Neurochem Res (2013) 38:1572–1579 DOI 10.1007/s11064-013-1058-4
ORIGINAL PAPER
Telmisartan Ameliorates Neurotrophic Support and Oxidative Stress in the Retina of Streptozotocin-Induced Diabetic Rats M. Shamsul Ola • Mohammed M. Ahmed • Hatem M. Abuohashish • Salim S. Al-Rejaie Abdullah S. Alhomida
•
Received: 3 March 2013 / Revised: 17 April 2013 / Accepted: 19 April 2013 / Published online: 27 April 2013 Ó Springer Science+Business Media New York 2013
Abstract Neurodegeneration is an early event in the diabetic retina which may lead to diabetic retinopathy. One of the potential pathways in damaging retinal neurons is the activation of renin angiotensin system including angiotensin II type 1 receptor (AT1R) in the diabetic retina. The purpose of this study was to determine the effect of telmisartan, an AT1R blocker on retinal level of brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and tyrosine hydroxylase (TH), glutathione (GSH) and caspase activity in the diabetic rats. The dysregulated levels of these factors are known to cause neurodegeneration in diabetic retina. Three weeks streptozotocin induced diabetic rats were orally treated or untreated with telmisartan (10 mg/kg/day). After 4 weeks of treatments, the levels of BDNF and GSH were found to be increased systemically in the sera as well as in the retina of diabetic rats compared to untreated rats as measured by enzymelinked immunosorbent assay and biochemical techniques (p \ 0.05). The caspase-3 activity in the telmisartan treated diabetic retina was decreased compared to untreated diabetic rats (p \ 0.05). Western blotting experiments showed the expression levels of BDNF, CNTF and TH were increased compared to untreated diabetic rats (p \ 0.05). Thus, our findings show a beneficial effect of AT1R blocker telmisartan in efficiently increasing neurotrophic support, endogenous antioxidant GSH content, and decreasing signs of apoptosis in diabetic retina. M. S. Ola (&) A. S. Alhomida Department of Biochemistry, College of Science, King Saud University, Riyadh 11415, Saudi Arabia e-mail:
[email protected];
[email protected] M. M. Ahmed H. M. Abuohashish S. S. Al-Rejaie Department of Pharmacology and Toxicology, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia
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Keywords Diabetic retinopathy Telmisartan Neurodegeneration Brain derived neurotrophic factor Retina Apoptosis
Introduction Hypertension has been widely recognized as a potential risk factor for the damage of vasculature in several diabetic induced complications including retinopathy and nephropathy [1–4]. In diabetes, the components of renin angiotensin system (RAS) were found to be increased both systemically and locally in several tissues causing hypertension and the tissue damage. Recent studies in rodent’s model have revealed that components of RAS comprising of renin, prorenin, angiotensin II and its receptors are expressed in the retina and diabetes caused an increase in their expression [5, 6]. In addition, increased levels of the components of RAS were also observed in the vitreous of patients with proliferative diabetic retinopathy (PDR) and macular edema [7, 8]. Several evidences support the pathological role of RAS components in the development and progression of diabetic retinopathy (DR) by exacerbating vascular pathology in the retina such as leakage, angiogenesis and inflammation [1, 5, 6, 9–11]. However, little is known about the role of RAS in the neuronal component of the retinas. Since early in the DR progression, neuronal components of the retina have been found to be compromised and retinal function deficit observed before any clinical signs of vascular damage appears [12, 13]. Few recent studies demonstrated the influence of RAS especially angiotensin II and its receptors on the neuronal cells in both animal models of glaucoma and diabetes [14, 15]. In the neural retina, ganglion cells and Muller cells have been found to express angiotensin II, angiotensin II
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type 1 receptor (AT1R) and AT2R [16–18]. AT1R is expressed in synaptic vesicles in the inner retina which is critical for the neurotransmission [16]. A number of studies suggest that diabetes induced activation of RAS plays a significant role in the pathogenesis of retinal neurodegeneration, since angiotensin II activates NADPH oxidase via AT1R stimulation and produces reactive oxygen species, subsequently inducing retinal ganglion cell impairment and death in the diabetic retina [19–23]. An elegant study by Kurihara et al. [14] showed that the increased level of AT1R in diabetic retina resulted in impaired neuronal function and the AT1R blocker telmisartan suppressed the impaired inner retinal function. In animal model of glaucoma, AT1R blocker treatment resulted in neuroprotection against retinal ganglion cell loss [15]. In this study, we utilized telmisartan since the drug has strongest affinity (more than 3,000 times) for AT1R than AT2R with less adverse effect and better tolerability in rodents and humans [24–26]. In addition, recent studies suggested beneficial effect of telmisartan in several brain diseases including suppression of impaired retinal function in diabetes [14, 27, 28]. Retina being a neuronal tissue expresses neurotrophic factors which play an important role in the cell survival. Reduced level of neurotrophins, especially brain derived neurotrophic factor (BDNF) in diabetic retina has been reported by us and others [29–31]. The reduced level of BDNF has also been shown to cause oxidative stress and neurodegeneration in diabetes [32, 33]. However, the specific role of activated RAS on the regulation and expression of neurotrophic factor including BDNF in diabetes is not well understood. BDNF may play an active role in oxidative stress induced neurogenic hypertension by participation in the maintenance of oxidative stress [27]. The precise role of telmisartan in protecting neurons via up-regulation of BDNF and/or by ameliorating oxidative stress in the diabetic retina has not been determined. It is critical to protect neurons in early diabetes, so that the functional deficit as well as neurovascular complications in the diabetic retina can be ameliorated. In this study, we have analyzed the effects of telmisartan on the levels of BDNF and glutathione (GSH) both systemically and locally in the retina. Previously, studies showed that induction of CNTF protected neurodegeneration in the retina [34], and AT1R antagonists reduced the degeneration of dopaminergic neurons [35, 36]. Therefore, we have also quantitated the expression level of ciliary neurotrophic factor (CNTF); another important neurotrophin and tyrosine hydroxylase (TH); a marker of dopaminergic neurons in the retina of telmisartan treated and untreated diabetic rats. We also measured caspase-3 activity as a marker of apoptosis in the retina of telmisartan treated and untreated diabetic rats.
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Methods Streptozotocin-Induced Diabetic Rats and Telmisartan Treatments Male Wistar rats, 9–10 weeks of age (250–280 g), fasted overnight and then single dose of streptozotocin (55 mg/kg in 100 mM sodium citrate buffer, pH 4.5; Sigma, St. Louis, MO) was administered intraperitoneally. Age matched non-diabetic animals were injected with an equal volume of citrate buffer. Diabetes was confirmed by assaying glucose concentration in blood from tail vein and glucose levels [300 mg/dl were classified as diabetic. Both nondiabetic (control) and 3 weeks diabetic rats were divided into two groups. During 4th week, one group of both control and diabetic were treated with telmisartan drug (10 mg/kg/day) by oral gavage for 4 weeks. Each group consists of six rats: Group 1 (Non-diabetic, control); Group 2 (Control plus telmisartan); Group 3 (diabetic, no drug); Group 4 (diabetic plus telmisartan). Telmisartan (Micardis) tablets (a gift from Boehringer-Ingelheim Company, Germany) were crushed and suspended into 0.5 % carboxymethyl cellulose (CMC) weight per volume and freshly prepared drug suspension was administered to rats (Group 2 and Group 4) daily at the same time. Similarly, the drug untreated rats (Group 1 and Group 3) were administered same dose of 0.5 % CMC by oral gavage. At the end of fourth week of treatments, rats were fasted overnight (12 h) and blood glucose and weight were measured. Rats were anesthetized and retinas dissected. The retinas were washed immediately in excess of ice-cold phosphate buffer saline to remove any blood/serum from the retina. Retinas were transferred into Eppendorf tubes, flash frozen in liquid nitrogen and stored at -70 °C until assay. After removing the retinas, the blood samples from each rat were collected from the heart in clean tubes. Blood samples were kept on ice for 30 min, centrifuged, serum collected and stored at -70 °C until assay. All procedures with animals were performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and were approved by the Institutional Animal Care and Use Committee.
Estimation of Serum Glucose Glucose concentrations were measured in the serum collected from telmisartan treated and untreated control and diabetic rats. Glucose levels were measured by using commercially available diagnostic kit (Human, Wiesbaden, Germany) as per the manufacturer’s instruction.
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BDNF Quantification in Serum and Retina by EnzymeLinked Immunosorbent Assay (ELISA) Brain derived neurotrophic factor level was measured in both retina and serum using ELISA kits (Quantikine Human Brain-Derived Neurotrophic Factor, R&D Systems, Minneapolis, MN, USA) according to manufacturer’s instruction. Retinal homogenate was prepared by applying short burst of ultrasonication in the 10 mM HEPES buffer (pH 7.4), containing 100 mM NaCl, 1 % triton X-100, 0.2 % SDS and a protease inhibitor cocktail. Retinal lysates were centrifuged at 15,000g for 10 min and supernatants were collected for BDNF quantification. Both serum and retina samples were diluted in calibrator diluents supplied with the kit. Fivefold diluted serum and twofold diluted retinal homogenate (150 ll/retina) were used for quantitative determination of BDNF in 96-well ELISA plates. Each assay was performed in duplicate. Using the 4-parameter fit logistic (4-PL) curve equation, the actual concentration of BDNF in each sample was calculated. The detection limit of BDNF ELISA kit was 20 picograms/mL (pg/mL). The ELISA plate readings were done using Auto Bio Labtech Instruments, Co, Ltd, China. The protein concentrations in each sample were estimated using Bio Rad protein assay kits. GSH Assay in the Serum and Retina The total GSH levels were measured in serum and retina of telmisartan treated and untreated diabetic and non-diabetic rats using Cayman’s GSH assay kit (Cayman Chemical Company, MI, USA). Retinal homogenate was prepared as described above. Both retinal homogenate and serum samples were deproteinized by adding an equal volume of metaphosphoric acid (2.5 % w/v). After 5 min, the mixture was centrifuged at 10,000 rpm and supernatant collected. In the supernatant, 5 ll of 4 M triethanolamine per 100 ll was added and assay performed using 50 and 100 ll supernatant from retina and serum, respectively. A standard curve of GSH was prepared from 0 to 10 lM, and unknown concentration of GSH in the samples was calculated by using linear regression program. Western Blotting To determine the BDNF protein levels in the retinas of telmisartan treated and untreated non-diabetic and diabetic rats, the retinal tissues were lysed by ultrasonication in the 10 mM HEPES buffer, pH 7.4, containing 100 mM NaCl, 1 mM Na3VO4, 10 mM sodium pyrophosphate, 10 mM NaF, 2 mM EDTA, 1 mM PMSF, 1 % triton X-100, 0.2 % SDS and a protease inhibitor cocktail. Samples were centrifuged at 15,000g for 10 min and supernatants collected
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and the protein concentrations estimated using the Bio-Rad protein assay kit. Protein samples were boiled in Laemmli’s sample buffer for 5 min and 50 lg of proteins were separated on 10 % SDS–polyacrylamide gels and transferred onto nitrocellulose membranes. After transferring the proteins, the membranes were blocked for 90 min at room temperature with 5 % non-fat milk made in Trisbuffered saline containing 0.1 % Tween-20 (TBS-T). The membranes were incubated overnight with mouse monoclonal anti-BDNF (1 lg/ml), anti-CNTF (1 lg/ml) and anti-TH (0.5 lg/ml primary antibodies (R&D System, Minneapolis, MN, USA). After overnight incubation with primary antibodies, membranes were washed three times with TBS-T (5 min each) and then incubated with their respective secondary horseradish peroxidase-conjugated antibodies (1:2,000, Santa Cruz Biotechnology, Inc., Santa Cruz, CA) at room temperature for 90 min. Membranes were then washed four times with TBS-T, 5 min each and the immunoreactivity of bands were visualized on a ProXima C16 Phi? Imaging System, Lab Mark, Czech Republic, using enhanced chemiluminescence (Western blotting luminol reagents (1:1), Santa Cruz Biotechnology, Inc., Santa Cruz, CA). Protein bands were quantified by densitometry analysis using Image-Lab 2.0.1 software (Biorad Laboratories Inc). For internal control, membranes were washed and incubated with a mouse monoclonal b-actin antibody (1:2,000, Santa Cruz Biotechnology, Inc., Santa Cruz, CA), and all the steps were followed as described above. Caspase Assay The increased enzymatic activity of the caspase-3 class of proteases in retinal tissue was measured by a caspase-3 colorimetric assay kit (R&D Systems, Minneapolis, MN, USA) as per manufacturer’s instructions. Briefly, the enzymatic reaction for caspase activity was carried out by the addition of 50 ll of rat retinal homogenate from a total of 150 ll/retina in a 96 well flat bottom microplate. The cleavage of Caspase-3 colorimetric substrate (DEVD-pNA) by the caspase, releases the chromophore pNA, which was quantitated spectrophotometrically at a wavelength of 405 nm using microplate reader (Auto Bio Labtech Instruments, Co, Ltd, China). The results were expressed as fold increase in caspase activity as represented by an increase in optical density in diabetic retina over control retina. Statistical Analysis The Mann–Whitney test was used to compare means from two independent groups in the case of drug treated and untreated control and diabetic rats. Statistical Package for
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the Social Sciences Version 12 (SPSS 12.0) was used for the statistical analyses. p value \0.05 was considered as significant.
Results Effect of Telmisartan on Serum Glucose in the Control and Diabetic Rats In both telmisartant treated and untreated diabetic rats, the fasting serum glucose level was several folds higher than that of non-diabetic control groups (Fig. 1). Telmisartan treatments to diabetic rats for 4 weeks could not affect the fasting serum glucose levels compared to drug untreated diabetic rats (Fig. 1). Also, there was no significant difference in the serum glucose level between untreated and drug treated control groups. Effects of Telmisartan on Retinal and Serum BDNF Levels
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p \ 0.05). Telmisartan treatment significantly increased the level of BDNF in the serum of diabetic rats (1.36 ± 0.14 to 1.82 ± 0.25 ng/ml serum, p \ 0.05) as compared to drug untreated diabetic rats (Fig. 2a). Similarly, in the retina of diabetic rat, the level of BDNF was significantly lower (16.36 ± 2.0 vs. 24.34 ± 2.8 pg/mg protein) as compared to corresponding control. Drug treatments significantly increased the level of BDNF in the retina of diabetic rats compared to untreated diabetic rats (16.36 ± 2.0 to 22.2 ± 2.5 pg/mg protein, p \ 0.05) (Fig. 2b). However, the drug administration in non-diabetic rats could not affect the level of BDNF both in the serum and retina from the corresponding controls. Effect of Telmisartan on BDNF, CNTF and TH Protein Expression Level in Diabetic Rat Retinas Brain derived neurotrophic factor, CNTF and TH protein expression level were quantified in retinas of non-diabetic control, diabetic and telmisartan treated diabetic rats by
The level of BDNF in the serum and retinal homogenate of telmisartan treated and untreated was measured in both non-diabetic and diabetic rats by the ELISA. No significant difference in serum BDNF level was found between telmisartan treated or untreated non-diabetic control groups. The level of BDNF in the serum of diabetic rats was significantly lower as compared to corresponding non-diabetic control group (1.36 ± 0.14 vs. 2.29 ± 0.30 ng/ml),
Fig. 1 Effects of telmisartan on serum glucose levels in control and diabetic rats. 3 weeks diabetic and their age matched control rats were treated with telmisartan drug (10 mg/kg/day) for 4 weeks. Serum glucose level in diabetic rats was almost fivefolds higher than control (*p \ 0.001). Telmisartan treatment did not influence the glucose level both control (C, open bars) as well as in diabetic rats (D, black bars). Data are expressed as mean ± SE for six determinations. *,#p \ 0.001 compared to both control and control treated with the drug
Fig. 2 BDNF concentration in the serum and retina of telmisartan treated or untreated control and diabetic rats. Serum BDNF (a) and retinal BDNF levels (b) were measured by ELISA kit. C (open bar) represents control and D (black bar) as diabetic. Reduced levels of BDNF in diabetic groups were compared to the level from nondiabetic controls and diabetic treated with telmisartan. Values are mean ± SE for six determinations, *,#p \ 0.001 compared to control and diabetic respectively
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Western blotting techniques (Fig. 3). Densitometric analysis of the protein bands showed that a significant reduction in the expression level of retinal BDNF in diabetic rats as compared to controls (Fig. 3). However, the drug treatment significantly increased the level of BDNF in the diabetic rat retina compared to the untreated diabetic rats. Similarly, the level of CNTF significantly decreased in diabetic retina as compared to the control rats, but the drug treatment increased the CNTF level in diabetic rats almost to the control level. TH level in diabetic retinas was also significantly lower compared to the non-diabetic animals. In drug treated diabetic rats, the level of TH significantly increased as compared to the diabetic rats. Effect of Telmisartan on GSH Level in Serum and Retina of Diabetic Rats The GSH level was measured both in serum and in the retinal tissues of control, diabetic and telmisartan treated diabetic rats. The level of GSH in the serum and retinal tissue were significantly diminished in diabetic rats as compared to the corresponding control rats (p \ 0.05). However, telmisartan treatments to the diabetic rats led to a marked increase in GSH concentration both in the serum and retina compared to diabetic rats (p \ 0.05) (Fig. 4). Capase-3 Activity We measured the caspase-3 activity in the retina of drug treated and untreated control and diabetic rats. Administration of telmisartan in control rats had no effect on
Fig. 3 Western blot analysis of retinas from control, diabetic and diabetic treated rats with telmisartan. Western blot analysis was performed using antibodies against BDNF, CNTF and TH followed by antibody against b-actin. The intensities of the bands were quantified by densitometry. a Representative immunoblots of BDNF, CNTF, TH and b-actin bands. b Data presented as ratios of those proteins bands to b-actin. Values are mean ± SE for six determinations. *,#p \ 0.05, significantly different from their controls (c) and diabetic rats (d) respectively. BDNF brain derived neurotrophic facor, CNTF ciliary neurotrophic factor, TH tyrosine hydroxylase
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caspase-3 level in the retina as compared to corresponding untreated control. Capsase-3 activity in the diabetic rat retinas was increased to almost twofold in the retina of diabetic rats as compared to the control groups (Fig. 5). However, telmisartan treatment to diabetic rats significantly decreased the caspase-3 activity in the retina nearly to the control level (p \ 0.05).
Discussion A number of studies suggested the beneficial effects of RAS receptors blockers in diabetic retinopathy by improving the hemodynamics and the vascular function, but might also be involved in neuroprotection. In diabetic retina, RAS has been found to be activated and play a pivotal role in damaging retinal neurons, a widely recognized early feature of diabetic retinopathy [14, 21, 23, 37, 38]. The purpose of this study was to uncover the three unknown aspects of telmisartan role in the diabetic retina; (1) the potential effect of telmisartan drug on the neurotrophic factors, (2) the effect of the drug on GSH level both systemically and locally in the retina of diabetic rats, and (3) the effect of the drug on caspase activity in diabetic rats retina. Our findings clearly suggest that telmisartan treatment to the diabetic rats could be beneficial as the drug increases levels of neurotrophic factors, decreases the caspase-3 activity and increases the GSH level in the diabetic retina. The effects of AT1R blockers including telmisartan are well studied in combating inflammation and oxidative
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Fig. 5 Effect of telmisartan on caspase-3 activity in diabetic rat retinas. The enzymatic activity of the caspase-3 in retinal tissue of control, diabetic and diabetic treated rats with telmisartan was measured by caspase-3 colorimetric assay. The results are expressed as fold increase in caspase activity as represented by an increase in optical density. The diabetic retina had significantly higher caspase activity compared to that of normal age matched controls (*p \ 0.01). Telmisartan treatments to diabetic rats reduced the increased caspase activity significantly (#p \ 0.01). Values are mean ± SE for seven determinations (*,#p \ 0.01)
Fig. 4 Effect of telmisartan on the levels of total glutathione in control and diabetic rats. Retina GSH (a) and serum GSH levels (b) were measured. C (open bar) represents control and D (black bar) as diabetic. Reduced levels of GSH in diabetic groups were compared to the level from non-diabetic controls and diabetic treated with telmisartan. The level of GSH was significantly decreased in diabetic retina and serum compared to control rats. Telmisartan treatments to diabetic rats increased GSH level significantly both in the retina (a) and serum (b) compared to untreated diabetic retina and serum respectively. Values are mean ± SE for six determinations (*,#p \ 0.05)
stress in the retinal microvasculature [2, 6, 20, 39–42]. However, the beneficial effect of AT1R blocker in diabetic induced retinal neurodegeneration and the cross talk between RAS and neurotophic factor is not well characterized. Among neurotrophins, BDNF is considered to be neuroprotective under metabolic stress conditions such as in diabetes [32, 33]. More recently, we have reported a decreased level of BDNF in the serum of diabetic patients and also in the diabetic rat retina [31]. However, to our knowledge, there is no report about the influence of RAS on the expression of neurotrophic factor(s), especially on the level of BDNF in the diabetic retina. Few studies in brain demonstrated the regulation of BDNF by hypertension in the ischemic hippocampus [32] and in the hippocampus of hypertensive rats [28]. We observed an increase in the level of BDNF both in the serum and retina of the telmisartan treated diabetic rats as compared to the drug
untreated diabetic rats. These results are in agreement with a previous study in which candesartan (a RAS receptor blocker), increased the level of BDNF and protected neurodegeneration in brain ischemia [43]. Our findings are also concomitant with another study where telmisartan treatment upregulated the level of BDNF in the hippocampus of hypertensive rats and thereby protected cognitive function [28]. Furthermore, we found that the level of CNTF was significantly increased in the retina after the drug administration in diabetic rats as compared to untreated diabetic rats. Thus, the telmisartan drug might protect the retinal neurons in diabetes by inducing the level of BDNF and CNTF as reported by others in which they demonstrated that both CNTF and BDNF protect the neurons in neurodegenerative retina [29, 34]. In addition, the expression level of TH in diabetic retina was found to be decreased similar to previous studies [29, 44]. TH protein level reflects the function of dopaminergic amacrine cells in the retina. We also demonstrated in this study that telmisartan ameliorated the TH level in diabetic retina. Our finding is in accordance with previous reports which suggest that AT1R blocker might play a protective role by increasing the expression of TH level in the diabetic retina [35, 36]. Overall, our results clearly indicate the beneficial effect of telmisartan in improving the protein expression level of BDNF, CNTF and TH in the diabetic retina. However, the mechanism of telmisartan induced regulation of BDNF needs to be investigated. Numerous studies suggest that in diabetic rats, the AT1R was upregulated by an increase in angiotensin II level
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which subsequently activated the NADPH oxidase via an increase in ROS production, thereby induce the neurodegeneration in diabetic retina [19–23]. The increased oxidative stress especially locally in the diabetic retina that has neurodegenerative influence is prevented by telmisartan treatments. Our findings are well supported by a recent report showing anti-oxidant effects of telmisartan in the brain [28]. However, the relationship between BDNF and oxidative stress is elusive. It has been suggested that moderate level of oxidative stress stimulates BDNF expression and high levels of oxidative stress inhibits secretion of BDNF in cells [27]. In diabetic retina, telmisartan might reduce the level of oxidative stress which in turn may induce the expression of BDNF as supported by a study by Sasaki et al. [30] showing lowering oxidative stress causes an increase in BDNF. But, the mechanistic link between the regulation of oxidative stress and BDNF in the drug treated diabetic retina requires further studies. Caspases are apoptotic markers, known to be activated early in diabetic retina, which has been considered as the major factor in neurodegeneration. Early in diabetes, retinal neuronal cells death occurs by apoptosis before any signs of vascular damage and increased caspase-3 activity has been known to cause apoptosis [12, 13]. Recently, Miao et al. [38] have demonstrated an up-regulation in AT1R expression level and the activation in caspase-3 level in the retina after chronic alcohol consumption. Consistent with previous studies capsase activity was high in diabetic retina however; telmisartan treatment efficiently decreased the caspase-3 activity in the diabetic retina indicating a protection of neuronal damage. Taken together, these data support the beneficial effect of telmisartan both systemically and also locally in the diabetic retina. The drug efficiently blocks the diabetes induced activation of AT1R thereby may inactivate NADPH oxidase which in turn reduces oxidative stress. The ameliorated level of oxidative stress by the drug in the diabetic retina may induce an increase in the level of BDNF and other neurotrophic factors. Thus, we speculate that the drug induced amelioration of oxidative stress and an increase in neurotrophic support in the retina may cause a decrease in diabetes induced apoptosis. Therefore, in addition to the therapeutic implication of the telmisartan in hypertension, it has also potential neuroprotective effect locally in the retina by decreasing oxidative stress and increasing neurotrophic support in order to protect neuronal damage in diabetes. Acknowledgments The authors acknowledge funding from the Deanship of Scientific Research (RGP-VPP-052) at King Saud University. Conflict of interest
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The authors declare no conflict of interest.
References 1. Matthews DR, Stratton IM, Aldington SJ, Holman RR, Kohner EM (2004) Risks of progression of retinopathy and vision loss related to tight blood pressure control in type 2 diabetes mellitus: UKPDS 69. Arch Ophthalmol 122:1631–1640 2. Clermont A, Bursell SE, Feener EP (2006) Role of the angiotensin II type 1 receptor in the pathogenesis of diabetic retinopathy: effects of blood pressure control and beyond. J Hypertens Suppl 24:S73–S80 3. Sjølie AK (2007) Prospects for angiotensin receptor blockers in diabetic retinopathy. Diabetes Res Clin Pract 1:S31–S39 4. Gurley SB, Coffman TM (2007) The renin-angiotensin system and diabetic nephropathy. Semin Nephrol 27:144–152 5. Satofuka S, Ichihara A, Nagai N, Noda K, Ozawa Y, Fukamizu A, Tsubota K, Itoh H, Oike Y, Ishida S (2009) (Pro)renin receptor-mediated signal transduction and tissue renin-angiotensin system contribute to diabetes-induced retinal inflammation. Diabetes 58:1625–1633 6. Nagai N, Izumi-Nagai K, Oike Y, Koto T, Satofuka S, Ozawa Y, Yamashiro K, Inoue M, Tsubota K, Umezawa K, Ishida S (2007) Suppression of diabetes-induced retinal inflammation by blocking the angiotensin II type 1 receptor or its downstream nuclear factorkappaB pathway. Invest Ophthalmol Vis Sci 48:4342–4350 7. Danser AH, van-den-Dorpel MA, Deinum J, Derkx FH, Franken AA, Peperkamp E, de-Jong PT, Schalekamp MA (1989) Renin, prorenin, and immunoreactive renin in vitreous fluid from eyes with and without diabetic retinopathy. J Clin Endocrinol Metab 68:160–167 8. Funatsu H, Yamashita H, Nakanishi Y, Hori S (2002) Angiotensin II and vascular endothelial growth factor in the vitreous fluid of patients with proliferative diabetic retinopathy. Br J Ophthalmol 86:311–315 9. Chaturvedi N, Porta M, Klein R, Orchard T, Fuller J, Parving HH, Bilous R, Sjølie AK (2008) DIRECT programme study group: effect of candesartan on prevention (DIRECT-Prevent 1) and progression (DIRECT-Protect 1) of retinopathy in type 1 diabetes: randomised, placebo-controlled trials. Lancet 372:1394–1402 10. Mauer M, Zinman B, Gardiner R, Suissa S, Sinaiko A, Strand T, Drummond K, Donnelly S, Goodyer P, Gubler MC, Klein R (2009) Renal and retinal effects of enalapril and losartan in type 1 diabetes. N Engl J Med 361:40–51 11. Ola MS, Nawaz MI, Siddiquei MM, Al-Amro S, Abu El-Asrar AM (2012) Recent advances in understanding the biochemical and molecular mechanism of diabetic retinopathy. J Diabetes Complications 26:56–64 12. Barber AJ, Lieth E, Khin SA, Antonetti DA, Buchanan AG, Gardner TW (1998) Neural apoptosis in the retina during experimental and human diabetes. Early onset and effect of insulin. J Clin Invest 102:783–791 13. Mohr S, Xi X, Tang J, Kern TS (2002) Caspase activation in retinas of diabetic and galactosemic mice and diabetic patients. Diabetes 51:1172–1179 14. Kurihara T, Ozawa Y, Nagai N, Shinoda K, Noda K, Imamura Y, Tsubota K, Okano H, Oike Y, Ishida S (2008) Angiotensin II type 1 receptor signaling contributes to synaptophysin degradation and neuronal dysfunction in the diabetic retina. Diabetes 57:2191–2198 15. Yang H, Hirooka K, Fukuda K, Shiraga F (2009) Neuroprotective effects of angiotensin II type 1 receptor blocker in a rat model of chronic glaucoma. Invest Ophthalmol Vis Sci 50:5800–5804 16. Kurihara T, Ozawa Y, Shinoda K, Nagai N, Inoue M, Oike Y, Tsubota K, Ishida S, Okano H (2006) Neuroprotective effects of angiotensin II type 1 receptor (AT1R) blocker, telmisartan, via modulating AT1R and AT2R signaling in retinal inflammation. Invest Ophthalmol Vis Sci 47:5545–5552
Neurochem Res (2013) 38:1572–1579 17. Pd S, Drazba J, Shadrach K, Milsted A, Rungger-Brandle E, Nishiyama K, Miura S, Karnik S, Sears JE, Hollyfield JG (2007) Angiotensin II and its receptor subtypes in the human retina. Invest Ophthalmol Vis Sci 48:3301–3311 18. Downie LE, Vessey K, Miller A, Ward MM, Pianta MJ, Vingrys AJ, Wilkinson-Berka JL, Fletcher EL (2009) Neuronal and glial cell expression of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in the rat retina. Neuroscience 161:195–213 19. Griendling KK, Minieri CA, Ollerenshaw JD, Alexander RW (1994) Angiotensin II stimulates NADH and NADPH oxidase activity in cultured vascular smooth muscle cells. Circ Res 74:1141–1148 20. Chen P, Guo AM, Edwards PA, Trick G, Scicli AG (2007) Role of NADPH oxidase and ANG II in diabetes-induced retinal leukostasis. Am J Physiol Regul Integr Comp Physiol 293:R1619– R1629 21. Silva KC, Rosales MA, Biswas SK, Lopes-de-Faria JB, Lopesde-Faria JM (2009) Diabetic retinal neurodegeneration is associated with mitochondrial oxidative stress and is improved by an angiotensin receptor blocker in a model combining hypertension and diabetes. Diabetes 58:1382–1390 22. Ozawa Y, Kurihara T, Sasaki M, Ban N, Yuki K, Kubota S, Tsubota K (2011) Neural degeneration in the retina of the streptozotocin-induced type 1 diabetes model. Exp Diabetes Res 2011:108328 23. Fujita T, Hirooka K, Nakamura T, Itano T, Nishiyama A, Nagai Y, Shiraga F (2012) Neuroprotective effects of angiotensin II type 1 receptor (AT1-R) blocker via modulating AT1-R signaling and decreased extracellular glutamate levels. Invest Ophthalmol Vis Sci 53:4099–4110 24. Kakuta H, Sudoh K, Sasamata M, Yamagishi S (2005) Telmisartan has the strongest binding affinity to angiotensin II type 1 receptor: comparison with other angiotensin II type 1 receptor blockers. Int J Clin Pharmacol Res 25(1):41–46 25. Zou Z, Xi GL, Yuan HB, Zhu QF, Shi XY (2009) Telmisartan versus angiotension-converting enzyme inhibitors in the treatment of hypertension: a meta-analysis of randomized controlled trials. J Hum Hypertens 23(5):339–349 26. Sleight P (2009) Clinical evidence from ONTARGET: the value of an angiotensin II receptor blocker and an angiotensin-converting enzyme inhibitor. J Hypertens Suppl 27(5):S23–S29 27. Chan SH, Wu CW, Chang AY, Hsu KS, Chan JY (2010) Transcriptional upregulation of brain-derived neurotrophic factor in rostral ventrolateral medulla by angiotensin II: significant in superoxide homeostasis and neural regulation of arterial pressure. Circ Res 107:1127–1139 28. Kishi T, Hirooka Y, Sunagawa K (2012) Sympathoinhibition caused by orally administeredtelmisartan through inhibition of the AT1 receptor in the rostralventrolateral medulla of hypertensive rats. Hypertens Res PMID: 22948091 29. Seki M, Tanaka T, Nawa H, Usui T, Fukuchi T, Ikeda K, Abe H, Takei N (2004) Involvement of brain-derived neurotrophic factor in early retinal neuropathy of streptozotocin-induceddiabetes in rats: therapeutic potential of brain-derived neurotrophic factor for dopaminergic amacrine cells. Diabetes 53:2412–2419 30. Sasaki M, Ozawa Y, Kurihara T, Kubota S, Yuki K, Noda K, Kobayashi S, Ishida S, Tsubota K (2010) Neurodegenerative
1579
31.
32.
33. 34.
35.
36.
37.
38.
39. 40.
41.
42.
43.
44.
influence of oxidative stress in the retina of a murine model of diabetes. Diabetologia 53:971–979 Ola MS, Nawaz MI, El-Asrar AA, Abouammoh M, Alhomida AS (2013a) Reduced Levels of Brain Derived Neurotrophic Factor (BDNF) in the Serum of Diabetic Retinopathy Patients and in the Retina of Diabetic Rats. Cell Mol Neurobiol PMID: 23271640 Lee TH, Yang JT, Kato H, Wu JH (2006) Hypertension downregulates the expression of brain-derived neurotrophic factor in the ischemic-vulnerable hippocampal CA1 and cortical areas after carotid artery occlusion. Brain Res 1116:31–38 Zacchigna S, Lambrechts D, carmeliet P (2008) Neurovascular signalling defects in neurodegeneration. Nat Rev 9:169–181 Pease ME, Zack DJ, Berlinicke C, Bloom K, Cone F, Wang Y, Klein RL, Hauswirth WW, Quigley HA (2009) Effect of CNTF on retinal ganglion cell survival in experimental glaucoma. Invest Ophthalmol Vis Sci 50:2194–2200 Grammatopoulos TN, Jones SM, Ahmadi FA, Hoover BR, Snell LD, Skoch J, Jhaveri VV, Poczobutt AM, Weyhenmeyer JA, Zawada WM (2007) Angiotensin type 1 receptor antagonist losartan, reduces MPTP-induced degeneration of dopaminergic neurons in substantia nigra. Mol Neurodegener 15(2):1 Mertens B, Varcin M, Michotte Y, Sarre S (2011) The neuroprotective action of candesartan is related to interference with the early stages of 6-hydroxydopamine-induced dopaminergic cell death. Eur J Neurosci 34:1141–1148 Ola MS, Nawaz MI, Khan HA, Alhomida AS (2013) Neurodegeneration and neuroprotection in diabetic retinopathy. Int J Mol Sci 14:2559–2572 Miao X, Lv H, Wang B, Chen Q, Miao L, Su G, Tan Y (2013) Deletion of angiotensin II Type 1 receptor gene attenuates chronic alcohol-induced retinal ganglion cell death with preservation of VEGF expression. Curr Eye Res 38:185–193 Wilkinson-Berka JL (2006) Angiotensin and diabetic retinopathy. Int J Biochem Cell Biol 38:752–765 Fletcher EL, Phipps JA, Ward MM, Vessey KA, WilkinsonBerka JL (2010) The renin-angiotensin system in retinal health and disease: its influence on neurons, glia and the vasculature. Prog Retin Eye Res 29:284–311 Miller AG, Tan G, Binger KJ, Pickering RJ, Thomas MC, Nagaraj RH, Cooper ME, Wilkinson-Berka JL (2010) Candesartan attenuates diabetic retinal vascular pathology by restoring glyoxalase-I function. Diabetes 59:3208–3215 Kagota S, Tada Y, Nejime N, Nakamura K, Kunitomo M, Shinozuka K (2011) Telmisartan provides protection against development of impaired vasodilation independently of metabolic effects in SHRSP.Z-Lepr(fa)/IzmDmcr rats with metabolic syndrome. Can J PhysiolPharmacol 89:355–364 Krikov M, Thone-Reineke C, Mu¨ller S, Villringer A, Unger T (2008) Candesartan but not ramipril pretreatment improves outcome after stroke and stimulates neurotrophin BNDF/TrkB system in rats. J Hypertens 26:544–552 Gastinger MJ, Singh RS, Barber AJ (2006) Loss of cholinergic and dopaminergic amacrine cells in streptozotocin-diabetic rat and Ins2Akita-diabetic mouse retinas. Invest Ophthalmol Vis Sci 47:3143–3150
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