| Aflatoxin B1(AFB1), a potent hepatotoxic agent, is classified by the InternationalAgency of Research on Cancer as Group I human carcinogen. Besides hepatitis B virus, AFB1is one of the two key factors that implicated in the aetiology of primary liver cancer. AFB1isa ubiquitous contaminant. It is thought to be closely related with the high incidence of humanliver cancer, and hence poses a significant health risk for human populations and animals.Therefore, developing agents that possess hepatoprotective effects against AFB1from naturalor synthetic products has become increasing important. Aloe is a traditional edible andmedicinal plant containing multiple bioactive components. It is now widely cultivated inChina, Africa and South America, which areas are highly polluted by AFB1. Recently, it wasreported that aloe exerted a potential hepatoprotective effect against experimental liver injuryinduced by various chemical toxins. However, no study on applying it for the prevention ofAFB1-induced hepatotoxicity has been reported. In this study, the potential hepatoprotectiveeffect of Aloe vera against AFB1-induced hepatotoxicity was firstly investigated. In order toclarify the specific functional components in Aloe vera, the main active componentspolysaccharides were then separated, purified and identified. And based on these, we tried tosystematically evaluate the hepatoprotective potential of the main active components in Aloevera, including aloe polysaccharides (AP) and aloin against AFB1-induced hepatotoxicity inboth acute and subchronic rat models, and elucidate the related mechanisms. The main studiesand results are as follows:1. The acute AFB1-intoxicated rat model was set up by intragastrically giving a singledose of AFB1(2mg/kg bw). And using this model, the possible hepatoprotective property ofAloe vera against AFB1-induced liver injury was then investigated. As a result, we found thatsupplementation of Aloe vera can effectively inhibit the weight loss of the AFB1-intoxicatedrats, and significantly reduce the serum alanine aminotransferase (ALT), aspartateaminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TBIL) levels. Inaddition, Aloe vera was shown to be effective in improving hepatic histopathological changes,lowering malondialdehyde (MDA), and elevating the levels of reduced glutathione (GSH),glutathione peroxidase (GSH-PX), superoxide dismutase (SOD) and glutathione-S-transferase (GST). These results showed that Aloe vera can remarkably enhance theantioxidant and detoxifying capacities of AFB1-intoxicated rats, and possess a potentprotective effect against AFB1-induced hepatotoxicity.2. To clarify the specific functional components in Aloe vera, polysaccharides (AP) wasseparated from the lyophilized Aloe vera gel power that was prepared on an industrial scale.The polysaccharides and O-acetyl contents of AP were found to be86.2, and80.8%，respectively. And it did not contain protein. Results from monosaccharide analysis indicatedthat AP mainly contained mannose, glucose, and galactose, and also contained trace amountsof galacturonic acid, arabinose, and rhamnose. Following further purification with a series ofchromatographic columns, AP was found to be mainly composed of two neutral acetylatedmannans, namely AP-1AA and AP-1C, respectively. Their molecular weights were207653, and107995, respectively. The chemical and spectroscopic analyses implied that AP-1AA andAP-1C had similar structures. Their main skeletons were β-(1â†'4)-D linkaged mannose withacetylation at C-3and C-6of manopyranosyl. However, the ratios of acetylation at C-3, C-6in AP-1AA and AP-1C were different.3. Using the acute AFB1-intoxicated rat model, the hepatoprotective potential of AP andaloin, the main active components in Aloe vera, against AFB1-induced liver damage wasinvestigated. The hepatic, serum biochemical indicators and hepatic histopathological changeswere measured for evaluating their potential hepatoprotective effects. And potentialmechanisms ranging from oxidative stress, mitochondrial function, hepatic AFB1metabolicenzymes to inflammatory response were involved. Severe liver damage with increased levelsof serum markers, liver index and spleen index due to the acute AFB1treatment wassignificantly attenuated by AP and aloin, which was reconfirmed by the attenuation of hepatichistopathological changes. Treatment of AP and aloin showed a significant improvement onthe hepatic antioxidant status in AFB1-intoxicated rats. They not only significantly inhibitedthe AFB1-dependent induction of reactive oxygen species (ROS), MDA formation, but alsoremarkably increased the levels of antioxidants in the liver. The up-regulations of cytochromeP4501A2and3A (CYP1A2and CYP3A) mRNA expression, as well as the activities ofCYP1A2and3A4in AFB1-treated rats were also markedly suppressed by thesupplementation of AP and aloin. In addition, the overexpressions of tumor necrosis factor-(TNF-), interleukin-1β (IL-1β) and interleukin-6(IL-6) were significantly attenuated by AP,while IL-1β and IL-6were significantly attenuated by aloin. These results highlight the abilityof AP and aloin to ameliorate the acute AFB1-induced hepatotoxicity, and the observedhepatoprotection was associated with their abilities to attenuate oxidative stress, suppressAFB1activation, and inhibit inflammation.4. The subchronic AFB1-intoxicated rat model was set up by continuously treated with200μg/kg bw of AFB1for5weeks. And using this model, we conducted experiments tofurther investigate the possible hepatoprotective property of AP and aloin on subchronicAFB1-induced liver injury. As a result, we found that both AP and aloin can effectivelysuppress or delay the development of subchronic AFB1-induced hepatotoxicity in rats. Theycan not only significantly inhibit the AFB1-induced reduction of feed intake and body weightgain, but also remarkably attenuate the atrophy of immune organ, spleen swelling, as well asthe hepatic histopathological changes. Results of hepatic antioxidant status showed that theexposure of AFB1for5weeks markedly elevated MDA formation, while significantlyreduced the levels of GSH, SOD, CAT and GSH-PX. However, supplementation of AP andaloin resulted in a significant improvement in all these parameters. According to the results ofreal-time PCR and immunohistochemistry, AP and aloin showed a significant inhibitoryeffect on the overexpression of major AFB1-metabolizing enzymes in both mRNA and proteinlevels. The activity assays indicated that AP and aloin can also remarkably decrease CYP1A2and3A4activities, while significantly elevated pahse II detoxifying enzyme GST level. Inaddition, AP attenuated the AFB1-dependent inflammation via down-regulating TNF-andIL-1β expression, while aloin suppressed inflammatory response through down-regulating theIL-1β expression. These results indicated that AP and aloin also possess a potent hepatoprotective effect on the subchronic AFB1-induced hepatotoxicity, and the observedhepatoprotection was probably due to their strong abilities in enhancing antioxidant capacity,accelerating detoxication, as well as suppressing AFB1activation and inflammatory response.All the above results demonstrated that Aloe vera possesses a potential preventive andtherapeutic effect on the AFB1-induced liver diseases. Polysaccharides and aloin are twofunctional components in Aloe vera that associated with its hepatoprotection. Their potenthepatoprotective effects on AFB1-intoxicated rats were probably closely related to theirexcellent capacities of anti-oxidation, anti-inflammation and the regulating effects onAFB1-metabolizing enzymes. The present study has a great significance on thecomprehensive exploitation and utilization of aloe products. |
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