Regional distribution of methionine adenosyltransferase in rat brain as measured by a rapid radiochemical method

Use of proteomic methods to identify serum biomarkers associated with rat liver toxicity or hypertrophy

BACKGROUND

Our objectives were to identify serum marker proteins in rats that might serve as sensitive indicators of hepatomegaly, hepatocellular necrosis, or hepatobiliary injury and to use them to analyze data from a collaborative proteomics project.

METHODS

In each of 4 studies comprising the collaborative project, rats were given 1 of 4 compounds that target the liver through different mechanisms. Sera and liver samples were collected by terminal bleeds at 1 of 3 postdose time points. Sera were depleted of major secretory proteins and then separated into protein features by 2-dimensional gel electrophoresis (2DGE). Liver specimens were also processed and subjected to 2DGE. Protein spots that significantly increased or decreased in quantity after drug treatment were recovered, digested, analyzed by mass spectroscopy, and compared with available databases for identification. Criteria for further consideration were (a) temporal expression (i.e., increase or decrease at early, fulminant, or recovery periods), (b) known biological function, (c) probable hepatic origin, and (d) any previous association with toxicity in published studies. Markers that changed significantly at the early time point were important because of their potential sensitivity for signaling minimal damage.

RESULTS

Vitamin D-binding protein, paraoxonase, cellular retinol-binding protein, malate dehydrogenase, F-protein, and purine nucleoside phosphorylase were identified as empirically confirmed serum markers for hepatic effects in drug-treated rats.

CONCLUSION

Proteomics can be applied for the identification and confirmation of peripheral biomarkers for altered liver function after toxicant exposure.

Brain ATP:L-methionine S-adenosyltransferase (MAT), S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH): regional distribution and age-related changes

The distribution of the activity of the enzyme methionine adenosyltransferase (ATP:L-methionine S-adenosyltransferase, EC 2.5.1.6, MAT) was investigated in human postmortem brains of individuals without a known history of neuropsychiatric disorders. The brain regions were the frontal, temporal, parietal and occipital cortices, nucleus caudatus, putamen, globus pallidus, thalamus and white matter. The activities in the nucleus caudatus and putamen were approximately 25% higher than the activities in the seven other brain regions, however, not on a statistically significant level. The apparent values of MAT Km and Vmax in the parietal cortex were 11.41 +/- 3.51 microM methionine and 25.72 +/- 3.90 nmol/mg protein/h, respectively. In the frontal cortex, a significant positive correlation between age and the activity of MAT was found (r = 0.997, P < 0.01). Concerning MAT stability in the rat brain, there was a steady decrease in the activity with postmortem time in the brains kept for 0-72 h at room temperature (23 degrees C), which reached the level of significance at 24 h. The activity did not change significantly when the brains were kept for 120 h at 4 degrees C, or by freezing and thawing the tissue before analysis. In a parallel study in rats of different ages (2-22 months), a homogeneous distribution of SAM and SAH was observed in the cortex, striatum, midbrain, hypothalamus, brainstem and cerebellum. The lowest levels of SAM and the highest levels of SAH observed in the striatum gave the lowest SAM/SAH ratio. The SAH content of rat cerebral cortex was highest in the oldest group.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain tumor protein synthesis and histological grades: a study by positron emission tomography (PET) with C11-L-Methionine

Brain protein synthesis may be evaluated in vivo by a PET three compartment methionine model. 14 human brain tumor patients were studied. Protein synthesis rate (PSR) was increased in any glial tumor even in low grades, but this increase was statistically more important in anaplastic tumor. Radiotherapy action was evaluated in two patients. Local tumoral PSR was reduced to normal brain PSR after treatment. No difference was seen in normal cortex contralateral to the lesion between pre and post radiotherapy examination. 11 C-L-Methionine incorporation measured by PET looks as a very sensitive method for studying tumor metabolism and treatment effects.

Effects of thyroxine on methionine adenosyltransferase activity in rat cerebral cortex and cerebellum during postnatal development

Methionine adenosyltransferase (MAT) activity was evaluated in cerebral cortex and cerebellum in controls and in rats treated with thyroxine. In controls the enzyme showed a different pattern in cerebral cortex and cerebellum during neonatal and late suckling periods. Hyperthyroid rats showed a significant increase of the enzyme in cerebral cortex only at the 2nd day of the neonatal period; in cerebellum the developmental pattern of MAT in neonatal period was anticipated temporally by 2-4 days. During the late suckling period thyroxine treatment produced in cerebellum a significant decrease in MAT activity at the 15th day after birth. From these data, we propose that hyperthyroidism may cause precocious induction of MAT both in cerebral cortex and in cerebellum and that the increased availability of S-adenosyl-L-methionine during the neonatal period could be related to its utilization also in polyamine biosynthesis.