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Effect of bis[curcumino]oxovanadium complex on non-diabetic and streptozotocin-induced diabetic rats
ARTICLE IN PRESS Journal of
Trace Elements in Medicine and Biology Journal of Trace Elements in Medicine and Biology 18 (2005) 211–217 www.elsevier.de/jtemb
BIOINORGANIC CHEMISTRY
Effect of bis[curcumino]oxovanadium complex on non-diabetic and streptozotocin-induced diabetic rats Jayesh B. Majithiya, R. Balaraman, Rajani Giridhar, Mange Ram Yadav Pharmacy Department, Faculty of Technology and Engineering, M.S. University of Baroda, Kalabhavan, Baroda-390001, Gujarat, India Received 26 April 2004; accepted 27 December 2004
Abstract The effect of the vanadium complex bis[curcumino]oxovanadium (BCOV) on blood glucose level, serum lipid levels, blood pressure and vascular reactivity were studied in non-diabetic and streptozotocin-induced diabetic (STZ-diabetic) rats and compared to that of vanadyl sulfate. Blood glucose level, serum lipid levels, and blood pressure were significantly increased in STZ-diabetic rats. Vascular reactivity to various agonists such as noradrenaline and acetylcholine were significantly increased in STZ-diabetic rats. Blood glucose and serum lipid levels were restored to normal in STZ-diabetic animals treated with vanadyl sulfate at a concentration of 0.5 mmol/kg/day (p.o.). However, vanadyl sulfate at a concentration of 0.2 mmol/kg/day (p.o.) did not produce any significant change in blood glucose and lipid levels. There was no significant effect of vanadyl sulfate (0.2 or 0.5 mmol/kg/day) treatment on blood pressure and vascular reactivity in STZ-diabetic rats. Vanadyl sulfate significantly reduced the body weight of non-diabetic and STZ-diabetic rats. Moreover, it also caused severe diarrhea in both groups of animals. Treatment with BCOV (0.05, 0.1 and 0.2 mmol/kg/day, p.o.) significantly decreased blood glucose level and serum lipids in STZ-diabetic rats. Furthermore, administration of BCOV to STZ-diabetic rats restored the blood pressure and vascular reactivity to agonists to normal. There was no significant change in the body weight of BCOV treated non-diabetic and STZdiabetic rats. Diarrhea was not observed in both BCOV treated groups. In conclusion, the present study shows that the vanadium complex BCOV has antidiabetic and hypolipedimic effects. In addition, it improves the cardiovascular complications associated with diabetes. r 2005 Elsevier GmbH. All rights reserved. Keywords: Bis[curcumino]oxovanadium; BCOV; Vanadyl sulfate; Diabetes; Streptozotocin-induced
Introduction Diabetes mellitus includes a heterogeneous group of diseases, which have become an important health concern in our society. Diabetes mellitus is characterized by hyperglycemia, alterations in carbohydrate and lipid Corresponding author. Tel.: +0265 2434187.
E-mail addresses: [email protected] (J.B. Majithiya), [email protected] (R. Balaraman). 0946-672X/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.jtemb.2004.12.001
metabolism, and vascular and neurological complications. Numerous therapies designed to supplement or enhance insulin action have been developed for the treatment of non-insulin-dependent diabetes mellitus (NIDDM). These therapies have proven to be fairly effective, but none is ideal. There is a need to find effective, orally ingestible drugs that mimic or enhance the properties of insulin. Vanadate was found to lower blood glucose in insulin-deficient rats [2] and in animal models of insulin
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J.B. Majithiya et al. / Journal of Trace Elements in Medicine and Biology 18 (2005) 211–217 CH
HO
CH
CH
C
C
CH
CH
OH
O MeO
O
O
OMe
O
OMe
V MeO HO
O CH
CH
CH
C
CH
CH
OH
CH
Fig. 1. Structure of bis[curcumino]oxovanadium (BCOV).
resistance [1]. The insulin-like properties of vanadium in isolated cells and tissues has generated considerable enthusiasm for its potential therapeutic value in human diabetes [3–6]. A major advance in the use of vanadium is the development of organic vanadium complexes. However, most of them have the common adverse effects of a narrow therapeutic window and high incidence of diarrhea [7,8]. The insulinomimetic properties of organic vanadium compounds raises the possibility of their use as insulin replacement in the treatment of diabetes mellitus. Therefore, as an advancement in the synthesis of organometallic complexes, we have chelated the vanadium centre with curcumin. Curcumin, an active constituent of curcuma longa, has been reported to have hypolipidemic, hypoglycemic and antioxidant activities [9–12]. Furthermore, curcumin is reported to attenuate diabetic complications such as nephropathy [13–14]. The concept of combining vanadium with a curcumin ligand to form a compound that exhibits synergistic activity is appealing. Therefore the present study was aimed to investigate the antidiabetic and antilipidemic effects of bis[curcumino]oxovanadium (BCOV), an organometallic vanadium complex with curcumin (Fig. 1), in streptozotocin-induced diabetic (STZ-diabetic) rats. In addition, the compound is evaluated for its antihypertensive effect, as hypertension is a common feature in STZ-diabetic rats.
Synthesis of bis[curcumino]oxovanadium The chelate bis[curcumino]oxovanadium [16] was prepared by reaction of curcumin (2 mole) and vanadyl sulfate (1 mole) in ethanol under alkaline conditions. The compound was isolated as a dark coloured complex. The vanadium content in the complex was determined by atomic absorption spectroscopy. It has one unpaired electron in the 3d orbital, characteristic of the vanadyl unit. It showed fairly strong V ¼ O stretching vibration at 974 cm1 in the IR spectrum. Briefly, 400 mg of curcumin was dissolved in 100 ml of ethanol. A total of 100 mg of vanadyl sulfate pentahydrate was dissolved in 2 ml distilled water and the resulting solution was added dropwise to the refluxing solution of curcumin in ethanol. The reaction mixture was alkalized by addition of ammonia solution, refluxed for 2 h in a water bath and concentrated. After cooling, the product crystallized out as dark coloured crystals (450 mg; melting point above 300 1C (d)). UV (MeOH): 416 nm (log 4.26) and 234 nm (log 4.36); IR: 1591, 1512, 1280, 1160, 1125, 974 cm1. C42H38O13V requires C, 62.92; H, 4.78; V, 6.35. Found: C, 62.55; H, 5.12; V, 6.82.
Animals All experiments and protocols described were approved by the Institutional Animal Ethics Committee (IAEC) of M.S. University, Baroda and are in accordance with the guidance of the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Ministry of Social Justice and Empowerment, Government of India. Studies were carried out on in-bred male wistar rats (225725 g). All animals were kept under standardized conditions (12 h light/dark cycle, 24 1C) and were provided free access to food and water.
Induction of diabetes
Materials and methods Reagents and chemicals Bis[curcumino]oxovanadium was synthesized as described below by the Medicinal Chemistry Department of the Pharmacy Department, Faculty of Technology and Engineering, M.S. University of Baroda. Curcumin was synthesized as described by Pabon [15]. Urethane, streptozotocin and vanadyl sulfate were obtained from Sigma, St. Louis, MO, USA. Streptozotocin was dissolved in 0.1 mol/l citrate buffer (pH 4.5). BCOV and vanadyl sulfate were suspended in 0.5% sodium carboxy methyl cellulose solution.
Rats were injected with a single intravenous dose of streptozotocin (45 mg/kg) dissolved in citrate buffer (pH 4.5). The control animals were injected with an equal volume of vehicle. Three days after the streptozotocin administration, blood was collected from the tail vein and serum samples were analyzed for blood glucose. Animals showing fasting (12 h) blood glucose higher than 14 mmol/l were selected and used for the study.
Experimental design Forty-eight non-diabetic rats (with a 12 h fasting blood glucose level between 5.27 and 4.44 mmol/l) and 48 STZ-diabetic rats (with a 12 h fasting blood glucose
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level higher than 14 mmol/l) were randomized based on blood glucose levels. They were divided into the following groups: Group 1:
Group 2:
Group 3:
Group 4:
Group 5:
Group 6:
Non-diabetic and STZ-diabetic controls (vehicle 0.5% sodium carboxy methyl cellulose) Non-diabetic and STZ-diabetic animals treated with 0.2 mmol/kg/day (p.o.) of vanadyl sulfate for 4 weeks Non-diabetic and STZ-diabetic animals treated with 0.5 mmol/kg/day (p.o.) of vanadyl sulfate for 4 weeks Non-diabetic and STZ-diabetic rats treated with 0.05 mmol/kg/day (p.o.) of BCOV for 4 weeks Non-diabetic and STZ-diabetic animals treated 0.1 mmol/kg/day (p.o.) of BCOV for 4 weeks Non-diabetic and STZ-diabetic animal treated with 0.2 mmol/kg/day (p.o.) of BCOV for 4 weeks.
The body weight was recorded daily in all groups for 4 weeks.
Blood glucose and lipids After 4 weeks of treatment with vanadyl sulfate or BCOV, blood was collected from the tail vein of the 12 h fasted rats. Serum was separated and blood glucose, triglycerides, total cholesterol, high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol were determined. Fasting blood glucose and lipids (triglycerides and total cholesterol) were determined by enzymatic assays using commercially available kits of Span Diagnostics, India. HDL was determined after precipitation of apoB-containing lipoproteins with phosphotungstic acid using kits of Monozyme Diagnostics, India. LDL was calculated by the Friedewald formula [17] using the HDL value obtained by precipitation.
Blood pressure and vascular reactivity The blood pressure was measured after 4 weeks of treatment according to the procedure described by Balaraman et al. [18]. Rats were anaesthetized with 1.2 g/kg (i.p.) of urethane. Tracheotomy was performed to facilitate breathing. The left common carotid artery and left femoral vein were cannulated with polyethylene tubing filled with heparinised saline (500 IU). Systolic and diastolic blood pressure were directly measured at the left common carotid by connecting the polyethylene tubing to the precalibrated pressure transducer SS13L
213
(BIOPAC systems, Inc., CA, USA) connected to the Biopac MP-30 data acquisition system (BIOPAC Systems, Inc.). Drugs were infused through the polyethylene tubing connected to the left femoral vein. After 30 min of equilibration, systolic and diastolic blood pressure and vascular reactivity to intravenous (i.v.) injection of noradrenaline (0.1 mmol/kg) and acetylcholine (0.1 mmol/kg) were recorded. Rats received a maintenance i.v. infusion of 0.9% sodium chloride at a rate of 1 ml/h throughout the experiment.
Statistical analysis The results are expressed as mean7standard error of the mean (SEM). The difference between groups are analysed by two way analysis of variance (ANOVA) followed by Dunnet’s test with 5% level of significance (po0.05) on neat values of non-diabetic and STZdiabetic treated groups (vanadyl sulfate and BCOV) with the respective controls.
Results Body weight The body weight of STZ-diabetic rats after 4 weeks significantly decreased as compared to their initial body weight (Table 1). After treatment with vanadyl sulfate (0.2 and 0.5 mmol/kg/day), the body weight of the STZdiabetic group also decreased significantly (po0.05) compared to the initial value. Similarly, the body weight of non-diabetic rats treated with vanadyl sulfate decreased significantly (po0.05), showing signs of vanadium toxicity. Significant (po0.05) increase in body weight was observed in BCOV (0.05, 0.1, 0.2 mmol/kg/day, 4 weeks) treated STZ-diabetic rats as compared to STZ-diabetic controls (Table 1). There was no significant difference in body weight of STZ-diabetic rats treated with BCOV (0.05, 0.1, 0.2 mmol/kg/day, 4 weeks) compared to non-diabetic rats treated with BCOV. Similarly, there was no significant difference in body weight of BCOV treated non-diabetic rats compared to the non-diabetic control group. In the vanadyl sulfate-treated groups (STZ-diabetic and non-diabetic rats), mild (0.2 mmol/kg/day groups) to severe (0.5 mmol/kg/day groups) diarrhea was observed, whereas no signs of diarrhea were observed in any of the groups (STZ-diabetic and non-diabetic rats) treated with BCOV.
Blood glucose level Administration of streptozotocin (45 mg/kg, i.v.) produced a significant increase in blood glucose
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Table 1. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on body weight of STZ-diabetic and non-diabetic rats Treatment
Groups
Body weight (g) Initial
1st week
2nd week
3rd week
4th week
Control
Non-diabetic STZ-diabetic
235710.9 238714.6
239712.3 233716.3
24479.33 228713.4
250711.7 224715.7
254713.4 221712.4*
0.2 mmol VaSO4
Non-diabetic STZ-diabetic
231712.2 234714.7
229711.5 230712.7
225713.4 225716.1
223712.3 220715.6
219710.8* 216716.4*
0.5 mmol VaSO4
Non-diabetic STZ-diabetic
237713.2 233714.1
229716.7 225713.4
222717.2 217716.5
213715.8 211715.6
207716.1* 201714.4*
0.05 mmol BCOV
Non-diabetic STZ-diabetic
228714.1 230716.9
232710.8 232715.8
237712.3 236716.6
242714.1 242717.2
247713.4 245716.1 # *
0.1 mmol BCOV
Non-diabetic STZ-diabetic
231711.7 229714.6
233713.4 230713.2
237716.6 234712.6
241715.6 238714.1
245714.4 242715.7 # *
0.2 mmol BCOV
Non-diabetic STZ-diabetic
227710.8 231712.3
230712.6 234710.8
234715.2 23779.77
237714.1 239711.6
242713.7 241710.6 # *
Values are expressed as mean 7SEM. * po0.05, significantly different from initial body weight. # po0.05, significantly different from STZ-diabetic control group.
Table 2. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on serum parameters of STZ-diabetic and non-diabetic rats Treatment
Groups
Glucose (mmol/l)
Cholesterol (mg/dl)
Triglycerides (mg/dl)
HDL (mg/dl)
LDL (mg/dl)
Control
Non-diabetic STZ-diabetic
4.7970.38 26.471.09
10477.66 220712.1
96.479.65 231714.8
26.675.48 21.674.65
58.272.25 15274.51
0.2 mmol VaSO4
Non-diabetic STZ-diabetic
4.7270.28 25.671.20
10177.86 218714.7
98.278.91 237716.2
22.773.32 24.374.85
53.875.21 147710.3
0.5 mmol VaSO4
Non-diabetic STZ-diabetic
4.1870.45 6.1070.63*
97.779.67 94.477.23*
10177.88 113711.5*
18.174.56 16.178.3
59.373.53 55.773.36*
0.05 mmol BCOV
Non-diabetic STZ-diabetic
4.6770.37 6.9370.43*
96.4711.2 97.476.33*
98.477.24 105711.2*
21.875.44 20.776.54
54.974.35 55.672.45*
0.1 mmol BCOV
Non-diabetic STZ-diabetic
4.3770.47 5.9370.70*
94.378.44 93.377.23*
95.774.47 95.376.87*
20.379.54 19.374.32
54.872.99 54.971.53*
0.2 mmol BCOV
Non-diabetic STZ-diabetic
4.5570.40 4.5170.28*
95.177.66 94.274.33*
94.375.77 94.878.37*
20.877.52 19.874.24
55.471.14 55.471.58*
Values are expressed as mean 7SEM, * po0.05, significantly different from STZ-diabetic control group.
concentrations. Administration of a low dose of vanadyl sulfate (0.2 mmol/kg/day) for 4 weeks produced no significant change in the blood glucose level of STZdiabetic rats, whereas administration of a higher dose of vanadyl sulfate (0.5 mmol/kg/day) for 4 weeks significantly (po0.05) reduced the blood glucose level in STZdiabetic rats (Table 2). There was no significant change in blood glucose concentrations of non-diabetic rats treated with vanadyl sulfate (0.2 or 0.5 mmol/kg/day). Treatment with BCOV (0.05, 0.1 and 0.2 mmol/kg/day) of STZ-diabetic rats produced a significant (po0.05)
dose-dependent decrease in blood glucose level. On the other hand, BCOV (0.05, 0.1, 0.2 mmol/kg/day) had no significant effect on blood glucose concentrations in non-diabetic rats (Table 2).
Serum lipids Administration of streptozotocin (45 mg/kg, i.v.) resulted in a significant (po0.05) increase in serum triglycerides and total cholesterol levels. Administration
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mm Hg
of a low dose of vanadyl sulfate (0.2 mmol/kg/day, 4 weeks) produced no significant change in total cholesterol and triglyceride levels of STZ-diabetic rats (Table 2). A significant (po0.05) decrease in total cholesterol and triglycerides was observed in STZ-diabetic rats treated with 0.5 mmol/kg/day vanadyl sulfate for 4 weeks. Treatment with vanadyl sulfate for 4 weeks at any dose used produced no significant change in total cholesterol and triglyceride levels in non-diabetic rats. BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks of STZ-diabetic rats significantly (po0.05) decreased total cholesterol and triglyceride levels, but had no effect on the lipid profile of non-diabetic rats (Table 2). Administration of vanadyl sulfate or BCOV had no significant effect on HDL levels of STZ-diabetic rats or non-diabetic rats. On the other hand, treatment with vanadyl sulfate and BCOV significantly decreased LDL levels in STZ-diabetic rats, but had no significant effect on LDL levels of non-diabetic rats (Table 2).
140
*
*
*
*
*
110 100 STZcontrol
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 3. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1, and 0.2 mmol/kg/day) treatment on (’) systolic blood pressure and (&) diastolic blood pressure of STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from control.
50
140
*
130 120
Blood pressure and vascular reactivity
#
40
∆ mm Hg
STZ-diabetic rats showed a significant (po0.05) increase in systolic and diastolic blood pressure as compared to non-diabetic rats (Fig. 3). Treatment with vanadyl sulfate (0.2 or 0.5 mmol/kg/day) of STZdiabetic rats had no significant effect on blood pressure. However, administration of BCOV (0.05, 0.1 or 0.2 mmol/kg/day) for 4 weeks produced a significant (po0.05) decrease in systolic and diastolic blood pressure as compared to STZ-diabetic control animals (Fig. 3). Non-diabetic rats treated with BCOV for 4 weeks showed no significant changes in blood pressure (Figs. 2 and 3). Vascular reactivity to noradrenaline (0.1 mmol/kg, i.v.) and acetylcholine (0.1 mmol/kg, i.v.) was significantly (po0.05) increased in STZ-diabetic rats (Figs. 4 and 5). Vanadyl sulfate treatment for 4 weeks had no
215
*
30
* 20
10
0 Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 4. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on vascular reactivity to 0.1 mmol/kg noradrenaline i.v. of (’) non-diabetic and (&) STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from STZ-diabetic control. # po0.05, significantly different from non-diabetic control.
130
mm Hg
120
significant effect on the vascular reactivity to noradrenaline and acetylcholine. On the other hand, BCOV treatment significantly (po0.05) restored vascular reactivity of STZ-diabetic rats to normal. Regarding the non-diabetic rats, administration of neither vanadyl sulfate nor BCOV had an effect on vascular reactivity (Figs. 4 and 5).
110 100 90 80 70 60 Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 2. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment on (’) systolic blood pressure and (&) diastolic blood pressure of non-diabetic rats. Values are expressed as mean7SEM.
Discussion and conclusions The study shows that BCOV (at concentrations of 0.05, 0.1 and 0.2 mmol/kg/day) attenuates diabetes more
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Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
0
∆ mm Hg
-10 -20 -30
*
*
*
-40
# -50
Fig. 5. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on vascular reactivity to 0.1 mmol/kg acetylcholine of (’) non-diabetic and (&) STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from STZ-diabetic control. # po0.05, significantly different from non-diabetic control.
efficaciously than vanadyl sulfate (at concentrations of 0.2 and 0.5 mmol/kg/day). Vanadyl sulfate when administered at a concentration of 0.2 mmol/kg/day had no significant effect on blood glucose, total cholesterol and triglyceride levels. Furthermore, it caused body weight loss and diarrhea in STZ-diabetic as well as non-diabetic rats showing signs of toxicity. Vanadyl sulfate at a concentration of 0.5 mmol/kg/day significantly reduced blood glucose, total cholesterol and triglyceride levels but it also caused body weight loss and severe diarrhea in STZ-diabetic and non-diabetic animals. On the other hand, BCOV significantly reduced blood glucose, total cholesterol and triglyceride levels without any adverse effects such as body weight loss or diarrhea. Despite of very low levels of vanadium intake (BCOV: 0.05, 0.1 and 0.2 mmol/kg/day as compared to vanadyl sulfate: 0.2 and 0.5 mmol/kg/day), BCOV ameliorates diabetes more efficaciously without any adverse effects. The effect of vanadyl sulfate and BCOV on high blood pressure associated with diabetes was also studied. Vanadyl sulfate (0.2 and 0.5 mmol/kg/day) treatment did not have any significant effect on blood pressure of STZ-diabetic rats, whereas BCOV (0.05, 0.1 and 0.2 mmol/kg/day) administration significantly reduced blood pressure of STZ-diabetic rats. Increased vascular reactivity to noradrenaline and acetylcholine is one of the major causes of hypertension associated with diabetes in the STZ-model. Vascular reactivity was restored back to normal by BCOV treatment, while vanadyl sulfate treatment had no significant effect on vascular reactivity. Inorganic vanadium is usually poorly (1–10%) absorbed in the gastrointestinal tract [8,20]. The organic ligand is expected to increase the lipophilicity of the vanadium complex and consequently its absorption [19]. Various authors [20–23] tested the normogly-
cemic activity of various vanadium complexes with organic ligands such as bis(maltolato)oxovanadium(IV) (BMOV), oxobis(picolinato)vanadium(IV) (VPA), bis (methylpicolinato)oxovanadium(IV) (VO-MPA), vanadyl bis(cycteine methyl ester) (VCME), oxobis(pyrrolidine-N-carbodithioto)vanadium(IV) (NAGLI-VAN), (N,N0 -disalicylidineethylenedamine)oxovanadium(IV) (VO-SALEN). They were administered at daily doses of 0.1–0.7 mmol/kg/day, in drinking water or by gavage [21–24]. These compounds showed antidiabetic activity but side effects like diarrhea were observed. Our results are in accordance with other studies where diarrhea was observed with vanadyl sulfate treatment [21–24]. Conversely there are also some reports of no incidence of diarrhea with vanadyl sulfate treatment [25]. BCOV showed antidiabetic activity at a much lower dose (0.05 mmol/kg/day). Moreover, diarrhea as a major side effect of vanadium complexes was not at all observed. The glucose lowering effect of vanadium is attributed to its insulinomimetic properties. In several studies, administration of vanadium complexes resulted in an activation of insulin receptor tyrosine kinase (IRTK), autophosphorylation at tyrosine residues and inhibition of phosphotyrosine phosphates [26–28]. The presence of the organic ligand curcumin in the vanadium complex increases the potency and decreases the toxicity of vanadium. The present study shows that BCOV is much safer and efficacious in treatment of diabetes in STZ-diabetic rats and at much lower doses than vanadyl sulfate. Moreover, it also reduces high blood pressure associated with diabetes. Therefore, apart from its use in diabetes therapy, BCOV could also be useful in the treatment of cardiovascular complications associated with diabetes.
Acknowledgement Financial assistance for the first author provided by University Grants Commissions (UGC) Govt. of India is highly acknowledged.
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[18] Balaraman R, Gulati OD, Bhatt JD, Rathod SP, Hemavathi KG. Cadmium-induced hypertension in rats. Pharmacology 1989;38(4):226–34. [19] Yuen VG, Orvig C, McNeill JH. Glucose lowering effects of a new organic vanadium complex, bis(maltolato)oxovanadium(IV). Can J Physiol Pharmacol 1993;71: 263–9. [20] Yuen VG, Orvig C, Thompson KH, McNeill JH. Improvement in cardiac dysfunction in streptozotocininduced diabetic rats following chronic oral administration of bis(maltolato)oxovanadium(IV). Can J Physiol Pharmacol 1993;71:270–6. [21] Yuen VG, Orvig C, McNeill JH. Comparision of the glucose lowering properties of vanadyl sulfate and bis(maltolato)oxovanadium(IV) following acute and chronic administration. Can J Physiol Pharmacol 1995; 73:55–64. [22] Thomson KH, McNeill JH, Orvig C. Vanadium compounds as insulin mimics. Chem Rev 1999;99:2561–71. [23] Cam MC, Cros GH, Serrano JJ, Lazaro R, McNeill JH. In vivo antidiabetic actions of naglivan, an organic vanadyl compound in streptozotocin-induced diabetes. Diabetes Res Clin Pract 1993;20(2):111–21. [24] Orvig C, Thompson KH, Cam MC, McNeill JH. Vanadium compounds as possible insulin modifiers. In: Farrell NP, editor. Uses of inorganic chemistry in medicine. Berlin: Springer; 1999. p. 93–108. [25] Mongold JJ, Cros GH, Vian L, Tep A, Ramanadham S, Siou G, Diaz J, McNeill JH, Serrano JJ. Toxicological aspects of vanadyl sulphate on diabetic rats: effects on vanadium levels and pancreatic B-cell morphology. Pharmacol. Toxicol. 1990;67:192–8. [26] Posner BI, Faure R, Burgess JW, Bevan AP, Lachance D, Zhang-Sun G, Fantus IG, Ng JB, Hall DA, Lum BS, Shaver A. Peroxovanadium compounds. A new class of potent phosphotyrosine phosphatase inhibitors which are insulin mimetics. J Biol Chem 1994; 269:4596–604. [27] Bevan AP, Drake PG, Yale J-F, Shaver A, Posner BI. Peroxovanadium compounds: biological actions and mechanism of insulin-mimesis. Mol Cell Biochem 1995; 153:49–58. [28] Grillo S, Gremeaux T, Casamayor A, Alessi DR, Le Marchand-Brustel Y, Tanti J-F. Peroxovanadate induces tyrosine phosphorylation of phosphoinositide-dependent protein kinase-1. Potential involvement of Src kinase. Eur J Biochem 2000;267:6642–9.
Trace Elements in Medicine and Biology Journal of Trace Elements in Medicine and Biology 18 (2005) 211–217 www.elsevier.de/jtemb
BIOINORGANIC CHEMISTRY
Effect of bis[curcumino]oxovanadium complex on non-diabetic and streptozotocin-induced diabetic rats Jayesh B. Majithiya, R. Balaraman, Rajani Giridhar, Mange Ram Yadav Pharmacy Department, Faculty of Technology and Engineering, M.S. University of Baroda, Kalabhavan, Baroda-390001, Gujarat, India Received 26 April 2004; accepted 27 December 2004
Abstract The effect of the vanadium complex bis[curcumino]oxovanadium (BCOV) on blood glucose level, serum lipid levels, blood pressure and vascular reactivity were studied in non-diabetic and streptozotocin-induced diabetic (STZ-diabetic) rats and compared to that of vanadyl sulfate. Blood glucose level, serum lipid levels, and blood pressure were significantly increased in STZ-diabetic rats. Vascular reactivity to various agonists such as noradrenaline and acetylcholine were significantly increased in STZ-diabetic rats. Blood glucose and serum lipid levels were restored to normal in STZ-diabetic animals treated with vanadyl sulfate at a concentration of 0.5 mmol/kg/day (p.o.). However, vanadyl sulfate at a concentration of 0.2 mmol/kg/day (p.o.) did not produce any significant change in blood glucose and lipid levels. There was no significant effect of vanadyl sulfate (0.2 or 0.5 mmol/kg/day) treatment on blood pressure and vascular reactivity in STZ-diabetic rats. Vanadyl sulfate significantly reduced the body weight of non-diabetic and STZ-diabetic rats. Moreover, it also caused severe diarrhea in both groups of animals. Treatment with BCOV (0.05, 0.1 and 0.2 mmol/kg/day, p.o.) significantly decreased blood glucose level and serum lipids in STZ-diabetic rats. Furthermore, administration of BCOV to STZ-diabetic rats restored the blood pressure and vascular reactivity to agonists to normal. There was no significant change in the body weight of BCOV treated non-diabetic and STZdiabetic rats. Diarrhea was not observed in both BCOV treated groups. In conclusion, the present study shows that the vanadium complex BCOV has antidiabetic and hypolipedimic effects. In addition, it improves the cardiovascular complications associated with diabetes. r 2005 Elsevier GmbH. All rights reserved. Keywords: Bis[curcumino]oxovanadium; BCOV; Vanadyl sulfate; Diabetes; Streptozotocin-induced
Introduction Diabetes mellitus includes a heterogeneous group of diseases, which have become an important health concern in our society. Diabetes mellitus is characterized by hyperglycemia, alterations in carbohydrate and lipid Corresponding author. Tel.: +0265 2434187.
E-mail addresses: [email protected] (J.B. Majithiya), [email protected] (R. Balaraman). 0946-672X/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.jtemb.2004.12.001
metabolism, and vascular and neurological complications. Numerous therapies designed to supplement or enhance insulin action have been developed for the treatment of non-insulin-dependent diabetes mellitus (NIDDM). These therapies have proven to be fairly effective, but none is ideal. There is a need to find effective, orally ingestible drugs that mimic or enhance the properties of insulin. Vanadate was found to lower blood glucose in insulin-deficient rats [2] and in animal models of insulin
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J.B. Majithiya et al. / Journal of Trace Elements in Medicine and Biology 18 (2005) 211–217 CH
HO
CH
CH
C
C
CH
CH
OH
O MeO
O
O
OMe
O
OMe
V MeO HO
O CH
CH
CH
C
CH
CH
OH
CH
Fig. 1. Structure of bis[curcumino]oxovanadium (BCOV).
resistance [1]. The insulin-like properties of vanadium in isolated cells and tissues has generated considerable enthusiasm for its potential therapeutic value in human diabetes [3–6]. A major advance in the use of vanadium is the development of organic vanadium complexes. However, most of them have the common adverse effects of a narrow therapeutic window and high incidence of diarrhea [7,8]. The insulinomimetic properties of organic vanadium compounds raises the possibility of their use as insulin replacement in the treatment of diabetes mellitus. Therefore, as an advancement in the synthesis of organometallic complexes, we have chelated the vanadium centre with curcumin. Curcumin, an active constituent of curcuma longa, has been reported to have hypolipidemic, hypoglycemic and antioxidant activities [9–12]. Furthermore, curcumin is reported to attenuate diabetic complications such as nephropathy [13–14]. The concept of combining vanadium with a curcumin ligand to form a compound that exhibits synergistic activity is appealing. Therefore the present study was aimed to investigate the antidiabetic and antilipidemic effects of bis[curcumino]oxovanadium (BCOV), an organometallic vanadium complex with curcumin (Fig. 1), in streptozotocin-induced diabetic (STZ-diabetic) rats. In addition, the compound is evaluated for its antihypertensive effect, as hypertension is a common feature in STZ-diabetic rats.
Synthesis of bis[curcumino]oxovanadium The chelate bis[curcumino]oxovanadium [16] was prepared by reaction of curcumin (2 mole) and vanadyl sulfate (1 mole) in ethanol under alkaline conditions. The compound was isolated as a dark coloured complex. The vanadium content in the complex was determined by atomic absorption spectroscopy. It has one unpaired electron in the 3d orbital, characteristic of the vanadyl unit. It showed fairly strong V ¼ O stretching vibration at 974 cm1 in the IR spectrum. Briefly, 400 mg of curcumin was dissolved in 100 ml of ethanol. A total of 100 mg of vanadyl sulfate pentahydrate was dissolved in 2 ml distilled water and the resulting solution was added dropwise to the refluxing solution of curcumin in ethanol. The reaction mixture was alkalized by addition of ammonia solution, refluxed for 2 h in a water bath and concentrated. After cooling, the product crystallized out as dark coloured crystals (450 mg; melting point above 300 1C (d)). UV (MeOH): 416 nm (log 4.26) and 234 nm (log 4.36); IR: 1591, 1512, 1280, 1160, 1125, 974 cm1. C42H38O13V requires C, 62.92; H, 4.78; V, 6.35. Found: C, 62.55; H, 5.12; V, 6.82.
Animals All experiments and protocols described were approved by the Institutional Animal Ethics Committee (IAEC) of M.S. University, Baroda and are in accordance with the guidance of the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Ministry of Social Justice and Empowerment, Government of India. Studies were carried out on in-bred male wistar rats (225725 g). All animals were kept under standardized conditions (12 h light/dark cycle, 24 1C) and were provided free access to food and water.
Induction of diabetes
Materials and methods Reagents and chemicals Bis[curcumino]oxovanadium was synthesized as described below by the Medicinal Chemistry Department of the Pharmacy Department, Faculty of Technology and Engineering, M.S. University of Baroda. Curcumin was synthesized as described by Pabon [15]. Urethane, streptozotocin and vanadyl sulfate were obtained from Sigma, St. Louis, MO, USA. Streptozotocin was dissolved in 0.1 mol/l citrate buffer (pH 4.5). BCOV and vanadyl sulfate were suspended in 0.5% sodium carboxy methyl cellulose solution.
Rats were injected with a single intravenous dose of streptozotocin (45 mg/kg) dissolved in citrate buffer (pH 4.5). The control animals were injected with an equal volume of vehicle. Three days after the streptozotocin administration, blood was collected from the tail vein and serum samples were analyzed for blood glucose. Animals showing fasting (12 h) blood glucose higher than 14 mmol/l were selected and used for the study.
Experimental design Forty-eight non-diabetic rats (with a 12 h fasting blood glucose level between 5.27 and 4.44 mmol/l) and 48 STZ-diabetic rats (with a 12 h fasting blood glucose
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level higher than 14 mmol/l) were randomized based on blood glucose levels. They were divided into the following groups: Group 1:
Group 2:
Group 3:
Group 4:
Group 5:
Group 6:
Non-diabetic and STZ-diabetic controls (vehicle 0.5% sodium carboxy methyl cellulose) Non-diabetic and STZ-diabetic animals treated with 0.2 mmol/kg/day (p.o.) of vanadyl sulfate for 4 weeks Non-diabetic and STZ-diabetic animals treated with 0.5 mmol/kg/day (p.o.) of vanadyl sulfate for 4 weeks Non-diabetic and STZ-diabetic rats treated with 0.05 mmol/kg/day (p.o.) of BCOV for 4 weeks Non-diabetic and STZ-diabetic animals treated 0.1 mmol/kg/day (p.o.) of BCOV for 4 weeks Non-diabetic and STZ-diabetic animal treated with 0.2 mmol/kg/day (p.o.) of BCOV for 4 weeks.
The body weight was recorded daily in all groups for 4 weeks.
Blood glucose and lipids After 4 weeks of treatment with vanadyl sulfate or BCOV, blood was collected from the tail vein of the 12 h fasted rats. Serum was separated and blood glucose, triglycerides, total cholesterol, high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol were determined. Fasting blood glucose and lipids (triglycerides and total cholesterol) were determined by enzymatic assays using commercially available kits of Span Diagnostics, India. HDL was determined after precipitation of apoB-containing lipoproteins with phosphotungstic acid using kits of Monozyme Diagnostics, India. LDL was calculated by the Friedewald formula [17] using the HDL value obtained by precipitation.
Blood pressure and vascular reactivity The blood pressure was measured after 4 weeks of treatment according to the procedure described by Balaraman et al. [18]. Rats were anaesthetized with 1.2 g/kg (i.p.) of urethane. Tracheotomy was performed to facilitate breathing. The left common carotid artery and left femoral vein were cannulated with polyethylene tubing filled with heparinised saline (500 IU). Systolic and diastolic blood pressure were directly measured at the left common carotid by connecting the polyethylene tubing to the precalibrated pressure transducer SS13L
213
(BIOPAC systems, Inc., CA, USA) connected to the Biopac MP-30 data acquisition system (BIOPAC Systems, Inc.). Drugs were infused through the polyethylene tubing connected to the left femoral vein. After 30 min of equilibration, systolic and diastolic blood pressure and vascular reactivity to intravenous (i.v.) injection of noradrenaline (0.1 mmol/kg) and acetylcholine (0.1 mmol/kg) were recorded. Rats received a maintenance i.v. infusion of 0.9% sodium chloride at a rate of 1 ml/h throughout the experiment.
Statistical analysis The results are expressed as mean7standard error of the mean (SEM). The difference between groups are analysed by two way analysis of variance (ANOVA) followed by Dunnet’s test with 5% level of significance (po0.05) on neat values of non-diabetic and STZdiabetic treated groups (vanadyl sulfate and BCOV) with the respective controls.
Results Body weight The body weight of STZ-diabetic rats after 4 weeks significantly decreased as compared to their initial body weight (Table 1). After treatment with vanadyl sulfate (0.2 and 0.5 mmol/kg/day), the body weight of the STZdiabetic group also decreased significantly (po0.05) compared to the initial value. Similarly, the body weight of non-diabetic rats treated with vanadyl sulfate decreased significantly (po0.05), showing signs of vanadium toxicity. Significant (po0.05) increase in body weight was observed in BCOV (0.05, 0.1, 0.2 mmol/kg/day, 4 weeks) treated STZ-diabetic rats as compared to STZ-diabetic controls (Table 1). There was no significant difference in body weight of STZ-diabetic rats treated with BCOV (0.05, 0.1, 0.2 mmol/kg/day, 4 weeks) compared to non-diabetic rats treated with BCOV. Similarly, there was no significant difference in body weight of BCOV treated non-diabetic rats compared to the non-diabetic control group. In the vanadyl sulfate-treated groups (STZ-diabetic and non-diabetic rats), mild (0.2 mmol/kg/day groups) to severe (0.5 mmol/kg/day groups) diarrhea was observed, whereas no signs of diarrhea were observed in any of the groups (STZ-diabetic and non-diabetic rats) treated with BCOV.
Blood glucose level Administration of streptozotocin (45 mg/kg, i.v.) produced a significant increase in blood glucose
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Table 1. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on body weight of STZ-diabetic and non-diabetic rats Treatment
Groups
Body weight (g) Initial
1st week
2nd week
3rd week
4th week
Control
Non-diabetic STZ-diabetic
235710.9 238714.6
239712.3 233716.3
24479.33 228713.4
250711.7 224715.7
254713.4 221712.4*
0.2 mmol VaSO4
Non-diabetic STZ-diabetic
231712.2 234714.7
229711.5 230712.7
225713.4 225716.1
223712.3 220715.6
219710.8* 216716.4*
0.5 mmol VaSO4
Non-diabetic STZ-diabetic
237713.2 233714.1
229716.7 225713.4
222717.2 217716.5
213715.8 211715.6
207716.1* 201714.4*
0.05 mmol BCOV
Non-diabetic STZ-diabetic
228714.1 230716.9
232710.8 232715.8
237712.3 236716.6
242714.1 242717.2
247713.4 245716.1 # *
0.1 mmol BCOV
Non-diabetic STZ-diabetic
231711.7 229714.6
233713.4 230713.2
237716.6 234712.6
241715.6 238714.1
245714.4 242715.7 # *
0.2 mmol BCOV
Non-diabetic STZ-diabetic
227710.8 231712.3
230712.6 234710.8
234715.2 23779.77
237714.1 239711.6
242713.7 241710.6 # *
Values are expressed as mean 7SEM. * po0.05, significantly different from initial body weight. # po0.05, significantly different from STZ-diabetic control group.
Table 2. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on serum parameters of STZ-diabetic and non-diabetic rats Treatment
Groups
Glucose (mmol/l)
Cholesterol (mg/dl)
Triglycerides (mg/dl)
HDL (mg/dl)
LDL (mg/dl)
Control
Non-diabetic STZ-diabetic
4.7970.38 26.471.09
10477.66 220712.1
96.479.65 231714.8
26.675.48 21.674.65
58.272.25 15274.51
0.2 mmol VaSO4
Non-diabetic STZ-diabetic
4.7270.28 25.671.20
10177.86 218714.7
98.278.91 237716.2
22.773.32 24.374.85
53.875.21 147710.3
0.5 mmol VaSO4
Non-diabetic STZ-diabetic
4.1870.45 6.1070.63*
97.779.67 94.477.23*
10177.88 113711.5*
18.174.56 16.178.3
59.373.53 55.773.36*
0.05 mmol BCOV
Non-diabetic STZ-diabetic
4.6770.37 6.9370.43*
96.4711.2 97.476.33*
98.477.24 105711.2*
21.875.44 20.776.54
54.974.35 55.672.45*
0.1 mmol BCOV
Non-diabetic STZ-diabetic
4.3770.47 5.9370.70*
94.378.44 93.377.23*
95.774.47 95.376.87*
20.379.54 19.374.32
54.872.99 54.971.53*
0.2 mmol BCOV
Non-diabetic STZ-diabetic
4.5570.40 4.5170.28*
95.177.66 94.274.33*
94.375.77 94.878.37*
20.877.52 19.874.24
55.471.14 55.471.58*
Values are expressed as mean 7SEM, * po0.05, significantly different from STZ-diabetic control group.
concentrations. Administration of a low dose of vanadyl sulfate (0.2 mmol/kg/day) for 4 weeks produced no significant change in the blood glucose level of STZdiabetic rats, whereas administration of a higher dose of vanadyl sulfate (0.5 mmol/kg/day) for 4 weeks significantly (po0.05) reduced the blood glucose level in STZdiabetic rats (Table 2). There was no significant change in blood glucose concentrations of non-diabetic rats treated with vanadyl sulfate (0.2 or 0.5 mmol/kg/day). Treatment with BCOV (0.05, 0.1 and 0.2 mmol/kg/day) of STZ-diabetic rats produced a significant (po0.05)
dose-dependent decrease in blood glucose level. On the other hand, BCOV (0.05, 0.1, 0.2 mmol/kg/day) had no significant effect on blood glucose concentrations in non-diabetic rats (Table 2).
Serum lipids Administration of streptozotocin (45 mg/kg, i.v.) resulted in a significant (po0.05) increase in serum triglycerides and total cholesterol levels. Administration
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mm Hg
of a low dose of vanadyl sulfate (0.2 mmol/kg/day, 4 weeks) produced no significant change in total cholesterol and triglyceride levels of STZ-diabetic rats (Table 2). A significant (po0.05) decrease in total cholesterol and triglycerides was observed in STZ-diabetic rats treated with 0.5 mmol/kg/day vanadyl sulfate for 4 weeks. Treatment with vanadyl sulfate for 4 weeks at any dose used produced no significant change in total cholesterol and triglyceride levels in non-diabetic rats. BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks of STZ-diabetic rats significantly (po0.05) decreased total cholesterol and triglyceride levels, but had no effect on the lipid profile of non-diabetic rats (Table 2). Administration of vanadyl sulfate or BCOV had no significant effect on HDL levels of STZ-diabetic rats or non-diabetic rats. On the other hand, treatment with vanadyl sulfate and BCOV significantly decreased LDL levels in STZ-diabetic rats, but had no significant effect on LDL levels of non-diabetic rats (Table 2).
140
*
*
*
*
*
110 100 STZcontrol
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 3. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1, and 0.2 mmol/kg/day) treatment on (’) systolic blood pressure and (&) diastolic blood pressure of STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from control.
50
140
*
130 120
Blood pressure and vascular reactivity
#
40
∆ mm Hg
STZ-diabetic rats showed a significant (po0.05) increase in systolic and diastolic blood pressure as compared to non-diabetic rats (Fig. 3). Treatment with vanadyl sulfate (0.2 or 0.5 mmol/kg/day) of STZdiabetic rats had no significant effect on blood pressure. However, administration of BCOV (0.05, 0.1 or 0.2 mmol/kg/day) for 4 weeks produced a significant (po0.05) decrease in systolic and diastolic blood pressure as compared to STZ-diabetic control animals (Fig. 3). Non-diabetic rats treated with BCOV for 4 weeks showed no significant changes in blood pressure (Figs. 2 and 3). Vascular reactivity to noradrenaline (0.1 mmol/kg, i.v.) and acetylcholine (0.1 mmol/kg, i.v.) was significantly (po0.05) increased in STZ-diabetic rats (Figs. 4 and 5). Vanadyl sulfate treatment for 4 weeks had no
215
*
30
* 20
10
0 Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 4. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on vascular reactivity to 0.1 mmol/kg noradrenaline i.v. of (’) non-diabetic and (&) STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from STZ-diabetic control. # po0.05, significantly different from non-diabetic control.
130
mm Hg
120
significant effect on the vascular reactivity to noradrenaline and acetylcholine. On the other hand, BCOV treatment significantly (po0.05) restored vascular reactivity of STZ-diabetic rats to normal. Regarding the non-diabetic rats, administration of neither vanadyl sulfate nor BCOV had an effect on vascular reactivity (Figs. 4 and 5).
110 100 90 80 70 60 Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
Fig. 2. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment on (’) systolic blood pressure and (&) diastolic blood pressure of non-diabetic rats. Values are expressed as mean7SEM.
Discussion and conclusions The study shows that BCOV (at concentrations of 0.05, 0.1 and 0.2 mmol/kg/day) attenuates diabetes more
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Control
VaSO4 0.2mM
VaSO4 0.5mM
BCOV 0.05mM
BCOV 0.1mM
BCOV 0.2mM
0
∆ mm Hg
-10 -20 -30
*
*
*
-40
# -50
Fig. 5. Effect of vanadyl sulfate (0.2 and 0.5 mmol/kg/day) and BCOV (0.05, 0.1 and 0.2 mmol/kg/day) treatment for 4 weeks on vascular reactivity to 0.1 mmol/kg acetylcholine of (’) non-diabetic and (&) STZ-diabetic rats. Values are expressed as mean7SEM. * po0.05, significantly different from STZ-diabetic control. # po0.05, significantly different from non-diabetic control.
efficaciously than vanadyl sulfate (at concentrations of 0.2 and 0.5 mmol/kg/day). Vanadyl sulfate when administered at a concentration of 0.2 mmol/kg/day had no significant effect on blood glucose, total cholesterol and triglyceride levels. Furthermore, it caused body weight loss and diarrhea in STZ-diabetic as well as non-diabetic rats showing signs of toxicity. Vanadyl sulfate at a concentration of 0.5 mmol/kg/day significantly reduced blood glucose, total cholesterol and triglyceride levels but it also caused body weight loss and severe diarrhea in STZ-diabetic and non-diabetic animals. On the other hand, BCOV significantly reduced blood glucose, total cholesterol and triglyceride levels without any adverse effects such as body weight loss or diarrhea. Despite of very low levels of vanadium intake (BCOV: 0.05, 0.1 and 0.2 mmol/kg/day as compared to vanadyl sulfate: 0.2 and 0.5 mmol/kg/day), BCOV ameliorates diabetes more efficaciously without any adverse effects. The effect of vanadyl sulfate and BCOV on high blood pressure associated with diabetes was also studied. Vanadyl sulfate (0.2 and 0.5 mmol/kg/day) treatment did not have any significant effect on blood pressure of STZ-diabetic rats, whereas BCOV (0.05, 0.1 and 0.2 mmol/kg/day) administration significantly reduced blood pressure of STZ-diabetic rats. Increased vascular reactivity to noradrenaline and acetylcholine is one of the major causes of hypertension associated with diabetes in the STZ-model. Vascular reactivity was restored back to normal by BCOV treatment, while vanadyl sulfate treatment had no significant effect on vascular reactivity. Inorganic vanadium is usually poorly (1–10%) absorbed in the gastrointestinal tract [8,20]. The organic ligand is expected to increase the lipophilicity of the vanadium complex and consequently its absorption [19]. Various authors [20–23] tested the normogly-
cemic activity of various vanadium complexes with organic ligands such as bis(maltolato)oxovanadium(IV) (BMOV), oxobis(picolinato)vanadium(IV) (VPA), bis (methylpicolinato)oxovanadium(IV) (VO-MPA), vanadyl bis(cycteine methyl ester) (VCME), oxobis(pyrrolidine-N-carbodithioto)vanadium(IV) (NAGLI-VAN), (N,N0 -disalicylidineethylenedamine)oxovanadium(IV) (VO-SALEN). They were administered at daily doses of 0.1–0.7 mmol/kg/day, in drinking water or by gavage [21–24]. These compounds showed antidiabetic activity but side effects like diarrhea were observed. Our results are in accordance with other studies where diarrhea was observed with vanadyl sulfate treatment [21–24]. Conversely there are also some reports of no incidence of diarrhea with vanadyl sulfate treatment [25]. BCOV showed antidiabetic activity at a much lower dose (0.05 mmol/kg/day). Moreover, diarrhea as a major side effect of vanadium complexes was not at all observed. The glucose lowering effect of vanadium is attributed to its insulinomimetic properties. In several studies, administration of vanadium complexes resulted in an activation of insulin receptor tyrosine kinase (IRTK), autophosphorylation at tyrosine residues and inhibition of phosphotyrosine phosphates [26–28]. The presence of the organic ligand curcumin in the vanadium complex increases the potency and decreases the toxicity of vanadium. The present study shows that BCOV is much safer and efficacious in treatment of diabetes in STZ-diabetic rats and at much lower doses than vanadyl sulfate. Moreover, it also reduces high blood pressure associated with diabetes. Therefore, apart from its use in diabetes therapy, BCOV could also be useful in the treatment of cardiovascular complications associated with diabetes.
Acknowledgement Financial assistance for the first author provided by University Grants Commissions (UGC) Govt. of India is highly acknowledged.
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