BioAssay Research Database (BARD): chemical biology and probe-development enabled by structured metadata and result types.

BARD, the BioAssay Research Database (https://bard.nih.gov/) is a public database and suite of tools developed to provide access to bioassay data produced by the NIH Molecular Libraries Program (MLP). Data from 631 MLP projects were migrated to a new structured vocabulary designed to capture bioassay data in a formalized manner, with particular emphasis placed on the description of assay protocols. New data can be submitted to BARD with a user-friendly set of tools that assist in the creation of appropriately formatted datasets and assay definitions. Data published through the BARD application program interface (API) can be accessed by researchers using web-based query tools or a desktop client. Third-party developers wishing to create new tools can use the API to produce stand-alone tools or new plug-ins that can be integrated into BARD. The entire BARD suite of tools therefore supports three classes of researcher: those who wish to publish data, those who wish to mine data for testable hypotheses, and those in the developer community who wish to build tools that leverage this carefully curated chemical biology resource.

Response of antioxidant enzymes to intermittent and continuous hyperbaric oxygen.

Rats and guinea pigs were exposed to O2 at 2.8 ATA (HBO) delivered either continuously or intermittently (repeated cycles of 10 min of 100% O2 followed by 2.5 min of air). The O2 time required to produce convulsions and death was increased significantly in both species by intermittency. To determine whether changes in brain and lung superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSHPx) correlated with the observed tolerance, enzyme activities were measured after short or long HBO exposures. For each exposure duration, one group received continuous and one intermittent HBO; O2 times were matched. HBO had marked effects on these enzymes: lung SOD increased (guinea pigs 47%, rats 88%) and CAT and GSHPx activities decreased (33%) in brain and lung. No differences were seen in lung GSHPx or brain CAT in rats or brain SOD in either species. In guinea pigs, but less so in rats, the observed changes in activity were usually modulated by intermittency. Increases in hematocrit, organ protein, and lung DNA, which may also reflect ongoing oxidative damage, were also slowed with intermittency in guinea pigs. Intermittency benefited both species by postponing gross symptoms of toxicity, but its modulation of changes in enzyme activities and other biochemical variables was more pronounced in guinea pigs than in rats, suggesting that there are additional mechanisms for tolerance.

Role of cerebral blood flow in seizures from hyperbaric oxygen exposure.

Hyperbaric O2 exposure causes seizures by an unknown mechanism. Cerebral blood flow (CBF) may affect seizure latency, although no studies have demonstrated a direct relationship. Awake rats (male, Sprague-Dawley, 350-450 g), instrumented for measuring electroencephalographic activity (EEG) and CBF (laser-Doppler flowmetry), were exposed to 100% O2 at 4 or 5 atm (gauge pressure) until EEG seizures. Compression with O2 caused vasoconstriction to about 70% of control flow that was maintained for various times. CBF then suddenly, but transiently, increased at a time that was reliably related to seizure latency (r=0.8, p<0.01). Additional animals were treated with agents that have diverse pharmacology and their effects on CBF and latency were measured. Glutamate receptor antagonists MK-801 (1 or 4 mg/kg) and ketamine (20-100 mg/kg) significantly increased CBF by 60-80% and decreased seizure latency from about 17+/-8 min (+/-S.D.) in controls to 5+/-1 and 6+/-2 min, respectively. In opposite, a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine (NNA)(25 mg/kg) decreased CBF by about 25% and increased time to seizure to 60+/-16 min. If these effects occur in humans, non-invasive measurement of CBF could potentially improve the safety and reliability of hyperbaric O2 usage in clinical and diving applications. It also appears that the effect of drugs on seizure latency can be explained, at least in part, by their effect on CBF.

Attenuation of brain hyperbaric oxygen toxicity by fasting is not related to ketosis.

The effect of 24 h of fasting and changes in blood glucose and beta-hydroxybutyrate (BHB) level on latency to seizures in hyperbaric oxygen (HBO2) was studied. Conscious, unrestrained rats implanted with cortical electroencephalogram electrodes were exposed to 0.5 MPa (gauge pressure) O2 until seizures were observed. Fasting for 24 h significantly (P < 0.01) decreased blood glucose (from 8.6 +/- 0.9 in fed to 6.9 +/- 0.7 mM in the fasted group), increased blood BHB (0.07 +/- 0.02 mM to 0.38 +/- 0.10 mM, respectively), and prolonged the latency to seizures compared with normally fed animals (21.0 +/- 9.8 vs. 34.6 +/- 17.7 min, P < 0.05). Injection of the ketone precursor 1,3-butanediol (BD) to the fed animals increased blood BHB level to 0.72 +/- 0.32; however, seizure latency remained the same as in fed animals. Restoration of blood glucose in fasted animals to the same level as in the fed group did not reverse the protection achieved by fast; instead it increased the latency to seizures. The results indicate that the protection against HBO2 seizures by fasting in short starvation is not related to the increase in circulating ketone bodies or decrease in blood glucose.

Increased red cell osmotic fragility and hematocrit after hyperbaric O2 exposure are related to acidosis.

Exposure to hyperbaric O2 (0.6 MPa) until convulsion occurred resulted in increased red blood cell osmotic fragility, increased hematocrit, and acidosis. Correction of the mixed metabolic and respiratory acidosis in arterial blood samples completely restored osmotic fragility and lowered hematocrit by 20%. Rats exposed to intermittent hyperbaric O2 (repeated cycles of 7 minutes of O2 and 7 minutes of air) tolerated significantly more O2 time than those exposed continuously. Intermittently exposed animals had smaller increases in osmotic fragility and less-severe acidosis. We verified the influence of pH on osmotic fragility and hematocrit in rats made acutely acidotic and corrected in vivo. Acidosis caused by CO2 inhalation and lactic and hydrochloric acid infusion raised osmotic fragility and hematocrit; these effects were completely reversed in the animal when we restored normal acid-base status. These studies demonstrate that conditions causing acidosis, including hyperbaric O2 exposure, increase red cell fragility and size and increase hematocrit.

Effect of MK-801 on seizures induced by exposure to hyperbaric oxygen: comparison with AP-7.

The effect of the noncompetitive N-methyl-d-aspartate (NMDA)-receptor antagonist MK-801 on seizures induced by hyperbaric oxygen in relation to changes in cerebral blood flow (CBF) was investigated. Rats were injected with MK-801 (0.005-8 mg/kg) 30 min before exposure to 100% O2 at 5 atm (gauge pressure). MK-801 administration resulted in a biphasic response in seizure latency. Doses of 0.1-4 mg/kg significantly decreased time to EEG and motor seizures, while 8 mg/kg had no effect on seizure latency. MK-801 had no effect on seizure duration. In a dose range 0.1-8 mg/kg MK-801 increased CBF in awake animals, which might be responsible for the decreased seizure latency. The gradual increase in seizure latency with increasing MK-801 doses suggests involvement of an additional factor probably related to the drug's anticonvulsive effect. Unlike MK-801, a competitive NMDA receptor antagonist, AP-7, at a dose 250 mg/kg had no effect on latency to seizures or CBF.