Postnatal development of gamma-GT activity in rat brain microvessels corresponds to capillary growth and differentiation

Identification of neurological complications in childhood influenza: a random forest model

BACKGROUND

Among the neurological complications of influenza in children, the most severe is acute necrotizing encephalopathy (ANE), with a high mortality rate and neurological sequelae. ANE is characterized by rapid progression to death within 1-2 days from onset. However, the knowledge about the early diagnosis of ANE is limited, which is often misdiagnosed as simple seizures/convulsions or mild acute influenza-associated encephalopathy (IAE).

OBJECTIVE

To develop and validate an early prediction model to discriminate the ANE from two common neurological complications, seizures/convulsions and mild IAE in children with influenza.

METHODS

This retrospective case-control study included patients with ANE (median age 3.8 (2.3,5.4) years), seizures/convulsions alone (median age 2.6 (1.7,4.3) years), or mild IAE (median age 2.8 (1.5,6.1) years) at a tertiary pediatric medical center in China between November 2012 to January 2020. The random forest algorithm was used to screen the characteristics and construct a prediction model.

RESULTS

Of the 433 patients, 278 (64.2%) had seizures/convulsions alone, 106 (24.5%) had mild IAE, and 49 (11.3%) had ANE. The discrimination performance of the model was satisfactory, with an accuracy above 0.80 from both model development (84.2%) and internal validation (88.2%). Seizures/convulsions were less likely to be wrongly classified (3.7%, 2/54), but mild IAE (22.7%, 5/22) was prone to be misdiagnosed as seizures/convulsions, and a small proportion (4.5%, 1/22) of them was prone to be misdiagnosed as ANE. Of the children with ANE, 22.2% (2/9) were misdiagnosed as mild IAE, and none were misdiagnosed as seizures/convulsions.

CONCLUSION

This model can distinguish the ANE from seizures/convulsions with high accuracy and from mild IAE close to 80% accuracy, providing valuable information for the early management of children with influenza.

PTZ-induced seizures in rats: effects of age and strain

The susceptibility to pentylenetetrazol (PTZ)-induced seizures during postnatal ontogeny [postnatal day (PN) 10-220] was investigated in two rat strains. The WAG/Rij strain, genetically prone for developing generalized absence epilepsy, and Wistar rats were tested and compared at PN 10, 26, 30, 70, 90, 125, and 220 on the PTZ-convulsive threshold. A subconvulsive dose of 25-mg/kg PTZ was administered every 15 min, and the occurrence of clonic and tonic-clonic seizures was scored. The 10-day-old pups were quite sensitive to PTZ and showed mainly clonic seizures. The highest threshold and latency of PTZ-induced clonic and tonic-clonic convulsions were observed at PN 26 in both strains. From that age onwards, the seizure threshold significantly decreased and reached a minimum at PN 220. Between strain comparisons showed that WAG/Rij rats have a lower tonic-clonic seizure threshold than Wistar rats. The data indicate that changes in susceptibility first quickly decreases until PN 26-30 and then tend to monotonically increase with age, and that genetically prone nonconvulsive WAG/Rij rats are more vulnerable to convulsive seizures induced by PTZ than Wistar rats.

Structure of the 5' sequences of the human gamma-glutamyltransferase gene

In humans, five distinct mRNAs code for gamma-glutamyltransferase (GGT). Their coding regions are identical and their 5' untranslated regions exhibit both common and type-specific sequences. To elucidate the mecanisms that generate these different mRNAs, we cloned and determined the structure of the 5' region of the human GGT gene. The common regions of the 5' UTR are encoded by five exons, localized within a 2.4-kb region of the genomic DNA. Three of them are separated only by intron-donor or intron-acceptor sites at their boundaries. Alternative splicing of these exons may determine the unique pattern of the different GGT mRNA 5' UTRs in a tissue-specific manner. In addition, we have isolated a genomic fragment containing the most distal 5' sequences of the major GGT mRNA in HepG2 cells. Primer extension analysis revealed one major transcription initiation site while 5' RACE indicated that one more distal initiation site could be present. In the putative promoter sequence neither classical TATA or CAAT boxes were found. However, sites for AP1, AP2, CREB, GRE and SP1 transcription factors were identified. Chimeric plasmids, containing this genomic region fused to the luciferase gene, were transiently expressed in three cell lines of different origin: HeLa cells, ovarian carcinoma A2780 cells and V79 lung fibroblasts. The significant promoter activities obtained indicate a transcription start within this region. However, differences in the level of expression were found between the different cell lines used. These data suggest that the human GGT gene employs regulatory sequences and alternative splicing, and gene expression may therefore be regulated in tissue specific and cell-type-specific manners.

Developmental pattern of reactive oxygen species generation and antioxidative defense machinery in rat cerebral microvessels

The developmental profile of certain enzymatic antioxidants as well as the generation of reactive oxygen species was studied in the rat cerebral microvessels during first three weeks of life and the levels were compared to those present in adults. The data showed a higher generation of superoxide anion (+67%) and H2O2 (+200%) at postnatal day (PND) 21. Superoxide anion production was significantly lower (-24%) at PND 14 and almost comparable to adult values at PND 7. The activity of superoxide dismutase increased with development and attained an adult level at PND 21. Catalase was higher in neonates with a maximum activity at PND 7 and 14 (+68, 69%). The measurement of microvessel glutathione and glutathione-related antioxidant enzymes showed that glutathione level was higher at PND 7, which declined to an adult level at PND 14. Se-dependent GPx showed a marked increase between PND 14 and 21, however, it declined in adults. The activity of Se-independent glutathione peroxidase was very low in cerebral microvessels. Glutathione reductase activity in 7-day-old, that was comparable to adult level, declined at PND 14 and 21. The level of glutathione S-transferase was higher (+43%) at PND 21. The activity of microvessel marker enzyme gamma-glutatmyl transpeptidase increased with age, whereas, alkaline phosphatase showed a slight increase up to PND 14 and thereafter it declined. Lipid peroxidation was found to be significantly lower (-18%) at PND 21 as compared to adults. It may be concluded that developing cerebral microvessels contain high levels of several antioxidant enzymes that are more or equal to those present in adult brain microvessels.

An intronic promoter controls the expression of truncated human gamma-glutamyltransferase mRNAs

We have identified and characterized a genomic DNA fragment containing the coding sequences corresponding to the human gamma-glutamyltransferase type 1 mRNA. The coding part of the gene spans over 16 kb and comprises 12 exons and 11 introns exhibiting a similar organization as for the mouse and rat GGT genes. The exons 1-7 encode the heavy subunit whereas exons 8-12 which encode the carboxy-terminal part of the heavy subunit (exon 8) and the light subunit are clustered in a 1.6-kb BglII fragment. Exons 7 and 8 are separated by a 3.9-kb intron containing in its 3' part the sequences corresponding to the 5'-UTRs of the truncated GGT mRNAs described for human lung. Sequence analysis upstream this transcribed region exhibited putative promoter sequences and after transient transfection significant promoter activities were measured in V79 lung fibroblasts and KYN-2 hepatoma cells but not in A2780 ovarian cells. This specificity disappeared when only 550 bp upstream the transcription start site were used as promoter. These results argue for a promoter of truncated GGT mRNAs in intron 7, specifically regulated in human tissues.

Biochemical characteristics of gamma-glutamyl transpeptidase in capillaries from entorhinohippocampal complex of quinolinate-lesioned rat brain

Quinolinic acid (QUIN) is an endogenous excitotoxic agonist of the N-methyl-D-aspartate (NMDA) type of glutamate receptor, which causes slowly progressing degeneration of vulnerable neurons in some brain regions. Using changes in the activity of membrane-bound gamma-glutamyl transpeptidase (GGT) as a marker of cell damage, we found a significant decrease of this enzyme activity, which was preferentially located in the ipsilateral hippocampal formation and entorhinal cortex, 4 d after the unilateral intracerebroventricular (icv) injection of 0.5 mumol QUIN. The dose of QUIN divided into two half-doses injected bilaterally led to a symmetrical decline of GGT activity in hippocampal areas. The lesion was characterized by a suppression of GGT activity in hippocampal and entorhinal capillaries, corresponding to 60 and 81% of their initial value, respectively, but no significant changes were ascertained in synaptosomal membranes. The changes in the activity of capillary GGT were associated with the decrease of apparent maximal velocity Vmaxapp, whereas apparent Michaelis constant K(m)app (0.69-0.79 mM) remained unaffected. In the nonlesioned brain, concanavalin A (Con A) affinity chromatography revealed five glycoforms of synaptosomal GGT in contrast to only one found in hippocampal and entorhinal capillaries. The results document that neither the saccharide moiety of GGT nor the value of enzyme K(m)app is significantly affected by the QUIN-induced lesion of the rat brain. However, the suppression of GGT activity, which is accompanied by a decrease in the value of Vmaxapp in brain microvessels, may suggest dysfunction of the blood-brain barrier (BBB) in the QUIN-injured rat brain.

Synergistic stimulation of gamma-glutamyl transpeptidase and alkaline phosphatase activities by retinoic acid and astroglial factors in immortalized rat brain microvessel endothelial cells

The immortalized rat brain microvessel endothelial cell line RBE4 was used to investigate the in vitro regulation of two blood-brain barrier specific enzymes, gamma-glutamyl transpeptidase (GTP) and alkaline phosphatase (ALP). The effects of bFGF, astroglial factors, and retinoic acid (a cell differentiation agent) on GTP and ALP activities were separately or simultaneously studied in order to define optimal culture conditions for induction of these two specific enzymes of the blood-brain barrier. In the present study, a phenotypically distinct subpopulation of endothelial cells has been shown to develop from confluent cobblestone monolayers of RBE4 immortalized cerebral endothelial cells. These distinct cells were present within multicellular aggregates and specifically exhibited GTP and ALP activities. Addition of bFGF, astroglial factors, or retinoic acid induced the formation of these three-dimensional structures and in consequence an increase in GTP and ALP activities. For retinoic acid and astroglial factors, this increase could also be explained by the stimulation of either GTP or ALP expression in the phenotypically distinct positive cells associated with aggregates. Simultaneous treatment with retinoic acid and astroglial factors had a synergistic effect on GTP and ALP expression and thus may allow these distinct cells to evolve toward a more differentiated state. Since such results were also obtained with physiological concentrations of retinoic acid, we suggest that addition of this agent might contribute to greater differentiation of cells in in vitro blood-brain barrier models where endothelial cells are cocultured with astrocytes.

Molecular and functional characterization of recombinant human gamma-glutamyltransferase. Coupling of its activity to glutathione levels in V79 cells

We previously described the establishment of a transfected cell line (V79HGGT) that stably produces the highest recombinant human gamma-glutamyltransferase (GGT) activity. We now report the utilization of V79HGGT as a model system for studying human GGT. The papain-solubilized recombinant enzyme has been highly purified from cultured cells by a new procedure. Studies on the purified enzyme, either by N-terminal sequencing or by characterization of its enzymic activities, confirmed that recombinant GGT shares structural and catalytic identity with native human enzymes. The circular dichroism analysis indicated an alpha-helical content of 19%. Based on these data, we have undertaken a study on the functional consequences of elevated GGT activity on the reduced glutathione (GSH) content. GSH status was followed in V79 and V79HGGT cells throughout growth. A particular pattern was observed for each cell line, depending on, but differentially affected by, alteration of the culture medium. Elevated GGT activity was associated with a 2.5-fold reduced GSH content, clearly suggesting a negative influence of the highly expressed enzyme on the GSH level under normal growth conditions. Possible mechanisms involved are proposed. Our findings pointed out that, among the GSH-related enzymes, GGT could constitute an important factor determining the steady-state content of GSH.

Normal and abnormal development of the blood-brain barrier

The blood-brain barrier is responsible for the maintenance of the neuronal microenvironment. This is accomplished by isolation of the brain from the blood by the tight junctions that join endothelial cells in cerebral microvessels, and by selective transport and metabolism of substances from blood or brain by the endothelial cells. This review describes the growth and maturation of the brain vasculature, and the development of the special properties of the endothelia at the blood-brain interface. Evidence suggests that the development of the unique properties of the brain microvasculature is a consequence of tissue-specific interactions between endothelial cells of extraneural origin and developing brain cells. The cellular and molecular mechanisms that control these processes are as yet unknown but this review will include experimental studies which have used in vivo and in vitro systems to investigate what factors may be involved, and some pathological conditions in which abnormal barrier development is thought to be an important aspect of the disease process.

Regulation of gamma-glutamyl transpeptidase and alkaline phosphatase activities in immortalized rat brain microvessel endothelial cells

Rat brain microvessel endothelial cells were immortalized by transfection with a plasmid containing the E1A adenovirus gene. One clone, called RBE4, was further characterized. These cells display a nontransformed phenotype and express typical endothelial markers, Factor VIII-related antigen and Bandeiraea simplicifolia binding sites. When RBE4 cells were grown in the presence of bFGF and on collagen-coated dishes, confluent cultures developed sprouts that extend above the monolayer and organized into three-dimensional structures. The activity of the blood-brain barrier-associated enzyme, gamma-glutamyl transpeptidase (gamma GTP), was expressed in these structures, not in the surrounding monolayer. Similar results were obtained with the microvessel-related enzyme alkaline phosphatase (ALP). Addition of agents that elevate intracellular cAMP reduced the formation of three-dimensional structures, but every cell inside the aggregates still expressed gamma GTP and ALP activities. Such structures, associated with high levels of gamma GTP and ALP activities, were also induced by astroglial factors, including (1) plasma membranes from newborn rat primary astrocytes or rat glioma C6 cells, (2) C6 conditioned media, or (3) diffusible factors produced by primary astrocytes grown in the presence of, but not in contact with RBE4 cells. RBE4 cells thus remain sensitive to angiogenic and astroglial factors for the expression of the blood-brain barrier-related gamma GTP activity, as well as for ALP activity, and could constitute the basis of a valuable in vitro model of the blood-brain barrier.

Developmental changes of enzymes involved in peptide degradation in isolated rat brain microvessels

The specific activities of aminopeptidase A (APA), aminopeptidase M (APM), and dipeptidyl-aminopeptidase IV (DP IV) were determined in isolated brain microvessels and in brain homogenate of rats with different ages (between 1 and 8 weeks old). In addition, the blood-brain barrier (BBB)-specific enzymes gamma-glutamyltranspeptidase (gamma-GT) and alkaline phosphatase (ALP) were measured. As similarly described by others, gamma-GT activity increased during this time period by fourfold, whereas ALP increased between weeks 1 and 2 and declined thereafter. DP IV activity increased fivefold during the first 8 weeks after birth and APM activity increased by twofold. A decrease of APA activity was found between weeks 1 and 2 after birth followed by an increase thereafter. The development of aminopeptidase activities responsible for the processing of specific neuropeptides acting on brain microvessels may be important in the development of regulation processes for cerebral blood flow and BBB permeability in the maturing animal.

Developmental changes in enzymatic systems involved in protection against peroxidation in isolated rat brain microvessels

Activities of 3 enzymes involved in the major detoxification pathway for peroxides were assessed in rat brain microvessels. Between the 7th and 60th day after birth, glutathione peroxidase specific activity remained constant in microvessels, while glutathione reductase specific activity increased from day 14 to day 60. On the other hand, the specific activity of these two enzymes evolved similarly in total brain homogenate: they increased between day 7 and day 30, and then reached a plateau. In contrast, catalase specific activity in microvessels was markedly decreased from day 7 to day 60. A significant decrease in this enzyme specific activity was also observed in brain homogenate during development. However, in microvessels, catalase specific activity remained higher than that of brain homogenate throughout the time period studied. Our results support the idea that enzymatic mechanisms against peroxidative damage are required in early age, and could be potent at the level of the blood-brain barrier.

Permeability of bovine brain microvessel endothelial cells in vitro: Barrier tightening by a factor released from astroglioma cells

It has been shown both in vivo and in culture that astrocytes communicate with brain microvessel endothelial cells (BMECs) to induce many of the blood-brain barrier characteristics attributed to these unique cells. However, the results using cultured cells are conflicting as to whether this communication is dependent upon cell-cell contact. In this study we used primary cultures of bovine BMECs grown as monolayers on polycarbonate filters to study the formation of the barrier in vitro and examine its modulation by rat C6 glioma cells. Effects were examined by treating postconfluent BMEC monolayers with medium conditioned continually by C6 cells from the basolateral side to mimic the in vivo orientation. Cell monolayer integrity was assessed using electrical resistance and by measuring diffusion of uncharged molecules. BMEC monolayers form a functionally polarized and leaky barrier, with maximal resistance of 160 omega . cm2 and significant flux of molecules of molecular weight less than 350 Da. Treatment with rat or human astroglioma cells rather than pericytoma cells or transformed fibroblasts results in a concentration-dependent 200-440% increase in electrical resistance and a coincident 50% decrease in permeability to sucrose and dextran (70 kDa). The decrease in passive diffusion is most likely due to a change in tight junctions and not to transcellular vesicular traffic. The findings support that astroglioma cells release one or more signals that are required for cultured BMECs to express a "differentiated" phenotype associated with a tighter barrier, increased gamma-glutamyl transpeptidase activity, and decreased pinocytic activity. The relative ease and quickness of this culture system makes it amenable to studies on cell-cell interaction and regulation of barrier maintenance.

?-Glutamyl Transpeptidase Activity in Brain Microvessels Exhibits Regional Heterogeneity

Brain microvessels form a tight blood-tissue permeability barrier and express high levels of specific enzymes, including gamma-glutamyl transpeptidase (GGTP). This differentiation is thought to be induced by perivascular astrocytes. By using histochemical methods, we found that the percentage of GGTP-positive vessels varied considerably in different areas of rat brain. Enzyme activity was not found in the pineal gland or the median eminence, where the blood-brain barrier is not expressed. In areas where the blood-brain barrier is expressed, the percentage of GGTP-positive vessels varied from 8% in the optic nerve to 100% in the anterior commissure. The neocortex showed a lower percentage of GGTP-positive vessels (2-15%) than anterior olfactory nucleus (42%), subiculum (70%), hippocampus (48%), and striatum (50-58%). Alkaline phosphatase, another brain microvessel-enriched enzyme, did not show these marked regional differences. The morphometric histochemical results were verified by enzymatic assays in homogenates of different regions from rat and bovine brain and in microvessel preparations of bovine putamen and neocortex. During the postnatal development of rat brain, the difference between neocortex and striatum appeared after day 20. The regional heterogeneity of brain microvessels may be caused by astrocytic heterogeneity and reflect regional heterogeneity in microvascular function.

Variations in the effects of L-methionine-DL-sulfoximine on the activity of cerebral gamma-glutamyl transpeptidase in rats as a function of age

Changes in the activity of gamma-glutamyl transpeptidase (GGTP) and the effects of a subacute dose (150 mg/kg b.wt.) of methionine sulfoximine (MSO) on its activity were studied in cerebral cortex, cerebellum and brainstem of rats of 4 different age groups. GGTP activity increased with increasing age between days 10 and 180 after birth and decreased between 180 and 360 days of age in these 3 regions of the brain. Older animals showed convulsions and succumbed to the toxic effects of MSO. In the younger animals, wobbly gait and splayed leggedness were noticed in the earlier time periods and these animals recovered from the toxic effects of the drug. Following the administration of MSO, GGTP activity was suppressed in all the regions (excepting the cerebral cortex and cerebellum of 90-day-old animals). In 10- and 90-day-old animals). In 10- and 90-day-old animals, there was a complete recovery of enzyme activity which exceeded the control value as the time progressed. No such recovery was observed in 180- and 360-days-old animals. Parallel changes were observed in the GGTP activity and the behavioural pattern of the animals. These results were discussed in relation to the localization of this enzyme in astrocytes and capillaries.

Quantitative detection of blood-brain barrier-associated enzymes in cultured endothelial cells of porcine brain microvessels

The present study deals with a rapid and convenient assay for blood-brain barrier (BBB)-associated enzymes, gamma-glutamyl transpeptidase (gamma-GTP) and alkaline phosphatase (ALP), in cultured endothelial cells and other cells. These enzyme activities in cultured cells could be efficiently measured by direct incubation of each substrate in the culture plates without pretreatment of the cells. This new direct in situ-in plate assay was more rapid and convenient than conventional ex-plate assays, and these assays gave similar values for specific enzyme activities. gamma-GTP and ALP activities could be detected by this in situ method in primary-cultured endothelial cells of porcine brain microvessels, but their levels were lower than those before culture. The degree of loss due to culture differed between gamma-GTP and ALP; a relatively large amount of ALP remained but the gamma-GTP level decreased greatly. In this direct in situ-in plate assay, cultured porcine aortic endothelial cells exhibited negligibly small activities for both enzymes, whereas cultured astroglial cells of neonatal porcine brain showed moderate gamma-GTP activity and a trace of ALP activity. This direct in situ-in plate assay can be used for microculture and automatic measurement and offers a convenient means for studying the possible regulatory mechanisms of the expression of the BBB-associated enzymes.

Differential postnatal development of monoamine oxidases A and B in the blood-brain barrier of the rat

We studied the monoamine metabolizing mitochondrial enzyme, monoamine oxidase (MAO), in cerebral microvessels obtained from postnatally developing rats by measuring the specific binding of [3H]pargyline, an irreversible inhibitor of MAO, and the rate of oxidation of three known MAO substrates: benzylamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and tryptamine. MAO activity increased postnatally, with the greatest increase occurring in the second week and reaching a peak at 3 weeks of age. A concomitant increase in MAO of the cerebral cortex also occurred, but was several-fold less than that of cerebral microvessels. Using clorgyline and deprenyl, relatively specific inhibitors of MAO-A and MAO-B, we showed that cerebral microvessels contain both forms of MAO at all ages, but there was a major preponderance in the postnatal development of MAO-B. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of rat microvessels after [3H]pargyline binding also showed two distinct bands of radioactivity at all ages. These two bands corresponded to molecular weights of approximately 65,000 for MAO-A and approximately 60,000 for MAO-B. SDS-PAGE results of brain microvessels obtained from 1-, 14-, and 42-day-old rats confirm the differential postnatal development of MAO-B in rat brain microvessels.