4-hydroxynonenal induces apoptosis via caspase-3 activation and cytochrome c release

Role of AKR1B10 in inflammatory diseases

Inflammation is an important pathophysiological process in many diseases; it has beneficial and harmful effects. When exposed to various stimuli, the body triggers an inflammatory response to eliminate invaded pathogens and damaged tissues to maintain homeostasis. However, uncontrollable persistent or excessive inflammatory responses may damage tissues and induce various diseases, such as metabolic diseases (e.g. diabetes), autoimmune diseases, nervous system-related diseases, digestive system-related diseases, and even tumours. Aldo-keto reductase 1B10 (AKR1B10) is an important player in the development and progression of multiple diseases, such as tumours and inflammatory diseases. AKR1B10 is upregulated in solid tumours, such as hepatocellular carcinoma (HCC), non-small cell lung carcinoma, and breast cancer, and is a reliable serum marker. However, information on the role of AKR1B10 in inflammation is limited. In this study, we summarized the role of AKR1B10 in inflammatory diseases, including its expression, functional contribution to inflammatory responses, and regulation of signalling pathways related to inflammation. We also discussed the role of AKR1B10 in glucose and lipid metabolism and oxidative stress. This study provides novel information and increases the understanding of clinical inflammatory diseases.

Lipid peroxidation: Reactive carbonyl species, protein/DNA adducts, and signaling switches in oxidative stress and cancer

Under the exposure of lipids to reactive oxygen species (ROS), lipid peroxidation proceeds non-enzymatically and generates an extremely heterogeneous mixture of reactive carbonyl species (RCS). Among them, HNE, HHE, MDA, methylglyoxal, glyoxal, and acrolein are the most studied and/or abundant ones. Over the last decades, significant progress has been achieved in understanding mechanisms of RCS generation, protein/DNA adduct formation, and their identification and quantification in biological samples. In our review, we critically discuss the advancements in understanding the roles of RCS-induced protein/DNA modifications in signaling switches to provide adaptive cell response under physiological and oxidative stress conditions. At non-toxic concentrations, RCS modify susceptible Cys residue in c-Src to activate MAPK signaling and Cys, Lys, and His residues in PTEN to cause its reversible inactivation, thereby stimulating PI3K/PKB(Akt) pathway. RCS toxic concentrations cause irreversible Cys modifications in Keap1 and IKKβ followed by stabilization of Nrf2 and activation of NF-κB, respectively, for their nuclear translocation and antioxidant gene expression. Dysregulation of these mechanisms causes diseases including cancer. Alterations in RCS, RCS detoxifying enzymes, RCS-modified protein/DNA adducts, and signaling pathways have been implicated in various cancer types.

Tribbles Gene Expression Profiles in Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of death due to cancer in the world. Therefore, the identification of novel druggable targets is urgently needed. Tribbles proteins belong to a pseudokinase family, previously recognized in CRC as oncogenes and potential therapeutic targets. Here, we analyzed the expression of TRIB1, TRIB2, and TRIB3 simultaneously in 33 data sets from CRC based on available GEO profiles. We show that all three Tribbles genes are overrepresented in CRC cell lines and primary tumors, though depending on specific features of the CRC samples. Higher expression of TRIB2 in the tumor microenvironment and TRIB3 overexpression in an early stage of CRC development, unveil a potential and unexplored role for these proteins in the context of CRC. Differential Tribbles expression was also explored in diverse cellular experimental conditions where either genetic or pharmacological approaches were used, providing novel hints for future research. This comprehensive bioinformatic analysis provides new insights into Tribbles gene expression and transcript regulation in CRC.

Tribbles Gene Expression Profiles in Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of death due to cancer in the world. Therefore, the identification of novel druggable targets is urgently needed. Tribbles proteins belong to a pseudokinase family, previously recognized in CRC as oncogenes and potential therapeutic targets. Here, we analyzed the expression of TRIB1, TRIB2, and TRIB3 simultaneously in 33 data sets from CRC based on available GEO profiles. We show that all three Tribbles genes are overrepresented in CRC cell lines and primary tumors, though depending on specific features of the CRC samples. Higher expression of TRIB2 in the tumor microenvironment and TRIB3 overexpression in an early stage of CRC development, unveil a potential and unexplored role for these proteins in the context of CRC. Differential Tribbles expression was also explored in diverse cellular experimental conditions where either genetic or pharmacological approaches were used, providing novel hints for future research. This comprehensive bioinformatic analysis provides new insights into Tribbles gene expression and transcript regulation in CRC.

Lipid Peroxidation in Atherosclerotic Cardiovascular Diseases

Significance: Atherosclerotic cardiovascular diseases (ACVDs) continue to be a primary cause of mortality worldwide in adults aged 35-70 years, occurring more often in countries with lower economic development, and they constitute an ever-growing global burden that has a considerable socioeconomic impact on society. The ACVDs encompass diverse pathologies such as coronary artery disease and heart failure (HF), among others. Recent Advances: It is known that oxidative stress plays a relevant role in ACVDs and some of its effects are mediated by lipid oxidation. In particular, lipid peroxidation (LPO) is a process under which oxidants such as reactive oxygen species attack unsaturated lipids, generating a wide array of oxidation products. These molecules can interact with circulating lipoproteins, to diffuse inside the cell and even to cross biological membranes, modifying target nucleophilic sites within biomolecules such as DNA, lipids, and proteins, and resulting in a plethora of biological effects. Critical Issues: This review summarizes the evidence of the effect of LPO in the development and progression of atherosclerosis-based diseases, HF, and other cardiovascular diseases, highlighting the role of protein adduct formation. Moreover, potential therapeutic strategies targeted at lipoxidation in ACVDs are also discussed. Future Directions: The identification of valid biomarkers for the detection of lipoxidation products and adducts may provide insights into the improvement of the cardiovascular risk stratification of patients and the development of therapeutic strategies against the oxidative effects that can then be applied within a clinical setting.

Progress in the mechanism and targeted drug therapy for COPD

Chronic obstructive pulmonary disease (COPD) is emphysema and/or chronic bronchitis characterised by long-term breathing problems and poor airflow. The prevalence of COPD has increased over the last decade and the drugs most commonly used to treat it, such as glucocorticoids and bronchodilators, have significant therapeutic effects; however, they also cause side effects, including infection and immunosuppression. Here we reviewed the pathogenesis and progression of COPD and elaborated on the effects and mechanisms of newly developed molecular targeted COPD therapeutic drugs. Among these new drugs, we focussed on thioredoxin (Trx). Trx effectively prevents the progression of COPD by regulating redox status and protease/anti-protease balance, blocking the NF-κB and MAPK signalling pathways, suppressing the activation and migration of inflammatory cells and the production of cytokines, inhibiting the synthesis and the activation of adhesion factors and growth factors, and controlling the cAMP-PKA and PI3K/Akt signalling pathways. The mechanism by which Trx affects COPD is different from glucocorticoid-based mechanisms which regulate the inflammatory reaction in association with suppressing immune responses. In addition, Trx also improves the insensitivity of COPD to steroids by inhibiting the production and internalisation of macrophage migration inhibitory factor (MIF). Taken together, these findings suggest that Trx may be the ideal drug for treating COPD.

Novel drug delivery systems targeting oxidative stress in chronic obstructive pulmonary disease: a review

Oxidative stress is significantly involved in the pathogenesis and progression of chronic obstructive pulmonary disease (COPD). Combining antioxidant drugs or nutrients results in a noteworthy therapeutic value in animal models of COPD. However, the benefits have not been reproduced in clinical applications, this may be attributed to the limited absorption, concentration, and half-life of exogenous antioxidants. Therefore, novel drug delivery systems to combat oxidative stress in COPD are needed. This review presents a brief insight into the current knowledge on the role of oxidative stress and highlights the recent trends in novel drug delivery carriers that could aid in combating oxidative stress in COPD. The introduction of nanotechnology has enabled researchers to overcome several problems and improve the pharmacokinetics and bioavailability of drugs. Large porous microparticles, and porous nanoparticle-encapsulated microparticles are the most promising carriers for achieving effective pulmonary deposition of inhaled medication and obtaining controlled drug release. However, translating drug delivery systems for administration in pulmonary clinical settings is still in its initial phases.

The relevance of pathophysiological alterations in redox signaling of 4-hydroxynonenal for pharmacological therapies of major stress-associated diseases

Modern analytical methods combined with the modern concepts of redox signaling revealed 4-hydroxy-2-nonenal (4-HNE) as particular growth regulating factor involved in redox signaling under physiological and pathophysiological circumstances. In this review current knowledge of the relevance of 4-HNE as "the second messenger of reactive oxygen species" (ROS) in redox signaling of representative major stress-associated diseases is briefly summarized. The findings presented allow for 4-HNE to be considered not only as second messenger of ROS, but also as one of fundamental factors of the stress- and age-associated diseases. While standard, even modern concepts of molecular medicine and respective therapies in majority of these diseases target mostly the disease-specific symptoms. 4-HNE, especially its protein adducts, might appear to be the bioactive markers that would allow better monitoring of specific pathophysiological processes reflecting their complexity. Eventually that could help development of advanced integrative medicine approach for patients and the diseases they suffer from on the personalized basis implementing biomedical remedies that would optimize beneficial effects of ROS and 4-HNE to prevent the onset and progression of the illness, perhaps even providing the real cure.

Enantioselective high-performance liquid chromatography analysis of oxygenated polyunsaturated fatty acids

Oxygenated polyunsaturated fatty acids (PUFAs)play an outstanding role in the physiological and pathological regulation of several biological processes. These oxygenated metabolites can be produced both enzimatically, yielding almost pure enantiomers, and non-enzymatically. The free radical-mediated non-enzymatic oxidation commonly produces racemic mixtures which are used as biomarkers of oxidative stress and tissue damage. The biological activity of oxygenated PUFAs is often associated with only one enantiomer, making it necessary of availing of lipidomics platforms allowing to disclose the role of single enantiomers in health and disease. Polysaccharide-based chiral stationary phases (CSPs) play a dominating part in this setting. As for the cellulose backbone, 4-methylbenzoate derivatives exhibit very high chiral recognition ability towards this class of compounds. Concerning the phenylcarbamate derivatives of cellulose and amylose, the tris(3,5-dimethylphenylcarbamate) variants show the best enantioresolving ability for a variety of oxygenated PUFAs. Moreover, also the amylose tris(5-chloro-2-methylphenylcarbamate)-based selector produces relevant chromatographic performances. The extreme versatility of those CSPs mostly depends on their compatibility with the most relevant elution modes: normal- and reversed-phase, as well as polar organic/ionic-mode. In this review article, a selection of enantioseparation studies of different oxygenated PUFAs is reported, with both tris(benzoates) and tris(phenylcarbamates) of cellulose and amylose.

4-Hydroxynonenal-induced GPR109A (HCA2 receptor) activation elicits bipolar responses, Gαi -mediated anti-inflammatory effects and Gβγ -mediated cell death

BACKGROUND AND PURPOSE

In this study, we examined the possibility that 4-hydroxynonenal (4-HNE) acting as a ligand for the HCA₂ receptor (GPR109A) elicits both anti-inflammatory and cell death responses.

EXPERIMENTAL APPROACH

Agonistic activity of 4-HNE was determined by observing the inhibition of cAMP generation in CHO-K1-GPR109A-G_i cell line, using surface plasmon resonance (SPR) binding and competition binding assays with [³ H]-niacin. 4-HNE-mediated signalling pathways and cellular responses were investigated in cells expressing GPR109A and those not expressing these receptors.

KEY RESULTS

Agonistic activity of 4-HNE was stronger than that of niacin or 3-OHBA at inhibiting forskolin-induced cAMP production and SPR binding affinity. In ARPE-19 and CCD-841 cells, activation of GPR109A by high concentrations of the agonists 4-HNE (≥10 μM), niacin (≥1000 μM) and 3-OHBA (≥1000 μM) induced apoptosis accompanied by elevated Ca²⁺ and superoxide levels. This 4-HNE-induced cell death was blocked by knockdown of GPR109A or NOX4 genes, or treatment with chemical inhibitors of G_βγ (gallein), intracellular Ca²⁺ (BAPTA-AM), NOX4 (VAS2870) and JNK (SP600125), but not by the cAMP analogue 8-CPT-cAMP. By contrast, low concentrations of 4-HNE, niacin and 3-OHBA down-regulated the expression of pro-inflammatory cytokines IL-6 and IL-8. These 4-HNE-induced inhibitory effects were blocked by a cAMP analogue but not by inhibitors of G_βγ -downstream signalling molecules.

CONCLUSIONS AND IMPLICATIONS

These results revealed that 4-HNE is a strong agonist for GPR109A that induces G_αi -dependent anti-inflammatory and G_βγ -dependent cell death responses. Moreover, the findings indicate that specific intracellular signalling molecules, but not GPR109A, can serve as therapeutic targets to block 4-HNE-induced cell death.

Resolving the Role of Lipoxygenases in the Initiation and Execution of Ferroptosis

Lipoxygenases (LOXs) have been implicated as central players in ferroptosis, a recently characterized cell death modality associated with the accumulation of lipid hydroperoxides: the products of LOX catalysis. To provide insight on their role, human embryonic kidney cells were transfected to overexpress each of the human isoforms associated with disease, 5-LOX, p12-LOX, and 15-LOX-1, which yielded stable cell lines that were demonstrably sensitized to ferroptosis. Interestingly, the cells could be rescued by less than half of a diverse collection of known LOX inhibitors. Furthermore, the cytoprotective compounds were similarly potent in each of the cell lines even though some were clearly isoform-selective LOX inhibitors. The cytoprotective compounds were subsequently demonstrated to be effective radical-trapping antioxidants, which protect lipids from autoxidation, the autocatalytic radical chain reaction that produces lipid hydroperoxides. From these data (and others reported herein), a picture emerges wherein LOX activity may contribute to the cellular pool of lipid hydroperoxides that initiate ferroptosis, but lipid autoxidation drives the cell death process.

Age-related NMDA signaling alterations in SOD2 deficient mice

Oxidative stress affects the survival and function of neurons. Hence, they have a complex and highly regulated machinery to handle oxidative changes. The dysregulation of this antioxidant machinery is associated with a wide range of neurodegenerative conditions. Therefore, we evaluated signaling alterations, synaptic properties and behavioral performance in 2 and 6-month-old heterozygous manganese superoxide dismutase knockout mice (SOD2^+/- mice). We found that their low antioxidant capacity generated direct oxidative damage in proteins, lipids, and DNA. However, only 6-month-old heterozygous knockout mice presented behavioral impairments. On the other hand, synaptic plasticity, synaptic strength and NMDA receptor (NMDAR) dependent postsynaptic potentials were decreased in an age-dependent manner. We also analyzed the phosphorylation state of the NMDAR subunit GluN2B. We found that while the levels of GluN2B phosphorylated on tyrosine 1472 (synaptic form) remain unchanged, we detected increased levels of GluN2B phosphorylated on tyrosine 1336 (extrasynaptic form), establishing alterations in the synaptic/extrasynaptic ratio of GluN2B. Additionally, we found increased levels of two phosphatases associated with dephosphorylation of p-1472: striatal-enriched protein tyrosine phosphatase (STEP) and phosphatase and tensin homolog deleted on chromosome Ten (PTEN). Moreover, we found decreased levels of p-CREB, a master transcription factor activated by synaptic stimulation. In summary, we describe mechanisms by which glutamatergic synapses are altered under oxidative stress conditions. Our results uncovered new putative therapeutic targets for conditions where NMDAR downstream signaling is altered. This work also contributes to our understanding of processes such as synapse formation, learning, and memory in neuropathological conditions.

Mitochondrial dysfunction and oxidative stress in aging and cancer

Aging and cancer are the most important issues to research. The population in the world is growing older, and the incidence of cancer increases with age. There is no doubt about the linkage between aging and cancer. However, the molecular mechanisms underlying this association are still unknown. Several lines of evidence suggest that the oxidative stress as a cause and/or consequence of the mitochondrial dysfunction is one of the main drivers of these processes. Increasing ROS levels and products of the oxidative stress, which occur in aging and age-related disorders, were also found in cancer. This review focuses on the similarities between ageing-associated and cancer-associated oxidative stress and mitochondrial dysfunction as their common phenotype.

Intraperitoneal Administration of Oxygen/Ozone to Rats Reduces the Pancreatic Damage Induced by Streptozotocin

Background: The rat model of streptozotocin (STZ)-induced pancreatic damage was used to examine whether a systemic oxygen/ozone mixture could be beneficial for the pancreas by reducing the machinery of the local detrimental mediators released by STZ. Results: The results showed that oxygen/ozone administration (150 µg/Kg i.p.) for ten days in STZ rats increased the endogenous glutathione-s-transferase (GST) enzyme and nuclear factor-erythroid 2-related factor 2 (Nrf2) into the pancreatic tissue, together with reduction of 4-hydroxynonenal (4-HNE) and PARP-1 compared to STZ rats receiving O₂ only. Interestingly, these changes resulted in higher levels of serum insulin and leptin, and pancreatic glucagon immunostaining. Consequently, glucose metabolism improved as evidenced by the monitoring of glycemia throughout. Conclusions: This study provides evidence that systemic administration of oxygen/ozone reduces the machinery of detrimental mediators released by STZ into the pancreas with less local damage and better functionality.

A label-free and blocker-free photoelectrochemical strategy for highly sensitive caspase-3 assay

Based on CC-DEVD-peptide modified nitrogen-doped porous carbon-ZnO nanopolyhedra/CdS hybrids, a label-free and blocker-free photoelectrochemical strategy was developed for caspase-3 assay.

Enhanced phototoxicity of photodynamic treatment by Cx26-composed GJIC via ROS-, calcium- and lipid peroxide-mediated pathways

In spite of the promising initial treatment responses presented by photodynamic therapy (PDT), 5-year recurrence rates remain high level. Therefore, improvement in the efficacy of PDT is needed. There are reports showing that connexin(Cx) 26-composed gap junctional intercellular communication (GJIC) enhances the intercellular propagation of "death signal", thereby increasing chemotherapeutic cytotoxicity. However, it is unclear whether Cx26-formed GJIC has an effect on PDT phototoxicity. The results in the present study showed that Cx26-composed GJ formation at high density enhances the phototoxicity of Photofrin-PDT. When the Cx26 is not expressed or Cx26 channels are blocked, the phototoxicity in high-density cultures substantially reduces, indicating that the enhanced PDT phototoxicity at high density is mediated by Cx26-composed GJIC. The GJIC-mediated increase in PDT phototoxicity was associated with ROS, calcium and lipid peroxide-mediated stress signaling pathways. The work presents the ability of Cx26-composed GJIC to enhance the sensitivity of malignant cells to PDT, and indicates that maintenance or increase of Cx26-formed GJIC may be a profitable strategy towards the enhancement of PDT therapeutic efficiency. Picture: The survival response of Photofrin-PDT in Dox-treated (Cx26 expressing, GJ-formed) and Dox-untreated cells (Cx26 non-expressing, GJ-unformed) at high-cell density condition.

Pro-apoptotic effects of lipid oxidation products: HNE at the crossroads of NF-κB pathway and anti-apoptotic Bcl-2

The axis between lipid oxidation products and cell death is explicitly linked. 4-Hydroxynonenal (HNE), as well as other lipid oxidation products was also established to induce apoptosis in various experimental settings. Yet, the decision leading to apoptotic execution not only includes upregulation of pro-apoptotic signals but also involves a downregulation of anti-apoptotic signals. Within the frames of this paradigm, HNE acts significantly different from other lipid oxidation products in the regulation of two widely known anti-apoptotic elements, Nuclear Factor-κB (NF-κB) transcription factors and its target anti-apoptotic B-Cell Lymphoma-2 (Bcl-2) protein. Even so, a review inclusively linking these anti-apoptotic factors and their crosstalk upon HNE exposure is still at demand. In order to elucidate presence of such crosstalk, reports on the link between HNE and NF-κB pathway, on the link between HNE and anti-apoptotic Bcl-2 and on the crossroad of these links during HNE exposure were summarized and discussed. IKK, the upstream kinase of NF-κB, has been shown to regulate HNE mediated phosphorylation and inactivation of Bcl-2 by our group. Based on this observation and other studies reporting on HNE-NF-κB pathway interaction, IKK was proposed to mediate the crosstalk of NF-κB pathway and anti-apoptotic Bcl-2 protein, when HNE is present. These reports further suggested that HNE based inhibition of NF-κB pathway is highly likely. Besides, evidence on the HNE-anti-apoptotic Bcl-2 axis supported the deduction of HNE mediated NF-κB pathway inhibition and IKK mediated Bcl-2 inactivation. In conclusion, through combining all evidences, three possible scenarios intervening the HNE mediated crosstalk between NF-κB pathway and anti-apoptotic Bcl-2 protein, was extrapolated.

Peptide-fluorophore/AuNP conjugate-based two-photon excited fluorescent nanosensor for caspase-3 activity imaging assay in living cells and tissue

In the present study, a novel fluorescence resonance energy transfer (FRET) strategy-based two-photon excited nanosensor via the assembly of two-photon dye-labeled peptides on the gold nanoparticle's surface has been developed and successfully applied in the caspase-3 imaging assay in living cells and ischemia-reperfusion surgery-treated rat liver tissue slices.

The neuroprotective effect of melatonin on the hippocampus exposed to diclofenac sodium during the prenatal period

Melatonin (Mel) has strong antioxidant properties since it is a direct scavenger of oxygen-based free radicals and related species. The main aim of this study is to show whether the effects of Mel can prevent the potential adverse effects of diclofenac sodium (DS), used as a non-steroidal anti-inflammatory drug (NSAID) during the prenatal period, on the newborn experimental rat brain tissues using stereological methods Twenty-four male 12-week old Wistar albino rats were used. The study involved four groups (each containing six rats), those exposed, during the prenatal period, to saline 1ml/kg (Saline group), to diclofenac sodium 3.6mg/kg (DS group), or to diclofenac sodium+melatonin 50mg/kg (DS+Mel group), and a control group (Cont group). At the end of the experiment, the brains were removed from the cranium for histological and stereological analyses. Cell loss in the hippocampus exposed to DS was observed compared to the Cont group (p<0.01), and a similar side-effect was also seen in the Saline group (p<0.01). However, there was no significant difference in cell numbers between the Cont and DS+Mel groups (p>0.05). These results suggest that exposure to DS during pregnancy causes a decrease in the number of cells in the hippocampus and dentate gyrus in the postnatal period. Using Mel, a neuroprotective agent, reduced the toxic effects of DS.

Novel organotin(iv) complexes derived from 4-fluorophenyl-selenoacetic acid: synthesis, characterization and in vitro cytostatic activity evaluation

A cluster of novel organotin(iv) complexes were designed, synthesized, and characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopy as well as single-crystal X-ray diffraction.

Uric Acid Amplifies Aβ Amyloid Effects Involved in the Cognitive Dysfunction/Dementia: Evidences From an Experimental Model In Vitro

There is still a considerable debate concerning whether uric acid is neuroprotective or neurotoxic agent. To clarify this topic, we tested the effects of uric acid on neuronal cells biology by using differentiated SHSY5Y neuroblastoma cells incubated with amyloid β to reproduce an in vitro model of Alzheimer's disease. The incubation of cells with uric acid at the dose of 40 µM or higher significantly reduced cell viability and potentiated the proapoptotic effect of amyloid β. Finally, uric acid enhanced the generation of 4-hydroxynonenal and the expression of PPARβ/δ promoted by amyloid β, indicating a prooxidant effects. In conclusion, uric acid could exert a detrimental influence on neuronal biology being this influence further potentiated by the concomitant exposure to neurotoxic stimuli. This effect is evident for uric acid concentrations close to those achievable in cerebrospinal fluid in presence of mild hyperuricemia thus suggesting a potential role of uric acid in pathophysiology of cognitive dysfunction. These effects are influenced by the concentrations of uric acid and by the presence of favoring conditions that commonly occur in neurodegenerative disorders and well as in the aging brain, including increased oxidative stress and exposure to amyloid β. J. Cell. Physiol. 232: 1069-1078, 2017. © 2016 Wiley Periodicals, Inc.

Phospholipase A₂-Generated Lipid Mediators in the Brain: The Good, the Bad, and the Ugly

Phospholipase A2 (PLA2) generates arachidonic acid, docosahexaenoic acid, and lysophospholipids from neural membrane phospholipids. These metabolites have a variety of physiological effects by themselves and also are substrates for the synthesis of more potent lipid mediators such as eicosanoids, platelet activating factor, and 4-hydroxynonenal (4-HNE). At low concentrations, these mediators act as second messengers. They affect and modulate several cell functions, including signal transduction, gene expression, and cell proliferation, but at high concentrations, these lipid mediators cause neurotoxicity. Among the metabolites generated by PLA2, 4-HNE is the most cytotoxic metabolite and is associated with the apoptotic type of neural cell death. Levels of 4-HNE are markedly increased in neurological disorders such as Alzheimer disease, Parkinson disease, ischemia, spinal cord trauma, and head injury. The purpose of this review is to summarize and integrate the vast literature on metabolites generated by PLA2 for a wider audience. The authors hope that this discussion will jump-start more studies not only on the involvement of PLA2 in neurological disorders but also on the importance of PLA2-generated lipid mediators in physiological and pathological processes.

Covalent Modification of CDK2 by 4-Hydroxynonenal as a Mechanism of Inhibition of Cell Cycle Progression

Oxidative stress is a contributing factor in a number of chronic diseases, including cancer, atherosclerosis, and neurodegenerative diseases. Lipid peroxidation that occurs during periods of oxidative stress results in the formation of lipid electrophiles, which can modify a multitude of proteins in the cell. 4-Hydroxy-2-nonenal (HNE) is one of the most well-studied lipid electrophiles and has previously been shown to arrest cells at the G1/S transition. Recently, proteomic data have shown that HNE is capable of covalently modifying CDK2, the kinase responsible for the G1/S transition. Here, we identify the sites adducted by HNE using recombinant CDK2 and show that HNE treatment suppresses the kinase activity of the enzyme. We further identify sites of adduction in HNE-treated intact human colorectal carcinoma cells (RKO) and show that HNE-dependent modification in cells is long-lived, disrupts CDK2 function, and correlates with a delay of progression of the cells into S-phase. We propose that adduction of CDK2 by HNE directly alters its activity, contributing to the cell cycle delay.

Mitochondrial Dysfunction in Cancer and Neurodegenerative Diseases: Spotlight on Fatty Acid Oxidation and Lipoperoxidation Products

In several human diseases, such as cancer and neurodegenerative diseases, the levels of reactive oxygen species (ROS), produced mainly by mitochondrial oxidative phosphorylation, is increased. In cancer cells, the increase of ROS production has been associated with mtDNA mutations that, in turn, seem to be functional in the alterations of the bioenergetics and the biosynthetic state of cancer cells. Moreover, ROS overproduction can enhance the peroxidation of fatty acids in mitochondrial membranes. In particular, the peroxidation of mitochondrial phospholipid cardiolipin leads to the formation of reactive aldehydes, such as 4-hydroxynonenal (HNE) and malondialdehyde (MDA), which are able to react with proteins and DNA. Covalent modifications of mitochondrial proteins by the products of lipid peroxidation (LPO) in the course of oxidative cell stress are involved in the mitochondrial dysfunctions observed in cancer and neurodegenerative diseases. Such modifications appear to affect negatively mitochondrial integrity and function, in particular energy metabolism, adenosine triphosphate (ATP) production, antioxidant defenses and stress responses. In neurodegenerative diseases, indirect confirmation for the pathogenetic relevance of LPO-dependent modifications of mitochondrial proteins comes from the disease phenotypes associated with their genetic alterations.

WO3/Pt nanoparticles are NADPH oxidase biomimetics that mimic effector cells in vitro and in vivo

To provide a means of delivering an artificial immune effector cell-like attack on tumor cells, we report the tumoricidal ability of inorganic WO3/Pt nanoparticles that mimic a leukocyte's functional abilities. These nanoparticles route electrons from organic structures and electron carriers to form hydroxyl radicals within tumor cells. During visible light exposure, WO3/Pt nanoparticles manufacture hydroxyl radicals, degrade organic compounds, use NADPH, trigger lipid peroxidation, promote lysosomal membrane disruption, promote the loss of reduced glutathione, and activate apoptosis. In a model of advanced breast cancer metastasis to the eye's anterior chamber, we show that WO3/Pt nanoparticles prolong the survival of 4T1 tumor-bearing Balb/c mice. This new generation of inorganic photosensitizers do not photobleach, and therefore should provide an important therapeutic advance in photodynamic therapy. As biomimetic nanoparticles destroy targeted cells, they may be useful in treating ocular and other forms of cancer.

Electrochemiluminescent Sensing for Caspase-3 Activity Based on Ru(bpy)3(2+)-Doped Silica Nanoprobe

Caspase-3 is one of the most frequently activated cysteine proteases during the apoptosis process and has been identified as a well-established cellular marker of apoptosis. In this study, a novel approach for the sensitive determination of caspase-3 activity was proposed using electrochemiluminescence (ECL) of Ru(bpy)3(2+)-doped silica (Ru@SiO2) with tripropylamine (TPA) as coreactant. A nanocomposite containing gold nanoparticles (AuNPs), poly(dimethyldiallyl ammonium chloride) (PDDA), and multiwalled carbon nanotubes (CNTs) was fabricated as an ECL platform. The biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) was immobilized on the nanocomposite surface via the strong bonding interaction between AuNPs and the thiol group. Then the streptavidin-modified Ru(bpy)3(2+)-doped silica (Ru@SiO2-SA) was immobilized on the ECL platform via the specific interaction between biotin and streptavidin to generate ECL signal. Caspase-3 can specifically recognize and cleave the N-terminus of DEVD, leading to the loss of the biotin label and the decrease of ECL intensity to determine the activity of caspase-3. The results revealed a new ECL avenue for the sensitive and specific monitor of caspase-3, and the platform could be utilized to evaluate anticancer drugs.

NADP(+)-dependent dehydrogenase activity of carbonyl reductase on glutathionylhydroxynonanal as a new pathway for hydroxynonenal detoxification

An NADP(+)-dependent dehydrogenase activity on 3-glutathionyl-4-hydroxynonanal (GSHNE) was purified to electrophoretic homogeneity from a line of human astrocytoma cells (ADF). Proteomic analysis identified this enzymatic activity as associated with carbonyl reductase 1 (EC 1.1.1.184). The enzyme is highly efficient at catalyzing the oxidation of GSHNE (KM 33 µM, kcat 405 min(-1)), as it is practically inactive toward trans-4-hydroxy-2-nonenal (HNE) and other HNE-adducted thiol-containing amino acid derivatives. Combined mass spectrometry and nuclear magnetic resonance spectroscopy analysis of the reaction products revealed that carbonyl reductase oxidizes the hydroxyl group of GSHNE in its hemiacetal form, with the formation of the corresponding 3-glutathionylnonanoic-δ-lactone. The relevance of this new reaction catalyzed by carbonyl reductase 1 is discussed in terms of HNE detoxification and the recovery of reducing power.

Age Progression of Neuropathological Markers in the Brain of the Chilean Rodent Octodon degus, a Natural Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and the leading cause of age-related dementia worldwide. Several models for AD have been developed to provide information regarding the initial changes that lead to degeneration. Transgenic mouse models recapitulate many, but not all, of the features of AD, most likely because of the high complexity of the pathology. In this context, the validation of a wild-type animal model of AD that mimics the neuropathological and behavioral abnormalities is necessary. In previous studies, we have reported that the Chilean rodent Octodon degus could represent a natural model for AD. In the present work, we further describe the age-related neurodegeneration observed in the O. degus brain. We report some histopathological markers associated with the onset progression of AD, such as glial activation, increase in oxidative stress markers, neuronal apoptosis and the expression of the peroxisome proliferative-activated receptor γ coactivator-1α (PGC-1α). With these results, we suggest that the O. degus could represent a new model for AD research and a powerful tool in the search for therapeutic strategies against AD.

Formation of electrophilic oxidation products from mitochondrial cardiolipin in vitro and in vivo in the context of apoptosis and atherosclerosis

Emerging evidence indicates that mitochondrial cardiolipins (CL) are prone to free radical oxidation and this process appears to be intimately associated with multiple biological functions of mitochondria. Our previous work demonstrated that a significant amount of potent lipid electrophiles including 4-hydroxy-nonenal (4-HNE) was generated from CL oxidation through a novel chemical mechanism. Here we provide further evidence that a characteristic class of CL oxidation products, epoxyalcohol-aldehyde-CL (EAA-CL), is formed through this novel mechanism in isolated mice liver mitochondria when treated with the pro-apoptotic protein t-Bid to induce cyt c release. Generation of these oxidation products are dose-dependently attenuated by a peroxidase inhibitor acetaminophen (ApAP). Using a mouse model of atherosclerosis, we detected significant amount of these CL oxidation products in liver tissue of low density lipoprotein receptor knockout (LDLR −/−) mice after Western diet feeding. Our studies highlight the importance of lipid electrophiles formation from CL oxidation in the settings of apoptosis and atherosclerosis as inhibition of CL oxidation and lipid electrophiles formation may have potential therapeutic value in diseases linked to oxidant stress and mitochondrial dysfunctions.

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4-HNE and other electrophilic lipids are formed from mitochondrial cardiolipin.

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Novel electrophilic oxidation products EAA-CL were identified in vitro and in vivo.

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Level of EAA-CL in liver tissue of LDLR −/− mice is higher with Western diet feeding.

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ApAP dose-dependently inhibits EAA-CL formation during t-Bid induced cyt c release.

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CL electrophilic lipid formation is important in apoptosis and atherosclerosis.

Involvement of peroxisome proliferator-activated receptor β/δ (PPAR β/δ) in BDNF signaling during aging and in Alzheimer disease: possible role of 4-hydroxynonenal (4-HNE)

Aging and many neurological disorders, such as AD, are linked to oxidative stress, which is considered the common effector of the cascade of degenerative events. In this phenomenon, reactive oxygen species play a fundamental role in the oxidative decomposition of polyunsaturated fatty acids, resulting in the formation of a complex mixture of aldehydic end products, such as malondialdehyde, 4-hydroxynonenal, and other alkenals. Interestingly, 4-HNE has been indicated as an intracellular agonist of peroxisome proliferator-activated receptor β/δ. In this study, we examined, at early and advanced AD stages (3, 9, and 18 months), the pattern of 4-HNE and its catabolic enzyme glutathione S-transferase P1 in relation to the expression of PPARβ/δ, BDNF signaling, as mRNA and protein, as well as on their pathological forms (i.e., precursors or truncated forms). The data obtained indicate a novel detrimental age-dependent role of PPAR β/δ in AD by increasing pro-BDNF and decreasing BDNF/TrkB survival pathways, thus pointing toward the possibility that a specific PPARβ/δ antagonist may be used to counteract the disease progression.

Regulation and therapeutic strategies of 4-hydroxy-2-nonenal metabolism in heart disease

4-Hydroxy-2-nonenal (4-HNE), a reactive aldehyde, is generated from polyunsaturated fatty acids (PUFAs) in biological membranes. Reactive oxygen species (ROS) generated during oxidative stress react with PUFAs to form aldehydes like 4-HNE, which inactivates proteins and DNA by forming hybrid covalent chemical addition compounds called adducts. The ensuing chain reaction results in cellular dysfunction and tissue damage. It includes a wide spectrum of events ranging from electron transport chain dysfunction to apoptosis. In addition, 4-HNE directly depresses contractile function, enhances ROS formation, modulates cell signaling pathways, and can contribute to many cardiovascular diseases, including atherosclerosis, myocardial ischemia-reperfusion injury, heart failure, and cardiomyopathy. Therefore, targeting 4-HNE could help reverse these pathologies. This review will focus on 4-HNE generation, the role of 4-HNE in cardiovascular diseases, cellular targets (especially mitochondria), processes and mechanisms for 4-HNE-induced toxicity, regulation of 4-HNE metabolism, and finally strategies for developing potential therapies for cardiovascular disease by attenuating 4-HNEinduced toxicity.

Cell death and diseases related to oxidative stress: 4-hydroxynonenal (HNE) in the balance

During the last three decades, 4-hydroxy-2-nonenal (HNE), a major α,β-unsaturated aldehyde product of n-6 fatty acid oxidation, has been shown to be involved in a great number of pathologies such as metabolic diseases, neurodegenerative diseases and cancers. These multiple pathologies can be explained by the fact that HNE is a potent modulator of numerous cell processes such as oxidative stress signaling, cell proliferation, transformation or cell death. The main objective of this review is to focus on the different aspects of HNE-induced cell death, with a particular emphasis on apoptosis. HNE is a special apoptotic inducer because of its abilities to form protein adducts and to propagate oxidative stress. It can stimulate intrinsic and extrinsic apoptotic pathways and interact with typical actors such as tumor protein 53, JNK, Fas or mitochondrial regulators. At the same time, due to its oxidant status, it can also induce some cellular defense mechanisms against oxidative stress, thus being involved in its own detoxification. These processes in turn limit the apoptotic potential of HNE. These dualities can imbalance cell fate, either toward cell death or toward survival, depending on the cell type, the metabolic state and the ability to detoxify.

RNA-seq data analysis at the gene and CDS levels provides a comprehensive view of transcriptome responses induced by 4-hydroxynonenal

Reactive electrophiles produced during oxidative stress, such as 4-hydroxynonenal (HNE), are increasingly recognized as contributing factors in a variety of degenerative and inflammatory diseases. Here we used the RNA-seq technology to characterize transcriptome responses in RKO cells induced by HNE at subcytotoxic and cytotoxic doses. RNA-seq analysis rediscovered most of the differentially expressed genes reported by microarray studies and also identified novel gene responses. Interestingly, differential expression detection at the coding DNA sequence (CDS) level helped to further improve the consistency between the two technologies, suggesting the utility and importance of the CDS level analysis. RNA-seq data analysis combining gene and CDS levels yielded an informative and comprehensive picture of gradually evolving response networks with increasing HNE doses, from cell protection against oxidative injury at low dose, initiation of cell apoptosis and DNA damage at intermediate dose to significant deregulation of cellular functions at high dose. These evolving dose-dependent pathway changes, which cannot be observed by the gene level analysis alone, clearly reveal the HNE cytotoxic effect and are supported by IC50 experiments. Additionally, differential expression at the CDS level provides new insights into isoform regulation mechanisms. Taken together, our data demonstrate the power of RNA-seq to identify subtle transcriptome changes and to characterize effects induced by HNE through the generation of high-resolution data coupled with differential analysis at both gene and CDS levels.

The electrophile responsive proteome: integrating proteomics and lipidomics with cellular function

SIGNIFICANCE

The process of lipid peroxidation is emerging as an important mechanism that mediates the post-translational modification of proteins. Through advanced analytical techniques, lipidomics is now emerging as a critical factor in our understanding of the pathology of a broad range of diseases.

RECENT ADVANCES

During enzymatic or nonenzymatic lipid peroxidation, the simple structure of an unsaturated fatty acid is converted to an oxylipidome, many members of which are electrophilic and form the reactive lipid species (RLS). This aspect of lipid biology is particularly important, as it directly connects lipidomics with proteomics through the post-translational modification of a sub-proteome in the cell. This arises, because the electrophilic members of the oxylipidome react with proteins at nucleophilic amino-acid residues and so change their structure and function to form electrophile-responsive proteomes (ERP).

CRITICAL ISSUES

Biological systems have relatively few but well-defined and mechanistically distinct pro-oxidant pathways generating RLS. Defining the ERPs and the mechanisms underlying their formation and action has been a major focus for the field of lipidomics and redox signaling.

FUTURE DIRECTIONS

We propose that a unique oxylipidome can be defined for specific oxidants and will predict the biological responses through the reaction with proteins to form a specific ERP. In this review, we will describe the ERPs that modulate antioxidant and anti-inflammatory protective pathways, including the activation of Keap1/Nrf2 and the promotion of cell death through interactions with mitochondria.

Role of physiological levels of 4-hydroxynonenal on adipocyte biology: implications for obesity and metabolic syndrome

Lipid peroxidation products such as 4-hydroxynonenal (HNE) are known to be increased in response to oxidative stress, and are known to cause dysfunction and pathology in a variety of tissues during periods of oxidative stress. The aim of the current study was to determine the chronic (repeated HNE exposure) and acute effects of physiological concentrations of HNE toward multiple aspects of adipocyte biology using differentiated 3T3-L1 adipocytes. Our studies demonstrate that acute and repeated exposure of adipocytes to physiological concentrations of HNE is sufficient to promote subsequent oxidative stress, impaired adipogenesis, alter the expression of adipokines, and increase lipolytic gene expression and subsequent increase in free fatty acid (FFA) release. These results provide an insight in to the role of HNE-induced oxidative stress in regulation of adipocyte differentiation and adipose dysfunction. Taken together, these data indicate a potential role for HNE promoting diverse effects toward adipocyte homeostasis and adipocyte differentiation, which may be important to the pathogenesis observed in obesity and metabolic syndrome.

Spatiotemporal autophagic degradation of oxidatively damaged organelles after photodynamic stress is amplified by mitochondrial reactive oxygen species

Although reactive oxygen species (ROS) have been reported to evoke different autophagic pathways, how ROS or their secondary products modulate the selective clearance of oxidatively damaged organelles is less explored. To investigate the signaling role of ROS and the impact of their compartmentalization in autophagy pathways, we used murine fibrosarcoma L929 cells overexpressing different antioxidant enzymes targeted to the cytosol or mitochondria and subjected them to photodynamic (PD) stress with the endoplasmic reticulum (ER)-associated photosensitizer hypericin. We show that following apical ROS-mediated damage to the ER, predominantly cells overexpressing mitochondria-associated glutathione peroxidase 4 (GPX4) and manganese superoxide dismutase (SOD2) displayed attenuated kinetics of autophagosome formation and overall cell death, as detected by computerized time-lapse microscopy. Consistent with a primary ER photodamage, kinetics and colocalization studies revealed that photogenerated ROS induced an initial reticulophagy, followed by morphological changes in the mitochondrial network that preceded clearance of mitochondria by mitophagy. Overexpression of cytosolic and mitochondria-associated GPX4 retained the tubular mitochondrial network in response to PD stress and concomitantly blocked the progression toward mitophagy. Preventing the formation of phospholipid hydroperoxides and H(2)O(2) in the cytosol as well as in the mitochondria significantly reduced cardiolipin peroxidation and apoptosis. All together, these results show that in response to apical ER photodamage ROS propagate to mitochondria, which in turn amplify ROS production, thereby contributing to two antagonizing processes, mitophagy and apoptosis.

Inflammation and cancer: chemical approaches to mechanisms, imaging, and treatment

The inflammatory response represents a first line of defense against invading pathogens and is important to human health. Chronic inflammation contributes to the etiology of multiple diseases, especially those associated with aging, such as cancer and cardiovascular disease. The chemistry of the inflammatory response is complex and involves the generation of highly reactive oxidants and electrophiles designed to kill the pathogen as well as the release of small molecule and protein mediators of intercellular signaling, chemotaxis, vasoconstriction, and wound-healing. Oxidation of unsaturated fatty acids--either nonenzymatic or enzymatic--contributes to the inflammatory response and associated cellular pathologies. The current perspective summarizes our research on unsaturated fatty acid oxidation in the context of inflammation and cancer. In addition to understanding the consequences of DNA and protein modification by lipid electrophiles, our research has focused on the development of molecularly targeted agents to image and treat cancer.

Role of 4-hydroxynonenal in chemopreventive activities of sulforaphane

Chemoprevention of cancer via herbal and dietary supplements is a logical approach to combating cancer and currently it is an attractive area of research investigation. Over the years, isothiocyanates, such as sulforaphane (SFN) found in cruciferous vegetables, have been advocated as chemopreventive agents, and their efficacy has been demonstrated in cell lines and animal models. In vivo studies with SFN suggest that in addition to protecting normal healthy cells from environmental carcinogens, it also exhibits cytotoxicity and apoptotic effects against various cancer cell types. Among several mechanisms for the chemopreventive activity of SFN against chemical carcinogenesis, its effect on drug-metabolizing enzymes that cause activation/neutralization of carcinogenic metabolites is well established. Recent studies suggest that SFN exerts its selective cytotoxicity to cancer cells via reactive oxygen species-mediated generation of lipid peroxidation products, particularly 4-hydroxynonenal (HNE). Against the background of the known biochemical effects of SFN on normal and cancer cells, in this article we review the underlying molecular mechanisms responsible for the overall chemopreventive effects of SFN, focusing on the role of HNE in these mechanisms, which may also contribute to its selective cytotoxicity to cancer cells.

Free radical oxidation of cardiolipin: chemical mechanisms, detection and implication in apoptosis, mitochondrial dysfunction and human diseases

Cardiolipin (CL) is a mitochondria-specific phospholipid and is critical for maintaining the integrity of mitochondrial membrane and mitochondrial function. CL also plays an active role in mitochondria-dependent apoptosis by interacting with cytochrome c (cyt c), tBid and other important Bcl-2 proteins. The unique structure of CL with four linoleic acid side chains in the same molecule and its cellular location make it extremely susceptible to free radical oxidation by reactive oxygen species including free radicals derived from peroxidase activity of cyt c/CL complex, singlet oxygen and hydroxyl radical. The free radical oxidation products of CL have been emerged as important mediators in apoptosis. In this review, we summarize the free radical chemical mechanisms that lead to CL oxidation, recent development in detection of oxidation products of CL by mass spectrometry and the implication of CL oxidation in mitochondria-mediated apoptosis, mitochondrial dysfunction and human diseases.

4-Hydroxynonenal induces mitochondrial-mediated apoptosis and oxidative stress in SH-SY5Y human neuronal cells

Excessive and sustained increases in oxidative stress and apoptosis have been implicated in the pathogenesis of many diseases. In this study, we demonstrated that 4-hydroxynonenal (4-HNE), a product of lipid peroxidation in a range of concentration (0.1-50 μM) showed cytotoxic effects on SH-SY5Y cell culture at a concentration >5 μM at 4 hr of exposure. 4-HNE dose dependently decreased cell viability and significantly promoted reactive oxygen species formation and enhanced oxidative stress as reflected in the increased level of lipid peroxidation and catalase activity and decreased glutathione peroxidase activity as well as glutathione levels. 4-HNE-induced oxidative stress was associated with increased transcriptional and translational expressions of Bax and p53 in SH-SY5Y cells. Mitochondrial-mediated apoptosis was confirmed by increased expression and activity of caspase-3. Our data demonstrate that 4-HNE induces neuronal cell death through abnormal expression of apoptotic markers (p53, Bax and caspase-3). Oxidative stress may be involved in the initial priming of SH-SY5Y cells to 4-HNE-induced cytotoxicity in vitro.

Uncoupling proteins and the control of mitochondrial reactive oxygen species production

Reactive oxygen species (ROS), natural by-products of aerobic respiration, are important cell signaling molecules, which left unchecked can severely impair cellular functions and induce cell death. Hence, cells have developed a series of systems to keep ROS in the nontoxic range. Uncoupling proteins (UCPs) 1-3 are mitochondrial anion carrier proteins that are purported to play important roles in minimizing ROS emission from the electron transport chain. The function of UCP1 in this regard is highly contentious. However, UCPs 2 and 3 are generally thought to be activated by ROS or ROS by-products to induce proton leak, thus providing a negative feedback loop for mitochondrial ROS production. In our laboratory, we have not only confirmed that ROS activate UCP2 and UCP3, but also demonstrated that UCP2 and UCP3 are controlled by covalent modification by glutathione. Furthermore, the reversible glutathionylation is required to activate/inhibit UCP2 and UCP3, but not UCP1. Hence, our findings are consistent with the notion that UCPs 2 and 3 are acutely activated by ROS, which then directly modulate the glutathionylation status of the UCP to decrease ROS emission and participate in cell signaling mechanisms.

Apoptotic effect of eugenol in human colon cancer cell lines

Eugenol, a natural compound available in honey and various plants extracts including cloves and Magnoliae flos, is exploited for various medicinal applications. Since most of the drugs used in the cancer are apoptotic inducers, the apoptotic effect and anticancer mechanism of eugenol were investigated against colon cancer cells. Antiproliferative effect was estimated using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay]. Earlier events like MMP (mitochondrial membrane potential), thiol depletion and lipid layer break were measured by using flow cytometry. Apoptosis was evaluated using PI (propidium iodide) staining, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling) assay and DNA fragmentation assay. MTT assay signified the antiproliferative nature of eugenol against the tested colon cancer cells. PI staining indicated increasing accumulation of cells at sub-G1-phase. Eugenol treatment resulted in reduction of intracellular non-protein thiols and increase in the earlier lipid layer break. Further events like dissipation of MMP and generation of ROS (reactive oxygen species) were accompanied in the eugenol-induced apoptosis. Augmented ROS generation resulted in the DNA fragmentation of treated cells as shown by DNA fragmentation and TUNEL assay. Further activation of PARP (polyadenosine diphosphate-ribose polymerase), p53 and caspase-3 were observed in Western blot analyses. Our results demonstrated molecular mechanism of eugenol-induced apoptosis in human colon cancer cells. This research will further enhance eugenol as a potential chemopreventive agent against colon cancer.