Inhibition of Tyrosine Aminotransferase by β-N-Oxalyl-l-α,β-Diaminopropionic Acid, the Lathyrus sativus Neurotoxin

Abstract: Species differences in susceptibility are a unique feature associated with the neurotoxicity of β-N-oxalyl-l -α,β-diaminopropionic acid (l -ODAP), the Lathyrus sativus neurotoxin, and the excitotoxic mechanism proposed for its mechanism of toxicity does not account for this feature. The present study examines whether neurotoxicity of l -ODAP is the result of an interference in the metabolism of any amino acid and if it could form the basis to explain the species differences in susceptibility. Thus, Wistar rats and BALB/c (white) mice, which are normally resistant to l -ODAP, became susceptible to it following pretreatment with tyrosine (or phenylalanine), exhibiting typical neurotoxic symptoms. C57BL/6J (black) mice were, however, normally susceptible to l -ODAP without any pretreatment with tyrosine. Among the various enzymes associated with tyrosine metabolism examined, the activity of only tyrosine aminotransferase (TAT) was inhibited specifically by l -ODAP. The inhibition was noncompetitive with respect to tyrosine (K_i = 2.0 ± 0.1 mM) and uncompetitive with respect to α-ketoglutarate (K_i = 8.4 ± 1.5 mM). The inhibition of TAT was also reflected in a marked decrease in the rate of oxidation of tyrosine by liver slices, an increase in tyrosine levels of liver, and also a twofold increase in the dopa and dopamine contents of brain in l -ODAP-injected black mice. The dopa and dopamine contents in the brain of only l -ODAP-injected white mice did not show any change, whereas levels of these compounds were much higher in tyrosine-pretreated animals. Also, the radioactivity associated with tyrosine, dopa, and dopamine arising from [¹⁴C]tyrosine was twofold higher in both liver and brain of l -ODAP-treated black mice. Thus, a transient increase in tyrosine levels following the inhibition of hepatic TAT by l -ODAP and its increased availability for the enhanced synthesis of dopa and dopamine and other likely metabolites (toxic?) resulting therefrom could be the mechanism of neurotoxicity and may even underlie the species differences in susceptibility to this neurotoxin.     

Photoproduction of hydrogen, nitrogenase and hydrogenase activities of free and immobilized whole cells of Rhodobacter sphaeroides O.U. 001

Abstract Photoproduction of hydrogen, nitrogenase activity (acetylene reduction) and hydrogenase activity (methylene blue dye reduction) were studied in free and alginate immobilized whole cells of a purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides O.U. 001. Four-fold increase in hydrogen production, two-fold increase in nitrogenase activity and 1.2-fold increase in the hydrogenase activity were observed in immobilized cells compared to free cells. Effect of various inhibitors (CO and C₂H₂) and electron donor (H₂) on the above three functions by free and immobilized cells has also been studied.     

Electron microscopic changes on the DMBA induced oral precancerous and cancerous lesion in hamster cheek pouch

Experiments were performed to study the early and late ultrastructural changes during hamster cheek pouch carcinogenesis using a regimen of topical application of 9,10 dimethyl-1-1-2 benzanthracene (DMBA) twice a week in liquid paraffin oil. The DMBA was administered for a period of 2 and 4 1/2 months. Hamsters exposed to DMBA for 2 months developed moderate precancerous changes, whereas the hamsters treated with DMBA for 4 1/2 months developed frank and multiple oral tumors with a cauliflower appearance. The ultrastructural pathological changes seen were considerably increased at 4 1/2 months compared with a 2 month period of DMBA treatment. Untreated and solvent control hamsters cheek pouch treated for 2 and 4 1/2 months with liquid paraffin oil alone did not show any premalignant or malignant changes during this period.     

Measurement of 7-dehydrocholesterol and cholesterol in hair can be used in the diagnosis of Smith-Lemli-Opitz syndrome

7-dehydrocholesterol (7-DHC) and cholesterol (CHOL) are biomarkers of Smith-Lemli-Opitz Syndrome (SLOS), a congenital autosomal recessive disorder characterized by elevated 7-DHC level in patients. Hair samples have been shown to have great diagnostic and research value, which has long been neglected in the SLOS field. In this study, we sought to investigate the feasibility of using hair for SLOS diagnosis. In the presence of antioxidants (2,6-ditert-butyl-4-methylphenol and triphenylphosphine), hair samples were completely pulverized and extracted by micro-pulverized extraction in alkaline solution or in n-hexane. After microwave-assisted derivatization with N,O-Bis(trimethylsilyl)trifluoroacetamide, the analytes were measured by GC-MS. We found that the limits of determination for 7-DHC and CHOL were 10 ng/mg and 8 ng/mg, respectively. In addition, good linearity was obtained in the range of 50–4000 ng/mg and 30–6000 ng/mg for 7-DHC and CHOL, respectively, which fully meets the requirement for SLOS diagnosis and related research. Finally, by applying the proposed method to real hair samples collected from 14 healthy infants and two suspected SLOS patients, we confirmed the feasibility of hair analysis as a diagnostic tool for SLOS. In conclusion, we present an optimized and validated analytical method for the simultaneous determination of two SLOS biomarkers using human hair.