ABSTRACT
Recent studies indicate that Extracellular Superoxide (EC-SOD) may not be as scarce in some tissues as was initially believed. The EC-SOD is the major isoenzyme of SOD in the umbilical cord and is a major source of SOD activity in the uterus. The possible role of EC-SOD in gestational diabetes has not been reported. Hence, the present study was planned to study EC-SOD in healthy non-pregnant, healthy normotensive pregnant women and women with gestational diabetes. The present study was carried out in twenty healthy Non-Pregnant (NPW) controls (in age group 18-35 years), twenty healthy age-matched normotensive pregnant women (28-36 weeks gestation) and twenty (age-and parity-matched) women with gestational diabetes. Serum Extracellular Superoxide Dismutase Activity (EC-SOD) and superoxide generation was analyzed in these women. The EC-SOD levels were significantly decreased in G-DM as compared to HPW, NPW controls (p<0.001) and superoxide generation was raised in G-DM as compared to HPW (p<0.001). A significant negative correlation was observed between EC-SOD levels and superoxide generation (r = -0.175, p<0.05) in G-DM. These findings indicate that radical scavenging antioxidants are consumed by enhanced levels of free radicals produced during glucose induced oxidative stress.
PDF Abstract XML References Citation
How to cite this article
DOI: 10.3923/rjog.2010.1.4
URL: https://scialert.net/abstract/?doi=rjog.2010.1.4
INTRODUCTION
Gestational diabetes is one of the most prevalent complications of pregnancy and cause a large quantity of foetal wastage. Foetuses born to mothers with gestational diabetes are at increased risk of developing respiratory distress, fetal macrosomia, fetal anomalies and platelet hyperaggregability (Rao et al., 1998).
Low insulin sensitivity has been suggested to be the cause of oxidative stress in diabetes which eventually leads to free radical generation (Hunt and Wolff, 1991). Extracellular superoxide dismutase (EC-SOD) is major isoenzyme of SOD in the umbilical cord and is a major source of SOD activity in uterus (Sandstrom et al., 1993). Nitric Oxide (NO) has been shown to an important mediator in maintaining a relaxed uterus during pregnancy (Conrad et al., 1993) and EC-SOD may play an important role in modulating NO-dependant relaxation of uterus.
High blood glucose level induce oxidative stress and decrease antioxidant defences, thus leading to increased free radical formation. Several reports have implicated role of lipid peroxidation in gestational diabetes (Kharb, 2000a, b; Bates et al., 1997). Evidence of involvement of oxygen free radicals and lipid peroxidation products in pre-eclampsia and gestational diabetes (Rao et al., 1998; Kharb, 2000a, b; Bates et al., 1997; Uotila et al., 1993) are available. The possible role of EC-SOD in gestational diabetes has not been reported. Hence, the present study was planned to study EC-SOD in healthy non-pregnant, healthy normotensive pregnant women and women with gestational diabetes.
MATERIALS AND METHODS
The study was carried out in 60 women attending/admitted in Obstetrics and Gynecology Department (during 2001-2005), in Department of Biochemistry, Pt.B.D.Sharma, PGIMS, Rohtak (India). The control groups included 20 healthy non pregnant volunteers (NPW) in age group 18-35 years and 20 healthy age-matched normotensive pregnant women (28-36 weeks gestation) (HPW). The study group consisted of 20 pregnant women (age and parity-matched) who were diagnosed as having gestational diabetes (G-DM) after undergoing oral glucose tolerance test with 100 g of glucose (Kharb, 2000a, b). All these subjects had a negative history of diabetes mellitus, hypertension, hepatic dysfunction, obesity, any vitamin supplement or drug intake. No women were in labour at the time of venepuncture. Anticubital maternal venous samples were taken after overnight fasting and serum was separated on centrifugation. Serum EC-SOD activity was estimated according to method of Misra and Fridovich (1972), on the basis of property of SOD to inhibit autoxidation of epinephrine to adrenochrome at pH 10.5. Superoxide anion generation was carried out by reduction of Nitroblue Tetrazotium method (NBT) (Kharb et al., 2000). The data was expressed as Mean±SD and differences were compared by students t-test.
RESULTS
The clinical characteristics of study and control groups are given in Table 1. The mean fasting, 1, 2 and 3 h, glucose levels in gestational diabetes are given in Table 2.
The EC-SOD levels were significantly decreased in G-DM as compared to HPW, NPW control (Table 3, p<0.01). EC-SOD levels were lower in HPW as compared to NPW, but the difference was not significant. Superoxide generation was significantly raised in GDM as compared to HPW (p<0.001). A significant negative correlation was observed between superoxide generation and EC-SOD levels in G-DM (r = -0.175, p<0.05).
Table 1: | Clinical characteristics (mean values) |
Table 2: | Glucose tolerance in various groups (Mean±SD, mg%) |
Table 3: | EC-SOD activity and superoxide generation in various groups (Mean±SD) |
*p-non significant as compared to NPW; **p<0.01 as compared to HPW; +p<0.001 as compared to NPW |
DISCUSSION
The EC-SOD levels were decreased in G-DM as compared to controls in the present study (p<0.01) EC-SOD levels were lower in HPW as compared to NPW, but the difference was not significant (Table 3). Several studies have found evidence of involvement of oxygen free radicals and lipid peroxidation products in preeclampsia and gestational diabetes (Rao et al., 1998; Kharb, 2000a, b; Bates et al., 1997; Uotila et al., 1993). The possible role of EC-SOD in gestational diabetes has not been reported. The EC-SOD is present in human placenta, uterus and at the site of placental implantation. The level of SOD activity (unclassified iso-form) in the placenta has, however, been shown to increase during the progression of pregnancy (Sekiba and Yoshioka, 1979). The EC-SOD has been reported to exist in high concentration in organs that contain large amount of smooth muscle and blood vessels (Kharb et al., 2000; Oury et al., 1996a, b). Nitric Oxide (NO) is known to be exquisitely sensitive to inactivation by superoxide and forms peroxynitrite anion which itself is a strong oxidizing species. Any extracellular superoxide production will dramatically reduce the effects of No. Thus, any superoxide in extracellular matrix between endothelial cells and smooth muscle cells will rapidly react with EDRF and inhibit smooth muscle relaxation.
In the present study, subjects with G-DM had higher superoxide generation as compared to healthy pregnant women (p<0.001, Table 3). Also, a significant correlation was observed between fall in EC-SOD levels and rise in superoxide generation in G-DM (r = -0.175, p<0.05).
Superoxide production has shown to be increased in presence of glycated proteins (formed by high glucose concentrations in diabetes ) and these effects would interfere with balance of superoxide and nitric oxide species in the vessels of diabetic patients (Mullarkey et al., 1990) and the same mechanism may play an important role in the pathogenesis of gestational diabetes.
The EC-SOD exist in high concentrations in organs that contain large amounts of smooth muscle and has a particularly strong association with vascular smooth muscle (Oury et al., 1996a). Considering, the well-documented role of nitric oxide in mediating relaxation of smooth muscle, particularly in vasculature and the high reactivity of nitric oxide with superoxide to produce peroxynitrite anion, which will interfere with intracellular signaling of nitric oxide (Oury et al., 1996b). It is likely that EC-SOD has pivotal role in regulating these processes in vessels. The possible role of EC-SOD in gestational diabetes has not been reported. Scavenging of extracellular superoxide by EC-SOD is likely to play an important role in mediating these nitric oxide responses. Therefore, EC-SOD may play an important role in modulating nitric oxide-dependent relaxation of the uterus in a scenario of glucose induced oxidative stress.
The possible role of EC-SOD in gestational diabetes has not been reported. The results of the present study also suggested that in gestational diabetes, there is decrease in EC-SOD activity and increased superoxide generation indicating that possibly radical scavenging antioxidants are consumed by enhanced levels of free radicals.
CONCLUSION
There is decrease in EC-SOD activity and increased superoxide generation indicate that radical scavenging antioxidants are consumed by enhanced levels of free radicals produced during glucose induced oxidative stress.
REFERENCES
- Bates, J.H., I.S. Young, L. Galway, A.I. Tarub and D.R. Hadden, 1997. Antioxidant status and lipid peroxidation in diabetic pregnancy. Br. J. Nutr., 78: 523-532.
CrossRefDirect Link - Conrad, K.P., G.M. Joffe, H. Kruxzyna, R. Kruszyna and L.G. Rochelle et al., 1993. Identification of increased nitric oxide bio-synthesis during pregnancy in rats. FASEB J., 7: 566-571.
Direct Link - Hunt, J. and S.P. Wolff, 1991. Oxidative glycation and free radical production: A causal mechanism of diabetic complications. Free Rad. Res. Commun., 12: 115-123.
Direct Link - Rao, G., U. Kamath, C. Raghothama, L. Rai and Pragna Rao, 1998. Erythrocyte indicators of Oxidative stress in gestational diabetes. Acta Paediatr, 87: 676-679.
CrossRefDirect Link - Kharb, S., 2000. Lipid peroxidation in pregnancy with preeclampsia and diabetes. Gynecol. Obstet. Invest., 50: 113-116.
CrossRefDirect Link - Kharb, S., 2000. Low whole blood glutathione levels in pregnancies complicated by preeclampsia and diabetes. Clin. Chim. Acta, 294: 179-183.
PubMedDirect Link - Kharb, S., N. Gulati, V. Singh and G.P. Singh, 2000. Superoxide formation and glutathione levels in patients of preeclampsia. Gynecol. Obstet. Invest., 49: 28-30.
PubMedDirect Link - Misra, H.P. and I. Fridovich, 1972. The role of superoxide anion in the autoxidation of epinephrine and a simple assay for superoxide dismutase. J. Biol. Chem., 247: 3170-3175.
CrossRefPubMedDirect Link - Mullarkey, C.J., D. Edelstein and M. Brownlee, 1990. Free radical generation by early glycation products: A mechanism for accelerated atherogenesis in diabetes. Biochem. Biophys. Res. Commun., 173: 932-939.
CrossRefDirect Link - Oury, T.D., B.J. Day and J.D. Crapo, 1996. Extracellular superoxide dismutase: A regulator of nitric oxide bioavailability. Lab. Invest., 75: 617-636.
PubMedDirect Link - Oury, T.D., B.J. Day and J.D. Crapo, 1996. Extracellular superoxide dismutase in vessels and airways of humans and baboons. Free. Rad. Biol. Med., 20: 957-965.
CrossRef - Sandstrom, J., K. Karlssonm, T. Edlund and S.L. Marklund, 1993. Heparin-affinity patterns and composition of extracellular superoxide dismutase in human plasma and tissues. Biochem. J., 294: 853-857.
PubMedDirect Link - Sekiba, K. and T. Yoshioka, 1979. Changes of lipid peroxidation and superoxide dismutase activity in the human placenta. Am. J. Obstet. Gynecol., 135: 68-71.
PubMedDirect Link - Uotila, J.T., R.J. Tuimala and T.M. Aarnio, 1993. Findings of lipid peroxidation and antioxidant function in hypertensive complications of pregnancy. Br. J. Obstet. Gynecol., 10: 270-276.
PubMedDirect Link