Oxidative stress mechanisms and potential therapeutics in Alzheimer disease

Oxidative damage of biological macromolecules is a hallmark of most neurodegenerative disorders such as Alzheimer, Parkinson and diffuse Lewy body diseases. Another important phenomenon involved in these disorders is the alteration of iron and copper homeostasis. Data from the literature support the involvement of metal homeostasis in mitochondrial dysfunction, protein alterations and nucleic acid damage which are relevant in brain function and consequently, in the development of neurodegenerative disorders. Although alterations in transition metal homeostasis, redox activity, and localization are well documented, it must be determined how alterations of specific copper- and iron-containing metalloenzymes are also involved in Alzheimer disease. The clarification of these phenomena can open a new window for understanding the mechanisms underlying neurodegeneration and, consequently, for the development of new therapeutic strategies such as gene therapy and new pharmaceutical formulations with antioxidant and chelating properties.

Phylogeography of Bufo fowleri at its northern range limit

Many of the species that recolonized previously glaciated areas in the Great Lakes basin of North America over the past 10-12,000 years exhibit genetic evidence of multiple invasion routes and present-day secondary contact between deeply divergent lineages. With this in mind, we investigated the phylogeographical structure of genetic variability in Fowler's toads (Bufo fowleri) at the northern edge of its distribution where its range encircles the Lake Erie basin. Because B. fowleri is so closely tied to habitats along the Lake Erie shoreline, we would expect to find clear evidence of the number of invasions leading to the species' colonization of the northern shore. A 540 bp sequence from the mitochondrial control region was amplified and analysed for 158 individuals from 21 populations. Interpopulation sequence variation ranged from 0% to 6%. Phylogenetic analysis of p-distance using the neighbor-joining method revealed two deeply divergent (6% sequence divergence) mtDNA lineages (Phylogroup 1 and 2), possibly arising as a result of secondary contact of populations that entered the region from two separate glacial refugia. However, the phylogeographical pattern was not simple. The populations at Long Point, on the north shore of Lake Erie, clustered with the population from Indiana Dunes on Lake Michigan to form Phylogroup 2 whereas all other B. fowleri populations examined from both sides of Lake Erie constituted Phylogroup 1. Furthermore, mtDNA sequences from the related species Bufo americanus, obtained from populations outside the range of B. fowleri, clustered with mtDNA haplotypes of B. fowleri Phylogroup 1, indicating the possibility of partial introgression of mitochondria from one species to the other.

TNF-α expression patterns as potential molecular biomarker for human skin cells exposed to vesicant chemical warfare agents: sulfur mustard (HD) and Lewisite (L)

Studies were conducted to examine the effect of two vesicant chemical warfare agents (VCWA), one of them an arsenical, on cytokine gene expression in normal human epidermal keratinocyte (NHEK) cells. We tested 2,2'-dichlorethylsulfide (sulfur mustard, military designation HD) and 2,chlorovinyldichloroarsine (Lewisite, military designation L), which have significant differences in their chemical, physical, and toxicological properties. Human tumor necrosis factor-alpha (hTNF-alpha) cytokine was detected by using the enzyme-linked immunosorbent assay, a protein multiplex immunoassay, Luminex100, and reverse transcription-polymerase chain reaction (RT-PCR). The messenger RNA expression of hTNF-alpha was determined to provide a semi-quantitative analysis. HD-stimulated NHEK induced secretion of hTNF-alpha in a dose-dependent manner. Dose response effect of Lewisite decreased hTNF-alpha levels. Time-response data indicated that the maximum response for HD occurred at 24 h with an associated cytotoxic concentration of 10(-4) mol/L. NHEK cells stimulated with 10(-4) mol/L HD for 24 h at 37 degrees C increased detectable levels of hTNF-alpha from 5 to 28 ng/ml at an index of cell viability between 85 to 93% as detected by Luminex100. Our results indicated that the increased levels of hTNF-alpha by HD are dependent on the primary cultures, cell densities, and chemical properties of the stimulation. Lewisite under the same conditions as HD caused a reduction of hTNF-alpha from control levels of 1.5 ng/ml to 0.3 ng/ml after stimulation (10(-4) mol/L), with an index of cell viability of reverse similar 34%. We analyzed the transcriptional of hTNF-alpha gene and found that HD (10(-6) to 10(-4) mol/L) activates hTNF-alpha gene in cultured NHEK and that L at 10(-6) to 10(-4) mol/L markedly reduces hTNF-alpha gene. We conclude that the pro-inflammatory mediator, hTNF-alpha, could be a potential biomarker for differentiating between exposure of HD or L.

Hypoxia tolerance in mammalian heterotherms

Heterothermic mammals tolerate severe hypoxia, as well as a variety of central nervous system insults, better than homeothermic mammals. Tolerance to hypoxia may stem from adaptations associated with the ability to survive hibernation and periodic arousal thermogenesis. Here, we review evidence and mechanisms of hypoxia tolerance during hibernation, euthermy and arousal in heterothermic mammals and consider potential mechanisms for regenerative-like processes, such as synaptogenesis, observed within hours of hypoxic stress associated with arousal thermogenesis.

Mitotic and Gender Parallels in Alzheimer Disease: Therapeutic Opportunities

In this review, we discuss the role of cell cycle dysfunction in the pathogenesis of Alzheimer disease and propose that such mitotic catastrophe, as one of the earliest events in neuronal degeneration, may, in fact, be sufficient to initiate the neurodegenerative cascade. The question as to what molecule initiates cell cycle dysfunction is now beginning to become understood and, in this regard, the gender-predication, age-related penetrance and regional susceptibility of specific neuronal populations led us to consider luteinizing hormone as a key mediator of the abnormal mitotic process. As such, agents targeted toward luteinizing hormone or downstream sequelae may be of great therapeutic value in the treatment of Alzheimer disease.

The impact of PET scanning on management of paediatric oncology patients

PURPOSE

Limited information is available on the use of positron emission tomography (PET) in paediatric oncology. The aim of this study was to review the impact of PET on the management of paediatric patients scanned over a 10-year period.

METHODS

One hundred and sixty-five consecutive oncology patients aged 11 months to 17 years were included. Two hundred and thirty-seven scans were performed. Diagnoses included lymphoma (60 patients), central nervous system (CNS) tumour (59), sarcoma (19), plexiform neurofibroma with suspected malignant change (13) and other tumours (14). A questionnaire was sent to the referring clinician to determine whether the PET scan had altered management and whether overall the PET scan was thought to be helpful.

RESULTS

One hundred and eighty-nine (80%) questionnaires for 126 patients were returned (63 relating to lymphoma, 62 to CNS tumours, 30 to sarcoma, 16 to plexiform neurofibroma and 18 to other tumours). PET changed disease management in 46 (24%) cases and was helpful in 141 (75%) cases. PET findings were verified by histology, clinical follow-up or other investigations in 141 cases (75%). The returned questionnaires indicated that PET had led to a management change in 20 (32%) lymphoma cases, nine (15%) CNS tumours, four (13%) sarcomas, nine (56%) plexiform neurofibromas and four (22%) cases of other tumours. PET was thought to be helpful in 47 (75%) lymphoma cases, 48 (77%) CNS tumours, 24 (80%) sarcomas, 11 (69%) neurofibromas and 11 (61%) cases of other tumours. PET findings were verified in 44 (70%) lymphoma cases, 53 (85%) CNS tumours, 21 (70%) sarcomas, 12 (75%) neurofibromas and 11 (61%) other tumour cases.

CONCLUSION

PET imaging of children with cancer is accurate and practical. PET alters management and is deemed helpful (with or without management change) in a significant number of patients, and the results are comparable with the figures published for the adult oncology population.

Pathobiology of familial hypercholesterolemic atherosclerosis

Many factors play a role in the development of atherosclerotic lesions. One of the leading risk factors for development of atherosclerosis is familial hypercholesterolemia (FH). FH is a genetic disease characterized by a deficiency, and/or mutation, of receptors for low density lipoprotein (LDL) on the plasmalemma of endothelial cells (EC), a high level of low density lipoprotein in the plasma, and early, spontaneous development of atherosclerosis and skin xanthoma. In this review we describe Watanabe heritable hyperlipidemic (WHHL) rabbits, which represent such an animal model for human FH. This strain of the rabbits is characterized by a genetic deficiency or mutation of functional LDL receptors and develops severe atherosclerosis, which is pathologically similar to familial homozygous hyperlipidemic patients. The most completely characterized animal model is the Watanabe rabbit, a model of homozygous and heterozygous type IIa hypercholesterolemia related to an LDL receptor deficiency. Additional manipulation such as aortic injury in this rabbit model induces the development of atherosclerotic lesions that are structurally similar to those found in humans. Thus, this model of hypercholesterolemia fulfils the above criteria set, i.e. it is able to provide new insights for a better understanding of the pathogenesis of atherosclerosis and for testing new treatment strategies.

An investigation of the MEK/ERK inhibitor U0126 in acute myeloid leukemia

Blockade of mitogen-activated protein kinase kinase (MEK1/2), part of the extracellular signal-regulated kinase (ERK) or p44/42 mitogen-activated protein kinase (MAPK) pathway, has been shown in some instances to cause apoptosis in leukemic blast cells. This investigation examined the effect of the potent MEK/ERK inhibitor U0126 on apoptosis in acute myeloblastic leukemia (AML) cell lines, and acute leukemic and non-leukemic patient samples. The pro-apoptotic effect of the inhibitor varied across the five cell lines tested (KG1a, HEL, TF-1, MO7e, and THP-1) from highly significant induction of apoptosis to no apparent response. The pro-apoptotic effect of U0126 in the most sensitive cell line, KG1a, appeared to be related to its CD34 positivity. Three of five leukemic bone marrow samples showed considerable sensitivity to the inhibitor and a similar association with CD34 expression was evident. Interestingly, control marrow cells from six non-leukemic patients did not show a significant effect when exposed to U0126. These results suggest that this agent may offer a potential alternative to standard chemotherapy with a particular role in the most primitive types of leukemia, these often being the most resistant to standard chemotherapy.

Agonist and antagonist effects of benzodiazepines on motor performance: influence of intrinsic efficacy and task difficulty

Previous studies have shown that low-efficacy benzodiazepines may function as full agonists, partial agonists or antagonists, depending upon the sensitivity of the assay to detect a drug's agonist effects. To date, these differential effects have only been observed across tasks, as these drugs rarely produce full agonist and antagonist effects in a single preparation. The purpose of the present study was to examine the agonist and antagonist effects of various benzodiazepines in a motor task in which the sensitivity of the task differed across conditions. To this end, rats were trained to walk on a rotorod apparatus rotating at low (4 rpm), medium (20 rpm) and high (36 rpm) speeds, and the motor-impairing effects of representative low (bretazenil), intermediate (clonazepam) and high (diazepam) efficacy benzodiazepines were examined. Diazepam and clonazepam reduced the latency for rats to fall from the rotorod at all three speeds, with both drugs being more potent at the high speed than at lower speeds. Bretazenil was also effective at decreasing motor performance at the high speed, but was not effective at lower speeds. In drug combination tests, bretazenil antagonized the effects of diazepam and clonazepam under conditions in which it was not effective when administered alone, effectively demonstrating both full agonist and antagonist effects in the same preparation. These data indicate that the sensitivity of a motor task to detect a drug's agonist effects can be manipulated by altering its relative level of difficulty, and that lower-efficacy benzodiazepines are more sensitive than higher-efficacy benzodiazepines to these manipulations.

A population-based study of acute stroke and TIA diagnosis

BACKGROUND

Acute stroke therapy is heavily dependent on the diagnostic acumen of the physician in the emergency department (ED).

OBJECTIVE

To determine this diagnostic accuracy in a population-based multiethnic stroke study.

METHODS

The Brain Attack Surveillance in Corpus Christi (BASIC) Project prospectively ascertained all acute stroke or TIA cases in an urban Texas county of 313,645 residents without an academic medical center. Cases were validated by board-certified neurologists using source documentation. Case validation was used as the gold standard to compare the diagnosis given by the ED physician.

RESULTS

From January 2000 to August 2002, a total of 13,015 patients were screened. Of these, 1,800 were validated as stroke/TIA. Overall sensitivity of the emergency physician for the BASIC-validated diagnosis was 92%, and positive predictive value was 89%. Of the cases that the emergency physician thought were stroke, 11% were validated as no stroke. In multivariable modeling, motor symptoms was an independent predictor of protection from false-negative ED diagnosis of stroke/TIA (odds ratio [OR] = 0.61; 95% CI 0.41 to 0.89). Protection from false-positive stroke/TIA diagnosis was predicted by sensory symptoms (OR = 0.43; 95% CI 0.28 to 0.66), motor symptoms (OR = 0.44; 95% CI 0.32 to 0.62), and severe neurologic deficit (OR = 0.33; 95% CI 0.14 to 0.78). History of stroke/TIA predicted false-positive stroke diagnosis (OR = 1.72; 95% CI 1.23 to 2.40). The majority of disagreements occurred in patients with generalized neurologic or acute medical, nonneurologic syndromes.

CONCLUSIONS

Physicians practicing in the ED are sensitive for stroke/TIA diagnosis. The modest positive predictive value argues for a systems approach with neurology support so that proper decisions regarding acute stroke therapy can be made.

The p53 homologue p73 accumulates in the nucleus and localizes to neurites and neurofibrillary tangles in Alzheimer disease brain

The molecular mechanisms that regulate neuronal survival vs. death during Alzheimer disease (AD) remain unclear. Nonetheless, a number of recent studies indicate that increased expression or altered subcellular distribution of numerous cell cycle proteins during AD may contribute to disease pathogenesis. Because homologues of p53, a key regulatory protein in the cell cycle, such as p73, have been identified and shown to participate in cellular differentiation and death pathways, we examined the expression and distribution of p73 in the hippocampus of eight control and 16 AD subjects. In control subjects, hippocampal pyramidal neurones exhibit p73 immunoreactivity that is distributed predominately in the cytoplasm. In AD hippocampus, increased levels of p73 are located in the nucleus of pyramidal neurones and p73 is located in dystrophic neurites and cytoskeletal pathology. Immunoblot analysis confirmed the presence of p73 in the hippocampus. These data indicate that p73 is expressed within hippocampal pyramidal neurones and exhibits altered subcellular distribution in AD.

Characterization of the G91del CRYBA1/3-crystallin protein: a cause of human inherited cataract

Congenital cataract is a leading cause of visual disability in children. Inherited isolated (non-syndromic) cataract represents a significant proportion of cases and the identification of genes responsible for inherited cataract will lead to a better understanding of the mechanism of cataract formation at the molecular level both in congenital and age-related cataract. Crystallins are abundantly expressed in the developing human lens and represent excellent candidate genes for inherited cataract. A genome-wide search of a five-generation family with autosomal dominant lamellar cataract demonstrated linkage to the 17p12-q11 region. Screening of the CRYBA1/3 gene showed a 3 bp deletion, which resulted in a G91del mutation within the tyrosine corner, that co-segregated with disease and was not found in 96 normal controls. In order to understand the molecular basis of cataract formation, the mutant protein was expressed in vitro and its unfolding and refolding characteristics assessed using far-UV circular dichroism spectroscopy. Defective folding and a reduction in solubility were found. As the wild-type protein did not refold into the native conformation following unfolding, a corresponding CRYBB2 mutant was genetically engineered and its refolding characteristics analysed and compared with wild-type CRYBB2. Its biophysical properties support the hypothesis that removal of the glycine residue from the tyrosine corner impairs the folding and solubility of beta-crystallin proteins. This study represents the first comprehensive description of the biophysical consequences of a mutant beta-crystallin protein that is associated with human inherited cataract.

Enhanced sensitivity to the antinociceptive effects of kappa opioids in naltrexone-treated rats: dose- and time-dependent effects

The purpose of the present study was to examine sensitivity to the antinociceptive effects of kappa opioids during chronic treatment with the nonselective opioid antagonist naltrexone. In a warm-water tail-withdrawal procedure, rats were restrained and the latencies to remove their tails from water maintained at 50 and 55 degrees C were recorded. Prior to chronic treatment, spiradoline, U50,488 and (-)-pentazocine produced dose-dependent increases in tail-withdrawal latencies at both 50 and 55 degrees C. Chronic treatment with 3.0 mg/kg naltrexone twice daily (b.i.d.) failed to alter sensitivity to the antinociceptive effects of spiradoline when tested 24 h following naltrexone administration. When the maintenance dose of naltrexone was increased to 30 mg/kg b.i.d., sensitivity to the effects of spiradoline was reduced when tested 24 h after naltrexone administration, but enhanced when tested 48 h after naltrexone administration. Enhanced sensitivity was also observed to the antinociceptive effects of U50,488 and (-)-pentazocine when tested 48 h after chronic treatment with 30 mg/kg naltrexone. After termination of chronic treatment, sensitivity to the antinociceptive effects of spiradoline, U50,488 and (-)-pentazocine returned to that originally observed prior to naltrexone treatment. These data indicate that chronic naltrexone treatment enhances sensitivity to the antinociceptive effects of kappa opioids, and that this effect is both dose and time dependent.

Cerebral perfusion in infants and neonates: preliminary results obtained using dynamic susceptibility contrast enhanced magnetic resonance imaging

BACKGROUND

Previous studies have used the dynamic susceptibility contrast enhanced (DSCE) magnetic resonance (MR) imaging technique to measure cerebral perfusion in adults.

OBJECTIVE

To assess the feasibility of the technique in a heterogeneous cohort of sick human infants and identify cerebral perfusion abnormalities.

METHODS

Perfusion measurements were made by characterising the changing concentration of an injected bolus of contrast agent using a series of MR images acquired during the first pass of the contrast bolus. Qualitative values of relative cerebral blood flow (rCBF) were then calculated from these data on a pixel by pixel basis to generate parametric maps of perfusion.

RESULTS

Images of perfusion were successfully calculated from 12 out of 27 neonates and infants, all with established cerebral pathology. Normal vascular anatomical structures such as the circle of Willis were identified within all calculated images. Values of rCBF were generally larger in grey matter than in white matter. In several patients, perfusion abnormalities resulted in structural abnormalities which were detected in conventional MR imaging at follow up. The acquisition of perfusion data was most difficult when the least mature brains were examined because of motion artefacts and a smaller head size with a lower level of rCBF than adults.

CONCLUSIONS

This preliminary study shows that: (a) maps of rCBF can be acquired from neonates and infants; (b) characterisation of the bolus passage becomes progressively easier as the brain matures; (c) early abnormalities in cerebral perfusion may have negative prognostic implications; (d) the main difficulty when using the DSCE technique to study neonates relates to image artefacts resulting from bulk head motion.

Can FDG PET be used to successfully direct preoperative biopsy of soft tissue tumours?

Magnetic resonance imaging (MRI) has been the most useful tool in the anatomical definition of soft tissue sarcoma, although there remains the problem of defining the lesions as benign or malignant. The management of such lesions requires biopsy prior to surgical resection. If the most malignant area could be defined more accurately, then this area could be targeted for biopsy. Fluorodeoxyglucose positron emission tomography (FDG PET) has been found to be useful in identifying malignancy and variations in grade in soft tissue masses. The aim of this study was to assess the use of FDG PET scanning with or without co-registered MRI to indicate the most appropriate biopsy site. Twenty consecutive patients presented with soft tissue masses with clinical signs of malignancy. All patients underwent MRI and FDG PET scanning and the two images were co-registered. A biopsy site that was the most likely to be malignant was defined on the PET scan. All patients underwent an initial biopsy and then complete surgical resection of the mass. The histological results from the mass were compared with those from the biopsy specimen obtained from the site suggested by the PET scan. In malignant masses the biopsy site suggested by the FDG PET scan was found to be representative of the most malignant site on the whole mass histology. Benign lesions had low or no FDG uptake. In no case did the co-registered image add significantly to the appropriate biopsy site. FDG PET can be used to appropriately direct biopsy in soft tissue sarcoma and potentially may lead to computed tomography/MRI directed outpatient biopsy prior to definitive treatment.

X-ray contrast media induce aortic endothelial damage, which can be prevented with prior heparin treatment

X-ray contrast media induce damage to the endothelial layer of vessels and initiate the formation of thrombosis, which is a complication for clinical diagnostic procedures. The future determination of the mechanisms, which underlie the damaging effect of X-ray contrast medium on vascular wall cells, especially vascular endothelium and possible prevention of this damage by vasoprotector, will result in a larger application in diagnostic procedures. The aim of the present study is to analyze the effect of X-ray contrast media (Verographin, Iodamid and Iodolipol) on the arterial endothelium morphology by using ultrastructural techniques (scanning and transmission electron microscopy, SEM and TEM respectively). Experiments have been carried out on New Zealand white rabbits (6 month old) and Wistar rats (6-8 month old) after a single injection of X-ray contrast media with and without prior heparin treatment. Control groups of animals were exposed to the same procedure but without X-ray contrast media injection and only received isotonic saline solution. The following time points were selected: 1, 6, 24, 72 h and 7 days. At the end of the experiments, animals were anesthetized by pentobarbital and then perfused with a balanced buffer for 1 min and followed by perfusion fixation with Karnovsky's fixative containing buffered solution of 2.5% paraformaldehyde and 2.5% glutaraldehyde (pH 7.36) at least 30 min. The aortic tissue was removed and immediately placed into a fresh portion of the same fixative. Aortic samples were then prepared for scanning and transmission electron microscopy (SEM and TEM respectively). Immediately after the injection of X-ray contrast media, the number of microvilli and blebs on the luminal surface of the endothelial cells (EC) significantly increased. Very often, nuclear portions of the EC sharply protruded into the vessel lumen. Clusters of spindle-shaped EC were seen throughout the endothelial monolayer. These changes persist through the 72-h period after X-ray contrast media injection. Moreover, the desquamation and denudation of the EC from the monolayer is often observed and this is accompanied by the presence of a microthrombus on the vessel surface. Seven days after the post-injection period, endothelial monolayers still show severe damage, which often coexists with the presence of a different sized microthrombus on the vessel surface. However, the degree of lesion formation in most areas is substantially decreased as compared to the early period of post-injection (24 and 72 h). Heparin treated group shows intact morphology similar to the control experimental groups (saline injected group). Infrequently, minimal morphological changes of the endothelium, such as increased number of microblebs and microvilli, were seen with heparin treatment. We conclude that the negative side effects of the X-ray contrast media can be eliminated by a single injection of heparin or other vasoprotector prior to the diagnostic procedure.

Oxidative stress and predominant Abeta42(43) deposition in myopathies with rimmed vacuoles

This study was undertaken to determine the C terminus of amyloid beta protein (Abeta), accumulated in vacuolated muscle fibers, and compare these findings to the level of oxidative stress. Eight patients with myopathies characterized by rimmed vacuoles (RVs) were analyzed. Monoclonal antibodies specific to Abeta40 or Abeta42(43) revealed that the Abeta42(43) immunoreactivity was solely distributed in the vacuolated muscle fibers, and that only a part was also immunopositive for anti-Abeta40. Quantitative analyses in four specimens, in which eight or more vacuolated muscle fibers were observed, revealed that the mean incidence of Abeta42(43)-positive muscle fibers was 79.5+/-6.2% in total vacuolated muscle fibers, whereas that of the Abeta40-positive fibers was 42.9+/-12.6%. The predominance of Abeta42(43) deposition was statistically significant ( P<0.05). Abeta deposition was then compared with the distribution of oxidative nucleic acid damage in muscle fibers using a monoclonal antibody against 8-hydroxy-2'-deoxyguanosine and 8-hydroxyguanosine (8OHdG&G). The cytoplasmic staining for anti-8OHdG&G was found not only in vacuolated muscle fibers, but also in other muscle fibers including morphologically normal ones. Positive staining was completely abolished by RNase pretreatment and, thus, was suggested to reflect an increase of cellular RNA oxidation. The distribution of 8OHdG&G was much broader than the Abeta deposition. These data suggest that Abeta42(43) is predominantly involved in the pathogenesis of muscle fiber degeneration with RVs, and that oxidative damage may precede Abeta deposition in muscle fibers and play a key role in the pathomechanism of myopathies with RVs.

Hydrogen-peroxide-induced toxicity of rat striatal neurones involves activation of a non-selective cation channel

Striatal neurones are particularly vulnerable to hypoxia/ischaemia-induced damage, and free radicals are thought to be prime mediators of this neuronal destruction. It has been shown that hydrogen peroxide (H2O2), through the production of free radicals, induces rat insulinoma cell death by activation of a non-selective cation channel, which leads to irreversible cell depolarization and unregulated Ca2+ entry into the cell. In the study presented here, we demonstrate that a subpopulation of striatal neurones (medium spiny neurones) is depolarized by H2O2 through the production of free radicals. Cell-attached recordings from rat cultured striatal neurones demonstrate that exposure to H2O2 opens a large-conductance channel that is characterized by extremely long open times (seconds). Inside-out recordings show that cytoplasmically applied beta-nicotinamide adenine dinucleotide activates a channel with little voltage dependence, a linear current-voltage relationship and a single-channel conductance of between 70 and 90 pS. This channel is permeable to Na+, K+ and Ca2+ ions. Fura-2 imaging from cultured striatal neurones reveals that H2O2 exposure induces a biphasic intracellular Ca2+ increase in a subpopulation of neurones, the second, later phase resulting in Ca2+ overload. This later component of the Ca2+ response is dependent on the presence of extracellular Ca2+ and is independent of synaptic activity or voltage-gated Ca2+ channel opening. Consequently, this channel may be an important contributor to free radical-induced selective striatal neurone destruction. These results are remarkably similar to those observed for insulinoma cells and suggest that this family of non-selective cation channels has a widespread distribution in mammalian tissues.

Reactive oxygen: its sources and significance in Alzheimer disease

Over the past decade, oxidative stress has been established as the earliest cytological feature of Alzheimer disease and an attractive therapeutic target. The major challenges now are establishing the source of the reactive oxygen and what oxidative stress tells us about the etiology of Alzheimer disease. These are complex issues since a variety of enzymatic and non-enzymatic processes are involved in reactive oxygen formation and damage to macromolecules. In this review, we consider disease mechanisms that show the greatest promise for future research.

Role of the antioxidant ascorbate in hibernation and warming from hibernation

Ground squirrels tolerate up to 90% reductions in cerebral blood flow during hibernation as well as rapid reperfusion upon periodic arousal from torpor without apparent neurological damage. Thus, hibernation is studied as a model of tolerance to cerebral ischemia and other types of brain injury. Metabolic suppression likely plays a primary adaptive role that allows hibernating species to tolerate dramatic fluctuations in blood flow. Several other aspects of hibernation physiology are also consistent with tolerance to ischemia and reperfusion suggesting that multiple neuroprotective adaptations may work in concert during hibernation. The purpose of the present work is to review evidence for enhanced antioxidant defense systems during hibernation, with a focus on ascorbate, and discuss potential roles of these antioxidants during hibernation. In concert with dramatic decreases in blood flow, nutrient and oxygen delivery, plasma concentrations of the antioxidant ascorbate [(Asc)p] increase 3-5-fold during hibernation. In contrast, during re-warming, [Asc]p declines at a relatively rapid rate that peaks at the time of maximal O(2) consumption. This peak in O(2) consumption also coincides with a brief rise in plasma urate concentration consistent with a surge in reactive oxygen species production. Overall, data suggest that elevated concentration of plasma ascorbate is poised for distribution to metabolically active tissues during the surge in oxidative metabolism that accompanies re-warming during hibernation. This pool of ascorbate, as well as increased expression of other antioxidant defense systems, may protect vulnerable tissues from oxidative stress during hibernation and re-warming from hibernation. Better understanding of the role of ascorbate in hibernation may guide use of ascorbate and other antioxidants in treatment of stroke, head trauma and neurodegenerative disease.

Evaluation of image quality in terahertz pulsed imaging using test objects

As with other imaging modalities, the performance of terahertz (THz) imaging systems is limited by factors of spatial resolution, contrast and noise. The purpose of this paper is to introduce test objects and image analysis methods to evaluate and compare THz image quality in a quantitative and objective way, so that alternative terahertz imaging system configurations and acquisition techniques can be compared, and the range of image parameters can be assessed. Two test objects were designed and manufactured, one to determine the modulation transfer functions (MTF) and the other to derive image signal to noise ratio (SNR) at a range of contrasts. As expected the higher THz frequencies had larger MTFs, and better spatial resolution as determined by the spatial frequency at which the MTF dropped below the 20% threshold. Image SNR was compared for time domain and frequency domain image parameters and time delay based images consistently demonstrated higher SNR than intensity based parameters such as relative transmittance because the latter are more strongly affected by the sources of noise in the THz system such as laser fluctuations and detector shot noise.

A systematic review of the precision and accuracy of dose measurements in photon radiotherapy using polymer and Fricke MRI gel dosimetry

The purpose of this work is to undertake a critical appraisal of the evidence in the published literature concerning the basic parameters of accuracy and precision associated with the use of Fricke and polymer gels (in conjunction with MR imaging) as radiation dosimeters in photon radiotherapy, condensing and analysing the body of published information (to the end of April 2002). A systematic review was undertaken addressing specific issues of precision and accuracy asking defined questions of the published literature. Accuracy and precision in relation to gel dosimetry were defined. Information was obtained from published, peer-reviewed journals. A defined search strategy utilizing MeSH headings and keywords, with extensive use of cross-referencing, identified 115 references dealing with gel dosimetry. Exclusion criteria were used to select only data from publications which would give unequivocal evidence. For accuracy, results had to be compared with an ionization chamber as gold standard and all gel samples had to be manufactured in the same batch. For precision, in addition to gels being from the same batch, samples must all have been irradiated at the same time and scanned simultaneously (or within a short time frame). Many results were found demonstrating 'dose mapping' examples using gels. However, there were very few publications containing firm evidence of precision and accuracy. There was no evidence which fulfilled our criteria about accuracy or precision using Fricke gels. For polymer gels only one paper was found for accuracy (4% (Low et al 1999 Med. Phys. 26 1542-51)) and precision (1.7% (Baldock et al 1998 Phys. Med. Biol. 43695-702)); however, both were carried out at only one dose level. If the exclusion criteria were relaxed to include accuracy results comparing gel to a non gold standard dosimeter (e.g. TLD), results give a median accuracy of 10% (range 8-23.5%) for polymer gel (Cosgrove et al 2000 Phys. Med. Biol. 45 1195-210, De Deene et al 1998 Radiother: Oncol. 48 283-91, Farajollahi et al 2000 Br. J. Radiol. 72 1085-92, McJury et al 1999b Phys. Med. Biol. 44 2431-44, Murphy et al 2000b Phys. Med. Biol. 45 835-45, Oldham et al 2001 Med. Phys. 28 1436-45) and 5% for Fricke gel (Chan and Ayyangar 1995b Med. Phys. 22 1171-5). Evidence also points to accuracy worsening at lower dose levels for both gels. The precision data should be viewed with caution as repeated MR measurements were not performed with the same samples. The only precision data for Fricke gels was 1.5% (Johansson Back et al 1998 Phys. Med. Biol. 43 261-76), but for zero dose. In conclusion, despite the amount of published data, sparse research has been undertaken which provides clear evidence of the accuracy and precision for both gels. That which has been published has used higher doses than would be routine in radiotherapy. The basic radiation dosimeter qualities of accuracy and precision have yet to be fully quantified for polymer and Fricke gels at clinically relevant dose levels.