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.

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.

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.

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.

Individual fumonisin exposure and sphingoid base levels in rural populations consuming maize in South Africa.

Low and high oesophageal cancer incidence areas of the former Transkei region of South Africa have been associated with corresponding low and high levels of fumonisin contaminated home-grown maize. This is the first study in South Africa assessing fumonisin B (FB) mycotoxin exposure by quantifying individual maize consumption with weighed food records and FB levels from maize in each participant's household and concurrently evaluating sphinganine (Sa), sphingosine (So) and Sa/So ratios in plasma and urine of these participants as possible biomarkers of FB exposure. The high consumption of maize in Bizana (n=36) and Centane (n=30) of 0.41+/-0.21 and 0.39+/-0.19 kg/day, respectively, confirms the reliance on maize as the dietary staple. Mean total FB (FB(1)+FB(2)+FB(3)) levels in home-grown maize were 0.495+0.880 and 0.665+0.660 mg/kg in Bizana and Centane, respectively. Mean fumonisin exposure based on individual consumption was 3.9+/-7.3 and 4.1+/-7.6 microg/kg body weight/day, respectively, for Bizana and Centane. The mean combined sphinganine/sphingosine ratios in Bizana and Centane were similar and ranged from 0.10-0.55 in plasma (n=41) and urine (n=62). There was no association between sphingoid base levels and/or Sa/So ratios in the plasma and urine and individual fumonisin exposure, negating the sphingoid bases as potential biomarkers of fumonisin exposure in humans.

Exposure assessment for fumonisins in the former Transkei region of South Africa.

The fumonisins are mycotoxins produced mainly by Fusarium verticillioides and F. proliferatum in maize, the predominant cereal staple for subsistence farming communities in southern Africa. In order to assess exposure to these mycotoxins in the Bizana (now known as Mbizana) and Centane magisterial areas of the former Transkei region of the Eastern Cape Province of South Africa, the actual maize consumption by different age groups in these communities was measured. In the groups 1-9 years (n = 215) and 10-17 (n = 240) years, mean consumption (+/-standard error) was 246 +/- 10.8 and 368 +/- 10.3 g per person day(-1), respectively, with no significant difference (p > 0.05) between the magisterial areas. For adults (18-65 years) mean maize consumption in Bizana (n = 229) and Centane (n = 178) were significantly different (p < 0.05) at 379 +/- 10.5 and 456 +/- 11.9 g per person day(-1), respectively. An exposure assessment was performed by combining the maize consumption distribution with previously determined levels of total fumonisin (fumonisins B(1) and B(2) combined) contamination in home-grown maize in these two areas. Assuming an individual adult body weight of 60 kg, fumonisin exposure in Bizana, an area of relatively low oesophageal cancer incidence, was 3.43 +/- 0.15 microg kg(-1) body weight day(-1), which was significantly lower (p < 0.05) than that in Centane (8.67 +/- 0.18 microg kg(-1) body weight day(-1)), an area of high oesophageal cancer incidence. Mean fumonisin exposures in all age groups in both Bizana and Centane were above the provisional maximum tolerable daily intake (PMTDI) of 2 microg kg(-1) body weight day(-1) set by the Joint FAO/WHO Expert Committee on Food Additives.

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).

Lecithin has no effect on serum lipoprotein, plasma fibrinogen and macro molecular protein complex levels in hyperlipidaemic men in a double-blind controlled study.

OBJECTIVE: To examine the effects of lecithin on serum lipoprotein, plasma fibrinogen and macro molecular protein complex (MPC) levels. SUBJECTS AND STUDY DESIGN: Twenty free living hyperlipidaemic men participated in this double-blind study which controlled for possible indirect effects. The subjects were randomly assigned to one of three treatments: frozen yoghurt or frozen yoghurt with 20 g soya bean lecithin or frozen yoghurt with 17 g sunflower oil. Sunflower oil was used to control for the increased energy and linoleic acid intake from lecithin. Yoghurt served as the 'vehicle' for the lecithin and sunflower oil and yoghurt alone was given to one group to control for possible effects due to the yoghurt 'vehicle', as well as other environmental influences. Variables were measured with standard methods twice at baseline and after 2 and 4 weeks of treatment. RESULTS: Plasma linoleic acid levels increased significantly with lecithin and sunflower oil treatments indicating that compliance to the treatments were obtained. Lecithin treatment did not have significant effects on serum total cholesterol, triglyceride, high density lipoprotein cholesterol, low density lipoprotein cholesterol, apolipoprotein A, apolipoprotein B or lipoprotein (a) levels. Plasma fibrinogen and MPC levels were also not affected by lecithin therapy. Sunflower oil treatment resulted in significant increased body weight, serum TC and decreased MPC levels. CONCLUSION: Lecithin treatment had no independent effects on serum lipoprotein, plasma fibrinogen or MPC levels in hyperlipidaemic men.

Adenosine deaminase isoenzymes in typhoid fever.

The activity of serum adenosine deaminase and its isoenzymes (ADA1 and ADA2) was measured in the sera of 55 patients with clinically diagnosed typhoid fever, 46 of whom were seropositive for Salmonella typhi infection. At presentation 95% of the serologically positive patients had increased serum adenosine deaminase activity. The increase in activity was greater than that of other frequently measured enzymes. Isoenzyme ADA2 accounted for 84% of the activity, indicating a monocyte/macrophage origin. Results show that in patients with typhoid fever, serum adenosine deaminase, particularly its isoenzyme ADA2, may be regarded as a marker for monocyte/macrophage activation and could be valuable in diagnosis.

Isolation and 1H-NMR spectroscopic identification of poly(3-hydroxybutanoate) from prokaryotic and eukaryotic organisms. Determination of the absolute configuration (R) of the monomeric unit 3-hydroxybutanoic acid from Escherichia coli and spinach.

Trace amounts of poly[(R)-3-hydroxybutanoate] were isolated from competent Escherichia coli, spinach, bovine serum albumin, beef heart mitochondria, and aortal tissues, all sources in which it is not accumulated as storage material. Its identity was in all cases proved by 1H-NMR spectroscopy. In some runs, the poly[(R)-3-hydroxybutanoate] isolated from competent E. coli also contained some 3-hydroxyvalerate, an observation confirmed by 1H-NMR spectroscopy and gas chromatography. The absolute configuration of the polymers isolated from E. coli and spinach was shown to be (all-R) by gas chromatography on chiral columns.