URIC ACID AND ASCORBIC ACID LEVELS
IN PREGNANCY WITH PREECLAMPSIA AND
DIABETES
Dr. Simmi Kharb
Prof Biochemistry
Pt. BDS PGIMS, Rohtak (Haryana)
Mailing Address :
Dr. Simmi Kharb
1447, Sector-1, Urban Estate,
Rohtak – 124001 (Haryana)
E.mail : simmikh@rediffmail.com
Running title :
Keywords :
uric acid-ascorbic acid /diabetic preeclampsia
gestational diabetes, preeclampsia, diabetic preeclamptics,
uric acid, ascorbic acid
ABSTRACT
Serum uric acid (SUA) and ascorbic acid levels were evaluated in 40
patients preclampsia [18-diabetic pre-eclamptic women (DM-PRW) & 22
without diabetes (PRW)]; 20 normotensive pregnant women [8 with
gestational diabetes (G-DM) & rest 12 were healthy pregnant women
(HPW)]; and control group consisting of 20 healthy non-pregnant women.
SUA values were significantly increased in PRW & DM-PRW as compared
to controls and were higher in PRW than DM-PRW (p >0.05). Also, SUA
was significantly increased in G-DM as compared to HNPW (p<0.001).
Serum ascorbic levels showed a significant fall in PRW and DM-PRW
(p<0.01) with DM-PRW being still lower (p >0.05). Also, ascorbate levels
were lowered in G-DM as compared to HNPW (p <0.001).
PRW showed a significant negative correlation between ascorbate and
uric acid levels (p <0.01). Thus, the elevated circulating concentration of
uric acid, a valuable marker of pre-eclampsia that we propose may be a
marker of free radical generation, may also serve a protective role.
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INTRODUCTION
In men and in nonpregnant women there is a well-defined relationship
between essential hypertension and glucose intolerance, which has been
termed the insulin-resistance syndrome syndrome X [1,2]. The relationship
between hypertensive disorders of pregnancy and glucose intolerance,
however, is less well established. High blood glucose levels induce oxidative
stress and decrease antioxidant defences, thus leading to increased free
radical formation [3]. Recently increased oxidative stress and formation of
reactive oxygen species (ROS) have been proposed as another contributing
source of hyperuricemia noted in preeclampia aapart from renal dysfunction
[4].
The most important physiological aqueous antioxidants are vitamin C
(ascorbic acid) and uric acid, while bilirubin and thiol-containing molecules
make a comparatively small contribution [5]. Hence, the present study was
planned to evaluate uric acid and ascorbic acid levels in diabetic
preeclamptic, non-diabetic preeclamptic and gestational diabetic women in
relation to blood glucose levels.
MATERIALS AND METHODS
The study was carried out in 80 women attending / admitted in
Antenatal Clinics of Obstetrics and Gynecology Department at Pt. BDS
PGIMS, Rohtak (India). Informed consent was taken. The diagnosis of
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preeclampsia was established in accordance with the definitions of the
American College of Obstetrics and Gynaecologists [6]. Inclusion criteria
was : age 18-35 years, primigravida, 28-40 weeks gestation, absence of
labour contractions, absence of any other medical complications (such as
renal disease, primary hypertension, cardiovascular disease, connective
tisene disease) concurrent with preeclampsia.
Fasting samples were collected from three groups of women. The first
group consisted of 40 patients of preeclampsia : 18 with diabetes (DMPRW) and 22 without diabetes (PRW). The second group consisted of 20
normotensive pregnant women of which 8 were having gestational diabetes
(G-DM) and rest 12 were healthy pregnant women (HPW). The control
group consists of 20 healthy non-pregnant, volunteers (HNPW) in the age
group 18-35 years.
Patients with family history of diabetes mellitus, hypertension and
obesity were excluded from the study. None were taking any vitamin
supplements or drugs. Oral glucose tolerance was carried according to
criteria laid down by O’Sullivan and Mahan [7] by giving 100g glucose
dissolved in water and estimating blood glucose at fasting, one, two and
three hours by glucose oxidase perioxidase method [7]. Serum uric acid
levels were measured by colorimetric assay [8] and ascorbic acid levels were
estimated spectrophotometrically [9].
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RESULTS
Table 1 shows the clinical data on the study and control groups. The
mean fasting, one hour, 2 hours and 3 hours blood glucose levels in DMPRW, PRW, G-DM are given in Table 2.
The mean serum uric acid (SUA) values were significantly increased
in both preeclamptic and diabetic preeclamptic women as compared to
control (p < 0.01) SUA levels were higher in PRW as compared to DM –
PRW (p > 0.05). Also, SUA was significantly increased in gestational
diabetics as compared to HNPW (p < 0.001).
Significant fall in ascorbic acid levels were observed in both PRW as
well as DM-PRW (p<0.01) Diabetic preeclamptic women showed a greater
fall in ascorbic acid as compared to preeclamptics (p > 0.05). Aslo ascorbate
levels were lower on G-DM as compared to HNPW (p<0.001).
Decrease in ascorbate levels and rise in uric acid levels showed a
significant negative correlation (r = —0.41, p<0.01) in case of PRW, but not
statistically significant in case of DM-PRW and G-DM (r = 0.18 p > 0.05
and r = 0.21, p > 0.05 respectively).
DISCUSSION
Consistent with previous reports [4,10], mean serum uric acid levels
are significantly higher in preeclampsia than in normal pregnant in the
present study. The most commonly accepted explanation is increased
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reabsorption and decreased excretion of uric acid in proximal tubules,
similar to the physiologic response to hypovolemia.
Uric acid possesses antioxidant properties, and contributes about 60%
of free radical scavenging activity in human serum [5]. The observed uric
acid elevation may be a protective response, capable of opposing harmful
effects of free radical activity and oxidative stress.
The relationship between hypertensive disorders of pregnancy and
glucose intolerance is not established. Earlier reports had shown attenuated
glucose response to intravenous insulin in preeclampsia suggesting an
association between preeclampsia and insulin resistance [11,12]. In contrast,
a recent study has reported a reduced insulin resistance during preeclampsia
together with lack of correlation between mean arterial blood pressure and
insulin sensitivity thereby suggesting that insulin resistance is not involved
in the pathophysiology of raised blood pressure in preeclampsia [13].
Elevated serum uric acid is a consistant feature of insulin resistance
syndromes [14], though no reports are available in literature regards uric
acid levels in diabetic preeclamptics and gestational diabetes. Insulin has a
physiological action on renal tubules causing reduced sodium and uric acid
clearance [15]. Because plasma insulin is characteristically elevated,
hyperuricemia may arise as a consequence of enhanced renal insulin activity.
Elevated serum uric acid concentrations predict development of diabetes
mellitus [16] and hypertension [17], even in the presence of normal
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creatinine clearance and plasma glucose concentration, and therefore may be
a subtle, early marker of peripheral insulin resistance syndromes.
In addition, an elevated SUA concentration may reflect impaired
endothelial integrity, in which endothelial dependent vascular relaxation
produced by nitric oxide (NO) is reduced [18]. In diabetic subjects, the
problem is not a failure of generate NO; instead NO is removed through the
scavenging action of oxygen free radicals. SUA may, therefore, be linked to
cardiovascular disease because it reflects increased xanthine oxidase activity
[19], which is present in endothelial cells and is a powerful generator of
oxygen free radicals. The observed SUA elevation may be a protective
response, capable of opposing the harmful effects of free-radical activity and
oxidative stress.
There is further evidence that hydrophilic antioxidants play a pivotal
role in cardiovascular system by preventing lipid peroxidation. Several
reports implicate role of lipid peroxidation in preeclampsia and gestational
diabetes [20-23].
Substantial evidence from animal models suggests that oxidative stress in
diabetic pregnancy might contribute to risk of fetal abnormality and this can
be prevented by antioxidants [24].
In the present study, we observed low ascorbic levels in PRW and
DM-PRW as compared to controls (Table 3, p <0.01). Also, ascorbic acid
levels were lower in G-DM as compared to controls (p<0.01). Although
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preeclamptic women showed the lower levels as compared to diabetic
preeclamptic, the difference is not statistically significant (p >0.05). Little
information is available with regard to antioxidant defenses and diabetic
preeclamptics and gestational diabetes. However, reports are available
regarding antioxidant defenses in preeclampsia [20,23,25]
Short term administration of vitamin C in diabetic subjects,
hypertensive subjects and those who use tobacco regularly with low
circulating vitamin C concentration, leads to restoration of normal vascular
function [26] and offering further evidence that endothelial dysfunction may
be consequence of oxidative stress. A recent randomized study of effects of
systemic uric acid administration, 1000mg), in healthy volunteers, compared
with vitamin C (1000 mg) has shown a significant increase in serum
antioxidants scavenging capacity [27].
Both ascorbic acid and uric acid are most important physiological
aqueous antioxidants and uric acid is found significantly in higher
concentrations than ascorbic acid. As a result of higher concentration uric
acid provides most abundant source of scavenging activity in human serum
(as much as 60%). High blood glucose levels, ischaemia reperfusion,
hypoxia, induce oxidative stress and decrease antioxidant defences, thus
leading to impaired oxidative metabolism. The resulting free radicals may
damage not only the organ in which they are formed but if released into
circulation also remote organs. Fetus is a potential source of substrate for
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xanthine dehydrogenase/oxidase and hypoxanthine on crossing placenta
provides substrate for maternal xanthine dehydrogenase/oxidase, would
amplify reactive oxygen species generation distant site.
Thus, the elevated circulating concentration of uric acid, a valuable
marker of preeclampsia may be a marker of free radical generation in these
conditions.
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REFERENCES
1.
Reaven GM. Insulin resistance, hyperinsulinemia, hypertriglyceridemia, and hypertension : parallels between human disease and
rodent nodels. Diabetes Care 1991; 14 : 195-202.
2.
Ferrannini E, Buzzigoli G, Bonadonna R, Giorico MA,Oleggini M,
Graziadei L, et al. Insulin resistance in essential hypertension. N Engl
J Med 1987; 317 : 350-7.
3.
Hunt JV,Wolff SP. Oxidative glycation and free radical formation, a
causal mechanism of diabetes complications. Free Rad Res Comms
1991; 12-3 : 115-23.
4.
Many A, Hubel CA, Roberts JM. Hyperuricemia and xanthine oxidase
in preeclampsia, revisited. Am J Obstet Gynecol 1996, 174 : 288-91.
5.
Waring
WS.
Antioxidants
in
prevention
and
treatment
of
cardiovascular disease. Proc R Coll Physicians Edinb 2001; 31 : 28892.
6.
American College of Obstetrics and Gynecologists. Management of
preeclampsia, Washington DC : American College of Obstetricians
and Gynecologists (Technical Bulletin No. 91) ; 1986.
7.
O’ Sullivan JB, Mahan CM, Charles D, Dandroo RV. Medical
treatment of gestational diabetes. Obstet Gynecol 1974 ; 43 : 817-21.
10
8.
Henry RJ, Sobel C, Kin L. Estimation of uric acid in blood. Am J Clin
Path 1957; 28 : 152-7.
9.
Kyaw AA. Simple colorimetric method for ascorbic determination in
blood, plasma. Clin Chim Acta 1978, 86 : 153-7.
10.
Hickman PE, Michael CA, Polter JM, Serum uric acid as a marker of
pregnancy -induced hypertension. Aust NZ J Obstet Gynecol 1982; 22
: 198-202.
11.
Sower JR, Saleh AA, sokol RJ. Hyperinsulinemia and insulin
resistance are associated with preeclampsia in Africans-Americans.
Am J Hypertens 1995; 8 :1-4.
12.
Bauman WA, Maimen M,Langer O. An association between
hyperinsulinemia and hypertension during the third trimester of
pregnancy. Am J Obstet Gynecol 1988; 159 : 446-50.
13.
Roberts RN, Henrikson JE, Hadden DR. Insulin sensitivity in
preeclampsia. Br J Obstet Gynecol 1998; 105 : 1095-1100.
14.
WaringWS, Webb DJ, Maxwell SRJ : Uric acid as a risk factor for
cardiovascular disease. QJ Med 2000; 93 : 707-13.
15.
Muscelli E, Natali A, Bianchi S, Bigazzi R, Galvan AQ, Sironi AM,
Frascerra S, et al. Effect of insulin on renal sodium and uric acid
handling in essential hypertension. Am J Hypertens 1996, 9 : 746-52.
16.
Perry IJ, Wannamethee SG, Walker MK, Thomson AG, Whincup PH,
Shaper AG. Prospective study of risk factors for development of non11
insulin dependent diabetes in middle aged British men. BMJ 1995;
310 : 560-4.
17.
Selby IV, Friedman GD, Quesenberry CPJ. Precursors of essential
hypertension : pulmonary function, heart rate, uric acid, serum
cholesterol, and other serum chemistries. Am J Epidemiol 1990; 131 :
1017-27.
18.
Alderman MH. Uric acid and cardiovascular risk. Curr Opin
Pharmacol 2002; 2 : 126-30.
19.
White CR, Darley O, Usmar V, Berrington WR, Gore MM Jr,
Thompson J, Parks DA, Tarpcy MM, Freeman BA. Circulating
plasma xanthine oxidase contributes to vascular dysfunction in
hypercholesterolemic rabbits. Proc Natl Acad Sci USA 1996; 93 :
8745-9.
20.
Kharb S, Gulati N, Singh V, Singh GP. Lipid peroxidation and
vitamin E levels in preeclampsia. Gynecol Obstet Invest 1998; 46/4 :
238-40.
21.
Hubel CA, Roberts JM, Taylor RN, Musci JT Rogers GM, Mc
Laughlin ML. Lipid peroxidation in pregnancy : new perspectives on
preeclampsia. Am J Obstet Gynecol 1989; 161 : 1025-34.
22.
Kamath U, Rao G. Raghothama C, Rai L, Rao P. Erythrocyte
indicators of oxidative stress in gestational diabetes. Acta Paed 1998;
87 : 676-9.
12
23.
Uotila JT, Tuimala RJ, Aarnio JM. Findings on lipid peroxidation and
antioxidant function in hypertensive complications of pregnancy. Br J
Obstet Gynecol 1993; 100 : 270-6.
24.
Eriksson UJ, Borg LAH. Embryonic malformations in diabetic
environment are caused by mitochondrial generation of oxygen free
radicals. Diabetologia 1991, 34 (Suppl 2) : A5-10.
25.
Mikail MS, Anyaegbunam A, Garfinkel D, Palan PK, Basu J, Romney
SL. Preeclampsia and antioxidant nutrients : decreased plasma levels
of reduced ascorbic acid, alpha tocopheol, and beta carotene in
women with preclampsia. Am J Obstet Gynecol 1994; 171: 150-7.
26.
Waring
WS,Webb
DJ,
Maxwell
SRJ.
Systemic
uric
acid
administration increases serum antioxiant capacity in healthy
volunteers. J. Cardiovasc Pharmacol 2001; 38/3 : 365-71.
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Table –1 : Clinical characteristics of study groups (mean values)
HPW
G-DM
PRW
DM-PRW
Age (y)
21
20.8
23.8
22.6
Hemoglobin (g%)
9.8
9.6
9.3
9.7
Delivery (wk)
38.2
38
36.4
37.2
Birth weight (g)
2500
2400
2200
2800
Gestational age at
Table 2 : Glucose tolerance in various groups (mean ± SD, mg%)
Fasting
60 min.
120 min.
180 min.
DM-PRW
67.08±8.43 c,ii
92.5±15.41 b,ii
87.4±12.12 a,i
77.88±9.68 a
G.DM
76.68 ± 14.18
119.48 ± 28.0
110.8 ±28.7
89.24±26.49
HPW
72.8±11.17
108.0±25.4
110.0±24.0
90.92±15.15
a
b
c
As compared to HPW
As compared to HPW
As compared to HPW
p <0.001
p <0.01
p < 0.05
i
ii
As compared to G-DM
As compared to G-DM
p <0.01
p <0.05
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Table 3 : Uric acid and ascorbic acid levels in various groups
(means ± SD, mg%)
S Uric acid
S ascorbic acid
Control (HPNW) n=20
2.36±0.41
2.05 ± 0.32
HPW (n = 12)
3.73 ± 0.14*
1.46 ± 0.124 *
G – DM (n = 8)
5.23 ± 0.33 a
1.395 ± 0.09*
PRW (n= 22)
5.71 ± 1.08 *
0.968 ± 0.23 *
DMPRW (n = 18)
5.68 ± 0.91 *
1.01 ± 0.21 *
* P < 0.01 as compared to controls.
a p < 0.001 as compared to controls.
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