Modulation of key lipid raft constituents in primary rat hepatocytes by fumonisin B1 - Implications for cancer promotion in the liver.

Fumonisin B1 (FB1), a group 2B natural occurring carcinogenic mycotoxin, modulated lipid and fatty acid (FA) constituents of lipid rafts isolated from primary hepatocytes following exposure to a cytotoxic concentration of FB1 (250 µM). The major effects observed in rafts, included a significant (p < 0.05) increase in raft cholesterol (CHOL) and glycerophospholipid such as phosphatidylethanolamine (PE), whereas sphingomyelin (SM) decreased (p < 0.05). Changes in lipid constituents resulted in the disruption of important membrane fluidity parameters represented as a decreased (p < 0.05) in the phosphatidylcholine (PC)/PE and PC/(PE+SM) ratios and an increase (p < 0.05) in the CHOL/PL (PL=PC+PE) ratio, suggesting the preservation of lipid raft rigidity and integrity. Observed FA changes in the raft PE fraction included a significant (p < 0.05) increase in C18:2ω-6, C20:3ω-6, C20:4ω-6, C22:4ω-6, C22:5ω-3 and C22:6ω-3, with an increase in total ω-6 and ω-3 polyunsaturated fatty acids (PUFAs). Modulation of the FA content in PE, specifically the C20:4ω-6 PC/PE ratio and PUFA levels, together with changes in CHOL and SM are key determinants regulating the integrity and function of lipid rafts. In primary hepatocytes these changes are associated with the inhibition of cell proliferation and induction of apoptosis. A lipogenic mechanism is proposed whereby FB1 modulates lipid rafts and differentially target cell survival indices of normal and preneoplastic hepatocytes during cancer promotion in the liver.

Differential modulation of the lipid metabolism as a model for cellular resistance to fumonisin B1-induced cytotoxic effects in vitro.

Differential sensitivity of primary hepatocytes and Chang cells to the cancer promoter fumonisin B1 (FB1)-induced cytotoxic effects were investigated in relation to changes in membrane lipid distribution. In contrast to primary hepatocytes, Chang cells were resistant to FB1-induced cytotoxic effects. This was associated with a high cholesterol (Chol) and sphingomyelin (SM) and low phosphatidylcholine (PC) content, resulting in a significant (P<0.05) decrease in phosphatidylethanolamine (PE)/PC ratio, increased Chol/total phosphoglyceride (TPG) ratios and low total polyunsaturated fatty acids (PUFA) content in PC and PE, suggesting a more rigid membrane structure. High levels of C18:1 and reduced polyunsaturated fatty acid (PUFA) levels are likely to provide selective resistance to FB1-induced oxidative stress. FB1-associated lipid changes included decreases in SM and Chol, increases in sphinganine (Sa) and PE with the increases in key saturated, monounsaturated, and PUFAs in PE as key role players in the differential responses to FB1-induced cell growth responses in cells.

Induction of an altered lipid phenotype by two cancer promoting treatments in rat liver.

Changes in lipid metabolism have been associated with tumor promotion in rat liver. Similarities and differences of lipid parameters were investigated using the mycotoxin fumonisin B1 (FB1) and the 2-acetylaminofluorene/partial hepatectomy (AAF/PH) treatments as cancer promoters in rat liver. A typical lipid phenotype was observed, including increased membranal phosphatidylethanolamine (PE) and cholesterol content, increased levels of C16:0 and monounsaturated fatty acids in PE and phosphatidylcholine (PC), as well as a decrease in C18:0 and long-chained polyunsaturated fatty acids in the PC fraction. The observed lipid changes, which likely resulted in changes in membrane structure and fluidity, may represent a growth stimulus exerted by the cancer promoters that could provide initiated cells with a selective growth advantage. This study provided insight into complex lipid profiles induced by two different cancer promoting treatments and their potential role in the development of hepatocyte nodules, which can be used to identify targets for the development of chemopreventive strategies against cancer promotion in the liver.

Dietary PUFA and cancer.

The aim of the present paper is to give a brief overview on the role of dietary fat in carcinogenesis and as possible anticancer agents. Dietary fat is an essential nutrient and important source for the essential fatty acids (FA), linoleic and α-linolenic acids, which contribute to proper growth and development. However, dietary fat has been associated with the development of colorectal, breast, prostate, endometrial and ovarian cancers, with the type and quality of fat playing an underlying role. Tumour growth is the disruption of the homoeostatic balance regulating cell differentiation, proliferation and apoptosis and is associated with altered lipid metabolism. Animal cancer models and human cancer biopsy tissue demonstrate that a characteristic lipid profile is associated with the growth and development of neoplastic lesions. This entails alterations in membrane cholesterol, phospholipid and PUFA metabolism. Particularly, alterations in cell membrane FA metabolism involving the n-6 and n-3 PUFA, are associated with changes in membrane structure, function, cellular oxidative status, activity of enzymes and signalling pathways. These events are a driving force in sustaining the altered growth of cancerous lesions and provide unique targets for intervention/cancer modulation. Challenges in utilising FA in cancer modulation exist regarding intake and effect on cell structure and biochemical interactions within the cell in the prevention of cancer development. Therefore, utilising dietary PUFA in a specific n-6:n-3 ratio may be an important chemopreventive tool in altering the growth characteristics of cancer cells.

The mycotoxin distribution in maize milling fractions under experimental conditions.

Mycotoxin contamination of maize and maize-based food and feed products poses a health risk to humans and animals if not adequately controlled and managed. The current study investigates the effect of dry milling on the reduction of fumonisins (FB), deoxynivalenol (DON) and zearalenone (ZEA) in maize. Five composite samples, constructed to represent different mycotoxin contamination levels were degermed yielding degermed maize and the germ. The degermed maize was milled under laboratory conditions and four major milling fractions (SPECIAL, SUPER, semolina (SEM) and milling hominy feed) collected. The whole maize, degermed maize and total hominy feed (germ+milling hominy feed) were reconstructed to ensure homogenous samples for mycotoxin analyses. For comparison, commercial dry milling fractions (whole maize, SPECIAL, SUPER and total hominy feed), collected from three South African industrial mills, were analysed for the same mycotoxins and hence a more accurate assessment of the distribution between the different milling fractions. The distribution of the mycotoxins during the experimental dry milling of the degermed maize differs, with FB mainly concentrated in the SPECIAL, DON in the SEM whereas ZEA was equally distributed between the two milling fractions. Distribution of mycotoxins between the fractions obtained during commercial dry milling generally provided similar results with the total hominy feed containing the highest and the SUPER milling fractions the lowest mycotoxin levels although variations existed. Although milling is an effective way to reduce mycotoxins in maize, kernel characteristics and resultant fungal colonisation may impact on the distribution of specific mycotoxins among the different milling fractions. Differences in industrial dry milling practices and problems encountered in sampling bulk maize remain a large problem in assessing mycotoxin contamination in milling fractions intended for human consumption.

Controversies in fumonisin mycotoxicology and risk assessment.

Fusarium verticillioides causes several animal diseases and the contamination maize suggests that it could adversely affect human health. The fumonisin B mycotoxins were characterized from the fungal culture material and shown to be the causative principle responsible for the major mycotoxicological effects of the fungus in experimental and farm animals. The main focus was on the toxicological effects in rats and mice, the outcome of which played an important role in setting risk assessment parameters for exposure of the fumonisins to humans. The International Agency for Research on Cancer characterized the fumonisins as Group 2B carcinogens. Several controversial findings regarding the toxicological effects of the culture material of the fungus, the genotoxicity and carcinogenicity of pure fumonisin B(1) (FB(1)) in rats have been reported that should be clarified prior to assessing the risk in humans. The underlying differences between the diets with the high protein levels are likely to sensitize the kidneys to FB(1)-induced toxic and carcinogenic effects. Several other dietary factors, such as plant extracts (antioxidants) and dietary Fe, could either stimulate or inhibit cancer induction of FB(1), which complicates the comparison of toxicological effects in experimental animals. Cognisance should be taken of the modulating role of dietary constituents as it will determine the outcome of toxicological assays and determine the threshold of an adverse effect in a specific target organ to be used in determining risk assessment parameters.

Simple intervention method to reduce fumonisin exposure in a subsistence maize-farming community in South Africa.

In the Centane magisterial area of South Africa, high rates of oesophageal cancer have been associated with home-grown maize contaminated with fumonisins. The aim of this study was to implement a simple intervention method to reduce fumonisin exposure in a subsistence-farming community. The hand-sorting and washing procedures, based on traditional maize-based food preparation practices, were previously customised under laboratory-controlled conditions. Home-grown maize and maize-based porridge collected at baseline were analysed for fumonisin B(1), B(2) and B(3). The geometric mean (95% confidence interval) of fumonisin contamination in the home-grown maize at baseline was 1.67 (1.21-2.32) mg kg(-1) and 1.24 (0.75-2.04) mg kg(-1) (dry weight) in the porridge. Fumonisin exposure was based on individual stiff porridge consumption and the specific fumonisin levels in the porridge (dry weight) consumed. Porridge (dry weight) consumption at baseline was 0.34 kg day(-1) and fumonisin exposure was 6.73 (3.90-11.6) µg kg(-1) body weight day(-1). Female participants (n = 22) were trained to recognise and remove visibly infected/damaged kernels and to wash the remaining maize kernels. The discarded kernels represented 3.9% by weight and the fumonisins varied from 17.1 to 76.9 mg kg(-1). The customised hand-sorting and washing procedures reduced fumonisin contamination in the maize and porridge by 84 and 65%, respectively. The intervention reduced fumonisin exposure by 62% to 2.55 (1.94-3.35) µg kg(-1) body weight day(-1). This simple intervention method has the potential to improve food safety and health in subsistence-farming communities consuming fumonisin-contaminated maize as their staple diet.

Antifungal activity of four weedy plant extracts against selected mycotoxigenic fungi.

AIMS: To investigate the antifungal activity of aqueous and organic extracts of four weedy plant species viz. Tagetes minuta, Lippia javanica, Amaranthus spinosus and Vigna unguiculata against isolates of four agriculturally important fungi, i.e. Fusarium verticillioides, F. proliferatum, Aspergillus flavus and A. parasiticus. METHODS AND RESULTS: Dried powdered aerial parts of the plants were extracted sequentially with hexane, dichloromethane, methanol and water and tested for activity using a serial microdilution assay. Results were read every day over 120 h. All extracts except for the water extracts showed growth inhibitory activity against most isolates of the Fusarium spp. The most active were the methanol and hexane extracts of V. unguiculata and A. spinosus with minimum inhibitory concentration (MIC) values of <0.5 mg ml(-1) after 48 h against Fusarium spp. No inhibition of the Aspergillus spp. tested was observed, but conidium formation was stimulated on plates treated with plant extracts when visually compared to the growth controls. CONCLUSIONS: The results obtained from this study indicated that chemical constituents from these plant species may be developed as potential agrochemical fungicides. SIGNIFICANCE AND IMPACT OF THE RESEARCH: Food and feed are subject to infection by a variety of micro-organisms that can induce spoilage and/or produce metabolites that are toxic to humans and animals. Extracts of V. unguiculata and A. spinosus were most active and maybe developed into environmentally friendly fungicides, which are affordable to rural farmers in developing countries.

Dietary fumonisin exposure in a rural population of South Africa.

A validated culturally specific dietary assessment method was used to determine the habitual maize intakes of black Xhosa-speaking Africans living in the Centane region of the Eastern Cape Province to assess their exposure to the carcinogenic fumonisin mycotoxins. The mean total dry weight maize intakes of home-grown, commercial or combined (both maize sources) were 474, 344, 462 g day(-1), respectively. When considering the total mean levels of fumonisin in home-grown maize (1142 microg kg(-1)) and commercial maize (222 microg kg(-1)), the probable daily intakes (PDI's), expressed as microg kg(-1) body weight day(-1) were 12.1 (95%CI: 0.3-4926.5) and 1.3 (95%CI: 1.0-1.8) for men and 6.7 (95%CI: 1.0-457.8) and 1.1 (95%CI: 0.9-1.3) for women, consuming home-grown and commercial maize, respectively. Based on the different maize-based beer drinking frequencies the PDI's varied between 6.9 and 12.0 microg kg(-1)/drinking event. Depending on the maize intake patterns an exposure "window" exists where fumonisin exposure is below the recommended group provisional maximum tolerable daily intake (PMTDI) for fumonisins of 2 microg kg(-1)bw day(-1). The assessment of fumonisin exposure and development of preventative strategies depend, not only the accurate determination of total fumonisin levels in maize, but also on the distinct dietary patterns of a specific population.

Altered lipid profile, oxidative status and hepatitis B virus interactions in human hepatocellular carcinoma.

Altered membrane integrity in hepatocellular carcinoma (HCC) tissue was indicated by an elevation in cholesterol and significant decrease in phosphatidylcholine (PC). The resultant decreased phosphatidylcholine/phosphatidylethanolamine (PC/PE) and increased cholesterol/phospholipid ratios are associated with decreased fluidity in the carcinoma tissue. The lower PC was associated with a decrease in the quantitative levels of the saturated (C16:0, C18:0), omega6 (C18:2, C20:4) and omega3 (C22:5, C22:6) fatty acids (FAs), resulting in reduced long-chain polyunsaturated fatty acids (LCPUFAs), total PUFA and an increase in omega6/omega3 FA ratio. In PE, the saturated and omega3 (C22:5, C22:6) FAs were reduced while the total omega6 FA level was not affected, leading to an increased omega6/omega3 FA ratio. Increased levels of C18:1omega9, C20:2omega6 and reduction of 22:6omega3 in PC and PE suggest a dysfunctional delta-6 desaturase. The reduced PC/PE ratio resulted in a decreased C20:4omega6 (PC/PE) ratio, implying a shift towards synthesis of the 2-series eicosanoids. Lipid peroxidation was reduced in both hepatitis B negative (HBV(-)) and positive (HBV(+)) HCC tissues. Glutathione (GSH) was decreased in HCC while HBV had no effect, suggesting an impairment of the GSH redox cycle. In contrast HBV infection enhanced GSH in the surrounding tissue possibly to counter oxidative stress as indicated by the increased level of conjugated dienes. Apart from the reduced LCPUFA, the low level of lipid peroxidation in the carcinoma tissue was associated with increased superoxide dismutase and glutathione peroxidase activity. The disruption of the redox balance, resulting in increased cellular antioxidant capacity, could create an environment for resistance to oxidative stress in the carcinoma tissue. Alterations in membrane cholesterol, phospholipids, FA parameters, C20:4omega6 membrane distribution and low lipid peroxidation are likely to be important determinants underlying the selective growth advantage of HCC cells.

Degradation of aflatoxin B(1) by fungal laccase enzymes.

The enzymatic degradation of aflatoxin B(1) (AFB(1)) by white rot fungi through laccase production was investigated in different liquid media. A significant (P<0.0001) correlation was observed between laccase activity and AFB(1) degradation exhibited by representatives of Peniophora and Pleurotus ostreatus cultivated in minimal salts (MSM) (r=0.93) and mineral salts - malt extract (MSB-MEB) (r=0.77) liquid media. Peniophora sp. SCC0152 cultured in MSB-MEB liquid medium supplemented with veratryl alcohol and sugarcane bagasse showed high laccase activity (496U/L), as well as 40.45% AFB(1) degradation as monitored using high performance liquid chromatography. P.ostreatus St2-3 cultivated in MSM liquid medium supplemented with veratryl alcohol resulted in laccase activity of 416.39U/L and 35.90% degradation of AFB(1). Aflatoxin B(1) was significantly (P<0.0001) degraded when treated with pure laccase enzyme from Trametes versicolor (1U/ml, 87.34%) and recombinant laccase produced by Aspergillus niger D15-Lcc2#3 (118U/L, 55%). Aflatoxin B(1) degradation by laccase enzyme from T. versicolor and recombinant laccase enzyme produced by A. niger D15-Lcc2#3 coincided with significant (P<0.001) loss of mutagenicity of AFB(1), as evaluated in the Salmonella typhimurium mutagenicity assay. The degradation of AFB(1) by white rot fungi could be an important bio-control measure to reduce the level of this mycotoxin in food commodities.

South African herbal teas: Aspalathus linearis, Cyclopia spp. and Athrixia phylicoides--a review.

Rooibos (Aspalathus linearis (Brum.f) Dahlg.) and honeybush (Cyclopia Vent. species) are popular indigenous South African herbal teas enjoyed for their taste and aroma. Traditional medicinal uses of rooibos in South Africa include alleviation of infantile colic, allergies, asthma and dermatological problems, while a decoction of honeybush was used as a restorative and as an expectorant in chronic catarrh and pulmonary tuberculosis. Traditional medicinal uses of Athrixia phylicoides DC., or bush tea, another indigenous South African plant with very limited localised use as herbal tea, include treatment of boils, acne, infected wounds and infected throats. Currently rooibos and honeybush are produced for the herbal tea market, while bush tea has potential for commercialisation. A summary of the historical and modern uses, botany, distribution, industry and chemical composition of these herbal teas is presented. A comprehensive discussion of in vitro, ex vivo and in vivo biological properties, required to expand their applications as nutraceutical and cosmeceutical products, is included, with the main emphasis on rooibos. Future research needs include more comprehensive chemical characterisation of extracts, identification of marker compounds for extract standardisation and quality control, bioavailability and identification of bio-markers of dietary exposure, investigation of possible herb-drug interactions and plant improvement with regards to composition and bioactivity.

Cancer initiating properties of fumonisin B1 in a short-term rat liver carcinogenesis assay.

The nature of cancer initiation by fumonisin B(1) (FB(1)) was investigated in rat liver by monitoring the effect of phenobarbital (PB) as cancer promoter and evaluating the involvement of spontaneously initiated cells. A PB promoting regimen (0.05% in the diet) stimulated the outgrowth of FB(1)-induced placental glutathione S-transferase (GSTP) positive initiated hepatocytes. Reversion of the FB(1)-induced GSTP(+) foci was noticed in the absence of a promoting regimen. Younger rats were shown to be more sensitive to the induction of GSTP(+) foci by FB(1). Cancer initiation by FB(1) was associated with a hepatotoxic effect, which was less pronounced in older rats presumably due to a reduced intake. A specific role of spontaneously initiated cells and their promotion by FB(1) into the development of eosinophilic clear cell foci could not be established under the present experimental conditions. The ability of different stimuli to selectively promote the outgrowth of FB(1) initiated cells further verifies the cancer initiating potency of this apparent non-genotoxic mycotoxin. The underlying mechanism(s) involved in the genesis of the initiated hepatocytes is not known at present.

Altered lipid parameters in hepatic subcellular membrane fractions induced by fumonisin B1.

Alteration of lipid constituents of cellular membranes has been proposed as a possible mechanism for cancer promotion by fumonisin B(1 )(FB(1)). To further investigate this hypothesis a dietary dosage which initiates and promotes liver cancer (250 mg FB(1)/kg) was fed to male Fischer rats for 21 days and the lipid composition of plasma, microsomal, mitochondrial and nuclear subcellular fractions determined. The effect of FB(1) on the cholesterol, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), as well as sphingomyelin (SM) and the phospholipids-associated fatty acid (FA) profiles, were unique for each subcellular membrane fraction. PE was significantly increased in the microsomal, mitochondrial and plasma membrane fractions, whereas cholesterol was increased in both the microsomal and nuclear fraction. In addition SM was decreased and increased in the mitochondrial and nuclear fractions, respectively. The decreased PC/PE and polyunsaturated/saturated (P/S) FA ratio in the different membrane fractions suggest a more rigid membrane structure. The decreased levels in polyunsaturated fatty acids in PC together with a pronounced increase in C18:1omega9 and C18:2omega6 were indicative of an impaired delta-6 desaturase. The increased omega6/omega3 ratio and decreased C20:4omega6 PC/PE ratio due to an increase in C20:4omega6 in PE relatively to PC in the different subcellular fractions suggests a shift towards prostanoid synthesis of the E2 series. Changes in the PE and C20:4omega6 parameters in the plasma membrane could alter key growth regulatory and/or other cell receptors in lipid rafts known to be altered by FB(1). An interactive role between C20:4omega6 and ceramide in the mitochondria, is suggested to regulate the balance between proliferation and apoptosis in altered initiated hepatocytes resulting in their selective outgrowth during cancer promotion effected by FB(1).

A comparative study on the antimutagenic properties of aqueous extracts of Aspalathus linearis (rooibos), different Cyclopia spp. (honeybush) and Camellia sinensis teas.

Antimutagenic activity of aqueous extracts of the South African herbal teas, Aspalathus linearis (rooibos) and Cyclopia spp. (honeybush) was compared with that of Camellia sinensis (black, oolong and green) teas in the Salmonella mutagenicity assay using aflatoxin B(1) (AFB(1)) and 2-acetylaminofluorene (2-AAF) as mutagens. The present study presents the first investigation on antimutagenic properties of C. subternata, C. genistoides and C. sessiliflora. The herbal teas demonstrated protection against both mutagens in the presence of metabolic activation, with the exception of "unfermented" (green/unoxidised) C. genistoides against 2-AAF, which either protected or enhanced mutagenesis depending on the concentration. Antimutagenic activity of "fermented" (oxidised) rooibos was significantly (P<0.05) less than that of Camellia sinensis teas against AFB(1), while for 2-AAF it was less (P<0.05) than that of black tea and similar (P>0.05) to that of oolong and green teas. Antimutagenic activity of unfermented C. intermedia and C. subternata exhibited a similar protection as fermented rooibos against AFB(1). Against 2-AAF, fermented rooibos exhibited similar protective properties than unfermented C. intermedia and C. sessiliflora. Unfermented rooibos was less effective than the C. sinensis teas and fermented rooibos, but had similar (P>0.05) antimutagenicity to that of fermented C. sessiliflora against AFB(1) and fermented C. subternata against 2-AAF. Fermented C. intermedia and C. genistoides exhibited the lowest protective effect against 2-AAF, while fermented C. intermedia exhibited the lowest protection when utilising AFB(1) as mutagen. Aspalathin and mangiferin, major polyphenols in rooibos and Cyclopia spp., respectively, exhibited weak to moderate protective effects when compared to the major green tea catechin, (-)epigallocatechin gallate (EGCG). Antimutagenic activity of selected herbal tea phenolic compounds indicated that they contribute towards (i) observed antimutagenic activity of the aqueous extracts against both mutagens and (ii) enhancement of the mutagenicity of 2-AAF by unfermented C. genistoides. Antimutagenic activity of the South African herbal teas was mutagen-specific, affected by fermentation and plant material, presumably due to changes and variation in phenolic composition.

Ex vivo modulation of chemical-induced mutagenesis by subcellular liver fractions of rats treated with rooibos (Aspalathus linearis) tea, honeybush (Cyclopia intermedia) tea, as well as green and black (Camellia sinensis) teas.

Male Fischer rats were given unprocessed (not oxidized) and processed (oxidized) rooibos and honeybush teas as well as green and black teas as a sole source of drinking fluid for 10 weeks, and sub cellular liver fractions were prepared. Cytosolic fractions of rats consuming the unprocessed herbal teas, green and black teas significantly (P < 0.05) protected against 2-acetylaminofluorene (2-AAF)-induced mutagenesis in the Salmonella mutagenicity test with strain TA 98, using Aroclor 1254-induced microsomes. A marginal or no protection was obtained with the processed herbal teas. The mutagenic response of aflatoxin B1 (AFB1) against Salmonella strain TA 100 was significantly (P < 0.05) inhibited by cytosolic fractions from rats treated with processed and unprocessed herbal teas, while no effect was obtained with the green and black teas. Microsomal fractions prepared from livers of rats treated with both the processed and unprocessed rooibos teas and the unprocessed honeybush tea, significantly (P < 0.05) reduced the activation of AFB1 while no protection was observed against 2-AAF-induced mutagenesis. In contrast, microsomal fractions from rats treated with the green, black and unprocessed honeybush teas significantly (P < 0.05) enhanced the mutagenic response of 2-AAF. None of the tea treatments significantly affected the concentration of the microsomal liver cytochrome P450.

Fumonisin contamination of a corn sample associated with the induction of hepatocarcinogenesis in rats-role of dietary deficiencies.

A corn sample associated with a field outbreak of equine leukoencephalomalacia in Pennsylvania, USA, during 1983/1984 and induced hepatotoxic and hepatocarcinogenic effects when fed to male Fischer rats was analyzed mycologically and chemically for the presence of fumonisins (FB), hydrolysed FB derivatives and aflatoxins (AFB). Fusarium verticillioides was found to be the predominant fungal contaminant in the corn sample but Aspergillus flavus was also present. Trace amounts (0.1 microg/kg) of AFB(1) and AFB(2) and a total FB level of 33.5 mg/kg (FB(1):FB(2):FB(3) ratio of 9:2.3:1) were found. No hydrolysed FB derivatives or AFG(1) and AFG(2) were detected. Based on the chemical stability of the fumonisins in different corn cultures of F. verticillioides kept at 4 degrees C over a period of 13-20 years, a level of approximately 55 mg/kg of total FB is estimated in the original corn sample. A possible role of certain dietary constituents such as the high protein content and deficiencies in certain micronutrients is evaluated to address differences in the organ-specific toxicity of FB(1) in rats using commercial, semi-purified, purified and corn-only diets.

Dietary modulation of fatty acid profiles and oxidative status of rat hepatocyte nodules: effect of different n-6/n-3 fatty acid ratios.

Male Fischer rats were fed the AIN 76A diet containing varying n-6/n-3 FA ratios using sunflower oil (SFO), soybean oil (SOY), and SFO supplemented with EPA-50 and GLA-80 (GLA) as fat sources. Hepatocyte nodules, induced using diethylnitrosamine followed by 2-acetylaminofluorene/partial hepatectomy promotion, were harvested, with surrounding and respective dietary control tissues, 3 mon after partial hepatectomy. The altered growth pattern of hepatocyte nodules in rats fed SFO is associated with a distinct lipid pattern entailing an increased concentration of PE, resulting in increased levels of 20:4n-6. In addition, there is an accumulation of 18:1 n-9 and 18:2n-6 and a decrease in the end products of the n-3 metabolic pathway in PC, suggesting a dysfunctional delta-6-desaturase enzyme. The hepatocyte nodules of the SFO-fed rats exhibited a significantly reduced lipid peroxidation level that was associated with an increase in the glutathione (GSH) concentration. The low n-6/n-3 FA ratio diets significantly decreased 20:4n-6 in PC and PE phospholipid fractions with a concomitant increase in 20:5n-3, 22:5n-3, and 22:6n-3. The resultant changes in the 20:4/20:5 FA ratio and the 20:3n-6 FA level in the case of the GLA diet suggest a reduction of prostaglandin synthesis of the 2-series. The GLA diet also counteracted the increased level of 20:4n-6 in PE by equalizing the nodule/surrounding ratio. The low n-6/n-3 ratio diets significantly increased lipid peroxidation levels in hepatocyte nodules, mimicking the level in the surrounding and control tissue while GSH was decreased. An increase in n-3 FA levels and oxidative status resulted in a reduction in the number of glutathione-S-transferase positive foci in the liver of the GLA-fed rats. Modulation of cancer development with low n-6/n-3 ratio diets containing specific dietary FA could be a promising tool in cancer intervention in the liver.

Lipids and delta6-desaturase activity alterations in rat liver microsomal membranes induced by fumonisin B1.

Alterations in the membrane structure and function of hepatocyte membranes by fumonisin B1 (FB1) have been proposed to play an important role in the disruption of growth regulatory effects and hence in the cancer-promoting ability of the mycotoxin. Detailed analyses of lipids in liver microsomal fractions of rats exposed to different dietary levels of FB1 over a period of 21 d indicated an increase in PC, PE, PI, and cholesterol (Chol). These changes decreased the PC/PE and increased the total phospholipid/Chol ratios. When considering FA content, the quantities of total FA increased (P < 0.05) in the major phospholipid fractions as a result of the increased phospholipid levels. However, when considering the relative levels (mg/100 mg of the total FA) of specific FA, the monounsaturated FA (16:1 n-7 and 18:1n-9) and 18:2n-6 increased (P < 0.05), whereas the long-chain PUFA decreased (P < 0.05) in the main phospholipid fractions. Enzyme analyses indicated that the activity of the delta6-desaturase was significantly reduced in liver microsomal preparations in a dose-dependent manner. An increase in the 20:3n-6/20:4n-6 ratio also suggested a decrease in the activity of the delta5-desaturase. Disruption of microsomal lipid metabolism at different levels by FB1 could play an important role in the alteration of growth regulatory effects in the liver.

Interaction of fumonisin B(1) and aflatoxin B(1) in a short-term carcinogenesis model in rat liver.

The co-existence of the fumonisin and aflatoxin mycotoxins in corn merited studies to investigate their possible synergistic toxicological and carcinogenic effects. When utilising a short-term carcinogenesis model in rat liver, both the compounds exhibited slow cancer initiating potency as monitored by the induction of foci and nodules stained positively for the placental form of gluthatione-S-transferase (GSTP(+)). However, when rats were treated in a sequential manner with AFB(1) and FB(1) the number and size of GSTP(+) lesions significantly increased as compared to the separate treatments. Histopathological analyses indicated that the individual treatments showed far less toxic effects, including occasional hepatocytes with dysplastic nuclei, oval cell proliferation and, in the case of FB(1), a few apoptotic bodies in the central vein regions. The sequential treatment regimen induced numerous foci and dysplastic hepatocyte nodules, and with oval cells extending from the periportal regions into the centrilobular regions. This would imply that, in addition to the cancer promoting activity of FB(1) of AFB(1)-initiated hepatocytes, the AFB(1) pre-treatment enhanced the FB(1) initiating potency, presumably by rendering the liver more susceptible to the toxic effects of FB(1). The co-occurrence of AFB(1) and FB(1) in corn consumed as a staple diet could pose an increased risk and should be included in establishing risk assessment parameters in humans.