Aspergillus derived mycotoxins in food and the environment: Prevalence, detection, and toxicity

Aspergillus species are the paramount ubiquitous fungi that contaminate various food substrates and produce biochemicals known as mycotoxins. Aflatoxins (AFTs), ochratoxin A (OTA), patulin (PAT), citrinin (CIT), aflatrem (AT), secalonic acids (SA), cyclopiazonic acid (CPA), terrein (TR), sterigmatocystin (ST) and gliotoxin (GT), and other toxins produced by species of Aspergillus plays a major role in food and human health. Mycotoxins exhibited wide range of toxicity to the humans and animal models even at nanomolar (nM) concentration. Consumption of detrimental mycotoxins adulterated foodstuffs affects human and animal health even trace amounts. Bioaerosols consisting of spores and hyphal fragments are active elicitors of bronchial irritation and allergy, and challenging to the public health. Aspergillus is the furthermost predominant environmental contaminant unswervingly defile lives with a 40-90 % mortality risk in patients with conceded immunity. Genomics, proteomics, transcriptomics, and metabolomics approaches useful for mycotoxins' detection which are expensive. Antibody based detection of toxins chemotypes may result in cross-reactivity and uncertainty. Aptamers (APT) are single stranded DNA (ssDNA/RNA), are specifically binds to the target molecules can be generated by systematic evolution of ligands through exponential enrichment (SELEX). APT are fast, sensitive, simple, in-expensive, and field-deployable rapid point of care (POC) detection of toxins, and a better alternative to antibodies.

A cloned human DNA restriction fragment determines expression of a GDP-L-fucose: beta-D-galactoside 2-alpha-L-fucosyltransferase in transfected cells. Evidence for isolation and transfer of the human H blood group locus

We have described previously a gene transfer system for the isolation of human DNA sequences that determine expression of a mammalian GDP-fucose: beta-D-galactoside-2-alpha-L-fucosyltransferase (alpha-(1,2)-fucosyltransferase) (Ernst, L. K., Rajan, V. P., Larsen, R. D., Ruff, M. M., and Lowe, J. B. (1989) J. Biol. Chem. 264, 3436-3447). With this system, we found that de novo expression of the fucosyltransferase in mouse recipient cells was associated with the transfer and stable genomic integration of characteristic human DNA restriction fragments. We report here the results of experiments designed to determine the genetic origin of the fucosyltransferase determined by these sequences. First, we characterize the fucosyltransferases found in these mouse transfectants and in the human cell line used as a DNA donor. We compare their properties to those displayed by the human H and Secretor blood group fucosyltransferases. We find that the enzymes in the transfected cells have properties similar or identical to those of the human H alpha-(1,2)-fucosyltransferase. However, their properties differ significantly from the properties of the human Secretor alpha-(1,2)-fucosyltransferase and are also distinct from the properties of a murine alpha-(1,2)-fucosyltransferase. To confirm further that these transfected human sequences determine the H phenotype of the transfectants, we cloned the two human EcoRI restriction fragments common to each H-expressing secondary transfectant. The larger of these two fragments directs de novo expression of an alpha-(1,2)-fucosyltransferase when transfected into COS-1 cells. The pH activity profile of this alpha-(1,2)-fucosyltransferase and its apparent Michaelis constants for substrate and acceptor mirror those we determined for the human H alpha-(1,2)-fucosyltransferase. We conclude that genetic information sufficient to determine expression of this alpha-(1,2)-fucosyltransferase resides within the 3.4-kilobase pair human EcoRI restriction fragment and that this most likely represents the human H blood group locus.

Synthesis and interaction with uridine phosphorylase of 5'-deoxy-4',5-difluorouridine, a new prodrug of 5-fluorouracil

5'-Deoxy-4',5-difluorouridine (4'-F-5'-dFUrd) (10) has been synthesized on the basis of the rationale that the labilization of the glycosidic linkage caused by the 4'-fluoro substituent might allow this compound to be a better prodrug form of the anticancer drug 5-fluorouracil (FUra) than is the widely studied fluoropyrimidine 5'-deoxy-5-fluorouridine (5'-dFUrd). The rate of solvolytic hydrolysis of the glycosidic linkage of 4'-F-5'-dFUrd at pH 1 was about 500-fold faster than that of 5'-dFUrd. Since uridine phosphorylase is thought to be the enzyme that causes degradation of 5'-dFUrd in vivo to generate FUra, we compared the substrate interactions of 5'-dFUrd and 4'-F-5'-dUrd with this enzyme. The Vmax for hydrolysis of 4'-F-5'-dFUrd to FUra by uridine phosphorylase was about 5-fold greater than that of 5'-dFUrd, whereas the Km value of 4'-F-5'-dFUrd was 10-fold lower. The combination of these two factors results in 4'-F-5'-dFUrd having a 50-fold higher value of V/K than does 5'-dFUrd. Against L1210 cells in culture, the IC50 value for growth inhibition by 4'-F-5'-dFUrd was 3 X 10(-7) compared to 3 X 10(-6) for 5'-dFUrd.

Effects of incorporation of 6-thioguanine into SV40 DNA

The antileukemic agent 6-thioguanine (TG) is thought to inhibit DNA synthesis as a result of its incorporation into DNA. In the present study we have examined the nature of this inhibition, using replication of SV40 viral DNA as a model system. Addition of TG to SV40-infected CV1P cells from 22 to 24 hr post infection causes a dose-dependent inhibition of viral DNA synthesis. This inhibition plateaus between 250 and 2500 microM TG, resulting in a maximum decrease of viral DNA synthesis of about 50%. Pulse-chase experiments showed no detectable slowing of elongation of nascent DNA chains, whereas measurement of the conversion of incorporated 3H-dThd into supercoiled viral DNA suggested that elongation might be slightly inhibited, but by no more than 20%. Since inhibition of elongation could not account for the total depression of DNA synthesis, we hypothesized that inhibition of initiation of DNA replication takes place. This hypothesis was tested by radioactively labeling newly synthesized viral DNA and then assessing the ability of these molecules to reenter the replicating pool by density labeling with bromodeoxyuridine. The fraction of TG-containing molecules able to re-initiate replication was decreased 15%, compared to control. This effect, which was dependent on the concentration of TG added to the medium, was closely correlated to the extent of TG incorporation into the viral genome. We concluded that a portion of SV40 viral DNA synthesis inhibited by TG is due to an effect on initiation, and hypothesized that this effect may be caused by the substitution of TG for guanine in critical recognition sequences at the origin of replication. We proceeded to test this hypothesis by constructing SV40 origin sequences containing TG and then measuring their ability to bind T-antigen in vitro. The necessary deoxynucleoside triphosphate, TdGTP, was obtained by chemical phosphorylation of thiodeoxyguanosine. In order to selectively place TG within the desired region, a plasmid containing the T-antigen binding sequences was linearized so as to place these sequences at one end of the molecule, and then digested briefly with exonuclease III. The excised strand was resynthesized by use of the Klenow fragment of DNA polymerase I along with various nucleotide mixtures. Although resynthesis with mixtures containing TdGTP in place of dGTP was impeded somewhat, it was possible to achieve complete resynthesis with this analog.(ABSTRACT TRUNCATED AT 400 WORDS)

DNA degradation by bleomycin: evidence for 2'R-proton abstraction and for C-O bond cleavage accompanying base propenal formation

Reaction of poly(dA-[2'S-3H]dU) with activated bleomycin yields [3H]uracil propenal that completely retains the tritium label. In contrast, we have previously shown that reaction of poly(dA-[2'R-3H]dU) with activated bleomycin affords unlabeled uracil propenal [Wu, J. C., Kozarich, J. W., & Stubbe, J. (1983) J. Biol. Chem. 258, 4694-4697]. We have also prepared both cis- and trans-thymine propenals by chemical synthesis and have observed that the trans isomer is the exclusive product of the bleomycin reaction. Moreover, the cis isomer was found to be stable to the conditions of bleomycin-induced DNA degradation. Taken together, these results establish that the formation of trans-uracil propenal occurs via an anti-elimination mechanism with the stereospecific abstraction of the 2'R proton. The question of phosphodiester bond cleavage during base propenal formation has also been addressed by the analysis of the fate of oxygen-18 in poly(dA-[3'-18O]dT) upon reaction with activated bleomycin. The 5'-monophosphate oligonucleotide ends produced from thymine propenal formation have been converted to inorganic phosphate by the action of alkaline phosphatase, and the phosphate has been analyzed for 18O content by 31P NMR spectroscopy. The oxygen-18 is retained in the inorganic phosphate, establishing that the formation of thymine propenal by activated bleomycin proceeds with C-O bond cleavage at the 3'-position.

Synthesis and biological activity of 5-fluoro-2',3'-dideoxy-3'-fluorouridine and its 5'-phosphate

5-Fluoro-2',3'-dideoxy-3'-fluorouridine (3'-FFdUrd) and 5-fluoro-2',3'-dideoxy-3'-fluorouridine 5'-phosphate (3'-FFdUMP) have been synthesized, and their interactions with thymidine (dThd) phosphorylase and thymidylate (dTMP) synthetase, respectively, have been examined. 3'-FFdUrd is not a substrate for dThd phosphorylase, but is a weak, noncompetitive inhibitor (Ki = 1.7 mM). 3'-FFdUMP inhibits dTMP synthetase competitively with deoxyuridylate (Ki = 0.13 mM) when both the substrate and inhibitor are present simultaneously. However, in the presence of 5,10-methylenetetrahydrofolate, the inhibition increases with time in a first-order manner (konobsd = 0.029 s-1). A complex is formed between [6-3H]3'-FFdUMP and dTMP synthetase, which is isolable on nitrocellulose filters, and has a dissociation rate (koffobsd = 1.4 X 10(-2) min-1) similar to that of the potent inhibitor 5-fluoro-2'-deoxyuridylate (koffobsd = 1.3 X 10(-2) min-1) from its ternary complex with dTMP synthetase. These results are explained in terms of a two-stage model involving the initial formation of a reversible adsorption complex, followed by a slow conversion to a tight-binding catalytic complex.

Synthesis and biological activity of 5'-substituted 5-fluoropyrimidine nucleosides

5'-Deoxy-5-fluorouridine (5'-dFUrd, 1) possesses a significantly higher chemotherapeutic index than other fluoropyrimidines as a result of its being selectivity cleaved in tumors to 5-fluorouracil (FUra) by uridine phosphorylase. Because 1 is a relatively poor substrate for this enzyme, we synthesized a series of 5'-deoxy-5'-substituted-5-fluorouridine (FUrd) derivatives in an effort to obtain compounds that might have improved substrate interactions compared to 1 and thus possibly be better prodrugs of FUra. Three derivatives, 5'-O-tosyl-FUrd (13), 5'-O-mesyl-FUrd (14), and 5'-deoxy-5'-bromo-FUrd (15), had cytostatic activity against L1210 and CCRF-CEM leukemic cells in culture superior to that of 1. In preliminary in vivo antitumor studies against L1210 leukemic cells in mice, 5'-deoxy-5'-chloro-FUrd (4), 5'-O-mesyl-FUrd (14), an 5'-deoxy-5'-fluoro-FUrd (18) gave percent increases in life span of 64, 58, and 58, respectively, compared to a value of 20 for compound 1.