4-hydroxynonenal is degraded to mercapturic acid conjugate in rat kidney

The Disposal of Reactive Carbonyl Species through Carnosine Conjugation: What We Know Now

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Reactive Carbonyl Species are electrophiles generated by the oxidative cleavage of lipids and sugars. Such compounds have been described as important molecules for cellular signaling, whilst their accumulation has been found to be cytotoxic as they may trigger aberrant modifications of proteins (a process often referred to as carbonylation).

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A correlation between carbonylation of proteins and human disease progression has been shown in ageing, diabetes, obesity, chronic renal failure, neurodegeneration and cardiovascular disease. However, the fate of reactive carbonyl species is still far from being understood, especially concerning the mechanisms responsible for their disposal as well as the importance of this in disease progression.

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In this context, some data have been published on phase I and phase II deactivation of reactive carbonyl species. In the case of phase II mechanisms, the route involving glutathione conjugation and subsequent disposal of the adducts has been extensively studied both in vitro and in vivo for some of the more representative compounds, e.g. 4-hydroxynonenal.

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There is also emerging evidence of an involvement of carnosine as an endogenous alternative to glutathione for phase II conjugation. However, the fate of carnosine conjugates is still poorly investigated and, unlike glutathione, there is little evidence of the formation of carnosine adducts in vivo. The acquisition of such data could be of importance for the development of new drugs, since carnosine and its derivatives have been proposed as potential therapeutic agents for the mitigation of carbonylation associated with disease progression.

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Herein, we wish to review our current knowledge of the binding of reactive carbonyl species with carnosine together with the disposal of carnosine conjugates, emphasizing those aspects still requiring investigation such as conjugation reversibility and enzyme assisted catalysis of the reactions.

Enzymatic and non-enzymatic detoxification of 4-hydroxynonenal: Methodological aspects and biological consequences

4-Hydroxynonenal (HNE), an electrophilic end-product deriving from lipid peroxidation, undergoes a heterogeneous set of biotransformations including enzymatic and non-enzymatic reactions. The former mostly involve red-ox reactions on the HNE oxygenated functions (phase I metabolism) and GSH conjugations (phase II) while the latter are due to the HNE capacity to spontaneously condense with nucleophilic sites within endogenous molecules such as proteins, nucleic acids and phospholipids. The overall metabolic fate of HNE has recently attracted great interest not only because it clearly determines the HNE disposal, but especially because the generated metabolites and adducts are not inactive molecules (as initially believed) but show biological activities even more pronounced than those of the parent compound as exemplified by potent pro-inflammatory stimulus induced by GSH conjugates. Similarly, several studies revealed that the non-enzymatic reactions, initially considered as damaging processes randomly involving all endogenous nucleophilic reactants, are in fact quite selective in terms of both reactivity of the nucleophilic sites and stability of the generated adducts. Even though many formed adducts retain the expected toxic consequences, some adducts exhibit well-defined beneficial roles as documented by the protective effects of sublethal concentrations of HNE against toxic concentrations of HNE. Clearly, future investigations are required to gain a more detailed understanding of the metabolic fate of HNE as well as to identify novel targets involved in the biological activity of the HNE metabolites. These studies are and will be permitted by the continuous progress in the analytical methods for the identification and quantitation of novel HNE metabolites as well as for proteomic analyses able to offer a comprehensive picture of the HNE-induced adducted targets. On these grounds, the present review will focus on the major enzymatic and non-enzymatic HNE biotransformations discussing both the molecular mechanisms involved and the biological effects elicited. The review will also describe the most important analytical enhancements that have permitted the here discussed advancements in our understanding of the HNE metabolic fate and which will permit in a near future an even better knowledge of this enigmatic molecule.

4-Hydroxynonenal metabolites and adducts in pre-carcinogenic conditions and cancer

4-hydroxy-2-nonenal (HNE) is an amazing reactive compound, originating from lipid peroxidation within cells but also in food and considered as a "second messenger" of oxidative stress. Due to its chemical features, HNE is able to make covalent links with DNA, proteins and lipids. The aim of this review is to give a comprehensive summary of the chemical properties of HNE and of the consequences of its reactivity in relation to cancer development. The formation of exocyclic etheno-and propano-adducts and genotoxic effects are addressed. The adduction to cellular proteins and the repercussions on the regulation of cell signaling pathways involved in cancer development are reviewed, notably on the Nrf2/Keap1/ARE pathway. The metabolic pathways leading to the inactivation/elimination or, on the contrary, to the bioactivation of HNE are considered. A special focus is given on the link between HNE and colorectal cancer development, due to its occurrence in foodstuffs and in the digestive lumen, during digestion.

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.

Method for the simultaneous determination of free/protein malondialdehyde and lipid/protein hydroperoxides

A simple and sensitive method is presented for the simultaneous quantification (spectrophotometric and spectrofluorimetric) of the main lipid and protein peroxidation products after their initial fractionation: free malondialdehyde (FrMDA), protein-bound malondialdehyde (PrMDA), total hydroperoxides (LOOH), and protein hydroperoxides (PrOOH). FrMDA and PrMDA (released from proteins by alkaline hydrolysis) are measured after the reaction of MDA with thiobarbituric acid (TBA) under acidic conditions, by the specific fluorimetric quantification of the resulting MDA-(TBA)2 adduct chromophore. The measurement of LOOH and PrOOH is based on the reaction of Fe(3+) (resulting from the reaction of LOOH and PrOOH with Fe(2+)) with xylenol orange (XO) and the photometric quantification of the resulting XO-Fe complex. The sensitivity of the assays for FrMDA/PrMDA and LOOH/PrOOH is 20 and 100pmol, respectively. The method was applied successfully on human plasma and can be used for the evaluation of oxidative stress in both basic and clinical research.

Ozone: a new therapeutic agent in vascular diseases

In this article, we scientifically evaluate the bio-oxidative procedure known as oxygen-ozone therapy. Research over a decade has established a comprehensive framework for understanding and recommending this type of autohemotherapy in vascular diseases. In contrast, a non-specific immunomodulation therapy, using heavily oxidized and denatured blood, has been recently used in studies involving a total of approximately 3000 patients and has led to 'disappointing' results. Such a treatment appears to be an inappropriate example of the so-called minor autohemotherapy, and its poor outcomes may discourage any further studies. Therefore it appears necessary to clarify that the use of only a minimal ozone dose and a valid experimental protocol is likely to produce beneficial results. Millions of people suffer from chronic limb, brain, and heart ischemia, and such patients may benefit if appropriate ozone therapy could be implemented. Accordingly, we propose the need for a well designed, multicenter, clinical trial to be conducted.

Ozone acting on human blood yields a hormetic dose-response relationship

The aim of this paper is to analyze why ozone can be medically useful when it dissolves in blood or in other biological fluids. In reviewing a number of clinical studies performed in Peripheral Arterial Diseases (PAD) during the last decades, it has been possible to confirm the long-held view that the inverted U-shaped curve, typical of the hormesis concept, is suitable to represent the therapeutic activity exerted by the so-called ozonated autohemotherapy. The quantitative and qualitative aspects of human blood ozonation have been also critically reviewed in regard to the biological, therapeutic and safety of ozone. It is hoped that this gas, although toxic for the pulmonary system during prolonged inhalation, will be soon recognized as a useful agent in oxidative-stress related diseases, joining other medical gases recently thought to be of therapeutic importance. Finally, the elucidation of the mechanisms of action of ozone as well as the obtained results in PAD may encourage clinical scientists to evaluate ozone therapy in vascular diseases in comparison to the current therapies.

Metabolism of 4-hydroxy-2-nonenal in human polymorphonuclear leukocytes

Intracellular metabolism of 4-hydroxy-2-nonenal (HNE), a major product and mediator of oxidative stress and inflammation, is analyzed in resting and fMLP-stimulated human polymorphonuclear leukocytes (PMNL), where this compound is generated during activation of the respiratory burst. HNE consumption rate in PMNL is very low, if compared to other cell types (rat hepatocytes, rabbit fibroblasts), where HNE metabolism is always an important part of secondary antioxidative defense mechanisms. More than 98% of HNE metabolites are identified. The pattern of HNE intermediates is quite similar in stimulated and resting PMNL - except for higher water formation in resting PMNL - while the initial velocity of HNE degradation is somewhat higher in resting cells, 0.44 instead of 0.28 nmol/(min×10(6) cells). The main products of HNE metabolism are 4-hydroxynonenoic acid (HNA), 1,4-dihydroxynonene (DHN) and the glutathione adducts with HNE, HNA, and DHN. Protein-bound HNE and water account for about 3-4% of the total HNE derivatives in stimulated cells, while in resting cells protein-bound HNE and water are 4% and 20%, respectively. Cysteinyl-glycine-HNE adduct and mercapturic acids contribute to about 5%.

The ozone paradox: ozone is a strong oxidant as well as a medical drug

After five decades characterized by empiricism and several pitfalls, some of the basic mechanisms of action of ozone in pulmonary toxicology and in medicine have been clarified. The present knowledge allows to understand the prolonged inhalation of ozone can be very deleterious first for the lungs and successively for the whole organism. On the other hand, a small ozone dose well calibrated against the potent antioxidant capacity of blood can trigger several useful biochemical mechanisms and reactivate the antioxidant system. In detail, firstly ex vivo and second during the infusion of ozonated blood into the donor, the ozone therapy approach involves blood cells and the endothelium, which by transferring the ozone messengers to billions of cells will generate a therapeutic effect. Thus, in spite of a common prejudice, single ozone doses can be therapeutically used in selected human diseases without any toxicity or side effects. Moreover, the versatility and amplitude of beneficial effect of ozone applications have become evident in orthopedics, cutaneous, and mucosal infections as well as in dentistry.

gamma-Glutamyltranspeptidase-dependent metabolism of 4-hydroxynonenal-glutathione conjugate

A major pathway for detoxification of the highly reactive lipid peroxidation product, 4-hydroxy-2,3-trans-nonenal (HNE) is through the conjugation with glutathione (GSH). We have studied the metabolism of GS-HNE conjugate by the enzyme gamma-glutamyltranspeptidase (GGT) using its purified form, as well as a GGT-overexpressing fibroblast cell line (V79 GGT). Using mass spectrometry analysis we identified for the first time cysteinylglycine-HNE (CysGly-HNE) as the GGT metabolite of GS-HNE. Furthermore, the GGT-dependent metabolism of GS-HNE in the V79 GGT cell line was associated with a considerable increase of cytotoxicity as compared to a control cell line which does not express GGT (V79 Cl). The cytotoxic effect was dose- and time-dependent (100% cellular death at 200 microM GS-HNE after 24 h incubation) in V79 GGT cells, whereas no decrease of viability was observed in V79 Cl cells. A similar cytotoxic effect was obtained when cells were incubated directly with CysGly-HNE, demonstrating that this GGT-dependent metabolite unlike GS-HNE, exhibits cytotoxic properties.

The ability of mineral dusts and fibres to initiate lipid peroxidation. Part II: relationship to different particle-induced pathological effects

Exposure to pathogenic mineral dusts and fibres is associated with pulmonary changes including fibrosis and cancer. Investigations into aetiological mechanisms of these diseases have identified modifications in specific macromolecules as well as changes in certain early processes, which have preceded fibrosis and cancer. Peroxidation of lipids is one such modification, which is observed following exposure to mineral dusts and fibres. Their ability to initiate lipid peroxidation and the parameters that determine this ability have recently been reviewed. Part II of this review examines the relationship between the capacity of mineral dusts and fibres to initiate lipid peroxidation and a number of pathological changes they produce. The oxidative modification of polyunsaturated fatty acids is a major contributor to membrane damage in cells and has been implicated in a great variety of pathological processes. In most pathological conditions where an induction of lipid peroxidation is observed it is assumed to be the consequence of disease, without further establishing if the induction of lipid peroxidation may have preceded or accompanied the disease. In the great majority of instances, however, despite the difficulty in proving this association, a causal relationship between lipid peroxidation and disease cannot be ruled out.

Glutathione conjugation of 4-hydroxy-trans-2,3-nonenal in the rat in vivo, the isolated perfused liver and erythrocytes

The formation of glutathione (GSH) conjugates of racemic 4-hydroxy-trans-2,3-nonenal (4-HNE) in the rat in vivo in the perfused rat liver and rat erythrocytes has been studied. An HPLC system was developed for the assay of 4-HNE-glutathione conjugates (HNE-SG). The very sensitive electrochemical detection method (detection limit 5 pmol) can also be used to study endogenously formed HNE-SG. Three diastereomeric HNE-SG conjugates could be separated by this system. Rat liver cytosol catalyzed the formation of 2 of the 3 conjugates. When 17 micromol/kg [(3)H] 4-HNE was injected intravenously in the rat, 21% of the radioactivity was excreted within 90 min in bile and 37% in urine. Most of the 4-HNE in bile was present as 2 of the HNE-SG conjugates (molecular mass 463). In addition, 25% was excreted as a third GSH conjugate (molecular mass of 461), which was identified as the lactone of the 4-hydroxynonenoic acid glutathione conjugate. Erythrocytes in vitro eliminated 4-HNE very rapidly, in part by GSH conjugation, suggesting that they may also play an important role in vivo. To study the role of the liver selectively, we used the recirculating perfused rat liver without erythrocytes in the perfusion medium; the same conjugates were found, but the third conjugate was a minor component. These results present direct evidence for the in vivo formation of 4-HNE glutathione conjugates in which the liver may play an important role.

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.

Efficient hepatic uptake and concentrative biliary excretion of a mercapturic acid

The role of the liver in the disposition of circulating mercapturic acids was examined in anesthetized rats and in the isolated perfused rat liver using S-2,4-dinitrophenyl-N-acetylcysteine (DNP-NAC) as the model compound. When DNP-NAC was infused into the jugular vein (150 or 600 nmol over 60 min) it was rapidly and nearly quantitatively excreted as DNP-NAC into bile (42-36% of the dose) and urine (48-62% of dose). Some minor metabolites were detected in bile (<4%), with the major metabolite coeluting on HPLC with the DNP conjugate of glutathione (DNP-SG). Isolated rat livers perfused single pass with 3 microM DNP-NAC removed 72 +/- 9% of this mercapturic acid from perfusate. This rapid DNP-NAC uptake was unaffected by sodium omission, or by L-cysteine, L-glutamate, L-cystine, or N-acetylated amino acids, but was decreased by inhibitors of hepatic sinusoidal organic anion transporters (oatp), indicating that DNP-NAC is a substrate for these transporters. The DNP-NAC removed from perfusate was promptly excreted into bile, eliciting a dose-dependent choleresis. DNP-NAC itself constituted approximately 75% of the total dose recovered in bile, reaching a concentration of 9 mM when livers were perfused in a recirculating mode with an initial DNP-NAC concentration of 250 microM. Other biliary metabolites included DNP-SG, DNP-cysteinylglycine, and DNP-cysteine. DNP-SG was likely formed by a spontaneous retro-Michael reaction between glutathione and DNP-NAC. Subsequent degradation of DNP-SG by biliary gamma-glutamyltranspeptidase and dipeptidase activities accounts for the cysteinylglycine and cysteine conjugates, respectively. These findings indicate the presence of efficient hepatic mechanisms for sinusoidal uptake and biliary excretion of circulating mercapturic acids in rat liver and demonstrate that the liver plays a role in their whole body elimination.

Enhanced gamma-glutamyl transpeptidase expression and selective loss of CuZn superoxide dismutase in hepatic iron overload

Liver injury caused by iron overload is presumed to involve lipid peroxidation and the formation of products such as 4-hydroxynonenal (4HNE), which has been implicated in hepatic fibrogenesis. Cellular antioxidants that modulate the formation and detoxification of compounds such as 4HNE may represent important protective mechanisms involved in the response to iron overload. This study examines the relationship between 4HNE, collagen content, and antioxidant defenses in the livers of rats fed carbonyl iron for 10 weeks. Iron-loading resulted in significant increases in iron (8.8-fold), 4HNE (1.7-fold), and hydroxyproline (1.5-fold). Total glutathione content was unchanged by iron, but gamma-glutamyl transpeptidase activity (GGT) increased sixfold and CuZn superoxide dismutase (CuZnSOD) activity decreased >9%. GGT colocalized with iron deposition and was associated with increased GGT mRNA. Decreased CuZnSOD activity was paralleled by a reduction in CuZnSOD protein on Western blot and immunohistochemistry, but no decrease in CuZnSOD mRNA. Glutathione S-transferase (GST) and Mn superoxide dismutase (MnSOD) activities were also significantly increased by iron loading. These results demonstrate that iron overload significantly alters the expression of antioxidant enzymes associated with glutathione (GGT and GST) and superoxide metabolism (CuZnSOD and MnSOD). Furthermore, the localized induction of GGT may enhance detoxification of lipid peroxidation-derived aldehydes via glutathione-dependent pathways in iron-loaded hepatocytes. These alterations in antioxidant defenses may represent an adaptive response, limiting accumulation 4HNE, and thus, stimulation of collagen synthesis, accounting for the mild fibrogenic response seen in this model of iron overload.

High metabolic rates of 4-hydroxynonenal in brain capillary endothelial cells during hypoxia/reoxygenation

We measured the accumulation of 4-hydroxynonenal (HNE), a major lipid peroxidation product during hypoxia/reoxygenation of brain capillary endothelial cells (BCEC). The concentration of HNE after 2 h of hypoxia was 0.23 nmol/mg protein and rose up to 0.28 nmol/mg protein after 30 min of reoxygenation. That reflects a 1.5-fold increase, whereas aortic endothelial cells (AEC) increased the HNE level 5-fold, compared to the control. Therefore, the ability of BCEC to degrade exogenously added HNE was tested. The HNE consumption in BCEC achieved a rate of about 600 nmol.min-1.mg protein-1, about two times higher than in AEC. The higher ability of BCEC to degrade HNE is probably the reason of the 2-fold higher IC50 value against the aldehyde. Therefore, we concluded that the high ability of BCEC to degrade HNE is a substantial part of the secondary antioxidative defense of the brain.

Disposition in rat of [2-3H]-trans-4-hydroxy-2,3-nonenal, a product of lipid peroxidation

1. 4-Hydroxy-2,3-nonenal (HNE) is an end product of lipid peroxidation (LPO) and a well known cytotoxic aldehyde that exhibits a variety of biological effects. In this study the in vivo disposition and covalent binding of i.p. administered [2-3H]HNE was examined in the rat. 2. It was found that several metabolites of [2-3H]HNE are excreted in urine among which at least four mercapturic acids. 1,4-Dihydroxynonane mercapturic acid (DHN-MA) appeared to be the most abundant mercapturic acid excreted in urine (3.5% of the dose) and the excretion of the other three mercapturic acids amounted to 2% of the dose. 3. Within 48 h following i.p. administration of 5 or 25 mumol/kg bodyweight [2-3H]HNE (specific activity 4 microCi/mumol) about 25% of the radioactivity was excreted in urine, whereas 18% of the radioactivity appeared in the faeces. 4. After 48 h, 7% of the radioactivity was still present in the liver and 0.2% in other organs, but this radioactivity appeared to not to be covalently bound to cellular macromolecules. It was found that only 0.13% of the radioactivity was covalently bound in the liver and even less in other organs.