P W Snijman

Stellenbosch University, Stellenbosch, Western Cape, South Africa

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Publications (16)38.29 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 11/2010; 25(44).
  • I. R. GREEN, S. NEFDT, V. I. HUGO, P. W. SNIJMAN
    ChemInform 01/2010; 26(19).
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    ABSTRACT: The antioxidant activity of rooibos flavonoids, including the dihydrochalcones aspalathin and nothofagin and their corresponding flavone glycosides, was evaluated using the ABTS radical cation, metal chelating, and Fe(II)-induced microsomal lipid peroxidation assays. Epigallocatechin gallate (EGCG) and Trolox were used as reference standards. Optimized geometric conformers of aspalathin and nothofagin, in addition to calculated physicochemical properties, were considered to explain interaction with the microsomal membrane structure and thus relative potency of the dihydrochalcones. The most potent radical scavengers were aspalathin (IC50 = 3.33 microM) and EGCG (IC50 = 3.46 microM), followed by quercetin (IC50 = 3.60 microM) and nothofagin (IC50 = 4.04 microM). The least effective radical scavengers were isovitexin (IC50 = 1224 microM) and vitexin (IC50 > 2131 microM). Quercetin (IC50 = 17.5 microM) and EGCG (IC50 = 22.3 microM) were the most effective inhibitors of lipid peroxidation. Aspalathin (IC50 = 50.2 microM) and catechin (IC50 = 53.3 microM) displayed similar potencies. Nothofagin (IC50 = 1388 microM) was almost as ineffective as its flavone glycoside analogues.
    Journal of Agricultural and Food Chemistry 08/2009; 57(15):6678-84. · 3.11 Impact Factor
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    ABSTRACT: The antimutagenic properties of the most prevalent flavonoids in rooibos (Aspalathus linearis) were compared in the Salmonella typhimurium mutagenicity assay using tester strains TA98 and TA100 with, respectively, 2-acetamido-fluorene (2-AAF) and aflatoxin B(1) (AFB(1)) as mutagens in the presence of metabolic activation. The flavonoids included the dihydrochalcones aspalathin and nothofagin and their flavone analogues, orientin and isoorientin, and vitexin and isovitexin, respectively, as well as luteolin, chrysoeriol, (+)-catechin, quercetin, isoquercitrin, hyperoside and rutin. Flavonoid-mutagen interactions ranged from antimutagenic, comutagenic and promutagenic to mutagenic, while dose-response effects were mutagen-specific and ranged from typical to atypical including biphasic and threshold effects. Aspalathin and nothofagin and their structural flavonoid analogues displayed moderate antimutagenic properties while luteolin and to some extent, chrysoeriol, showed activities comparable to those of the green tea flavonoid (-) epigallocatechin gallate (EGCG). Apart from their mutagenic and promutagenic properties, quercetin and isoquercitrin exhibited concentration-dependent comutagenic and/or antimutagenic effects against 2-AAF- and AFB(1)-induced mutagenesis. Different structural parameters known to affect the antimutagenic properties of flavonoids include their hydrophilic or lipophilic nature due to the extent of hydroxylation and O-methylation, glycosylation on the A and B rings, the C4-keto group and the C2-C3 double bond. The C ring does not appear to be a prerequisite when comparing for the antimutagenic activity of the dihydrochalcones when compared of the dihydrochalcones with the structural flavone analogues.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 08/2007; 631(2):111-23. · 3.90 Impact Factor
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    ABSTRACT: 1H and 13C NMR spectroscopy of both fumonisin B3 and B4, as well as high-performance liquid chromatography (HPLC) analysis of samples of fumonisin B3 used as standards, showed in each case the presence of two stereoisomers, which could not be separated by preparative chromatography. The 2,3-anti relative configuration for the two minor stereoisomers of fumonisin B3 and B4 was deduced from the NMR data, and their 2S,3R absolute configurations were established by application of Mosher's method using the fumonisin B3 sample. Samples of fumonisin B3 and B4 can contain between 10 and 40% of fumonisin B compounds of the 3-epi series. The 3-epi-FB3, determined by HPLC with fluorescence detection of the o-phthaldialdehyde derivative and confirmed by liquid chromatography-tandem mass spectrometry, was found to occur naturally in a range of maize samples at levels much lower than FB3 (< 20%). The identification of members of the 3-epi-fumonisin B series provides insight into the order and selectivity of steps in fumonisin biosynthesis.
    Journal of Agricultural and Food Chemistry 06/2007; 55(11):4388-94. · 3.11 Impact Factor
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    ABSTRACT: 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).
    Lipids 05/2007; 42(3):249-61. · 2.56 Impact Factor
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    ABSTRACT: 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.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 12/2006; 611(1-2):42-53. · 3.90 Impact Factor
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    ABSTRACT: We conducted a chronic feeding study in vervet monkeys (Cercopithecus aethiops) over 13.5 years. The experimental design consisted of two dietary treatment groups, each including males and females, fed varying levels of culture material of Fusarium verticillioides (Sacc.) Nirenberg (= F. moniliforme Sheldon) strain MRC 826 mixed into their daily food ration. Two females were included as treatment controls. We conducted blood chemical analyses bimonthly and recorded all clinical signs during the course of the experiment. We took liver biopsies at various stages during the initial phase of the experiment. Several monkeys were terminated in extremis during the experiment. Detailed feed intake profiles were determined 5 years after the experiment began, and the fumonisin B (FB) mycotoxin content of the feed was determined during the final stages of the experiment. The apparent FB consumption patterns were related to changes observed in the biochemical parameters in the blood and urine, including the liver function enzymes and creatinine clearance as well as differential blood counts and sphingolipid levels in the serum and urine. An apparent no-effect threshold for kidney and liver damage is estimated to be between 0.11 and 0.18 mg FB/kg body weight (bw)/day, which corresponds to a feed contamination level of between 8.21 and 13.25 mg FB/kg bw diet. Apart from the effects on the liver and kidney, a wide variety of parameters, including cholesterol and creatine kinase, were also adversely affected. Several blood parameters, including white and red blood cells, also significantly decreased in the treated animals. The serum sphinganine level and the sphingosine/sphinganine ratio, monitored toward the end of the experiment, significantly increased in both the low-dose and high-dose animals. The present study provides important information about the diversity of lesions induced by culture material of F. verticillioides in vervet monkeys and the dosage levels of fumonisins to be used in long-term studies in nonhuman primates.
    Environmental Health Perspectives 06/2001; 109 Suppl 2:267-76. · 7.26 Impact Factor
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    ABSTRACT: The toxicity of low dietary levels of fumonisin B(1) (FB(1)), i.e. 1, 10 and 25 mg FB(1)/kg diet, were monitored in rats over a period of 24 months. No effects on the body weight gain and feed intake profiles were noticed, while the relative liver weight was significantly (P<0.05) reduced in the FB(1)-treated rats. Mild toxic effects, including single cell necrosis (apoptosis), proliferation of bile duct epithelial cells (DEC), and early signs of fibrosis, bile duct hyperplasia and in one case, adenofibrosis, were noticed in the liver of the rats fed the highest (25 mg/FB(1)/kg diet) dietary level. A significant (P<0.05) increase in the level of oxidative damage was also noticed in the liver of the rats of high dosage dietary group. The toxic effects were less severe in the 10 mg FB(1)/kg dietary group, whilst only a few ground glass foci were observed in the 1 mg FB(1)/kg dietary group. Hepatocyte nodules, staining positively for glutathione-S-transferase (placental form, PGST), were observed macroscopically in the 25 mg FB(1)/kg treated group and to a lesser extent in the 10 mg FB(1)/kg treated rats. The most prominent toxic lesions by FB(1) (10 and 25 mg FB(1)/kg dietary groups) in the kidneys were restricted to the tubular epithelium manifesting as granular cast, necrosis, apoptosis, calcification and the presence of regenerative foci in the proximal convoluted tubules. The existence of a cytotoxic/proliferative threshold with respect to cancer induction by FB(1) in rat liver became apparent, with a dietary level of <10-mg FB(1)/kg diet as a no effect threshold for the induction of hepatocyte nodules.
    Toxicology 03/2001; 161(1-2):39-51. · 4.02 Impact Factor
  • G S Shephard, P W Snijman
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    ABSTRACT: The mycotoxin fumonisin B2 (FB2), which can be present at significant levels in maize infected with the fungus Fusarium moniliforme, was dosed both iv and by gavage to vervet monkeys. It was rapidly eliminated from the plasma of vervet monkeys dosed i.v. with 2 mg FB2/kg body mass. The concentration of FB2 in plasma after the iv dose was characterized by an initial distributional phase and a subsequent elimination phase with a mean half-life of 18 min. When two monkeys were dosed by gavage with a single bolus (7.5 mg/kg body mass), only one showed detectable trace levels of FB2 in plasma (25-40 ng/ml over the 3-5 hr period after dosing). This indicates that, like FB1, FB2 has a limited bioavailability. Urinary excretion of FB2 was extremely low, even after i.v. dosing. In total, a mean of 4.1% of the i.v. dose and 0.2% of the gavage dose was recovered in urine over a 7-day period. The predominant route of excretion was via the faeces, mainly as the unmetabolized toxin or as a partially hydrolysed analogue, with the latter accounting for between 6% and 47% of the dose. Limited amounts (maximum of 1.1%) of the fully hydrolysed aminopolyol backbone of FB2 were recovered in faeces.
    Food and Chemical Toxicology 01/1999; 37(2-3):111-6. · 3.01 Impact Factor
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    ABSTRACT: A liquid chromatographic (LC) method for simultaneous determination of fumonisins B1 (FB1), B2 (FB2), and B3 (FB3) in corn was subjected to a collaborative study involving 12 participants from 10 countries, in which the accuracy and reproducibility characteristics of the method were established. Mean analyte recoveries from corn ranged from 81.1 to 84.2% for FB1 (at a spiking range of 500 to 8000 ng/g), from 75.9 to 81.9% for FB2 (at a spiking range of 200 to 3200 ng/g), and from 75.8 to 86.8% for FB3 (at a spiking range of 100 to 1600 ng/g). The valid data were statistically evaluated after exclusion of outliers. Relative standard deviations for within-laboratory repeatability ranged from 5.8 to 13.2% for FB1, from 7.2 to 17.5% for FB2, and from 8.0 to 17.2% for FB3. Relative standard deviations for between-laboratory reproducibility varied from 13.9 to 22.2% for FB1, from 15.8 to 26.7% for FB2, and from 19.5 to 24.9% for FB3. HORRAT ratios, calculated for the individual toxin analogues, ranged from 0.75 to 1.73. The LC method for determination of fumonisins B1, B2, and B3 in corn (at concentrations of 800-12800 ng total fumonisins/g) has been adopted by AOAC INTERNATIONAL.
    Journal of AOAC International 01/1996; 79(3):688-96. · 1.23 Impact Factor
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    ABSTRACT: Fumonisin B2 (FB2), a secondary metabolite of the fungus Fusarium moniliforme, was administered at a dose of 7.5 mg/kg body weight to male BD IX rats by ip injection or by gavage. FB2 was rapidly absorbed from the peritoneum, its level in plasma reaching a maximum within 20 min after injection. It was rapidly eliminated from plasma with a half-life of 26 min. After 24 hr, FB2 could not be detected in plasma (< 20 ng/ml). Analysis of rat plasma for FB2 following a gavage dose failed to detect any toxin over a 6-hr period after dosing. The elimination of FB2 in the urine and faeces was determined over a 3-day period after dosing. After i.p. injection, the mean urinary excretion over this period was 1.2% and faecal elimination accounted for 84.1% of the dose. Similarly, after dosing by gavage, 0.2 and 82.0% of the dose was recovered in urine and faeces, respectively. FB2 appeared to be excreted unmetabolized.
    Food and Chemical Toxicology 08/1995; 33(7):591-5. · 3.01 Impact Factor
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    ABSTRACT: Fumonisin B2 (FB2), a secondary metabolite of the fungus Fusarium moniliforme, was administered at a dose of 7.5 mg/kg body weight to male BD IX rats by ip injection or by gavage. FB2 was rapidly absorbed from the peritoneum, its level in plasma reaching a maximum within 20 min after injection. It was rapidly eliminated from plasma with a half-life of 26 min. After 24 hr, FB2 could not be detected in plasma (
    Food and Chemical Toxicology - FOOD CHEM TOXICOL. 01/1995; 33(7):591-595.
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    ABSTRACT: Comparative Claisen rearrangements of 4-hydroxy - (7) and 4-acetoxy-1-allyloxy-5,8-ethano-5,8-dihydro-5-methoxynaphthalene (1) leading after chemoselective methylation to 4-acetoxy-2-allyl-1,5-dimethoxy-naphthalene (9) were investigated. Lewis acid mediated Fries rearrangements of 4-acetoxy-2-allyl-alkoxy-5-ethoxynaphthalenes lead to the formation of a naphtho[1,2 - b]furan in one case only.
    Synthetic Communications 12/1994; 24(22):3189-3196. · 1.06 Impact Factor
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    ABSTRACT: A new and efficient synthesis for 3-acetyl-5-methoxy-1,4-naphthoquinone has been developed. The synthesis involves inter alia pyrolysis of an acetylated Diels-Alder adduct and a regiospecific Fries rearrangement reaction.
    Synthetic Communications 01/1994; 24(1):23-28. · 1.06 Impact Factor
  • Victor I. Hugo, Petra W. Snijman, Ivan R. Green
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    ABSTRACT: Convenient syntheses for 1,5-dimethoxy-4-naphthol and 2-allyl-5-methoxy-1,4-naphthoquinone have been developed. A key step in the formation of the title compounds involved methylation or allylation of an intermediate Diels-Alder adduct.
    Synthetic Communications 03/1993; 23(5):577-584. · 1.06 Impact Factor