Chronic Administration of Monosodium Glutamate under Chronic Variable Stress Impaired Hypothalamic-Pituitary-Adrenal Axis Function in Rats.

The hypothalamic-pituitary-adrenal (HPA) axis is the primary endocrine system to respond to stress. The HPA axis may be affected by increased level of corticotrophin-releasing factors under chronic stress and by chronic administration of monosodium glutamate (MSG). The purpose of this study was to investigate whether chronic MSG administration aggravates chronic variable stress (CVS)-induced behavioral and hormonal changes. Twenty-four adult male Sprague-Dawley rats, weighing 200~220 g, were divided into 4 groups as follows: water administration (CON), MSG (3 g/kg) administration (MSG), CVS, and CVS with MSG (3 g/kg) administration (CVS+MSG). In addition, for the purpose of comparing the effect on plasma corticosterone levels between chronic stress and daily care or acute stress, 2 groups were added at the end of the experiment; the 2 new groups were as follows: naïve mice (n=7) and mice exposed to restraint stress for 2 h just before decapitation (A-Str, n=7). In an open field test performed after the experiment, the CVS+MSG group significant decrease in activity. The increase in relative adrenal weights in the CVS and CVS+MSG group was significantly greater than those in the CON and/or MSG groups. In spite of the increase in the relative adrenal weight, there was a significant decrease in the plasma corticosterone levels in the CVS+MSG group as compared to all other groups, except the naïve group. These results suggest that impaired HPA axis function as well as the decrease in the behavioral activity in adult rats can be induced by chronic MSG administration under CVS rather than CVS alone.

The assessment of bee venom responses in an experimental model of mono-arthritis using Tc-99m DPD bone scintigraphy.

OBJECTIVES: Several recent studies have shown that bee venom (BV) has an anti-nociceptive and anti-inflammatory effect on arthritis. However, objective methods for evaluation of the therapeutic effect of BV is insufficient in animal studies and clinical trials. Our purpose was to determine the usefulness of bone scintigraphy using Tc-99m DPD (3,3-diphosphono-1,2-propan-dicarbonacid) about effects of BV applied to carrageenan-induced mono-arthritis (CIA) model. METHODS: Mono-arthritis was induced by an intra-articular injection of carrageenan in Sprague-Dawley rats. Administration of BV (0.8 mg/kg) was performed at 30 min before and at 4 h after the induction of mono-arthritis. We assigned rats to BV-before, BV-after, control-before and control-after groups and compared the results of each group by the weight-loading test and bone scintigraphy. The rats received an intravenous injection of 37 MBq of Tc-99m DPD by the tail vein and then scanning was performed at 4 and 24 h after the injection. Visual assessment and quantitative analysis were performed for both knees. RESULTS: The BV-before and BV-after groups were more improved than the control groups on the weight load test (p < 0.05). Bone scintigraphy showed lower activity in the BV-before group than in the control-before group (p < 0.05) on the 4 h imaging. However, a significant difference in the BV-before and BV-after groups was not observed on the 24 h imaging. CONCLUSIONS: BV had therapeutic effects by anti-nociceptive and anti-inflammatory activity in the CIA and bone scintigraphy performed on 4 h imaging provided visual and quantitative information for the assessment of the therapeutic response to BV as an objective method in mono-arthritis model.

p38 MAP kinase regulates benzo(a)pyrene-induced apoptosis through the regulation of p53 activation.

Polycyclic aromatic hydrocarbons, such as benzo(a)pyrene (BaP), are widespread in the environment and cause untoward effects, including carcinogenesis, in mammalian cells. However, the molecular mechanism of apoptosis by BaP is remained to be elusive. Pharmacological inhibition of p38 kinase markedly inhibited the BaP-induced cytotoxicity, which was proven as apoptosis characterized by an increase in sub-G(0)/G(1) fraction of DNA content, ladder-pattern fragmentation of genomic DNA, and catalytic activation of caspase-3 with PARP cleavage. Our data also demonstrated that activation of caspase-3 was accompanied with activation of caspase-9 and mitochondrial dysfunction, which was also apparently suppressed by pretreatment with p38 kinase inhibitors. Also, pharmacological inhibition of p38 markedly inhibited the phosphorylation, accumulated expression, and transactivation activity of p53 in BaP-treated cells. Adenoviral overexpression of human p53 (wild-type) further augmented in increase of PARP cleavage and the sub-G(0)/G(1) fraction of DNA content. Furthermore, p53 mediated apoptotic activity in BaP-treated cells was inhibited by p38 kinase inhibitor. The current data collectively indicate that BaP induces apoptosis of Hepa1c1c7 cells via activation of p53-related signaling, which was, in part, regulated by p38 kinase.