Biological Trace Element Research

, Volume 158, Issue 2, pp 219–223

The Protective Effect of Vanadium Against Diabetic Cataracts in Diabetic Rat Model

Authors

  • Lei Sun
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
  • De-Jing Shi
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
  • Xiang-Chun Gao
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
  • Shu-Yong Mi
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
  • Ying Yu
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
    • Department of OphthalmologyThe Fourth Hospital of Harbin Medical University
Article

DOI: 10.1007/s12011-014-9925-7

Cite this article as:
Sun, L., Shi, D., Gao, X. et al. Biol Trace Elem Res (2014) 158: 219. doi:10.1007/s12011-014-9925-7

Abstract

The present study was designed to investigate the effect of vanadium in alloxan-induced diabetes and cataract in rats. Different doses of vanadium was administered once daily for 8 weeks to alloxan-induced diabetic rats. To know the mechanism of action of vanadium, lens malondialdehyde (MDA), protein carbonyl content, activity of superoxide dismutase (SOD), activities of aldose reductase (AR), and sorbitol levels were assayed, respectively. Supplementation of vanadium to alloxan-induced diabetic rats decreased the blood glucose levels due to hyperglycemia, inhibited the AR activity, and delayed cataract progression in a dose-dependent manner. The observed beneficial effects may be attributed to polyol pathway activation but not decreased oxidative stress. Overall, the results of this study demonstrate that vanadium could effectively reduce the alloxan-induced hyperglycemia and diabetic cataracts in rats.

Keywords

VanadiumDiabetesBlood glucoseCataract

Introduction

Diabetes recently has reached almost epidemic levels worldwide. Diabetic cataract is one of the earliest secondary complications of diabetes, and it is characterized by opacification of the eye lens [1]. Approximately 42 % of the world’s blindness can be attributed to diabetic cataracts [2]. Diabetes-associated cataractogenesis is well known to be initiated by osmotic stress caused by the intralenticular accumulation of polyols produced by the polyol pathway [3, 4]. In diabetes, excess glucose enters the sorbitol pathway. The consequences of increased sorbitol pathway activity in the lens include intracellular sorbitol accumulation and resulting osmotic stress [5]. A longer duration of diabetes and a higher level of hemoglobin A1c (HbA1c) have been reported to be significantly associated with a higher prevalence of diabetic cataracts [6, 7].

Very few drugs can directly prevent diabetic complications independent of the glucose levels. To prevent the development of diabetic complications, the different metabolic derangements occurring in diabetes need to be controlled. Many transition elements have been studied and found effective in controlling the altered glucose homeostasis in diabetes [8, 9]. Vanadium, element number 23, atomic weight 50.94, is normally present at very low concentrations (<10−8 M) in virtually all cells in plants and animals. As a potential therapeutic agent, it is attracting increasing attention. Vanadium compounds have the ability to imitate action of insulin [10, 11]. Oral administration of inorganic vanadium (IV, V) salts has shown an antidiabetic activity in patients [12]. Preet [13] have reported that lower doses of vanadium administered in combination with Trigonella was the most effective in controlling the altered glucose metabolism and antioxidant status in diabetic lenses. So, the present study reports the efficacy of vanadium in delaying cataract in diabetic rat model.

Materials and Methods

Chemicals

Alloxan, analytical grade, was purchased from Sigma. Sodium vanadate (analytical grade) was purchased from Beijing Chemical Factory, China. Sodium vanadate (0.45, 0.9, and 1.8 g, respectively) was dissolved in 100 ml of normal saline. An ampule was filled with 0.4 ml of sodium vanadate (SV).

Animals

Wistar rats of either sex weighing 150–200 g were housed in polypropylene cages (six animals per cage) under controlled temperature (27 ± 2 °C) and in a natural light/dark cycle. They were fed with standard laboratory pellets. Food and water were provided ad libitum. The guidance suggestions for care of laboratory animals was followed according to the guidelines for caring for experimental animals published by the Ministry of Science and Technology of the People’s Republic of China. Care was taken to minimize discomfort, distress, and pain to the animals.

Experimental Design

Healthy rats were made diabetic by intraperitoneal injection of alloxan (75 mg/kg). Serum glucose levels were measured 7 days after the injection, and animals showing hyperglycemia (the blood glucose level greater than 300 mg/dl) were selected as diabetic rats. They were randomly divided into various groups and treated orally with 4 ml of saline (alloxan), 0.45SV (0.05 mmol/kg body weight), 0.9SV (0.1 mmol/kg body weight), and 1.8SV (0.2 mmol/kg body weight), respectively. It was prepared each time before treatment. The other six normal rats were injected (iv) with the normal saline and used as the control group.

Measurement of Body Weight, Blood Glucose, and HbA1c

The body weights of the rats were measured on the 0th, 1st, 2nd, 3rd, and 4th weeks. On the 45th day, blood samples were collected from the orbital veins to measure the blood glucose and the HbA1c levels.

Cataract Study

The intensity of cataract was scored once in a week for eight consecutive weeks. The cataract scores of ACO-treated groups were compared with normal group and diabetic control group. The cataract scores were determined using a slit lamp microscope. Progression and maturation of lenticular opacity was graded into five stages: stage 0, clear lenses and no vacuoles present; stage 1, vacuoles cover approximately one half of the surface of the anterior pole forming a subcapsular cataract; stage 2, some vacuoles have disappeared, and the cortex exhibits a hazy opacity; stage 3, a hazy cortex remains, and dense nuclear opacity is present; and stage 4, a mature cataract is observed as a dense opacity in both the cortex and nucleus. Opacity index was calculated to quantitatively evaluate the degree of lens opacity by the following formula:

Opacity index = (Number of eyes in each stage × Stage of the eye) / Total number of eyes.

Molecular Basis for the Delay of Cataract

At the end of 8 weeks, animals were sacrificed by CO2 asphyxiation, and lenses were dissected by posterior approach and stored at −70 °C until further analysis. Lens malondialdehyde (MDA), as thiobarbituric acid-reacting substances (TBARSs); protein carbonyl content; and activities of aldose reductase (AR) and sorbitol levels were determined according to the methods described previously [14]. The specific activity of superoxide dismutase (SOD) was assayed according to the reported methods [14].

Data Analysis

All data were analyzed by one-way analysis of variance, and the differences between means were established by Duncan’s multiple-range test. The data represents means and standard deviations. The significant level of 5 % (p < 0.05) was used as the minimum acceptable probability for the difference between the means.

Results and Discussion

Experimentally, alloxan cause a chronic diabetic condition that is characterized by high levels of blood glucose and insufficient levels of insulin. Prolonged exposure to chronic hyperglycemia can lead to the complication of diabetic cataracts [15]. Alloxan-induced diabetic cataracts represent a dramatic accumulation of sorbitol in the lens, which results in the quick development of lens opacification [16]. These models have been extensively used effectively to induce the diabetic complication of cataracts in various experimental animals to evaluate the therapeutic potential of drugs [17].

Hyperglycemia and body weight loss are commonly used as markers of alloxan-induced diabetes in experimental animals. The present study measured body weight, blood glucose, and HbA1c levels over the 4 weeks of experimentation, and the results are shown in Fig. 1 and Tables 1 and 2.
https://static-content.springer.com/image/art%3A10.1007%2Fs12011-014-9925-7/MediaObjects/12011_2014_9925_Fig1_HTML.gif
Fig. 1

Effect of vanadium on body weight. Values are shown as means ± SEM. *p < 0.05 vs. alloxan group

Table 1

Effect of vanadium on blood glucose levels in alloxan-hyperglycemic rats

Different groups

Blood glucose (mmol/l)

Alloxan-treated

21.0 ± 2.0

0.45SV-treated

18.9 ± 2.0

0.9SV-treated

19.4 ± 3.0*

1.8SV-treated

10.5 ± 2.0**

Control group

5.5 ± 1.5

Values are shown as means ± SEM

*p < 0.05 vs. alloxan group; **p < 0.01 vs. alloxan group

Table 2

Effect of vanadium on HbA1c levels in alloxan-induced hyperglycemic rats

Different groups

Results of HbA1c

Alloxan-treated

10.8 ± 0.20

0.45SV-treated

9.7 ± 0.30

0.9SV-treated

10.0 ± 0.26*

1.8SV-treated

7.8 ± 0.28*

Control group

4.6 ± 0.20

Values are shown as means ± SEM

*p < 0.05 vs. alloxan group

Body weights of the diabetic group (p < 0.01) were significantly lowered at the end of the study. Vanadate (1.8SV) treatment was found to cause an increment in body weight gain (Fig. 1). The results of blood glucose from hyperglycemic rats induced by alloxan are presented in Table 1. The levels of blood glucose decreased after an administration of 1.8SV and 0.9SV (p < 0.01 and p < 0.05, respectively). It is consistent with the findings of other studies by Gil [10] and Shechter [11]. The HbA1c which can be taken as a marker for the glycosylation of proteins was found to be significantly increased (p < 0.01) in diabetic rats. The different treatments (1.8SV and 0.9SV) given to the diabetic animals prevented the glycosylation of hemoglobin (Table 2).

Hyperglycemia plays a key role in the diabetes-associated changes in lens metabolism and cataract formation, and alloxan-induced hyperglycemia leads to a further enhancement of the degree of hyperopia [16]. Vanadium is known to control the diabetes-induced hyperglycemia [10]. Here, we first tested the effect of vanadium on the cataract progression in alloxan-induced diabetic rats. It was found that vanadium could effectively prevent cataract progression (Fig. 2). All lenses in control groups were clear throughout the experimental period. The cataract occurrence first appeared at the 4th week after injections of alloxan to rats. The onset of cataractogenesis started to decrease on the 7th and 8th weeks, respectively, in the case of vanadium (1.8SV and 0.9SV, respectively) (Fig. 3). This is evident by a decrease in opacity index from 3.6 to 1.5 and 2.7 on the 8th week (Fig. 4). These studies suggest that vanadium protects the lens against the development of sugar cataracts induced by hyperglycemia
https://static-content.springer.com/image/art%3A10.1007%2Fs12011-014-9925-7/MediaObjects/12011_2014_9925_Fig2_HTML.gif
Fig. 2

Representative photographs showing the effect of vanadium in the prevention of cataract. a Control rat, b alloxan-treated rat, c 1.8SV-treated rat

https://static-content.springer.com/image/art%3A10.1007%2Fs12011-014-9925-7/MediaObjects/12011_2014_9925_Fig3_HTML.gif
Fig. 3

Effect of 8 weeks of treatment with vanadium on incidence of cataract in alloxan-induced diabetic rats. Values are shown as means ± SEM. *p < 0.05 vs. alloxan group; **p < 0.01 vs. alloxan group

https://static-content.springer.com/image/art%3A10.1007%2Fs12011-014-9925-7/MediaObjects/12011_2014_9925_Fig4_HTML.gif
Fig. 4

Effect of 8 weeks of treatment with vanadium on opacity index in alloxan-induced diabetic rats. Values are shown as means ± SEM. *p < 0.05 vs. alloxan group

It is well known that oxidative stress plays a major role in the etiology of diabetic cataract. In the lens, oxidative stress can cause direct modifications of the inner lens proteins, leading to their cross-linking, aggregation, and precipitation. Several lines of evidence have demonstrated that an antioxidant treatment can delay the progression of cataracts in diabetic rats [18]. As shown in Table 3, the rise in MDA levels and protein carbonyl content in diabetic group compared to control group indicates increased lipid peroxidation and enhanced protein oxidation in the lens. Furthermore, altered activity of antioxidant enzyme SOD (Table 3) suggests an increased oxidative stress in diabetic cataract lens. However, both the 1.8SV and 0.9SV prevented the alterations in MDA, protein carbonyls, and SOD, considered to be statistically insignificant. It suggested that the beneficial effects of vanadium on the cataracts induced by hyperglycemia were not directly through alleviated oxidative stress.
Table 3

Effect of vanadium on MDA, protein carbonyls, and SOD in rat lens

Different groups

MDA

Protein carbonyls

SOD

Alloxan-treated

9.00 ± 2.37

7.09 ± 1.76

62.10 ± 4.30

0.45SV-treated

8.49 ± 1.46

6.68 ± 1.76

60.00 ± 0.77

0.9SV-treated

8.10 ± 0.66

6.22 ± 1.33

59.00 ± 0.33

1.8SV-treated

7.50 ± 2.13

6.00 ± 1.66

55.01 ± 0.55

Control group

6.50 ± 2.10

5.88 ± 1.61

53.00 ± 0.55

Values are shown as means ± SEM. MDA levels are expressed in nanomoles per gram lens, protein carbonyls in nanomoles per milligram protein, and SOD activity in units per minute per 100 mg protein

The AR is the key enzyme in the polyol pathway. The activation of AR severely modifies the process of osmoregulation, ultimately leading to cataract formation [19]. The AR activity of the diabetic group was significantly increased compared with that in the control group (p < 0.01). At the same time, the increase in sorbitol, a product of AR-catalyzed reaction, was remarkably high. Vanadium treatment to the diabetic animals caused an insignificant decline in AR activity. Lens sorbitol concentrations of diabetic rats were increased obviously compared with those of normal rats. Treatment with vanadium decreased such increase in a dose-dependent manner significantly, as shown in Table 4.
Table 4

Effect of vanadium on aldose reductase (AR) activity and sorbitol levels in rat lens

Different groups

AR

Sorbitol

Alloxan-treated

57.82 ± 2.20

2.811 ± 0.20

0.45SV-treated

56.74 ± 5.30

2.223 ± 0.16

0.9SV-treated

54.0 ± 6.26

2.108 ± 0.16

1.8SV-treated

50.80 ± 2.28*

1.463 ± 0.14*

Control group

43.66 ± 5.20**

0.612 ± 0.20**

Values are shown as means ± SEM. AR activity is expressed in micromoles of NADPH oxidized per hour per 100 mg protein and sorbitol levels in micromoles per gram lens

*p < 0.05 vs. alloxan group; **p < 0.01 vs. alloxan group

Conclusions

Our findings show that vanadium prevented the progression of existing cataracts. Although the cataracts did not disappear during the treatment period, agents that can prevent the progression of existing cataracts are useful for the treatment of this complication. The observed beneficial effects may be attributed to polyol pathway activation but not decreased oxidative stress. Overall, the results of this study demonstrate that vanadium could effectively reduce the alloxan-induced hyperglycemia and diabetic cataracts in rats.

Copyright information

© Springer Science+Business Media New York 2014