Polymorphism of extracellular superoxide dismutase (EC-SOD) gene: relation to the mutation responsible for high EC-SOD level in serum

Review Article on Molecular Mechanism of Regulation of Hypertension by Macro-elements (Na, K, Ca and Mg), Micro-elements/Trace Metals (Zn and Cu) and Toxic Elements (Pb and As)

Hypertension (HT) is a medical condition arising due to increase in blood pressure (BP) prevalent worldwide. The balanced dietary intakes of macro-elements and micro-elements including Na, K, Ca, Mg, Zn, and Cu have been described to maintain BP in humans by regulating the osmolarity of blood, cells/tissues, prevention of generation of oxidative and nitrosative stress (OANS), and endothelial damage through their functioning as important components of renin-angiotensin-aldosterone system (RAAS), antioxidant enzyme defense system, and maintenance of blood vascular-endothelial and vascular smooth muscle cell (VSMC) functions. However, inadequate/excess dietary intakes of Na/K, Ca/Mg, and Zn/Cu along with higher Pb and As exposures recognized to induce HT through common mechanisms including the followings: endothelial dysfunctions due to impairment of vasodilatation, increased vasoconstriction and arterial stiffness, blood clotting, inflammation, modification of sympathetic activity and higher catecholamine release, increased peripheral vascular resistance, and cardiac output; increased OANS due to reduced and elevated activities of extracellular superoxide dismutase and NAD(P)H oxidase, less nitric oxide bioavailability, decrease in cGMP and guanylate cyclase activity, increase in intracellular Ca2+ ions in VSMCs, and higher pro-inflammatory cytokines; higher parathyroid and calcitriol hormones; activation/suppression of RAAS resulting imbalance in blood Na+, K+, and water regulated by renin, angiotensin II, and aldosterone through affecting natriuresis/kaliuresis/diuresis; elevation in serum cholesterol and LDL cholesterol, decrease in HDL cholesterol due to defect in lipoprotein metabolism. The present study recommends the need to review simple dietary mineral intervention studies/supplementation trials before keeping their individual dietary excess intakes/exposures in consideration because their interactions lead to elevation and fall of their concentrations in body affecting onset of HT.

Concentration/activity of superoxide dismutase isozymes and the pro-/antioxidative status, in context of type 2 diabetes and selected single nucleotide polymorphisms (genes: INS, SOD1, SOD2, SOD3) - Preliminary findings

The alterations in concentration/activity of superoxide dismutase isozymes in the context of type 2 diabetes or obesity are well-described. Moreover, many hereditary factors, including single-nucleotide polymorphisms (SNPs) of genes for coding insulin, insulin receptors, or insulin receptor substrates (INS, INSR, IRS1, IRS2) or superoxide dismutase isozymes (SOD1, SOD2, SOD3), have been linked with the incidence of obesity and diabetes. However, the underlying changes in the plasma concentration/activity of superoxide dismutase isozymes and their potential connection with the said hereditary factors remain unexplored. Previously, we have observed that the plasma concentration/activity of superoxide dismutase isozymes differs in the context of obesity and/or rs2234694 (SOD1) and rs4880 (SOD2) and that the concentrations of SOD1, SOD2, SOD3 are correlated with each other. Intersexual variability of SOD1 concentration was detected regardless of obesity. In this study, the variability of concentration/activity of superoxide dismutase isozymes in plasma is considered in the context of type 2 diabetes and/or SNPs: rs2234694 (SOD1), rs5746105 (SOD2), rs4880 (SOD2), rs927450 (SOD2), rs8192287 (SOD3). Genotypic variability of SNP rs3842729 (INS), previously studied in the context of insulin-dependent diabetes, is investigated in terms of selected clinical parameters associated with type 2 diabetes. This study revealed higher SOD1 concentration in diabetic men compared to women, and extremely high SOD1 concentration, higher total superoxide dismutase, and copper-zinc superoxide dismutase activity, and lower superoxide dismutase and copper-zinc superoxide dismutase activity (when adjusted for the concentration of SODs) in the diabetic group regardless of sex. Multiple logistic regression, applied to explore possible links between the studied SNPs and other factors with the odds of type 2 diabetes or obesity, revealed that the genotypic variability of rs4880 (SOD2) could affect these odds, supporting the findings of several other studies.

Alterations in Concentration/Activity of Superoxide Dismutases in Context of Obesity and Selected Single Nucleotide Polymorphisms in Genes: SOD1, SOD2, SOD3

Little is known about the contribution of each of the three superoxide dismutase isozymes (SODs) to the total SOD activity in extracellular fluids. This study was aimed to investigate the alterations in concentration/activity of (SODs) in plasma, in context of sex, obesity, exposition to cigarette smoke, and genotypic variability of five selected single nucleotide polymorphisms (SNPs) in genes SOD1, SOD2, SOD3. Men showed higher SOD1 concentration, lower SOD3 concentration and higher total antioxidative capacity (TAC) values. Intersexual variability was observed in concentration of copper, zinc, and cadmium. The obese showed higher total oxidative capacity regardless of sex. An increase in SOD2 activity was coexistent with obesity in men, and exposition to cigarette smoke in non-obese individuals. Additionally, in state of this exposition, Cu,Zn-SOD contribution to the total SOD was lower. Interestingly, over 90% of the obese were of C/T genotype of rs4880 (SOD2). Non-obese of T/T genotype (rs4880) were of lower total SOD activity due to decrease in both Cu,Zn-SOD and Mn-SOD activities. SNP rs2234694 was associated with differences in concentration of SODs, depending on obesity status. Correlations indicate that both TAC and SODs, together, may adapt to insulin resistance and inflammation-derived oxidative stress found in obesity. This topic should be further investigated.

SOD3 and eNOS genotypes are associated with SOD activity and NOx

Oxidative stress, characterized by increased reactive oxygen species production and/or decreased antioxidant enzyme activity, plays an important role in the pathogenesis of hypertension. The identification of molecular markers corresponding to the oxidative stress status of hypertension may assist in the antioxidant therapy of hypertension. In the present study, superoxide dismutase (SOD) and endothelial nitric oxide synthase (eNOS) were analyzed as markers of hypertension responding to oxidative stress. The plasma SOD activity and mononitrogen oxides (NO_x) concentration were measured, and the SOD3 Ala58Thr and eNOS Glu298Asp polymorphisms were genotyped in hypertensive patients and normotensive controls. Further association experiments were replicated in an extended population, including 343 hypertensive patients and 290 controls. The results demonstrated that no statistically significant differences in the total SOD activity and NO_x concentration were identified between the hypertensive patients and controls. However, the plasma SOD activity levels in the SOD3 Ala/Ala homozygote carriers (80.51±27.68 U/ml) were significantly lower compared with the Thr allele carriers (92.18±16.37 U/ml; P=0.031). In addition, the plasma NO_x concentration in the eNOS Glu/Glu homozygote carriers (129.66±59.15 μmol/l) was significantly lower compared with the Asp allele carriers (169.84± 55.18 μmol/l; P=0.010). Notably, the altered SOD activity levels and NO_x concentration were in concordance in 56.3% of the 80 participants. Therefore, the concordance of decreased SOD activity and NO_x concentration, combined with genotypes of SOD3 Ala/Ala and/or eNOS Glu/Glu in hypertensive patients, may be useful in directing the antioxidant therapy of hypertension.

The Ala-9Val (Mn-SOD) and Arg213Gly (EC-SOD) polymorphisms in the pathogenesis of preeclampsia in Romanian women: association with the severity and outcome of preeclampsia

OBJECTIVE

To check whether individual or combined mutated genotypes for Ala-9Val (Mn-SOD) and Arg213Gly (EC-SOD) are associated with preeclampsia; to check the influence of the mutated genotypes on the degree of severity and perinatal outcome of preeclampsia.

METHODS

We genotyped 97 pregnant women (47 with preeclampsia and 50 normal pregnant women) using PCR-RFLP analysis.

RESULTS

The Val/Val (Mn-SOD) genotype (OR 5.99, p = 0.004) but not the Gly/Gly (EC-SOD) genotype (OR 4.23, p = 0.027) was significantly associated with preeclampsia. Higher frequency of both polymorphisms in women with preeclampsia (42.55%) compared to normal pregnant women (8%). Higher frequency of women diagnosed with PIH (27.27%, OR 4.31), mild (50%, OR 11.5) and severe preeclampsia (37.5%, OR 6.9) positive for both polymorphism compared to control women (8%). There was a statistically significant difference in gestational age at delivery according to Mn-SOD (Ala/Ala vs. Val/Val, 39 ± 1.41 weeks vs. 32.77 ± 3.7 weeks) and EC-SOD genotypes (Arg/Arg vs. Gly/Gly, 37.05 ± 3.18 weeks vs. 31.5 ± 3.84 weeks). There also was a statistically significant difference in birth weight according to Mn-SOD (grams, Ala/Ala vs. Val/Val, 3080 ± 481.66 vs. 2376.92 ± 916.88) and EC-SOD genotypes (grams, Arg/Arg vs. Gly/Gly, 2934.09 ± 662.14 vs. 2080 ± 721.19).

CONCLUSIONS

Our study demonstrates a relationship between these two mutated genes, the clinical severity and the perinatal outcome of preeclampsia.

Polymorphism of the superoxide dismutase gene family in the bay scallop (Argopecten irradians) and its association with resistance/susceptibility to Vibrio anguillarum

The superoxide dismutases (SODs) are a family of enzymes that function as the first line of antioxidant defense against highly reactive superoxide radicals. The bay scallop Argopecten irradians contains three unique superoxide dismutases: Ai-icCuZnSOD, Ai-MnSOD and Ai-ecCuZnSOD, which were characterized in our previous studies. qRT-PCR was also performed to characterize the temporal expression of SODs in the hemocytes of bay scallops injected with the bacterium Vibrio anguillarum. To characterize the SOD family in A. irradians completely, we evaluated the polymorphism in the SOD genes and investigated the association of this polymorphism with resistance/susceptibility to V. anguillarum. Fifty-nine SNPs were identified in the promoter, exon and partial intron sequences of the three SOD genes. AiECSOD contained the most SNPs, as compared to AiCuZnSOD and AiMnSOD, and the majority of these were located in the promoter. Among them, the genotypes of -1739 T-C SNP in the AiCuZnSOD promoter and alleles of the -498 A-T and -267 G-A SNPs in the AiECSOD promoter showed a significant association with resistance/susceptibility to V. angullarum (P<0.05). The only non-synonymous SNP that was identified, E1-38 C-A in Ai-ecCuZnSOD, was a dimorphism caused by a C to A transition that resulted in a Thr to Lys substitution at position 13 in the signal peptide. The Thr allele was associated with increased susceptibility to V. anguillarum (P<0.05). To confirm the presumption, another independent challenge experiment was performed, in which the cumulative mortality of Ai-icCuZnSOD Q-1739 genotype TT was significantly lower than TC (P<0.05). Ai-ecCuZnSOD Q-498 genotype AA and AT were significantly lower than TT (P<0.05), Ai-ecCuZnSOD E1-3 genotype AA was significantly higher than CA and CC (P<0.05). The results suggested that these three polymorphic loci could be potential gene markers for the future molecular selection of strains that are resistant to diseases caused by V. anguillarum.

Extracellular superoxide dismutase (ecSOD) in vascular biology: an update on exogenous gene transfer and endogenous regulators of ecSOD

Extracellular superoxide dismutase (ecSOD) is the major extracellular scavenger of superoxide (O(2)(.-)) and a main regulator of nitric oxide (NO) bioactivity in the blood vessel wall, heart, lungs, kidney, and placenta. Involvement of O(2)(.-) has been implicated in many pathological processes, and removal of extracellular O(2)(.-) by ecSOD gene transfer has emerged as a promising experimental technique to treat vascular disorders associated with increased oxidant stress. In addition, recent studies have clarified mechanisms that regulate ecSOD expression, tissue binding, and activity, and they have provided new insight into how ecSOD interacts with other factors that regulate vascular function. Finally, studies of a common gene variant in humans associated with disruption of ecSOD tissue binding suggest that displacement of the enzyme from the blood vessel wall may contribute to vascular diseases. The purpose of this review is to summarize recent research findings related to ecSOD function and gene transfer and to stimulate other investigations into the role of this unique antioxidant enzyme in vascular pathophysiology and therapeutics.

Mineral factors controlling essential hypertension--a study in the Chandigarh, India population

Essential hypertension (EH) is a major public health problem world over and in India. Recent data on EH in the population of Chandigarh (Union Territory and capital of Punjab and Haryana States of India) revealed that the prevalence of EH has become double in the last 30 years in the residents of Chandigarh (26.9 to 45.80% in the year 1968 and 2002). Zinc (Zn), copper (Cu), magnesium (Mg), and manganese (Mn) in the serum are considered important in maintaining the human hypertension. The high Zn intake was considered to increase the blood pressure (BP) and to affect the other mineral status in the body. Recent survey on the trace metal status of different vegetables in the State of Punjab around Chandigarh (India) revealed that Zn level is significantly higher (40 mg/kg or more in above ground vegetables and 120 mg/kg or above in underground vegetables) in underground water-irrigated vegetables, but the levels of Cu and Mg are within prescribed limit. The present study was conducted on Chandigarh population to evaluate the levels of Zn, Cu, Mg, and Mn in the blood and urine of normotensive (NT) control and hypertensive (HT) subjects matched with number, age and sex. Atomic absorption spectrophotometer studies reevaluated that the levels of serum Zn, Mg, and Mn were significantly higher (p < 0.001), but the level of Cu was low in the HT subjects (BP = 160/93) compared to NT control (BP = 140/83). Higher levels of urinary Zn, Cu, Mg, and Mn were observed in the HT subject vs NT control (p < 0.001). Positive correlations were evaluated between the levels of serum Zn, Mg, and Mn vs systolic and diastolic pressures (DP and SP), respectively (r = 0.928, 0.863, 0.876, 0.808, 0.404, 0.326, p < 0.01), but negative and positive nonsignificant correlations between the serum Cu with SP and DP were recorded (r = -0.032, r = 0.024). Positive correlations were also evaluated between urinary levels of Zn, Cu, Mg, and Mn vs SP and DP (r = 0.718, 0.657, 0.750, 0.681, 0.630, 0.578, 0.516, 0.461, p < 0.01). Prevalence of essential hypertension may be due to higher Zn level in the food chain that makes the individuals vulnerable to other diseases over the time related to essential hypertension.

Extracellular superoxide dismutase gene polymorphism is associated with insulin resistance and the susceptibility to type 2 diabetes

Oxidative stress has been implicated in pancreatic beta-cell damage, insulin resistance and vascular function in diabetic patients and the dysfunction of antioxidant enzymes may be associated with the pathogenesis of diabetes. Extracellular superoxide dismutase (EC-SOD) is found in the extracellular matrix of tissues and the major scavenger of superoxide radical. To investigate the role of genetic variability for the pathogenesis of type 2 diabetes, we scanned the protein coding exon and flanking introns of EC-SOD gene for mutation in Japanese type 2 diabetic patients. We identified two missense mutations, Ala40Thr (GCG-->ACG) and Arg213Gly (CGG-->GGG), and a silent mutation, Leu53Leu (CTG-->TTG). For one of these variants, the Ala40Thr polymorphism, the frequency of Thr allele and the number of subjects with Thr allele (Ala/Thr+Thr/Thr) were higher in type 2 diabetic patients (n=205) than those in non-diabetic subjects (n=220) (33.2% versus 24.1%, p=0.003 and 55.6% versus 42.7%, p=0.008, respectively). The patients with Thr allele also showed earlier age at diagnosis of diabetes (42.2+/-7.8 years versus 44.4+/-6.9 years, p=0.037) and higher prevalence of hypertension (53.5% versus 38.5%, p=0.032) than those without the allele. Insulin sensitivity, furthermore, was evaluated in 71 type 2 diabetic patients with short insulin tolerance test (SITT). The patients with Thr allele showed lower insulin sensitivity (Kitt value of SITT) than those without the allele (1.78+/-0.78%/min versus 2.33+/-1.02%/min, p=0.012), although no significant differences in other clinical and biochemical characteristics were observed between two groups. These results suggest that the genetic variant of EC-SOD gene is associated with insulin resistance and the susceptibility to type 2 diabetes.

The intracellular proteolytic processing of extracellular superoxide dismutase (EC-SOD) is a two-step event

Extracellular superoxide dismutase (EC-SOD) is a tetramer composed of either intact (Trp(1)-Ala(222)) or proteolytically cleaved (Trp(1)-Glu(209)) subunits. The latter form is processed intracellularly before secretion and lacks the C-terminal extracellular matrix (ECM)-binding region ((210)RKKRRRESECKAA(222)-COOH). We have previously suggested that the C-terminal processing of EC-SOD is either a one-step mechanism accomplished by a single intracellular endoproteolytic event cleaving the Glu(209)-Arg(210) peptide bond or a two-step mechanism involving two proteinases (Enghild, J. J., Thogersen, I. B., Oury, T. D., Valnickova, Z., Hojrup, P., and Crapo, J. D. (1999) J. Biol. Chem. 274, 14818-14822). In the latter case, an initial endoproteinase cleavage occurs somewhere in the region between Glu(209) and Glu(216). A carboxypeptidase specific for basic amino acid residues subsequently trims the remaining basic amino acid residues to Glu(209). A naturally occurring mutation of EC-SOD substituting Arg(213) for Gly enabled us to test these hypotheses. The mutation does not prevent proteolysis of the ECM-binding region but prevents a carboxypeptidase B-like enzyme from trimming residues beyond Gly(213). The R213G mutation is located in the ECM-binding region, and individuals carrying this mutation have an increased concentration of EC-SOD in the circulatory system. In this study, we purified the R213G EC-SOD variant from heterozygous or homozygous individuals and determined the C-terminal residue of the processed subunit to be Gly(213). This finding supports the two-step processing mechanism and indicates that the R213G mutation does not disturb the initial endoproteinase cleavage event but perturbs the subsequent trimming of the C terminus.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

The dual nature of human extracellular superoxide dismutase: one sequence and two structures

Human extracellular superoxide dismutase (EC-SOD; EC 1.15.1.1) is a scavenger of superoxide anions in the extracellular space. The amino acid sequence is homologous to the intracellular counterpart, Cu/Zn superoxide dismutase (Cu/Zn-SOD), apart from N- and C-terminal extensions. Cu/Zn-SOD is a homodimer containing four cysteine residues within each subunit, and EC-SOD is a tetramer composed of two disulfide-bonded dimers in which each subunit contains six cysteines. The amino acid sequences of all EC-SOD subunits are identical. It is known that Cys-219 is involved in an interchain disulfide. To account for the remaining five cysteine residues we purified human EC-SOD and determined the disulfide bridge pattern. The results show that human EC-SOD exists in two forms, each with a unique disulfide bridge pattern. One form (active EC-SOD) is enzymatically active and contains a disulfide bridge pattern similar to Cu/Zn-SOD. The other form (inactive EC-SOD) has a different disulfide bridge pattern and is enzymatically inactive. The EC-SOD polypeptide chain apparently folds in two different ways, most likely resulting in different three-dimensional structures. Our study shows that one gene may produce proteins with different disulfide bridge arrangements and, thus, by definition, different primary structures. This observation adds another dimension to the functional annotation of the proteome.

Extracellular superoxide dismutase in biology and medicine

Accumulated evidence has shown that reactive oxygen species (ROS) are important mediators of cell signaling events such as inflammatory reactions (superoxide) and the maintenance of vascular tone (nitric oxide). However, overproduction of ROS such as superoxide has been associated with the pathogenesis of a variety of diseases including cardiovascular diseases, neurological disorders, and pulmonary diseases. Antioxidant enzymes are, in part, responsible for maintaining low levels of these oxygen metabolites in tissues and may play key roles in controlling or preventing these conditions. One key antioxidant enzyme implicated in the regulation of ROS-mediated tissue damage is extracellular superoxide dismutase (EC-SOD). EC-SOD is found in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. In addition, EC-SOD is likely to play an important role in mediating nitric oxide-induced signaling events, since the reaction of superoxide and nitric oxide can interfere with nitric oxide signaling. This review will discuss the regulation of EC-SOD and its role in a variety of oxidant-mediated diseases.

Effects of endurance training on three superoxide dismutase isoenzymes in human plasma

The effects of endurance training and acute exhaustive exercise on plasma levels of three superoxidedismutase (SOD) isoenzymes and the ability of superoxide generation in neutrophils were studied. Eighteen healthy male students, aged 17-22 years, who volunteered for this study, underwent three months of endurance training in swimming or running. Before and after the training course, they performed acute exercise and blood samples were collected before and after this exercise. The endurance training significantly increased maximal oxygen uptake (VO2max) in all subjects. Neither the endurance training nor the acute exercise affected the plasma CuZn-SOD level. Acute exercise after the training, but not before the training, increased both the plasma Mn-SOD and extracellular SOD (EC-SOD) levels by 33.6 and 33.5%, respectively. The training decreased the EC-SOD level at rest by 22.2%. Acute exercise after the training, but not before the training, increased the plasma lipid peroxide level, suggesting higher oxidative stress in trained subjects during exhaustive exercise. The ability of neutrophils to generate superoxide was increased by the acute exercise, but induction of the superoxide was suppressed after training. These results indicate that EC-SOD levels were changed in a different manner from the CuZn-SOD and Mn-SOD: it was decreased by training but was increased by acute exercise, suggesting that endurance training increases the reserve of EC-SOD in tissues. The results also suggest the possibility of plasma EC-SOD assay as a new index of endurance training.

Superoxide dismutases in the lung and human lung diseases

The lungs are directly exposed to higher oxygen concentrations than most other tissues. Increased oxidative stress is a significant part of the pathogenesis of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease, parenchymal lung diseases (e.g., idiopathic pulmonary fibrosis and lung granulomatous diseases), and lung malignancies. Lung tissue is protected against these oxidants by a variety of antioxidant mechanisms among which the superoxide dismutases (SODs) are the only ones converting superoxide radicals to hydrogen peroxide. There are three SODs: cytosolic copper-zinc, mitochondrial manganese, and extracellular SODs. These enzymes have specific distributions and functions. Their importance in protecting lung tissue has been confirmed in transgenic and knockout animal studies. Relatively few studies have been conducted on these enzymes in the normal human lung or in human lung diseases. Most human studies suggest that there is induction of manganese SOD and, possibly, extracellular SOD during inflammatory, but not fibrotic, phases of parenchymal lung diseases and that both copper-zinc SOD and manganese SOD may be downregulated in asthmatic airways. Many previous antioxidant therapies have been disappointing, but newly characterized SOD mimetics are being shown to protect against oxidant-related lung disorders in animal models.

Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Three unique and highly compartmentalized mammalian superoxide dismutases have been biochemically and molecularly characterized to date. SOD1, or CuZn-SOD (EC 1.15.1.1), was the first enzyme to be characterized and is a copper and zinc-containing homodimer that is found almost exclusively in intracellular cytoplasmic spaces. SOD2, or Mn-SOD (EC 1.15.1.1), exists as a tetramer and is initially synthesized containing a leader peptide, which targets this manganese-containing enzyme exclusively to the mitochondrial spaces. SOD3, or EC-SOD (EC 1.15.1.1), is the most recently characterized SOD, exists as a copper and zinc-containing tetramer, and is synthesized containing a signal peptide that directs this enzyme exclusively to extracellular spaces. What role(s) these SODs play in both normal and disease states is only slowly beginning to be understood. A molecular understanding of each of these genes has proven useful toward the deciphering of their biological roles. For example, a variety of single amino acid mutations in SOD1 have been linked to familial amyotrophic lateral sclerosis. Knocking out the SOD2 gene in mice results in a lethal cardiomyopathy. A single amino acid mutation in human SOD3 is associated with 10 to 30-fold increases in serum SOD3 levels. As more information is obtained, further insights will be gained.

Furin proteolytically processes the heparin-binding region of extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD) is an antioxidant enzyme that attenuates brain and lung injury from oxidative stress. A polybasic region in the carboxyl terminus distinguishes EC-SOD from other superoxide dismutases and determines EC-SOD's tissue half-life and affinity for heparin. There are two types of EC-SOD that differ based on the presence or absence of this heparin-binding region. It has recently been shown that proteolytic removal of the heparin-binding region is an intracellular event (Enghild, J. J., Thogersen, I. B., Oury, T. D., Valnickova, Z., Hojrup, P., and Crapo, J. D. (1999) J. Biol. Chem. 274, 14818-14822). By using mammalian cell lines, we have now determined that removal of the heparin-binding region occurs after passage through the Golgi network but before being secreted into the extracellular space. Specific protease inhibitors and overexpression of intracellular proteases implicate furin as a processing protease. In vitro experiments using furin and purified EC-SOD suggest that furin proteolytically cleaves EC-SOD in the middle of the polybasic region and then requires an additional carboxypeptidase to remove the remaining lysines and arginines. A mutation in Arg(213) renders EC-SOD resistant to furin processing. These results indicate that furin-dependent processing of EC-SOD is important for determining the tissue distribution and half-life of EC-SOD.

Oxidative stress, human genetic variation, and disease

Oxidative stress has been implicated in numerous pathophysiological conditions and also aging. The tools for studying oxidative stress are now expanding as a result of the human genome effort and, in particular, expanding knowledge on human genetic variation. A few genetic variants, mostly in the form of single nucleotide polymorphisms of relevance to oxidative stress are already studied by a molecular epidemiologic approach. A review of the current knowledge on variant human genes that are directly implicated in human protection against oxidative stress is presented.

Polymorphisms in the Mn-SOD and EC-SOD genes and their relationship to diabetic neuropathy in type 1 diabetes mellitus

BACKGROUND

Oxidative stress, resulting in a marked increase in the level of oxygen free radicals (OFR), has been implicated in the etiology of diabetic neuropathy (DN). Antioxidant enzymes may protect against the rapid onset and progression of DN, by reducing the excess of OFR and peroxide. Mutations and polymorphisms in the genes encoding such enzymes may therefore result in predisposition to DN. We investigated the role of genes encoding two antioxidant enzymes, mitochondrial (Mn-SOD) and extracellular (EC-SOD) superoxide dismutase, in DN pathogenesis in a Russian population. We studied Ala(-9)Val and Ile58Thr polymorphisms of the Mn-SOD gene and Arg213Gly dimorphism of the EC-SOD gene in type 1 diabetic patients with (n = 82) and without DN (n = 84).

RESULTS

We developed and used a new polymerase chain reaction (PCR) assays for rapid detection of polymorphisms. These assays involved the use of mismatch PCR primers to create restriction sites in the amplified product only in presence of the polymorphic base. The PCR product was than digested with BshTI, Eco32I or Eco52I to detect Ala(-9)Val, Ile58Thr or Arg213Gly polymorphic site respectively. The frequencies of the Ala allele (50.6% vs. 68.5%, p < 0.002) and the Ala/Ala genotype (17.1% vs. 39.3%, p < 0.005) of the Mn-SOD gene were significantly lower in DN patients than in diabetic subjects without DN. In contrast, the Val allele (49.4% vs. 31.5%, p < 0.002) and the Val/Val genotype (15.9% vs. 2.4%, p < 0.01) were significantly more frequent in the DN patients than in the control group.

CONCLUSIONS

Ala(-9)Val substitution in the Mn-SOD gene was associated with DN in a Russian population

Endothelial function in hypertension: the role of superoxide anion

Much attention has been focused on the role of nitric oxide in hypertension and cardiovascular disease. More recently, the role of superoxide anion and its interaction with nitric oxide has been investigated in this context. This review will concentrate on the role of superoxide in human and experimental hypertension, paying particular attention to the potential sources of superoxide within the vasculature and discussing some of the molecular mechanisms surrounding its production and dismutation. We discuss what is known about the human superoxide dismutase enzymes. We conclude that the balance between nitric oxide and superoxide is more important than the absolute levels of either alone.