Lipid peroxidation and irreversible damage in the rat hepatocyte model. Protection by the silybin-phospholipid complex IdB 1016

Primary human hepatocytes are protected against prolonged and repeated exposure to ethanol by silibinin-dihemisuccinate

AIMS AND METHODS

We investigated the effect of silibinin-C-2',3'-dihydrogensuccinate (SDH) on primary human hepatocytes when exposed to ethanol for 14 days. At regular intervals, the medium was refreshed and liver enzymes and secreted protein in the medium were determined.

RESULTS

The ethanol-induced release of lactate dehydrogenase (at 34 mM ethanol) was completely blocked by 20 microM SDH. SDH itself stimulated fibrinogen release and had no toxic effect.

CONCLUSIONS

We can conclude that SDH has a beneficial effect on human hepatocytes when exposed to ethanol in vitro.

Silymarin inhibits TNF-alpha-induced expression of adhesion molecules in human umbilical vein endothelial cells

Silymarin is known to have an anti-atherosclerotic activity, but the mechanism responsible for it remains unclear. Here, we demonstrate a possible mechanism involved in the anti-atherosclerotic activity of silymarin. Silymarin inhibited THP-1 cell adhesion to human umbilical vein endothelial cells (HUVECs). Silymarin also suppressed the TNF-alpha-induced protein and mRNA expression of adhesion molecules, such as VCAM-1, ICAM-1 and E-selectin, in HUVECs. Moreover, silymarin suppressed the TNF-alpha-induced DNA binding of NF-kappaB/Rel in HUVECs. Taken together, these results demonstrate that silymarin exerts an anti-atherosclerotic activity, at least in part, by inhibiting the expression of adhesion molecules.

Cutaneous photodamage, oxidative stress, and topical antioxidant protection

New methods to protect skin from photodamage from sun exposure are necessary if we are to conquer skin cancer and photoaging. Sunscreens are useful, but their protection is not ideal because of inadequate use, incomplete spectral protection, and toxicity. Skin naturally uses antioxidants (AOs) to protect itself from photodamage. This scientific review summarizes what is known about how photodamage occurs; why sunscreens--the current gold standard of photoprotection--are inadequate; and how topical AOs help protect against skin cancer and photoaging changes. This review is intended to be a reference source, including pertinent comprehensive reviews whenever available. Although not all AOs are included, an attempt has been made to select those AOs for which sufficient information is available to document their potential topical uses and benefits. Reviewed are the following physiologic and plant AOs: vitamin C, vitamin E, selenium, zinc, silymarin, soy isoflavones, and tea polyphenols. Their topical use may favorably supplement sunscreen protection and provide additional anticarcinogenic protection. (J Am Acad Dermatol 2003;48:1-19.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should have an understanding of current information about how the sun damages skin to produce skin cancer and photoaging changes, how the skin naturally protects itself from the sun, the shortcomings of sunscreens, and the added advantages of topical AOs for photoprotection.

Treatment of amatoxin poisoning: 20-year retrospective analysis

BACKGROUND

Amatoxin poisoning is a medical emergency characterized by a long incubation time lag, gastrointestinal and hepatotoxic phases, coma, and death. This mushroom intoxication is ascribed to 35 amatoxin-containing species belonging to three genera: Amanita, Galerina, and Lepiota. The major amatoxins, the alpha-, beta-, and gamma-amanitins, are bicyclic octapeptide derivatives that damage the liver and kidney via irreversible binding to RNA polymerase II.

METHODS

The mycology and clinical syndrome of amatoxin poisoning are reviewed. Clinical data from 2108 hospitalized amatoxin poisoning exposures as reported in the medical literature from North America and Europe over the last 20 years were compiled. Preliminary medical care, supportive measures, specific treatments used singly or in combination, and liver transplantation were characterized. Specific treatments consisted of detoxication procedures (e.g., toxin removal from bile and urine, and extracorporeal purification) and administration of drugs. Chemotherapy included benzylpenicillin or other beta-lactam antibiotics, silymarin complex, thioctic acid, antioxidant drugs, hormones and steroids administered singly, or more usually, in combination. Supportive measures alone and 10 specific treatment regimens were analyzed relative to mortality.

RESULTS

Benzylpenicillin (Penicillin G) alone and in association was the mostfrequently utilized chemotherapy but showed little efficacy. No benefit was found for the use of thioctic acid or steroids. Chi-square statistical comparison of survivors and dead vs. treated individuals supported silybin, administered either as mono-chemotherapy or in drug combination and N-acetylcysteine as mono-chemotherapy as the most effective therapeutic modes. Future clinical research should focus on confirming the efficacy of silybin, N-acetylcysteine, and detoxication procedures.

Silymarin protects dopaminergic neurons against lipopolysaccharide-induced neurotoxicity by inhibiting microglia activation

An inflammatory response in the central nervous system mediated by activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. Silymarin is a polyphenolic flavanoid derived from milk thistle that has anti-inflammatory, cytoprotective and anticarcinogenic effects. In this study, we first investigated the neuroprotective effect of silymarin against lipopolysaccharide (LPS)-induced neurotoxicity in mesencephalic mixed neuron-glia cultures. The results showed that silymarin significantly inhibited the LPS-induced activation of microglia and the production of inflammatory mediators, such as tumour necrosis factor-alpha and nitric oxide (NO), and reduced the damage to dopaminergic neurons. Therefore, the inhibitory mechanisms of silymarin on microglia activation were studied further. The production of inducible nitric oxide synthase (iNOS) was studied in LPS-stimulated BV-2 cells as a model of microglia activation. Silymarin significantly reduced the LPS-induced nitrite, iNOS mRNA and protein levels in a dose-dependent manner. Moreover, LPS could induce the activation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase but not extracellular signal-regulated kinase. The LPS-induced production of NO was inhibited by the selective p38 MAPK inhibitor SB203580. These results indicated that the p38 MAPK signalling pathway was involved in the LPS-induced NO production. However, the activation of p38 MAPK was not inhibited by silymarin. Nevertheless, silymarin could effectively reduce LPS-induced superoxide generation and nuclear factor kappaB (NF-kappaB) activation. It suggests that the inhibitory effect of silymarin on microglia activation is mediated through the inhibition of NF-kappaB activation.

Flavonoid antioxidant silymarin and skin cancer

Oxidative stress is one of the key players in skin carcinogenesis, and therefore identifying nontoxic strong antioxidants to prevent skin cancer is an important area of research. In both animal and cell culture studies, we have shown that silymarin, a naturally occurring polyphenolic flavonoid antioxidant, exhibits preventive and anticancer effects against skin cancer. For example, silymarin strongly prevents both photocarcinogenesis and skin tumor promotion in mice, in part, by scavenging free radicals and reactive oxygen species and strengthening the antioxidant system. We also found that this effect of silymarin is by inhibiting endogenous tumor promoter tumor necrosis factor alpha in mouse skin, a central mediator in skin tumor promotion. In mechanistic studies, silymarin inhibits mitogenic and cell survival signaling and induces apoptosis. Furthermore, silymarin effectively modulates cell-cycle regulators and check points toward inhibition of proliferation, and growth arrest in G0-G1 and G2-M phases of the cell cycle. Thus, due to its mechanism-based chemopreventive and anticancer effects in experimental models, silymarin is an important candidate for the prevention and/or therapy of skin cancer, as well as other cancers of epithelial origin in humans.

Arsenic trioxide and breast cancer: analysis of the apoptotic, differentiative and immunomodulatory effects

Arsenic trioxide (As2O3) is used clinically to treat acute promyelocytic leukemia and has activity in vitro against several solid tumour cell lines, where induction of differentiation and apoptosis are the prime effects. To investigate the potential therapeutic application of As2O3 to breast cancer, we analysed the effects of As2O3 on the growth of four human breast cancer cell lines: MCF7, MDA-MB-231, T-47D and BT-20. Cells were cultured in 0.5, 2 and 5 microM AS2O3, a range of pharmacologically achievable concentrations of AS2O3. At > or = 2 microM, AS2O3 rapidly induced cell death by apoptosis in MCF7 and MDA-MB-231 while T-47D and BT-20 were partially resistant. At 0.5 microM, As2O3 was subapoptotic but induced features of differentiation consisting in upregulation of ICAM-1 (CD54), a marker of mammary epithelial differentiation, and cell cultures appeared morphologically more organized. Furthermore, we demonstrate by standard cytotoxicity assays that As2O3 treatment can augment breast cancer cell lysis by lymphokine-activated killer cells and demonstrate an important role of the ICAM-1/LFA-1 interaction in this process. This additional activity of As2O3 could translate into improved antitumour immunosurveillance in vivo. In conclusion, As2O3 induced varying degrees of differentiation, apoptosis and lysis in these model cell lines, and may be a promising adjuvant to current treatments of breast cancer by virtue of its triple apoptotic, differentiative and immunomodulatory effects.

Hepatoprotective activity of Achyrocline satureioides(Lam) D. C

Aerial parts of Achyrocline satureioides(Lam) D. C. (Asteraceae) are used in folk medicine as infusions or decoctions for the management of several diseases including gastrointestinal and hepatic disorders. These data and the presence of flavonoids and caffeoyl derivatives have led us to study its hepatoprotective and choleretic activities. The hepatoprotective activity was evaluated in the bromobenzene- (BB-) induced hepatotoxicity model in mice through the measurement of the serum levels of alanine-aminotransferase (ALT) and aspartate transaminase (AST), thiobarbituric acid reacting substances (TBARS) and glutathione levels. The aqueous extract of the aerial parts of A. satureioides administered before BB, at the dose of 300 mg kg(-1)p.o., demonstrated significant inhibition (P< 0.01) in the BB increase of liver ALT and AST and in the BB-induced increase of liver TBARS content. Also it was able to significantly increase (P< 0.05) the depleted levels of liver glutathione. In addition, at the same dose, a significant increase (P< 0.01) in the bile flow of rats was found. The results obtained with the aqueous extract of A. satureioides support its use in popular medicine as a hepatoprotective and digestive agent, and the effects might be mediated through the antioxidant and choleretic activities.

Evaluation of hepatoprotective activity of legumes

Mung bean, adzuki bean, black bean and rice bean are foods and folk medicines of Taiwan. We evaluated the effects of various water extract concentrations (100, 500 and 1000 mg/kg body wt.) and silymarin (25 mg/kg body wt. on acetaminophen-induced liver injury by measuring serum glutamate-oxalate-transaminase (sGOT) and serum glutamate-pyruvate-transaminase (sGPT) activities in rats. The results showed that the sGOT and the sGPT activities, increased by APAP, were decreased significantly (P < 0.05) through treatment with inceasing amounts up to 1000 mg/kg body wt. of the exracts. In particular, the mung bean aqueous extract showed the best hepatoprotective effect on APAP-induced hepatotoxicity. The pathological changes of liver injury caused by APAP improved by the treatment with all of the legume extracts, which were compared to silymarin as a standardized drug. In addition to these results, the extract of mung bean acted as a potential hepatoprotective agent in dietary supply.

The role of cyclooxygenase and lipoxygenase in cancer chemoprevention

The involvement of prostaglandins (PGs) and other eicosanoids in the development of human cancer has been known for over two decades. Importantly, an increase in PG synthesis may influence tumor growth in human beings and experimental animals, and numerous studies have illustrated the effect of PG synthesis on carcinogen metabolism, tumor cell proliferation and metastatic potential. PGs produced by cyclooxygenases (COXs) are represented by a large series of compounds that mainly enhance cancer development and progression, acting as carcinogens or tumor promoters, with profound effects on carcinogenesis. Further investigations suggest that arachidonic acid (AA) metabolites derived from lipoxygenase (LOX) pathways play an important role in growth-related signal transduction, implying that intervention through these pathways should be useful for arresting cancer progression. We discuss here the implications of COX and LOX in colon, pancreatic, breast, prostate, lung, skin, urinary bladder and liver cancers. Select inhibitors of COX and LOX are described, including nonsteroidal antiinflammatory drugs (NSAIDs), selective COX-2 inhibitors, curcumin, tea, silymarin and resveratrol, as well as a method useful for evaluating inhibitors of COX. Although a substantial amount of additional work is required to yield a better understanding of the role of COX and LOX in cancer chemoprevention, it is clear that beneficial therapeutic effects can be realized through drug-mediated modulation of these metabolic pathways.

Antioxidant and hepatoprotective effects of punicalagin and punicalin on acetaminophen-induced liver damage in rats

Punicalagin and punicalin were isolated from the leaves of Terminalia catappa L., a Combretaceous plant distributed throughout tropical and subtropical beaches, which is used for the treatment of dermatitis and hepatitis. Our previous studies showed that both of these compounds exert antioxidative activity. In this study, the antihepatotoxic activity of punicalagin and punicalin on acetaminophen-induced toxicity in the rat liver was evaluated. After evaluating the changes of several biochemical functions in serum, the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were increased by acetaminophen administration and reduced by punicalagin and punicalin. Histological changes around the hepatic central vein and oxidative damage induced by acetaminophen were also recovered by both compounds. The data show that both punicalagin and punicalin exert antihepatotoxic activity, but treatment with larger doses enhanced liver damage. These results suggest that even if punicalagin and punicalin have antioxidant activity at small doses, treatment with larger doses will possibly induce some cell toxicities.

Antioxidative properties of natural coelenterazine and synthetic methyl coelenterazine in rat hepatocytes subjected to tert-butyl hydroperoxide-induced oxidative stress

Coelenterazine (CLZn; 3, 7-dihydro-2-(p-hydroxybenzyl)-6-(p-hydroxyphenyl)-8-benzylimidazolo++ +[1 ,2-a]pyrazin-3-one), the substrate for bioluminescence reactions in many marine animals, is endowed with high antioxidant properties. This work investigated the antioxidative properties of CLZn in primary cultures of rat hepatocytes subjected to the oxidant tert-butyl hydroperoxide (t-BHP). Micromolar concentrations of CLZn increased survival and decreased lipid peroxidation in rat hepatocytes subjected for 6 hr to 2.5 x 10(-4) M t-BHP. However, the extent of protection was limited by a strong toxicity of CLZn (IC(50) = 6.9 x 10(-5) M). The presence of t-BHP increased the cellular toxicity of CLZn. Methyl coelenterazine (CLZm, 3, 7-dihydro-2-methyl-6-(p-hydroxyphenyl)-8 benzylimidazolo[1, 2-a]pyrazin-3-one), a synthetic analogue of CLZn, demonstrated excellent antioxidant properties, even at very low (3 x 10(-6) M) concentrations and was not toxic throughout most of its effective concentration range. CLZm proved far more effective than reference antioxidants such as Trolox C(R), alpha-tocopherol, BHT, and probucol. The assay of thiobarbituric reactive substances (TBARS) associated with cells and in the culture medium indicated that 10(-5) M CLZm provided a total protection against t-BHP-induced lipid peroxidation. This coelenterazine analogue could be used as a model compound for investigating the action mechanism of imidazolopyrazinones in mammalian hepatocytes.

Inhibitory effect of a flavonoid antioxidant silymarin on benzoyl peroxide-induced tumor promotion, oxidative stress and inflammatory responses in SENCAR mouse skin

In this communication, we investigate the preventive effect of a flavonoid antioxidant, silymarin, on free radical-generating skin tumor promoting agent benzoyl peroxide (BPO)-induced tumor promotion, oxidative stress and inflammatory responses in SENCAR mouse skin. Topical application of silymarin at a dose of 6 mg prior to BPO resulted in a highly significant protection against BPO-induced tumor promotion in 7,12-dimethylbenz[a]anthracene-initiated SENCAR mouse skin. The preventive effect of silymarin was evident in terms of a 70% reduction (P < 0.001) in tumor incidence, a 67% reduction (P < 0.001) in tumor multiplicity and a 44% decrease (P < 0.001) in tumor volume/tumor. In oxidative stress studies, topical application of BPO resulted in 75, 87 and 61% depletion in superoxide dismutase (SOD), catalase and glutathione peroxidase (GPX) activities in mouse epidermis, respectively. These decreases in antioxidant enzyme activities were significantly (P < 0.005-0.001) reversed by pre-application of silymarin in a dose-dependent manner. The observed effects of silymarin were 18-66, 32-72 and 20-67% protection against BPO-induced depletion of SOD, catalase and GPX activity in mouse epidermis, respectively. Silymarin pre-treatment also resulted in a dose-dependent inhibition (35-87%, P < 0.05-0. 001) of BPO-induced lipid peroxidation in mouse epidermis. In inflammatory response studies, silymarin showed a strong inhibition of BPO-induced skin edema (62-85% inhibition, P < 0.001), myeloperoxidase activity (42-100% inhibition, P < 0.001) and interleukin-1alpha protein level in epidermis (36-81% inhibition, P < 0.001). These results, together with our other recent studies, suggest that silymarin could be useful in preventing a wide range of carcinogen and tumor promoter-induced cancers.

Silymarin Suppresses TNF-Induced Activation of NF-κB, c-Jun N-Terminal Kinase, and Apoptosis

Silymarin is a polyphenolic flavonoid derived from milk thistle (Silybum marianum) that has anti-inflammatory, cytoprotective, and anticarcinogenic effects. How silymarin produces these effects is not understood, but it may involve suppression of NF-κB, a nuclear transcription factor, which regulates the expression of various genes involved in inflammation, cytoprotection, and carcinogenesis. In this report, we investigated the effect of silymarin on NF-κB activation induced by various inflammatory agents. Silymarin blocked TNF-induced activation of NF-κB in a dose- and time-dependent manner. This effect was mediated through inhibition of phosphorylation and degradation of ΙκBα, an inhibitor of NF-κB. Silymarin blocked the translocation of p65 to the nucleus without affecting its ability to bind to the DNA. NF-κB-dependent reporter gene transcription was also suppressed by silymarin. Silymarin also blocked NF-κB activation induced by phorbol ester, LPS, okadaic acid, and ceramide, whereas H2O2-induced NF-κB activation was not significantly affected. The effects of silymarin on NF-κB activation were specific, as AP-1 activation was unaffected. Silymarin also inhibited the TNF-induced activation of mitogen-activated protein kinase kinase and c-Jun N-terminal kinase and abrogated TNF-induced cytotoxicity and caspase activation. Silymarin suppressed the TNF-induced production of reactive oxygen intermediates and lipid peroxidation. Overall, the inhibition of activation of NF-κB and the kinases may provide in part the molecular basis for the anticarcinogenic and anti-inflammatory effects of silymarin, and its effects on caspases may explain its role in cytoprotection.

Tissue distribution of silibinin, the major active constituent of silymarin, in mice and its association with enhancement of phase II enzymes: implications in cancer chemoprevention

Polyphenolic antioxidants are being identified as cancer preventive agents. Recent studies in our laboratory have identified and defined the cancer preventive and anticarcinogenic potential of a polyphenolic flavonoid antioxidant, silymarin (isolated from milk thistle). More recent studies by us found that these effects of silymarin are due to the major active constituent, silibinin, present therein. Here, studies are done in mice to determine the distribution and conjugate formation of systemically administered silibinin in liver, lung, stomach, skin, prostate and pancreas. Additional studies were then performed to assess the effect of orally administered silibinin on phase II enzyme activity in liver, lung, stomach, skin and small bowel. For tissue distribution studies, SENCAR mice were starved for 24 h, orally fed with silibinin (50 mg/kg dose) and killed after 0.5, 1, 2, 3, 4 and 8 h. The desired tissues were collected, homogenized and parts of the homogenates were extracted with butanol:methanol followed by HPLC analysis. The column eluates were detected by UV followed by electrochemical detection. The remaining homogenates were digested with sulfatase and beta-glucuronidase followed by analysis and quantification. Peak levels of free silibinin were observed at 0.5 h after administration in liver, lung, stomach and pancreas, accounting for 8.8 +/- 1.6, 4. 3 +/- 0.8, 123 +/- 21 and 5.8 +/- 1.1 (mean +/- SD) microg silibinin/g tissue, respectively. In the case of skin and prostate, the peak levels of silibinin were 1.4 +/- 0.5 and 2.5 +/- 0.4, respectively, and were achieved 1 h after administration. With regard to sulfate and beta-glucuronidate conjugates of silibinin, other than lung and stomach showing peak levels at 0.5 h, all other tissues showed peak levels at 1 h after silibinin administration. The levels of both free and conjugated silibinin declined after 0.5 or 1 h in an exponential fashion with an elimination half-life (t((1/2))) of 57-127 min for free and 45-94 min for conjugated silibinin in different tissues. In the studies examining the effect of silibinin on phase II enzymes, oral feeding of silibinin at doses of 100 and 200 mg/kg/day showed a moderate to highly significant (P < 0.1-0.001, Student's t-test) increase in both glutathione S-transferase and quinone reductase activities in liver, lung, stomach, skin and small bowel in a dose- and time-dependent manner. Taken together, the results of the present study clearly demonstrate the bioavailability of and phase II enzyme induction by systemically administered silibinin in different tissues, including skin, where silymarin has been shown to be a strong cancer chemopreventive agent, and suggest further studies to assess the cancer preventive and anticarcinogenic effects of silibinin in different cancer models.

A conservative triple antioxidant approach to the treatment of hepatitis C. Combination of alpha lipoic acid (thioctic acid), silymarin, and selenium: three case histories

BACKGROUND

There has been an increase in the number of adults seeking liver transplantation for hepatitis C in the last few years and the count is going up rapidly. There is no reliable and effective therapy for chronic hepatitis C since interferon and antivirals work no more than 30% of the time, and liver transplant surgery is uncertain and tentative over the long run. This is because, ultimately, residual hepatitis C viremia infects the new liver. Furthermore, liver transplantation can be painful, disabling and extremely costly.

TREATMENT PROGRAM

The author describes a low cost and efficacious treatment program in 3 patients with cirrhosis, portal hypertension and esophageal varices secondary to chronic hepatitis C infection. This effective and conservative regimen combines 3 potent antioxidants (alpha-lipoic acid [thioctic acid], silymarin, and selenium) that possess antiviral, free radical quenching and immune boosting qualities.

CONCLUSION

There are no remarkably effective treatments for chronic hepatitis C in general use. Interferon and antivirals have less than a 30% response rate and because of the residual viremia, a newly transplanted liver usually becomes infected again. The triple antioxidant combination of alpha-lipoic acid, silymarin and selenium was chosen for a conservative treatment of hepatitis C because these substances protect the liver from free radical damage, increase the levels of other fundamental antioxidants, and interfere with viral proliferation. The 3 patients presented in this paper followed the triple antioxidant program and recovered quickly and their laboratory values remarkably improved. Furthermore, liver transplantation was avoided and the patients are back at work, carrying out their normal activities, and feeling healthy. The author offers a more conservative approach to the treatment of hepatitis C, that is exceedingly less expensive. One year of the triple antioxidant therapy described in this paper costs less than $2,000, as compared to mor than $300,000 a year for liver transplant surgery. It appears reasonable, that prior to liver transplant surgery evaluation, or during the transplant evaluation process, the conservative triple antioxidant treatment approach should be considered. If these is a significant betterment in the patient's condition, liver transplant surgery may be avoided.

Milk thistle (Silybum marianum) for the therapy of liver disease

Silymarin, derived from the milk thistle plant, Silybum marianum, has been used for centuries as a natural remedy for diseases of the liver and biliary tract. As interest in alternative therapy has emerged in the United States, gastroenterologists have encountered increasing numbers of patients taking silymarin with little understanding of its purported properties. Silymarin and its active constituent, silybin, have been reported to work as antioxidants scavenging free radicals and inhibiting lipid peroxidation. Studies also suggest that they protect against genomic injury, increase hepatocyte protein synthesis, decrease the activity of tumor promoters, stabilize mast cells, chelate iron, and slow calcium metabolism. In this article we review silymarin's history, pharmacology, and properties, and the clinical trials pertaining to patients with acute and chronic liver disease.

Evaluation of hepatic antioxidant systems after intravenous administration of polymeric nanoparticles

We have investigated the modifications of the levels of intracellular markers of the oxidative stress in hepatocytes, after single or repeated injections of poly(isobutyl cyanoacrylate) (PIBCA) and polystyrene (PS) nanoparticles. Nanoparticles were administered intravenously at single doses of 20 and 100 mg kg 1 for 14 days. Levels of reduced (GSH) and oxidized (GSSG) glutathione, superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CT) and the peroxidation of membrane lipids were measured. Single and repeated administration of PIBCA and PS nanoparticles induced a transient depletion of GSH and GSSG levels, a transient inhibition of SOD activity and a slight increase in CT activity. However, GPx activity was not modified and lipid peroxidation was not observed, suggesting that hepatocytes are not strongly affected by these modifications. Since nanoparticles do not distribute in hepatocytes, oxidative species could proceed from hepatic macrophages, activated after nanoparticle phagocytosis. It is unlikely that poly(alkyl cyanoacrylate) degradation products might be responsible for the oxidative attack because non-biodegradable PS nanoparticles induced the same effect. Uptake of polymeric nanoparticles by Kupffer cells in the liver induce modifications in hepatocyte antioxidant systems, probably due to the production of radical oxygen species. However, the depletion in glutathione was not great enough to initiate hepatocyte damage, since no changes in lipid peroxidation and reversible alterations were observed. This is an important factor to be considered in the use of polymeric nanoparticles as drug carriers.

Scavenging effect of silipide, a new silybin-phospholipid complex, on ethanol-derived free radicals

Ethanol metabolism by cytochrome P4502E1 (CYP2E1) produces free radical intermediates, identified as hydroxyethyl radicals. We have observed that in vitro addition or in vivo pretreatment of rats with Silipide, a new 1:1 complex of silybin with phosphatidyl-choline, is able to decrease the spin trapping of hydroxyethyl radicals in microsomes from chronic alcohol-fed rats. This effect is not due to an interference with the metabolism of ethanol by CYP2E1, but is rather related to the capacity of the silybin molecule to scavenge hydroxyethyl radicals. However, such an effect is lost when pure silybin in amounts comparable to those present in Silipide is administered instead, due to the low bioavailability of uncomplexed flavonoid. Further experiments in vivo have shown that Silipide administration also decreases hydroxyethyl radical signals detectable in the bile of rats acutely treated with ethanol. The ability of Silipide to scavenge ethanol-derived radicals along with its antioxidant activity suggests that this drug might be potentially useful in counteracting free radical-mediated injuries involved in the development of liver damage caused by alcohol abuse.

The evaluation of hepatoprotective effects of Taiwan folk medicine 'teng-khia-u'

'Teng-khia-u' is a folk medicine of Taiwan, derived from the entire plants of Elephantopus scaber L., E. mollis H.B.K. and Pseudoelephantopus spicatus (Juss.) Rohr. The hepatoprotective effects of water extracts of these three plants against beta-D-galactosamine (D-GalN)- and acetaminophen (APAP)-induced acute hepatic damage were determined in rats. The results indicated that the serum glutamate-oxalate-transaminase (sGOT) and the serum glutamate-pyruvate-transaminase (sGPT) levels caused by D-GalN and APAP decreased after treatment with crude extracts of 'teng-khia-u' (P < 0.005). The pathological changes of hepatic lesions, caused by D-GalN and APAP, improved following treatment with the drug extracts mentioned above.

Influence of a series of natural flavonoids on free radical generating systems and oxidative stress

1. A series of flavonoids isolated from Indian medicinal plants: kaempferol-3-O-galactoside, hispidulin, nepetin, scutellarein, scutellarein-7-O-glucuronide, hibifolin and morelloflavone were studied for their activity as inhibitors of microsomal lipid peroxidation and scavengers of oxygen free radicals in vitro as well as in a model of xenobiotic toxicity in mouse. 2. All compounds inhibited lipid peroxidation in vitro. The most potent compounds were nepetin (non-enzymic lipid peroxidation) and morelloflavone (enzymic lipid peroxidation) with IC50's in the micromolar range. Some of the compounds behaved as scavengers of hydroxyl radical in the deoxyribose degradation assay, with a calculated rate constant for kaempferol-3-O-galactoside of 1.55 x 10(10) M-1 s-1. 3. Scutellarein and nepetin were found to be inhibitors of xanthine oxidase activity, whereas morelloflavone acted as a scavenger of superoxide generated by hypoxanthine/xanthine oxidase. 4. Treatment of mice with scutellarein, hispidulin, nepetin and kaempferol-3-O-galactoside after bromobenzene intoxication decreased serum glumate-pyruvate transaminase activity, although only the last flavonoid was able to significantly reduce hepatic lipid peroxidation products and to increase the reduced glutathione level. In contrast, morelloflavone increased bromobenzene toxicity.

The role of glutathione and protein thiols in CBrCl3-induced cytotoxicity in isolated rat hepatocytes

The role of glutathione (GSH) and protein thiols in the pathobiochemical process of CBrCl3 cytotoxicity was investigated in isolated hepatocytes. Administration of 0.5, 1.0 and 1.5 mmol/l CBrCl3 affected cellular viability as assessed by trypan blue exclusion, release of lactate dehydrogenase and loss of intracellular potassium in a dose-dependent manner. Intracellular glutathione and the capacity to reduce 3-(4,5-dimethylthiazolyl-2-)-2,5-diphenyltetrazolium bromide (MTT, thiazolyl blue) decreased almost independently of the CBrCl3 concentration. Protein thiols were not markedly oxidized in the presence of CBrCl3. However, compromising cellular defence mechanisms by either inhibition of glutathione regeneration or depletion of glutathione enhanced the cytotoxicity of CBrCl3 and induced a loss of protein thiols in the late phase of cellular injury. Under these conditions the thiol-dependent Na+,K+ATPase revealed high sensitivity towards CBrCl3. Thus, glutathione proved to exert effective cytoprotection, and sulfhydryl groups of particular proteins were supposed to be an important target of radical attack.

Hepatoprotective mechanism of silymarin: no evidence for involvement of cytochrome P450 2E1

The involvement of the alcohol-inducible cytochrome P450 2E1 in the hepatoprotective mechanism of the plant flavonoid extract silymarin, and its main active component silybin, was investigated in isolated hepatocytes. Allyl alcohol toxicity, associated lipid peroxidation and GSH depletion was efficiently counteracted by silymarin (0.01-0.5 mM), and at higher concentrations by silybin. Cell damage by t-butyl hydroperoxide was also prevented by silymarin and silybin, but less efficiently. However, the covalent binding of the acetaminophen intermediate, formed via P450 2E1, was unaffected by addition of the flavonoids. Silybin did not influence microsomal 2E1-catalyzed demethylation of N-nitrosodimethylamine. Neither did demethylation of N-nitrosodimethylamine or aminopyrine by isolated microsomes affect the in vivo administration of silybin. Addition of silymarin or silybin to primary cultures of isolated hepatocytes did not prevent cell damage induced by exposure to the P450 2E1 substrate CCl4. In contrast, the mere presence of low concentrations (25-50 microM) of these compounds was found to inhibit cell attachment to the matrix and eventually resulted in cell damage. We conclude that contrary to earlier reports we found no evidence for an interaction of silymarin or silybin with cytochrome P450 2E1. This suggests that the antioxidant and free radical scavenging properties may account for most of the therapeutic effect of these compounds. The untoward effect of silymarin on cultured cells may have consequences when considering long-term prescription of this therapeutic agent.

Hispidulin protection against hepatotoxicity induced by bromobenzene in mice

The effects of the natural flavonoid hispidulin (6-methoxy-5,7,4'-trihydroxyflavone) on bromobenzene-induced hepatotoxicity in mice were investigated. We found a correlation between liver injury and hepatic lipid peroxidation besides a strong liver glutathione depletion due to the toxicant. Hispidulin at doses between 50 and 150 mg/kg i.p. compared favourably with the reference compound N-acetyl-L-cysteine for inhibition of liver injury and lipid peroxidation. The flavonoid at the highest dose tested was also able to counteract reduced glutathione depletion induced by bromobenzene in starved mice. These hepatoprotective effects can be related to the antioxidant properties of hispidulin.