Centrilobular endothelial cell injury by diquat in the selenium-deficient rat liver

Vascular endothelium, a promising target for effectively treating fulminant diquat intoxication?

Following the withdrawal of paraquat, diquat (DQ) has emerged as the predominant herbicide. When people come into contact with or ingest DQ, may lead to poisoning and potentially fatal outcomes. Reports suggest that the mortality of DQ poisoning can be as high as 50%. DQ poisoning can be categorized as mild, moderate or severe. In cases of severe poisoning, victims often succumb to multiple organ failure within 48 h. This presents a significant challenge in the clinical management. Scholars have discovered that oxidative stress, inflammatory injury, and cell apoptosis play crucial roles in the DQ poisoning. However, the underlying connection of the extensive organ damage remains unknown. The abnormal function and activity of endothelial cells (EC) should play a crucial role in tissue damage caused by DQ due to rich microcirculation and high sensitivity to perfusion in the vulnerable organs. However, reports on DQ-induced EC injury is rare. We made a significant discovery-the presence of severe vascular endothelial damage in the kidneys and lungs affected by DQ. Therefore, we hypothesize that DQ poisoning may be attributed to oxidative stress damage and cell apoptosis in EC, ultimately resulting in multiple organ failure.

Vascular endothelium, a promising target for effectively treating fulminant diquat intoxication?

Following the withdrawal of paraquat, diquat (DQ) has emerged as the predominant herbicide. When people come into contact with or ingest DQ, may lead to poisoning and potentially fatal outcomes. Reports suggest that the mortality of DQ poisoning can be as high as 50%. DQ poisoning can be categorized as mild, moderate to severe or fulminant. In cases of fulminant poisoning, victims often succumb to multiple organ failure within 48 h. This presents a significant challenge in the clinical management. Scholars have discovered that oxidative stress, inflammatory injury, and cell apoptosis play crucial roles in the DQ poisoning. However, the underlying connection of the extensive organ damage remains unknown. The abnormal function and activity of endothelial cells (EC) should play a crucial role in tissue damage caused by DQ due to rich microcirculation and high sensitivity to perfusion in the vulnerable organs. However, reports on DQ-induced EC injury is rare. We made a preliminary discovery-the presence of severe vascular endothelial damage in the kidneys and lungs affected by DQ. Therefore, we hypothesize that DQ poisoning may be attributed to EC damage, ultimately resulting in multiple organ failure.

Selenocompounds and Sepsis-Redox Bypass Hypothesis: Part B-Selenocompounds in the Management of Early Sepsis

Significance: Endothelial barrier damage, which is in part caused by excess production of reactive oxygen, halogen and nitrogen species (ROHNS), especially peroxynitrite (ONOO^-), is a major event in early sepsis and, with leukocyte hyperactivation, part of the generalized dysregulated immune response to infection, which may even become a complex maladaptive state. Selenoenzymes have major antioxidant functions. Their synthesis is related to the need to limit deleterious oxidant redox cycling by small selenocompounds, which may be of therapeutic cytotoxic interest. Plasma selenoprotein-P is crucial for selenium transport from the liver to the tissues and for antioxidant endothelial protection, especially against ONOO^-. Above micromolar concentrations, sodium selenite (Na₂SeO₃) becomes cytotoxic, with a lower cytotoxicity threshold in activated cells, which has led to cancer research. Recent Advances: Plasma selenium (<2% of total body selenium) is mainly contained in selenoprotein-P, and concentrations decrease rapidly in the early phase of sepsis, because of increased selenoprotein-P binding and downregulation of hepatic synthesis and excretion. At low concentrations, Na₂SeO₃ acts as a selenium donor, favoring selenoprotein-P synthesis in physiology, but probably not in the acute phase of sepsis. Critical Issues: The cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes, especially the most immature forms that liberate ROHNS, may be beneficial, but they may also be harmful for activated endothelial cells. Endothelial protection against ROHNS by selenoprotein-P may reduce Na₂SeO₃ toxicity, which is increased in sepsis. Future Direction: The combination of selenoprotein-P for endothelial protection and the cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes may be a promising intervention for early sepsis. Antioxid. Redox Signal. 37, 998-1029.

Delayed increase of plasma selenoproteins and absence of side effect induced by infusion of pharmacological dose of sodium selenite in septic shock: Secondary analysis of a multicenter, randomized controlled trial

BACKGROUND

In sepsis, neutrophil respiratory bursts participate in endothelium damage, the first step to multiple organ failure. In plasma two antioxidant selenoenzymes, which protect the endothelium, decrease: selenoprotein-P, and to a lesser extent glutathione peroxidase (GPX3). Sodium selenite (Na₂SeO₃) is a Se donor, but also an oxidant chemotherapy drug depending on its concentration. In a previous published study, Na₂SeO₃ continuous infusion in septic shock patients at a pharmacological dose of 4 mg¹ Se/day on day-1, followed by a high nutritional dose of 1 mg Se/day during 9 days, showed no beneficial effect on weaning of catecholamine nor on survival. In this ancillary study, we report clinical and biological effects of such continuous infusion of Na₂SeO_3. METHODS: This was a multicenter, placebo-controlled, double-blind study on 60 patients. Na₂SeO₃ or placebo in continuous infusion as described above. Evolution with time of plasma Se, selenoprotein-P, GPX3, Organ dysfunction (sequential organ failure assessment SOFA scores, including PaO2/FiO2, for respiratory failure, and plasma lactate) and quality of life at 6 months (by SF36 scores) were analyzed using two-way (time, treatment) non-parametric repeated-measures analysis of variance (Friedman test).

MAIN RESULTS

At baseline, plasma Se was about a quarter of reference values. From baseline to day-4 plasma Se, selenoprotein-P and GPX3 significantly increased by 3.9, 2.7 and 1.8 respectively in the Na₂SeO₃ group as compared with placebo and remained elevated by 2.3, 2.7 and 2.1 at day-14 respectively (p < 0.001). Na₂SeO₃ did not affect global and organ by organ SOFA Scores and plasma lactate concentration at day-1 and later up to day-14. The evolution of PaO2/FiO2 until day-14 was similar in the two groups. Quality of life in the surviving patients at 6 months was similar between the two groups.

CONCLUSION

Continuous infusion of Na₂SeO₃ at 4 mg Se at day-1 seems to have neither beneficial nor toxic effect at day-1 or later and induces a late increase of selenoprotein-P at day-4. Preclinical studies are required to confirm the use of Na₂SeO₃ as a cytotoxic drug against neutrophils and protection of the endothelium by selenoprotein-P.

Research progress on separation of selenoproteins/Se-enriched peptides and their physiological activities

Selenium (Se) is an essential nutrient associated with several physiological processes in humans and has raised interest because of its antioxidant and immune properties. Se deficiency is related to a variety of diseases and dysfunctions in humans. Due to its higher bioavailability and lower toxicity, organic Se is more recommendable than inorganic Se in the frame of a balanced diet. Se is present in 25 identified selenoproteins that commonly occur in human organisms. As part of selenocysteine (SeC), Se becomes co-translationally incorporated into the polypeptide chain and involved in the regulation of oxidative stress, redox mechanisms, and other crucial cellular processes responsible for innate and adaptive immune responses. This review presents the current information regarding the presence of selenoproteins in the human body, and the separation of selenoproteins and selenopeptides from various plants and their physiological roles in the immune and oxidation systems of humans. In general, the application of selenoproteins and Se-enriched peptides are practically important for the clinical arena, whereby it can be used for exploring new healthy foods.

Effects of Bariatric Surgeries on Fetuin-A, Selenoprotein P, Angiopoietin-Like Protein 6, and Fibroblast Growth Factor 21 Concentration

Obesity is a civilization disease representing a global health problem. Excessive body weight significantly reduces the quality of life. It is also associated with the leading causes of death, including type 2 diabetes mellitus, cardiovascular diseases, and numerous types of cancer. The mainstay of therapy is a dietary treatment. However, in morbidly obese patients, dietary treatment is often insufficient. In these patients, the most effective procedure is bariatric surgery, but it is still difficult to predict its outcome and metabolic changes. Hepatokines are proteins secreted by hepatocytes. Many of them, including fetuin-A, selenoprotein P, angiopoietin-like protein 6, and fibroblast growth factor 21, have been linked to metabolic dysfunctions. In this context, hepatokines may prove helpful. This review investigates the possible changes in hepatokine profiles after selected bariatric surgery protocols. In this regard, Roux-en-Y gastric bypass is the most studied type of surgery. The overall analysis of published research identified fetuin-A as a potential marker of metabolic alternations in patients after bariatric surgery.

Selenium and hydrogen selenide: essential micronutrient and the fourth gasotransmitter?

Selenium (Se) is an essential micronutrient required by organisms of diverse lineage. Dietary Se is converted to hydrogen selenide either enzymatically or by endogenous antioxidant proteins. This convergent biochemical step crucially underlies the subsequent biological activity of Se and argues for inclusion of hydrogen selenide as the fourth endogenous gasotransmitter alongside nitric oxide, carbon monoxide and hydrogen sulfide.Endogenously generated hydrogen selenide is incorporated into numerous 'selenoprotein' oxidoreductase enzymes, essential for maintaining redox-status homeostasis in health and disease. Direct effects of endogenous hydrogen selenide on cellular and molecular targets are currently unknown. Given exogenously, hydrogen selenide acts as a modulator of metabolism via transient inhibition of mitochondrial cytochrome C oxidase. Here we provide an overview of Se biology, its impact on several physiological systems (immune, endocrine, cardiovascular and metabolic) and its utility as a supplement in acute and critical illness states. We further explore the evidence base supporting its role as the fourth gasotransmitter and propose a strategic case towards generation of novel selenomimetic therapeutics.

Characterization of Selenoprotein P cDNA of the Antarctic toothfish Dissostichus mawsoni and its role under cold pressure

Our previous study using comparative genome analysis revealed a significant gene copy number gain of Dissostichus mawsoni selenoprotein P (Dm-SEPP) during the evolutionary radiation of Antarctic notothenioids, suggesting that Dm-SEPP contribute to this process, but the detailed structure and function of this gene product remain unclear. In the present study, the Dm-SEPP cDNA was cloned and characterized. The Dm-SEPP cDNA contains 17 selenocysteines (Sec) encoded by TGA codons and 2 typical SECIS elements located in the 3'-UTR. Evolutionary analysis of the Dm-SEPP gene revealed that it's closely related to the SEPP gene of zebrafish (Danio rerio), showing 51% amino acid similarity. Over-expression of Dm-SEPP could protect mammalian cells under cold pressure, probably via eliminating ROS. Further study showed an increase of endogenous SEPP in zebrafish ZF4 cells under cold pressure, and knockdown of SEPP decreased cell viability, accompanied with increased ROS. Our results suggested a protective role of Dm-SEPP in cold adaptation in Antarctic notothenioids.

Longitudinal Changes in Serum Levels of Angiopoietin-Like Protein 6 and Selenoprotein P After Gastric Bypass Surgery

BACKGROUND

Bariatric surgery has beneficial effects on weight loss and metabolic profiles. Recent evidence suggests that liver-derived hepatokines play a role in the pathophysiology of metabolic diseases. However, few studies have reported longitudinal changes in hepatokines after gastric bypass surgery. We investigated changes in the serum levels of angiopoietin-like protein 6 (Angptl6) and selenoprotein P after gastric bypass surgery.

METHODS

We followed 10 patients who were treated with gastric bypass for weight loss. We measured metabolic parameters and the serum levels of Angptl6 and selenoprotein P before, 1 month after, and 9 months after surgery. We investigated the changes in those hepatokines after surgery and the associations between changes in Angptl6 and selenoprotein P, respectively, and metabolic parameters.

RESULTS

Body mass index decreased linearly. Levels of hemoglobin A1c (HbA1c), aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma glutamyltransferase (GGT), total cholesterol, triglyceride, LDL cholesterol, and Angptl6 were significantly lower 1 and 9 months after surgery. Fasting plasma glucose was normal throughout the study. Fasting insulin decreased 1 month after surgery but increased 9 months post-surgery. Levels of selenoprotein P increased linearly. Significant correlations were detected between the levels of Angptl6 and LDL cholesterol and fasting insulin. Changes in Angptl6 levels were significantly correlated with changes in total cholesterol and LDL cholesterol. Selenoprotein P levels were inversely correlated with GGT, and changes in selenoprotein P were inversely correlated with changes in homeostasis model assessment for insulin resistance (HOMA-IR).

CONCLUSIONS

Our results suggest that gastric bypass may alter the serum levels of hepatokines independent of weight loss, and these changes are related to certain hepatic metabolic changes.

Protective effect of diphenylmethyl selenocyanate against CCl4-induced hepatic injury

Organoselenocyanates represent an important class of chemopreventive agent, which possess antioxidative, antimutagenic as well as cancer chemopreventive properties. The present study is an attempt to evaluate the protective effect of diphenylmethyl selenocyanate -- a synthetic organoselenocyanate against carbon tetrachloride (CCl(4))-induced hepatic damage in Swiss albino mice in vivo. Mice were pretreated with the Se-compound orally in a duration dependent manner (7 and 15 days) to observe its protective action against an acute toxic dose (24 h) of CCl(4) (single injection at a dose of 20 microl and 50 microl kg(-1) b.w.) that induced hepatic necrosis and caused DNA damage (strand breaks) in the hepatocytes. This study revealed that pretreatment with the Se-compound reduced the extent of massive hepatic necrosis in a duration dependent manner, but it had no modulatory effect on hepatocellular apoptosis caused by acute toxic doses of CCl(4). It was also found that the Se-compound could significantly (P < 0.01) prevent the CCl(4)-induced elevation of DNA damage in hepatocytes measured by comet assay in a duration dependent manner. So these findings will further strengthen the view that organoselenocyanate is an effective chemopreventive agent against acute hepatic damage, caused by halogenated alkanes such as CCl(4).

From selenium to selenoproteins: synthesis, identity, and their role in human health

The requirement of the trace element selenium for life and its beneficial role in human health has been known for several decades. This is attributed to low molecular weight selenium compounds, as well as to its presence within at least 25 proteins, named selenoproteins, in the form of the amino acid selenocysteine (Sec). Incorporation of Sec into selenoproteins employs a unique mechanism that involves decoding of the UGA codon. This process requires multiple features such as the selenocysteine insertion sequence (SECIS) element and several protein factors including a specific elongation factor EFSec and the SECIS binding protein 2, SBP2. The function of most selenoproteins is currently unknown; however, thioredoxin reductases (TrxR), glutathione peroxidases (GPx) and thyroid hormone deiodinases (DIO) are well characterised selenoproteins involved in redox regulation of intracellular signalling, redox homeostasis and thyroid hormone metabolism. Recent evidence points to a role for selenium compounds as well as selenoproteins in the prevention of some forms of cancer. A number of clinical trials are either underway or being planned to examine the effects of selenium on cancer incidence. In this review we describe some of the recent progress in our understanding of the mechanism of selenoprotein synthesis, the role of selenoproteins in human health and disease and the therapeutic potential of some of these proteins.

New roles for an old selenoenzyme: evidence from glutathione peroxidase-1 null and overexpressing mice

Cellular glutathione peroxidase-1 (GPX1) is the first identified and the most abundant selenoprotein in mammals. Although GPX1 has been widely considered to be a major antioxidant enzyme, there has been no direct evidence for such role in vivo until GPX1 transgenic and null mice became available 10 y ago. Using these new models, we demonstrated that GPX1 protects against oxidative stress mediated by reactive oxygen species (ROS), and the physiologic importance of this protection varies with insult level and body Se status. Full expression of GPX1 is needed, and overexpression of GPX1 is beneficial for Se-adequate mice to defend against severe oxidative stress. This function of GPX1 is associated with attenuating the prooxidant-induced oxidation of NADPH, NADH, lipid, and protein in various tissues. In Se-deficient mice, a minute amount of GPX1 activity (4% of adequate levels) protects against hepatic aponecrosis induced by mild oxidative stress. In contrast, knockout of GPX1 renders mice and their hepatocytes resistant to oxidative stress related to reactive nitrogen species (RNS). More intriguingly, mice overexpressing GPX1 develop insulin resistance and obesity, accompanied by a downregulation of insulin-mediated phosphorylations of insulin receptor and Akt protein. In conclusion, GPX1 seems to play contrasting roles in coping with ROS vs. RNS, and its metabolic functions extend beyond redox regulation.

Selenoprotein P: an extracellular protein with unique physical characteristics and a role in selenium homeostasis

Selenoprotein P is an abundant extracellular glycoprotein that is rich in selenocysteine. It has two domains with respect to selenium content. The N-terminal domain of the rat protein contains one selenocysteine residue in a UxxC redox motif. This domain also has a pH-sensitive heparin-binding site and two histidine-rich amino acid stretches. The smaller C-terminal domain contains nine selenocysteine and ten cysteine residues. Four isoforms of selenoprotein P are present in rat plasma. They share the same N terminus and amino acid sequence. One isoform is full length and the three others terminate at the positions of the second, third, and seventh selenocysteine residues. Selenoprotein P turns over rapidly in rat plasma with the consequence that approximately 25% of the amount of whole-body selenium passes through it each day. Evidence supports functions of the protein in selenium homeostasis and oxidant defense. Selenoprotein P knockout mice have very low selenium concentrations in the brain, the testis, and the fetus, with severe pathophysiological consequences in each tissue. In addition, those mice waste moderate amounts of selenium in the urine. Selenoprotein P binds to endothelial cells in the rat, and plasma levels of the protein correlate with prevention of diquat-induced lipid peroxidation and hepatic endothelial cell injury. The mechanisms of these apparent functions remain speculative and much work on the mechanism of selenoprotein P function lies ahead. Measurement of selenoprotein P in human plasma has shown that it is depressed by selenium deficiency and by cirrhosis. Selenium supplementation of selenium-deficient human subjects showed that glutathione peroxidase activity was optimized before selenoprotein P concentration was optimized, indicating that plasma selenoprotein P is the better index of human selenium nutritional status.

Mass spectrometric determination of selenenylsulfide linkages in rat selenoprotein P

The reversible formation of a selenenylsulfide linkage in mammalian thioredoxin reductase was identified as having a key role in its activity. Identification of selenenylsulfide and/or diselenide linkages is therefore critical to the determination of the structure and function of selenoproteins. A selenopeptide, (298)SGSAITUQCAENLPSLCSUQGLFAEEK(324) (U=selenocysteine), was isolated from a tryptic digest of rat selenoprotein P. Its two cysteine residues and two selenocysteine (Sec) residues were determined to be present in oxidized form by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The selenopeptide was subjected to partial reduction by dithiothreitol with immediate alkylation by iodoacetamide. This process was monitored by MALDI-TOFMS to determine the number of alkylations that had taken place. The partially reduced and alkylated peptides were then analyzed by nano-electrospray ionization tandem mass spectrometry and the results indicated that selenenylsulfide linkages Sec304-Cys314 and Cys306-Sec316 were present. It is concluded that selenoprotein P contains these two selenenylsulfide bonds.

Isoprostanes and the liver

The liver has been central to our understanding of the physiology and biology of the F2-isoprostanes. The discovery of F2-IsoPs and the initial demonstration that they could be used to localize oxidative stress was first demonstrated in a rat model of oxidative liver injury (carbon tetrachloride), and the first demonstration that plasma concentrations are increased in a human disease was in patients with liver failure and the hepatorenal syndrome [J. Clin. Invest. 90 (6) (1992b) 2502; J. Lipid Mediat. 6 (1/3) (1993) 417]. This article will cover the measurement of F2-IsoPs as markers of lipid peroxidation in vivo in liver disease, and review their biological activity as mediators of disease.

Identification of selenoprotein P fragments as a cell-death inhibitory factor

Megakaryoblastoma (Dami cells) cultured in a serum-free medium containing albumin, proliferated for three days but died on the fourth day. This cell death was not observed when human plasma was added, suggesting that human plasma contains a cell-death inhibitory factor. In order to identify this factor, we purified it from human plasma. N-terminal amino acid sequence analysis revealed that this factor is a mixture of C-terminal fragments of selenoprotein P, a major selenocysteine-containing protein in plasma. The specific activity (unit per pmol of selenium) of selenoprotein P fragments protein was 15-fold and 1900-fold higher than that of the full-length SeP and sodium selenite, respectively.

Selenoprotein metabolism and function: evidence for more than one function for selenoprotein P

Biological functions of selenium are exerted by selenoproteins that contain selenocysteine in their primary structure. Selenocysteine is synthesized and inserted into proteins cotranslationally by a complex process. Families of selenoproteins include the glutathione peroxidases, the iodothyronine deiodinases and the thioredoxin reductases. These are redox enzymes that take advantage of the chemical properties of selenium to catalyze, respectively, removal of hydroperoxides by glutathione, deiodination of thyroid hormones and support of cellular processes requiring reduction of disulfides. Approximately 10 additional selenoproteins have been identified. One of them, selenoprotein P, is an extracellular protein that contains most of the selenium in plasma. It associates with endothelial cells, probably through its heparin-binding properties. Selenoprotein P has been postulated to protect against oxidative injury and to transport selenium from the liver to peripheral tissues. Selenium-dependent protection against diquat-induced liver necrosis and lipid peroxidation in the rat correlates with the presence of selenoprotein P. Recent results support a transport function. When (75)SeO(3)(2-) was administered intravenously to rats, liver tissue took up (75)Se within minutes, associated with a rapid decline in plasma (75)Se. Brain tissue did not begin accumulating (75)Se until (75)Se-labeled selenoprotein P had begun appearing in the plasma after 30 min. These results suggest that tissues like liver can take up small-molecule forms of selenium whereas presence of the element in selenoprotein P facilitates uptake by tissues like brain. Thus, there is evidence for both antioxidant and selenium transport functions of selenoprotein P.

Deletion of selenoprotein P alters distribution of selenium in the mouse

Selenoprotein P (Se-P) contains most of the selenium in plasma. Its function is not known. Mice with the Se-P gene deleted (Sepp(-/-)) were generated. Two phenotypes were observed: 1) Sepp(-/-) mice lost weight and developed poor motor coordination when fed diets with selenium below 0.1 mg/kg, and 2) male Sepp(-/-) mice had sharply reduced fertility. Weanling male Sepp(+/+), Sepp(+/-), and Sepp(-/-) mice were fed diets for 8 weeks containing <0.02-2 mg selenium/kg. Sepp(+/+) and Sepp(+/-) mice had similar selenium concentrations in all tissues except plasma where a gene-dose effect on Se-P was observed. Liver selenium was unaffected by Se-P deletion except that it increased when dietary selenium was below 0.1 mg/kg. Selenium in other tissues exhibited a continuum of responses to Se-P deletion. Testis selenium was depressed to 19% in mice fed an 0.1 mg selenium/kg diet and did not rise to Sepp(+/+) levels even with a dietary selenium of 2 mg/kg. Brain selenium was depressed to 43%, but feeding 2 mg selenium/kg diet raised it to Sepp(+/+) levels. Kidney was depressed to 76% and reached Sepp(+/+) levels on an 0.25 mg selenium/kg diet. Heart selenium was not affected. These results suggest that the Sepp(-/-) phenotypes were caused by low selenium in testis and brain. They strongly suggest that Se-P from liver provides selenium to several tissues, especially testis and brain. Further, they indicate that transport forms of selenium other than Se-P exist because selenium levels of all tissues except testis responded to increases of dietary selenium in Sepp(-/-) mice.

Impacts of glutathione peroxidase-1 knockout on the protection by injected selenium against the pro-oxidant-induced liver aponecrosis and signaling in selenium-deficient mice

Previous research has suggested that repletion of cellular glutathione peroxidase (GPX1) activity by a single injection of Se was dissociated from the Se protection against the pro-oxidant-induced liver necrosis in Se-deficient rodents. Using the GPX1 knockout (GPX1-/-) mice, TUNEL assay, and apoptosis gene expression microarray, we have demonstrated strikingly different impacts of GPX1 knockout on hepatotoxicity and the related signaling induced by an intraperitoneal injection of 12.5 mg paraquat/kg body weight (b.wt.). In both Se-deficient GPX1-/- and wild-type (WT) mice, the paraquat did not induce typical liver necrosis, rather aponecrosis or necrapoptosis, a syncretic process of cell death sharing characteristics of both apoptosis and necrosis. The severity of liver aponecrosis and the associated mortality were reduced to a much greater extent by an injection of Se (ip, 50 microg/kg b.wt. as Na2SeO3) prior to paraquat stress in the WT mice, compared with the GPX1-/- mice. The induced liver aponecrosis seemed to be more apoptotic in the GPX1-/- mice but more necrotic in the WT mice. The paraquat-mediated gene or protein expression of proapoptotic Bax, Bcl-w, and Bcl-X(S), cell survival/death factors GADD45, MDM2, c-Myc, and caspase-3 was upregulated, but that of antiapoptotic Bcl-2 was downregulated in the GPX1-/- mice vs. the WT mice. Overall, these differences between the two groups of mice were related to a low level of liver GPX1 activity in the WT mice that represented < 4% of the normal physiological level. Therefore, the low level of GPX1 activity in the Se-deficient mice can exert a potent role in defending against liver aponecrosis induced by moderate oxidative stress.

Oxidative stress in viral and alcoholic hepatitis

Liver damage ranges from acute hepatitis to hepatocellular carcinoma, through apoptosis, necrosis, inflammation, immune response, fibrosis, ischemia, altered gene expression and regeneration, all processes that involve hepatocyte, Kupffer, stellate, and endothelial cells. Reactive oxygen and nitrogen species (ROS, RNS) play a crucial role in the induction and in the progression of liver disease, independently from its etiology. They are involved in the transcription and activation of a large series of cytokines and growth factors that, in turn, can contribute to further production of ROS and RNS. The main sources of free radicals are represented by hepatocyte mitochondria and cytochrome p450 enzymes, by endotoxin-activated macrophages (Kupffer cells), and by neutrophils. The consequent alteration of cellular redox state is potentiated by the correlated decrease of antioxidant and energetic reserves. Indices of free radical-mediated damage, such as the increase of malondialdehyde, 4-hydroxynonenal, protein-adducts, peroxynitrite, nitrotyrosine, etc., and/or decrease of glutathione, vitamin E, vitamin C, selenium, etc., have been documented in patients with viral or alcoholic liver disease. These markers may contribute to the monitoring the degree of liver damage, the response to antiviral therapies and to the design of new therapeutic strategies. In fact, increasing attention is now paid to a possible "redox gene therapy." By enhancing the antioxidant ability of hepatocytes, through transgene vectors, one could counteract oxidative/nitrosative stress and, in this way, contribute to blocking the progression of liver disease.

Heparin-binding histidine and lysine residues of rat selenoprotein P

Selenoprotein P is a plasma protein that has oxidant defense properties. It binds to heparin at pH 7.0, but most of it becomes unbound as the pH is raised to 8.5. This unusual heparin binding behavior was investigated by chemical modification of the basic amino acids of the protein. Diethylpyrocarbonate (DEPC) treatment of the protein abolished its binding to heparin. DEPC and [(14)C]DEPC modification, coupled with amino acid sequencing and matrix-assisted laser desorption ionization-time of flight mass spectrometry of peptides, identified several peptides in which histidine and lysine residues had been modified by DEPC. Two peptides from one region (residues 80-95) were identified by both methods. Moreover, the two peptides that constituted this sequence bound to heparin. Finally, when DEPC modification of the protein was carried out in the presence of heparin, these two peptides did not become modified by DEPC. Based on these results, the heparin-binding region of the protein sequence was identified as KHAHLKKQVSDHIAVY. Two other peptides (residues 178-189 and 194-234) that contain histidine-rich sequences met some but not all of the criteria of heparin-binding sites, and it is possible that they and the histidine-rich sequence between them bind to heparin under some conditions. The present results indicate that histidine is a constituent of the heparin-binding site of selenoprotein P. The presence of histidine, the pK(a) of which is 7.0, explains the release of selenoprotein P from heparin binding as pH rises above 7.0. It can be speculated that this property would lead to increased binding of selenoprotein P in tissue regions that have low pH.