Protective effect of casuarinin against glutamate-induced apoptosis in HT22 cells through inhibition of oxidative stress-mediated MAPK phosphorylation

Glutamate is the major excitatory neurotransmitter in the central nervous system and is involved in oxidative stress during neurodegeneration. In the present study, casuarinin prevented glutamate-induced HT22 murine hippocampal neuronal cell death by inhibiting intracellular reactive oxygen species (ROS) production. Moreover, casuarinin reduced chromatin condensation and annexin-V-positive cell production induced by glutamate. We also confirmed the underlying protective mechanism of casuarinin against glutamate-induced neurotoxicity. Glutamate markedly increased the phosphorylation of extracellular signal regulated kinase (ERK)-1/2 and p38, which are crucial in oxidative stress-mediated neuronal cell death. Conversely, treatment with casuarinin diminished the phosphorylation of ERK1/2 and P38. In conclusion, the results of this study suggest that casuarinin, obtained from natural products, acts as potent neuroprotective agent by suppressing glutamate-mediated apoptosis through the inhibition of ROS production and activation of the mitogen activated protein kinase (MAPK) pathway. Thus, casuarinin can be a potential therapeutic agent in the treatment of neurodegenerative diseases.     

Chebulinic acid attenuates glutamate-induced HT22 cell death by inhibiting oxidative stress,calcium influx and MAPKs phosphorylation

Glutamate-induced excitotoxicity and oxidative stress is a major causative factor in neuronal cell death in acute brain injuries and chronic neurodegenerative diseases. The prevention of oxidative stress is a potential therapeutic strategy. Therefore, in the present study, we aimed to examine a potential therapeutic agent and its protective mechanism against glutamate-mediated cell death. We first found that chebulinic acid isolated from extracts of the fruit of Terminalia chebula prevented glutamate-induced HT22 cell death. Chebulinic acid significantly reduced intracellular reactive oxygen species (ROS) production and Ca²⁺ influx induced by glutamate. We further demonstrated that chebulinic acid significantly decreased the phosphorylation of mitogen-activated protein kinases (MAPKs), including ERK1/2, JNK, and p38, as well as inhibiting pro-apoptotic Bax and increasing anti-apoptotic Bcl-2 protein expression. Moreover, we demonstrated that chebulinic acid significantly reduced the apoptosis induced by glutamate in HT22 cells. In conclusion, our results in this study suggest that chebulinic acid is a potent protectant against glutamate-induced neuronal cell death via inhibiting ROS production, Ca²⁺ influx, and phosphorylation of MAPKs, as well as reducing the ratio of Bax to Bcl-2, which contribute to oxidative stress-mediated neuronal cell death.     

Proteomic analysis of glutamate-induced toxicity in HT22 cells

In the present study, we have investigated the proteome changes associated with glutamate-induced HT22 cell death, a model system to study oxidative stress-mediated toxicity. Among a number of HT22 proteins exhibiting altered expression, several molecular chaperones demonstrated substantial changes. For example, the levels of Hsp90 and Hsp70 decreased as cell death progressed whereas that of Hsp60 increased dramatically. Interestingly, cytosolic Hsp60 increased more prominently than mitochondrial Hsp60. Concomitantly, the accumulation of poly-ubiquitylated proteins and differential regulation of the peptidase activities and the subunits of 26S proteasomes were observed in glutamate-treated HT22 cells. Our findings that the molecular chaperones and the ubiquitin-proteasome system undergo changes during glutamate-induced HT22 cell death may suggest the importance of a protein quality control system in oxidative damage-mediated toxicity.     

Activation of autophagy during glutamate-induced HT22 cell death

Recent evidence suggests that autophagy plays a role in oxidative injury-induced cell death. Here we examined whether glutamate-mediated oxidative toxicity induces autophagy in murine hippocampal HT22 cells and if autophagy induction affects the molecular events associated with cell death. Markers for autophagy induction including LC3 conversion, suppression of mTOR pathway, and GFP-LC3 dot formation were enhanced by glutamate treatment. By contrast, autophagy inhibition blocked glutamate-induced LC3 conversion and consequently reduced cell death. Activation of ERK1/2, a hallmark of glutamate-induced cytotoxicity, was also decreased by autophagy inhibition. Interestingly, autophagy inhibition also affected the expression of chaperones including Hsp60 and Hsp70, which are differentially regulated during HT22 cell death. Conversely, knock-down of Hsp60 greatly decreased LC3 conversion. Together these results suggest that glutamate-induced cytotoxicity involves autophagic cell death and chaperones may play a role in this process.     

生长分化因子11对甲醛诱导的海马神经细胞凋亡的影响

目的探讨生长分化因子11（GDF11）对甲醛诱导的海马神经（HT22）细胞毒性的影响。 方法把HT22细胞分为对照组（细胞未做任何处理）、甲醛组（50、100、200 μmol/ L甲醛处理细胞）和GDF11+甲醛组（GDF11转染细胞后用100 μmol/L甲醛处理）。细胞计数试剂盒（CCK8）法检测HT22细胞的活力;蛋白免疫印迹法检测HT22细胞凋亡相关蛋白Bax以及Bcl-2的变化;caspase-3活性检测试剂盒检测HT22细胞内caspase-3活性;DCFDA染色流式细胞仪检测HT22细胞中活性氧（ROS）水平。三组间比较采用单因素方差分析,组间两两比较采用LSD-t检验。 结果与对照组比较,甲醛组HT22细胞活力（92.23±0.20比56.12±0.61）和Bcl-2蛋白表达（220.32±2.21比150.25±0.31）水平均降低,差异具有统计学意义（P均< 0.05）;而caspase-3活性（95.36±1.74比190.17±2.14）、Bax蛋白表达（132.19±1.21比150.17±1.06）和ROS水平（1099.32±75.47比2802.17±126.49）均升高,差异具有统计学意义（P均< 0.05）。GDF11转染HT22细胞后,与甲醛组比较,GDF11+甲醛组HT22细胞活力升高（56.12±0.61比83.11±1.64）,Bax蛋白表达（270.03±0.17比150.17±1.06）降低,Bcl-2蛋白表达（150.25±0.31比187.34±1.52）升高,caspase-3活性降低（190.17±2.14比105.31±4.12）和ROS水平降低（2802.17±126.49比1305.36±68.45）,差异具有统计学意义（P均< 0.05）。 结论GDF11能够逆转甲醛对HT22细胞凋亡的诱导作用以及降低甲醛对HT22细胞ROS水平的增加作用,此机制对防治甲醛的神经毒性具有重要意义。     

Dual cell protective mechanisms activated by differing levels of oxidative stress in HT22 murine hippocampal cells

Oxidative stress is recognized as one of the pathogenic mechanisms involved in neurodegenerative disease. However, recent evidence has suggested that regulation of cellular fate in response to oxidative stress appears to be dependent on the stress levels. In this study, using HT22 cells, we attempted to understand how an alteration in the oxidative stress levels would influence neuronal cell fate. HT22 cell viability was reduced with exposure to high levels of oxidative stress, whereas, low levels of oxidative stress promoted cell survival. Erk1/2 activation induced by a low level of oxidative stress played a role in this cell protective effect. Intriguingly, subtoxic level of H₂O₂ induced expression of a growth factor, progranulin (PGRN), and exogenous PGRN pretreatment attenuated HT22 cell death induced by high concentrations of H₂O₂ in Erk1/2-dependent manner. Together, our study indicates that two different cell protection mechanisms are activated by differing levels of oxidative stress in HT22 cells.     

Functionalized acridin-9-yl phenylamines protected neuronal HT22 cells from glutamate-induced cell death by reducing intracellular levels of free radical species

The in vitro neuronal cell death model based on the HT22 mouse hippocampal cell model is a convenient means of identifying compounds that protect against oxidative glutamate toxicity which plays a role in the development of certain neurodegenerative diseases. Functionalized acridin-9-yl-phenylamines were found to protect HT22 cells from glutamate challenge at submicromolar concentrations. The Aryl¹-NH-Aryl² scaffold that is embedded in these compounds was the minimal pharmacophore for activity. Mechanistically, protection against the endogenous oxidative stress generated by glutamate did not involve up-regulation of glutathione levels but attenuation of the late stage increases in mitochondrial ROS and intracellular calcium levels. The NH residue in the pharmacophore played a crucial role in this regard as seen from the loss of neuroprotection when it was structurally modified or replaced. That the same NH was essential for radical scavenging in cell-free and cell-based systems pointed to an antioxidant basis for the neuroprotective activities of these compounds.     

Necrostatin-1 protects against glutamate-induced glutathione depletion and caspase-independent cell death in HT-22 cells

Glutamate, a major excitatory neurotransmitter in the CNS, plays a critical role in neurological disorders such as stroke and Parkinson's disease. Recent studies have suggested that glutamate excess can result in a form of cell death called glutamate-induced oxytosis. In this study, we explore the protective effects of necrostatin-1 (Nec-1), an inhibitor of necroptosis, on glutamate-induced oxytosis. We show that Nec-1 inhibits glutamate-induced oxytosis in HT-22 cells through a mechanism that involves an increase in cellular glutathione (GSH) levels as well as a reduction in reactive oxygen species production. However, Nec-1 had no protective effect on free radical-induced cell death caused by hydrogen peroxide or menadione, which suggests that Nec-1 has no antioxidant effects. Interestingly, the protective effect of Nec-1 was still observed when cellular GSH was depleted by buthionine sulfoximine, a specific and irreversible inhibitor of glutamylcysteine synthetase. Our study further demonstrates that Nec-1 significantly blocks the nuclear translocation of apoptosis-inducing factor (a marker of caspase-independent programmed cell death ) and inhibits the integration of Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (a pro-death member of the Bcl-2 family) into the mitochondrial membrane. Taken together, these results demonstrate for the first time that Nec-1 prevents glutamate-induced oxytosis in HT-22 cells through GSH related as well as apoptosis-inducing factor and Bcl-2/adenovirus E1B 19 kDa-interacting protein 3-related pathways.     

Distinct nuclear factor-kappaB/Rel proteins have opposing modulatory effects in glutamate-induced cell death in HT22 cells

Members of the nuclear factor-κB (NF-κB)/Rel family (p50, p52, p65 (RelA), RelB and c-Rel) is sequestered in the cytoplasm through its tight association with the inhibitor of NF-κB (IκB). NF-κB has been shown to function as key regulators of either cell death or survival in neurons after activation of the cells by various extracellular signals. In the study presented here, we investigated whether the selective activation of diverse NF-κB/Rel family members in HT22 cells might lead to distinct effects on glutamate-induced cell death. Exposing HT22 cells to glutamate, which blocks cystine uptake into the cells via inhibition of the glutamate-cystine antiporter, resulted in a transient activation of IκB and NF-κB/Rel and caused delayed cell death. Aspirin, which has been shown to block phosphorylation of the IκB component of the cytoplasmic NF-κB complex, significantly suppressed glutamate-induced cell death, whereas the NF-κB decoy oligonucleotide potentiated it. The inhibition of NF-κB/Rel protein expression by antisense oligonucleotides showed that p65 is involved in glutamate-mediated cell death, whereas p50 is involved in inhibitory pathways of the cell death. These findings suggest that in HT22 cells, the balance between promoting and presenting cell death to glutamate-induced oxidative stress relies on the activation of distinct NF-κB proteins.     

Indirubin derivatives protect against endoplasmic reticulum stress-induced cytotoxicity and down-regulate CHOP levels in HT22 cells

Indirubin and its derivatives have been reported to exhibit anti-cancer and anti-inflammatory activities. Recently, some of its derived analogs have been shown to have neuroprotective potential. Endoplasmic reticulum (ER) stress has been demonstrated to contribute to the pathogenesis of various neurodegenerative diseases, whereas the effects of indirubin derivatives on ER stress-induced cell death have not been addressed. In the present study, a series of 44 derivatives of indirubin was prepared to search for a novel class of neuroprotective agents against ER stress-induced neuronal death. The MTT reduction assay indicated that tunicamycin (TM), an inducer of ER stress, significantly decreased the viability of hippocampal neuronal HT22 cells. Among the compounds tested, eight showed significant inhibitory activity against TM-induced cell death. Western blot analysis showed that application of these analogs to the cells simultaneously with TM reduced the TM-induced expression of CHOP, an established mediator of ER stress. Our results suggest that the preventive effect of these indirubin derivatives against ER stress-induced neuronal death may be due, at least in part, to attenuation of the CHOP-dependent signaling system.     

Glutamate levels control HT22 murine hippocampal cell death by regulating biphasic patterns of Erk1/2 activation: role of metabolic glutamate receptor 5

Extracellular glutamate concentration is a critical determinant of neuronal cell fate. We recently demonstrated that HT22 murine hippocampal cell viability was reduced by exposure to high concentrations of glutamate, whereas low concentrations promoted cell survival. Extracellular signal-regulated kinase (Erk)1/2 activation by glutamate is important for both glutamate-induced cell death and survival. In this study, we investigated the role of glutamate-induced or hydrogen peroxide (H₂O₂)-induced Erk1/2 activation in HT22 cell fate determination. Glutamate and H₂O₂ treatment similarly induced early (<1 h) Erk1/2 phosphorylation regardless of concentration. On the other hand, persistent Erk1/2 phosphorylation (16–24 h) was observed only in the presence of excess glutamate. Only the latter contributed to glutamate-induced cell death, which involved metabolic glutamate receptor 5. Our findings suggest that glutamate concentration modulates two distinct phases of Erk1/2 activation, which can explain the glutamate concentration-dependent determination of HT22 cell fate.     

α-Synuclein induced cell death in mouse hippocampal (HT22) cells is mediated by nitric oxide-dependent activation of caspase-3

Our previous studies indicated that exogenous α-synuclein (ASN) activates neuronal nitric oxide (NO) synthase (nNOS) in rat brain slices. The present study, carried out on immortalized hippocampal neuronal cells (HT22), was designed to extend the previous results by showing the molecular pathway of NO-mediated cell death induced by exogenous ASN. Extracellular ASN (10 μM) was found to stimulate nitric oxide synthase (NOS) and increase caspase-3 activity in HT22 cells, leading to poly(ADP-ribose) polymerase (PARP-1) cleavage. The inhibitor of Ca²⁺-dependent NOS (N-nitro-l-arginine, 100 μM) prevented ASN-evoked caspase-3 activation and PARP-1 degradation. ASN exposure resulted in apoptotic death of HT22 cells and this effect was reversed by inhibition of NO synthesis and caspase-3 activity. Our results demonstrated that extracellular ASN induces neuronal cell death by NO-mediated caspase-3 activation.     

Bacterial GroEL-like heat shock protein 60 protects epithelial cells from stress-induced death through activation of ERK and inhibition of caspase 3

Bacterial heat shock proteins (hsps) can have various effects on human cells. We investigated whether bacterial hsp60s can protect epithelial cells from cell death by affecting the mitogen-activated protein kinase (MAPK) signal pathways. Cell protection was studied by adding bacterial hsp60s to skin keratinocyte cultures (HaCaT cell line) before UV radiation. The results show that hsp60 significantly protected against UV radiation-induced cell death. Effects of UV radiation and exogenous hsp60 on phosphorylation of MAPKs and on activation of caspase 3 were examined by Western blot analysis. UV radiation strongly induced phosphorylation of p38 MAPK and formation of active caspase 3. A p38 inhibitor, SB 203580, totally blocked UV radiation-mediated activation of caspase 3. Preincubation with hsp60 strongly induced phosphorylation of ERK1/2 and inhibited UV radiation-mediated activation of caspase 3. PD 98059, a specific inhibitor of the ERK1/2 pathway, blocked this inhibitory effect of exogenous hsp60. Studies on the association between activity of MAPKs or caspase 3 and cell death showed that the ERK1/2 pathway inhibitor reversed protective effect of hsp60 while specific inhibition of p38 and caspase 3 reduced cell death. These results indicate that in HaCaT cells UV radiation mediates cell death through activation of p38 followed by caspase 3 activation. Exogenous hsp60 partially protects against UV radiation-mediated epithelial cell death through activation of ERK1/2, which inhibits caspase 3 activation.     

Calpain-1 C2L domain peptide protects mouse hippocampus-derived neuronal HT22 cells against glutamate-induced oxytosis

Calpains are Ca²⁺-dependent cysteine proteases; their aberrant activation is associated with several neurodegenerative diseases. The μ-calpain catalytic subunit, calpain-1, is located in the cytoplasm as well as in the mitochondria. Mitochondrial calpain-1 cleaves apoptosis-inducing factor (AIF), leading to apoptotic cell death. We have previously reported that short peptides of calpain-1 C2-like domain conjugated with cell penetrating peptide HIV-Tat (Tat-μCL) selectively inhibit mitochondrial calpain-1 and effectively prevent neurodegenerative diseases of the eye. In this study, we determined whether mitochondrial calpain-1 mediates oxytosis (oxidative glutamate toxicity) in hippocampal HT22 cells using Tat-μCL and newly generated polyhistidine-conjugated μCL peptide and compared their efficacies in preventing oxytosis. TUNEL assay and single strand DNA staining revealed that both μCL peptides inhibited glutamate-induced oxytosis. Additionally, both the peptides suppressed the mitochondrial AIF translocation into the nucleus. All polyhistidine-μCL peptides (containing 4–16 histidine residues) showed higher cell permeability than Tat-μCL. Notably, tetrahistidine (H4)-μCL exerted the highest cytoprotective activity. Thus, H4-μCL may be a potential peptide drug for calpain-1-mediated neurodegenerative diseases such as Alzheimer's disease.     

Tat‐antioxidant 1 protects against stress‐induced hippocampal HT‐22 cells death and attenuate ischaemic insult in animal model

Oxidative stress‐induced reactive oxygen species (ROS) are responsible for various neuronal diseases. Antioxidant 1 (Atox1) regulates copper homoeostasis and promotes cellular antioxidant defence against toxins generated by ROS. The roles of Atox1 protein in ischaemia, however, remain unclear. In this study, we generated a protein transduction domain fused Tat‐Atox1 and examined the roles of Tat‐Atox1 in oxidative stress‐induced hippocampal HT‐22 cell death and an ischaemic injury animal model. Tat‐Atox1 effectively transduced into HT‐22 cells and it protected cells against the effects of hydrogen peroxide (H₂O₂)‐induced toxicity including increasing of ROS levels and DNA fragmentation. At the same time, Tat‐Atox1 regulated cellular survival signalling such as p53, Bad/Bcl‐2, Akt and mitogen‐activate protein kinases (MAPKs). In the animal ischaemia model, transduced Tat‐Atox1 protected against neuronal cell death in the hippocampal CA1 region. In addition, Tat‐Atox1 significantly decreased the activation of astrocytes and microglia as well as lipid peroxidation in the CA1 region after ischaemic insult. Taken together, these results indicate that transduced Tat‐Atox1 protects against oxidative stress‐induced HT‐22 cell death and against neuronal damage in animal ischaemia model. Therefore, we suggest that Tat‐Atox1 has potential as a therapeutic agent for the treatment of oxidative stress‐induced ischaemic damage.     

Glutamate-induced cell death in neuronal HT22 cells is attenuated by extracts from St. John''s wort (Hypericum perforatum L.)

Glutamate-induced cell death of hippocampal HT22 cells is a model system for neuronal disorders due to depletion of glutathione levels and increase of intracellular reactive oxygen species. Standardized extracts of Hypericum perforatum (HPE) contain flavonoids known for antioxidative properties. In the above model, cytoprotective effects at a concentration of 0.05% HPE by attenuation of calcium fluxes and cellular energy statuses are reported.     

Bcl-2 protects against Abeta(25-35)-induced oxidative PC12 cell death by potentiation of antioxidant capacity

A substantial body of data indicates that reactive oxygen intermediates (ROIs) are implicated in pathogenesis of diverse human diseases. Oxidative stress induced by ROIs often causes cell death via apoptosis that is regulated by a plenty of functional genes and their protein products. Bcl-2 is one such protein that blocks apoptosis induced by various death stimuli. In spite of extensive research, the molecular mechanisms underlying antiapoptotic function of Bcl-2 are not fully clarified. In the present work, we have investigated the role of bcl-2 in protecting against beta-amyloid (Abeta)-induced oxidative death in rat pheochromocytoma (PC12) cells. Transfection with the antiapoptotic bcl-2 gene rescued PC12 cells from apoptotic death induced by Abeta. Addition of an NF-kappaB inhibitor, such as pyrrolidine dithiocarbamate or N-tosyl-l-phenylalanine chloromethyl ketone, to the media aggravated Abeta-induced PC12 cell death. PC12 cells overexpressing bcl-2 exhibited higher levels of constitutively activated NF-kappaB compared with vector-transfected controls, which appear to be mediated by the elevated activation of Akt/protein kinase B. The ectopic expression of bcl-2 enhanced both the expression and the activity of catalase, which were attenuated by NF-kappaB blockers. These results suggest that NF-kappaB plays a role in bcl-2-mediated protection against Abeta-induced apoptosis in PC12 cells through augmentation of cellular antioxidant capacity.     

Vitamin D3 protects against respiratory syncytial virus-induced barrier dysfunction in airway epithelial cells via PKA signaling pathway

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infection in infants and young children globally and is responsible for hospitalization and mortality in the elderly population. Virus-induced airway epithelial barrier damage is a critical step during RSV infection, and emerging studies suggest that RSV disrupts the tight junctions (TJs) and adherens junctions (AJs) between epithelial cells, increasing the permeability of the airway epithelial barrier. The lack of commercially available vaccines and effective antiviral drugs for RSV emphasizes the need for new management strategies. Vitamin D₃ is a promising intervention for viral infection due to its critical role in modulating innate immune responses. However, there is limited evidence on the effect of vitamin D₃ on RSV pathogenies. Here, we investigated the impact of vitamin D₃ on RSV-induced epithelial barrier dysfunction and the underlying mechanisms. We found that pre-incubation with 1,25(OH)₂D₃, the active form of vitamin D₃, alleviated RSV-induced epithelial barrier disruption in a dose-dependent manner without affecting viability in 16HBE cells. 1,25(OH)₂D₃ induced minor changes in the protein expression level of TJ/AJ proteins in RSV-infected cells. We observed increased CREB phosphorylation at Ser133 during 1,25(OH)₂D₃ exposure, indicating that vitamin D₃ triggered protein kinase A (PKA) activity in 16HBE. PKA inhibitors modified the restoration of barrier function by 1,25(OH)₂D₃ in RSV-infected cells, implying that PKA signaling is responsible for the protective effects of vitamin D₃ against RSV-induced barrier dysfunction in airway epithelial cells. Our findings suggest vitamin D₃ as a prophylactic intervention to protect the respiratory epithelium during RSV infections.     

Compound K protects MIN6N8 pancreatic β‐cells against palmitate‐induced apoptosis through modulating SAPK/JNK activation

Chronic elevation of NEFAs (non‐esterified fatty acids) due to insulin resistance and obesity has been shown to be associated with increased β‐cell apoptosis and with the aetiology of the reduced β‐cell mass of Type 2 diabetes. SAPK (stress‐activated protein kinase)/JNK (c‐Jun N‐terminal kinase) have been implicated in the control of apoptosis. C‐K [compound K; 20‐O‐β‐d ‐glucopyranosyl‐20(S)‐protopanaxadiol] is the main intestinal bacterial metabolite of protopanaxadiol ginsenosides. Currently, little is known about the effects of C‐K on β‐cells with the presence of NEFAs. The aim of the present study was to investigate the in vitro protective effect of C‐K on MIN6N8 mouse insulinoma β‐cells against NEFA‐induced apoptosis, as well as the modulating effect on SAPK/JNK activation. Our results have shown that C‐K inhibited the palmitate‐induced apoptosis through modulating SAPK/JNK activation. We conclude that C‐K protects against β‐cell death and that, by anti‐apoptotic activity, C‐K may contribute to the previously reported anti‐diabetic actions of ginseng.     

Signaling events in apoptotic photokilling of 5-aminolevulinic acid-treated tumor cells: Inhibitory effects of nitric oxide

Antitumor photodynamic therapy (PDT) employs a photosensitizing agent, molecular oxygen, and visible light to produce reactive oxygen species that can destroy tumor and tumor vasculature cells. NO produced by these cells could be procarcinogenic by inhibiting apoptosis and promoting angiogenesis and tumor growth. We recently showed that NO from a chemical donor or activated macrophages makes COH-BR1 breast tumor cells more resistant to photokilling sensitized by 5-aminolevulinic acid (ALA)-generated protoporphyrin IX (PpIX). Signaling events associated with this hyperresistance have now been examined. ALA-treated COH-BR1 cells containing mitochondria-localized PpIX died mainly by apoptosis after being irradiated. Underlying redox signaling associated with MAP kinase (ERK1/2, p38, JUN) phosphorylation–activation, and heme oxygenase-1 (HO-1) upregulation was studied using immunoprecipitation and Western blot methodology. ALA/light treatment resulted in activation of proapoptotic JNK and p38α, and deactivation of prosurvival p38β and ERK1/2. Involvement of both JNK and p38 in apoptosis was established by using a specific inhibitor for each. Spermine NONOate-derived NO, introduced immediately before irradiation, provided substantial protection against apoptosis. This was accompanied by greater HO-1 induction and a strong inhibition of each MAP kinase effect seen in the absence of NO. Downstream of JNK and p38α activation, a marked upregulation/activation of proapoptotic Bax and Bid was observed along with down-regulation of antiapoptotic Bcl-xL, each response being reversed by NO. These findings provide new insights into signaling activity associated with the intrinsic apoptotic pathway in ALA-PDT and how this activity can be modulated by NO.