Cerebral ischemia enhances polyamine oxidation: identification of enzymatically formed 3-aminopropanal as an endogenous mediator of neuronal and glial cell death.

To elucidate endogenous mechanisms underlying cerebral damage during ischemia, brain polyamine oxidase activity was measured in rats subjected to permanent occlusion of the middle cerebral artery. Brain polyamine oxidase activity was increased significantly within 2 h after the onset of ischemia in brain homogenates (15.8 +/- 0.9 nmol/h/mg protein) as compared with homogenates prepared from the normally perfused contralateral side (7.4 +/- 0.5 nmol/h/mg protein) (P <0.05). The major catabolic products of polyamine oxidase are putrescine and 3-aminopropanal. Although 3-aminopropanal is a potent cytotoxin, essential information was previously lacking on whether 3-aminopropanal is produced during cerebral ischemia. We now report that 3-aminopropanal accumulates in the ischemic brain within 2 h after permanent forebrain ischemia in rats. Cytotoxic levels of 3-aminopropanal are achieved before the onset of significant cerebral cell damage, and increase in a time-dependent manner with spreading neuronal and glial cell death. Glial cell cultures exposed to 3-aminopropanal undergo apoptosis (LD50 = 160 microM), whereas neurons are killed by necrotic mechanisms (LD50 = 90 microM). The tetrapeptide caspase 1 inhibitor (Ac-YVAD-CMK) prevents 3-aminopropanal-mediated apoptosis in glial cells. Finally, treatment of rats with two structurally distinct inhibitors of polyamine oxidase (aminoguanidine and chloroquine) attenuates brain polyamine oxidase activity, prevents the production of 3-aminopropanal, and significantly protects against the development of ischemic brain damage in vivo. Considered together, these results indicate that polyamine oxidase-derived 3-aminopropanal is a mediator of the brain damaging sequelae of cerebral ischemia, which can be therapeutically modulated.

Tumor necrosis factor is a brain damaging cytokine in cerebral ischemia.

Two contrasting roles, one beneficial and the injurious, have been proposed for tumor necrosis factor (TNF) in the pathogenesis of cerebral ischemia. Reported here are results obtained in a standard model of permanent focal cortical ischemia in rats, in which the volume of cerebral infarction is measured after permanent occlusion of the middle cerebral artery. Administration of neutralizing anti-rat TNF antibodies (P114) into the brain cortex significantly reduced ischemic brain damage (85% reduced infarct volume as compared with preimmune-treated controls). Similar results were achieved by systemic administration of CNI-1493, a recently described tetravalent guanylhydrazone compound, which effectively inhibited endogenous brain TNF synthesis and conferred significant protection against the development of cerebral infarction (80% reduced infarct volume as compared with vehicle controls treated 1 h postischemia with 10 mg/kg). P114 anti-TNF and CNI-1493 were each cerebroprotective when given within a clinically relevant time window for up to 2 h after the onset of ischemia. These findings establish an important, pathophysiological role of TNF in mediating the progression of ischemic brain damage, and suggest that inhibiting TNF with CNI-1493 may be beneficial in the future treatment of stroke.

Expression of TNF and TNF receptors (p55 and p75) in the rat brain after focal cerebral ischemia.

Cerebral ischemia induces a rapid and dramatic up-regulation of tumor necrosis factor (TNF) protein and mRNA, but the cellular sources of TNF in the ischemic brain have not been defined. The diverse activities of TNF are mediated via ligand interaction with two distinct receptors, p55 and p75, which activate separate intracellular signal transduction pathways, leading to distinct biological effects. Since the effects of cerebral ischemia on TNF receptor (TNFR) expression are unknown, we examined the cellular localization and protein expression of TNF and its two receptors in the rat cerebral cortex in response to permanent middle cerebral artery (MCA) occlusion. The results indicate that focal. cerebral ischemia up-regulates expression of TNF and both TNFRs within the ischemic cortex. The most abundant type of TNF immunoreactivity (IR) was a punctate and filamentous pattern of transected cellular processes; however, cell bodies of neurons, astrocytes, and microglia, as well as infiltrating polymorphonuclear (PMN) leukocytes also showed TNF IR. Brain vasculature displayed TNF IR not only within endothelial cells but also in the perivascular space. MCA occlusion induced significant up-regulation of TNF receptors, with p55 IR appearing within 6 hr, significantly before the appearance of p75 IR at 24 hr after the onset of ischemia. Since p55 has been implicated in transducing cytotoxic signalling of TNF, these results support the proposed injurious role of excessive TNF produced during the acute response to cerebral ischemia.

Cerebroprotective effects of aminoguanidine in a rodent model of stroke.

BACKGROUND AND PURPOSE: During a cerebral infarction, a complex cascade of cytotoxic events ultimately determines the volume of brain cell loss. The studies presented here demonstrate that aminoguanidine, an experimental therapeutic currently in clinical trials to prevent diabetic complications, is cerebroprotective in focal cerebral infarction. METHODS: Adult Lewis rats (n = 6 to 12 per group) were anesthetized with ketamine and subjected to focal cerebral infarction by tandem permanent occlusion of the right middle cerebral artery and ipsilateral common carotid artery (CCA), followed by temporary occlusion of the contralateral CCA. Infarct volume (cortical) was assessed 24 hours after the onset of ischemia by planimetric analysis of coronal brain slices stained with tetrazolium. RESULTS: Aminoguanidine (320 mg/kg IP) administered 15 minutes after the onset of ischemia resulted in a significant reduction of infarct volume (7.6 +/- 2.6% of hemisphere in controls versus 1.3 +/- 0.2% of hemisphere in aminoguanidine-treated rats; P < .05). Administration of aminoguanidine conferred significant cerebroprotection even when administered 1 or 2 hours after the onset of ischemia (88% and 85% reduction from control, respectively; P < .05). Cerebroprotection by aminoguanidine was independent of systemic physiological variables known to influence stroke size (eg, temperature, mean arterial blood pressure, blood glucose, and arterial pH, PCO2, and PO2). CONCLUSIONS: These results indicate that the stroke-reducing properties of aminoguanidine are dose and time dependent, with substantial cerebroprotection persisting even with drug delivery up to 2 hours after the onset of ischemia. It is now plausible to pursue development of aminoguanidine as an experimental therapeutic in stroke, and possible mechanisms of these cerebroprotective effects are under consideration.

Adopting a corporate perspective on databases. Improving support for research and decision making.

The Veterans Health Administration (VHA) is at the forefront of designing and managing health care information systems that accommodate the needs of clinicians, researchers, and administrators at all levels. Rather than using one single-site, centralized corporate database VHA has constructed several large databases with different configurations to meet the needs of users with different perspectives. The largest VHA database is the Decentralized Hospital Computer Program (DHCP), a multisite, distributed data system that uses decoupled hospital databases. The centralization of DHCP policy has promoted data coherence, whereas the decentralization of DHCP management has permitted system development to be done with maximum relevance to the users'local practices. A more recently developed VHA data system, the Event Driven Reporting system (EDR), uses multiple, highly coupled databases to provide workload data at facility, regional, and national levels. The EDR automatically posts a subset of DHCP data to local and national VHA management. The development of the EDR illustrates how adoption of a corporate perspective can offer significant database improvements at reasonable cost and with modest impact on the legacy system.

Neurotoxicity of advanced glycation endproducts during focal stroke and neuroprotective effects of aminoguanidine.

Cerebral infarction (stroke) is a potentially disastrous complication of diabetes mellitus, principally because the extent of cortical loss is greater in diabetic patients than in nondiabetic patients. The etiology of this enhanced neurotoxicity is poorly understood. We hypothesized that advanced glycation endproducts (AGEs), which have previously been implicated in the development of other diabetic complications, might contribute to neurotoxicity and brain damage during ischemic stroke. Using a rat model of focal cerebral ischemia, we show that systemically administered AGE-modified bovine serum albumin (AGE-BSA) significantly increased cerebral infarct size. The neurotoxic effects of AGE-BSA administration were dose- and time-related and associated with a paradoxical increase in cerebral blood flow. Aminoguanidine, an inhibitor of AGE cross-linking, attenuated infarct volume in AGE-treated animals. We conclude that AGEs may contribute to the increased severity of stroke associated with diabetes and other conditions characterized by AGE accumulation.

An inhibitor of macrophage arginine transport and nitric oxide production (CNI-1493) prevents acute inflammation and endotoxin lethality.

BACKGROUND: Nitric oxide (NO), a small effector molecule produced enzymatically from L-arginine by nitric oxide synthase (NOS), is a mediator not only of important homeostatic mechanisms (e.g., blood vessel tone and tissue perfusion), but also of key aspects of local and systemic inflammatory responses. Previous efforts to develop inhibitors of NOS to protect against NO-mediated tissue damage in endotoxin shock have been unsuccessful, largely because such competitive NOS antagonists interfere with critical vasoregulatory NO production in blood vessels and decrease survival in endotoxemic animals. Accordingly, we sought to develop a pharmaceutical approach to selectively inhibit NO production in macrophages while sparing NO responses in blood vessels. MATERIALS AND METHODS: The process of cytokine-inducible L-arginine transport and NO production were studied in the murine macrophage-like cell line (RAW 264.7). A series of multivalent guanylhydrazones were synthesized to inhibit cytokine-inducible L-arginine transport. One such compound (CNI-1493) was studied further in animal models of endothelial-derived relaxing factor (EDRF) activity, carrageenan inflammation, and lethal lipopolysaccharide (LPS) challenge. RESULTS: Upon activation with cytokines, macrophages increase transport of L-arginine to support the production of NO by NOS. Since endothelial cells do not require this additional arginine transport to produce NO, we reasoned that a competitive inhibitor of cytokine-inducible L-arginine transport would not inhibit EDRF activity in blood vessels, and thus might be effectively employed against endotoxic shock. CNI-1493, a tetravalent guanylhydrazone, proved to be a selective inhibitor of cytokine-inducible arginine transport and NO production, but did not inhibit EDRF activity. In mice, CNI-1493 prevented the development of carrageenan-induced footpad inflammation, and conferred protection against lethal LPS challenge. CONCLUSIONS: A selective inhibitor of cytokine-inducible L-arginine transport that does not inhibit vascular EDRF responses is effective against endotoxin lethality and significantly reduces inflammatory responses.

Reliability of computer-generated prediction tracing.

The reliability of a commercially available computer prediction program (Quick Ceph II) was evaluated using pretreatment and posttreatment cephalograms of 30 patients who were treated during an active period of growth. The computer prediction was compared with the actual treatment result, and the growth forecast with the computer program was compared with the growth forecast using a manual method. Using paired student's t-tests, predictions for 5 of the 10 variables measured were found to be statistically reliable. Comparing the relative accuracy of growth prediction in terms of absolute values, the computer came closer to the actual result in four of the nine variables, while the manual method came closer in three variables. Predictions for the other two variables were virtually the same using both methods. The manual method of prediction was sufficient to give a reasonably good graphic representation of growth changes to create a VTO. However, the computer offers the added advantages of quicker access to information and somewhat greater accuracy in producing the tracing, as well as its use in patient education.

Evaluation of neural network performance by receiver operating characteristic (ROC) analysis: examples from the biotechnology domain.

A need exists for an unbiased measure of the accuracy of feed-forward neural networks used for classification. Receiver operating characteristic (ROC) analysis is suited for this measure, and has been used to assess the performance of several different network weights. The area under an ROC and its standard error were used to compare different network weight sets, and to follow the performance of a network during the course of training. The ROC is not sensitive to the prior probabilities of examples in the testing set nor to the system's decision bias. The area under an ROC curve is a readily understood measure, and should be used to evaluate neural networks and to report results of learning experiments. Examples are provided from experiments with data from the biotechnology domain.

Treatment objectives and planning in compromised adult cases.

The compromised adult orthodontic patient requires a coordinated, multidisciplinary approach to treatment to achieve the ideal resolution of the existing dental problems. Careful analysis of complete orthodontic records will define the scope of the problem and suggest treatment alternatives. Case presentations are used to demonstrate the principles of diagnosis and treatment planning.

A cephalometric appraisal of edgewise Class II nonextraction treatment with extraoral force.

The purpose of this study was to determine the treatment effects of nonextraction edgewise therapy combined with cervical headgear on Class II, Division 1 malocclusions. Data from a sample of 43 treated patients with a mean age of 11 years 11 months and a mean treatment time of 2 years 8 months were recorded. A cephalometric appraisal was done and the initial and final measurements of points, lines, and angles based on accepted cephalometric analyses were compared. Student's t test for paired cases was used to evaluate the significance of all measurement changes. The significant findings were as follows: the inhibition of forward growth of the maxilla, downward tipping of the anterior part of the palate, reduction of flaring of the maxillary incisors, reduction of the facial convexity, and extrusion and mesial movement of maxillary and mandibular first molars. The overall results tend to indicate the efficacy of this treatment modality in the treatment of the Class II, Division 1 malocclusion.

A cephalometric appraisal of nonextraction Begg treatment of Class II malocclusions.

Initial and final cephalometric evaluations are compared in a sample of 42 patients with Class II malocclusions treated in a nonextraction manner with the Begg appliance. The sample was analyzed as a group. Subgroups of patients with Division 1 and Division 2 characteristics were analyzed separately. To depict skeletal and dental changes, measurements were made using the sella nasion, palatal, and mandibular planes as reference planes. The findings show that on the average: The upper first molar maintained its anteroposterior position at the same time that SNA was reduced. This suggests a restriction of anterior maxillary growth. The mandibular first molar moved forward by 1.2 mm. Part of this change was attributed to anchorage consumption. Vertical changes in both the maxilla and the mandible were found to be within the normal range. No significant change in occlusal or mandibular plane angles was observed except for the Division 1 subgroup in whom a mild increase in the mandibular plane angle was observed.

A cephalometric evaluation of hard- and soft-tissue changes during the third stage of Begg treatment.

This study examined the effect of lingual root torque during the third stage of Begg treatment upon the maxillary central incisor, hard-tissue Point A, and soft-tissue Point A. Lateral cephalograms were taken, at the beginning and end of Stage III, of eighteen patients undergoing Begg treatment. Linear and angular measurements were made in an attempt to find the anteroposterior changes which occurred in the above structures as well as the superior-inferior changes which occurred in the maxillary first molar and the maxillary central incisor. It was found that the apex of the maxillary incisor, Point A, and soft-tissue Point A moved posteriorly a significant amount following Stage III mechanics. Also, the incisal edge of the maxillary central incisor moved anteriorly and extruded significantly. Weak correlations between hard- and soft-tissue changes may be due to changes in thickness of the upper lip related to growth and to growth of the nose.