Activation of the ornithine decarboxylase-polyamine system and induction of c-fos and p53 expression in relation to excitotoxic neuronal apoptosis in normal and microencephalic rats

Positive effects of meal frequency and calorie restriction on antioxidant systems in rats

OBJECTIVE:

In living organisms, there is a balance between the oxidant and antioxidant systems. Reactive products continuously formed by exogenous and endogenous sources are rendered harmless by the antioxidant system. Oxidative stress is an etiological factor in aging and the development of various diseases. In the present study, the aim was to investigate the effects of meal frequency and calorie restriction on oxidant-antioxidant systems in rat serum and tissue.

METHODS:

Nine adult male Wistar Albino rats were used for the pilot study, and another 24 adult male Wistar Albino rats, also weighing 200 to 250 g each, were included in the main study. The rats were divided into 3 groups based on nutrition: the ad libitum group (AL) (n=8), the 2-meal group (TM) (n=8), and the 2-meal with calorie restriction group (TM-CR) (n=8). Following the 4-week pilot study, nutrition regulation was performed in all groups for 20 weeks, 7 days a week, with 60 minutes allotted per meal. Serum and tissues of rats were isolated at the end of the experiment. Total antioxidant status (TAS) and total oxidant status (TOS) were determined using the Erel method. Oxidative stress index (OSI) was calculated using the formula OSI = TOS/TAS. Liver tissue was examined histopathologically. Statistical analyses were performed using the IBM SPSS Statistics for Windows, Version 20.0 (IBM Corp., Armonk, NY, USA) program.

RESULTS:

There were significant differences between the AL and TM, and the AL and TM-CR groups in adipose tissue TOS and OSI, and between the AL and TM groups in the liver TAS of the rats (p<0.05).

CONCLUSION:

Calorie restriction and sparse meal frequency can increase the activity of antioxidants and can reduce oxidative stress. Thus, many diseases caused by oxidative stress may be prevented with the correct regulation of feeding.

Dietary restriction differentially protects from neurodegeneration in animal models of excitotoxicity

Reduced caloric intake obtained through long-term dietary restriction has been found beneficial in some animal models of neurodegeneration. We report here that rats maintained under dietary restriction from the second to the eighth month of age are fully protected towards degeneration of GABAergic neurons in the hippocampus and the olfactory-entorhinal cortex caused by systemic administration of the convulsant toxin, kainic acid. However, in a different model of excitotoxic neurodegeneration, injection of ibotenic acid in the forebrain magnocellular basal nucleus, the decrease of a cholinergic marker in the target areas of the cortex was only partially protected by dietary restriction. Thus, in different experimental models neurodegeneration can be differentially rescued by dietary restriction. Analysis of alterations in the expression of relevant genes in different experimental conditions, could help in better understanding these differences.

Role of polyamine metabolism in kainic acid excitotoxicity in organotypic hippocampal slice cultures

Polyamines are ubiquitous cations that are essential for cell growth, regeneration and differentiation. Increases in polyamine metabolism have been implicated in several neuropathological conditions, including excitotoxicity. However, the precise role of polyamines in neuronal degeneration is still unclear. To investigate mechanisms by which polyamines could contribute to excitotoxic neuronal death, the present study examined the role of the polyamine interconversion pathway in kainic acid (KA) neurotoxicity using organotypic hippocampal slice cultures. Treatment of cultures with N1,N(2)-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527), an irreversible inhibitor of polyamine oxidase, resulted in a partial but significant neuronal protection, especially in CA1 region. In addition, this pre-treatment also attenuated KA-induced increase in levels of lipid peroxidation, cytosolic cytochrome C release and glial cell activation. Furthermore, pre-treatment with a combination of cyclosporin A (an inhibitor of the mitochondrial permeability transition pore) and MDL 72527 resulted in an additive and almost total neuronal protection against KA toxicity, while the combination of MDL 72527 and EUK-134 (a synthetic catalase/superoxide dismutase mimetic) did not provide additive protection. These data strongly suggest that the polyamine interconversion pathway partially contributes to KA-induced neurodegeneration via the production of reactive oxygen species.

Sustained, long-lasting inhibition of nitric oxide synthase aggravates the neural damage in some models of excitotoxic brain injury

Brain nitric oxide (NO) can be a mediator of physiological and neuroprotective actions and an effector of neural damage. The effectiveness of acute or chronic inhibition of NO production in in vivo experiments of neurotoxicity/neuroprotection is controversial. We report here on the effects of a chronic, sustained inhibition of nitric oxide synthase (NOS) on the neurodegenerative damage caused by three different excitotoxic lesions. The damage caused by intrastriatal injection of ibotenic or kainic acid was aggravated in rats subjected to chronic NOS inhibition. On the contrary, the drop of cortical cholinergic input consequent to ibotenic acid-mediated degeneration of basal forebrain neurons was not altered by chronic NOS inhibition. The worsening of the damage was not related to any overt differential sensitivity to excitotoxicity of NOS-containing striatal neurons under conditions of NOS inhibition. These results suggest that, contrary to what has been often reported for short-term, mild inhibition of NO production, chronic and sustained NOS inhibition may exacerbate neuropathology. Thus, long-lasting shortage of NO may be detrimental when neuroprotective mechanisms related to the physiological action of this free radical are severely impaired. Although we cannot exclude that inhibition of the endothelial NOS isoform could have contributed to the worsening of neuropathology, differences among the paradigms of neurotoxicity used in the present study suggest a primary involvement of the neuronal NOS isoform. In view of the potential therapeutic use of NOS inhibitors, the effects of a too drastic alteration of the balance between neuroprotective and neurodegenerative actions of NO should be carefully considered.

CROC-4: a novel brain specific transcriptional activator of c-fos expressed from proliferation through to maturation of multiple neuronal cell types

A novel, brain-specific cDNA, denoted CROC-4, was cloned from human brain by a contingent replication of cDNA procedure capable of detecting transcriptional activators of the human c-fos proto-oncogene promoter. CROC-4 encoded an 18-kDa serine/threonine-rich polypeptide containing a P-loop motif and an SH3-binding region with phosphorylation sites for a variety of protein kinases (cdc2, CDK2, MAPK, CDK5, protein kinase C, Ca(2+)/calmodulin protein kinase 2, casein kinase 2) involved in cell proliferation and differentiation. Immunohistochemistry revealed that during early development, expression was associated with proliferating and migrating cells throughout the rodent brain, initially appearing in the proliferative ventricular zones. During late development and in adult human brain, CROC-4 was expressed in diverse brain regions including the thalamus, subthalamic nucleus, corpus callosum, substantia nigra, caudate nucleus, amygdala, and hippocampus. The association of CROC-4 expression with proliferating regions of developing brain and retention in regions of the adult brain, as well as the punctate nuclear location, suggest that CROC-4 participates in brain-specific c-fos signaling pathways involved in cellular remodeling of brain architecture.

Spermine triggers the activation of caspase-3 in a cell-free model of apoptosis

Polyamines are ubiquitous organic cations required for cell proliferation. However, some evidence suggested that their excessive accumulation can induce apoptosis. We show here that, in a post-nuclear extract from U937 cells, the addition of spermine triggers the death program, represented by cytochrome c exit from mitochondria, the dATP-dependent processing of pro-caspase-3 and the onset of caspase activity. Spermine is more effective than spermidine, whereas putrescine has no effect. Polyamine acetylation abolishes their pro-apoptotic power. These data demonstrate a direct mechanism responsible for polyamine toxicity and also suggest that an excessive elevation of free polyamines could be involved in the transduction of a death signal.

c-fos expression in brains of patients with Down syndrome

c-fos is a protooncogene serving in multiple physiological processes in brain from signalling to proliferation and synaptic plasticity. We therefore decided to determine this transcription factor in control and Down Syndrome (DS) brain with the Rationale that c-fos may be linked to brain damage in DS. We determined mRNA steady state levels in frontal, parietal, occipital, temporal cortex and cerebellum of 9 patients with DS and 9 controls using RT-PCT. Significantly increased levels of mRNA c-fos normalized versus the housekeeping gene beta-actin mRNA were found in frontal, parietal and temporal cortex of DS brain. c-fox mRNA levels comparable to controls were found in occipital cortex and cerebellum. Deteriorated c-fos expression in the individual brain regions may be linked to increased apoptosis and neurodegeneration, overexcitation by excitatory amino acids of reactive oxygen species.