A new nitroxyl-probe with high retention in the brain and its application for brain imaging

In order to estimate free radical reactions and image them in the brain of living animals, a nitroxyl spin-probe, carboxy-PROXYL acetoxymethyl ester (CxP-AM) was newly synthesized. CxP-AM was designed to be hydrolyzed by esterase, but not by lipase, so that it would pass through the blood-brain barrier and be retained in the cytosolic phase of parenchymal cells in the brain after intravenous injection. The pharmacokinetics of CxP-AM was compared with those of carboxy-PROXYL (CxP) and its methyl ester (CxP-M). Carboxyl esterase almost completely hydrolyzed CxP-AM within 3 min. After intravenous injection, the brain retained 1.8 times more CxP-AM than CxP-M, and retained it for more than 30 min. Electron spin resonance computed tomographic (ESR-CT) imaging of CxP-AM in the heads of mice produced marked contrast in the encephalon region, while CxP was distributed only in the extracranial region and CxP-M was distributed in both regions, confirming the pharmacokinetics of CxP-AM. The decay rate of CxP-AM determined with time-resolved ESR-CT imaging was different in the two brain regions, suggesting regional differences in the total reducing capability. CxP-AM should become a powerful probe for the investigation and diagnosis of free radical reactions and their imaging in the brain.

Presynaptic L-type Ca(2)+ channels on excessive dopamine release from rat caudate putamen

We investigated by means of behavioral and neurochemical studies the role of the nerve terminal L-type voltage sensitive Ca(2)+ channel on dopamine (DA) release. Microinjection of Bay K 8644 (BAYK), an L-type Ca(2)+ channel stimulant, into the rat caudate putamen increased locomotor activity and rearing behavior in a dose-dependent manner, whereas injections into the amygdala had no effect. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Significant increases of extracellular DA levels were detected by microdialysis 20 min after BAYK administration into caudate putamen and then declined. This increase was influenced by tetrodotoxin, an axonal Na(+) channel blocker. Pretreatment with nimodipine and nicardipine, but not nifedipine, which are 1, 4-dihydropyridine L-type Ca(2)+ channel antagonists, administered into the caudate putamen significantly blocked BAYK-induced hyperactivity and DA efflux. These results indicate that the extraordinary DA release in the caudate putamen was mediated by extreme stimulation of the nicardipine and nimodipine-sensitive L-type Ca(2)+ channel present in the nerve terminal of striatal DA neurons.

Direct evidence for increased hydroxyl radicals originating from superoxide in the failing myocardium

Experimental and clinical studies have suggested an increased production of reactive oxygen species (ROS) in the failing myocardium. The present study aimed to obtain direct evidence for increased ROS and to determine the contribution of superoxide anion (*O(2)(-)), H(2)O(2), and hydroxy radical (*OH) in failing myocardial tissue. Heart failure was produced in adult mongrel dogs by rapid ventricular pacing at 240 bpm for 4 weeks. To assess the production of ROS directly, freeze-clamped myocardial tissue homogenates were reacted with the nitroxide radical, 4-hydroxy-2,2,6, 6,-tetramethyl-piperidine-N-oxyl, and its spin signals were detected by electron spin resonance spectroscopy. The rate of electron spin resonance signal decay, proportional to *OH level, was significantly increased in heart failure, which was inhibited by the addition of dimethylthiourea (*OH scavenger) into the reaction mixture. Increased *OH in the failing heart was abolished to the same extent in the presence of desferrioxamine (iron chelator), catalase (H(2)O(2) scavenger), and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; LaMotte) (*O(2)(-) scavenger), indicating that *OH originated from H(2)O(2) and *O(2)(-). Further, *O(2)(-) produced in normal myocardium in the presence of antimycin A (mitochondrial complex III inhibitor) could reproduce the increase of H(2)O(2) and *OH seen in the failing tissue. There was a significant positive relation between myocardial ROS level and left ventricular contractile dysfunction. In conclusion, in the failing myocardium, *OH was produced as a reactive product of *O(2)(-) and H(2)O(2), which might play an important role in left ventricular failure.

COLLABORATIVE WORK TO EVALUATE TOXICITY ON MALE REPRODUCTIVE ORGANS BY REPEATED DOSE STUDIES IN RATS : 6)2-AND 4-WEEKS ADMINISTRATION STUDY OF HALOPERIDOL

Haloperidol, a neuroleptic, was orally given to Sprague-Dawley rats for 2 or 4 weeks, starting at 8 and 6 weeks of age. The dose levels were 0, 30 and 60 mg/kg/day for the 4-week treatment groups, and 0, 30, 60 and 80 mg/kg/day for the 2-week treatment groups. On the day after the last administration, rats were anesthetized and sacrificed at 10 weeks of age. The absolute weights of the testes and epididymides were decreased after 2- and 4-weeks at 30 mg/kg/day or above. The absolute and relative weights of the prostate and seminal vesicles were also decreased after 2-weeks at 60 mg/kg/day or above, and 4-weeks at 30 mg/kg/day or above. The histopathological alterations observed after 2-weeks at 30 mg/kg/day were as follows: atrophy of Leydig cells, numerous necrotic pachytene spermatocytes in seminiferous tubules of stage VII, retention of mature spermatids, exfoliation of round spermatids in lumina of seminiferous tubules, cell debris in lumina of the epididymis. At 60 mg/kg/day or above, these alterations were pronounced. Histopathological changes were comparable to those detected after 4-weeks treatment. It was concluded that alterations of the male reproductive organs are detectable by a 2-week administration of haloperidol in rats to almost the same degree as after 4-weeks treatment.

Delayed transfection of DNA after riboflavin mediated photosensitization increases G:C to C:G transversions of supF gene in Escherichia coli mutY strain

We have previously reported that the majority of base substitution mutations of the Escherichia coli supF gene induced by riboflavin mediated photosensitization were G:C to C:G changes, in addition to G:C to T:A changes which were probably caused by 8-hydroxyguanine (oh(8)Gua), in wild type and mutM mutator mutant strains. This implies that lesions other than oh(8)Gua are produced by riboflavin-photosensitization. G:C to C:G base substitutions have been found in the mutations induced by ionizing radiation and reactive oxygen species, as well as spontaneous mutation. To characterize the G:C to C:G mutation, riboflavin- photosensitized plasmid DNA carrying the supF gene was left at room temperature for 5 h in the dark before transfection. The delayed transfection gave a mutational spectrum different from that for immediate transfection. G:C to C:G transversions significantly increased in mutY mutator strain, in which the transversion was not detected in the immediate transfection. Lesions causing G:C to C:G changes increased during 5-h holding after photosensitization and MutY protein presumably takes part in this type of base change mutation.

Mitochondrial electron transport complex I is a potential source of oxygen free radicals in the failing myocardium

Oxidative stress in the myocardium may play an important role in the pathogenesis of congestive heart failure (HF). However, the cellular sources and mechanisms for the enhanced generation of reactive oxygen species (ROS) in the failing myocardium remain unknown. The amount of thiobarbituric acid reactive substances increased in the canine HF hearts subjected to rapid ventricular pacing for 4 weeks, and immunohistochemical staining of 4-hydroxy-2-nonenal ROS-induced lipid peroxides was detected in cardiac myocytes but not in interstitial cells of HF animals. The generation of superoxide anion was directly assessed in the submitochondrial fractions by use of electron spin resonance spectroscopy with spin trapping agent, 5, 5'-dimethyl-1-pyrroline-N-oxide, in the presence of NADH and succinate as a substrate for NADH-ubiquinone oxidoreductase (complex I) and succinate-ubiquinone oxidoreductase (complex II), respectively. Superoxide production was increased 2.8-fold (P<0.01) in HF, which was due to the functional block of electron transport at complex I. The enzymatic activity of complex I decreased in HF (274+/-13 versus 136+/-9 nmol. min(-1). mg(-1) protein, P<0.01), which may thus have caused the functional uncoupling of the respiratory chain and the deleterious ROS production in HF mitochondria. The present study provided direct evidence for the involvement of ROS in the mitochondrial origin of HF myocytes, which might be responsible for both contractile dysfunction and structural damage to the myocardium.

Amiodarone protects cardiac myocytes against oxidative injury by its free radical scavenging action

BACKGROUND

Oxidative stress plays an important role in the pathophysiology of ischemic heart disease and heart failure, and antioxidants might be beneficial in the treatment of these patients. This study was performed to determine the scavenging effects of amiodarone on oxygen free radicals and its protective effects against oxygen radical-mediated injury in cardiac myocytes.

METHODS AND RESULTS

The formation of the radical spin adduct with hydroxy radical (.OH) in the presence of H(2)O(2) (10 mmol/L) and Fe(3+)-nitrilotriacetate (20 micromol/L) was monitored by electron paramagnetic resonance spectroscopy combined with a spin trapping agent, 5,5-dimethyl pyrroline-N-oxide (DMPO). Amiodarone decreased the intensity of the DMPO-OH signals in a dose-dependent manner (0.1 to 100 micromol/L), whereas other antiarrhythmia drugs such as disopyramide and atenolol had no such effects. Furthermore, amiodarone (10 micromol/L) protected intact adult canine cardiac myocytes against.OH-mediated myocyte injury, as assessed by the degree of morphological change from rod shape to the irreversible hypercontracture state during the exposure of cells to H(2)O(2) and Fe(3+) in vitro.

CONCLUSIONS

Amiodarone can protect cardiac myocytes against oxidative stress-mediated injury by directly scavenging oxygen free radicals. Antioxidant action of amiodarone might potentially contribute to the beneficial effects of this drug in the treatment of patients with ischemic heart disease and congestive heart failure.

Detection of hypoxic cells in murine tumors using the comet assay: comparison with a conventional radiobiological assay

The comet (single-cell electrophoresis) assay has been developed as a method for measuring DNA damage in single cells after irradiation. We have developed our own methods and image analysis system for the comet assay to identify hypoxic fractions. In vitro, we tested our system using a cultured tumor cell line (SCCVII). In vivo, we compared the hypoxic fractions detected by this assay with those determined by the in vivo-in vitro clonogenic assay using two rodent tumors (SCCVII/ C3H, EMT6/KU/balb/c), which exhibit different types of hypoxia: acute and chronic. In vitro, our method could differentiate hypoxic cells from oxic cells, using the parameter of tail moment. In vivo, there were good correlations between the hypoxic fractions determined by the comet assay and by the clonogenic assay, in SCCVII/C3H (r=0.85) and in EMT6/KU/balb/c (r=0.75) tumors. By comparison of the two methods in chronically hypoxic and acutely hypoxic tumors, we further confirmed that the comet assay is clinically useful for estimating hypoxic fractions of solid tumors.

[Non-invasive measurement of in vivo free radical reactions]

It was proven that in vivo free radicals roles in various physiological phenomena and many diseases such as inflammation, ischemic disease, digestive problems and neurodegeneration, thus making measurements of free radicals very important for determining the mechanisms of these diseases. Spin trapping method using ESR, salicylic acid methods using high performance liquid chromatography and chemiluminescent methods are reported for ex vivo and in situ measurements. And, among these techniques, in vivo ESR is the most powerful for performing non-invasive measurements in animals. In in vivo ESR, exogenous nitroxyl radicals are administered to animal and then by measuring the signal change, the radical reaction can be indirectly determined. The signal decay rate is enhanced by oxidative stress, and this enhanced signal decay is suppressed by giving radical scavengers, etc. By analyzing the enhancement of this attenuation in detail, it is possible to specify the type of radical or the location at which the free radicals are produced. Such non-invasive techniques to measure free radicals like the present in vivo ESR technique should provide considerable information for elucidating the mechanisms of diseases.

Glial cell line-derived neurotrophic factor induces barrier function of endothelial cells forming the blood-brain barrier

Since a deep involvement of astrocytes, a kind of glial cells, in differentiation of the blood-brain barrier (BBB) has been suggested, we examined the relation of glial cell line-derived neurotrophic factor (GDNF) to the BBB. First, immunohistochemical examination of the cerebral cortex of rats revealed that glial cell line-derived neurotrophic factor receptor (GFRalpha1) was preferentially expressed on the cell membranes of capillary endothelial cells. Second, to elucidate the effects of GDNF on the BBB, capillary endothelial cells isolated from the porcine cerebral cortex were cultured and then changes in tight junction function of the endothelial cells were examined after addition of GDNF, in terms of transendothelial electrical resistance (TER) and permeability. GDNF at concentrations of 0.1 and 1 ng/ml significantly activated the barrier function of the endothelial cells in the presence of cAMP. Since GDNF is secreted from astrocytes sheathing capillary endothelial cells in the brain cortex, our results strongly suggest that GDNF enhances the barrier function of tight junctions of the BBB on the one hand, and also supports the survival of neurons on the other hand.

Generation of free radicals and the damage done to the sarcoplasmic reticulum during reperfusion injury following brief ischemia in the canine heart

Free radical generation was studied by the electron spin resonance (ESR) technique using alpha-phenyl N tert butyl nitrone (PBN) in a brief ischemia-reperfusion model of the canine heart, and correlated with biochemical changes of the sarcoplasmic reticulum (SR). ESR spectra (aH=0.3-0.4mT, aN=1.43-1.58mT) were observed as PBN spin adducts, which peaked at levels 5-fold above the control levels at 5 min after reperfusion. The simulated coupling constants of PBN spin adducts suggested that the sample should contain at least 2 carbon-centered radicals at 5 min after reperfusion (radical A: aH=0.350mT, aN=1.485mT; radical B: aH=0.370mT, aN=1.615 mT). At this time point, a significant reduction in Ca-ATPase activity of the SR was found without degradation of the major ATPase protein. Superoxide dismutase (SOD) significantly reduced the intensity of the PBN spin adduct signals and preserved the Ca-ATPase activity of the SR to 80% of the control level. Reperfusion injury after brief ischemia may be the result of inactivation of intracellular Ca-ATPase by free radicals generated during reperfusion, and SOD contributes to the protective effect by scavenging the radicals.

Noninvasive evaluation of in vivo free radical reactions catalyzed by iron using in vivo ESR spectroscopy

The noninvasive, real time technique of in vivo electron spin resonance (ESR) spectroscopy was used to evaluate free radical reactions catalyzed by iron in living mice. The spectra and signal decay of a nitroxyl probe, carbamoyl-PROXYL, were observed in the upper abdomen of mice. The signal decay was significantly enhanced in mice subcutaneously loaded with ferric citrate (0.2 micromol/g body wt) and the enhancement was suppressed by pre-treatment with either desferrioxamine (DF) or the chain breaking antioxidant Trolox, but only slightly suppressed by the hydroxyl radical scavenger DMSO. To determine the catalytic form of iron, DF was administered at different times with respect to iron loading: before, simultaneously, and after 20 and 50 min. The effect of DF on signal decay, liver iron content, iron excretion, and lipid peroxidation (TBARs) depended on the time of the treatment. There was a good correlation between the signal decay, iron content, and lipid peroxidation, indicating that "chelatable iron" contributed to the enhanced signal decay. The nitroxyl probe also exhibited in vivo antioxidant activity, implying that the process responsible for the signal decay of the nitroxyl probe is involved in free radical oxidative stress reactions catalyzed by iron.

Mechanisms related to reduction of radical in mouse lung using an L-band ESR spectrometer

Reduction of radicals in mouse lung was characterized in whole animals using an L-band ESR technique and nitroxide radicals as probes. An aqueous solution of nitroxide radical was immediately instilled intratracheally to mouse after euthanasia. Nitroxide radicals without charged groups were reduced significantly in the lung, while radicals with charged groups were only slightly reduced. Permeation rates across lung plasma membrane were not rate limiting of the stage of reduction of the noncharged nitroxides. Michaelis parameters, apparent Km and apparent Vmax, were obtained from the Lineweaver-Burk plots of the reduction. Among noncharged nitroxides with constant apparent Vmax, radicals with a larger n-octanol/water partition coefficient showed a lower apparent Km, thereby suggesting that the concentration of these nitroxides in the membrane contributes to apparent Km. The reduction rate of noncharged nitroxide, hydroxy-TEMPO, was influenced by noncharged SH reagents instilled together with the nitroxide; dithiothreitol stimulated the reduction, while the oxidized reagent inhibited it. The Lineweaver-Burk plots of the nitroxide reduction in the presence of various concentrations of dithiothreitol suggest the possibility that the reduction system for hydroxy-TEMPO is based on a kind of ping pong bi-reactant mechanism, and that the reduction system utilizes SH as an electron donor. Endogenous glutathione contributed partially to the reduction.

Dietary docosahexaenoic acid enhances ferric nitrilotriacetate-induced oxidative damage in mice but not when additional alpha-tocopherol is supplemented

Weaning mice were fed a diet supplemented with beef tallow (BT) or BT plus docosahexaenoic acid (DHA) containing 100 mg alpha-tocopherol/kg (alpha-Toc100) or 500 mg alpha-tocopherol/kg (alpha-Toc500) for 4 wk to modify membrane fatty acid unsaturation, and then were administered ferric nitrilotriacetate (Fe-NTA). The mortality caused by Fe-NTA was higher in the group fed the DHA (alpha-Toc100) diet than in the BT diet groups but the DHA (alpha-Toc500) diet suppressed this increase. Serum and kidney alpha-tocopherol contents were slightly influenced by the dietary fatty acids but not significantly. These results indicate that the increased unsaturation of tissue lipids enhances oxidative damage induced by Fe-NTA in mice fed DHA (alpha-Toc100) but not when additional alpha-tocopherol is supplemented. The apparent discrepancy between the observed enhancement by dietary DHA of oxidative damage and the beneficial effects of dietary DHA on the so-called free radical diseases is discussed in terms of strong bolus oxidative stress and moderate chronic oxidative stress.

Specificity of mutations induced by riboflavin mediated photosensitization in the supF gene of Escherichia coli

Riboflavin-mediated photosensitization has been shown to produce 8-hydroxyguanine (oh8Gua) in DNA. We investigated the specificity of mutation of photosensitized supF gene induced in Escherichia coli. The oh8Gua repair deficient E. coli mutant mutM and mutY were transformed with plasmid pUB3 carrying the supF gene irradiated with white light in the presence of riboflavin. Under these conditions, riboflavin photosensitization increased the amounts of oh8Gua in pUB3 DNA. Three types of a single base substitution occurring at G:C pairs were detected in both wild-type and mutM mutant strains. Almost all base substitutions were transversions to T:A or C:G pairs occurring at a similar extent in both wild-type and mutM strains. Mutations derived from mutY strain transformed with photosensitized DNA were only G:C to T:A transversions. These G:C to T:A transversions observed in the mutY strain were suggested to be the result of mispairing of oh8Gua with adenine. Riboflavin-mediated photosensitization may also produce lesions on DNA causing G:C to C:G changes by unknown mechanisms.

[Clinical features and treatment of sarcoidosis involving the central nervous system]

PURPOSE

The purpose of this study was to investigate the clinical features, diagnosis, and treatment modalities of three cases with neurosarcoidosis, which involved the central nervous system (CNS).

CASES

Three men with neurosarcoidosis, aged 27, 29 and 60 years, are presented. Two of them had previously been given a diagnosis of sarcoidosis. The clinical symptoms of these cases included diabetes insipidus, pituitary dysfunction, seizure, mental disorder, visual field disturbance and pyramidal tract signs. In these cases, CT scan and MRI showed the presence of a tumor near the pituitary gland, diffuse nodules in the subarachnoid space or meningoencephalitis associated with angitis. The level of angiotensin converting enzyme (ACE) in the sera and in the cerebrospinal fluid, were elevated in the two cases who had no brain biopsy. All three cases were treated with steroids; two of them received pulse steroid therapy.

RESULTS

The two cases who received pulse steroid therapy responded quickly, with improvement in clinical features, serum ACE levels and neuroradiological findings. Under oral administration of steroids, all three cases recovered with complete remission of neurosarcoidosis except for endocrinological symptoms.

DISCUSSION

The main pathological changes of neurosarcoidosis are granulomatous angitis of the venular walls and occasionally, of the capillaries near the meninx and Virchow-Robin space. The patients also had symptoms of secondary meningoencephalitis. These changes were mainly located in the hypothalamus and pituitary gland. The patients had complex symptoms resulting from endocrine system granuloma, as well as from cerebral ischemia. The severity of the disease and effectiveness of treatment, can be evaluated by measuring ACE levels in the cerebrospinal fluid (over 1. 0 IU/l), and by Gd-enhanced MRI. Early pulse steroid therapy with subsequent oral steroid administration is thought to be important for neurosarcoidosis treatment, in order to prevent irreversible damage in the CNS.

Oxidative stress measurement by in vivo electron spin resonance spectroscopy in rats with streptozotocin-induced diabetes

Enhanced oxidative stress in diabetic patients may contribute to the pathogenesis of diabetic angiopathy. We have recently developed a method to determine the electron spin resonance (ESR, electron paramagnetic resonance; EPR) of reactive oxygen species and free radicals in vivo, using the nitroxide derivative, carbamoyl-PROXYL as a probe. In this study, diabetes was induced in Wistar rats by streptozotocin (STZ) injection (65 mg/kg, body weight, intravenously). Two, 4, and 8 weeks later, the animals received carbamoyl-PROXYL (300 nmol/g, intravenously), and ESR was measured at the upper abdominal level at a frequency of 300 MHz. The intensity of the carbamoyl-PROXYL ESR signal decreased gradually after the injection, and the spin clearance rate was determined over the first 5 min. At all time points, the spin clearance rate was significantly greater in the diabetic rats than in control rats. Moreover, the spin clearance rate in the diabetic rats was significantly correlated with urinary malondialdehyde (MDA) levels, which serve as a marker for lipid peroxidation. Daily treatment with 4 units neutral protamin Hagedorn (NPH) insulin for 4 weeks reduced the spin clearance rate in the diabetic rats. Simultaneous injection of carbamoyl-PROXYL and superoxide dismutase reduced the spin clearance rate in the diabetic rats in a dose-dependent manner. Injection of the antioxidant alpha-tocopherol (40 mg/kg, intraperitoneally) for 2 weeks restored the spin clearance rate in the diabetic rats without concomitant glycaemic restoration. These results suggest that a diabetic state enhances the generation of free radicals in vivo, and that both glycaemic control and antioxidant treatment can reduce this oxidative stress. Non-invasive in vivo ESR measurement may be useful for evaluating oxidative stress in diabetes.

Presence of emerinopathy in cases of rigid spine syndrome

Rigid spine syndrome (RSS) shows clinical similarities to Emery-Dreifuss muscular dystrophy (EDMD). Differential diagnosis between EDMD and RSS is essential because EDMD is often associated with life-threatening cardiomyopathy that can be cured by an implantation of a cardiac pacemaker. To determine if any of the patients with RSS had mutations of the emerin gene (responsible gene for X-linked EDMD or emerinopathy), we screened the patients for mutations. We found seven patients with a clinical picture consistent with RSS in the 6500 diagnostic muscle biopsies in our National Center over the last 19 years. We identified a novel mutation in the gene (1-bp frame-shift deletion in the exon 1) in one of the seven patients with RSS. This mutation created a premature termination at codon 12 and was expected to produce a severely truncated emerin. Emerin was not detected in the skeletal muscle. The unaffected mother of the patient was a heterozygous carrier for the mutation. The remaining six patients with RSS had no mutation in the gene and showed normal expression of emerin in the skeletal muscle. Our results emphasize the presence of clinical overlap between possible RSS and EDMD, and reinforce the necessity of molecular genetic diagnosis of emerin to exclude emerinopathy in a patient population that has a clinical diagnosis of RSS.

Characterization of transgenic tobacco with an increased alpha-linolenic acid level

Microsomal omega-3 fatty acid desaturase catalyzes the conversion of 18:2 (linoleic acid) to 18:3 (alpha-linolenic acid) in phospholipids, which are the main constituents of extrachloroplast membranes. Transgenic tobacco (Nicotiana tabacum) plants with increased 18:3 contents (designated SIIn plants) were produced through the introduction of a construct with the tobacco microsomal omega-3 fatty acid desaturase gene under the control of the highly efficient promoter containing the E12Omega sequence. 18:3 contents in the SIIn plants were increased by about 40% in roots and by about 10% in leaves compared with the control plants. With regard to growth at 15 degreesC and 25 degreesC and the ability to tolerate chilling at 1 degreesC and 5 degreesC, there were no discernible differences between the SIIn and the control plants. Freezing tolerance in leaves and roots, which was assessed by electrolyte leakage, was almost the same between the SIIn and the control plants. The fluidity of plasma membrane from the SIIn plants was almost the same as that of the control plants. These results indicate that an increase in the 18:3 level in phospholipids is not directly involved in compensation for the diminishment in growth or membrane properties observed under low temperatures.

Homologous recombination and non-homologous end-joining pathways of DNA double-strand break repair have overlapping roles in the maintenance of chromosomal integrity in vertebrate cells

Eukaryotic cells repair DNA double-strand breaks (DSBs) by at least two pathways, homologous recombination (HR) and non-homologous end-joining (NHEJ). Rad54 participates in the first recombinational repair pathway while Ku proteins are involved in NHEJ. To investigate the distinctive as well as redundant roles of these two repair pathways, we analyzed the mutants RAD54(-/-), KU70(-/-) and RAD54(-/-)/KU70(-/-), generated from the chicken B-cell line DT40. We found that the NHEJ pathway plays a dominant role in repairing gamma-radiation-induced DSBs during G1-early S phase while recombinational repair is preferentially used in late S-G2 phase. RAD54(-/-)/KU70(-/-) cells were profoundly more sensitive to gamma-rays than either single mutant, indicating that the two repair pathways are complementary. Spontaneous chromosomal aberrations and cell death were observed in both RAD54(-/-) and RAD54(-/-)/KU70(-/-) cells, with RAD54(-/-)/KU70(-/-) cells exhibiting significantly higher levels of chromosomal aberrations than RAD54(-/-) cells. These observations provide the first genetic evidence that both repair pathways play a role in maintaining chromosomal DNA during the cell cycle.

Establishment and characterization of a hypocatalasemic mouse cell strain

Contact-inhibited catalase-deficient fibroblast cell strain has been established from the homozygous hypocatalasemic C3H/Csb mutant mouse. This cell strain has low level of catalase enzyme activity and has normal level of enzyme activities of both glutathione peroxidase and superoxide dismutase. Catalase-deficient C3H/Csb mutant cell strain is markedly more sensitive to the toxicity of hydrogen peroxide compared to wild-type C3H/Csa cell strain. In addition, mutant cell strain is sensitive to X-rays and near-UV compared to wild-type cell strain, but shows the same sensitivities to topoisomerase II inhibitors, adriamycin and 4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA), and the DNA cross-linking agents, cisdiamminedichloroplatinum (II) (cis-Pt) and trans-diamminedichloroplatinum (II) (trans-Pt). These cell strains will be of use in the study of the roles which catalase plays in the intracellular prevention of DNA damage induced by oxidative stress.

The effects of acute phencyclidine treatment on neuropeptide Y (NPY) neuronal system in the rat arcuate nucleus studied by immunocytochemistry and in situ hybridization

Phencyclidine (PCP) is a dissociative drug and an antagonist of N-methyl-D-aspartate (NMDA) receptor. The effects of PCP treatment on neuropeptide Y (NPY) system in the arcuate nucleus of the rat hypothalamus were examined both by immunocytochemistry and in situ hybridization. In acute PCP-treated rats, the NPY-immunoreactive perikarya appeared in the arcuate nucleus but no perikarya were detected in controls, without colchicine pretreatment. The signals of NPY mRNA by in situ hybridization increased in the PCP-treated rats than those of controls. These results suggest that the NPY system in the arcuate nucleus might be partly controlled by glutamatergic neurons.

Glycosaminoglycan binding properties of annexin IV, V, and VI

We have previously demonstrated that annexin IV, one of the calcium/phospholipid-binding annexin family proteins, binds to glycosaminoglycans (GAGs) in a calcium-dependent manner (Kojima, K., Yamamoto, K., Irimura, T., Osawa, T., Ogawa, H., and Matsumoto, I. (1996) J. Biol. Chem. 271, 7679-7685). In this study, we investigated the GAG binding specificities of annexins IV, V, and VI by affinity chromatography and solid phase assays. Annexin IV was found to bind in a calcium-dependent manner to all the GAG columns tested. Annexin V bound to heparin and heparan sulfate columns but not to chondroitin sulfate columns. Annexin VI was adsorbed to heparin and heparan sulfate columns in a calcium-independent manner, and to chondroitin sulfate columns in a calcium-dependent manner. An N-terminal half fragment (A6NH) and a C-terminal half fragment (A6CH) of annexin VI, each containing four units, were prepared by digestion with V8 protease and examined for GAG binding activities. A6NH bound to heparin in the presence of calcium but not to chondroitin sulfate C, whereas A6CH bound to heparin calcium-independently and to chondroitin sulfate C calcium-dependently. The results showed that annexin IV, V, and VI have different GAG binding properties. Some annexins have been reported to be detected not only in the cytoplasm but also on the cell surface or in extracellular components. The findings suggest that the some annexins function as recognition elements for GAGs in extracellular space.

Formation of 8-hydroxyguanine and 2,6-diamino-4-hydroxy-5-formamidopyrimidine in DNA by riboflavin mediated photosensitization

Calf thymus DNA was photoirradiated in the presence of riboflavin. Altered bases were detected and quantified by the GC/MS-SIM method after hydrolysis and derivatization of DNA. Seven types of modified purine bases were detected in control DNA. Among them, the yields of 8-OH-Gua and FapyGua increased significantly in DNA photo-irradiated with riboflavin, whereas the yields of xanthine, 8-OH-Ade, 2-OH-Ade, FapyAde and hypoxanthine were not affected. A dose dependent increase in the formation of 8-OH-Gua was observed with increasing riboflavin concentration for 30 min irradiation. On the other hand, FapyGua reached plateau at 10 micrograms/ml of riboflavin for 30 min irradiation. Our results indicate that guanine moiety in DNA is the most susceptible to riboflavin mediated photosensitization.