Developmental Changes in the Activity of Enzymes of Purine Metabolism in Rat Neuronal Cells in Culture and in Whole Brain

Abstract

The activities (Vmax) of several enzymes of purine nucleotide metabolism were assayed in premature and mature primary rat neuronal cultures and in whole rat brains. In the neuronal cultures, representing 90% pure neurons, maturation (up to 14 days in culture) resulted in an increase in the activities of guanine deaminase (guanase), purine-nucleoside phosphorylase (PNP), IMP 5'-nucleotidase, adenine phosphoribosyltransferase (APRT), and AMP deaminase, but in no change in the activities of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), adenosine deaminase, adenosine kinase, and AMP 5'-nucleotidase. In whole brains in vivo, maturation (from 18 days of gestation to 14 days post partum) was associated with an increase in the activities of guanase, PNP, IMP 5'-nucleotidase, AMP deaminase, and HGPRT, a decrease in the activities of adenosine deaminase and IMP dehydrogenase, and no change in the activities of APRT, AMP 5'-nucleotidase, and adenosine kinase. The profound changes in purine metabolism, which occur with maturation of the neuronal cells in primary cultures in vitro and in whole brains in vivo, create an advantage for AMP degradation by deamination, rather than by dephosphorylation, and for guanine degradation to xanthine over its reutilization for synthesis of GMP. The physiological meaning of the maturational increase in these two ammonia-producing enzymes in the brain is not yet clear. The striking similarity in the alterations of enzyme activities in the two systems indicates that the primary culture system may serve as an appropriate model for the study of purine metabolism in brain.

Purine nucleosides protect injured neurons and stimulate neuronal regeneration by intracellular and membrane receptor‐mediated mechanisms

“…Guanine, the product of guanine nucleotide degradation, can be anabolically metabolized (salvaged) by HPRT or be degraded by guanase to xanthine, the degradation end product of guanine nucleotides in brain (we could not detect xanthine oxidase activity in rat brain and in the cultured neurons or glia) [Brosh et al, 1990;ZorefShani et al, 1995]. With maturation of cultured neurons [Brosh et al, 1990] and glia [Zoref-Shani et al, 1995] in vitro and of brain in vivo [Brosh et al, 1990] guanase exhibited the highest increase in activity, 6-, 25-, and 113-fold of the immature activity, respectively, much exceeding that of HPRT (2.2-, 5.8-, and 2.8-fold of the immature activity, respectively).…”

“…To mention just a few [for references, see Brosh et al, 1990]: GTP binding to G proteins and GTP binding proteins regulate the response of multiple membrane receptors to external stimuli; GTP is involved in the polymerization of tubulin essential to axonal transport, and is an essential substrate for protein and nucleic acid synthesis. Recently, guanine derivatives were found to be neurotrophic .…”

“…Recently, guanine derivatives were found to be neurotrophic . Furthermore, three inborn errors of purine nucleotide metabolism are associated with neurological abnormalities: deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT; EC 2.4.2.8), causing Lesch-Nyhan syndrome; deficiency of purine nucleoside phosphorylase (PNP; EC 2.4.2.1) and of adenylosuccinate lyase (EC 4.3.2.2) [for references, see Brosh et al, 1990]. The following is a short review of our studies aimed at improving our knowledge concerning the metabolism of guanine nucleotides in brain.…”

Cloning and Characterization of Human Guanine Deaminase

“…There are greater than 50-fold differences in guanine deaminase among different regions of the mouse brain; the cerebral cortex and amygdala have the highest activity (4), whereas there is essentially no activity in the cerebellum of the mouse or cat (4,5). There are greater than 10-fold increases in the level of expression of guanine deaminase in the liver, kidney, and brain during the 40-day postnatal development of the rat (6), and alterations in embryonic expression have also been characterized (7). In the adult mouse, fractional increases in brain and liver enzyme activity occur in response to intraperitoneal administration of a bolus of guanine (8).…”

Postnatal Expression of Hypoxanthine Guanine Phosphoribosyltransferase in the Mouse Brain

“…The severe neurolog ical abnormalities which characterize the syn drome are developed between 2 and 16 years of age [4], Such developmental changes sug gest that HGPRT has a significant physiologi cal function in the postnatal developmental changes of the brain. On this basis, the postna tal developmental changes in HGPRT activi ty have been investigated in man [5], the rat [5,7] and primary rat neuronal cultures [8], However, the developmental changes in the activity have not so far provided significant data concerning the mechanism underlying the neurological dysfunction observed in the Lesch-Nyhan syndrome.…”