Kiwao Nakano

Significance of increased secretion of glucocorticoids in mice and rats injected with bacterial endotoxin

Injection of mice or rats with lipopolysaccharide (LPS) is associated with an increased secretion of glucocorticoids. The high level of mortality following injection of LPS that is noted in adrenalectomized rats can be reversed by dexamethasone or corticosterone. That histamine may be an endogenous mediator of the release of corticosterone caused by LPS is suggested by an attenuation of this corticosterone response by promethazine, an H1 antihistamine. Additional support that LPS-dependent glucocorticoid secretion is mediated, in part, by histamine, is suggested by spleen cell transfer studies revealing differences in the induction of histidine decarboxylase (HDC) synthesis and corticosterone release by the C3H/HeN and C3H/HeJ strains of mice that are differentially sensitive to LPS effects. These and other data on increased levels of histamine and HDC during mitogen-induced lymphocyte blastogenesis, as well as experiments revealing immunomodulatory effects of histamine and histamine agonists and antagonists on lymphocyte blastogenesis, are consistent with the hypothesis that following infection with gram-negative bacteria, the histamine-induced increase in glucocorticoid secretion results in inhibition of HDC in splenocytes, a concomitant attenuation of histamine production, and a resulting return to immune homeostasis.

Regulation of histamine synthesis in mouse CD4+ and CD8+ T lymphocytes

Abstract.Objectives: Previously, we have shown that mouse T lymphocytes produce de novo histamine in response to mitogens. The aim of this study was to examine which subsets of T cells produce histamine and to clarify the regulatory mechanisms of the reaction.¶Materials: CD4+ and CD8+ T lymphocytes were separated from spleen cells of mast cell-deficient WBB6/F1 (W/Wv) mice using anti-CD4- and anti-CD8-coupled magnetic beads, respectively.¶Results: Both CD4+ T cells and CD8+ T cells released histamine when treated with Con A as a function of incubation time. Since histamine bound to each cell fraction was negligible before and after the treatment, it is highly likely that this indicates de novo synthesis of histamine by these cells. Granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3 strongly enhanced the Con A-induced histamine formation. IL-1-α also potentiated the Con A-dependent histamine production. Dexamethasone, but not progesterone, significantly inhibited the Con A-dependent as well as Con A-independent histamine synthesis. Both GM-CSF and IL-3 caused a marked accumulation of histidine decarboxylase (HDC, EC 4.11.22) mRNAs in the cells.¶Conclusions: These results suggest that GM-CSF and IL-3 enhance histamine synthesis in CD4+ T cells and CD8+ T cells.

High levels of quinolinic acid in brain of epilepsy-prone E1 mice

Quinolinic acid (QUIN) may act.as an excitotoxin when it is abundant in the brain. We have shown previously that the activity of 3-hydroxyanthranilate 3,4-dioxygenase, a QUIN-synthesizing enzyme, was abnormally high in the brains of epilepsy-prone E1 mice as compared with that of ddY mice. Here, we estimated the QUIN contents in the brains of these mice. The results showed that the basal QUIN content in the cerebral cortex of E1 mice was twice as high as that of ddY mice. Systemic injection of 400 mumol/kg body weight of L-tryptophan (L-Trp) increased the cortical levels of QUIN in both E1 mice and ddY mice by 189% and 118%, respectively. Administration of 400 mumol/kg each of L-threonine and D,L-methionine had no appreciable effect on the L-Trp-caused increase in the cortical QUIN levels. Co-administration of 5-fluorotryptophan or 5-methyltryptophan, tryptophan analogs, with L-Trp did not reduce but rather enhanced the cortical QUIN levels (by 18% and 92%, respectively). No significant change in the cortical QUIN concentrations was observed with injection of 2 mg/kg body weight of E. coli lipopolysaccharide (LPS) in E1 mice. However, injection of L-Trp in the LPS-treated E1 mice produced a more marked increase in the cortical QUIN levels than that injected with L-Trp alone. These results suggest that the brain QUIN contents of E1 mice are dependent not only on the activity of QUIN-synthesizing enzyme but also on the rate of flux of its substrate, L-Trp or its metabolite(s), in the brain.

Tryptophan and its metabolite, kynurenine, stimulate expression of nerve growth factor in cultured mouse astroglial cells.

Effects of L-tryptophan and its metabolites were evaluated on expression of nerve growth factor (NGF) in primary culture of mouse astroglial cells. L-Tryptophan produced concentration-dependent increases in accumulation of NGF transcripts in the cells. L-Kynurenine, a metabolite of the kynurenine pathway, markedly increased the levels of mRNAs for NGF, the maximal increases (4-5 fold) occurred at its dose of 1 microM. Kynurenine-induced increase in mRNA levels for NGF occurred as early as 1 h after the addition of the compound, peaked at 4 h and declined thereafter. In contrast to kynurenine, other tryptophan metabolites such as quinolinic acid, kynurenic acid and serotonin had little effect on the levels of NGF mRNA.

Regulation of interleukin-6, and macrophage colony-stimulating factor mRNA levels by histamine in stromal cell line (MC3T3-G2/PA6)

Abstract.Objective: The aim of this study was to examine the role of histamine in regulation of IL-6 and M-CSF gene expression in bone marrow stromal cells. Total cellular synthesis was also estimated for IL-6.¶Materials: The effects of the amine were evaluated using the stromal cell line, MC3T3-G2/PA6 (PA6).¶Results: Histamine caused a distinct accumulation of IL-6 mRNA in the cells, whereas it decreased M-CSF transcripts. Both pyridylethylamine, a H1 agonist, and dimaprit, a H2 agonist, caused a large increase in the level of IL-6 mRNA in PA6 cells. The histamine-induced expression of IL-6 mRNA was associated with enhanced secretion of IL-6, as determined by ELISA.¶Conclusions: These results, together with the results of our previous studies, suggest that histamine produced by stromal macrophages differentially regulates the production of IL-6 and M-CSF in other kinds of stromal cells and hence promotes differentiation and/or proliferation of hematopoietic progenitor cells.

Increase in histamine synthesis by liver macrophages in CCl4-injured mast cell-deficient W/WV mice

This study set out to examine the possible role of liver macrophages in histamine synthesis in the injured liver. The effects of the hepatotoxins Escherichia coli lipopolysaccharide (LPS) and CCl4 on histamine synthesis in the liver of mice were evaluated. C3H/HeJ mice were resistant to LPS in including histidine decarboxylase (HDC) in the liver compared with C3H/HeN mice and mast cell-deficient W/Wv mice. However, C3H/HeJ mice did respond strongly to another hepatotoxin, CCl4, leading to a significant increase in HDC activity. CCl4 also caused a marked increase in HDC activity and histamine levels in the liver of W/Wv mice. In addition, injection of CCl4 produced a large increase in the activity of HDC in the spleen and lung of W/Wv mice. HDC activity was confined to the nonparenchymal cells, with parenchymal cells expressing essentially no HDC activity. The CCl4-induced increase in HDC activity was confined, at least in part, to the liver macrophages. These results indicate that the macrophages are responsible for the increase in HDC-dependent histamine production in the liver caused by the injection of hepatotoxins. The possible role of histamine in liver regeneration after injury is discussed.

Redistribution of vitamin A in tissues of rats with imposed chronic confinement stress

1. The effect of confinement stress on the metabolism of vitamin A was studied in rats by following changes in tissue distribution of the vitamin for 29 d. In order to minimize predicted errors which might result from fluctuation of vitamin A intake, the effect of the stress was investigated in rats fed on a vitamin A-free diet. 2. Daily stress for 6 h induced an enlargement of the adrenals with a concomitant involution of the thymus and spleen, values returning to normal within 11-15 d. 3. The stress caused an immediate decrease in the content of vitamin A in serum. 4. Feeding rats a vitamin A-free diet resulted in significant increase in the vitamin A content of the kidney. Imposing stress on these rats inhibited markedly the increase in kidney vitamin A content. 5. The stress produced no appreciable change in levels of the vitamin in the liver and testes. 6. There was a preferential accumulation of the vitamin in the adrenals of the stress-imposed rats even though they were fed on a vitamin A-free diet. 7. In conclusion, the results of the present study demonstrated that chronic immobilization stress produced marked tissue-dependent changes in their vitamin A content.

Increased expression of 3-hydroxyanthranilate 3,4-dioxygenase gene in brain of epilepsy-prone El mice

The El mouse is an established animal model for human epilepsy. We previously reported that the level of quinolinic acid (QUIN), an excitotoxin, was high in the brain of epilepsy-prone El mice and that the increased production of QUIN was secondary to an increased activity of 3-hydroxyanthranilate 3,4-dioxygenase (3-HAO, EC 1.13.11. 6) in the brains of these mice. In this study, we cloned and sequenced the cDNA for 3-HAO and showed that its expression in the brain of El mice was higher than that of control ddY mice. These results suggest that a genetic defect leading to derepression of the 3-HAO gene expression in the brain may be involved in the pathogenesis for the epileptic diseases of El mice.

Increased expression of mitochondrial respiratory enzymes in the brain of epilepsy-prone, naive EL mice

The present studies demonstrate that expression of both type 5 and type 6 subunits of NADH dehydrogenase and the type 1 subunit of cytochrome oxidase is enhanced significantly in the brains of naive, epilepsy-prone EL mice. In contrast, no apparent change in expression occurred with type 1 and type 2 subunits of NADH dehydrogenase. When expression of type 5 and 6 subunits of NADH dehydrogenase was determined at 24 h after a single series of vestibular stimulation, significant down-regulation was detected. The expression of subunit 2 of NADH dehydrogenase augmented gradually after vestibular stimulation. The increased expression of these mitochondrial respiratory enzymes may reflect enhanced demand for energy due to inherent, spontaneous neuronal hyperactivity in the brains of EL mice.

Enhanced Fos expression in the hippocampus of El mice after short-term vestibular stimulation

The El mouse is an animal model for human epilepsy. The mouse manifest seizures in response to periodically repeated vestibular stimuli such as being tossing-up. Although this technique has been traditionally employed to accelerate this disease in the mouse, its meaning remained obscure. The present study was conducted to estimate the effects of tossing-up stimuli on expression of c-fos, a well-known marker of neuronal activation. Expression of c-fos was significantly increased even after single tossing-up specimen. It was blocked by pretreatment of the mouse with MK-801, a NMDA receptor antagonist. A marked expression of the oncoprotein was observed in the granule cell layer of dentate gyrus and CA1-3 pyramidal cell layer in the hippocampus of the mouse. These results suggest that the El mice are genetically hyper-sensitive to the vestibular stimuli.