Ability of different hepatoma cells to metabolize 4-hydroxynonenal

Oxidative Stress-Related Mechanisms in Melanoma and in the Acquired Resistance to Targeted Therapies

Melanoma is a highly aggressive cancer with the poorest prognosis, representing the deadliest form of skin cancer. Activating mutations in BRAF are the most frequent genetic alterations, present in approximately 50% of all melanoma cases. The use of specific inhibitors towards mutant BRAF variants and MEK, a downstream signaling target of BRAF in the MAPK pathway, has significantly improved progression-free and overall survival in advanced melanoma patients carrying BRAF mutations. Nevertheless, despite these improvements, resistance still develops within the first year of therapy in around 50% of patients, which is a significant problem in managing BRAF-mutated advanced melanoma. Understanding these mechanisms is one of the mainstreams of the research on BRAFi/MEKi acquired resistance. Both genetic and epigenetic mechanisms have been described. Moreover, in recent years, oxidative stress has emerged as another major force involved in all the phases of melanoma development, from initiation to progression until the onsets of the metastatic phenotype and chemoresistance, and has thus become a target for therapy. In the present review, we discuss the current knowledge on oxidative stress and its signaling in melanoma, as well as the oxidative stress-related mechanisms in the acquired resistance to targeted therapies.

Cancer growth regulation by 4-hydroxynonenal

While reactive oxygen species (ROS) gain their carcinogenic effects by DNA mutations, if generated in the vicinity of genome, lipid peroxidation products, notably 4-hydroxynonenal (HNE), have much more complex modes of activities. Namely, while ROS are short living and have short efficiency distance range (in nm or µm) HNE has strong binding affinity for proteins, thus forming relatively stable adducts. Hence, HNE can diffuse from the site or origin changing structure and function of respective proteins. Consequently HNE can influence proliferation, differentiation and apoptosis of cancer cells on one hand, while on the other it can affect genome functionality, too. Although HNE is considered to be important factor of carcinogenesis due to its ability to covalently bind to DNA, it might also be cytotoxic for cancer cells, as well as it can modulate their growth. In addition to direct cytotoxicity, HNE is also involved in activity mechanisms by which several cytostatic drugs and radiotherapy exhibit their anticancer effects. Complementary to that, the metabolic pathway for HNE detoxification through RLIP76, which is enhanced in cancer, may be a target for anti-cancer treatments. In addition, some cancer cells can undergo apoptosis or necrosis, if exposed to supraphysiological HNE levels in the cancer microenvironment, especially if challenged additionally by pro-oxidative cytostatics and/or inflammation. These findings could explain previously observed disappearance of HNE from invading cancer cells, which is associated with the increase of HNE in non-malignant cells close to invading cancer utilizing cardiolipin as the source of cancer-inhibiting HNE.

4-Hydroxy-nonenal-A Bioactive Lipid Peroxidation Product

This review on recent research advances of the lipid peroxidation product 4-hydroxy-nonenal (HNE) has four major topics: I. the formation of HNE in various organs and tissues, II. the diverse biochemical reactions with Michael adduct formation as the most prominent one, III. the endogenous targets of HNE, primarily peptides and proteins (here the mechanisms of covalent adduct formation are described and the (patho-) physiological consequences discussed), and IV. the metabolism of HNE leading to a great number of degradation products, some of which are excreted in urine and may serve as non-invasive biomarkers of oxidative stress.

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.

Overview on major lipid peroxidation bioactive factor 4-hydroxynonenal as pluripotent growth-regulating factor

The reactive aldehyde 4-hydroxynonenal (HNE) is major bioactive marker of lipid peroxidation generated under oxidative stress from polyunsaturated fatty acids. Biomedical significance of HNE was first revealed in pathogenesis of various degenerative and malignant diseases. Thus, HNE was considered for decades only as cytotoxic molecule, "second toxic messenger of free radicals" responsible for numerous undesirable consequences of oxidative stress. However, the increase of knowledge on physiology of redox signaling revealed also desirable, physiological roles of HNE, especially in the field of cellular signaling pathways regulating proliferation, differentiation, and apoptosis. These pluripotent effects of HNE can be explained by its concentration-dependent interactions with the cytokine networks and complex cellular antioxidant systems also showing cell and tissue specificities. Therefore, this paper gives a comprehensive, yet short overview on HNE as pluripotent growth-regulating factor.

4-Hydroxy-2-nonenal adduction of extracellular signal-regulated kinase (Erk) and the inhibition of hepatocyte Erk-Est-like protein-1-activating protein-1 signal transduction

4-Hydroxy-2-nonenal (4-HNE) is a major lipid peroxidation (LPO) product formed during oxidative stress. 4-HNE is highly reactive toward cellular nucleophiles and is implicated in the evolution of numerous pathologies associated with oxidative stress and LPO. Recent evidence suggests that chronic prooxidant exposure results in the loss of extracellular signal-regulated kinase (Erk)-1/2 phosphorylation in vivo, a signaling pathway associated with cellular proliferation, survival, and homeostasis. Immunodetection and molecular analysis were used in this study to evaluate the hypothesis that 4-HNE modification of Erk-1/2 inhibits constitutive Erk-Est-like protein (Elk)-1-activating protein (AP)-1 signaling. Primary rat hepatocytes treated with subcytotoxic, pathologically relevant concentrations of 4-HNE demonstrated a concentration-dependent loss of constitutive Erk-1/2 phosphorylation, activity, and nuclear localization. These findings were consistent with iron-induced intracellular LPO, which also resulted in a concentration-dependent decrease in hepatocyte Erk-1/2 phosphorylation and activity. 4-HNE and iron-induced inhibition of Erk-1/2 was inversely correlated with the accumulation of 4-HNE-Erk-1/2 monomer adducts. 4-HNE treatment of hepatocytes decreased nuclear total and phosphorylated Erk-1/2, Elk-1, and AP-1 phosphorylation as well as cFos and cJun activities. The cytosolic modification of unphosphorylated Erk-1/2 was evaluated in vitro using molar ratios of inactive Erk-2 to 4-HNE consistent with increasing oxidative stress in vivo. Liquid chromatography combined with tandem mass spectrometry confirmed monomer adduct formation and identified the major adduct species at the histidine 178 residue within the kinase phosphorylation lip. These novel results show that the formation of 4-HNE-Erk-1/2 monomer-adducts results in the inhibition of Erk-Elk-AP-1 signaling in hepatocytes and implicates the His 178 residue with the mechanism of inhibition.

Intracellular metabolism of 4-hydroxynonenal

4-hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert a multitude of biological, cytotoxic, and signal effects. Mammalian cells possess highly active pathways of HNE metabolism. The metabolic fate of HNE was investigated in various mammalian cells and organs such as hepatocytes, intestinal enterocytes, renal tubular cells, aortic and brain endothelial cells, synovial fibroblasts, neutrophils, thymocytes, heart, and tumor cells. The experiments were carried out at 37 degrees C at initial HNE concentrations between 1 microM--that means in the range of physiological and pathophysiologically relevant HNE levels--to 100 microM. In all cell types which were investigated, 90-95% of 100 microM HNE were degraded within 3 min of incubation. At 1 microM HNE the physiological blood serum level of about 0.1-0.2 microM was restored already after 10-30 s. As primary products of HNE in hepatocytes and other cell types the glutathione-HNE-1:1-conjugate, the hydroxynonenoic acid and the corresponding alcohol of HNE, the 1,4-dihydroxynonene, were identified. Furthermore, the beta-oxidation of hydroxynonenoic acid including the formation of water was demonstrated. The quantitative share of HNE binding to proteins was low with about 2-8% of total HNE consumption. The glycine-cysteine-HNE, cysteine-HNE adducts and the mercapturic acid from glutathione-HNE adduct were not formed in the most cell types, but in kidney cells and neutrophils. The rapid metabolism underlines the role of HNE degrading pathways in mammalian cells as important part of the secondary antioxidative defense mechanisms in order to protect proteins from modification by aldehydic lipid peroxidation products.

Diabetes impairs the enzymatic disposal of 4-hydroxynonenal in rat liver

This study assesses whether the HNE accumulation we formerly observed in liver microsomes and mitochondria of BB/Wor diabetic rats depends on an increased rate of lipoperoxidation or on impairment of enzymatic removal. There are three main HNE metabolizing enzymes: glutathione-S-transferase (GST), aldehyde dehydrogenase (ALDH), and alcohol dehydrogenase (ADH). In this study we show that GST and ALDH activities are reduced in liver microsomes and mitochondria of diabetic rats; in contrast, ADH activity remains unchanged. The role of each enzyme in HNE removal was evaluated by using enzymatic inhibitors. The roles of both GST and ALDH were markedly reduced in diabetic rats, while ADH-mediated consumption was significantly increased. However, the higher level of lipohydroperoxides in diabetic liver indicated more marked lipoperoxidation. We therefore think that HNE accumulation in diabetic liver may depend on both mechanisms: increased lipoperoxidation and decreased enzymatic removal. We suggest that glycoxidation and/or hyperglycemic pseudohypoxia may be involved in the enzymatic impairment observed. Moreover, since HNE exerts toxic effects on enzymes, HNE accumulation, deficiency of HNE removal, and production of reactive oxygen species can generate vicious circles able to amplify the damage.

Increase in class 2 aldehyde dehydrogenase expression by arachidonic acid in rat hepatoma cells

Aldehyde dehydrogenase (ALDH) is a family of several isoenzymes important in cell defence against both exogenous and endogenous aldehydes. Compared with normal hepatocytes, in rat hepatoma cells the following changes in the expression of ALDH occur: cytosolic class 3 ALDH expression appears and mitochondrial class 2 ALDH decreases. In parallel with these changes, a decrease in the polyunsaturated fatty acid content in membrane phospholipids occurs. In the present study we demonstrated that restoring the levels of arachidonic acid in 7777 and JM2 rat hepatoma cell lines to those seen in hepatocytes decreases hepatoma cell growth, and increases class 2 ALDH activity. This latter effect appears to be due to an increased gene transcription of class 2 ALDH. To account for this increase, we examined whether peroxisome-proliferator-activated receptors (PPARs) or lipid peroxidation were involved. We demonstrated a stimulation of PPAR expression, which is different in the two hepatoma cell lines: in the 7777 cell line, there was an increase in PPAR alpha expression, whereas PPAR gamma expression increased in JM2 cells. We also found increased lipid peroxidation, but this increase became evident at a later stage when class 2 ALDH expression had already increased. In conclusion, arachidonic acid added to the culture medium of hepatoma cell lines is able to partially restore the normal phenotype of class 2 ALDH, in addition to a decrease in cell growth.

Analysis in the rat of 4-hydroxynonenal metabolites excreted in bile: evidence of enterohepatic circulation of these byproducts of lipid peroxidation

4-Hydroxynonenal (HNE) is a cytotoxic product resulting from the lipid peroxidation of membrane polyunsaturated fatty acids. In vitro, metabolism mainly leads to the corresponding alcohol (DHN), carboxylic acid (HNA), and the glutathione conjugate, whereas in vivo, mercapturic acid conjugates of HNE, DHN, HNA, and HNA-lactone and, more recently, dicarboxylic acids and related mercapturate conjugates were identified in urine of rats. In the study presented here, the identity of the HNE biotransformation products in the bile of rats following a single iv administration of [4-(3)H]HNE and the potential for enterohepatic recycling of HNE metabolites were investigated. The identity of metabolites was assessed by comparison of their HPLC retention times with those of the corresponding synthesized standards and by mass spectrometry analysis. Five metabolites were present in the bile; two of them corresponded to HNE- and DHN-glutathione conjugates. Two others metabolites were identified as DHN- and HNA-lactone mercapturic acid conjugates. The fifth metabolite was isolated but remained unidentified. As previously observed for urinary elimination, the kinetic excretion of biliary metabolites exhibited a rapid metabolism of HNE in rats. Within 4 h of injection, the bile accounted for 19.5% (+/-2.8%) of the injected radioactivity, whereas only 3% was found in the feces within 48 h [Alary, J., et al. (1995) Chem. Res. Toxicol. 8, 34-39]. The extent of HNE enterohepatic recycling was estimated utilizing a modified version of the linked rat model in three animals. All rat recipients were found to have measurable levels of HNE metabolites in bile, confirming that HNE is likely to undergo enterohepatic recirculation in the rat. The extent of recycling was approximatly 7. 7% of the total dose in this model. Two unknown metabolites were present in the bile of recipient rats and not found in the bile of donors rats, suggesting that intestinal microflora and/or intestinal mucosa could biotransform HNE-related compounds before or during the reabsorption process.

Lipoperoxidation in hepatic subcellular compartments of diabetic rats

It is known that an accumulation of lipoperoxidative aldehydes malondialdehyde (MDA) and 4-hydroxynonenal (HNE) takes place in liver mitochondria during aging. The existence and role of an increased extra- and intra-cellular oxidative stress in diabetes, an aging-accelerating disease, is currently under discussion. This report offers evidence that lipoperoxidative aldehydes accumulate in liver microsomes and mitochondria at a higher rate in spontaneously diabetic BB/WOR rats than in control non-diabetic animals (HNE content, diabetes vs. control: microsomes 80.6+/-19.9 vs. 25.75+/-3.6 pmol/mg prot, p = .024; mitochondria 77.4+/-15.4 vs. 26.5+/-3.5 pmol/mg prot, p = .0103). Liver subcellular fractions from diabetic rats, when exposed to the peroxidative stimulus ADP/Fe, developed more lipoperoxidative aldehydes than those from non diabetic rats (HNE amount, diabetes vs. control: microsomes 3.60+/-0.37 vs. 2.33+/-0.22 nmol/mg prot, p = .014; mitochondria 3.62+/-0.26 vs. 2.30+/-0.17 nmol/mg prot, p = .0009). Liver subcellular fractions of diabetic rats developed more fluorescent chromolipids related to HNE-phospholipid adducts, either after in vitro peroxidation (microsomes: p = .0045; mitochondria: p = .0023) or by exposure to exogenous HNE (microsomes: p = .049; mitochondria: p = .0338). This higher susceptibility of diabetic liver membranes to the non-enzymatic attack of HNE may be due to an altered phospholipid composition. Moreover, a decreased activity of the HNE-metabolizing systems can be involved: diabetic liver mitochondria and microsomes were unable to consume exogenous HNE at the same rate as non-diabetic membranes; the difference was already significant after 5' incubation (microsomes p<.001; mitochondria p<.001). These data show an increased oxidative stress inside the hepatocytes of diabetic rats; the impairment of the HNE-metabolizing systems can play a key role in the maintenance and propagation of the damage.

4-Hydroxynonenal as a biological signal: molecular basis and pathophysiological implications

Reactive oxygen intermediates (ROI) and other pro-oxidant agents are known to elicit, in vivo and in vitro, oxidative decomposition of omega-3 and omega-6 polyunsaturated fatty acids of membrane phospholipids (i.e, lipid peroxidation). This leads to the formation of a complex mixture of aldehydic end-products, including malonyldialdehyde (MDA), 4-hydroxy-2,3-nonenal (HNE), and other 4-hydroxy-2,3-alkenals (HAKs) of different chain length. These aldehydic molecules have been considered originally as ultimate mediators of toxic effects elicited by oxidative stress occurring in biological material. Experimental and clinical evidence coming from different laboratories now suggests that HNE and HAKs can also act as bioactive molecules in either physiological and pathological conditions. These aldehydic compounds can affect and modulate, at very low and nontoxic concentrations, several cell functions, including signal transduction, gene expression, cell proliferation, and, more generally, the response of the target cell(s). In this review article, we would like to offer an up-to-date review on this particular aspect of oxidative stress--dependent modulation of cellular functions-as well as to offer comments on the related pathophysiological implications, with special reference to human conditions of disease.

Effect of oxidative stress by iron on 4-hydroxynonenal formation and proliferative activity in hepatomas of different degrees of differentiation

It has been shown previously that oxidative stress by ferrous iron in vitro leads to an inhibition of proliferation of murine ascites tumour cells in vivo. This effect is associated with increased lipid peroxidation in terms of formation of the highly reactive aldehyde 4-hydroxynonenal (HNE), which has been shown to inhibit the proliferation of numerous tumours and to induce differentiation. It was the purpose of this article to study the occurrence and metabolism of HNE and its inducibility by oxidative stress in hepatomas of different degrees of differentiation to find further evidence for a possible role of HNE in proliferation and/or differentiation, because it is known that in hepatoma cells with a very low degree of differentiation basal lipid peroxidation is hardly detectable, while in normal hepatocytes the basal level of thiobarbituric acid reactive substances (TBArS) is rather high. MH1C1 hepatoma cells and Yoshida AH-130 hepatoma cells were chosen as highly differentiated and poorly differentiated tumour cells, respectively, and rat hepatocytes served as a control for normal liver phenotype. Ferrous histidinate (Fe/His) did not have a cytotoxic effect on Yoshida and MH1C1 cells, as measured by the LDH release test. In cell culture studies Fe/His revealed a dose dependent inhibition of the proliferation of Yoshida cells. The incorporation of 3H-thymidine into DNA of these cells was also inhibited by Fe/His in a dose-dependent manner, while the precursor uptake into the cytoplasm was unaffected. The basal levels of HNE were in the order: hepatocytes > MH1C1 cells > Yoshida cells. Both hepatocytes and Yoshida cells responded to the presence of Fe/His with increased formation of TBArS. Compared with hepatocytes the response of the Yoshida cells was greatly reduced. The response of cells to Fe/His with respect to HNE formation was decreased in the order: hepatocytes > MH1C1 cells > Yoshida cells, but in this case the differences were not very pronounced. The metabolic capacity of the cells to consume HNE was also decreased in the order: hepatocytes > MH1C1 cells > Yoshida cells. In this case the differences were very pronounced. These findings support the view that Yoshida cells with a low degree of differentiation and a low basal level of HNE are released from an inhibitory effect of HNE operative in hepatocytes and that HNE is causally involved in the iron induced inhibition of proliferation of poorly differentiated hepatoma cells.