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Differential Effects of Quercetin and Quercetin Glycosides on Human α7 Nicotinic Acetylcholine Receptor-Mediated Ion Currents.

Lee BH, Choi SH, Kim HJ, Jung SW, Hwang SH, Pyo MK, Rhim H, Kim HC, Kim HK, Lee SM, Nah SY - Biomol Ther (Seoul) (2016)

Bottom Line: Quercetin is a flavonoid usually found in fruits and vegetables.Quercetin glycosides mediated an inhibition of IACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent.These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea.

ABSTRACT
Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actions. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin- 3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated ion currents. However, the role of the carbohydrates attached to quercetin in the regulation of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (IACh) in Xenopus oocytes expressing the α7 nAChR. IACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced IACh, whereas quercetin glycosides inhibited IACh. Quercetin glycosides mediated an inhibition of IACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent. The order of IACh inhibition by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated IACh enhancement was not affected by ACh concentration and appeared voltage-independent. Furthermore, quercetin-mediated IACh inhibition can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulation and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruption of quercetin action. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.

No MeSH data available.


Effects of quercetin and its glycosides on IACh in oocytes expressing human α7 nAChRs. (A–B) Acetylcholine (ACh; 200 μM) was applied first, followed by co- or pre-application of quercetin (Que) or quercetin glycosides (Rham1, Rutin, Rham2) and ACh. Co-application of 100 μM quercetin with ACh enhanced IACh and pre-application of 100 μM quercetin with ACh further enhanced IACh. Whereas, co-application of 100 μM of quercetin glycosides with ACh inhibited IACh and pre-application of 100 μM quercetin glycosides with ACh further inhibited IACh. Traces represent six separate oocytes from three different batches of frogs. (C) Summary of IACh enhancement by co- or pre-application of quercetin (*p<0.05, **p<0.005 compared to the control; #p<0.005, compared to the co-application of quercetin). Each point represents the means ± S.E.M. (n=9–12/group).
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f2-bt-24-410: Effects of quercetin and its glycosides on IACh in oocytes expressing human α7 nAChRs. (A–B) Acetylcholine (ACh; 200 μM) was applied first, followed by co- or pre-application of quercetin (Que) or quercetin glycosides (Rham1, Rutin, Rham2) and ACh. Co-application of 100 μM quercetin with ACh enhanced IACh and pre-application of 100 μM quercetin with ACh further enhanced IACh. Whereas, co-application of 100 μM of quercetin glycosides with ACh inhibited IACh and pre-application of 100 μM quercetin glycosides with ACh further inhibited IACh. Traces represent six separate oocytes from three different batches of frogs. (C) Summary of IACh enhancement by co- or pre-application of quercetin (*p<0.05, **p<0.005 compared to the control; #p<0.005, compared to the co-application of quercetin). Each point represents the means ± S.E.M. (n=9–12/group).

Mentions: Treatment of ACh (200 μM) to oocytes injected with human α7 nAChR cRNA induced a large inward current (IACh) (Fig. 2A) but the application of ACh did not induce any inward current in H2O-injected control oocytes (data not shown) (Lee et al., 2010). Although quercetin (100 μM) itself had no effect on oocytes expressing α7 nAChRs at a holding potential of −80 mV (data not shown), the co-application of quercetin with ACh enhanced IACh in oocytes expressing α7 AChR (Fig. 2A, n=9 from three different frogs). The co-application of quercetin with ACh induced an enhancement of IACh by 46.5 ± 6.5% (Fig. 2B, **p<0.005 versus unexposed controls). In addition, pre-application of quercetin (100 μM) alone for 30 s before co-application with ACh (200 μM) induced a much larger enhancement of IACh in oocytes expressing α7 nAChRs than the enhancement observed after co-application as we previously demonstrated (Fig. 2A, #p<0.005, compared to co-treatment) (Lee et al., 2010). Next, we examined the effects of quercetin glycosides on IACh. Quercetin glycosides (100 μM each) themselves showed no effect on oocytes expressing the α7 nAChRs at a holding potential of −80 mV. Co-application of quercetin glycosides with ACh decreased the amplitude of IACh reversibly (13.2 ± 2.7%, 15.0 ± 2.9%, and 4.7 ± 1.2% inhibition by Rham1, Rutin, and Rham2, respectively) (Fig. 2C). Pre-application of quercetin glycosides alone for 30 s before co-application with ACh induced a much larger inhibitory effect on IACh (39.4 ± 3.5%, 42.1 ± 4.7%, and 13.1 ± 4.5% inhibition by Rham1, Rutin, and Rham2, respectively) (Fig. 2B, 2C, n=8–11 from three different frogs). Thus, the IACh inhibitory potency order appeared where Rutin≈Rham1>Rham2, also indicating that the regulatory pattern of quercetin glycosides on α7 nAChR channel activity is different from that of quercetin (Fig. 2).


Differential Effects of Quercetin and Quercetin Glycosides on Human α7 Nicotinic Acetylcholine Receptor-Mediated Ion Currents.

Lee BH, Choi SH, Kim HJ, Jung SW, Hwang SH, Pyo MK, Rhim H, Kim HC, Kim HK, Lee SM, Nah SY - Biomol Ther (Seoul) (2016)

Effects of quercetin and its glycosides on IACh in oocytes expressing human α7 nAChRs. (A–B) Acetylcholine (ACh; 200 μM) was applied first, followed by co- or pre-application of quercetin (Que) or quercetin glycosides (Rham1, Rutin, Rham2) and ACh. Co-application of 100 μM quercetin with ACh enhanced IACh and pre-application of 100 μM quercetin with ACh further enhanced IACh. Whereas, co-application of 100 μM of quercetin glycosides with ACh inhibited IACh and pre-application of 100 μM quercetin glycosides with ACh further inhibited IACh. Traces represent six separate oocytes from three different batches of frogs. (C) Summary of IACh enhancement by co- or pre-application of quercetin (*p<0.05, **p<0.005 compared to the control; #p<0.005, compared to the co-application of quercetin). Each point represents the means ± S.E.M. (n=9–12/group).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4930285&req=5

f2-bt-24-410: Effects of quercetin and its glycosides on IACh in oocytes expressing human α7 nAChRs. (A–B) Acetylcholine (ACh; 200 μM) was applied first, followed by co- or pre-application of quercetin (Que) or quercetin glycosides (Rham1, Rutin, Rham2) and ACh. Co-application of 100 μM quercetin with ACh enhanced IACh and pre-application of 100 μM quercetin with ACh further enhanced IACh. Whereas, co-application of 100 μM of quercetin glycosides with ACh inhibited IACh and pre-application of 100 μM quercetin glycosides with ACh further inhibited IACh. Traces represent six separate oocytes from three different batches of frogs. (C) Summary of IACh enhancement by co- or pre-application of quercetin (*p<0.05, **p<0.005 compared to the control; #p<0.005, compared to the co-application of quercetin). Each point represents the means ± S.E.M. (n=9–12/group).
Mentions: Treatment of ACh (200 μM) to oocytes injected with human α7 nAChR cRNA induced a large inward current (IACh) (Fig. 2A) but the application of ACh did not induce any inward current in H2O-injected control oocytes (data not shown) (Lee et al., 2010). Although quercetin (100 μM) itself had no effect on oocytes expressing α7 nAChRs at a holding potential of −80 mV (data not shown), the co-application of quercetin with ACh enhanced IACh in oocytes expressing α7 AChR (Fig. 2A, n=9 from three different frogs). The co-application of quercetin with ACh induced an enhancement of IACh by 46.5 ± 6.5% (Fig. 2B, **p<0.005 versus unexposed controls). In addition, pre-application of quercetin (100 μM) alone for 30 s before co-application with ACh (200 μM) induced a much larger enhancement of IACh in oocytes expressing α7 nAChRs than the enhancement observed after co-application as we previously demonstrated (Fig. 2A, #p<0.005, compared to co-treatment) (Lee et al., 2010). Next, we examined the effects of quercetin glycosides on IACh. Quercetin glycosides (100 μM each) themselves showed no effect on oocytes expressing the α7 nAChRs at a holding potential of −80 mV. Co-application of quercetin glycosides with ACh decreased the amplitude of IACh reversibly (13.2 ± 2.7%, 15.0 ± 2.9%, and 4.7 ± 1.2% inhibition by Rham1, Rutin, and Rham2, respectively) (Fig. 2C). Pre-application of quercetin glycosides alone for 30 s before co-application with ACh induced a much larger inhibitory effect on IACh (39.4 ± 3.5%, 42.1 ± 4.7%, and 13.1 ± 4.5% inhibition by Rham1, Rutin, and Rham2, respectively) (Fig. 2B, 2C, n=8–11 from three different frogs). Thus, the IACh inhibitory potency order appeared where Rutin≈Rham1>Rham2, also indicating that the regulatory pattern of quercetin glycosides on α7 nAChR channel activity is different from that of quercetin (Fig. 2).

Bottom Line: Quercetin is a flavonoid usually found in fruits and vegetables.Quercetin glycosides mediated an inhibition of IACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent.These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea.

ABSTRACT
Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actions. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin- 3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated ion currents. However, the role of the carbohydrates attached to quercetin in the regulation of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (IACh) in Xenopus oocytes expressing the α7 nAChR. IACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced IACh, whereas quercetin glycosides inhibited IACh. Quercetin glycosides mediated an inhibition of IACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent. The order of IACh inhibition by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated IACh enhancement was not affected by ACh concentration and appeared voltage-independent. Furthermore, quercetin-mediated IACh inhibition can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulation and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruption of quercetin action. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.

No MeSH data available.