucosinolate-containing cruciferous vegetables, such as Brussels sprouts (Brassica oleraceae), has been linked to a decreased cancer risk, but the underlying mechanism is still unclear. The aim of this study was to reveal possible modulating effects of consumption of Brussels sprouts on duodenal, rectal and lymphocytic (i) glutathione S-transferase (GST) enzyme activity, (ii) GST isozyme levels and (iii) glutathione (GSH) content. Ten healthy non-smoking volunteers were randomly assigned to two groups in a cross-over design. Five persons started on a glucosinolate-free diet (control period), while the other five consumed 300 g/day cooked Brussels sprouts, at the expense of 300 g glucosinolate-free vegetables (sprouts period). After 7 days the regimen was changed for a further week. At the end of both periods blood samples and duodenal and rectal biopsies were taken. Mean GST activity showed marked differences between duodenal, rectal and lymphocytic cytosols (737 +/- 54, 321 +/- 29 and 154 +/- 14 nmol/min/mg protein respectively), but was uninfluenced by the dietary regimen. Isozyme distribution varied greatly between the tissues. In duodenum GST-alpha, -pi, and -mu isozymes were expressed in considerable amounts (8441 +/- 1365, 3002 +/- 223 and 536 +/- 248 ng/mg protein respectively). Rectal biopsies also contained above three GST classes, but here GST-pi was the most pronounced expressed isozyme (2849 +/- 246) followed by GST-mu (495 +/- 242), while GST-alpha was only present in minor quantities (149 +/- 31). In lymphocytes only GST-pi (755 +/- 96) and GST-mu (83 +/- 54) could be detected. As a result of the dietary regimen rectal GST-alpha and -pi levels were slightly increased at the end of the sprouts period, by 30 and 15% respectively. GSH contents were uninfluenced by the dietary regimen. In conclusion, consumption of glucosinolate-containing Brussels sprouts for 1 week results in increased rectal GST-alpha and -pi isozyme levels. We hypothesize that these enhanced detoxification enzyme levels may partly explain the epidemiological association between a high intake of glucosinolates (cruciferous vegetables) and a decreased risk of colorectal cancer.

Effects of consumption of brussels sprouts on plasma and urinary glutathione S-transferase class-alpha and -pi in humans.

The effects of consumption of glucosinolate-containing Brussels sprouts on plasma and urinary glutathione S-transferase (GST) class-alpha and -pi were investigated. Five male and five female non-smoking volunteers were randomly assigned to two groups in a crossover design. Five persons started on a glucosinolate-free diet (control period), while the other five consumed 300 g of cooked Brussels sprouts per day, at the expense of 300 g of glucosinolate-free vegetables (sprouts period). Dietary regimes were reversed after 1 week. GST levels were measured by enzyme-linked immunoabsorbent assay. At the end of the sprouts period, a significant increase (1.5-fold) in plasma class-alpha GST levels was observed in males but not in females (control versus sprouts, paired t-test; P-values 0.031 and 0.317 respectively), while plasma GST class-pi levels as well as secretion of urinary GST class-alpha and -pi levels remained unchanged. We conclude that (i) increased plasma GST class-alpha levels in males originate probably solely from the liver and not from stomach, intestine or kidney; (ii) males are more susceptible for induction of hepatic GSTs than females; and (iii) urinary GST concentration seems less useful as a biomarker for hepatic GST induction.

Enhancement of rat hepatic and gastrointestinal glutathione and glutathione S-transferases by alpha-angelicalactone and flavone.

The naturally occurring anticarcinogens flavone and alpha-angelicalactone incorporated separately and simultaneously in the diet at 0.5, 0.1, 0.05 and 0.01% w/w, were studied with respect to their effects on oesophageal, gastric, intestinal, colonic and hepatic (i) glutathione S-transferase (GST) enzyme activity, (ii) GST isozyme levels and (iii) glutathione (GSH) content in male Wistar rats. GST enzyme activity was significantly increased in the three treatment groups at one or more sites. The most substantial inductions were seen in oesophagus and stomach by 0.5% alpha-angelicalactone (1.9- and 2.3-fold respectively); and in small intestine, colon and liver by 0.5% combination diet (2.5-, 1.4- and 4.0-fold respectively). The inducing capacities declined with decreasing anticarcinogen concentrations. GST enzyme activity was induced in liver and to a lesser extent in small intestine and stomach. In general, in combination groups similar effects were seen as after treatment with alpha-angelicalactone or flavone separately. However, colonic GST enzyme activity was increased in the 0.5% combination group (1.4-fold), whereas in the corresponding flavone or alpha-angelicalactone groups no induction was observed. Concomitant changes in GST isozyme levels occurred. The involvement was the highest for GST-alpha (75%), followed by GST-mu (58%) and GST-pi (33%). Increased GSH levels were obtained in stomach and liver in all three treatment groups at various concentrations. These data demonstrate that dietary administration of flavone or alpha-angelicalactone, even at relatively low concentrations, may exert chemopreventive effects in stomach, small intestine, liver and to a lesser extent in oesophagus by enhancing the GST detoxification system, mainly by induction of GST-alpha and GST-mu isozymes. In addition, simultaneous administration of flavone and alpha-angelicalactone may result in anticarcinogenic effects in the colon by the same principle.

Quantification of induction of rat oesophageal, gastric and pancreatic glutathione and glutathione S-transferases by dietary anticarcinogens.

Four dietary, naturally occurring anticarcinogens (flavone, coumarin, alpha-angelicalactone and ellagic acid) were studied with respect to their effects on oesophageal, gastric and pancreatic (i) glutathione S-transferase (GST) enzyme activity, (ii) GST isozyme levels and (iii) glutathione (GSH) content in male Wistar rats. GST enzyme activity was significantly increased in the oesophagus by flavone, coumarin and alpha-angelicalactone (125, 240 and 155% respectively) and in the stomach by coumarin and alpha-angelicalactone (140 and 230%). No change in pancreatic GST activity was observed. In addition, class- and tissue-specific changes in GST isozyme levels occurred. Class alpha GSTs were induced in the oesophagus by flavone, coumarin and alpha-angelicalactone (570, 1580 and 570%), but did not change in the stomach. GST-alpha was undetectable in the pancreas. GST-mu was expressed at high levels in all three tissues investigated, but only pancreatic GST-mu levels of ellagic acid-fed rats were increased (160%). GST-pi was induced in the stomach by coumarin and alpha-angelicalactone (470 and 1120%) and in the pancreas by flavone (200%). GST-pi was detectable at low levels in rat oesophageal epithelium of coumarin-fed animals only. GSH concentrations were uninfluenced by the dietary anticarcinogens in all tissues. These results suggest that dietary ellagic acid and, more especially, flavone, coumarin and alpha-angelicalactone may exert strong chemoprotective effects by selective enhancement of members of the GST detoxification system in the oesophagus or stomach and, to a lesser extent, in the pancreas.

Induction of rat hepatic and intestinal glutathione S-transferases by dietary butylated hydroxyanisole.

To obtain insight into the protection mechanism of butylated hydroxyanisole (BHA), a widely used food preservative with anticarcinogenic properties, we investigated the effects of dietary BHA on rat hepatic and intestinal glutathione S-transferase (GST) enzyme activity, and GST isozyme levels. In the proximal small intestine and liver, BHA supplementation significantly increased GST enzyme activity as compared with controls (2.3- and 1.7-fold, respectively, P less than 0.05). GST class alpha and mu contents were significantly higher only in the small intestine (1.6-2.1-fold and 1.3-1.5-fold, respectively, P less than 0.05), whereas GST class pi was significantly induced in liver (4.6-fold, P less than 0.05).