Berberine Inhibits Doxorubicin-Triggered Cardiomyocyte Apoptosis via Attenuating Mitochondrial Dysfunction and Increasing Bcl-2 Expression

Cardiomyocyte apoptosis is an important event in doxorubicin (DOX)-induced cardiac injury. The aim of the present study was to investigate the protection of berberine (Ber) against DOX- triggered cardiomyocyte apoptosis in neonatal rat cardiomyocytes and rats. In neonatal rat cardiomyocytes, Ber attenuated DOX-induced cellular injury and apoptosis in a dose-dependent manner. However, Ber has no significant effect on viability of MCF-7 breast cancer cells treated with DOX. Ber reduced caspase-3 and caspase-9, but not caspase-8 activity in DOX-treated cardiomyocytes. Furthermore, Ber decreased adenosine monophosphate-activated protein kinase α (AMPKα) and p53 phosphorylation at 2 h, cytosolic cytochrome c and mitochondrial Bax levels and increased Bcl-2 level at 6 h in DOX-stimulated cardiomyocytes. Pretreatment with compound C, an AMPK inhibitor, also suppressed p53 phosphorylation and apoptosis in DOX-treated cardiomyocytes. DOX stimulation for 30 min led to a loss of mitochondrial membrane potential and a rise in the AMP/ATP ratio. Ber markedly reduced DOX-induced mitochondrial membrane potential loss and an increase in the AMP/ATP ratio at 1 h and 2 h post DOX exposure. In in vivo experiments, Ber significantly improved survival, increased stroke volume and attenuated myocardial injury in DOX-challenged rats. TUNEL and Western blot assays showed that Ber not only decreased myocardial apoptosis, caspase-3 activation, AMPKα and p53 phosphorylation, but also increased Bcl-2 expression in myocardium of rats exposed to DOX for 84 h. These findings indicate that Ber attenuates DOX-induced cardiomyocyte apoptosis via protecting mitochondria, inhibiting an increase in the AMP/ATP ratio and AMPKα phosphorylation as well as elevating Bcl-2 expression, which offer a novel mechanism responsible for protection of Ber against DOX-induced cardiomyopathy.     

Scutellarin Attenuates Doxorubicin-Induced Cardiotoxicity by Inhibiting Myocardial Fibrosis,Apoptosis and Autophagy in Rats

The anthracycline antibiotic doxorubicin (DOX) is an effective anticancer agent, but its clinical use is limited by dose-dependent cardiotoxicity. Scutellarin (SCU), a natural polyphenolic flavonoid, is used as a cardioprotective agent for infarction and ischemia-reperfusion injury. This study investigated the beneficial effect of SCU on DOX-induced chronic cardiotoxicity. Rats were injected intraperitoneally (i. p.) with DOX (2.5 mg/kg) twice a week for four weeks and then allowed to rest for two weeks to establish the chronic cardiotoxicity animal model. A dose of 10 mg/kg/day SCU was injected i. p. daily for six weeks to attenuate cardiotoxicity. SCU attenuated DOX-induced elevated oxidative stress levels and cardiac troponin T (cTnT), decreased left ventricular ejection fraction (LVEF) and fractional shortening (LVFS), elevated isovolumic relaxation time (IVRT), electrophysiology and histopathological alterations. In addition, SCU significantly attenuated DOX-induced cardiac fibrosis and reduced extracellular matrix (ECM) accumulation by inhibiting the TGF-β1/Smad2 signaling pathway. Furthermore, SCU also prevented against DOX-induced apoptosis and autophagy as evidenced by upregulation of Bcl-2, downregulation of Bax and cleaved caspase-3, inhibited the AMPK/mTOR pathway. These results revealed that the cardioprotective effect of SCU on DOX-induced chronic cardiotoxicity may be attributed to reducing oxidative stress, myocardial fibrosis, apoptosis and autophagy.     

C1qTNF-related protein-6 protects against doxorubicin-induced cardiac injury

The clinical use of doxorubicin (DOX) is limited by its toxic effect. However, there is no specific drug that can prevent DOX-related cardiac injury. C1qTNF-related protein-6 (CTRP6) is a newly identified adiponectin paralog with many protective functions on metabolism and cardiovascular diseases. However, little is known about the effect of CTRP6 on DOX-induced cardiac injury. The present study aimed to investigate whether CTRP6 could protect against DOX-related cardiotoxicity. To induce acute cardiotoxicity, the mice were intraperitoneally injected with a single dose of DOX (15 mg/kg). Cardiomyocyte-specific CTRP6 overexpression was achieved using an adenoassociated virus system at 4 weeks before DOX injection. The data in our study demonstrated that CTRP6 messenger RNA and protein expression were decreased in DOX-treated hearts. CTRP6 attenuated cardiac atrophy induced by DOX injection and inhibited cardiac apoptosis and improved cardiac function in vivo. CTRP6 also promoted the activation of protein kinase B (AKT/PKB) signaling pathway in DOX-treated mice. CTRP6 prevented cardiomyocytes from DOX-induced apoptosis and activated the AKT pathway in vitro. CTRP6 lost its protection against DOX-induced cardiac injury in mice with AKT inhibition. In conclusion, CTRP6 protected the heart from DOX-cardiotoxicity and improves cardiac function via activation of the AKT signaling pathway.     

Attenuation of doxorubicin-induced cardiotoxicity and genotoxicity by an indole-based natural compound 3,3′-diindolylmethane (DIM) through activation of Nrf2/ARE signaling pathways and inhibiting apoptosis

The most crucial complication related to doxorubicin (DOX) therapy is nonspecific cytotoxic effect on healthy normal cells. The clinical use of this broad-spectrum chemotherapeutic agent is restricted due to development of severe form of cardiotoxicity, myelosuppression, and genotoxicity which interfere with therapeutic schedule, compromise treatment outcome and may lead to secondary malignancy. 3,3′-diindolylmethane (DIM) is a naturally occurring plant alkaloid formed by the hydrolysis of indolylmethyl glucosinolate (glucobrassicin). Therefore, the present study was undertaken to investigate the protective role of DIM against DOX-induced toxicity in mice. DOX was administered (5?mg/kg b.w., i.p.) and DIM was administered (25?mg/kg b.w., p.o.) in concomitant and 15 days pretreatment schedule. Results showed that DIM significantly attenuated DOX-induced oxidative stress in the cardiac tissues by reducing the levels of free radicals and lipid peroxidation, and by enhancing the level of glutathione (reduced) and the activity of antioxidant enzymes. The chemoprotective potential of DIM was confirmed by histopathological evaluation of heart and bone marrow niche. Moreover, DIM considerably mitigated DOX-induced clastogenicity, DNA damage, apoptosis, and myeloid hyperplasia in bone marrow niche. In addition, oral administration of DIM significantly (p?相似文献   

Naringin and Sertraline Ameliorate Doxorubicin-Induced Behavioral Deficits Through Modulation of Serotonin Level and Mitochondrial Complexes Protection Pathway in Rat Hippocampus

The present study was designed to investigate the neuroprotective effect of naringin (NR) alone as well as its combination with sertraline (SRT) against doxorubicin (DOX)-induced neurobehavioral and neurochemical anomalies. DOX (15 mg/kg; i.p.) administration caused behavioral alterations, oxidative stress, neuroinflammation, mitochondrial dysfunction and monoamines alteration in male Wistar rats. NR (50 and 100 mg/kg; i.p.) and SRT (5 mg/kg; i.p.) treatment significantly attenuated DOX-induced anxiety and depressive-like behavior as evident from elevated plus maze (EPM) and modified forced swimming test (mFST), respectively. NR treatment significantly attenuated DOX-induced raised plasma corticosterone (CORT), tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) levels in the hippocampus (HC). Furthermore, we found that combination of NR and SRT regimen ameliorated DOX-induced behavioral anomalies through modulation of the 5-HT level and mitochondrial complexes protection pathway along with alleviation of oxidative stress in the HC region. Therefore, NR treatment alone or in combination with SRT could be beneficial against DOX-induced neurotoxicity.     

Suppression by metallothionein of doxorubicin-induced cardiomyocyte apoptosis through inhibition of p38 mitogen-activated protein kinases

Cardiomyopathy induced by doxorubicin (DOX) has long been a major impediment of clinical applications of this effective anticancer agent. Previous studies have shown that cardiac-specific metallothionein (MT)-overexpressing transgenic mice are highly resistant to DOX-induced cardiotoxicity. To investigate cellular and molecular mechanisms by which MT participates in this cytoprotection, transgenic mice containing high levels of cardiac MT and non-transgenic controls were treated intraperitoneally with DOX at a single dose of 15 mg/kg and sacrificed on the 4th day after treatment. Myocardial apoptosis was detected by a terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assay and confirmed by electron microscopy of immunogold staining of apoptotic nuclei. Dual staining of cardiac alpha-sarcomeric actin using an immunohistochemical method further identified apoptotic myocytes. Apoptosis was significantly inhibited in the transgenic myocardium. The anti-apoptotic effect of MT was further revealed in primary cultures of neonatal mouse cardiomyocytes. Furthermore, DOX activated p38 mitogen-activated protein kinase (MAPK), which was critically involved in the apoptotic process, as demonstrated by inhibition of DOX-induced apoptosis by a p38-specific inhibitor, SB203580. Both DOX-induced p38 MAPK activation and apoptosis were dramatically inhibited in the transgenic cardiomyocytes. The results thus demonstrate that DOX induces apoptosis in cardiomyocytes both in vivo and in vitro and MT suppresses this effect through at least in part inhibition of p38 MAPK activation.     

p53 Regulates oxidative stress-mediated retrograde signaling: a novel mechanism for chemotherapy-induced cardiac injury

The side effects of cancer therapy on normal tissues limit the success of therapy. Generation of reactive oxygen species (ROS) has been implicated for numerous chemotherapeutic agents including doxorubicin (DOX), a potent cancer chemotherapeutic drug. The production of ROS by DOX has been linked to DNA damage, nuclear translocation of p53, and mitochondrial injury; however, the causal relationship and molecular mechanisms underlying these events are unknown. The present study used wild-type (WT) and p53 homozygous knock-out (p53(-/-)) mice to investigate the role of p53 in the crosstalk between mitochondria and nucleus. Injecting mice with DOX (20 mg/kg) causes oxidative stress in cardiac tissue as demonstrated by immunogold analysis of the levels of 4-hydroxy-2'-nonenal (4HNE)-adducted protein, a lipid peroxidation product bound to proteins. 4HNE levels increased in both nuclei and mitochondria of WT DOX-treated mice but only in nuclei of DOX-treated p53((-/-)) mice, implicating a critical role for p53 in causing DOX-induced oxidative stress in mitochondria. The stress-activated protein c-Jun amino-terminal kinase (JNKs) was activated in response to increased 4HNE in WT mice but not p53((-/-)) mice receiving DOX treatment, as determined by co-immunoprecipitation of HNE and pJNK. The activation of JNK in DOX treated WT mice was accompanied by Bcl-2 dissociation from Beclin in mitochondria and induction of type II cell death (autophagic cell death), as evidenced by an increase in LC3-I/LC-3-II ratio and γ-H2AX, a biomarker for DNA damage. The absence of p53 significantly reduces mitochondrial injury, assessed by quantitative morphology, and decline in cardiac function, assessed by left ventricular ejection fraction and fraction shortening. These results demonstrate that p53 plays a critical role in DOX-induced cardiac toxicity, in part, by the induction of oxidative stress mediated retrograde signaling.     

Impact of peroxisome proliferator activated receptor agonist drugs in a model of nephrotoxicity in rats

Doxorubicin (DOX) is one of the basic anticancer drugs, nonetheless its use is restricted due to noxious side effects. Kidney failure is one of the main side effects that restrict its medical use. The current study assessed the nephroprotective effects of fenofibrate and pioglitazone against the renal injury induced by doxorubicin in rats and illustrated the probable mechanisms underlying these protective effects. For this purpose, Male Sprague–Dawley rats weighing (200–230 g) were allocated into seven groups treated for 15 days as following: control (50% corn oil + 50% DMSO p.o), fenofibrate (100 mg/kg p.o) and pioglitazone (10 mg/kg p.o) as well as four groups of DOX (15 mg/kg i.p on 11th day). DOX groups included DOX alone and DOX with protective drugs fenofibrate, pioglitazone or both of them. As a result of doxorubicin nephrotoxicity; serum creatinine and blood urea nitrogen were remarkably elevated. Moreover, renal glutathione was significantly reduced while tissue lipid peroxidation malondialdehyde, tumor necrosis factor-α, nuclear factor-kappa B p65 (NF-κB p65), interleukin-1β, p38 mitogen activated protein kinase (p38-MAPK) and caspase-3 (Casp-3) were significantly augmented. Treatment with fenofibrate and pioglitazone either alone or in combination markedly attenuated DOX-induced injury by suppression of oxidative stress, inflammation and apoptosis. The above-mentioned biochemical markers were affirmed by histological assessment. In conclusion, fenofibrate, pioglitazone, and their combination possess potential prophylactic effects against doxorubicin-induced renal injury through modulation of p38-MAPK/NF-κB p65 pathway with superiority to the combination.     

BRCA2 protein deficiency exaggerates doxorubicin-induced cardiomyocyte apoptosis and cardiac failure

The tumor suppressor breast cancer susceptibility gene 2 (BRCA2) plays an important role in the repair of DNA damage, and loss of BRCA2 predisposes carriers to breast and ovarian cancers. Doxorubicin (DOX) remains the cornerstone of chemotherapy in such individuals. However, it is often associated with cardiac failure, which once manifests carries a poor prognosis. Because BRCA2 regulates genome-wide stability and facilitates DNA damage repair, we hypothesized that loss of BRCA2 may increase susceptibility to DOX-induced cardiac failure. To this aim, we generated cardiomyocyte-specific BRCA2 knock-out (CM-BRCA2(-/-)) mice using the Cre-loxP technology and evaluated their basal and post-DOX treatment phenotypes. Although CM-BRCA2(-/-) mice exhibited no basal cardiac phenotype, DOX treatment resulted in markedly greater cardiac dysfunction and mortality in CM-BRCA2(-/-) mice compared with control mice. Apoptosis in left ventricular (LV) sections from CM-BRCA2(-/-) mice compared with that in corresponding sections from wild-type (WT) littermate controls was also significantly enhanced after DOX treatment. Microscopic examination of LV sections from DOX-treated CM-BRCA2(-/-) mice revealed a greater number of DNA double-stranded breaks and the absence of RAD51 focus formation, an essential marker of double-stranded break repair. The levels of p53 and the p53-related proapoptotic proteins p53-up-regulated modulator of apoptosis (PUMA) and Bax were significantly increased in samples from CM-BRCA2(-/-) mice. This corresponded with increased Bax to Bcl-2 ratios and elevated cytochrome c release in the LV sections of DOX-treated CM-BRCA2(-/-) mice. Taken together, these data suggest a critical and previously unrecognized role of BRCA2 as a gatekeeper of DOX-induced cardiomyocyte apoptosis and susceptibility to overt cardiac failure. Pharmacogenomic studies evaluating cardiac function in BRCA2 mutation carriers treated with doxorubicin are encouraged.     

Hsp70 regulates the doxorubicin-mediated heart failure in Hsp70-transgenic mice

The aim of this study was to investigate the potential protective effect of the Hsp70 protein in the cardiac dysfunction induced by doxorubicin (DOX) and the mechanisms of its action. For this purpose, we used both wild-type mice (F1/F1) and Hsp70-transgenic mice (Tg/Tg) overexpressing human HSP70. Both types were subjected to chronic DOX administration (3 mg/kg intraperitoneally every week for 10 weeks, with an interval from weeks 4 to 6). Primary cell cultures isolated from embryos of these mice were also studied. During DOX administration, the mortality rate as well as weight reduction were lower in Tg/Tg compared to F1/F1 mice (P < 0.05). In vivo cardiac function assessment by transthoracic echocardiography showed that the reduction in left ventricular systolic function observed after DOX administration was lower in Tg/Tg mice (P < 0.05). The study in primary embryonic cell lines showed that the apoptosis after incubation with DOX was reduced in cells overexpressing Hsp70 (Tg/Tg), while the apoptotic pathway that was activated by DOX administration involved activated protein factors such as p53, Bax, caspase-9, caspase-3, and PARP-1. In myocardial protein extracts from identical mice with DOX-induced heart failure, the particular activated apoptotic pathway was confirmed, while the presence of Hsp70 appeared to inhibit the apoptotic pathway upstream of the p53 activation. Our results, in this DOX-induced heart failure model, indicate that Hsp70 overexpression in Tg/Tg transgenic mice provides protection from myocardial damage via an Hsp70-block in p53 activation, thus reducing the subsequent apoptotic mechanism.     

Beneficial role of aminoguanidine on acute cardiomyopathy related to doxorubicin-treatment

Doxorubicin (DOX) is a broad-spectrum anthracycline antibiotic that has cardiotoxicity as a major side effect. One mechanism of this toxicity is believed to involve the reactive oxygen radical species (ROS); these agents likely account for the pathophysiology of DOX-induced cardiomyopathy. Aminoguanidine (AG) is an effective antioxidant and free radical scavenger which has long been known to protect against ROS formation. We investigated the effects of AG on DOX-induced changes in thiobarbituric acid reactive substances (TBARS) and reduced glutathione (GSH) content. The rats were divided into four groups:1) Control; 2) DOX group; injected intraperitoneally (i.p.) with DOX 20 mg/kg in a single dose 3) AG-treated group; injected i.p. in single dose of 20 mg/kg DOX plus 100 mg/kg AG 1 h before the DOX for 3 days, 4) AG group; injected i.p. with AG 100 mg/kg for 3 days. DOX administration to control rats increased TBARS and decreased GSH levels. AG administration before DOX injection caused significant decrease in TBARS and increase in GSH levels in the heart tissue when compared with DOX only. Morphological changes, including severe myocardial fibrosis and inflammatory cell infiltration were clearly observed in the DOX-treated heart. AG reversed the DOX-induced heart damage. Therefore AG could protect the heart tissue against free radical injury. The application of AG during cancer chemotherapy may attenuate tissue damage and improve the therapeutic index of DOX.     

L-carnitine attenuates doxorubicin-induced lipid peroxidation in rats.

Doxorubicin (DOX) was administered intraperitoneally to rats in six equal, 2.5 mg/kg doses over a 2-week period with or without L-carnitine. Injury was monitored by echocardiography, release of myosin light chain-1 (MLC-1), and by measurement of aldehydic lipid peroxidation products. General observation revealed that DOX alone caused more ascites than DOX plus L-carnitine. Animals sacrificed 2 h after the sixth dose had significantly higher aldehyde concentrations than 2 h after a single dose of DOX. Aldehydes in plasma and heart remained elevated for 3 weeks after the final dose of DOX, whereas L-carnitine prevented or attenuated the DOX-induced increases in lipid peroxidation. The increase in MLC-1 2 h after the sixth dose of DOX was greater than after a single dose, suggesting cumulative damage. Echocardiography did not detect either early injury or the protective effects of L-carnitine. These data indicate that lipid peroxidation following DOX occurs early, and parallels the cumulative characteristics of DOX-induced cardiotoxicity. The protective effects of L-carnitine may be due to improved cardiac energy metabolism and reduced lipid peroxidation.     

Herceptin, a recombinant humanized anti-ERBB2 monoclonal antibody, induces cardiomyocyte death

P53 protein levels are elevated by trastuzumab and the biologically similar rat ERBB2/HER2/NEU antibody; and that this coincides with enhanced apoptosis, increased cleaved caspase-3 levels and diminished cardiac function. We also demonstrate that MDM2 may be a regulatory target of anti-ERBB2 thereby implicating the MDM2/p53 axis as a potential molecular component for the undesirable cardiac outcomes noted with trastuzumab. Finally, we show that these MDM2/p53-mediated events are independent of both the ERK1/2 and Akt systems. In conclusion, our findings suggest that the adverse cardiac events observed with trastuzumab may stem from its negative regulation of MDM2 events which impairs p53 degradation resultantly promoting apoptosis leading to cardiac dysfunction. These observations may have important therapeutic implications since they suggest that anticancer agents that inhibit MDM2 and its downstream actions may curb tumor progression at the expense of increasing cardiac stress.     

Nutlin-3 protects kidney cells during cisplatin therapy by suppressing Bax/Bak activation

Nutlins, the newly developed small molecule antagonists of MDM2, activate p53 and induce apoptosis in cancer cells, offering a novel strategy of chemotherapy. Recent studies have further suggested synergistic effects of nutlins with other chemotherapeutic drugs. However, it is unclear whether nutlins increase or decrease the side effects of these drugs in normal non-malignant cells or tissues. Cisplatin is a widely used chemotherapy drug, which has a major side effect of kidney injury. Here we show that Nutlin-3 protected kidney cells against cisplatin-induced apoptosis. The cytoprotective effects of Nutlin-3 were not related to its regulation of p53 or consequent gene expression during cisplatin treatment. Moreover, the protective effects were shown in MDM2-, MDM4-, or p53-deficient cells. On the other hand, Nutlin-3 suppressed mitochondrial events of apoptosis during cisplatin incubation, including Bax activation and cytochrome c release. Nutlin-3 attenuated cisplatin-induced oligomerization of Bax and Bak but not their interactions with Bcl-XL. In isolated mitochondria, Nutlin-3 inhibited cytochrome c release induced by Ca2+, Bim peptide, and recombinant tBid. Importantly, it blocked both Bax and Bak oligomerization under these conditions. Together, the results have uncovered a new pharmacological function of nutlins, i.e. suppression of Bax and Bak, two critical mediators of apoptosis.     

Multiple actions of pifithrin-alpha on doxorubicin-induced apoptosis in rat myoblastic H9c2 cells

Doxorubicin (Dox) is a chemotherapeutic agent that causes significant cardiotoxicity. We showed previously that Dox activates p53 and induces apoptosis in mouse hearts. This study was designed to elucidate the molecular events that lead to p53 stabilization, to examine the pathways involved in Dox-induced apoptosis, and to evaluate the effectiveness of pifithrin-alpha (PFT-alpha), a p53 inhibitor, in blocking apoptosis of rat H9c2 myoblasts. H9c2 cells that were exposed to 5 muM Dox had elevated levels of p53 and phosphorylated p53 at Ser15. Dox also triggered a transient activation of p38, p42/p44ERK, and p46/p54JNK MAP kinases. Caspase activity assays and Western blot analysis showed that H9c2 cells treated with Dox for 16 h had marked increase in the levels of caspases-2, -3, -8, -9, -12, Fas, and cleaved poly(ADP ribose) polymerase (PARP). There was a concomitant increase in p53 binding activity, cytochrome c release, and apoptosis. These results suggest that Dox can trigger intrinsic, extrinsic, and endoplasmic reticulum-associated apoptotic pathways. Pretreatment of cells with PFT-alpha followed by Dox administration attenuated Dox-induced increases in p53 levels and p53 binding activity and partially blocked the activation of p46/p54JNK and p42/p44ERK. PFT-alpha also led to decreased levels of caspases-2, -3, -8, -9, -12, Fas, PARP, cytochrome c release, and apoptosis. Our results suggest that p53 stabilization is a focal point of Dox-induced apoptosis and that PFT-alpha interferes with multiple steps of Dox-induced apoptosis.     

Nitric oxide and oxidative stress in brain and heart of normal rats treated with doxorubicin: role of aminoguanidine

Doxorubicin (DOX) is a potent antitumor antibiotic drug known to cause severe cardiac toxicity. Moreover, its adverse effects were found to be extended to the cerebral tissue. Several mechanisms for this toxicity have been ascribed. Currently, one of the most accepted mechanisms is through free radicals; however, the exact role of nitric oxide (NO) is still unclear. Accordingly, a NO-synthase inhibitor with some antioxidant property, aminoguanidine (AG), was selected to examine its potential protective effect against DOX-induced toxicity. Male Wistar albino rats (150-200 g) were allocated into a normal control group, DOX-induced toxicity group, and DOX + AG-treated group. DOX was injected i.p. at a dose of 10 mg/kg divided into four equal injections over a period of 2 weeks. AG was injected i.p. at a dose of 100 mg/kg 1 h before each DOX injection. The animals were sacrificed 24 h after the last DOX injection and the following parameters were measured: serum lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) activities, cardiac and cerebral contents of malondialdehyde (MDA), conjugated diene (CD), glutathione (GSH), NO, and cytosolic calcium, as well as superoxide dismutase (SOD) and glutathione peroxidase (GSHP(X)) activities. Cardiotoxicity was manifested by a marked increase in serum LDH and CPK in addition to the sharp increase in MDA reaching eightfolds the basal level. This was accompanied by significant increase in CD, NO, cytosolic calcium, SOD, and GSHP(X) content/activity by 69, 85, 76, 125, and 41% respectively as compared to normal control. On the other hand, GSH was significantly depressed. In brain, only significant increase in MDA and GSHP(X) and decrease in GSH were obtained but to a lesser extent than the cardiac tissue. AG treatment failed to prevent the excessive release of cardiac enzymes; however, it alleviated the adverse effects of DOX in heart. AG administration resulted in marked decrease in the elevated levels of MDA, NO, SOD, and GSHP(X), however, MDA level was still pathological. The altered parameters in brain were restored by AG. It is concluded that, AG could not provide complete protection against DOX-induced toxicity. Therefore, it is recommended that, maintenance of the endogenous antioxidant, GSH, and regulation of calcium homeostasis must be considered, rather than NO formation, to guard against DOX-induced toxicity.     

MDM2 is required for suppression of apoptosis by activated Akt1 in salivary acinar cells

Chronic damage to the salivary glands is a common side effect following head and neck irradiation. It is hypothesized that irreversible damage to the salivary glands occurs immediately after radiation; however, previous studies with rat models have not shown a causal role for apoptosis in radiation-induced injury. We report that etoposide and gamma irradiation induce apoptosis of salivary acinar cells from FVB control mice in vitro and in vivo; however, apoptosis is reduced in transgenic mice expressing a constitutively activated mutant of Akt1 (myr-Akt1). Expression of myr-Akt1 in the salivary glands results in a significant reduction in phosphorylation of p53 at serine(18), total p53 protein accumulation, and p21(WAF1) or Bax mRNA following etoposide or gamma irradiation of primary salivary acinar cells. The reduced level of p53 protein in myr-Akt1 salivary glands corresponds with an increase in MDM2 phosphorylation in vivo, suggesting that the Akt/MDM2/p53 pathway is responsible for suppression of apoptosis. Dominant-negative Akt blocked phosphorylation of MDM2 in salivary acinar cells from myr-Akt1 transgenic mice. Reduction of MDM2 levels in myr-Akt1 primary salivary acinar cells with small interfering RNA increases the levels of p53 protein and renders these cells susceptible to etoposide-induced apoptosis in spite of the presence of activated Akt1. These results indicate that MDM2 is a critical substrate of activated Akt1 in the suppression of p53-dependent apoptosis in vivo.