George C. Yang

Aflatoxin and Reye's Syndrome: A Study of Livers from Deceased Cases

In order to reinvestigate a strong reported association, we attempted to identify aflatoxin in the livers of 12 children who presumably died of Reyes Syndrome and in the liver of one child who died accidentally. Aflatoxins were detected, but not confirmed in only one of the liver specimens (limits of detection 20 ppt). In addition, the microscopic appearance of the livers was reviewed. Although most of the cases fit the clinical definition of Reyes Syndrome, the microscopic appearance of the liver was varied. We conclude that aflatoxin is not regularly recoverable from cases of Reyes Syndrome at a high rate, and question the proposed etiologic relationship. We confirm the varied appearance of the liver late in the course of Reyes Syndrome; however, microvesicular fat was present in most cases.

Studies on the action of nystatin on cultured rat myocardial cells and cell membranes, isolated rat hearts, and intact rats.

The action of nystatin, a polyene antibiotic, was studied in rat myocardial cells, isolated rat hearts, and intact rats. Myocardial cells responded to 10 and 25 micrograms nystatin/ml with arrhythmias that could be minimized by elevated concentrations of K+ and Mg2+ or reversed by washing the cells. Similarly, the isolated heart responded to 100 micrograms nystatin/ml with arrhythmias that could be tempered by addition of elevated concentrations of K+ and Mg2+. The i.v. injection of the drug caused heart failure in intact animals at the 4-mg/kg dose level. At the subcellular level, nystatin made the myocardial cell membranes more rigid, as measured by electron spin resonance spectrometry. These findings indicate a parallel between physiocochemical changes caused by nystatin in the myocardial cell membrane and the biological changes caused by this drug in myocardial cells, isolated heart, and heart of the intact animal.

[7] Spin immunoassay

Publisher Summary This chapter describes the development of spin immunoassay (SIA). A spin-labeled 2,4-dinitrophenyl (SL-DNP) hapten was observed to bind, with high affinity to antibodies, against DNP. A marked change in the electron spin resonance spectrum of SL-DNP was observed on addition of anti-DNP antibody, indicating that the tumbling motion of the SL-DNP was severely restricted on interaction with antibody. It is found that morphine, spin-labeled [SL(5)] through an ether linkage at the 3-position, was strongly immobilized by antisera from the rabbits immunized with morphine-bovine serum albumin (BSA) antigen. The spin-labeled hapten was prepared by attaching an amine-SL(5) to progesterone 11α-hemisuccinate, using N -ethoxycarbonyl-2-ethoxy-1,2-dihydroquinone. The resulting SIA could detect the levels of 20-50 ng/ml progesterone in male serum. Antibodies against prednisone and prednisolone were harvested from rabbits immunized with prednisone or prednisolone succinate-BSA conjugate. This SIA could detect 2 ng of prednisole or prednisolone in a 400-μl sample. It is found that the antiprednisone antibodies showed considerable cross-reactivity for other similar steroids.

Activation and Specificity of Aflatoxin B 1 Binding on hhc M , a Human Oncogene of Low Efficiency, and Cell Transformation

Aflatoxin B1 (AFB1), a metabolite of Aspergillus flavus, chemically classified as a furocoumarin, is known to be the most potent hepatocarcinogen experimentally tested in various species including trout, rat, hamster, dog and rhesus monkey.13,21 The carcinogenic effect resides in the mutagenic potential of AFB1 upon metabolic conversion into the epoxide form by liver mixed function oxidases. By mode of nucleophilic attack, AFB1-epoxide binds to DNA forming covalent bonds with the N7 of deoxyguanine (dG), thus inducing an erroneous base-pairing with deoxyadenine (dA) instead of deoxycytidine (dC) (Fig. 1). In eukaryotes, such as hepatocytes, a strong DNA repair enzyme system usually safeguards against such mistakes by excising the mis-paired base, and an organism depends on continual repair of DNA (Fig. 2). If this erroneous base-pairing eluded the cell’s DNA repair enzyme, at subsequent DNA replication a conversion of dG.dC --> T.dA ensures, thus resulting in a point-mutation.7 Such a mutation generates an irreversible DNA lesion (Fig. 2) and if it is of survival value, it usually produces an altered gene product. On the other hand, a disruption of the open reading frame results if the DNA repairing process excised the mis-paired base without replacement with the correct base, i.e. generated a deletion mutation, or if the T.dA substitution of dG.dC generated a nonsense, i.e. stop codon. This usually results in a lethal mutation.