A multi-omics investigation of the lung injury induced by PM2.5 at environmental levels via the lung-gut axis

Long-term exposure to fine particulate matter (PM2.5) posed injury for gastrointestinal and respiratory systems, ascribing with the lung-gut axis. However, the cross-talk mechanisms remain unclear. Here, we attempted to establish the response networks of lung-gut axis in mice exposed to PM2.5 at environmental levels. Male Balb/c mice were exposed to PM2.5 (dose of 0.1, 0.5, and 1.0 mg/kg) collected from Chengdu, China for 10 weeks, through intratracheally instillation, and examined the effect of PM2.5 on lung functions of mice. The changes of lung and gut microbiota and metabolic profiles of mice in different groups were determined. Furthermore, the results of multi-omics were conjointly analyzed to elucidate the primary microbes and the associated metabolites in lung and gut responsible for PM2.5 exposure. Accordingly, the cross-talk network and key pathways between lung-gut axis were established. The results indicated that exposed to PM2.5 0.1 mg/kg induced obvious inflammations in mice lung, while emphysema was observed at 1.0 mg/kg. The levels of metabolites guanosine, hypoxanthine, and hepoxilin B3 increased in the lung might contribute to lung inflammations in exposure groups. For microbiotas in lung, PM2.5 exposure significantly declined the proportions of Halomonas and Lactobacillus. Meanwhile, the metabolites in gut including L-tryptophan, serotonin, and spermidine were up-regulated in exposure groups, which were linked to the decreasing of Oscillospira and Helicobacter in gut. Via lung-gut axis, the activations of pathways including Tryptophan metabolism, ABC transporters, Serotonergic synapse, and Linoleic acid metabolism contributed to the cross-talk between lung and gut tissues of mice mediated by PM2.5. In summary, the microbes including Lactobacillus, Oscillospira, and Parabacteroides, and metabolites including hepoxilin B3, guanosine, hypoxanthine, L-tryptophan, and spermidine were the main drivers. In this lung-gut axis study, we elucidated some pro- and pre-biotics in lung and gut microenvironments contributed to the adverse effects on lung functions induced by PM2.5 exposure.

L-arginine metabolism inhibits arthritis and inflammatory bone loss

OBJECTIVES

To investigate the effect of the L-arginine metabolism on arthritis and inflammation-mediated bone loss.

METHODS

L-arginine was applied to three arthritis models (collagen-induced arthritis, serum-induced arthritis and human TNF transgenic mice). Inflammation was assessed clinically and histologically, while bone changes were quantified by μCT and histomorphometry. In vitro, effects of L-arginine on osteoclast differentiation were analysed by RNA-seq and mass spectrometry (MS). Seahorse, Single Cell ENergetIc metabolism by profilIng Translation inHibition and transmission electron microscopy were used for detecting metabolic changes in osteoclasts. Moreover, arginine-associated metabolites were measured in the serum of rheumatoid arthritis (RA) and pre-RA patients.

RESULTS

L-arginine inhibited arthritis and bone loss in all three models and directly blocked TNFα-induced murine and human osteoclastogenesis. RNA-seq and MS analyses indicated that L-arginine switched glycolysis to oxidative phosphorylation in inflammatory osteoclasts leading to increased ATP production, purine metabolism and elevated inosine and hypoxanthine levels. Adenosine deaminase inhibitors blocking inosine and hypoxanthine production abolished the inhibition of L-arginine on osteoclastogenesis in vitro and in vivo. Altered arginine levels were also found in RA and pre-RA patients.

CONCLUSION

Our study demonstrated that L-arginine ameliorates arthritis and bone erosion through metabolic reprogramming and perturbation of purine metabolism in osteoclasts.

Targeting NAD+ metabolism of hepatocellular carcinoma cells by lenvatinib promotes M2 macrophages reverse polarization, suppressing the HCC progression

BACKGROUND

Lowered nicotinamide adenine dinucleotide (NAD+) levels in tumor cells drive tumor hyperprogression during immunotherapy, and its restoration activates immune cells. However, the effect of lenvatinib, a first-line treatment for unresectable hepatocellular carcinoma (HCC), on NAD+ metabolism in HCC cells, and the metabolite crosstalk between HCC and immune cells after targeting NAD+ metabolism of HCC cells remain unelucidated.

METHODS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and ultra-high-performance liquid chromatography multiple reaction monitoring-mass spectrometry (UHPLC-MRM-MS) were used to detect and validate differential metabolites. RNA sequencing was used to explore mRNA expression in macrophages and HCC cells. HCC mouse models were used to validate the effects of lenvatinib on immune cells and NAD+ metabolism. The macrophage properties were elucidated using cell proliferation, apoptosis, and co-culture assays. In silico structural analysis and interaction assays were used to determine whether lenvatinib targets tet methylcytosine dioxygenase 2 (TET2). Flow cytometry was performed to assess changes in immune cells.

RESULTS

Lenvatinib targeted TET2 to synthesize and increase NAD+ levels, thereby inhibiting decomposition in HCC cells. NAD+ salvage increased lenvatinib-induced apoptosis of HCC cells. Lenvatinib also induced CD8+ T cells and M1 macrophages infiltration in vivo. And lenvatinib suppressed niacinamide, 5-Hydroxy-L-tryptophan and quinoline secretion of HCC cells, and increased hypoxanthine secretion, which contributed to proliferation, migration and polarization function of macrophages. Consequently, lenvatinib targeted NAD+ metabolism and elevated HCC-derived hypoxanthine to enhance the macrophages polarization from M2 to M1. Glycosaminoglycan binding disorder and positive regulation of cytosolic calcium ion concentration were characteristic features of the reverse polarization.

CONCLUSIONS

Targeting HCC cells NAD+ metabolism by lenvatinib-TET2 pathway drives metabolite crosstalk, leading to M2 macrophages reverse polarization, thereby suppressing HCC progression. Collectively, these novel insights highlight the role of lenvatinib or its combination therapies as promising therapeutic alternatives for HCC patients with low NAD+ levels or high TET2 levels.

Identification of Biosynthetic and Metabolic Genes of 2-Azahypoxanthine in Lepista sordida Based on Transcriptomic Analysis

2-Azahypoxanthine was isolated from the fairy ring-forming fungus Lepista sordida as a fairy ring-inducing compound. 2-Azahypoxanthine has an unprecedented 1,2,3-triazine moiety, and its biosynthetic pathway is unknown. The biosynthetic genes for 2-azahypoxanthine formation in L. sordida were predicted by a differential gene expression analysis using MiSeq. The results revealed that several genes in the purine and histidine metabolic pathways and the arginine biosynthetic pathway are involved in the biosynthesis of 2-azahypoxanthine. Furthermore, nitric oxide (NO) was produced by recombinant NO synthase 5 (rNOS5), suggesting that NOS5 can be the enzyme involved in the formation of 1,2,3-triazine. The gene encoding hypoxanthine-guanine phosphoribosyltransferase (HGPRT), one of the major phosphoribosyltransferases of purine metabolism, increased when 2-azahypoxanthine content was the highest. Therefore, we hypothesized that HGPRT might catalyze a reversible reaction between 2-azahypoxanthine and 2-azahypoxanthine-ribonucleotide. We proved the endogenous existence of 2-azahypoxanthine-ribonucleotide in L. sordida mycelia by LC-MS/MS for the first time. Furthermore, it was shown that recombinant HGPRT catalyzed reversible interconversion between 2-azahypoxanthine and 2-azahypoxanthine-ribonucleotide. These findings demonstrate that HGPRT can be involved in the biosynthesis of 2-azahypoxanthine via 2-azahypoxanthine-ribonucleotide generated by NOS5.

Oxygenation of the newborn. The impact of one molecule on newborn lives

Hypoxanthine is a purine metabolite which increases during hypoxia and therefore is an indicator of this condition. Further, when hypoxanthine is oxidized to uric acid in the presence of xanthine oxidase, oxygen radicals are generated. This was the theoretical basis for suggesting and studying, beginning in the 1990s, resuscitation of newborn infants with air instead of the traditional 100% O2. These studies demonstrated a 30% reduction in mortality when resuscitation of term and near term infants was carried out with air compared to pure oxygen. The mechanism for this is not fully understood, however the hypoxanthine -xanthine oxidase system increases oxidative stress and plays a role in regulation of the perinatal circulation. Further, hyperoxic resuscitation inhibits mitochondrial function, and one reason may be that genes involved in ATP production are down-regulated. Thus, the study of one single molecule, hypoxanthine, has contributed to the global prevention of an estimated 2-500,000 annual infant deaths.

Effects of Donepezil Treatment on Brain Metabolites, Gut Microbiota, and Gut Metabolites in an Amyloid Beta-Induced Cognitive Impairment Mouse Pilot Model

Accumulated clinical and biomedical evidence indicates that the gut microbiota and their metabolites affect brain function and behavior in various central nervous system disorders. This study was performed to investigate the changes in brain metabolites and composition of the fecal microbial community following injection of amyloid β (Aβ) and donepezil treatment of Aβ-injected mice using metataxonomics and metabolomics. Aβ treatment caused cognitive dysfunction, while donepezil resulted in the successful recovery of memory impairment. The Aβ + donepezil group showed a significantly higher relative abundance of Verrucomicrobia than the Aβ group. The relative abundance of 12 taxa, including Blautia and Akkermansia, differed significantly between the groups. The Aβ + donepezil group had higher levels of oxalate, glycerol, xylose, and palmitoleate in feces and oxalate, pyroglutamic acid, hypoxanthine, and inosine in brain tissues than the Aβ group. The levels of pyroglutamic acid, glutamic acid, and phenylalanine showed similar changes in vivo and in vitro using HT-22 cells. The major metabolic pathways in the brain tissues and gut microbiota affected by Aβ or donepezil treatment of Aβ-injected mice were related to amino acid pathways and sugar metabolism, respectively. These findings suggest that alterations in the gut microbiota might influence the induction and amelioration of Aβ-induced cognitive dysfunction via the gut–brain axis. This study could provide basic data on the effects of Aβ and donepezil on gut microbiota and metabolites in an Aβ-induced cognitive impairment mouse model.

Biosynthesis of the Fairy Chemicals, 2-Azahypoxanthine and Imidazole-4-carboxamide, in the Fairy Ring-Forming Fungus Lepista sordida

Fairy rings resulting from a fungus-plant interaction appear worldwide. 2-Azahypoxanthine (AHX) and imidazole-4-carboxamide (ICA) were first isolated from the culture broth of one of the fairy ring-forming fungi, Lepista sordida. Afterward, a common metabolite of AHX in plants, 2-aza-8-oxohypoxanthine (AOH), was found in AHX-treated rice. The biosynthetic pathway of the three compounds that are named as fairy chemicals (FCs) in plants has been partially elucidated; however, that in mushrooms remains unknown. In this study, it was revealed that the carbon skeletons of AHX and ICA were constructed from Gly in L. sordida mycelia and the fungus metabolized 5-aminoimidazole-4-carboxamide (AICA) to both of the compounds. These results indicated that FCs were biosynthesized by a diversion of the purine metabolic pathway in L. sordida mycelia, similar to that in plants. Furthermore, we showed that recombinant adenine phosphoribosyltransferase (APRT) catalyzed reversible interconversion not only between 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranosyl 5'-monophosphate (AICAR) and AICA but also between ICA-ribotide (ICAR) and ICA. Furthermore, the presence of ICAR in L. sordida mycelia was proven for the first time by LC-MS/MS detection, and this study provided the first report that there was a novel metabolic pathway of ICA in which its ribotide was an intermediate in the fungus.

Exceptionally strong sorption of infochemicals to activated carbon reduces their bioavailability to fish

The addition of activated carbon (AC) to sediments is a relatively new approach to remediate contaminated sites. Activated carbon strongly sorbs hydrophobic organic contaminants, thereby reducing their bioavailability and uptake in organisms. Because of its high sorption capacity, AC might, however, also sorb other chemicals that are not contaminants but instead have ecological functions. Examples of such compounds are infochemicals or pheromones (i.e., compounds serving as chemical inter- and intraspecies information vectors). The present study investigated the sorption of 2 known infochemicals, hypoxanthine-3-N-oxide (H3NO) and pyridine-N-oxide (PNO), to 5 different powdered ACs. Sorption isotherms of these low-molecular-weight, polar fish kairomone substances appeared highly nonlinear, with logarithmic Freundlich sorption coefficients of up to 7.6. At physiologically relevant concentrations, sorption was up to 7 to 9 orders of magnitude stronger than expected on the basis of hydrophobic forces only (i.e., the compounds' log octanol-water partition coefficient, being approximately -1), indicating exceptionally strong binding to specific sites. This binding effectively reduced the bioavailability of H3NO to Sarasa goldfish, as was shown in a behavioral assay. The present study demonstrates the previously unrecognized potential of AC to sorb ecologically relevant chemicals. Whether this potential may lead to subtle, unwanted ecological effects in the field will have to be investigated in more detail during future research.

Release of hypoxanthine and phosphate from exercising human legs with and without arterial insufficiency

Release of hypoxanthine and phosphate from exercising legs was studied in eight subjects without known obstructive arterial disease and in 20 claudicants. Lower leg blood flow was measured with a thermodilution catheter in the popliteal/distal femoral vein. The catheter allowed blood sampling from the calf before, during and after exhaustive exercise on a bicycle ergometer at a stepwise increasing load. Resting plasma hypoxanthine levels were higher in claudicants than in normal subjects (p less than 0.05). Hypoxanthine concentrations increased 2-4-fold during exercise, amounting to values ten times higher than the resting levels 5 and 10 min post exercise, in the venous effluent of the normal legs. A similar rise was found in the claudicants despite half the exercise intensity at exhaustion. Popliteal venous concentrations of phosphate increased by approximately 25% during exercise without significant differences between the two groups. During exercise the release of hypoxanthine increased 38-fold and of phosphate 21-fold in the normal lower legs, while a ten-fold increase in both metabolites was recorded in the claudicating legs. The study demonstrated a high release of hypoxanthine and phosphate from the human lower leg during rhythmic, exhaustive exercise (with maximal vasodilation). The result is compatible with the assumption that metabolites from the catabolism of adenine nucleotides (adenosine) play a role in the autoregulation of blood flow in human skeletal muscle. Increased plasma hypoxanthine concentrations at rest may indicate peripheral arterial insufficiency.

Purine metabolism and control of cell proliferation

Exposure of normal lymphocytes to phytohaemagglutinin or other lectin mitogens results in increased concentrations of 5-phosphoribosyl-1-pyrophosphate (PP-ribose-P) within minutes. Subsequently, synthesis of purine nucleotides by both the de novo and the salvage pathways is facilitated. This change is prevented by proliferation-inhibiting concentrations of exogenous adenosine. The capacity of lymphocytes to metabolize both adenine and adenosine is increased several-fold by incubation with phytohaemagglutinin but the specific activities of the respective first-step enzymes are not significantly altered. These results suggest that the relatively low quantity of PP-ribose-P available in normal lymphocytes is a major factor limiting the synthesis of purine nucleotides and may be important for the maintenance of the quiescent state. Increased availability of PP-ribose-P may also be associated with proliferative activation of fibroblast-like cells: chick embryo fibroblast cultures released from density-dependent inhibition of growth by insulin, trypsin or serum rapidly increase the rate of adenine incorporation into nucleotides. Chick embryo fibroblasts transformed by Rous sarcoma virus, but not cells infected with the respective non-transforming leukosis virus, show PP-ribose-P concentrations higher than those observed in normal cells.

XRCC1 interactions with multiple DNA glycosylases: a model for its recruitment to base excision repair

Repair of chemically modified bases in DNA is accomplished through base excision repair (BER). This pathway is initiated by a specific DNA glycosylase that recognizes and excises the altered base to yield an abasic (AP) site. After cleavage of the AP site by APE1, repair proceeds through re-synthesis and ligation steps. In mammalian cells, the XRCC1 protein, essential for the maintenance of genomic stability, is involved in both base excision and single-strand break repair. XRCC1 participates in the first step of BER by interacting with the human DNA glycosylases hOGG1 and NEIL1. To analyze the possibility of a general mechanism involving the interaction of XRCC1 with DNA glycosylases we used XRCC1 to pull-down DNA glycosylases activities from human cell extracts. XRCC1 co-purifies with DNA glycosylase activities capable of excising hypoxanthine and dihydrothymine, in addition to 8-oxoguanine, but not uracil. Biochemical analyses with the purified proteins confirmed the interactions between XRCC1 and MPG, hNTH1 or hNEIL2. Furthermore, XRCC1 stimulates the activities of these enzymes. In vivo localization studies show that after genotoxic treatments these DNA glycosylases can be found associated with XRCC1 foci. Our results support a BER model in which XRCC1 is recruited to the repair of alkylated or oxidized bases by the enzyme recognizing the lesion. XRCC1 would then coordinate the subsequent enzymatic steps and modulate the activities of all the proteins involved.

Intestinal ischemic preconditioning: Less xanthine accumulation relates with less apoptosis

Ischemic preconditioning has shown to reduce apoptosis in the intestinal mucosa during ischemia/reperfusion. This study evaluated if the decrease of apoptotic events found during preconditioning could be related with a reduction of the substrate (i.e., xanthine/hypoxanthine) available for xanthine oxidase (XO). Animals were randomly assigned to the following study groups: C, control; I/R, ischemia/reperfusion; P+I/R, ischemic preconditioning; P+I/R+H/X, ischemic preconditioning plus hypoxanthine/xanthine, and P+I/R+H/X+Allo, ischemic preconditioning plus hypoxanthine/xanthine plus allopurinol. Caspase-3 activity, DNA fragmentation and TUNEL staining increased in the I/R group compared to control. Ischemic preconditioning (P+I/R group) was able to reverse these apoptotic variables to a level similar to that of control rats. The addition of hypoxanthine/xanthine to rats subjected to ischemic preconditioning (P+I/R+H/X group) showed the highest apoptotic activity; however, further addition of allopurinol (P+I/R+H/X+Allo group) decreased significantly apoptotic activity and events. In conclusion, intestinal ischemic preconditioning is able to reduce apoptosis during the following sustained ischemia/reperfusion event because of a reduced accumulation of xanthine/hypoxanthine nucleotide.

Definition of a second Bacillus subtilis pur regulon comprising the pur and xpt-pbuX operons plus pbuG, nupG (yxjA), and pbuE (ydhL)

In Bacillus subtilis expression of genes or operons encoding enzymes and other proteins involved in purine synthesis is affected by purine bases and nucleosides in the growth medium. The genes belonging to the PurR regulon (purR, purA, glyA, guaC, pbuO, pbuG, and the pur, yqhZ-folD, and xpt-pbuX operons) are controlled by the PurR repressor, which inhibits transcription initiation. Other genes are regulated by a less-well-described transcription termination mechanism that responds to the presence of hypoxanthine and guanine. The pur operon and the xpt-pbuX operon, which were studied here, are regulated by both mechanisms. We isolated two mutants resistant to 2-fluoroadenine in which the pur operon and the xpt-pbuX operon are expressed at increased levels in a PurR-independent manner. The mutations were caused by deletions that disrupted a potential transcription terminator structure located immediately upstream of the ydhL gene. The 5' part of the ydhL leader region contained a 63-nucleotide (nt) sequence very similar to the 5' ends of the leaders of the pur and xpt-pbuX operons. Transcripts of these regions may form a common tandem stem-loop secondary structure. Two additional genes with potential leader regions containing the 63-nt sequence are pbuG, encoding a hypoxanthine-guanine transporter, and yxjA, which was shown to encode a purine nucleoside transporter and is renamed nupG. Transcriptional lacZ fusions and mutations in the 63-nt sequence encoding the possible secondary structures provided evidence that expression of the pur and xpt-pbuX operons and expression of the ydhL, nupG, and pbuG genes are regulated by a common mechanism. The new pur regulon is designated the XptR regulon. Except for ydhL, the operons and genes were negatively regulated by hypoxanthine and guanine. ydhL was positively regulated. The derived amino acid sequence encoded by ydhL (now called pbuE) is similar to the amino acid sequences of metabolite efflux pumps. When overexpressed, PbuE lowers the sensitivity to purine analogs. Indirect evidence indicated that PbuE decreases the size of the internal pool of hypoxanthine. This explains why the hypoxanthine- and guanine-regulated genes are expressed at elevated levels in a mutant that overexpresses pbuE.

Effect of barbiturates on hydroxyl radicals, lipid peroxidation, and hypoxic cell death in human NT2-N neurons

BACKGROUND

Barbiturates have been shown to be neuroprotective in several animal models, but the underlying mechanisms are unknown. In this study, the authors investigated the effect of barbiturates on free radical scavenging and attempted to correlate this with their neuroprotective effects in a model of hypoxic cell death in human NT2-N neurons.

METHODS

Hydroxyl radicals were generated by ascorbic acid and iron and were measured by conversion of salicylate to 2,3-dihydroxybenzoic acid. The effect of barbiturates on lipid peroxidation measured as malondialdehyde and 4-hydroxynon-2-enal was also investigated. Hypoxia studies were then performed on human NT2-N neurons. The cells were exposed to 10 h of hypoxia or combined oxygen and glucose deprivation for 3 or 5 h in the presence of thiopental (50-600 microM), methohexital (50-400 microM), phenobarbital (10-400 microM), or pentobarbital (10-400 microM), and cell death was evaluated after 24 h by lactate dehydrogenase release.

RESULTS

Pentobarbital, phenobarbital, methohexital, and thiopental dose-dependently inhibited formation of 2,3-dihydroxybenzoic acid and iron-stimulated lipid peroxidation. There were significant but moderate differences in antioxidant action between the barbiturates. While phenobarbital (10-400 microM) and pentobarbital (10-50 microM) increased lactate dehydrogenase release after combined oxygen and glucose deprivation, thiopental and methohexital protected the neurons at all tested concentrations. At a higher concentration (400 microM), pentobarbital also significantly protected the neurons. At both 50 and 400 microM, thiopental and methohexital protected the NT2-N neurons significantly better than phenobarbital and pentobarbital.

CONCLUSIONS

Barbiturates differ markedly in their neuroprotective effects against combined oxygen and glucose deprivation in human NT2-N neurons. The variation in neuroprotective effects could only partly be explained by differences in antioxidant action.

Oxypurinol administration fails to prevent free radical-mediated lipid peroxidation during loaded breathing

The purpose of the present study was to determine whether it is possible to alter the development of fatigue and ablate free radical-mediated lipid peroxidation of the diaphragm during loaded breathing by administering oxypurinol, a xanthine oxidase inhibitor. We studied 1) room-air-breathing decerebrate, unanesthetized rats given either saline or oxypurinol (50 mg/kg) and loaded with a large inspiratory resistance until airway pressure had fallen by 50% and 2) unloaded saline- and oxypurinol-treated room-air-breathing control animals. Additional sets of studies were performed with animals breathing 100% oxygen. Animals were killed at the conclusion of loading, and diaphragmatic samples were obtained for determination of thiobarbituric acid-reactive substances and assessment of in vitro force generation. We found that loading of saline-treated animals resulted in significant diaphragmatic fatigue and thiobarbituric acid-reactive substances formation (P < 0.01). Oxypurinol administration, however, failed to increase load trial time, reduce fatigue development, or prevent lipid peroxidation in either room-air-breathing or oxygen-breathing animals. These data suggest that xanthine oxidase-dependent pathways do not generate physiologically significant levels of free radicals during the type of inspiratory resistive loading examined in this study.

The prebiotic synthesis of modified purines and their potential role in the RNA world

Modified purines are found in all organisms in the tRNA, rRNA, and even DNA, raising the possibility of an early role for these compounds in the evolution of life. These include N6-methyladenine, 1-methyladenine, N6,N6-dimethyladenine, 1-methylhypoxanthine, 1-methylguanine, and N2-methylguanine. We find that these bases as well as a number of nonbiological modified purines can be synthesized from adenine and guanine by the simple reaction of an amine or an amino group with adenine and guanine under the concentrated conditions of the drying-lagoon or drying-beach model of prebiotic synthesis with yields as high as 50%. These compounds are therefore as prebiotic as adenine and guanine and could have played an important role in the RNA world by providing additional functional groups in ribozymes, especially for the construction of hydrophobic binding pockets.

N2-amination of guanine to 2-hydrazinohypoxanthine, a novel in vivo nucleic acid modification produced by the hepatocarcinogen 2-nitropropane

2-Nitropropane, an industrial chemical and a hepatocarcinogen in rats, induces aryl sulfotransferase-mediated liver DNA and RNA base modifications [Sodum, R. S., Sohn, O. S., Nie, G., and Fiala, E. S. (1994) Chem. Res. Toxicol. 7, 344-351]. Two of these modifications were previously identified as 8-aminoguanine and 8-oxoguanine. We now report that the base moiety of the so far unidentified third nucleic acid modification, namely RX1 in RNA and DX1 in DNA, is 2-hydrazinohypoxanthine (N2-aminoguanine). 2-Hydrazinoinosine and 2-hydrazinodeoxyinosine, synthesized by adapting published procedures, cochromatographed with RX1 and DX1 of liver RNA and DNA, respectively, from 2-nitropropane-treated rats. 2-Hydrazinoinosine and 2-hydrazinodeoxyinosine are unstable in solution like the in vivo products RX1 and DX1. At neutral pH, hypoxanthine nucleoside is the major product of decomposition, while at pH 10 or above, xanthine nucleoside is also formed. RX1 and DX1 could be generated in the anaerobic reactions of hydroxylamine-O-sulfonic acid, an intermediate in the proposed activation pathway of 2-nitropropane, with guanine nucleosides. These results provide further evidence for the activation of 2-nitropropane and other carcinogenic secondary nitroalkanes to a reactive species capable of aminating nucleic acids and proteins.

Relation between left ventricular function and oxidative stress in patients undergoing bypass surgery

OBJECTIVE

To determine whether preoperative left ventricular ejection fraction (LVEF) is related to the degree of myocardial oxidative stress during bypass surgery in man.

DESIGN

Observational study.

SETTING

Tertiary care centre.

PATIENTS AND INTERVENTIONS

31 patients (LVEF range was 20% to 68%) undergoing elective coronary bypass surgery with blood cardioplegic reperfusion were studied. Arterial and coronary sinus blood was collected before aortic cross clamping (T0) and at 0 (T1), 15 (T2), and 30 (T3) minutes after unclamping. Transmural left ventricular biopsies were also obtained from 15 patients at T0 and at T1.

MAIN OUTCOME MEASURES

Glutathione and adenine nucleotides were measured in myocardial biopsies, while coronary sinus-artery differences for glutathione, nucleotides, and products of lipid peroxidation were calculated from blood specimens. Creatine kinase (myocardial band; CK-MB) was measured in plasma at four and 12 hours after operation.

RESULTS

Myocardial glutathione and adenine nucleotides were correlated (p < 0.02) with preoperative LVEF both at T0 (r = 0.909 and 0.672) and T1 (r = 0.603 and 0.605). Oxidised glutathione released from the heart during reperfusion was inversely correlated with LVEF (r = -0.448, -0.466, and -0461 at T1, T2, and T3, p < 0.01), while reduced glutathione (r = 0.519 and 0.640 at T1 and T2) and glutathione redox ratio (r = 0.647, 0.714, 0.645, and 0.702 at T0, T1, T2, and T3) showed a direct correlation (p < 0.01). Lipid peroxidation at T1 was negatively related to LVEF (r = -0.492). CK-MB was also negatively related to LVEF (r = -0.440 at 4 h and -0.462 at 12 h).

CONCLUSIONS

The capacity to counterbalance oxidative burst following ischaemia and reperfusion appears to be related to the functional ability of the heart.

Adenosine formation in contracting primary rat skeletal muscle cells and endothelial cells in culture

1. The present study examined the capacity for adenosine formation, uptake and metabolism in contracting primary rat muscle cells and in microvascular endothelial cells in culture. 2. Strong and moderate electrical simulation of skeletal muscle cells led to a significantly greater increase in the extracellular adenosine concentration (421 +/- 91 and 235 +/- 30 nmol (g protein)-1, respectively; P < 0.05) compared with non-stimulated muscle cells (161 +/- 20 nmol (g protein)-1). The ATP concentration was lower (18%; P < 0.05) in the intensely contracted, but not in the moderately contracted muscle cells. 3. Addition of microvascular endothelial cells to the cultured skeletal muscle cells enhanced the contraction-induced accumulation of extracellular adenosine (P < 0.05), whereas endothelial cells in culture alone did not cause extracellular accumulation of adenosine. 4. Skeletal muscle cells were found to have ecto-forms of several enzymes involved in nucleotide metabolism, including ATPases capable of converting extracellular ATP to ADP and AMP. 5. Adenosine added to the cell medium was taken up by muscle cells and incorporated into the adenine nucleotide pool so that after 30 min of incubation, over 95% of the adenosine label was present in ATP, ADP and AMP. A similar extent of incorporation of adenosine into the nucleotide pool was evident in the endothelial cells. 6. The present data suggest that contracting muscle cells induce an elevation in the extracellular adenosine concentration. Addition of endothelial cells to muscle cells enhances the contraction-induced formation of adenosine. Adenosine taken up by muscle and endothelial cells from the extracellular space is not likely to be used for storage in intracellular pools, but may serve to regulate muscle extracellular adenosine levels.

Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter

The transport properties of the nucleobase hypoxanthine were examined in the human umbilical vein endothelial cell line ECV 304. Initial rates of hypoxanthine influx were independent of extracellular cations: replacement of Na+ with Li+, Rb+, N-methyl-D-glucamine or choline had no significant effect on hypoxanthine uptake by ECV 304 cells. Kinetic analysis demonstrated the presence of a single saturable system for the transport of hypoxanthine in ECV 304 cells with an apparent K(m) of 320 +/- 10 microM and a Vmax of 5.6 +/- 0.9 pmol/10(6) cells per s. Hypoxanthine uptake was inhibited by the nucleosides adenosine, uridine and thymidine (apparent Ki 41 +/- 6, 240 +/- 27 and 59 +/- 8 microM respectively) and the nucleoside transport inhibitors nitrobenzylthioinosine (NBMPR), dilazep and dipyridamole (apparent Ki 2.5 +/- 0.3, 11 +/- 3 and 0.16 +/- 0.006 microM respectively), whereas the nucleobases adenine, guanine and thymine had little effect (50% inhibition at > 1 mM). ECV 304 cells were also shown to transport adenosine via both the NBMPR-sensitive and -insensitive nucleoside carriers. Hypoxanthine specifically inhibited adenosine transport via the NBMPR-insensitive system in a competitive manner (apparent Ki 290 +/- 14 microM). These results indicate that hypoxanthine entry into ECV 304 endothelial cells is mediated by the NBMPR-insensitive nucleoside carrier present in these cells.

Delay of adenosine triphosphate depletion and hypoxanthine formation in rabbit lung after death

BACKGROUND

If lungs could be retrieved for transplantation from non-heart-beating cadavers, the shortage of donors might be significantly alleviated.

METHODS

Adenosine triphosphate (ATP) and hypoxanthine levels were measured postmortem in rabbit lungs comparing deflation (group 1), ventilation with room air (group 2), inflation with room air (group 3), ventilation with oxygen (group 4), ventilation with cooled air (group 5), deflation plus cadaver cooling (group 6), and cooling by pulmonary arterial flush (group 7).

RESULTS

The level of ATP dropped to 25.9% and HYP increased elevenfold at 30 minutes in group 1 but remained constant during 24 hours in group 7. The ATP catabolism beyond 2 hours postmortem appeared less in group 2 compared with group 3 (3.58 +/- 1.24 versus 0.39 +/- 0.08 mumol/g dry weight for ATP and 3.03 +/- 0.49 versus 7.64 +/- 0.94 mumol/g dry weight for hypoxanthine at 24 hours, respectively; p < 0.05). Cadaver cooling significantly slowed ATP catabolism. Changes in ATP level were similar in groups 2, 4, and 5.

CONCLUSIONS

These data suggest that in the non-heart-beating cadaver (1) cooling, ventilation, and inflation can delay ATP catabolism; (2) postmortem ventilation but not inflation for more than 2 hours will inhibit further ATP breakdown; (3) ventilation with either oxygen or cooled air is not more beneficial than room air ventilation; and (4) cold flush more than cadaver cooling will prevent ATP depletion.

Hypoxanthine: a low molecular weight factor essential for growth of erythrocytic Plasmodium falciparum in a serum-free medium

A low molecular weight factor in a basal medium essential for erythrocytic Plasmodium falciparum development in a serum-free medium using a cell growth-promoting factor derived from adult bovine serum was detected. The factor was hypoxanthine. The optimal hypoxanthine concentration for parasite growth was between 15 and 120 microM. The contribution of hypoxanthine to increased parasite growth was clearly evident in cultures on day 4. Among various low molecular weight supplements tested, adenine, adenosine, AMP, ATP, cyclic AMP, guanine, guanosine, inosine, inosine monophosphate, xanthine, NAD, NADH, NADP, NADPH and deoxyguanosine triphosphate showed a similar effect to that of hypoxanthine in the serum-free culture system. On the other hand, the addition of uric acid, FAD, thymidine, uridine, orotic acid, deoxythymidine triphosphate, deoxycytidine triphosphate, deoxyadenosine triphosphate, ribose-1-phosphate, or ethanolamine was not beneficial to the parasite growth. The results presented here will not only be of practical value, but will provide important information about the developmental requirements of the parasite.

[The effect of an alpha-tocopherol analog, MDL 73404, on myocardial bioenergetics]

The authors investigated the effect of the synthetic analogue of MDL 73,404 alpha-tocopherol on bioenergetic processes of the cardiac muscle in a control group of rats. After a 10-day application of the presented preparation they analyzed the following parameters of energetic metabolism: ATP, ADP, AMP and inorganic phosphorus. Beside these, the authors investigate the levels of main indicators of the purine metabolism (xanthine, hypoxanthine, inosine and uric acid) in the myocardium. Under the influence of the given analogue of alpha-tocopherol a significant increase in ATP, ADP and hypoxanthine took place in the myocardium. Also the total concentration of adenine nucleotide and relative ATP/ADP ratio increased in the cardiac muscle. On the basis of the gained results the authors came to a conclusion that the synthetic analogue of alpha-tocopherol MDL 73,404 has a favourable effect on the bioenergetic conditions in the myocardium. MDL 73,404 has a favourable cardioprotective effect on the cardiac muscle assumedly by means of stabilization of mitochondrial membranes on the myocardium with a subsequent impact on cellular ATP concentration.

Vincristine resistant HL-60 cells show cross-resistance to hypoxanthine-xanthine oxidase

This is the first observation that active an oxygen-producing system showed cross-resistance to vincristine (VCR) resistant cells or other anticancer agent-resistant cells. The extent of cross-resistance against oxygen radicals and anticancer agents in wild type and VCR resistant human promyelocytic leukemia cell line, HL-60 and HL-60/VCR, is compared. Superoxide was generated by reaction with hypoxanthine(HX)-xanthine oxidase(XO). HL-60/VCR was 81-fold resistant to VCR, 11.8-fold resistant to adriamycin, and 8.5-fold resistant to the XO concentration required for 50% growth inhibition compared with HL-60. Because oxygen radicals injure the cell membrane, the results indicate an increased resistance to membrane damage by oxygen radicals in drug resistant cells.

Neurochemical monitoring using intracerebral microdialysis in patients with subarachnoid hemorrhage

The authors have developed a method for routine monitoring of disturbances in brain energy metabolism and extracellular levels of excitatory amino acids using intracerebral microdialysis in 10 patients with subarachnoid hemorrhage. Microdialysis was conducted for periods ranging from 6 to 11 days after ictus. Altogether, 16,054 chemical analyses from 1647 dialysate samples were performed. Concentrations of the energy-related substances lactate, pyruvate, glucose, and hypoxanthine were measured, and the lactate/pyruvate ratio was calculated. The excitatory amino acids glutamate and aspartate were measured. The microdialysis data were matched with computerized tomography findings, clinical course, and outcome. The results support the concepts that microdialysis is a promising tool for chemical monitoring of the human brain and that extracellular fluid levels of lactate, lactate/pyruvate ratio, glucose, hypoxanthine, and glutamate are useful markers of disturbances in brain energy metabolism in neurointensive care patients. These results have generated a working hypothesis that the pattern of these extracellular markers may help differentiate between various causes of energy perturbations, such as hypoxia and different degrees of ischemia. The correlation between the dialysate levels of excitatory amino acids and outcome supports the concept of glutamate receptor overactivation in acute human brain injury.

Attenuated purine production during subsequent ischemia in preconditioned rabbit myocardium is unrelated to the mechanism of protection

Preconditioned hearts release less purines during ischemia than virgin hearts. This study tested whether this reduced purine production is related to the mechanism of protection by ischemic preconditioning. Coronary effluent from isolated rabbit hearts was collected and purine (adenosine + inosine + hypoxanthine) levels were measured. All hearts underwent two cycles of 5 min global ischemia, each followed by 10 min reperfusion. In the first minute of reflow after the first ischemic period untreated hearts released 155 +/- 14 nmol purines per g wet weight, but only 104 +/- 16 nmol/g following the second bout of ischemia (P < 0.05). Thus, preconditioned hearts released less purines during ischemia. When 8-(p-sulfophenyl)theophylline (100 microM), which prevents the infarct size-limiting effect of ischemic preconditioning by blocking adenosine receptors was present in the perfusate, the pattern of purine release was not altered (151 +/- 13 nmol/g during the first minute after the first 5-min ischemic episode dropping to 117 +/- 6 nmol/g after the second ischemic period P < 0.05). Furthermore, pharmacological preconditioning with 5 min exposure of the heart to either adenosine (10 microM) or phenylephrine (0.1 microM) 15 min prior to the first ischemia did not affect purine release during early reperfusion after either the first (144 +/- 16 nmol/g and 153 +/- 12 nmol/g, respectively) or second (84 +/- 12 nmol/g and 111 +/- 9 nmol/g, respectively) bout of ischemia. Since the attenuated purine release was apparently unaffected by the presence or absence of a protected state, we conclude that this pattern is unrelated to the mechanism by which preconditioning protects the heart.

Superoxide anion reduces the ability of myeloperoxidase to damage lipids

The aim of this study was to determine whether lipids are damaged by myeloperoxidase (MP) not only with hydrogen peroxide (H2O2), but also with a H2O2-generating system. Using the hypoxanthine-xanthine oxidase-Cu,Zn-superoxide dismutase (HX-XO-SOD) system as an effective H2O2-generating system, we observed a reduction in the ability of MP to produce peroxylipids in the HX-XO-SOD-MP system, compared with the H2O2-MP system. We also noted that MP inhibited the production of monoepoxide by the H2O2-cytochrome c (Cyt c) system. These results suggest that MP plays a role as an absorber of active oxygen species and prevents phagocytes from self-destruction.

Enhanced acquisition of purine nucleosides and nucleobases by purine-starved Crithidia luciliae

The effects of purine starvation on the ability of the trypanosomatid Crithidia luciliae to accumulate purines were determined. Kinetic studies showed that the uptake of the nucleoside adenosine by purine-starved organisms was approximately 7-fold faster than by nutrient-replete cells. Further, these studies demonstrated that purine-starved organisms accumulated the nucleobases hypoxanthine and adenine at a rate > 100-fold faster than organisms cultivated under replete conditions. Activities of several intracellular purine-salvage enzymes were measured in organisms from both culture conditions. Of those measured, the activities of adenine deaminase and hypoxanthine phosphoribosyltransferase were elevated approximately 4-fold and approximately 11-fold, respectively, in purine-starved organisms. Competitive substrate specificity studies suggested that these elevated enzyme activities were not responsible for the increased rates of uptake by purine-starved cells. The results are consistent with the induction of novel surface membrane purine transporters expressed in response to purine starvation. These studies using C. luciliae may provide insights into the mechanisms of trypanosomatid adaptation to altered environments encountered during the course of the life cycle.

Crystalloid versus cold blood cardioplegia in patients operated on for myocardial revascularisation

Post-ischemic reperfusion phenomenon has been studied in two methods of myocardial protection: a crystalloid cardioplegia (St Thomas no.2) and a cold blood cardioplegia (Buckberg) during cardiopulmonary bypass for myocardial revascularisation in patients. Myocardial protection has been assessed from the evolution of hemodynamic parameters, reperfusion arrhythmias and biochemical analysis of the coronary flow after cross-clamp removal: creatinine phosphokinase (CPK_MB) and nucleotide adenine metabolites (adenosine, inosine, hypoxanthine, xanthine and uric acid). The study was performed in two groups of 14 patients. Hemodynamic conditions were similar in both groups during reperfusion in order to avoid different coronary flow. In those conditions, myocardial protection by cold blood cardioplegia reduced reperfusion arrhythmias, and resulted in a loss of CPK-MB release. Furthermore, the reduction of metabolites release, purine bases and oxypurine bases into coronary sinus after cold blood cardioplegia suggest a better protection of myocardial high energy phosphates in this group than after crystalloid cardioplegia. Our results also show that hypoxanthine is probably the final product of ATP degradation in human myocardial tissue.

In vitro antimalarial activity of vegetal extracts used in West African traditional medicine

Among strategies for the development of new antimalarials, a study of plants traditionally used in Africa against malaria has been pursued. Extracts obtained from the plants Azadirachta indica, Cinnamonum camphora, Lippia multiflora, Vernonia colorata, Guiera senegalensis, Combretum micranthum, and Ximenia americana, commonly used in Cote d'Ivoire by native healers for the treatment of malaria, were tested on two strains of Plasmodium falciparum: FcB1-Colombia (chloroquine-resistant) and F32-Tanzania (chloroquine-sensitive). Extracts were obtained after infusion and decoction, both techniques being used by most native healers. The antimalarial activities of the extracts were tested first by parasite 3H-hypoxanthine incorporation and second by visual evaluation of the activities of plant extracts on thin blood smears, which also permitted the determination of parasitic stages and parasite alteration. Among the seven plants tested, some had an apparent inhibitory effect on P. falciparum growth in vitro, while other seemed to be less efficient.

Purine metabolite washout and platelet aggregation at reflow after tourniquet ischemia: effect of intravenous regional lidocaine

Tourniquet ischemia will influence the biochemical milieu of tissue cells and affect the metabolism of purines in skeletal muscle distal to the occlusion. At reperfusion, generation of oxygen radicals by the hypoxanthine-xanthine oxidase system may ensue, influencing white blood cell and thrombocyte aggregation, causing damage to the endothelial cell barrier and inducing non-reflow type phenomena. Amide-type local anaesthetics are known to affect local vasotone, leukocyte adherence and platelet function but the influence of lidocaine on purine metabolite washout and platelet aggregation following tourniquet ischemia for lower limb surgery is not known in detail. Therefore, the effects of regional intravenous lidocaine during tourniquet ischemia for knee surgery on purine catabolite washout and platelet function following reflow were assessed. Eight patients served as control (C-group) and 8 (L-group) received 100 ml of lidocaine (2.5 mg/ml) in the emptied venous bed of the leg to be operated. All patients had spinal anaesthesia (0.5% bupivacaine). Effluent venous blood from the leg and radial arterial blood was collected and analysed for xanthine (X), hypoxanthine (HX), base excess (BE), pH and potassium before and after reperfusion. Platelet ADP-induced aggregation (ADP-agg.) and secretion of beta-thromboglobulin (beta-TG) were measured in the effluent blood as well as systemically. After tourniquet release (TR), X and HX were significantly increased in effluent venous blood but the washout was enhanced in the L-group during the initial reperfusion phase. BE was significantly higher in the L-group both before and after TR whereas pH and potassium washout was comparable between the groups. No systemic effects on platelets were detected after tourniquet release but ADP-agg. in effluent venous blood was attenuated in 6 out of 8 patients in the L-group (NS). It is concluded that HX and X are generated during leg ischemia. Regional intravenous lidocaine, most probably through a vasodilatory mechanism and inhibition of white blood cell activation, may attenuate non-reflow phenomena and thereby exert beneficial effects on post-ischemic recovery by enhancing post-ischemic tissue reperfusion.

Methionine recycling pathways and antimalarial drug design

5'-Deoxy-5'-(methylthio)adenosine (MTA) is an S-adenosylmethionine metabolite that is generated as a by-product of polyamine biosynthesis. In mammalian cells, MTA undergoes a phosphorolytic cleavage catalyzed by MTA phosphorylase to produce adenine and 5-deoxy-5-(methylthio)ribose-1-phosphate (MTRP). Adenine is utilized in purine salvage pathways, and MTRP is subsequently recycled to methionine. Whereas some microorganisms metabolize MTA to MTRP via MTA phosphorylase, others metabolize MTA to MTRP in two steps via initial cleavage by MTA nucleosidase to adenine and 5-deoxy-5-(methylthio)ribose (MTR) followed by conversion of MTR to MTRP by MTR kinase. In order to assess the extent to which these pathways may be operative in Plasmodium falciparum, we have examined a series of 5'-alkyl-substituted analogs of MTA and the related MTR analogs and compared their abilities to inhibit in vitro growth of this malarial parasite. The MTR analogs 5-deoxy-5-(ethylthio)ribose and 5-deoxy-5-(hydroxyethylthio)ribose were inactive at concentrations up to 1 mM, and 5-deoxy-5-(monofluoroethylthio)ribose was weakly active (50% inhibitory concentration = 700 microM). In comparison, the MTA analogs, 5'-deoxy-5'-(ethylthio)adenosine,5'-deoxy-5'-(hydroxyethylthio)ade nosine (HETA), and 5'-deoxy-5'-(monofluoroethylthio)adenosine, had 50% inhibitory concentrations of 80, 46, and 61 microM, respectively. Extracts of P. falciparum were found to have substantial MTA phosphorylase activity. Coadministration of MTA with HETA partially protected the parasites against the growth-inhibitory effects of HETA. Results of this study indicate that P. falciparum has an active MTA phosphorylase that can be targeted by analogs of MTA.

Mechanism of corepressor-mediated specific DNA binding by the purine repressor

The modulation of the affinity of DNA-binding proteins by small molecule effectors for cognate DNA sites is common to both prokaryotes and eukaryotes. However, the mechanisms by which effector binding to one domain affects DNA binding by a distal domain are poorly understood structurally. In initial studies to provide insight into the mechanism of effector-modulated DNA binding of the lactose repressor family, we determined the crystal structure of the purine repressor bound to a corepressor and purF operator. To extend our understanding, we have determined the structure of the corepressor-free corepressor-binding domain of the purine repressor at 2.2 A resolution. In the unliganded state, structural changes in the corepressor-binding pocket cause each subunit to rotate open by as much as 23 degrees, the consequences of which are the disengagement of the minor groove-binding hinge helices and repressor-DNA dissociation.

When does the lung die? Time course of high energy phosphate depletion and relationship to lung viability after "death"

The shortage of lung donors for clinical transplantation could be significantly alleviated if lungs could be retrieved from cadavers hours after death. However, the time course of loss of lung viability after circulatory arrest and organism death remains unclear. To determine postmortem adenine nucleotide tissue levels in the lung and their relationship to lung viability, Sprague-Dawley rats were sacrificed and then ventilated with 100% oxygen (n = 50, O2) or 100% nitrogen (n = 40, N2) or left nonventilated (n = 50). Lungs from control rats (n = 20) were retrieved immediately after sacrifice. Lungs in the three study groups were retrieved at successive intervals postmortem. Adenine nucleotides (ATP, ADP, and AMP) and hypoxanthine and xanthine metabolites of adenosine were extracted from lung tissue and measured using high-performance liquid chromatography. Pulmonary parenchymal cell viability was quantified by pulmonary artery infusion of trypan blue vital dye in the contralateral lung of each animal. By 4 hr postmortem, viability was 85 +/- 1% in the O2-ventilated cadaver rat lungs, significantly higher than in the N2-ventilated (43 +/- 8%) and in the nonventilated (48 +/- 4%) lungs, where the percentage of viable cells was similar. All of the groups showed a time-dependent decrement in ATP levels and total adenine nucleotide (TAN) levels after death, but this was markedly attenuated in O2-ventilated cadaveric rat lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosines scavenged hydroxyl radicals and prevented posttraumatic epilepsy

Intracortical injection of iron ions has been used as a model of posttraumatic epilepsy. Oxidation of lipids in neural membranes by reactive oxygen species, especially hydroxyl radicals (OH), is involved in the mechanisms responsible for iron-induced seizures. We examined the scavenging effects of adenosine (Ado) and 2-chloroadenosine (Cl-Ado) on OH radicals and superoxide (O2.-) using an electron spin resonance (ESR) spectrometer, and the occurrence of epileptic discharges in electrocorticogram (ECoG) induced by FeCl3 injection into the sensorimotor cortex of rats. Though DMPO-O2.- spin adducts generated by the hypoxanthine-xanthine oxidase system were not quenched by Ado or Cl-Ado, 5 mM of each showed a quenching effect on DMPO-OH spin adducts (5.3 x 10(16) spins/ml) generated by the Fenton reagent. In ECoG of rats, spike discharges appeared 15-45 min after FeCl3 injection (500 nmol) into the sensorimotor cortex, and polyspikes and/or ictal patterns were observed 70-90 min after the injection. Cl-Ado (1 mg/kg) or Ado (5 mg/kg) injected intraperitoneally 30 min prior to the FeCl3 injection suppressed or delayed the occurrence of epileptic discharges induced by FeCl3. Cl-Ado and Ado may suppress the occurrence of epileptic discharges by scavenging OH and by their anticonvulsant effect.

Mechanisms of nucleobase transport in rabbit choroid plexus. Evidence for a Na(+)-dependent nucleobase transporter with broad substrate selectivity

The overall goal of this study was to determine the mechanisms by which nucleobases are transported in the choroid plexus. Choroid plexus tissue slices were obtained from the lateral ventricles of rabbit brains and depleted of ATP with 2,4-dinitrophenol. In the presence of an initial inwardly directed Na+ gradient, hypoxanthine accumulated in the tissue slices against a concentration gradient. Na(+)-stimulated hypoxanthine uptake was saturable with a Km of 31.1 +/- 9.71 microM and a Vmax of 2.69 +/- 0.941 nmol/g/s (mean +/- S.E.). Na(+)-stimulated hypoxanthine uptake was inhibited by (100) microM naturally occurring purine and pyrimidine nucleobases (adenine, cytosine, guanine, hypoxanthine, thymine, uracil, and xanthine) as well as by the nucleoside analog, dideoxyadenosine. The stoichiometric coupling ratio between Na+ and hypoxanthine was 1.7:1. The data demonstrate the presence of a novel Na(+)-dependent nucleobase transporter in the choroid plexus, which is distinct from the previously described Na(+)-nucleoside transporter in choroid plexus and from Na(+)-dependent nucleobase transporters in other tissues in terms of its kinetics, substrate selectivity, and Na(+)-nucleobase stoichiometry. This transporter may play a role in the targeting of both salvageable nucleobases and therapeutic nucleoside analogs to the central nervous system.

Utility of ribotyping, restriction endonuclease analysis and pulsed-field gel electrophoresis to discriminate between isolates of Neisseria gonorrhoeae of serovar IA-2 which require arginine, hypoxanthine or uracil for growth

Neisseria gonorrhoeae isolates that require arginine--i.e., either citrulline (C), or ornithine (O)--uracil (U) and hypoxanthine (H) have generally been considered to be similar when characterised by auxotype, serovar and plasmid content. The MICs of penicillin, tetracycline, erythromycin, spectinomycin, cefoxitin and ceftriaxone for 552 isolates belonging to serovar IA-2 with these phenotypes were found to be similar. Therefore, restriction fragment length polymorphism analysis of rRNA genes (ribotyping), restriction enzyme (RE) analysis of chromosomal DNA, and pulsed-field gel electrophoresis (PFGE) were evaluated to determine whether these isolates could be distinguished by molecular methods. A subset of 27 isolates of N. gonorrhoeae that were OUH-requiring, CUH-requiring or OH-requiring, belonged to serovar IA-2 and carried a 2.6-MDa plasmid, were selected for further study. Based on the RE analysis of SmaI-digested genomic DNA, the 27 isolates fell into a single RE pattern, five ribotypes and 17 PFGE profiles which did not correlate with the specific arginine-requiring subtypes of these isolates. Each ribotype varied by the presence of only a single fragment, which was of a different size in each pattern, and 17 (63%) of the 27 isolates belonged to ribotype I. PFGE yielded the highest level of discrimination with 17 different profiles.

Innate lack of susceptibility of Ugandan Trypanosoma brucei rhodesiense to DL-alpha-difluoromethylornithine (DFMO)

Trypanosoma brucei rhodesiense isolates from South East Uganda were characterized for susceptibility to the drugs suramin, nifurtimox, melarsoprol and DL-alpha-difluoromethylornithine (DFMO). Two different assays were used to determine the drug susceptibility of the field isolates: the [3H]hypoxanthine incorporation assay (24 hours) and the long term viability assay (10 days). All trypanosome stocks were susceptible to suramin and nifurtimox. Differences in the susceptibility to melarsoprol were observed in the [3H]hypoxanthine incorporation assay, but could not be confirmed in the long term viability assay. All T. b. rhodesiense stocks were found in vitro to have innate tolerance to DFMO, under conditions where T. b. gambiense stocks from West Africa were susceptible to the drug. Ugandan T. b. rhodesiense stocks did respond to 25-100 micrograms/ml after 10 days of drug exposure, but the DFMO level reached in cerebrospinal fluid during treatment is only 16.3 +/- 7.8 micrograms/ml. Therefore, DFMO is not an appropriate alternative or backup drug for treatment of Rhodesian sleeping sickness in Uganda.

Comparative cytoprotection of cultured corneal endothelial cells by water-soluble antioxidants against free-radical damage

We reported previously that purpurogallin (PPG) markedly protects the cultured rabbit corneal endothelial cells (RCEC) against oxyradical damage generated with hypoxanthine (HX) and xanthine oxidase (XO)(1). In this study, we further compared the cytoprotective activities of PPG versus Trolox (TX, alpha-tocopherol, a water-soluble analogue of vitamin E) and ascorbate (Asc) in confluent cultured RCEC with phase contrast microscopy and confirmed by transmission electron microscopy. PPG prolonged survival of the oxyradical damaged cells longer than those without PPG present (18.6 +/- 1.4 min at 1.0 mM and 11.2 +/- 1.0 at 0.25 mM respectively vs. 7.3 +/- 0.8 min in control). At levels equimolar to PPG, TX, and Asc were less effective in delaying cell necrosis caused by HX and XO (p < 0.01). When exposed to superoxide radicals generated by menadione, RCEC necrosed at 29.8 +/- 1.5 min compared to PPG 47.2 +/- 1.0 min at 1.0 mM and 38.9 +/- 1.0 min at 0.25 mM. This was significantly different from TX and Asc at corresponding concentrations (p < 0.01). PPG scavenges not only HX-XO-generated oxyradicals, but also nonenzymatically produced superoxide radicals, more actively than two well known antioxidants--TX and Asc.

Effects of zinc-desferrioxamine on Plasmodium falciparum in culture

The zinc-desferrioxamine (Zn-DFO) complex is considered to be more permeative into parasitized erythrocytes than is the metal-free DFO. The former may penetrate the cell and exchange its bound zinc for ferric ions, rendering the iron unavailable for vital parasite functions. The effects of these compounds on the in vitro development of Plasmodium falciparum are compared. The results indicate that Zn-DFO is superior to DFO, especially at concentrations below 20 microM, as shown by decreased levels of hypoxanthine incorporation, lower levels of parasitemia, and interference with the life cycle of the parasite. At low concentrations, DFO even enhanced parasite growth. Such an enhancement was not observed following exposure to Zn-DFO. Experiments in which the compounds were removed from the cultures indicated that parasites treated with Zn-DFO are less likely to recover at a later stage. Since DFO has already been used in humans for the treatment of malaria, its complex with zinc, which is more effective in vitro, should also be examined in vivo.

Production of hydroxyl radical by iron(III)-anthraquinone complexes through self-reduction and through reductive activation by the xanthine oxidase/hypoxanthine system

The iron(III) complexes of doxorubicin and epirubicin were observed to undergo a self-reduction (autoxidation) reaction in the absence of added reductants under aerobic conditions that resulted in the formation of ferrous anthracycline complexes. These self-reduction reactions resulted in significant hydrogen peroxide-mediated hydroxyl radical formation, as determined by electron paramagnetic resonance spin trapping. In contrast, the iron(III) complexes of daunorubicin, idarubicin, and mitoxantrone produced no significant amount of hydroxyl radical formation. Only the anthraquinones with an alpha-ketol side chain were observed to undergo both self-reduction and hydroxyl radical formation. Thus, the alpha-ketol side chain must be undergoing concomitant oxidation. The rate of self-reduction of the iron(III)-doxorubicin complex is consistent with a mechanism in which unbound doxorubicin binds to an iron(III)-doxorubicin complex of decreased coordination and after binding undergoes an intramolecular electron transfer. Molecular modeling was used to identify iron(III)-doxorubicin complexes that could result in electron transfer from the doxorubicin side chain hydroxyl group to the iron(III). All of the iron(III)-anthracycline complexes were able to produce hydroxyl radicals at significantly increased rates in the presence of the xanthine oxidase/hypoxanthine superoxide-generating system. In this system the iron(III)-epirubicin complex gave the greatest rate of hydroxyl radical production, with iron(III)-idarubicin giving the least.

Lazaroids protect isolated rat pancreatic acinar cells against damage induced by free radicals

Lazaroids, 21-aminosteroids without gluco- and mineralocorticoid activity, protect against oxidative injury in nervous system cells and may therefore also have a potential for treatment of pancreatitis, where oxidative stress contributes to cell injury. The present study evaluates the protective potential of the lazaroids U-78518F, U-74500A, and U-74389F against damage to isolated pancreatic acinar cells exposed to two models of oxidative stress: (a) a XOD/HX model, consisting of xanthine oxidase, hypoxanthine, and chelated FeCl3; and (b) an ADP/Fe model, consisting of FeSO4 and the reducing agent ADP. Both models caused time-dependent cell injury as assessed by uptake of trypan blue and release of lactate dehydrogenase. Short-term peak production of free radicals in the XOD/HX model--as monitored by the deoxyribose assay--was more injurious to cells than continuous radical generation at lower levels in the ADP/Fe model. In general, lazaroids at 1-10 microM reduced oxidative damage and deoxyribose oxidation in both models. The degree of reduction of cell damage and deoxyribose oxidation depended on the type and concentration of the lazaroid and the model used. Lazaroid concentrations < 0.1 microM were ineffective, and concentrations > 50 microM even accelerated cell injury, although lazaroids still served as scavengers at high concentrations. At least part of the noxious effects of high lazaroid concentrations is due to nonspecific membrane damage because these concentrations caused cell injury also in the absence of oxidative stress. The limited range of protective concentrations has to be observed in further in vivo studies. Interestingly, acinar cells in the absence of lazaroids also reduced radical-induced deoxyribose degradation.(ABSTRACT TRUNCATED AT 250 WORDS)