Automating Quality Measures for Heart Failure Using Natural Language Processing: A Descriptive Study in the Department of Veterans Affairs

Background

We developed an accurate, stakeholder-informed, automated, natural language processing (NLP) system to measure the quality of heart failure (HF) inpatient care, and explored the potential for adoption of this system within an integrated health care system.

Objective

To accurately automate a United States Department of Veterans Affairs (VA) quality measure for inpatients with HF.

Methods

We automated the HF quality measure Congestive Heart Failure Inpatient Measure 19 (CHI19) that identifies whether a given patient has left ventricular ejection fraction (LVEF) <40%, and if so, whether an angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker was prescribed at discharge if there were no contraindications. We used documents from 1083 unique inpatients from eight VA medical centers to develop a reference standard (RS) to train (n=314) and test (n=769) the Congestive Heart Failure Information Extraction Framework (CHIEF). We also conducted semi-structured interviews (n=15) for stakeholder feedback on implementation of the CHIEF.

Results

The CHIEF classified each hospitalization in the test set with a sensitivity (SN) of 98.9% and positive predictive value of 98.7%, compared with an RS and SN of 98.5% for available External Peer Review Program assessments. Of the 1083 patients available for the NLP system, the CHIEF evaluated and classified 100% of cases. Stakeholders identified potential implementation facilitators and clinical uses of the CHIEF.

Conclusions

The CHIEF provided complete data for all patients in the cohort and could potentially improve the efficiency, timeliness, and utility of HF quality measurements.

Diffuse alterations in synaptic protein expression following focal traumatic brain injury in the immature rat

INTRODUCTION

The mechanisms responsible for cognitive decline after traumatic brain injury (TBI) in pediatric patients are poorly understood. The present study examined the potential role of synaptic alterations in this process by using an animal model of immature head injury to define the impact of TBI on expression of the synaptic protein, synaptophysin.

MATERIALS AND METHODS

After craniotomy, TBI was induced in postnatal day 17 (PND17) rats using controlled cortical impact delivered to the left hemisphere. NeuN, a neuronal marker, and synaptophysin expression were examined 1 day, 1 week, and 1 month after injury by immunohistochemistry and immunoblotting.

RESULTS

There were significant decreases in both NeuN and synaptophysin after 1 day and 1 week but not 1 month after injury within the hippocampus and neocortex adjacent to the impact site compared to sham-injured controls. The decrease in synaptophysin and NeuN was also noted in the contralateral hippocampus by 1 day after injury and in the contralateral neocortex by 1 week, indicating that changes in protein expression were not solely localized to the injury site but occurred in more distant regions as well.

DISCUSSION

In conclusion, the decrease and recovery in synaptophysin parallel the cognitive changes that occur after experimental TBI in the PND17 rat, which suggests that changes in this protein may contribute to cognitive declines after injury. The results also suggest that, in spite of the focal nature of the impact, diffuse alterations in protein expression can occur after immature TBI and may contribute to the subsequent cognitive dysfunction.

Sensitivity to radiation-induced apoptosis and neuron loss declines rapidly in the postnatal mouse neocortex

Therapeutic brain irradiation can cause progressive decline in cognitive function, particularly in children, but the reason for this effect is unclear. The study explored whether age-related differences in apoptotic sensitivity might contribute to the increased vulnerability of the young brain to radiation. Postnatal day 1 (P1) to P30 mice were treated with 0-16 Gy whole-body X-irradiation. Apoptotic cells were identified and quantified up to 48 h later using the TdT-UTP nick end-labelling method (TUNEL) and immunohistochemistry for activated caspase-3. The number of neuron-specific nuclear protein (NeuN)-positive and -negative cells were also counted to measure neuronal and non-neuronal cell loss. Significantly greater TUNEL labelling occurred in the cortex of irradiated P1 animals relative to the other age groups, but there was no difference among the P7, P14 and P30 groups. Irradiation decreased the %NeuN-positive cells in the mice irradiated on P1, whereas in P14 animals, irradiation led to an increase in the %NeuN-positive cells. These data demonstrate that neocortical neurons of very young mice are more susceptible to radiation-induced apoptosis. However, this sensitivity decreases rapidly after birth. By P14, acute cell loss due to radiation occurs primarily in non-neuronal populations.

Neuronal death is an active, caspase-dependent process after moderate but not severe DNA damage

Mild insults to neurons caused by ischemia or glutamate induce apoptosis, whereas severe insults induce non apoptotic death, such as necrosis. The molecular targets that are damaged by these insults and ultimately induce cell death are not fully established. To determine if DNA damage can induce apoptotic or non apoptotic death depending on the severity, neurons were treated with up to 128 Gy of ionizing radiation. Such treatment induced a dose-related increase in DNA single-strand breaks but no immediate membrane disruption or lipid peroxidation. Following moderate doses of < or = 32 Gy, neuronal death had many characteristics of apoptosis including nuclear fragmentation and DNA laddering. Nuclear fragmentation and membrane breakdown after moderate DNA damage could be blocked by inhibition of active protein synthesis with cycloheximide and by inhibition of caspases. In contrast, cell death after doses of > 32 Gy was not blocked by cycloheximide or caspase inhibitors, and membrane breakdown occurred relatively early in the cell death process. These data suggest that cell death after high dose irradiation and severe DNA damage can occur by non apoptotic mechanisms and that blocking apoptotic pathways may not prevent death after severe damage.

Excitotoxicity is required for induction of oxidative stress and apoptosis in mouse striatum by the mitochondrial toxin, 3-nitropropionic acid

Excitotoxicity is implicated in the pathogenesis of several neurologic diseases, such as chronic neurodegenerative diseases and stroke. Recently, it was reported that excitotoxicity has a relationship to apoptotic neuronal death, and that the mitochondrial toxin, 3-nitropropionic acid (3-NP), could induce apoptosis in the striatum. Although striatal lesions produced by 3-NP could develop through an excitotoxic mechanism, the exact relationship between apoptosis induction and excitotoxicity after 3-NP treatment is still not clear. The authors investigated the role of excitotoxicity and oxidative stress on apoptosis induction within the striatum after intraperitoneal injection of 3-NP. The authors demonstrated that removal of the corticostriatal glutamate pathway reduced superoxide production and apoptosis induction in the denervated striatum of decorticated mice after 3-NP treatment. Also, the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, prevented apoptosis in the striatum after 3-NP treatment for 5 days, whereas the non-NMDA receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline, was ineffective. The authors also evaluated the initial type of neuronal death by 3-NP treatment for different durations from 1 to 5 days. In early striatal damage, apoptotic neuronal death initially occurred after 3-NP treatment. Our data show that excitotoxicity related to oxidative stress initially induces apoptotic neuronal death in mouse striatum after treatment with 3-NP.

Long-term impairment of subependymal repopulation following damage by ionizing irradiation

In the mammalian brain, the subependyma (SE) contains stem cells capable of producing neurons and glia. In normal brain these stem cells are responsible, in part, for maintaining the morphologic and functional integrity of the SE; what role the cells of the SE play in brain injury has not yet been elucidated. The present study was designed to determine the long-term regenerative potential of the rat SE after significant depletion of stem cells. Ionizing irradiation was used to deplete cells of the SE and subsequent cellular responses were quantified using immunohistochemical analyses on formalin-fixed, paraffin-embedded tissues. A histomorphometric approach was used to quantify total cell number, number of proliferating cells, number of immature neurons, astrocytes, and undifferentiated components of the SE. Because there are no markers specific for stem cells, we used a repopulation assay as an indirect measure of stem cell response after injury. Our data showed clear radiation dose-dependencies in our quantitative endpoints, implying that there was progressively more stem cell damage with increasing radiation dose. Repopulation of the SE in terms of total cell number, number of proliferating cells and numbers of immature neurons was impaired in a dose-dependent fashion up to 180 days after treatment. These data suggest that after irradiation, surviving stem cells are unable to regenerate the SE. This inability to regenerate after stem cell damage/depletion could have important implications with respect to the normal function of the SE and the function of the SE after brain injury.

A deconvolution method for evaluating indicator-dilution curves

Characteristics of blood flow in tissue can be measured by administering an intravascular tracer and then deconvolving and analysing the resulting indicator-dilution curves. Existing deconvolution methods are not typically generalizable to a variety of tissues. The authors have developed a more general deconvolution method using simulated indicator-dilution data. This method involves filtering the Fourier transform of indicator-dilution data with a modification of the Wiener filter, an adaptive deconvolution filter. Unlike the Wiener filter, this adaptive filter requires no previous knowledge of the noise frequency spectrum; it is derived by varying the magnitude of the noise spectrum until the oscillations in the deconvolved data fall below an optimal value. The optimal value corresponds to the setting of the noise spectrum that allows the most accurate and precise measurement of vascular characteristics from deconvolved data. Vascular characteristics measured in brain tissues using this deconvolution method on actual indicator-dilution data were similar to established values. It should be possible to use this method on time-concentration data collected from a variety of tissues using a number of different tracer measurement techniques, thereby allowing the accurate characterization of vascular physiology.

Reduced mitochondrial manganese-superoxide dismutase activity exacerbates glutamate toxicity in cultured mouse cortical neurons

Studies of neuronal injury and death after cerebral ischemia and various neurodegenerative diseases have increasingly focused on the interactions between mitochondrial function, reactive oxygen species (ROS) production and glutamate neurotoxicity. Recent findings suggest that increased mitochondrial ROS production precedes neuronal death after glutamate treatment. It is hypothesized that under pathological conditions when mitochondrial function is compromised, extracellular glutamate may exacerbate neuronal injury. In the present study, we focus on the relationship between mitochondrial superoxide production and glutamate neurotoxicity in cultured cortical neurons with normal or reduced levels of manganese-superoxide dismutase (MnSOD) activity. Our results demonstrate that neurons with reduced MnSOD activity are significantly more sensitive to transient exposure to extracellular glutamate. The increased sensitivity of cultured cortical neurons with reduced MnSOD activity is characteristically subject only to treatment by glutamate but not to other glutamate receptor agonists, such as N-methyl-d-aspartate, kainate and quisqualate. We suggest that the reduced MnSOD activity in neurons may exacerbate glutamate neurotoxicity via a mechanism independent of receptor activation.

Decreased expression of bcl-2 and bcl-x mRNA coincides with apoptosis following intracerebral administration of 3-nitropropionic acid

The mitochondrial toxin, 3-nitropropionic acid (3-NP), is an irreversible inhibitor of succinate dehydrogenase that induces apoptosis in vitro and in vivo. We injected 3-NP into the striatum of rats to examine the potential role of Bcl-2 or Bcl-x, proteins that can inhibit apoptosis, in brain injury due to 3-NP. Electrophoretic examination of striatal tissue indicated that 3-NP induced internucleosomal fragmentation typical of apoptosis. There was also histologic evidence of apoptosis based on staining by the terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) method. Apoptosis was first observed 6 h after injection, was maximal at 1 day, and was still observed on day 7. Expression of bcl-2, bcl-x, and c-jun mRNA expression was evaluated 1, 3, 6, and 12 h and 1, 3, 5, and 7 days after injection using in situ hybridization. Both bcl-2 and bcl-x mRNA expression in the striatum decreased starting at 6 h and continued to 5 days after injection. This was in contrast to an apparent increase in c-jun expression. The similarity in the time course of apoptosis to that of suppression of bcl-2 and bcl-x mRNA suggests that changes in expression of these genes may contribute to apoptosis following 3-NP injection.

Cerebrovascular effects of the bradykinin analog RMP-7 in normal and irradiated dog brain

The effects of an intravenous (i.v.) injection of the bradykinin analog RMP-7 (100 ng/kg) were assessed in normal dogs and dogs with focal, radiation-induced brain lesions. A dose of 20 Gy was delivered to a point 0.75 cm from a removable interstitial 125I source; parameters relating to blood flow and permeability were quantified using computed tomography 2-8 weeks after irradiation. Blood flow-related endpoints included regional cerebral blood flow (rCBF), mean transit time of blood and vascular volume, while endpoints related to permeability included blood-to-brain transfer constant (Ki), brain-to-blood transfer constant and plasma volume. In unirradiated brain, an i.v. bolus of RMP-7 administered through the left cephalic vein induced a rapid and transient hypotension and a statistically significant increase in vascular volume; no alterations in any parameter related to permeability were observed. After irradiation, changes in rCBF after RMP-7 depended upon time after exposure, effects presumably due to changing morphology in the irradiated tissues. In the radiation lesions, significant increases in Ki were observed 5 minutes after injection of RMP-7, but those increases were not related to time after irradiation or alteration in blood flow-related parameters. Our results showed that RMP-7 selectively increased permeability in already damaged vasculature without affecting the extent or volume of radiation-induced vasogenic edema. These data suggest that RMP-7 may provide an effective means to enhance the delivery of compounds to an already compromised brain while not exacerbating the potential adverse effects of pre-existing vasogenic edema.

Blood-brain barrier disruption, HSP70 expression and apoptosis due to 3-nitropropionic acid, a mitochondrial toxin

3-Nitropropionic acid (3-NP), a mitochondrial toxin, induces apoptosis in the striatum. We wanted to determine if there was a relationship between mitochondrial dysfunction, disruption of the blood-brain barrier (BBB), and apoptosis. BBB disruption following intrastriatal injection of 3-NP was assessed by Evans blue leakage, brain water content, and by the expression of the 70 kDa heat shock protein (HSP70) and mRNA. Apoptosis was assessed by in situ terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) and gel electrophoresis to detect internucleosomal DNA fragmentation. Microscopic evidence of Evans blue leakage due to 3-NP was present only 3 hr after injection. Both internucleosomal DNA fragmentation and TUNEL-labeling did not appear until 24 hr after injection. HSP70 (protein and mRNA) was also elevated by 24 hr. There was a quantitative increase in Evans blue leakage and brain water content due to 3-NP by 3 days after injection. Our results suggest that BBB disruption is an early event followed by increased HSP70 expression and apoptosis. We speculate that 3-NP damages endothelial cells, leading to vasogenic edema and apoptosis.

Response of postmitotic neurons to X-irradiation: implications for the role of DNA damage in neuronal apoptosis

The molecular changes responsible for inducing neuronal apoptosis are unknown. Rat cortical neurons were treated with x-irradiation 7 d after isolation to test for the role of DNA damage in neuronal death. The response of neurons to x-irradiation was compared with that of astrocytes that had been isolated 3 weeks earlier from newborn rats. At the time of irradiation, the neurons appeared well differentiated morphologically and were predominantly (90-95%) noncycling, based on flow cytometric analysis. There was a similar, linear increase in DNA double-strand breaks with increasing radiation dose in neurons and astrocytes. However, whereas doses as low as 2 Gy induced typical apoptotic changes in neurons, including nuclear fragmentation and/or internucleosomal DNA fragmentation, doses as high as 32 Gy caused little or no apoptosis in astrocytes. Radiation-induced apoptosis of neurons started 4-8 hr after irradiation, was maximal at 12 hr, and was dependent on dose up to 16 Gy. It was prevented when cycloheximide, a protein synthesis inhibitor, was added up to 6 hr after irradiation. In addition to their distinct apoptotic response, neurons rejoined radiation-induced DNA double-strand breaks more slowly than astrocytes. Treatment with benzamide to inhibit ADP-ribosylation and strand break repair increased apoptosis; splitting the dose of radiation to allow increased time for DNA repair decreased apoptosis. These data suggest that DNA damage may induce neuronal apoptosis, that the extent of damage may determine the degree of apoptosis induced, and that slow repair of damage may play a role in the susceptibility of neurons to apoptosis.

Nitric oxide- and superoxide-mediated toxicity in cerebral endothelial cells

Nitric oxide and superoxide are free radicals that appear to contribute to the pathogenesis of a number of brain disorders, and cerebral endothelial cells are a potential target of these agents. Because of the capacity for these two agents to combine, it has been suggested that nitric oxide might either enhance or inhibit the toxic effects of superoxide. To establish the effect of the generation of superoxide and nitric oxide alone and in combination, cerebral endothelial cells were exposed to sodium nitroprusside, a source of nitric oxide, and/or paraquat, a source of superoxide. Paraquat enhanced the toxicity of sodium nitroprusside, as did diethyldithiocarbamate, an inhibitor of superoxide dismutase, which supports the hypothesis that enhanced levels of superoxide can combine with nitric oxide to form a more toxic product. Also, the toxicity of paraquat could be partially inhibited by blocking endogenous nitric oxide synthesis using N(G)-monomethyl-L-arginine. When ascorbate was administered along with sodium nitroprusside to increase nitric oxide generation, as little as 5 microM sodium nitroprusside was toxic when superoxide dismutase was inhibited. Whereas concentrations of 50 to 500 microM sodium nitroprusside and 0.4 mM ascorbate caused approximately 100% toxicity, there was no measurable toxicity when these doses were accompanied by 2 mM glutathione or 50 U/ml of catalase; this suggests that peroxides may also contribute to nitric oxide toxicity. These results suggest that the simultaneous generation of nitric oxide and superoxide is synergistic, resulting in enhanced toxicity.

Apoptosis in the subependyma of young adult rats after single and fractionated doses of X-rays

Ionizing radiation is commonly used in the treatment of brain tumors but can cause significant damage to surrounding normal brain. The pathogenesis of this damage is uncertain, and understanding the response of potential target cell populations may provide information useful for developing strategies to optimize therapeutic irradiation. In the mammalian forebrain, the subependyma is a mitotically active area that is a source of oligodendrocytes and astrocytes, and it has been hypothesized that depletion of cells from this region could play a role in radiation-induced white matter injury. Using a distinct morphological pattern of nuclear fragmentation and an immunohistochemical method to specifically label the 3'-hydroxyl termini of DNA strand breaks (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling), we quantified apoptosis in the subependyma in the young adult rat brain after single and fractionated doses of X-rays. Significant increases in apoptotic index (percentage of cells showing apoptosis) were detected 3 h after irradiation, and the peak apoptotic index was detected at 6 h. Six h after irradiation, the dose response for apoptosis was characterized by a steep increase in apoptotic index between 0.5 and 2.0 Gy and a plateau from 2-30 Gy. The fraction of cells susceptible to apoptosis was estimated to be about 40%, and treatment of rats with cycloheximide inhibited apoptosis. When daily 1.5-Gy fractions of X-rays were administered, the first three fractions were equally effective at decreasing the cell population via apoptosis. There was no additional apoptosis or decrease in cellularity in spite of one to four additional doses of X-rays. Those data suggested some input of cells into the subependymal population during fractionated treatment, and subsequent studies showed that there was a significant rise in 5-bromo-2' deoxyuridine labeling index 2-3 days after irradiation, indicating increased cellular proliferation. The proliferative response after depletion of cells via apoptosis may represent the recruitment of a relatively quiescent stem cell population. It is possible that the radiation response of subependymal stem cells and not the apoptotic-sensitive population per se are critical elements in the response of the brain to radiation injury.

Apoptosis in the striatum of rats following intraperitoneal injection of 3-nitropropionic acid

The present study investigated the mechanism of cellular degeneration within the striatum following administration of the mitochondrial toxin, 3-nitropropionic (3-NP) acid. Internucleosomal fragmentation typical of apoptosis was present in the DNA of cells from the striatum of 3-NP-treated rats. DNA fragmentation was also evident in this region by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling. The data suggest that striatal cells die by apoptosis following administration of 3-NP.

Attenuation of acute and chronic damage following traumatic brain injury in copper, zinc-superoxide dismutase transgenic mice

To elucidate the role of oxygen-derived free radicals and superoxide dismutase in traumatic brain injury (TBI), blood-brain barrier (BBB) permeability, brain edema, behavioral function, and necrotic cavity volume (CV) were evaluated after TBI using nontransgenic (nTg) mice and heterozygous and homozygous transgenic (Tg) mice with a 1.5- (Tg 1.5x), 3.1-(Tg3.1x) and five- (Tg5x) fold increase in human copper, zinc-superoxide dismutase (CuZn-SOD) activity. Traumatic brain injury was produced by the weight-drop method. Evans blue dye leakage 4 hours after injury was attenuated in a CuZn-SOD dose-dependent manner with decreases of 18.6%, 40.9%, and 48.8%, in the Tg1.5x, Tg3.1x, and Tg5x groups, respectively. The water content 6 hours after injury in the Tg3.1x (79.64%) and Tg5x (79.45%) groups was significantly lower than in nTg mice (81.37%). There was an initial decrease in body weight and in motor performance, as measured by beam walk and beam balance tasks undertaken 1 day after TBI. However, the average reduction in beam balance and beam walk performance deficits and changes in body weight postinjury were significantly ameliorated in Tg mice. The CV was significantly smaller in Tg mice than in nTg mice (p < 0.01). These results indicate that superoxide radicals play a deleterious role following TBI. Furthermore, Tg mice provide a useful model for demonstrating the beneficial role of an antioxidant enzyme in TBI without the confounding effect of pharmacokinetics, toxicity, and BBB permeability associated with exogenous agents.

Microglial responses after focal radiation-induced injury are affected by alpha-difluoromethylornithine

PURPOSE

The objective of this study was to quantify microglial and astrocytic cell responses after focal 125I irradiation of normal brain and to determine the effects of an intravenous infusion of alpha-difluoromethylornithine (DFMO) on those responses.

METHODS AND MATERIALS

Adult beagle dogs were irradiated using high activity 125I sources. Saline or DFMO (75 mg/kg/day) was infused for 18 days, and 1 to 10 weeks later brain tissues were collected. Immunohistochemical stains were used to label phagocytes and amoeboid microglia (lectin RCA-1), astrocytes (GFAP), and cells synthesizing deoxyribonucleic acid (DNA) (BrdU). Cell densities (cells/mm2) and BrdU labeling indices were quantified.

RESULTS

In dogs infused with saline, increases in phagocytes and amoeboid microglia were observed at 1-2 weeks and 4 weeks, respectively. The labeling indices for phagocytes and amoeboid microglia peaked at 4 weeks with maximum values of 4.8 and 13.4%, respectively. Astrocyte cell numbers increased from 2-6 weeks following irradiation; increased labeling indices were observed after 2 weeks. An infusion of DFMO significantly suppressed BrdU labeling and delayed the increase in cell numbers for phagocytes and amoeboid microglia. In both treatment groups, the proportion of total BrdU labeling accounted for by phagocytes was maximum 1 week after irradiation and then decreased. The proportion of total BrdU labeling accounted for by amoeboid microglia and astrocytes was zero for 2 weeks and then increased.

CONCLUSIONS

Microglial reactions after focal irradiation involve the phagocytic and amoeboid cell forms and are characterized by increased BrdU uptake and increased cell number. DFMO significantly alters these responses. Changes in astrocyte cell number and BrdU labeling may be related to changes in microglia. Studies of cell responses and their modification may lead to a better understanding of the pathogenesis of radiation injury, and to new strategies to optimize the use of therapeutic irradiation.

Apoptosis is induced in the subependyma of young adult rats by ionizing irradiation

To determine if radiation-induced apoptosis occurred in young adult brain, we exposed 2-3-month old rats to single x-ray doses of 5 or 30 Gy. Apoptosis was quantified using the TdT-mediated dUTP-biotin nick end labeling (TUNEL) method and a morphologic assessment of nuclear fragmentation. Apoptosis occurred primarily in the subependyma but also in the corpus callosum, peaking 6 h after irradiation. At 48 h there were no apoptotic nuclei observed. These data are the first to show that apoptosis occurs in the young adult rat brain after ionizing irradiation. Further studies are required to define the particular cell type(s) involved and to address the role of this process in the pathogenesis of late radiation injury.

Cellular proliferation and infiltration following interstitial irradiation of normal dog brain is altered by an inhibitor of polyamine synthesis

PURPOSE

The objectives of this study were to quantitatively define proliferative and infiltrative cell responses after focal 125I irradiation of normal brain, and to determine the effects of an intravenous infusion of alpha-difluoromethylornithine (DFMO) on those responses.

METHODS AND MATERIALS

Adult beagle dogs were irradiated using high activity 125I sources. Saline (control) or DFMO (150 mg/kg/day) was infused for 18 days starting 2 days before irradiation. At varying times up to 8 weeks after irradiation, brain tissues were collected and the cell responses in and around the focal lesion were quantified. Immunohistochemical stains were used to label astrocytes (GFAP), vascular endothelial cells (Factor VIII), polymorphonuclear leukocytes (PMNs; MAC 387) and cells synthesizing deoxyribonucleic acid (DNA) (BrdU). Cellular responses were quantified using a histomorphometric analysis.

RESULTS

After radiation alone, cellular events included a substantial acute inflammatory response followed by increased BrdU labeling and progressive increases in numbers of capillaries and astrocytes. alpha-Difluoromethylornithine treatment significantly affected the measured cell responses. As in controls, an early inflammatory response was measured, but after 2 weeks there were more PMNs/unit area than in controls. The onset of measurable BrdU labeling was delayed in DFMO-treated animals, and the magnitude of labeling was significantly reduced. Increases in astrocyte and vessel numbers/mm2 were observed after a 2-week delay. At the site of implant, astrocytes from DFMO-treated dogs were significantly smaller than those from controls.

CONCLUSIONS

There is substantial cell proliferation and infiltration in response to interstitial irradiation of normal brain, and these responses are significantly altered by DFMO treatment. Although the precise mechanisms by which DFMO exerts its effects in this model are not known, the results from this study suggest that modification of radiation injury may be possible by manipulating the response of normal cells to injury.

Amelioration of hypoxic and hypoglycemic damage to cerebral endothelial cells. Effects of heat shock pretreatment

Induction of the 70 kDa heat shock protein (HSP70) by hypoxia and/or hypoglycemia and the effects of prior heat shock on injury owing to hypoxia and/or hypoglycemia were studied in rat cerebral endothelial cells. Hypoxia and/or hypoglycemia treatment resulted in increased expression of HSP70 only when such treatment was sufficient to cause detectable injury and when the initial treatment was followed by exposure of the cells to 24 h of normoxia and normoglycemia. Heat shock induced 24 h prior to treatment with 48 h of hypoxia slightly reduced endothelial cell damage as measured by fraction of lactate dehydrogenase release (10% decrease in injury). There was a more dramatic effect of prior heat shock on the moderate damage produced by 12 h of combined hypoxia and hypoglycemia (45% decrease), whereas the severe damage produced by 24 h of hypoxia and hypoglycemia was decreased by prior heat shock by only 16%. These results indicate that the hypoxia and hypoglycemia occurring in conjunction with ischemia are more likely to result in heat shock protein expression when there is injury to the tissue. Furthermore, heat shock protects cerebral endothelial cells from hypoxia and hypoglycemia either by slowing the initial development of injury or by delaying the onset of injury.

Response of cerebral endothelial cells to hypoxia: modification by fructose-1,6-bisphosphate but not glutamate receptor antagonists

Damage to the cerebral endothelium from ischemia could exacerbate brain injury by altering vascular integrity, but little is known concerning the response of cerebral endothelial cells to hypoxia. To address this issue, cerebral capillary endothelial cells were isolated from 14-day-old rats, grown to confluence, and placed in hypoxic chambers for up to 62 h. Cells were undamaged by 24 hours of hypoxia as assessed by lactate dehydrogenase release and ethidium bromide staining, but 48 h resulted in marked damage. Hypoxia was probably exacerbated by hypoglycemia because glucose levels fell to < 1 mM by 24 h, at which point ATP levels began to fall in hypoxic cultures (3.25 +/- 1.48 nmol/mg protein; mean +/- S.D.) relative to normoxic cultures (9.52 +/- 1.41 nmol/mg protein). Cells treated with 4 mM fructose-1,6-bisphosphate (FBP) had significantly less damage at 48 h of hypoxia than controls. FBP had little effect on rate of glucose depletion from the media, but ATP depletion due to hypoxia was significantly less. Thus, the protective effect of FBP may be mediated by the ability of treated cells to maintain higher ATP levels. Unlike FBP, glutamate receptor antagonists including MK-801, NBQX, DNQX, and kynurenic acid were ineffective in ameliorating hypoxia-induced endothelial cell injury.

Radiation brain injury is reduced by the polyamine inhibitor alpha-difluoromethylornithine

Alpha-difluoromethylornithine (DFMO) was used to reduce 125I-induced brain injury in normal beagle dogs. Different DFMO doses and administration schedules were used to determine if the reduction in brain injury was dependent on dose and/or dependent upon when the drug was administered relative to the radiation treatment. Doses of DFMO of 75 mg/kg/day and 37.5 mg/kg/day given 2 days before, during and for 14 days after irradiation reduced levels of putrescine (PU) in the cerebrospinal fluid relative to controls. Volume of edema was significantly reduced by 75 mg/kg/day of DFMO before, during and after irradiation and by the same dose when the drug was started immediately after irradiation. A reduction in edema volume after 37.5 mg/kg/day before, during and after irradiation was very near significance. Ultrafast CT studies performed on dogs that received a DFMO dose of 75 mg/kg/day before, during and after irradiation suggested that the reduced edema volume was associated with reduced vascular permeability. Volume of necrosis and volume of contrast enhancement (breakdown of the blood-brain barrier) were significantly lower than controls only after a DFMO dose of 75 mg/kg/day before, during and after irradiation. These latter data, coupled with the findings relative to edema, suggest that different mechanisms may be involved with respect to the effects of DFMO on brain injury, or that the extents of edema, necrosis and breakdown of the blood-brain barrier may depend upon different levels of polyamine depletion. The precise mechanisms by which DFMO exerts the effects observed here need to be determined.

Comparison of xenon-enhanced CT with ultrafast CT for measurement of regional cerebral blood flow

PURPOSE

To compare an ultrafast CT method for estimating regional cerebral blood flow with a more commonly used xenon-enhanced CT method.

METHODS

Xenon CT and ultrafast CT were used to estimate regional cerebral blood flow (rCBF) in 12 healthy beagle dogs. Measurements were obtained for left and right hemisphere, cortical gray matter, basal ganglia, and deep white matter. The ability of each method to show differences in blood flow between regions of high flow (gray matter) and low flow (white matter) was evaluated, both for large (> 0.75 cm3) and small (< 0.5 cm3) regions of interest. In addition, side-to-side differences in rCBF were evaluated to determine the minimum difference that would suggest a significant alteration in blood flow.

RESULTS

There was less interanimal variance in absolute rCBF measurements obtained using xenon CT; ultrafast CT appeared to accentuate rCBF differences between high flow and low flow regions. There were strong side-to-side correlations in rCBF when measured by ultrafast CT, which suggests that this technique may be particularly useful in detecting focal alterations in rCBF restricted to one hemisphere of the brain.

CONCLUSIONS

Ultrafast CT measures of rCBF compare favorably with those obtained using xenon CT.

Cerebrovascular response after interstitial irradiation

To characterize the role of the cerebrovascular response in the development of brain injury after focal irradiation, 125I sources were implanted in frontal white matter of the brain of normal dogs; dose was 20 Gy, 7.5 mm from the source. Cerebral blood flow, vascular volume and mean transit time of blood were quantified in irradiated tissues relative to tissues in the contralateral hemisphere and analyzed with respect to previously determined volumetric measurements of damage and the blood-to-brain transfer constant. Blood flow and vascular volume within the radiation-induced focal lesion were maximally reduced 3 weeks after implant, when necrosis volume was maximal. By 6 weeks, vascular volume and mean transit time were increased, suggesting a strong neovascular response. In tissues surrounding the lesion, blood flow and vascular volume were reduced 1-4 weeks after irradiation and approached normal at 6 weeks; average mean transit time was not altered significantly. Alterations in blood flow and mean transit time were significantly related to edema volume and transfer constant, but alterations in vascular volume were not, suggesting that edema-induced vascular compression was not responsible for changes in blood flow. Reductions of radiation-induced permeability of the blood-brain barrier and/or edema might limit radiation-induced changes in blood flow and the extent of tissue injury.

Modification of radiation-induced brain injury by alpha-difluoromethylornithine

The effect of alpha-difluoromethylornithine (DFMO) on 125I-induced brain injury was investigated in a dog model. Cerebrospinal putrescine levels were reduced from baseline levels 1-2 weeks after irradiation in animals treated with 125I and DFMO, while putrescine levels were elevated in 125I and saline-treated animals. In addition, the time course of changes in the volumes of edema, necrosis, and tissue showing evidence of blood-brain barrier breakdown was altered significantly by DFMO treatment. The most significant alterations occurred 2-4 weeks after irradiation, at which times the average volumes of damage in DFMO-treated animals were reduced compared to saline-treated animals. The time course of alterations in blood-to-brain transfer, brain-to-blood transfer, and vascularity following irradiation was also altered by DFMO treatment. Analysis of variance demonstrated a strong relationship of blood-to-brain transfer and vascularity to volume of edema, suggesting that the effect of DFMO on edema may be partially mediated by its effects on blood-brain barrier breakdown.

Normal brain response after interstitial microwave hyperthermia

The effects of interstitial hyperthermia were assessed in the normal brain after a single 30 min treatment using 2450 MHz microwaves. A single helical coil microwave antenna was inserted into the frontal white matter and reference temperatures of 40, 41, 42, 43 and 44 degrees C maintained for 30 min along a temperature sensing probe 5 mm away and parallel to the antenna. The extent of hyperthermia damage was quantified weekly for 6 weeks using computed tomography (CT), and changes in regional cerebral blood flow (rCBF), tissue vascularity and mean transit time were determined using ultrafast CT. Qualitative histopathological analysis was carried out on tissues at various times after heating. Heat lesions were radiographically characterized by rapid development and resolution and consisted of an area of focal low density surrounded by a ring of contrast enhancement. Histologically, the focus of low density corresponded to regions of tissue necrosis, whereas the ring enhancement showed local reactive changes, including endothelial cell proliferation and infiltration with macrophages. Tissue necrosis occurred at temperatures greater than 43.9 +/- 1.5 degrees C (mean +/- standard deviation), and volumes of necrosis and ring enhancement were at a maximum 1 week following treatment. Relative to the contralateral, unheated hemisphere, rCBF in the heated brain appeared to be reduced for the first 3 weeks after treatment but approached normal by week 4. The mean transit time of blood was increased for weeks 1-3 compared to the untreated hemisphere, and tissue vascularity reached a maximum, 3 weeks after treatment. The rapid CT changes together with ultrafast CT and histopathological findings suggest that focal heat lesions in the brain stimulate a significant and rapid vascular response.

Measurement of regional cerebral blood flow in the dog using ultrafast computed tomography. Experimental validation

The applicability, feasibility, reproducibility, and accuracy of the method of measuring regional cerebral blood flow using ultrafast computed tomography were evaluated in 25 dogs under varying physiological and pathophysiological conditions. Regional cerebral blood flow values were 75.6 +/- 29.4 ml/100 g/min (mean +/- standard deviation) for the hemisphere, 68.4 +/- 28.2 ml/100 g/min for the basal ganglia, 41.2 +/- 15.0 ml/100 g/min for the internal capsule, and 80.8 +/- 37.2 ml/100 g/min for the neocortex. Measurements made 10 minutes apart were significantly (p less than 0.05) correlated. Simultaneous measurements of regional cerebral blood flow by the microsphere and ultrafast computed tomography methods showed a significant (p less than 0.05) correlation for the hemisphere (r = 0.95), basal ganglia (r = 0.95), and neocortex (r = 0.94) but not for the internal capsule (r = 0.51). Microsphere and ultrafast computed tomography regional cerebral blood flow values were also in agreement in radiation-damaged brain with appreciable blood-brain barrier breakdown, and the two methods demonstrated similar responsiveness of regional cerebral blood flow to alterations in arterial carbon dioxide tension. The accuracy and sensitivity of the ultrafast computed tomography technique suggests that it affords a useful new tool for studying normal and abnormal regional cerebral blood flow.

Measurement of regional cerebral blood flow using ultrafast computed tomography. Theoretical aspects

Theoretical and practical limitations have prevented the measurement of regional cerebral blood flow using dynamic x-ray computed tomography. Development of the ultrafast computed tomography scanner has made it possible to overcome the practical limitations and measure changes in contrast concentration in the brain with excellent time and spatial resolution. By applying modifications of indicator dilution theory, we have derived a method to use these changes in contrast concentration determined using ultrafast computed tomography to measure the fractional vascular volume, mean transit time of blood, and blood flow within specific regions of the brain in a relatively simple and practical manner. This method could theoretically be used in the evaluation of physiological and pathophysiological alterations in cerebral blood flow.