4-Hydroxynonenal in Redox Homeostasis of Gastrointestinal Mucosa: Implications for the Stomach in Health and Diseases.

Event Abstract Back to Event 4-Hydroxynoneal as second messenger of free radicals in the blood-brain barrier Kamelija Zarkovic1*, Marina Cindric1, Danijela Kolenc1 and Neven Zarkovic2 1 Clinical Hospital Centre, Medical Faculty, Netherlands 2 Rudjer Boskovic Institute, Netherlands Excess in production of reactive oxygen species (ROS), process denoted as oxidative stress, is considered to play important role in various pathologies, such as cardiovascular diseases, cancer, metabolic disorders, autoimmune disorders and (neuro)degenerative processes. Although oxidative stress could be moderate and even physiological, as in case of physical exercise or wound healing, thus playing important role in oxidative homeostasis, if excess in production of ROS results in irreversible damage of the structure and function of major bioactive macromolecules, in particular nucleic acids and proteins, it becomes important component of acute and chronic disorders, as mentioned. Of particular relevance is aggressive process of lipid peroxidation, in particular of poly-unsaturated fatty acids (PUFA) in cellular membranous structures, which is a progressive, chain reaction of ROS production resulting in final disintegration of the membranes. The final products of lipid peroxidation, reactive aldehydes, are considered as “second toxic messengers of free radicals” because their biological activities often resemble bioactivities of ROS, although these aldehydes are not ROS. Among the end products of lipid peroxidation of particular relevance is 4- hydroxynonenal (HNE), which acts not only as a second (toxic) messenger of free radicals, but also as a growth regulating factor interfering with the effects of various cytokines [1]. HNE is nowadays considered as major bioactive marker of lipid peroxidation and a signaling molecule involved in proliferation, differentiation and apoptosis [2]. It is well known that HNE has strong affinity to bind to proteins, developing relatively stable and bioactive protein adducts, while recent studies have revealed that HNE-protein adducts are physiologically present in various human and animals tissues, indicating that not only oxidative stress but also lipid peroxidation could contribute to oxidative homeostasis [3]. However, while the physiological roles of such HNE-protein adducts have yet to be clarified, their relevance for various pathologies were intensively studied for year. These studies have shown that HNE-protein adducts could play important roles in neurodegenerative disorders, in particular in Alzheimer’s disease, spongiform encephalopathies and amyotrophic lateral sclerosis (ALS) [4]. Moreover, HNE-protein adducts were also found to be present in brain tumors, in particular astrocytomas, showing the distribution pattern specific for each types of the tumor and positive correlation with the level of malignancy of these neoplasms [5]. Of particular relevance might be findings of association of HNE-protein adducts with the tumor blood vessels, indicating that while HNE could be found physiologically in the blood vessel walls, its spread into the brain tissue might be associated with the development and progression of the tumor. Complementary to that, we have found HNE to be present in the blood-brain barrier (BBB) as presented on Figure 1, but only under pathological circumstances, such as relative hypoxia (reduced blood flow) or inflammation (sepsis) [6]. Biomedical relevance of the presence of HNE in the BBB could be very high, because the use of in vitro model of the BBB has shown that HNE makes the endothelial part of the BBB permeable within 10 minutes of exposure to the aldehyde, while astrocytic part of the BBB starts licking with 10-20 minutes delay after endothelium [7]. Therefore, the presence of HNE in the BBB in vivo might alter the function of the barrier allowing not only exchange of substances otherwise reduced by the BBB but also progressive pathological circumstances allowing secondary brain tissue damage. That could be further enhanced under conditions of hypoxia and/or inflammation, which allow the inflammatory cells, in particular granulocytes, to adhere to the endothelium under hypoxic and to migrate out of the blood vessels undergoing oxidative burst. Based on these facts we may assume that 4-hydroxynoneal acts as second messenger of free radicals in the BBB under various conditions of oxidative stress and makes preconditions for the disorders of the central nervous system (CNS) function. Accordingly, the use of some antioxidant substances that might attenuate production and bioactivities of HNE might be beneficial for the CNS disorders, while mild lipid peroxidation, within the levels of oxidative homeostasis might eventually also increase the permeability of the BBB and increase efficiency of some medicaments. Pic 1

Pathophysiological processes associated with disturbances in cell and tissue oxidative homeostasis, are associated with self-catalyzed process of lipid peroxidation. The end products of lipid peroxidation are reactive aldehydes such as 4-hydroxy-2-nonenal (HNE), acting as “second messengers of free radicals.” Although reactive aldehydes were first recognized only as cytotoxic, new evidence has come to light, related to their cell growth regulatory functions achieved through cell signaling. The variable appearance of HNE in several organs indicates that its mode of action might be related to an individual cell stress adaptation. The underlying mechanism could be that specific mutations and epigenetic changes on one hand interfere with hormesis on the other. The precise role of oxidative stress and lipid peroxidation in these processes still needs more clarification at molecular level. Finally, an individual approach to each patient, based on the individual cell response to stress, opens a new possibility of integrative medicine in cancer treatment and strongly supports modern concepts of personalized medicine.

Elevated levels of pro-oxidants and various markers of oxidative tissue damage were found in diabetic patients, indicating involvement of oxidative stress in the pathogenesis of diabetes mellitus (DM). On one side, physiological levels of reactive oxygen species (ROS) play an important role in redox signaling of various cells, while on the other, excessive ROS production can jeopardize the integrity and physiological functions of cellular macromolecules, in particular proteins, thus contributing to the pathogenesis of DM. Reactive aldehydes, especially 4-hydroxynonenal (HNE), are considered as second messengers of free radicals that act both as signaling molecules and as cytotoxic products of lipid peroxidation causing long-lasting biological consequences, in particular by covalent modification of macromolecules. Accordingly, the HNE and related reactive aldehydes may play important roles in the pathophysiology of DM, both in the development of the disease and in its progression and complications due to the following: (i) exposure of cells to supraphysiological levels of 4-hydroxyalkenals, (ii) persistent and sustained generation of 4-hydroxyalkenals that progressively affect vulnerable cells that lack an efficient bioactive aldehyde neutralization system, (iii) altered redox signaling influenced by reactive aldehydes, in particular by HNE, and (iv) induction of extracellular generation of similar aldehydes under secondary pathological conditions, such as low-grade inflammation.

Pathophysiological relevance of aldehydic protein modifications

The effects of angiotensin II and the oxidative stress mediator 4-hydroxynonenal on human osteoblast-like cell growth: possible relevance to otosclerosis

Contribution of the HNE-immunohistochemistry to modern pathological concepts of major human diseases

It is commonly believed that cancer development is irreversible, organ-specific as well as systemic malignant disorder, often associated with harmful oxidative stress and inflammation. However, there are also well-documented cases of spontaneous cancer regression, the causative mechanisms of which are not understood. It is known that inflammation is a negative pathophysiological process that may support the development of cancer, but it is also believed that the immune system as well as oxidative stress play important roles in prevention of cancer development and defense against tumor progression. Hence, in animal models spontaneous regression of cancer could be mediated by rapid inflammatory response of granulocytes, acting against cancer mostly as innate immune response. In addition, the administration of granulocytes at the site of solid tumors can lead to tumor regression or can slow down tumor growth and extend the overall survival of animals. In both cases, similar to the radiotherapy, surgery and various chemotherapies, oxidative stress occurs generating lipid peroxidation product 4-hydroxynonenal (4-HNE). This "second messenger of free radicals" acts as growth regulating signaling molecule that exerts relatively selective cytotoxicity against cancer cells. We hypothesize that abundant inflammation and metabolic changes caused by cancer and oxidative stress producing of 4-HNE may be crucial mechanisms for spontaneous cancer regression.

Breast cancer is a leading cause of mortality and morbidity in women, mostly due to high metastatic capacity of mammary carcinoma cells. It has been revealed recently that metastases of breast cancer comprise a fraction of specific stem-like cells, denoted as cancer stem cells (CSCs). Breast CSCs, expressing specific surface markers CD44(+)CD24(-/low)ESA(+) usually disseminate in the bone marrow, being able to spread further and cause late metastases. The fundamental factor influencing the growth of CSCs is the microenvironment, especially the interaction of CSCs with extracellular matrix (ECM). The structure and function of ECM proteins, such as the dominating ECM protein collagen, is influenced not only by cancer cells but also by various cancer treatments. Since surgery, radio and chemotherapy are associated with oxidative stress we analyzed the growth of breast cancer CD44(+)CD24(-/low)ESA(+) cell line SUM159 cultured on collagen matrix in vitro, using either native collagen or the one modified by hydroxyl radical. While native collagen supported the growth of CSCs, oxidatively modified one was not supportive. The SUM159 cell cultures were further exposed to a supraphysiological (35 microM) dose of the major bioactive lipid peroxidation product 4-hydroxynonenal (HNE), a well known as 'second messenger of free radicals', which has a strong affinity to bind to proteins and acts as a cytotoxic or as growth regulating signaling molecule. Native collagen, but not oxidised, abolished cytotoxicity of HNE, while oxidized collagen did not reduce cytotoxicity of HNE at all. These preliminary findings indicate that beside direct cytotoxic effects of anticancer therapies consequential oxidative stress and lipid peroxidation modify the microenvironment of CSCs influencing oxidative homeostasis that could additionally act against cancer.

Significance: It is commonly believed that diabetes mellitus may be associated with cancer. Hence, diabetic patients are at higher risk for hepatocellular carcinoma, pancreatic cancer, colorectal cancer, and breast cancer, but the mechanisms that may link these two severe diseases are not well understood. Recent Advances: A number of factors have been suggested to promote tumorigenesis in diabetic patients, including insulin resistance, hyperglycemia, dyslipidemia, inflammation, and elevated insulin-like growth factor-1 (IGF-1), which may also promote pro-oxidants, and thereby alter redox homeostasis. The consequent oxidative stress associated with lipid peroxidation appears to be a possible pathogenic link between cancer and diabetes. Critical Issues: Having summarized the above aspects of diabetes and cancer pathology, we propose that the major bioactive product of oxidative degradation of polyunsaturated fatty acids (PUFAs), the reactive aldehyde 4-hydroxynonenal (4-HNE), which is also considered a second messenger of free radicals, may be the key pathogenic factor linking diabetes and cancer. Future Directions: Because the bioactivities of 4-HNE are cell-type and concentration-dependent, are often associated with inflammation, and are involved in signaling processes that regulate antioxidant activities, proliferation, differentiation, and apoptosis, we believe that further research in this direction could reveal options for better control of diabetes and cancer. Controlling the production of 4-HNE to avoid its cytotoxicity to normal but not cancer cells while preventing its diabetogenic activities could be an important aspect of modern integrative biomedicine. Antioxid. Redox Signal. 37, 1222-1233.

Lipid peroxidation in brain tumors

In the recent years, numerous research on the pathology of oxidative stress has been completed by intense studies on redox signaling implementing various experimental models and clinical trials. [...].

Antioxidants and Second Messengers of Free Radicals

Oxidative stress has been implicated in pathophysiology of different human stress- and age-associated disorders, including osteoporosis for which antioxidants could be considered as therapeutic remedies as was suggested recently. The 1,4-dihydropyridine (DHP) derivatives are known for their pleiotropic activity, with some also acting as antioxidants. To find compounds with potential antioxidative activity, a group of 27 structurally diverse DHPs, as well as one pyridine compound, were studied. A group of 11 DHPs with 10-fold higher antioxidative potential than of uric acid, were further tested in cell model of human osteoblast-like cells. Short-term combined effects of DHPs and 50 µM H2O2 (1-h each), revealed better antioxidative potential of DHPs if administered before a stressor. Indirect 24-h effect of DHPs was evaluated in cells further exposed to mild oxidative stress conditions induced either by H2O2 or tert-butyl hydroperoxide (both 50 µM). Cell growth (viability and proliferation), generation of ROS and intracellular glutathione concentration were evaluated. The promotion of cell growth was highly dependent on the concentrations of DHPs used, type of stressor applied and treatment set-up. Thiocarbatone III-1, E2-134-1 III-4, Carbatone II-1, AV-153 IV-1, and Diethone I could be considered as therapeutic agents for osteoporosis although further research is needed to elucidate their bioactivity mechanisms, in particular in respect to signaling pathways involving 4-hydroxynoneal and related second messengers of free radicals.

Endogenous 4-hydroxy-2-nonenal in microalga Chlorella kessleri acts as a bioactive indicator of pollution with common herbicides and growth regulating factor of hormesis

Tumor growth is associated with oxidative stress, which causes lipid peroxidation. The most intensively studied product of lipid peroxidation is 4-hydroxy-2-nonenal (HNE), which is considered as a “second messenger of free radicals” that binds to proteins and acts as a growth-regulating signaling factor. The incidence of squamous cell carcinoma of the oropharynx is associated with smoking, alcohol and infection of human papilloma virus (HPV), with increasing incidence world-wide. The aim of this retrospective study involving 102 patients was to determine the immunohistochemical appearance of HNE-protein adducts as a potential biomarker of lipid peroxidation in squamous cell carcinoma of the oropharynx. The HNE-protein adducts were detected in almost all tumor samples and in the surrounding non-tumorous tissue, while we found that HNE is differentially distributed in squamous cell carcinomas in dependence of clinical stage and histological grading of these tumors. Namely, the level of HNE-immunopositivity was increased in comparison to the normal oropharyngeal epithelium in well- and in moderately-differentiated squamous cell carcinoma, while it was decreasing in poorly differentiated carcinomas and in advanced stages of cancer. However, more malignant and advanced cancer was associated with the increase of HNE in surrounding, normal tissue. This study confirmed the onset of lipid peroxidation, generating HNE-protein adducts that can be used as a valuable bioactive marker of carcinogenesis in squamous cell carcinoma of the oropharynx, as well as indicating involvement of HNE in pathophysiological changes of the non-malignant tissue in the vicinity of cancer.