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Research Article
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Curcumin and Tetrahydrocurcumin Restore the Impairment of Endothelium-dependent Vasorelaxation Induced by Homocysteine Thiolactone in Rat Aortic Rings |
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P. Tep-areenan
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A. Suksamrarn
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ABSTRACT
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The aim of the present study was to investigate the effects of curcumin and Tetra Hydro Curcumin (THC) on the inhibition of endothelium-dependent vasorelaxation of the isolated rat aorta by Homocysteine Thiolactone (HTL). Carbachol, an endothelium-dependent vasodilator, caused concentration-dependent vasorelaxation in rat aortic rings. Exposure of aortic rings to HTL (0.3 and 1 mM) for 90 min significantly inhibited endothelium-dependent vasorelaxation to carbachol. In addition, contractions induced by methoxamine were significantly reduced after pretreatment with 3 mM HTL. Curcumin (10 and 30 μM) significantly restored carbachol-induced vasorelaxation inhibited by HTL (1 mM). Similar effects were observed after pretreatment of aortic rings with THC (10 and 30 μM). Moreover, HTL-induced impairment of vasorelaxation to carbachol could be blocked by either L-arginine (3 mM), a precursor of nitric oxide or superoxide dismutase (SOD, 200 U mL-1), a scavenger of superoxide anion. These results demonstrate that impairment of endothelium-dependent vasorelaxation induced by HTL is due to a reduction of nitric oxide and the generation of oxygen free radicals. Interestingly, curcumin and THC could restore endothelial dysfunction induced by HTL which may be related to their antioxidant properties. The present study provides pharmacological data to support the hypothesis that curcumin and THC have vasoprotective effects in hyperhomocysteinemia.
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Received: November 04, 2011;
Accepted: February 13, 2012;
Published: March 07, 2012
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INTRODUCTION
Homocysteine, a sulfur-containing amino acid, is an intermediate product in
metabolism of L-methionine. Deficiencies of vitamin B12 and folate
cause an increase in plasma level of homocysteine, termed as hyperhomocysteinemia
(Alshatwi, 2007). Hyperhomocysteinemia is a powerful
independent risk factor for various cardiovascular disease such as atherosclerosis,
hypertension, myocardial infarction (Balakumar et al.,
2007; Joshaghani et al., 2007; Laghari
et al., 2009; Ravari et al., 2009;
Damorou et al., 2010; Williams
and Schalinske, 2010). In fact, homocysteine acts as a pro-thrombotic, pro-inflammatory
and vasorelaxation-imparing factor (Perla-Kajan et al.,
2007). Several studies have shown that endothelium-dependent vasorelaxations
are impaired in animals and human with hyperhomocysteinemia (Ungvari
et al., 1999; Boger et al., 2000;
Tawakol et al., 1997; Abahji
et al., 2007).
There is evidence that Homocysteine Thiolactone (HTL), a homocysteine-reactive
product, is involved in vascular damage due to homocysteine (Jakubowski,
2008; Karolczak and Olas, 2009). Protein N-homocysteinylation
induced by HTL may lead to cardiovascular disorders (Karolczak
and Olas, 2009). Incubation of rat aortic rings with HTL causes an impairment
of endothelium-dependent vasorelaxation (Liu et al.,
2007). The endothelial dysfunctions induced by HTL involve a decreased release
of nitric oxide from endothelial cells and increased generation of reactive
oxygen species (Liu et al., 2007; Jakubowski,
2008; Karolczak and Olas, 2009).
Curcumin (diferuloylmethane) is a phenolic compound from the plant Curcuma
longa or turmeric. Commonly, it is used as a spices and coloring agent (Srivastava
et al., 2011). Pharmacological studies have demonstrated that curcumin
has a variety of effects, including antispasmodic (Itthipanichpong
et al., 2003), antidepressant (Yu et al.,
2002), anti-oxidant (Manikandan et al., 2004;
Hussein and Abu-Zinadah, 2010; Sivabalan
and Anuradha, 2010), antibacterial (Negi et al.,
1999; Pandey et al., 2011), anti-inflammatory
(Kohli et al., 2005; Yuan
et al., 2006), anticarcinogenic (Yoysungnoen
et al., 2008), antinociceptive (Tajik et al.,
2007) Schistosomicidal properties (EL-Sherbiny et
al., 2006). Moreover, curcumin could lower plasma level of glucose (Sivabalan
and Anuradha, 2010). In addition, curcumin could restore endothelial dysfunction
(Ramaswami et al., 2004). Recent studies in diabetic
rats have shown that tetrahydrocurcumin, an active metabolite of curcumin, has
anti-oxidant (Murugan and Pari, 2006a), anti-diabetic
(Murugan and Pari, 2006b) and anti-hyperlipidemic effects
(Pari and Murugan, 2007). However, curcumin and THC
have not been studied in endothelial dysfunction induced by HTL. Thus, the aim
of this study was to investigate the effects of curcumin and THC against endothelial
dysfunction induced by HTL and mechanisms involved in their actions in the isolated
rat aorta.
MATERIALS AND METHODS Chemicals: All drugs and chemicals were purchased from Sigma Chemical Company (St. Louis, Missouri, USA) but zoletil was purchased from Virbac (Carros Cedex, France). Curcumin and THC were prepared by our laboratory. All drugs were dissolved in the Krebs solution, except curcumin and THC were dissolved in dimethyl sulphoxide.
Extraction of curcumin and tetrahydrocurcumin: The mixture of curcuminoid
extracted from the rhizomes of Curcuma longa was subjected to silica
gel column chromatography, using hexane-dichloromethane, dichloromethane and
dichloromethane-methanol as eluents to yield curcumin, the major compound. THC
was synthesized from curcumin as described by Yoysungnoen
et al. (2008). Structures of curcumin and THC were shown in Fig.
1.
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Fig. 1: |
Structures of curcumin and tetrahydocurcumin |
Tissue preparation: In 2010, experiments were performed using aorta obtained from male Wistar rats (300-350 g) bred and kept by the National Laboratory Animal Center, Mahidol University, Thailand. The rats were fed with standard laboratory rat chow and tap water and housed in standard environmental condition (25°C) under 12 h light/dark cycles. All experiments were reviewed and approved by the Animal Research Ethics Committee of the Faculty of Medicine, Srinakharinwirot University.
The rats were anaesthetized with zoletil 50 mg kg-1 (tiletamine
chloridrate and zolazepan chloridrate). Into quadriceps muscle and killed by
cervical dislocation (Tep-areenan and Sawasdee, 2011).
Following a thoracotomy, the thoracic aorta was dissected from the rat. The
aorta was cleaned of fat and connective tissue and cut into 4-5 mm ring segments.
Each ring was mounted between two stainless wires and then transferred to a
jacketed organ bath filled with 20 ml of modified Krebs-Henseleit solution (composition,
mM; NaCl 118, KCl 4.7, MgSO4 1.2, KH2PO4 1.2,
NaHCO3 25, CaCl2 2, D-glucose 10) that was maintained
at 37°C and bubbled continuously with 95% O2 and 5% CO2
mixture. The buffer in the organ bath was exchanged every 15 min for 1
h. The rings were mounted between two triangular stainless steel hooks that
were passed through the lumen and stretched to an optimal passive tension of
about 1 g and then allowed to equilibrate for 60 min before experiments were
started. Tension was measured by isometric force transducers (MLT 0210) connected
to a MacLab recording system (AD instruments, New South Wales, Australia).
Experimental protocol: Following a 1 h equilibration period, aortic rings of control were incubated with vehicle (distilled water) and the rings of HTL groups were incubated with HTL (0.3 and 1 mM) for 90 min. After 90 min of incubation, methoxamine, an alpha adrenoceptor agonist, was used to increase vascular tone by approximately 1 g. Once a stable tone was achieved, concentration-response curves of carbachol (1 nM-100 μM) were constructed. To investigate the effects of HTL on contractions induced by methoxamine, after aortic rings were allowed to equilibrate for 1 h at 1 g tension, aortic rings were incubated with vehicle or HTL (0.3 to 30 mM) for 90 min. After incubation period of 90 min, methoxamine (0.1-300 μM) was added cumulatively in the bath. To investigate the effects of antioxidants, curcumin and THC, on impairment of endothelium-dependent relaxation induced by HTL, curcumin (10 and 30 μM) and THC (10 and 30 μM), were co-incubation with 1 mM HTL for 90 min. In addition, the effects of L-arginine, a precursor of nitric oxide (NO) and SOD, a scavenger of superoxide anion, on inhibition of HTL were investigated. L-arginine (3 mM) and SOD (200 U mL-1) were co-incubation with 1 mM HTL for 90 min. This concentration of HTL was used as methoxamine could not induce tone after incubation of aortic rings with a higher concentration (3 mM) of HTL. After incubation of 90 min, tone was induced by addition of methoxamine. Then, concentration-response curves of carbachol were constructed.
Statistical analysis: The concentration of vasorelaxant giving half-maximal
relaxation (EC50) and maximal responses (Rmax) were obtained
from the concentration-response curve fitted to a sigmoidal logistic equation
using the GraphPad Prism package as described by Tep-areenan
et al. (2003). Rmax and pEC50 values (negative
logarithm of the EC50) were compared by analysis of variance (ANOVA)
with statistically significant differences between groups being determined by
Bonferronis post-hoc test. Results are expressed as mean+SE. A value of
p<0.05 was considered statistical significant. The number of animals in each
group is represented by n (Tep-areenan and Sawasdee, 2011).
RESULTS
Effects of HTL on relaxation and contraction of rat aortic rings: In
Fig. 2, contractions induced by 30 μM methoxamine were
significantly (p<0.001) inhibited in rings incubated with 3 mM HTL (Rmax:
control = 1.04±0.15 g, n = 6; 3 mM HTL = 1.04±0.15 g, n = 6) but
not 0.3 and 1 mM HTL.
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Fig. 2: |
Effects of pre-treatment
with homocysteine thiolactone (0.3 to 3 mM) for 90 min on contractions to
methoxamine (30 μM) in rat aortic rings. Data are shown as Mean±SEM
***Significantly different at p<0.001 |
In addition, 10 aortic mM or 30 mM of HTL completely inhibited methoxamine-induced
contraction (data not shown).
Carbachol caused concentration-dependent relaxation (Rmax = 101±3%
with EC50 = 6.24±0.08, n = 6). Endothelium-dependent vasorelaxations
to carbachol were significantly (p<0.001) reduced after incubation of aortic
rings with HTL (0.3 and 1 mM) (Rmax: control = 101±3%, n =
6; 0.3 mM HTL = 77.1±3.4%, n = 6; 1 mM HTL = 52.6±3.2%, n = 6,
Fig. 3).
Effects of curcumin and THC on endothelium-dependent vasorelaxation to carbachol
in rat aortic rings: Treatment of aortic rings with curcumin in different
concentrations (10 and 30 μM) significantly (p<0.001) prevented the inhibitory effects of HTL (1 mM) on relaxant responses to carbachol (Rmax:
control = 101±3%, n = 6; 1 mM HTL = 52.6±3.2%, n = 6; 10 μM
curcumin = 80.7±3.4%, n = 6; 30 μM curcumin = 80.9±3.5%,
n = 6; Fig. 4).
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Fig. 3: |
Effects of pre-treatment
with homocysteine thiolactone (0.3 and 1 mM HTL) for 90 min on carbachol-induced
vasorelaxation in rat aortic rings. Data are shown as Mean±SEM |
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Fig. 4: |
Effects of pre-treatment
with homocysteine thiolactone (HTL 1 mM) for 90 min on carbachol-induced
vasorelaxation in the presence of 10 and 30 μM curcumin (C) in rat
aortic rings. Data are shown as Mean±SEM |
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Fig. 5: |
Effects of pre-treatment
with homocysteine thiolactone (HTL 1 mM) for 90 min on carbachol-induced
vasorelaxation in the presence of 10 and 30 μM tetrahydrocurcumin (THC)
in rat aortic rings. Data are shown as Mean±SEM |
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Fig. 6: |
Effects of pre-treatment
with homocysteine thiolactone (HTL 1 mM) for 90 min on carbachol-induced
vasorelaxation in the presence of L-arginine (3 mM) and SOD (200 U mL-1)
in rat aortic rings. Data are shown as Mean±SEM |
Similarly, THC (10 and 30 μM) significantly
(p<0.001) restored impairment of relaxation to carbachol after treatment
with HTL (1 mM) (Rmax: control = 101±3%, n = 6; 1 mM HTL =
52.6±3.2%, n = 6; 10 μM THC = 85.1±3.5%, n = 6; 30 μM
THC = 93.5±3.9%, n = 6; Fig. 5). However, there was
no significant difference of the protective effects between curcumin and THC.
Effects of L-arginine and SOD on endothelium-dependent vasorelaxation to
carbachol in rat aortic rings: As shown in Fig. 6, co-incubation
of L-arginine (3 mM) or SOD (200 U mL-1) in the presence of HTL (1
mM) significantly restored carbachol-induced vasorelaxation (Rmax:
control = 101±3%, n=6; 1 mM HTL = 52.6±3.2%, n = 6; L-arginine
= 109±3%, n = 6; SOD = 108±4%, n = 6).
DISCUSSION
The present study in rat aortic rings demonstrated that HTL inhibited endothelium-dependent
vasorelaxation to carbachol and contraction to methoxamine, an alpha adrenoceptor
agonist. Interestingly, this is the first time that curcumin and THC have been
shown to restore HTL-induced impairment of endothelium-dependent vasorelaxation.
Hyperhomocysteinemia is though to induce arteriosclerosis and peripheral vascular
disease which cause dysfunctions of endothelial cells (Abahji
et al., 2007; Jakubowski, 2008). In the present
study, we showed that exposure of aortic rings to HTL (1 mM) caused a significant
attenuation of endothelium-dependent vasorelaxation to carbachol. Theses findings
are consistent with other studies in isolated animal vessels (Fu
et al., 2003; Ramaswami et al., 2004;
Liu et al., 2007). In addition, a high concentration
of HTL (3 mM) reduced contraction to methoxamine, alpha 1-adrenoceptor agonist.
These results suggest that HTL may affect the mechanisms involved in methoxamine-induced
contraction, including activation of protein kinase C to increase extracellular
Ca2+ influx through receptor-operated Ca2+ channels and/or
Ca2+ release from intracellular store (Burt et
al., 1996; Lyles et al., 1998).
Impairment of endothelial functions induced by homocysteine and HTL, a homocysteine-reactive
product, involves an increase in the formation of oxygen free radicals, especially
superoxide anion and lipid peroxidation products (Zappacosta
et al., 2001; Fu et al., 2003; Ramaswami
et al., 2004; Jakubowski, 2008). In agreement
with previous reports, the present study showed that SOD, a scavenger of superoxide
anion, inhibited impairment of endothelium-dependent relaxation induced by HTL
in rat aortic rings.
Superoxide anions are known to inhibit endothelium-dependent relaxation by
inactivating endothelium-dependent relaxing factors, mainly NO (Mercie
et al., 2000). Indeed, our results showed that impairment of relaxation
induced by HTL are restored after pretreatment with L-arginine, a precursor
of NO. These results suggest that endothelial dysfunctions caused by HTL are
likely to increase NO degradation by oxygen free radicals and/or decreasing
endothelium-derived NO synthesis.
We then investigate the effects of curcumin and its active metabolite, THC,
on endothelial dysfunctions induced by HTL. We found that curcumin reverse impairment
of endothelium-dependent relaxation induced by HTL in rat aortic rings. These
results are in agreement with a previous study showing that curcumin could restore
endothelial dysfunctions induced by homocysteine in porcine coronary arteries
(Ramaswami et al., 2004). Interestingly, we found
that THC had similar effects. From the present findings, it is suggested that
vasoprotective effects of both curcumin and THC may involve their antioxidant
property (Manikandan et al., 2004; Murugan
and Pari, 2006a; Hussein and Abu-Zinadah, 2010;
Sivabalan and Anuradha, 2010). These findings are supported
by a recent study showing that curcumin reduced production of superoxide anion
in porcine coronary arteries. Moreover, curcumin increase endothelial nitric
oxide synthase in porcine coronary arteries (Ramaswami et
al., 2004). Taken together, mechanisms of the inhibitory effects of
curcumin and THC on HTL-induced endothelial dysfunctions may involve decreasing
of superoxide anion and increasing production of NO. These may constitute significant
mechanisms of cardioprotection by curcumin and its metabolite, THC.
CONCLUSION
These findings demonstrate that curcumin and THC effectively reverse endothelial
dysfunction induced by HTL which may be related to scavenging oxygen free radicals
and enhancing NO production. The present findings provide pharmacological evidence
for mechanisms contributing to vasoprotective effects of curcumin and THC in
hyperhomocysteinemia. However, further investigation would need to be pursued
to examine other mechanisms including the interaction between THC and HTL.
ACKNOWLEDGMENTS
This study was funded by The Faculty of Medicine, Srinakharinwirot University
(Grant No. 084/2552). We would like to express our deepest gratitude to Dr.
Alfredo Villarroel for improving the English. We also thank Mr. Phongphat Wetchasit
for his technical support. The authors have no conflict of interest to report.
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REFERENCES |
1: Abahji, T.N., L. Nill, N. Ide, C. Keller, U. Hoffmann and N. Weiss, 2007. Acute hyperhomocysteinemia induces microvascular and macrovascular endothelial dysfunction. Arch. Med. Res., 38: 411-416. PubMed |
2: Alshatwi, A.A., 2007. Vitamin B12 and folate deficiencies and hyperhomocysteinemia in elderly. J. Med. Sci., 7: 402-407. CrossRef | Direct Link |
3: Balakumar, P., A.P. Singh, S.S. Ganti and M. Singh, 2007. Hyperhomocysteinemia and cardiovascular disorders: Is there a correlation? Trends Med. Res., 2: 160-166. CrossRef | Direct Link |
4: Boger, R.H., S.M. Bode-Boger, K. Sydow, D.D. Heistad and S.R. Lentz, 2000. Plasma concentration of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, is elevated in monkeys with hyperhomocyst(e)inemia or hypercholesterolemia. Arterioscler. Thromb. Vasc. Biol., 20: 1557-1564. PubMed |
5: Burt, R.P., C.R. Chapple and I. Marshall, 1996. The role of diacylglycerol and activation of protein kinase C in alpha 1A-adrenoceptor-mediated contraction to noradrenaline of rat isolated epididymal vas deferens. Br. J. Pharmacol., 117: 224-230. PubMed |
6: Damorou, F., T. Tcherou, K. Yayehd, S. Pessinaba and I.B. Diop, 2010. Homocysteine level and cardiovascular afflictions in the black african patients in lome. Res. J. Cardiol., 3: 1-8. CrossRef |
7: EL-Sherbiny, M., M.M. Abdel-Aziz, K.A. Elbakry, E.A. Toson and A.T. Abbas, 2006. Schistosomicidal effect of curcumin. Trends Applied Sci. Res., 1: 627-633. CrossRef | Direct Link |
8: Fu, Y.F., Y. Xiong and S.H. Fu, 2003. Captopril restores endothelium-dependent relaxation of rat aortic rings after exposure to homocysteine. J. Cardiovasc. Pharmacol., 42: 566-572. PubMed |
9: Hussein, H.K. and O.A. Abu-Zinadah, 2010. Antioxidant effect of curcumin extracts in induced diabetic Wister rats. Int. J. Zool. Res., 6: 266-276. CrossRef | Direct Link |
10: Itthipanichpong, C., N. Ruangrungsi, W. Kemsri and A. Sawasdipanich, 2003. Antispasmodic effects of curcuminoids on isolated guinea-pig ileum and rat uterus. J. Med. Assoc. Thai., 86: S299-S309. PubMed |
11: Jakubowski, H., 2008. The pathophysiological hypothesis of homocysteine thiolactone-mediated vascular disease. J. Physiol. Pharmacol., 59: 155-167. PubMed |
12: Joshaghani, H.R., A.A. Shirafkan and A. Marjani, 2007. Serum homocysteine levels in patients with myocardial infarction in Gorgan (in Northern Iran). Asian J. Biochem., 2: 157-160. CrossRef |
13: Karolczak, K. and B. Olas, 2009. Mechanism of action of homocysteine and its thiolactone in hemostasis system. Physiol. Res., 58: 623-633. PubMed |
14: Kohli, K., J. Ali, M.J. Ansari and Z. Raheman, 2005. Curcumin: A natural anti-inflammatory agent. Indian J. Pharmacol., 37: 141-147. CrossRef | Direct Link |
15: Laghari, A.H., A.N. Memon, A.M. Shah, S.F. Ahmed and M.S. Memon, 2009. Hyperhomocysteinemia, a risk factor for myocardial infarction in patients with type-2 diabetes in Southern Sindh, Pakistan. Pak. J. Nutr., 8: 1753-1755. CrossRef | Direct Link |
16: Liu, Y.H., Y. You, T. Song, S.J. Wu and L.Y. Liu, 2007. Impairment of endothelium-dependent relaxation of rat aortas by homocysteine thiolactone and attenuation by captopril. J. Cardiovasc. Pharmacol., 50: 155-161. PubMed |
17: Lyles, G.A., C. Birrell, G. Banchelli and R. Pirisino, 1998. Amplification of alpha 1D-adrenoceptor mediated contractions in rat aortic rings partially depolarized with KCl. Pharmacol. Res., 37: 437-454. PubMed |
18: Manikandan, P., M. Sumitra, S. Aishwarya, B.M. Manohar, B. Lokanadam and R. Puvanakrishnan, 2004. Curcumin modulates free radical quenching in myocardial ischaemia in rats. Int. J. Biochem. Cell Biol., 36: 1967-1980. CrossRef | PubMed |
19: Mercie, P., O. Garnier, L. Lascoste, M. Renard and C. Closse et al., 2000. Homocysteine-thiolactone induces caspase-independent vascular endothelial cell death with apoptotic features. Apoptosis, 5: 403-411. PubMed |
20: Murugan, P. and L. Pari, 2006. Antioxidant effect of tetrahydrocurcumin in Streptozotocin-nicotinamide induced diabetic rats. Life Sci., 79: 1720-1728. CrossRef | PubMed | Direct Link |
21: Murugan, P. and L. Pari, 2006. Effect of tetrahydrocurcumin on lipid peroxidation and lipids in streptozotocin-nicotinamide-induced diabetic rats. Basic Clin. Pharmacol. Toxicol., 99: 122-127. PubMed |
22: Negi, P.S., G.K. Jayaprakasha, L.J.M. Rao and K.K. Sakariah, 1999. Antibacterial activity of turmeric oil: A byproduct from curcumin manufacture. J. Agric. Food. Chem., 47: 4297-4300. CrossRef | Direct Link |
23: Pandey, A., R.K. Gupta, A. Bhargava and B. Agrawal, 2011. Antibacterial activities of curcumin bioconjugates. Int. J. Pharmacol., 7: 874-879. CrossRef |
24: Pari, L. and P. Murugan, 2007. Antihyperlipidemic effect of curcumin and tetrahydrocurcumin in experimental type 2 diabetic rats. Renal Failure, 29: 881-889. PubMed |
25: Perla-Kajan, J., T. Twardowski and H. Jakubowski, 2007. Mechanisms of homocysteine toxicity in humans. Amino Acids, 32: 561-572. PubMed |
26: Ramaswami, G., H. Chai, Q. Yao, P.H. Lin, A.B. Lumsden and C. Chen, 2004. Curcumin blocks homocysteine-induced endothelial dysfunction in porcine coronary arteries. J. Vasc. Surg., 40: 1216-1222. PubMed |
27: Ravari, H., M.R. Zafarghandi, D. Alvandfar and S. Saadat, 2009. Serum homocysteine in deep venous thrombosis, peripheral atherosclerosis and healthy Iranians: A case-control study. Pak. J. Biol. Sci., 12: 1019-1024. CrossRef | PubMed | Direct Link |
28: Pandey, A., R.K. Gupta and R. Srivastava, 2011. Curcumin-the yellow magic. Asian J. Applied Sci., 4: 343-354. CrossRef | Direct Link |
29: Sivabalan, S. and C.V. Anuradha, 2010. A comparative study on the antioxidant and glucose-lowering effects of curcumin and bisdemethoxycurcumin analog through in vitro assays. Int. J. Pharmacol., 6: 664-669. CrossRef | Direct Link |
30: Tajik, H., E. Tamaddonfard and N. Hamzeh-Gooshchi, 2007. Interaction between curcumin and opioid system in the formalin test of rats. Pak. J. Biol. Sci., 10: 2583-2586. CrossRef | PubMed | Direct Link |
31: Tawakol, A, T. Omland, M. Gerhard, J.T. Wu and M.A. Creager, 1997. Hyperhomocyst(e)inemia is associated with impaired endothelium-dependent vasodilation in humans. Circulation, 95: 1119-1121.
32: Tep-Areenan, P., D.A. Kendall and M.D. Randall, 2003. Mechanisms of vasorelaxation to testosterone in the rat aorta. Eur. J. Pharmacol., 465: 125-132.
33: Tep-Areenan, P. and P. Sawasdee, 2011. The vasorelaxant effects of Anaxagorea luzonensis A. Grey in the rat Aorta. Int. J. Pharmacol., 7: 119-124. CrossRef | Direct Link |
34: Ungvari, Z., P. Pacher, K. Rischak, L. Szollar and A. Koller, 1999. Dysfunction of nitric oxide mediation in isolated rat arterioles with methionine diet-induced hyperhomocysteinemia. Arterioscler. Thromb. Vasc. Biol., 19: 1899-1904. PubMed |
35: Williams, K.T. and K.L. Schalinske, 2010. Homocysteine metabolism and its relation to health and disease. Biofactors, 36: 19-24. PubMed |
36: Yoysungnoen, P., P. Wirachwong, C. Changtam, A. Suksamrarn and S. Patumraj, 2008. Anti-cancer and anti-angiogenic effects of curcumin and tetrahydrocurcumin on implanted hepatocellular carcinoma in nude mice. World J. Gastroenterol., 14: 2003-2009. PubMed |
37: Yu, Z.F., L.D. Kong and Y. Chen, 2002. Antidepressant activity of aqueous extracts of Curcuma longa in mice. J. Ethnopharmocol., 83: 161-165. CrossRef | PubMed | Direct Link |
38: Yuan, G., M.L. Wahlqvist, G. He, M. Yang and D. Li, 2006. Natural products and anti-inflammatory activity. Asia Pac. J. Clin. Nutr., 15: 143-152. PubMed | Direct Link |
39: Zappacosta, B., A. Mordente, S. Persichilli, A. Minucci and P. Carlino et al., 2001. Is homocysteine a pro-oxidant?. Free Radic. Res., 35: 499-505. PubMed |
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