Spermine prevents cytochrome c release in glucocorticoid-induced apoptosis in mouse thymocytes

Anti-apoptotic role of spermine against lead and/or gamma irradiation-induced hepatotoxicity in male rats

Exposure to either lead (Pb) or γ-irradiation (IR) results in oxidative stress in biological systems. Herein, we explored the potential anti-apoptotic effect of spermine (Spm) against lead and/or γ-irradiation-induced hepatotoxicity in male albino rats. Rats were divided into eight experimental groups of ten rats each: groups including negative control, whole body γ-irradiated (6 Gray (Gy)), lead acetate (PbAct) trihydrate orally administered (75 mg/kg bw ≡ 40 mg/kg bw Pb for 14 consecutive days), and Spm intraperitoneally dosed (10 mg/kg bw for 14 consecutive days) rats and groups subjected to combinations of Pb + IR, Spm + IR, Spm + Pb, and Spm + Pb followed by IR on day 14 (Spm + Pb + IR). A significant decrease in arginase activity as well as mRNA and protein levels of Bcl-2 and p21 was observed in rats intoxicated with Pb and/or γ-irradiation compared to controls, whereas Bax mRNA and protein levels were significantly increased. Also, an increased level of nitric oxide (NO) with a reduced arginase activity was observed in liver tissues of intoxicated rats. Spm co-treatment with lead and/or γ-irradiation attenuated the increase in Bax mRNA and protein expression, while it restored those of Bcl-2 and p21 together with NO levels and arginase activity to control values. Altogether, we suggest that Spm may be useful in combating free radical-induced apoptosis in Pb-intoxicated and/or γ-irradiated rats.

Depletion of the polyamines spermidine and spermine by overexpression of spermidine/spermine N¹-acetyltransferase 1 (SAT1) leads to mitochondria-mediated apoptosis in mammalian cells

The polyamines putrescine, spermidine and spermine are intimately involved in the regulation of cellular growth and viability. Transduction of human embryonic kidney (HEK) 293T cells with an adenovirus encoding a key polyamine catabolic enzyme, spermidine N¹-acetyltransferase 1 (SSAT1)/SAT1 (AdSAT1), leads to a rapid depletion of spermidine and spermine, arrest in cell growth and a decline in cell viability. Annexin V/propidium iodide FACS analyses, terminal uridine nucleotide end-labelling (TUNEL) and caspase 3 assays showed a clear indication of apoptosis in AdSAT1-transduced cells (at 24-72 h), but not in cells transduced with GFP-encoding adenovirus (AdGFP). Apoptosis in the polyamine-depleted cells occurs by the mitochondrial intrinsic pathway, as evidenced by loss of mitochondrial membrane potential, increase in pro-apoptotic Bax, decrease in anti-apoptotic Bcl-xl, Bcl2 and Mcl-1 and release of cytochrome c from mitochondria, upon transduction with AdSAT1. Moreover, TEM images of AdSAT1-transduced cells revealed morphological changes commonly associated with apoptosis, including cell shrinkage, nuclear fragmentation, mitochondrial alteration, vacuolization and membrane blebbing. The apoptosis appears to result largely from depletion of the polyamines spermidine and spermine, as the polyamine analogues α-methylspermidine (α-MeSpd) and N¹,N¹²-dimethylspermine (Me₂Spm) that are not substrates for SAT1 could partially restore growth and prevent apoptosis of AdSAT1-transduced cells. Inhibition of polyamine oxidases did not restore the growth of AdSAT1-transduced cells or block apoptosis, suggesting that the growth arrest and apoptosis were not induced by oxidative stress resulting from accelerated polyamine catabolism. Taken together, these data provide strong evidence that the depletion of the polyamines spermidine and spermine leads to mitochondria-mediated apoptosis.

The ameliorative effect of thymol against hydrocortisone-induced hepatic oxidative stress injury in adult male rats

The aim of the present study was to investigate whether hydrocortisone induces oxidative stress in hepatocytes and to evaluate the possible ameliorative effect of thymol against such hepatic injury. Twenty-four adult male rats were divided into control, thymol, hydrocortisone, and hydrocortisone+thymol groups. The 4 groups were treated daily for 15 days. Hydrocortisone significantly induced oxidative stress in the liver tissues, marked by increased serum levels of alanine transaminase (ALT), aspartate transaminase (AST), total oxidative capacity (TOC), and tumor necrosis factor-alpha (TNF-α) accompanied by marked decline of serum levels of total protein, albumin, and total antioxidant capacity (TAC). Also, marked elevation in the levels of the thiobarbituric acid reactive substances (TBARS) and TNF-α, beside significant decrease in the level of glutathione (GSH) in hepatic tissues were recorded. These biochemical alterations were accompanied by histopathological changes marked by destruction of the normal hepatic architecture, in addition to ultrastructural alterations represented by degenerative features covering almost all the cytoplasmic organelles of the hepatocytes. Supplementation of hydrocortisone-treated rats with thymol reversed most of the biochemical, histological, and ultrastructural alterations. The results of our study confirm that thymol has strong ameliorative effect against hydrocortisone-induced oxidative stress injury in hepatic tissues.

Akt and Erk1/2 activate the ornithine decarboxylase/polyamine system in cardioprotective ischemic preconditioning in rats: the role of mitochondrial permeability transition pores

Ornithine decarboxylase (ODC) is the first rate-limiting enzyme in polyamine biosynthesis, which is essential for cell survival. We hypothesized that the ODC/polyamine system is involved in ischemic preconditioning (IPC)-mediated cardioprotection through the activation of Erk1/2 and Akt and through the inhibition of the mitochondrial permeability transition (mPT). Isolated rat hearts were subjected to 40 min of ischemia either with or without IPC (3 cycles of 5-min global ischemia), and ODC protein expression, polyamine content, and Akt and Erk1/2 phosphorylation were evaluated after 30 min of reperfusion. IPC significantly upregulated the ODC/polyamine pathway, promoted Erk1/2 and Akt phosphorylation, and reduced the infarct size and heart dysfunction after reperfusion. An inhibitor of ODC, α-difluoromethylornithine (DFMO), abolished the IPC-induced cardioprotection. Moreover, the inhibition of the IPC-induced activation of Erk1/2 and Akt using PD98059 or wortmannin downregulated the ODC/polyamine system. In separate studies, the Ca(2+) load required to open the mPT pore was significantly lower in DFMO-treated cardiac mitochondria than in mitochondria from IPC hearts. Furthermore, spermine or spermidine significantly inhibited the mPT induced by CaCl2. These results suggest that IPC upregulates the ODC/polyamine system and mediates preconditioning cardioprotection, which may depend on the phosphorylation/activation of Erk1/2 and Akt and on the inhibition of the mPT during reperfusion.

Crude extract of Ceriporia lacerata has a protective effect on dexamethasone-induced cytotoxicity in INS-1 cells via the modulation of PI3K/PKB activity

Excessive and/or long-term glucocorticoid therapy reduces β-cell mass and induces hyperglycemia, which contribute to the development of steroid‑induced diabetes. Ceriporia (C.) lacerata is one of the white‑rot fungi and has been used in bioremediations, such as lignocellulose degradation, in nature. The pharmacologic effect of C. lacerata on steroid-induced β-cell toxicity is not known. In this study, we evaluated the effect of a crude extract from a submerged cultivation of C. lacerata on the survival and apoptosis of INS-1 rat insulin-secreting cells exposed to dexamethasone (Dex), a synthetic diabetogenic glucocorticoid. Treatment with the C. lacerata crude extract (CLCE) largely blocked the Dex-induced reduction in survival and apoptosis of INS-1 cells. Moreover, CLCE treatment inhibited Dex-induced protein kinase B (PKB) dephosphorylation without affecting Dex-induced extracellular signal-regulated protein kinase-1/2 dephosphorylation and MKP-1 upregulation. Importantly, the protective effect of CLCE on Dex-induced cytotoxicity in INS-1 cells was attenuated by LY294002, an inhibitor of PI3K/PKB. CLCE treatment, however, did not protect the INS-1 cells from the cytotoxic effects triggered by other insults, such as interleukin-1β (an inflammatory cytokine), streptozotocin (a diabetogenic drug), thapsigargin (a calcium mobilizing agent), and tunicamycin (an ER stress inducer). Collectively, these findings demonstrate for the first time the ability of CLCE to specifically protect INS-1 cells from Dex-induced cytotoxicity through the modulation of the PI3K/PKB pathway. It is suggested that CLCE may be applied for the prevention and/or treatment of steroid diabetes in which reduction of β-cell survival and induction of β-cell apoptosis play pathogenic roles.

Metabolic correlations of glucocorticoids and polyamines in inflammation and apoptosis

Glucocorticoid hormones (GC) are essential in all aspects of human health and disease. Their anti-inflammatory and immunosuppressive properties are reasons for therapeutic application in several diseases. GC suppress immune activation and uncontrolled overproduction and release of cytokines. GC inhibit the release of pro-inflammatory cytokines and stimulate the production of anti-inflammatory cytokines. Investigation of GC's mechanism of action, suggested that polyamines (PA) may act as mediators or messengers of their effects. Beside glucocorticoids, spermine (Spm) is one of endogenous inhibitors of cytokine production. There are many similarities in the metabolic actions of GC and PA. The major mechanism of GC effects involves the regulation of gene expression. PA are essential for maintaining higher order organization of chromatin in vivo. Spermidine and Spm stabilize chromatin and nuclear enzymes, due to their ability to form complexes with negatively charged groups on DNA, RNA and proteins. Also, there is an increasing body of evidence that GC and PA change the chromatin structure especially through acetylation and deacetylation of histones. GC display potent immunomodulatory activities, including the ability to induce T and B lymphocyte apoptosis, mediated via production of reactive oxygen species (ROS) in the mitochondrial pathway. The by-products of PA catabolic pathways (hydrogen peroxide, amino aldehydes, acrolein) produce ROS, well-known cytotoxic agents involved in programmed cell death (PCD) or apoptosis. This review is an attempt in the better understanding of relation between GC and PA, naturally occurring compounds of all eukaryotic cells, anti-inflammatory and apoptotic agents in physiological and pathological conditions connected to oxidative stress or PCD.

Glucocorticoid-induced apoptosis and cellular mechanisms of myopathy

Glucocorticoid-induced myopathy is a common side effect of chronic glucocorticoid therapy. Several mechanisms are currently being examined as ways in which glucocorticoid-induced myopathy occurs. These include apoptotic signaling through mitochondrial-mediated and Fas-mediated apoptosis, the role of the proteosome, the suppression of the IGF-1 signaling, and the role of ceramide in glucocorticoid-induced apoptosis and myopathy. It is difficult to differentiate which mechanism may be the initiating event responsible for the induction of apoptosis; however, all of the mechanisms play a vital role in glucocorticoid-induced myopathy.

Differential effects of paraquat on oxidative stress parameters and polyamine levels in two freshwater invertebrates

Paraquat is still a widely used herbicide in several countries. Its toxic action on plants occurs through a one-electron reduction interfering with the photosynthesis process. By a similar reaction, the herbicide may induce peroxidation processes in non-target animal species. Furthermore, paraquat may interfere with the cellular transport of polyamines. The aim of this work was to investigate some aspects related to paraquat-induction of oxidative stress (lipoperoxidation, enzymatic activities of catalase and superoxide dismutase) and also the levels of polyamines (putrescine, spermidine and spermine) in two species of freshwater invertebrates, the oligochaete Lumbriculus variegatus and the gastropod Biomphalaria glabrata. The results showed that both organisms elicited differential responses. In addition, the data suggested that polyamines may play an important role against lipoperoxidation processes.

Polyamine-modulated factor 1 represses glucocorticoid receptor activity

Polyamine-modulated factor 1 (PMF-1) has been reported to interact with NF-E2 related factor 2 (Nrf-2) and activate the polyamine-induced transcription of spermidine/spermine N(1)-acetyltransferase (SSAT) gene. Polyamines are important regulators of cell growth and cell death and have been implicated in glucocorticoid-induced apoptosis. In the present study, we have identified and characterized new functional binding partners for PMF-1. Our results demonstrate that PMF-1 binds to the glucocorticoid receptor (GR). PMF-1 also represses glucocorticoid-induced transcription. Furthermore, we show that PMF-1 has an intrinsic repression activity, which could contribute to the repressive effect on GR. PMF-1 can also interact with the GR corepressor, receptor-interacting protein 140 (RIP140), but does not further enhance the repressive effect of RIP140. Our results suggest that PMF-1 has a broader function in regulation of genes and can contribute to glucocorticoid signaling.

Redundant role for early growth response transcriptional regulators in thymocyte differentiation and survival

The early growth response (Egr) family of transcriptional regulators consists of four proteins that share highly conserved DNA-binding domains. In many cell types, they are coexpressed and appear to have cooperative roles in regulating gene expression during growth and differentiation. Three Egr proteins, Egr1, Egr2, and Egr3, are induced during thymocyte differentiation in response to pre-TCR signaling, suggesting they may be critical for some aspects of pre-TCR-mediated differentiation. Indeed, enforced expression of Egr proteins in developing thymocytes can recapitulate some aspects of pre-TCR signaling, but the mechanisms by which they contribute to beta-selection are still poorly understood. Egr3 stimulates proliferation of beta-selected thymocytes, and Egr3-deficient mice have hypocellular thymuses, defects in proliferation, and impaired progression from double-negative 3 to double-negative 4. Surprisingly, Egr1-deficient mice exhibit normal beta-selection, indicating that the functions of Egr1 during beta-selection are likely compensated by other Egr proteins. In this study, we show that mice lacking both Egr1 and Egr3 exhibit a more severe thymic atrophy and impairment of thymocyte differentiation than mice lacking either Egr1 or Egr3. This is due to a proliferation defect and cell-autonomous increase in apoptosis, indicating that Egr1 and Egr3 cooperate to promote thymocyte survival. Microarray analysis of deregulated gene expression in immature thymocytes lacking both Egr1 and Egr3 revealed a previously unknown role for Egr proteins in the maintenance of cellular metabolism, providing new insight into the function of these molecules during T cell development.

Inhibition of cell proliferation and induction of apoptosis by N1,N11-diethylnorspermine-induced polyamine pool reduction

Reduction of cellular polyamine pools results in inhibition of cell proliferation and sometimes in induction of cell death. Reduction of cellular polyamine pools can be achieved by several strategies involving all the mechanisms of polyamine homoeostasis, i.e. biosynthesis, catabolism and transport across the cell membrane. In the present paper, we concentrate on results achieved using the polyamine analogue DENSPM (N1,N11-diethylnorspermine) on different cell lines. We discuss polyamine levels in DENSPM-treated cells in relation to effects on cell cycle kinetics and induction of apoptosis. To really understand the role of polyamines in cell cycle regulation and apoptosis, we believe it is now time to go through the vast polyamine literature in a meta-analysis-based manner. This short review does not claim to be such a study, but it is our hope to stimulate such studies in the polyamine field. Such work is especially important from the viewpoint of introducing drugs that affect polyamine homoeostasis in the treatment of various diseases such as cancer.

Role of polyamines in myocardial ischemia/reperfusion injury and their interactions with nitric oxide

Polyamines (putrescine, spermidine, and spermine) are present in all higher eukaryotic cells and are essential for cell growth, differentiation and apoptosis. Sharing common precursor with polyamines, nitric oxide (NO) is associated with myocardial ischemia/reperfusion injury by the generation of peroxynitrite. Although polyamines have been implicated in tissue ischemia injury, their metabolism and interactions with NO in myocardial ischemia/reperfusion injury have not been fully understood. In our experiment, when Langendorff perfused rat hearts were subjected to 40 min ischemia without reperfusion, both ornithine decarboxylase (ODC) and Spermidine/spermine N(1)-acetyltransferase (SSAT) activities were up-regulated and putrescine accumulated. While after reperfusion, ODC activity decreased and SSAT activity increased, resulting in putrescine accumulation and decreased spermidine and spermine. Meanwhile NO content was increased. In addition, sodium nitroprusside (SNP, a NO donor) decreased ODC activity in cardiac tissue homogenate but increased SSAT activity in a dose-dependent manner. Pre-treatment of isolated heart with N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, an inhibitor of NO synthase) increased ODC activity. Exogenous spermine (1 mM) administration prior to ischemia prevented spermine decrease, reduced cardiac myocyte necrosis and apoptosis, and promoted the recovery of cardiac function after ischemia/reperfusion. These results suggest that acute heart ischemia activates myocardial polyamine stress response characterized by increased ODC and SSAT activities and accumulation of putrescine. Ischemia/reperfusion disturbs polyamine metabolism, and the loss of spermine might be associated with NO increase and thereby influences myocardial cell viability. Exogenous spermine may protect the hearts from myocardial ischemia/reperfusion injury.

Effects of glucocorticoids on polyamine metabolism in liver and spleen of guinea pig during sensitization

Glucocorticoids are potent anti-inflammatory and immunosuppressive agents. As endogenous inhibitors of cytokine synthesis, glucocorticoids suppress immune activation and uncontrolled overproduction of cytokines, preventing tissue injury. Also, polyamine spermine is endogenous inhibitor of cytokine production (inhibiting IL-1, IL-6 and TNF synthesis). The idea of our work was to examine dexamethasone effects on the metabolism of polyamines, spermine, spermidine and putrescine and polyamine oxidase activity in liver and spleen during sensitization of guinea pigs. Sensitization was done by application of bovine serum albumin with addition of complete Freund's adjuvant. Our results indicate that polyamine amounts and polyamine oxidase activity increase during immunogenesis in liver and spleen. Dexamethasone application to sensitized and unsensitized guinea pigs causes depletion of polyamines in liver and spleen. Dexamethasone decreases polyamine oxidase activity in liver and spleen of sensitized guinea pigs, increasing at the same time PAO activity in tissues of unsensitized animals.

Dexamethasone induces cell death in insulin-secreting cells, an effect reversed by exendin-4

Glucocorticoid excess induces hyperglycemia, which may result in diabetes. The present experiments explored whether glucocorticoids trigger apoptosis in insulin-secreting cells. Treatment of mouse beta-cells or INS-1 cells with the glucocorticoid dexamethasone (0.1 micromol/l) over 4 days in cell culture increased the number of fractionated nuclei from 2 to 7 and 14%, respectively, an effect that was reversed by the glucocorticoid receptor antagonist RU486 (1 micromol/l). In INS-1 cells, dexamethasone increased the number of transferase-mediated dUTP nick-end labeling-staining positive cells, caspase-3 activity, and poly-(ADP-) ribose polymerase protein cleavage; decreased Bcl-2 transcript and protein abundance; dephosphorylated the proapoptotic protein of the Bcl-2 family (BAD) at serine155; and depolarized mitochondria. Dexamethasone increased PP-2B (calcineurin) activity, an effect abrogated by FK506. FK506 (0.1 micromol/l) and another calcineurin inhibitor, deltamethrin (1 micromol/l), attenuated dexamethasone-induced cell death. The stable glucagon-like peptide 1 analog, exendin-4 (10 nmol/l), inhibited dexamethasone-induced apoptosis in mouse beta-cells and INS-1 cells. The protective effect of exendin-4 was mimicked by forskolin (10 micromol/l) but not mimicked by guanine nucleotide exchange factor with the specific agonist 8CPT-Me-cAMP (50 micromol/l). Exendin-4 did not protect against cell death in the presence of cAMP-dependent protein kinase (PKA) inhibition by H89 (10 micromol/l) or KT5720 (5 micromol/l). In conclusion, glucocorticoid-induced apoptosis in insulin-secreting cells is accompanied by a downregulation of Bcl-2, activation of calcineurin with subsequent dephosphorylation of BAD, and mitochondrial depolarization. Exendin-4 protects against glucocorticoid-induced apoptosis, an effect mimicked by forskolin and reversed by PKA inhibitors.

Polyamines and apoptosis

The natural polyamines putrescine, spermidine and spermine are in multiple ways involved in cell growth and the maintenance of cell viability. In the course of the last 15 years more and more evidence hinted also at roles in gene regulation. It is therefore not surprising that the polyamines are involved in events inherent to genetically programmed cell death. Following inhibition of ornithine decarboxylase, a key step in polyamine biosynthesis, numerous links have been identified between the polyamines and apoptotic pathways. Examples of activation and prevention of apoptosis due to polyamine depletion are known for several cell lines. Elevation of polyamine concentrations may lead to apoptosis or to malignant transformation. These observations are discussed in the present review, together with possible mechanisms of action of the polyamines. Contradictory results and incomplete information blur the picture and complicate interpretation. Since, however, much interest is focussed at present on all aspects of programmed cell death, a considerable progress in the elucidation of polyamine functions in apoptotic signalling pathways is expected, even though enormous difficulties oppose pinpointing specific interactions of the polyamines with pro- and anti-apoptotic factors. Such situation is quite common in polyamine research.

Comparison of three cytotoxicity tests in the evaluation of the cytotoxicity of a spermine analogue on human breast cancer cell lines

Using three cytotoxicity assays, we have investigated the effect of the spermine analogue N1,N11-diethylnorspermine (DENSPM) on four human breast cancer cell lines with different known genetic lesions. Cells were seeded in 96 well plates and DENSPM was added 24 h later to give final concentrations from 0.1 to 100 microM. At 24, 48 and 72 h of treatment, the protein content was determined with a modified Lowry assay. Mitochondrial activity was determined with the AlamarBlue and MTT assays. These two assays differ with respect to where in the electron transport chain the reduction of the substrate takes place. Treatment with increasing concentrations of DENSPM resulted in differential responses in the four cell lines. There was a good of agreement between the protein content and the MTT assay showing increased negative effect with increased dose of DENSPM. The AlamarBlue assay on the other hand showed a stimulation of substrate reduction compared to control at DENSPM concentrations that were inhibitory according to the protein content and MTT assay. Thus, the data clearly show that the MTT and AlamarBlue assays are not equivalent. Importantly, the AlamarBlue assay presumably also reflects cytoplasmic reduction of the substrate through DENSPM-induced mechanisms.

Neuroprotective effects of spermine following hypoxia‐ischemia‐induced brain damage: A mechanistic study

The polyamines (spermine, putrescine, and spermidine) can have neurotoxic or neuroprotective properties in models of neurodegeneration. However, assessment in a model of hypoxia-ischemia (HI) has not been defined. Furthermore, the putative mechanisms of neuroprotection have not been elucidated. Therefore, the present study examined the effects of the polyamines in a rat pup model of HI and determined effects on key enzymes involved in inflammation, namely, nitric oxide synthase (NOS) and arginase. In addition, effects on mitochondrial function were investigated. The polyamines or saline were administered i.p. at 10mg/kg/day for 6 days post-HI. Histological assessment 7 days post-HI revealed that only spermine significantly (P<0.01) reduced infarct size from 46.14 +/- 10.4 mm3 (HI + saline) to 4.9 +/- 2.7 mm3. NOS activity was significantly increased following spermine treatment in the left (ligated) hemisphere compared with nonintervention controls (P<0.01) and HI + saline (P<0.05). In contrast, spermine decreased arginase activity compared with HI + saline but was still significantly elevated in comparison to nonintervention controls (P<0.01). Assessment of mitochondrial function in the HI + saline group, revealed significant and extensive damage to complex-I (P<0.01) and IV (P<0.001) and loss of citrate synthase activity (P<0.05). No effect on complex II-III was observed. Spermine treatment significantly prevented all these effects. This study has therefore confirmed the neuroprotective effects of spermine in vivo. However, for the first time, we have shown that this effect may, in part, be due to increased NOS activity and preservation of mitochondrial function.

On the link between Bcl-2 family proteins and glucocorticoid-induced apoptosis

As immunosuppressive agents, glucocorticoids (GCs) act by inhibiting the expression of cytokines and adhesion molecules at the transcriptional and post-transcriptional levels. In addition, GCs exerted their effects by modulating apoptosis. In view of the central role of the Bcl-2 family protein in regulating apoptosis, it was tempting to speculate that GCs modulated apoptosis through modulation of the expression of proapoptotic (Bax, Bcl-X(S), Bak) and prosurvival (Bcl-2, Bcl-X(L), Bcl-w) Bcl-2 family members. Prosurvival Bcl-2 family members in various cell types antagonized GC-induced apoptosis, thereby suggesting a causal relationship between GC-induced apoptosis and Bcl-2 proteins. The antagonism of apoptosis afforded by prosurvival Bcl-2 proteins appeared to be specific for the GCs, as Bcl-2 and Bcl-x(L) blocked GC-induced apoptosis in T cell hybridomas but did not affect Fas or activation-induced apoptosis. Although it is speculated that GC-induced apoptosis may be mediated through the activation of proapoptotic Bcl-2 proteins, recent findings suggest that this may vary depending on the conditions and the cell types used. The mechanism by which Bcl-2 inhibited GC-induced apoptosis remains uncertain. It was suggested that Bcl-2 acted on outer mitochondrial membranes to preserve their function. Bcl-2 overexpression also inhibited GC-induced apoptotic events, including caspase activation and mitochondrial dysfunction. The cross-talk of the GC receptors with other secondary messengers could lead to modulation of the activity of Bcl-2 proteins through modification of their phosphorylation status, without ruling out the possibility of a physical interaction between activated GR with Bcl-2 proteins.

Effects of exercise and steroid on skeletal muscle apoptosis in themdx mouse

Reports concerning the influence of exercise loading and steroid administration on dystrophinopathy are inconsistent. To investigate the effect of muscle exercise in Duchenne muscular dystrophy (DMD), 15 control and 15 mdx mice, an animal model of DMD, were divided into free-living (n = 6), exercise (n = 6), and immobilization (n = 3) groups. Free-living and exercise groups were further divided into steroid-treated and sham-treated groups to evaluate the effect of steroid administration. We measured apoptotic changes by in situ DNA nick-end labeling (TUNEL), DNA fragmentation assay, and Western blotting for Bcl-2 and BAX. Apoptosis was most prominent in the sham-treated exercise group, and it was significantly reduced in the steroid-treated exercise group. The steroid-treated free-living group showed a higher rate of apoptotic change than the sham-treated free-living group. Apoptosis was minimized in the free-living condition, whereas exercise loading and immobilization caused apoptotic change in this muscular dystrophy animal model. Steroid administration induced apoptosis in muscle of free-living mice, but alleviated the apoptotic damage caused by exercise loading in mdx mice. These findings suggest that steroid administration may be effective in preventing a postexercise deterioration of skeletal muscle in animal models of DMD.