A sero-epidemiological cross-sectional study of hepatitis B virus in Zimbabwe.

Objective: To estimate the prevalence of hepatitis B viral markers.

Design: A sero-epidemiological community-based cross-sectional study.

Setting: All nine provinces of Zimbabwe.

Variant of hepatitis B virus isolated in Zimbabwe.

The polymerase chain reaction (PCR) was used to amplify an approximately 1.2 kb DNA fragment encompassing the pre-S/S gene region of HBV DNA from serum of patients with acute hepatitis B virus infection. Nucleotide sequence analysis revealed a number of interesting features in the S gene region.

Zimbabwe National Cancer Registry: summary data 1986-1989. National Cancer Registry Advisory Committee.

The Zimbabwe National Cancer Registry began operation in 1986. Between 1986-1989, a total of 8 276 cases were identified. Among men of African descent, oesophageal (11.

Low incidence of human papillomavirus type 16 DNA in bladder tumor detected by the polymerase chain reaction.

Human papillomavirus (HPV) detection was done using the polymerase chain reaction technique on tumor tissue from 44 patients with transitional cell carcinoma of the urinary bladder. Only one of the 44 was associated with HPV infection. The HPV-positive patient was not known to have immunodeficiency or genital warts, and the tumor was not morphologically different from the other tumors.

Cloning and sequencing of hepatitis B virus pre-S and S gene regions.

The polymerase chain reaction (PCR) was used to amplify the pre-S1, pre-S2 and S gene regions of hepatitis B virus (HBV). Sera from three different patients were used as the source of HBV DNA. The resulting 1.

The effect of schistosomiasis on the covalent binding of 2-acetylaminofluorene to mouse liver macromolecules in vivo and in vitro.

The covalent binding of [14C]acetylaminofluorene (AAF) to macromolecules in vivo and in vitro was measured in Schistosoma mansoni-infected and in non-infected mice. Liver microsomes from infected mice demonstrated a 42% decreased capacity to mediate covalent binding of AAF to DNA. In addition, the extent of binding of AAF to liver macromolecules in vivo was generally less in infected than non-infected mice.

Human exposure to aflatoxins in Zimbabwe.

In this communication, we report the detection of aflatoxins in human urine and breast milk. The 2553 urine samples were collected from donors of different ages and sexes at centres throughout Zimbabwe, while 54 breast milk samples were collected from breast feeding mothers. The most predominant aflatoxins found were AFM and AFG.

A survey of urinary aflatoxin in Zimbabwe.

In this study, 1228 urine samples were collected from different centres in Zimbabwe and were analysed for aflatoxin contamination. The urine samples were extracted with chloroform and analysed by thin layer chromatography and high-performance liquid chromatography. The most commonly observed contaminant was aflatoxin M1, at an average concentration of 4.

Aflatoxin detected in human breast milk by immunoassay.

Several epidemiological studies have shown a positive association between dietary exposure to aflatoxin (AF) and an increased incidence of primary hepatocellular carcinoma (PHC). One area in which little information is available is the exposure of newborn children to AF in human breast milk. We report the development, validation and application of an enzyme-linked immunosorbent assay (ELISA) to the detection of AF in human breast milk.

Chemical reclosure of opened imidazole ring of guanine.

Imidazole ring opened adenine and guanine residues similar to those generated by gamma-irradiation of nucleosides of DNA, were chemically synthesised. Reaction conditions that promote the chemical reclosure of opened imidazole rings of guanine have been identified. The optimal conditions for the reclosure of such rings was found to be 0.

The effect of schistosomiasis on the activation of aflatoxin B1.

This study examined activation of aflatoxin B1 (AFB1) in livers of Schistosoma mansoni-infected and noninfected mice by measuring covalent binding of [3H]AFB1 to cellular macromolecules in vivo and in vitro. During a one week time period after AFB1 treatment of animals, maximal binding of [3H]AFB1 to DNA, RNA and protein in liver occurred during the 1-6 hour period after treatment, with less binding throughout of AFB1 to macromolecules of infected mice. Experiments performed in vitro to determine the capacity of liver microsomes to mediate the binding of AFB1 to calf thymus DNA showed that microsomes from infected mice mediated the binding of less [3H]AFB1 to DNA than those from noninfected animals.

In situ enzymatic reclosure of opened imidazole rings of purines in DNA damaged by gamma-irradiation.

When aqueous solutions of DNA were treated with 10-500 grays of gamma-rays, the imidazole rings of some adenine and guanine residues underwent scission, resulting in the conversion of these purines to formamidopyrimidines. It was found that formamidopyrimidine-DNA glycosylase, known to remove imidazole-ring-opened 7-methylguanine from DNA, did not excise the radiation-induced non-alkylated formamidopyrimidines formed for adenine and guanine. The repair of these ring-opened purines was found to involve an enzymatic recyclizing of the opened imidazole ring that effects a restoration of the C-8 to N-9 bond.

A dose-response study on opening of imidazole ring of adenine in DNA by ionizing radiation.

A dose-response relationship between gamma-irradiation and the cleavage of the imidazole ring of adenine in DNA to form formamidopyrimidine has been demonstrated. When the DNA aqueous solution was irradiated with 0.1 Gy under N2O, there is little evidence of imidazole ring cleavage.

Excision of aflatoxin B1-imidazole ring opened guanine adducts from DNA by formamidopyrimidine-DNA glycosylase.

This investigation has confirmed the earlier reports that when aflatoxin B1-DNA adducts are stored under physiological conditions some aflatoxin B1-guanine adducts are converted to a secondary product in which fission of the imidazole ring of the adduct guanine has occurred. Incubation of DNA containing aflatoxin B1-guanine adducts for an increasing number of hours under physiological conditions resulted in a progressive increase in the number of adducts in which the imidazole rings of guanines underwent fission. It was shown that the Escherichia coli enzyme, formamidopyrimidine-DNA glycosylase exercises from the 6-day incubated DNA, an amount of imidazole ring opened guanines equivalent to 40% of the aflatoxin B1-guanine adducts present in the DNA.

Identification of N5-methyl-N5-formyl-2,5,6-triamino-4-hydroxypyrimidine as a major adduct in rat liver DNA after treatment with the carcinogens, N,N-dimethylnitrosamine or 1,2-dimethylhydrazine.

A major and previously undetected carcinogen-DNA adduct was found in the livers of rats given N,N-dimethylnitrosamine or 1,2-dimethylhydrazine. This adduct, which accounted for 55% of the total methyl residues in DNA at 72 hours after carcinogen treatment, was chromatographically identical to a synthetic purine ring-opened derivative of 7-methylguanine and could be released from the isolated hepatic DNA by a specific E. coli glycosylase.

Alkaline opening of imidazole ring of 7-methylguanosine. 2. Further studies on reaction mechanisms and products.

High performance liquid chromatography (HPLC) was used to follow the kinetics of the alkaline induced opening of the imidazole ring of 7-methyl-guanosine (7-meGuo). The kinetics show an initial rapid formation of a major transient intermediate and some minor products that were chromatographically separable into seven peaks. This phase of the reaction is followed by the formation of a dominant pyrimidine derivative whose liquid chromatography retention time in a 6% methanol, 0.

Alkaline opening of imidazole ring of 7-methylguanosine. 1. Analysis of the resulting pyrimidine derivatives.

Column chromatography and spectroscopy have been employed in analyzing pyrimidine derivatives obtained from alkaline-treated 7-methylguanosine (7-meGuo). High performance liquid chromatography (HPLC) revealed that the alkaline generated products consist predominantly of two forms of ring opened 7-methylguanine (rom7Gua) in equal amounts. Material from both Dowex 50 and Sephadex LH-20 columns was readily resolvable into two HPLC peaks.

Analysis and excision of ring-opened phosphoramide mustard-deoxyguanine adducts in DNA.

The reaction products formed by reacting deoxyguanosine with phosphoramide mustard at pH 7.4 have been analyzed by high-performance liquid chromatography and Schiff's reaction. The adducts consisted of five fractions of phosphoramide mustard-imidazole ring-opened deoxyguanosine complexes and one fraction of each of intact phosphoramide mustard-deoxyguanosine and phosphoramide mustard-dideoxyguanosine complexes.

Purification and characterization of Escherichia coli formamidopyrimidine-DNA glycosylase that excises damaged 7-methylguanine from deoxyribonucleic acid.

A DNA glycosylase that excises 7-methylguanines with alkali-opened imidazole rings (formamidopyrimidines) from DNA has been purified more than 8000-fold from Escherichia coli cell extracts. The enzyme does not cleave 3-methyladenine, uracil, and intact 7-methylguanine from DNA. In assays containing pyrimidine analogues like oxauracil, 2,4,6-triaminopyrimidine, 2,5,6-triamino-2-hydroxypyrimidine sulfate, formamidopyrimidine, and 5-nitroso-2,4,6-triaminopyrimidine, only the two compounds showed end product inhibition of the enzyme.

Release of 7-methylguanine residues whose imidazole rings have been opened from damaged DNA by a DNA glycosylase from Escherichia coli.

Double-stranded DNA containing 7-methylguanine residues whose imidazole rings have been opened, i.e. 2,6-diamino-4-hydroxy-5-N-methylformamido-pyrimidine residues, may be prepared by treatment of DNA with dimethyl sulfate followed by prolonged incubation at pH 11.

Sequence specific interaction of the chromosomal proteins with DNA.

Calf thymus chromatin was partially deproteinized by 0.6-1 M NaCl extraction. From the shape of the temperature derivative plot of its melting curve, the DNA in each chromatin was resolved into regions of exposed DNA, and DNA still complexed with proteins.

Age-associated structural alterations in senescent mouse brain DNA.

The maintenance of structural integrity in the DNA of aging mice has been examined with the amin in view of determining whether changes in genome structure constitute the molecular basis of aging. Cell lysate DNA from brains of differently aged mice was subjected to alkaline sucrose gradient sedimentation. The results show that brain DNA from young mice sediments mondispersely while that from senescent mice exhibits polydisperse sedimentation patterns, bainding in four peaks corresponding to number-average molecular weights of 1.