Energy metabolism and cerebral blood flow during cytotoxic brain edema induced by 6-aminonicotinamide

We investigated the progression of cytotoxic brain edema induced by 6-aminonicotinamide (6-ANA), a potent antimetabolite of nicotinamide, by measuring the time courses of changes in brain tissue water state (with MRI), histology (with H&E staining), energy metabolism (with 31P-NMR), brain hemoglobin concentration (with near-infrared spectroscopy; NIRS), cerebral blood flow and volume (CBF. CBV), mean arterial blood pressure (MABP), and brain activity (with EEG) up to 10 hours (h). Change in cerebrovascular autoregulation was also investigated. 6-ANA (120 mg/kg) was administered intraperitoneally to 30 male Wistar rats (250-350 g). After 10 h, the T2-weighted signal intensity was increased (p < 0.05), and H&E staining showed severe vacuolation of glial cells. ATP production/consumption and intracellular pH were well maintained up to 10 h, while the intensity of the phosphomonoesters (PME) signal was significantly increased (p < 0.05). Oxygen consumption gradually decreased from 4 to 10 h. CBF and MABP were all significantly increased (by 2.5-fold for CBF) (p < 0.05). Theta and delta wave amplitudes were reduced at 10 h. In summary, 6-ANA (120 mg/kg) induced cytotoxic brain edema from 4 to 10 h. Energy balance and brain activity were well maintained up to 10 h, though cerebrovascular autoregulation was impaired.

Metallothionein prevents neurodegeneration and central nervous system cell death after treatment with gliotoxin 6-aminonicotinamide

Transgenic expression of interleukin-6 (IL-6) in the CNS under the control of the glial fibrillary acidic protein (GFAP) gene promoter (GFAP-IL6 mice) induces significant inflammation and neurodegeneration but also affords neuroprotection against acute traumatic brain injury. This neuroprotection is likely mediated by the IL-6-induced protective factors metallothioneins-I and -II (MT-I+II). Here we evaluate the neuroprotective roles of IL-6 vs. MT-I+II during 6-aminonicotinamide (6-AN)-induced neurotoxicity, by using GFAP-IL6 mice and transgenic mice overexpressing MT-I (TgMT) as well as GFAP-IL6 mice crossed with TgMT mice (GFAP-IL6 x TgMT). 6-AN caused acute damage of brainstem gray matter areas identified by necrosis of astrocytes, followed by inflammatory responses. After 6-AN-induced toxicity, secondary damage was observed, consisting of oxidative stress, neurodegeneration, and apoptotic cell death. We hereby show that the primary injury caused by 6-AN was comparable in wild-type and GFAP-IL6 mice, but MT-I overexpression could significantly protect the brain tissue. As expected, GFAP-IL6 mice showed increased CNS inflammation with more gliosis, macrophages, and lymphocytes, including increased cytokine expression, relative to the other mice. However, GFAP-IL6 mice showed reduced oxidative stress (judged from nitrotyrosine, malondialdehyde, and 8-oxoguanine stainings), neurodegeneration (accumulation of neurofibrillary tangles), and apoptosis (determined from TUNEL and caspase-3). MT-I+II expression was significantly higher in GFAP-IL6 mice than in wild types, which may contribute to the IL-6-induced neuroprotection. In support of this, overexpression of MT-I in GFAP-IL6 x TgMT as well as TgMT mice protected the brainstem tissue significantly from 6-AN-induced toxicity and secondary brain tissue damage. Overall, the results demonstrate that brain MT-I+II proteins are fundamental neuroprotective factors, which in the future may become therapeutic agents.

Astrocyte-targeted expression of interleukin-6 protects the central nervous system during neuroglial degeneration induced by 6-aminonicotinamide

6-aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray matter astrocytes mainly in the brainstem. We have examined the role of interleukin-6 (IL-6) in this degenerative process by using transgenic mice with astrocyte-targeted IL-6 expression (GFAP-IL6 mice). This study demonstrates that transgenic IL-6 expression significantly increases the 6-AN-induced inflammatory response of reactive astrocytes, microglia/macrophages, and lymphocytes in the brainstem. Also, IL-6 induced significant increases in proinflammatory cytokines IL-1, IL-12, and tumor necrosis factor-alpha as well as growth factors basic fibroblast growth factor (bFGF), transforming growth factor-beta, neurotrophin-3, angiopoietin, vascular endothelial growth factor, and the receptor for bFGF. In accordance, angiogenesis was increased in GFAP-IL6 mice relative to controls after 6-AN. Moreover, oxidative stress and apoptotic cell death were significantly reduced by transgenic IL-6 expression. IL-6 is also a major inducer in the CNS of metallothionein I and II (MT-I+II), which were significantly increased in the GFAP-IL6 mice. MT-I+II are antioxidants and neuroregenerative factors in the CNS, so increased MT-I+II levels in GFAP-IL6 mice could contribute to the reduction of oxidative stress and cell death in these mice.

Genome scan for teratogen-induced clefting susceptibility loci in the mouse: evidence of both allelic and locus heterogeneity distinguishing cleft lip and cleft palate

Nonsyndromic clefting of the lip and palate in humans has a highly complex etiology, with both multiple genetic loci and exposure to teratogens influencing susceptibility. Previous studies using mouse models have examined only very small portions of the genome. Here we report the findings of a genome-wide search for susceptibility genes for teratogen-induced clefting in the AXB and BXA set of recombinant inbred mouse strains. We compare results obtained using phenytoin (which induces cleft lip) and 6-aminonicotinamide (which induces cleft palate). We use a new statistical approach based on logistic regression suitable for these categorical data to identify several chromosomal regions as possible locations of clefting susceptibility loci, and we review candidate genes located within each region. Because cleft lip and cleft palate do not frequently co-aggregate in human families and because these structures arise semi-independently during development, these disorders are usually considered to be distinct in etiology. Our data, however, implicate several of the same chromosomal regions for both forms of clefting when teratogen-induced. Furthermore, different parental strain alleles are usually associated with clefting of the lip versus that of the palate (i.e., allelic heterogeneity). Because several other chromosomal regions are associated with only one form of clefting, locus heterogeneity also appears to be involved. Our findings in this mouse model suggest several priority areas for evaluation in human epidemiological studies.

EFFECT OF 6-AMINONICOTINAMIDE ON CHICK-EMBRYO TISSUE CULTURES INFECTED WITH VACCINIA VIRUS

Lee, Spencer H. S. (Dalhousie University, Halifax, Nova Scotia). Effect of 6-aminonicotinamide on chick-embryo tissue cultures infected with vaccinia virus. J. Bacteriol. 88:885-892. 1964.-6-Aminonicotinamide (6-AN) was shown to render chick-embryo fibroblast (CEF) tissue cultures refractory to infection with vaccinia virus. Pretreatment of CEF cultures for 8 hr at 36 C with 5 mug/ml of 6-AN prior to addition of vaccinia virus reduced the titer of active virus to about 0.4% of the levels obtained in the untreated controls, when measured by the number of plaque-forming units per milliliter. The addition of 5 mug of 6-AN to CEF cultures before virus infection retarded the progress of vaccinial infection by 8 to 10 hr at 36 C. The inhibitory effect caused by 5 mug/ml of 6-AN could be reversed by the simultaneous addition of 5 to 50 mug/ml of nicotinamide, but not if added at a later time. 6-AN appears to act on the host cell and not on vaccinia virus. For these tests, a simple plaque assay method was devised, by use of a fluid overlay technique with screw-capped tubes (16 by 125 mm) containing CEF cultures.

Experimental models of congenital hydrocephalus and comparable clinical problems in the fetal and neonatal periods

Morphological and developmental changes of the ventricular system are analyzed in three major experimental models of congenital hydrocephalus in the rat: 6-aminonicotinamide (6-AN)-induced and LEW/Jms and HTX mutant hydrocephalus. The clinically comparable forms of hydrocephalus and problems occurring during each period of intrauterine hydrocephalus are then discussed. Comparative morphological study revealed that 6-AN-induced hydrocephalus was comparable to the Dandy-Walker syndrome and that the critical period regarding this syndrome in fetal life was at the time of "legal termination". The LEW/Jms and HTX mutant models were identical with regard to the form of progressive hydrocephalus in the postnatal period, but the condition underlying the hydrocephalus during the fetal period differed. The LEW/Jms model was comparable to primary congenital aqueductal stenosis (aqueductal agenesis), and the hydrocephalic state appeared in the period of "intrauterine preservation" before pulmonary maturation was completed. On the other hand, the HTX fetuses demonstrated secondary change of the aqueduct in the perinatal period, although the model was considered to be of congenital communicating hydrocephalus. Cerebrospinal fluid (CSF) dynamics studied in the fetuses with 6-AN-induced hydrocephalus disclosed considerable pathophysiology comparable to "hydromyelic hydrocephalus." The historical trends of animal experimental models of congenital hydrocephalus are reviewed and comparable clinical problems suggested by those models discussed further.

An immunohistochemical study of the intraventricular macrophages in induced hydrocephalus in prenatal rats following a maternal injection of 6-aminonicotinamide

Hydrocephalus was induced experimentally in prenatal rats following an injection of 6-aminonicotinamide (6-AN) into pregnant rats. The most remarkable change of the dilated lateral ventricles was in a marked increase in the number of intraventricular macrophages, some of which were laden with ingested erythrocytes. The immunoreactivity of the intraventricular macrophages was noticeably enhanced with the monoclonal antibodies OX-42 and OX-18 which marked the complement type 3 receptors (CR3) and major histocompatibility complex (MHC) class I antigen, respectively. Many immunoreactive cells with similar external morphology were observed to penetrate the ependymal lining at the roof of the ventricles. This, coupled with the concomitant depletion of the conglomeration of amoeboid microglia in the supraventricular corpus callosum, suggests that the upsurge of immunoreactive intraventricular macrophages in hydrocephalus was partly due to the influx of amoeboid microglia probably in response to the damage of the ventricular walls and possible alteration in the contents of the cerebrospinal fluid. The significance of the upregulation of complement type 3 receptors and major histocompatibility complex class I antigens on epiplexus cells in hydrocephalic rats remains to be explored, although our results suggest that the surface antigens may be involved in increased phagocytosis and/or a possible immune response.

Selective vulnerability in acute energy deprivation syndromes

The topography and cellular events in the experimental lesions caused by chlorosugars, 6-aminonicotinamide, dinitrobenzene and tribromoimidazole in animals are considered in relation to those features in human acute thiamine deficiency (Wernicke's) encephalopathy and for comparison in Leigh's disease. The topography and cellular changes when closely examined are different and particular to each condition, although there is a basic cellular process common to all. The pathogenesis of each condition must be considered as multifactorial and a search for the factors responsible for the neuronal and cellular selective vulnerability of different regions of the neuraxis will lead us to understanding the pathogenesis of the disease process in each instance. The experimental models offer much for the understanding of the human conditions, particularly in the search for satisfactory therapeutic strategies.

Effect of astroglial degeneration on the blood-brain barrier to protein in neonatal rats

Recent in vitro studies have suggested that astrocytes may be responsible for the induction of several blood-brain barrier (BBB) characteristics. To examine this hypothesis in an in vivo situation, we have investigated the effect of chronic astrocytic deprivation on the BBB to proteins in neonatal rats. Intraperitoneal injections of the gliotoxin 6-aminonicotinamide (6-AN) resulted in cytotoxic edema with subsequent necrobiosis of differentiated astrocytes and oligodendrocytes throughout the CNS. Animals were sacrificed 1-5 days after chronic exposure to 6-AN during the first postnatal week. Animals sacrificed 24 h after the final injection of 6-AN had the greatest depletion of perivascular astroglia. The BBB to exogenous protein, examined by intravascular administration of horseradish peroxidase, remained intact, as did the BBB to endogenous protein as determined by immunocytochemical detection of rat serum albumin. In no case was any leakage of protein found other than in areas that do not normally possess BBB characteristics. These data show that CNS endothelial cells retain BBB characteristics without a full complement of astrocytic contacts. Since the astroglial cytoplasm was destroyed and only membrane fragments remained, we suggest that factors continuously produced by astroglia cannot be responsible for the induction and maintenance of the BBB to protein, but that substances produced during the prenatal period may be the primary determinant of endothelial phenotype.

[Distribution and constitutional changes of edema fluid in cytotoxic brain edema analyzed by electron microscopy and differential scanning calorimetry]

To understand the pathogenesis of brain edema, we studied distribution and constitutional changes of brain-tissue water by morphological and thermoanalytical methods in cytotoxic brain edema induced by 6-aminonicotinamide (6-ANA). Ninety-two Wistar rats were divided into three groups; Group I rats receiving physiological salt solution intraperitoneally served as controls. Group II and III animals were intraperitoneally given 120 mg/kg and 36 mg/kg of 6-ANA respectively. All animals were starved after injection of drugs to exclude differences in water intake. Then they were decapitated at 3, 6, 12, 24, 36 or 48 hours to measure specific gravity (SG) of large brain tissue (1.1-1.5 g), and to evaluate water content (WC) and free water ratio (FWR) of small brain-tissue samples (15-35 mg) taken from the frontal cortex; WC was measured by a drying-weighing method, and FWR was analyzed with a differential scanning calorimeter. Moreover morphological changes of the frontal cortex of the brain were studied in Group II (n = 12) at 3, 6, 12, 24 and 48 hours with an electron microscope. Neurological status of animals administered 6-ANA (Group II and III) deteriorated with time. Morphological studies showed that perivascular astrocytes and astrocytic processes in the cerebral cortex were swollen most remarkably at 48 hours. However neuronal and endothelial cells were almost intact. The FWR of Group I decreased significantly about four per cent (p less than 0.001) after being starved for 48 hours. But the SG and WC of the group showed little change.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Aminonicotinamide-induced hydrocephalus in suckling mice

Following a single intraperitoneal injection of 6-aminonicotinamide (6-AN, 50 mg/kg of body weight) into newborn mice of the Institute of Cancer Research strain, hydrocephalus consistently developed nine days after injection, with rapid progression. All of these mice died before reaching adulthood. The most striking early histologic change in these mice was cytoplasmic vacuolation of ependymal cells, which was observed as early as 24 hours after injection. Vacuolation of subependymal astrocytes appeared during the next few days. After day seven, the aqueduct was obliterated by swollen vacuolated ependymal cells and subependymal astrocytes. The aqueduct remained obliterated even after the vacuolation of the ependymal cells subsided after day nine, when vacuolation of subependymal astrocytes was still pronounced. These morphological observations reveal that, in newborn mice, the ependymal cells are the most sensitive to the toxic action of 6-AN and suggest that the pathogenesis of 6-AN-induced hydrocephalus is likely to be due to the combination of ependymal cell damage and compression of the lumen by the edematous periaqueductal gray matter. This is a highly reproducible animal model of drug-induced hydrocephalus.

Mitotic index in mouse embryos with 6-aminonicotinamide-induced and inherited cleft lip

Three types of cleft lip were studied histologically before and during lip formation in mouse embryos. C57BL/6 embryos observed near term following treatment with 6-aminonicotinamide (6AN) at gestation D9/12 (vp day = day 0) had 18% median cleft lip. Treated embryos observed at D10 and D11 showed retarded somite and nasal placode development. Sections at lip closure time showed marked reduction of medial and some reduction of lateral nasal processes, and the mitotic index was significantly reduced in the nasal area on D10 and D11 but less consistently in the neural area. 6AN-treatment on D10/8, caused 22% lateral cleft lip. Treated embryos showed initial retardation of somite and nasal placode development that became normal by D11/14. Sections showed reduction of the medial and lateral nasal processes, and less organized denser nasal ectoderm. The mitotic index was significantly reduced in the nasal and neural areas on D10 and D11. In crosses having the major gene mutation dancer (Dc) 20% of embryos had lateral cleft lip and potential cleft lip mutant embryos showed reduced lateral and medial nasal processes. Mitotic index was not reduced in the nasal area but it was in the neural area. The CL/Fr strain, with a predisposing face shape in which 26% of the embryos have cleft lip of multifactorial origin, had a mitotic index similar to that of C57BL/6 (0% cleft lip) at lip closure time, D11/14, and prominent medial nasal processes. It is postulated that 6AN-induced median cleft lip is due to reduced cell proliferation in and size of the medial nasal processes; 6AN-induced lateral cleft lip to reduced cell proliferation and reduced medial and lateral nasal processes and dancer lateral cleft lip to reduction of the medial nasals.

Acute dimethyl sulfoxide therapy in experimental brain edema: part 2. Effect of dose and concentration on intracranial pressure, blood pressure, and central venous pressure

Albino rabbits with experimental brain edema produced by a combined cryogenic and metabolic 6-aminonicotinamide lesion were administered intravenous dimethyl sulfoxide in varying concentrations and doses in the following manner: Subgroup A (concentration response) received a 1.0-g/kg bolus as a 10%, 20%, 30%, or 40% solution. Subgroup B (dose response) received as a 20% solution a 1.0-g/kg bolus, 1.5-g/kg bolus, or 2.0-g/kg infusion. Simultaneous recording of intracranial pressure (ICP), systolic arterial pressure (SAP), and central venous pressure and electroencephalography were performed while the animals were being mechanically ventilated at a constant PaCO2 (38 to 42 torr). There was significant lowering of ICP when compared to pretreatment values in Subgroup A in the 10% subset at 30 minutes (p less than 0.05) and in the 20% subset at 5 (p less than 0.05) and 30 (p less than 0.05) minutes. ICP was not significantly decreased in the 30% and 40% subsets. All animals of Subgroup B displayed significant reductions of ICP when compared to their pretreatment values. There was no significant change in SAP in either subgroup.

Glucose utilization in the central nervous system in the acute gliopathy due to 6-aminonicotinamide

Sprague-Dawley rats were injected intraperitoneally with 5 mg. per kg. of 6-aminonicotinamide. The local glucose utilization rate (LGU) was measured throughout the central nervous system using the (14C) 2-deoxyglucose, quantitative autoradiographic technique at 3, 6, 12, and 24 hours after injection. The histologic appearance of selected areas of central nervous system was studied at 6, 12, and 24 hours and 3 and 10 days after injection, following perfusion by buffered aldehydes and plastic embedding. Decreases in LGU o 25 to 36 per cent were found in the lumbar ventral horn, caudal brain stem, and cerebellum at 3 and 6 hours. By 12 hours, virtually all of the structures examined showed decreases in LGU greater than 20 per cent with the reduction in the cord being 40 to 50 per cent. At 24 hours, the majority of areas exhibited definite recovery of LGU. Mild glial swelling, particularly of oligodendroglia, was noted at 12 hours and was obvious by 24 hours. Neuronal changes were not seen. These abnormalities were most marked in the intermediate and ventral gray matter of the cord and certain brain stem nuclei. 6-Aminonicotinamide has a known inhibitory effect on the pentose phosphate shunt and a secondary effect on the direct glycolytic pathway. The reduction in LGU is probably due to the inhibition of these pathways in both glia and neurons, but, the recovery LGU at 24 hours when the glial pathology was increasing suggests that the glia may metabolically protect the neuron at times of stress.

Alterations of the nervous susceptibility with aging

Lesions in the CNS induced by 6-aminonicotinamide (6-AN) presented a spongy state of the gray matter and neuronal chromatolysis. With aging of the experimental animals the lesions extended from the phylogenetically early developed structures to those developed later, i.e., from spinal gray matter, dentate nuclei, and brain stem nuclei through limbic structures and striatum to the cerebral cortex. Changes of the neurons were more prominent with aging. Lesions in the CNS of rats at the age, corresponding to the involutional period in the human, were similar to those of Creutzfeldt-Jakob disease (C-J) disease) in the presenile age. In recent years, the resemblance between C-J disease and pellagra encephalopathy had been noted by several authors, and they resemble the lesions caused by 6-AN, an antimetabolite of nicotinamide used in our experiment. This evidence, therefore, has led to the hypothesis that dysfunction of NAD(H)- or NADP(H)-dependent enzymes in the CNS of the aged, even if not the primary cause, may be one possible pathogenetic factor of C-J disease.

Genetic independence of the embryonic reactivity difference to cortisone- and 6-aminonicotinamide-induced cleft palate in the mouse

The A/J strain of mice is more reactive than C57BL/6J to both cortisone- and 6-aminonicotinamide-induced cleft palate. A breeding study was set up to determine the genetic control of the differences in embryonic reactivity between the two strains to the two teratogens. In this paper the test for possible association between the two response traits is presented. In the second-backcross generation of embryos where segregation of the two traits could be studied no association was found. Therefore, any embryonic genes making major contributions to differences in reactivity between the two strains are not the same for the two teratogens.

Lesions in the cat spinal cord following local injections of 6-aminonicotinamide

Lesions were made in the spinal cord of cats by means of local injections of 6-aminonicotinamide. The concentration needed to induce primary demyelination also caused extensive axonal death. In the early stages following injection there was evidence of astrocyte and oligodendrocyte destruction and with longer survival times most of the surviving demyelinated axons were remyelinated by Schwann cells. This experimental system indicates that Schwann cell remyelination of central axons follows astrocyte destruction, but it was not considered a suitable model system for the study of cellular relationships in remyelination because of the extensive concomitant axonal damage.

Differences in the size of the palatal processes in mouse embryos with cleft palate induced in two critical periods

Using planimetric measurements of projections of the space between the palatal processes of ICR-Velaz mouse embryos, we indirectly demonstrated that the pre-horizontalization size of the palatal processes after the i.m. administration of 7.5 mg cortsone acetate on the 12th day of gestation was smaller than in the controls. After horizontalization, the inadequate palatal processes were unable to meet in the midline as they do in the majority of normal embryos. The administration of 0.5 mg 6-amino-nicotinamide on the 14th day of gestation did not significantly affect the size of the palatal processes.

6-Aminonicotinamide-induced cleft palate in the mouse: the nature of the difference between the A/J and C57Bl/6J strains in frequency of response and its genetic basis

Cleft palate induction by 6-aminonicotinamide (6-AN) was examined in the A/J and C57BL/6J strains of mice to determine the nature of the strain difference in frequency of cleft-palate response. Probit analysis of the cleft-palate response to dose of different genotypes revealed a family of linear and parallel dose-response curves. The genotypes differ only in dosage tolerance (log ED50) to 6-AN that is required for the cleft-palate response. No evidence for a maternal cytoplasmic effect on 6-AN-induced cleft palate was found under the conditions of the present study. When the difference is dosage tolerance to 6-AN between A/J and C57BL/6J was examined with a single dose and measured by differences in frequency of induced cleft palate on a probit scale, there was some departure from genetic additivity. There was an indication off dominance deviation of the F1 embryos in the direction of C57BL/6J.A3-locus, epistatic model is proposed to account for the difference in embryonic tolerance ot 6-AN-induced cleft palate. There was a suggestion of association with the brown (b) locus.

Remyelination by Schwann cells of axons demyelinated by intraspinal injection of 6-aminonicotinamide in the rat

Focal areas of primary demyelination were produced in the spinal cords of rats by means of local injections of 6-aminonicotinamide. Both astrocytes and oligodendrocytes underwent degeneration in the demyelinated area. Nearly all the demyelinated axons were remyelinated by Schwann cells; only a very small number of axons located adjacent to normally myelinated axons were remyelinated by oligodendrocytes. The glial limiting membrane was reconstituted around the ecge of the area remyelinated by Schwann cells. This experiment offers further evidence for an important role of astrocytes in controlling Schwann cell invasion of the central nervous system, and in addition suggests that astrocytes are also needed for oligodendrocyte remyelination to take place.

Inhibition of ATP synthesis associated with 6-aminonicotinamide (6-AN) teratogenesis in rat embryos

Pregnant rats were injected ip with 6 mg/kg 6-aminonicotinamide (6-AN) at day 12 of gestation. Embryos removed between 1 and 48 h later had reduced adenosine triphosphate (ATP) concentrations, of about 50% of control values. All fetuses examined near term were malformed. Nicotinamide (NAM, 100 mg/kg) given ip 1 h after 6-AN afforded protection: malformations occurred in only 15% of the survivors; and there was minimal ATP reduction, 15% below control values. NAM given 2 and 4 h after 6-AN produced intermediate ATP concentrations and malformation frequencies. Thus, there was a relation between the embryotoxic and ATP-depressant actions of 6-AN in day 12 rat embryos.