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Biosci. Biotechnol. Biochem., 66 (3), 689–692, 2002 Luteolin, a Flavone, Does Not Suppress Postprandial Glucose AbsorptionThrough an Inhibition of a-Glucosidase Action Toshiro MATSUI,† Mio KOBAYASHI, Sachiko HAYASHIDA, and Kiyoshi MATSUMOTO Department of Bioscience and Biotechnology, Division of Bioresource and Bioenvironmental Sciences,Faculty of Agriculture, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-ku,Fukuoka 812-8581, Japan Received September 25, 2001; Accepted October 26, 2001 In order to clarify the postprandial glucose suppres- on the antioxidant,7) antimutagenic,8) and antihyper- sion via a-glucosidase (AGH) inhibitory action by tensive eŠects9) of ‰avonoids have been done. In natural compounds, ‰avonoids were examined in this addition, their alternative physiological function of study. Among the ‰avonoids (luteolin, kaempferol, suppression of glucose absorption at the small intes- chrysin, and galangin), luteolin showed the potent mal- tine has been also reported.1,10) Among the ‰avo- tase inhibitory activity with the IC50 of 2.3 mM, while noids, tea polyphenols such as catechins have been less inhibitions were observed against sucrase. In addi- found to inhibit AGH activity2) and glucose trans- tion, the eŠects of maltase inhibition by ‰avonoids were port.4) These ˆndings led us to make a further investi- observed in the descending order of potency of gation of ‰avonoids commonly present in plant and luteolinÀkaempferolÀchrysinÀgalangin. Apparently, food products for any anti-hyperglycemic eŠect. In the AGH inhibition power greatly increased with the this paper, we have examined the in vitro and in vivo replacement of hydroxyl groups at 3? and 4?-position of AGH inhibition abilities of naturally occurring ‰avo- the B-ring. However, the inhibitory power of luteolin noids, i.e., luteolin and chrysin as ‰avones, kaem- was poorer than a therapeutic drug (acarbose: IC50; 430 nM). As a result of a single oral administration of a-Glucosidase (AGH, EC 3.2.1.20, 2.2 U Wmg) maltose or sucrose (2 g Wkg) in SD rats, no signiˆcant from rat intestinal acetone powder was purchased change in blood glucose level with the doses of 100 and from Sigma Chemical Co. (St. Louis, MO, U.S.A.).
200 mg Wkg of luteolin was observed. These ˆndings All of the ‰avonoids used in this study were strongly suggested that luteolin given at less than purchased from Wako Pure Chemical Institute, Co.
200 mg Wkg did not possess the ability to suppress the (Osaka, Japan). The AGH inhibitory assay was done glucose production from carbohydrates through the according to our proposed immobilized AGH inhibition of AGH action in the gut.
(i AGH) assay system.11) The immobilization of AGHpartially puriˆed from rat acetone powder on CNBr- a-glucosidase; ‰avonoids; phenolic acids; activated Sepharose 4B (Pharmacia Biotech AB, Upsala, Sweden) were described in detail in our previous paper.11) In the i AGH assay, the i AGH sup-port (10 mg wet gel, 4.1 mU Wmg wet gel) was taken in To assess the prophylaxis of noninsulin-dependent an end-capped ASSIST Mini-column with 45–90 mm diabetes mellitus (NIDDM) disease by dietary food of polyethylene ˆlter (CC-07, 5 ml, ASSIST, Tokyo, intake, many natural resources have been examined Japan), and the assay was started after adding 100 ml with respect to the exertion of an a-glucosidase of inhibitor solution and 900 ml of the model intesti- (AGH, EC 3.2.1.20) or a-amylase inhibitory activi- nal ‰uid containing maltose (10 mM) or sucrose ty.1,2) The retardation of membrane-bound AGH (45 mM) to it. After incubation with a rotating culti- reaction3) and Wor inhibition of passive glucose trans- vator (4 rpm, RT-5, TAITEC, Saitama, Japan) at port4) would successfully ‰atten the postprandial C for 30 min (maltase assay) or 60 min (sucrase blood glucose excursions or reduce hyperglycemia. In assay), the reaction was stopped by ˆltration of the our studies on AGH inhibition by food compo- solution in the column. Maltase activity was meas- nents,5,6) acylated anthocyanins were found to cause ured by the liberated glucose from maltose in the the beneˆt of suppression of glucose production ˆltrate by Glucose-Test Wako (Wako Pure Chemical from dietary carbohydrates. To date, many studies Institute, Co., Osaka, Japan). When sucrose was † To whom correspondence should be addressed. Tel: 81-92-642-3012; Fax: 81-92-642-3012; E-mail: tmatsui＠agr.kyushu-u.ac.jp Abbreviations : AGH, a-glucosidase; noninsulin-dependent diabetes mellitus, NIDDM; BGL, blood glucose level used as a substrate, F-kit Glucose (Roche Diagnos-tics, Co., Tokyo, Japan) was used for measuring su-crase activity, since sucrose itself interfered with theglucose measurement by the Glucose-Test Wako.
The ‰avonoids assayed in this system were dissolvedin dimethylsulfoxide (DMSO). One unit of maltaseor sucrase activity was deˆned as the amount of en-zyme that hydrolyzed 1 mmol of substrate per min un-der the above assay conditions. The concentration ofAGH inhibitor required for inhibiting 50z of theAGH activity under these assay conditions wasdeˆned as the IC50 value. The animal experiments inSD rat were done as follows. Male 6-week-oldSprague-Dawley rats (SPF WVAF Crj:SD, Charles River Japan, Kanagawa) were fed a laboratory diet(CE-2, Clea Japan, Tokyo) and given water ad libi-tum. All rats were housed for 1 week at 21±19 AGH Inhibitory Activity of Flavonoids Estimated by the 55±5z humidity under controlled lighting from One mg of ‰avonoid per 1 ml of DMSO solution was put 8:30 to 20:30. Before the experiment, food was through the immobilized AGH assay. Maltase (open bars) and withheld for 16 h. A single oral administration of a sucrase (closed bars) inhibitory activities were evaluated by us- ‰avonoid sample via a stomach sonde was done in ing maltose (10 mM) and sucrose (45 mM) as substrates at 379C.
SD rats (n＝4, 238.7±4.3 g) with either a dosage of100 or 200 mg Wkg sample. The sample dissolved in 1 ml of DMSO was orally administered. After 5 min, of 23.2z: the IC50 value for luteolin, 2.3 mM; kaem- 2 g Wkg of substrate (maltose or sucrose) dissolved in pferol, 17.3 mM. However, the i AGH (maltase) inhi- 1 ml of deionized water was administered to each rat.
bition power of four ‰avonoids was much less than Control rats were administered with the same volume those of acarbose (IC50; 430 nM) and voglibose (IC50; of substrate solution without ‰avonoid. At each sam- 5.5 nM) as a therapeutic AGH inhibitor.11) ple time to 120 min, about 20 ml of blood sample was On the basis of the result that luteolin had the collected from the tail vein, then immediately the strongest i AGH (maltase) inhibitory activity among blood glucose level (BGL) was measured by a dispos- the four ‰avonoids (Fig. 1), changes in the BGL after able glucose sensor (Glutest Pro, Sanwa Chemical the administration of luteolin with maltose were exa- Research, Co., Tokyo, Japan). Each result for the mined in SD rats. Acarbose with the dose of 3 mg Wkg administration study is expressed as the mean of was used in this study as a positive control. As seen in BGL (mg Wdl)±SEM (z). Statistical diŠerences of Fig. 2, no dose-dependent and no signiˆcant change BGL in control (without ‰avonoid) and ‰avonoid in the BGL with the doses of 100 and 200 mg Wkg of groups at each administration time were evaluated by luteolin was observed against control SD rats ad- the unpaired Student's t-test. P valuesº0.05 were ministered maltose during the experimental period of considered to be signiˆcant. The care and treatment 120 min. The BGL of 200 mg-dose of luteolin at 0 h of the experimental rats conformed to Kyushu seems to be lower than other groups, but there was University guidelines for the ethical treatment of no signiˆcant diŠerence among the groups. On the other hand, acarbose showed a marked BGL reduc- Figure 1 shows the i AGH inhibition behavior of tion of 52.3 mg Wdl 30 min after administration four ‰avonoids, i.e., luteolin, kaempferol, chrysin, ( Pº0.01 vs. control). Thus, to elicit the postprandial and galangin at the ˆnal concentration of 0.1 mg Wml- BGL reduction by luteolin, a dosage of more than DMSO. For maltase inhibition, the eŠects were 200 mg Wkg (À0.17 molWrat body) would be needed.
observed in the descending order of potency of This strongly supported the ˆnding that luteolin was luteolinÀkaempferolÀchrysinÀgalangin.
a poor i AGH inhibitor with the IC50 of 2.3 mM ently, this suggested that the i AGH inhibition power against maltase (Fig. 1). Though data are not shown, was greatly aŠected by the replacement of hydroxyl the in vivo experiment of sucrose administration in groups at 3?- and 4?-position of the B-ring, not by the SD rats also showed no eŠect (BGL30min,control; diŠerence in the aglycone structure of ‰avone and 152.7±1.5 mg Wdl, BGL30min,luteolin; 154.0±2.0).
‰avonol. Sucrase inhibitions showed the same It has already been proved that the catechins typi- descending order as maltase inhibition, but their cal in tea polyphenols elicited potent sucrase inhibito- power was lower than maltase inhibition. Thus, the ry activity, in particular esteriˆed catechins such as ‰avonoids used in this study inhibited maltase in epigallocatechin gallate.2) Matsumoto et al.12) demon- preference to sucrase. Among them, luteolin was the strated the favorable BGL reduction at À10 mg dose strongest maltase inhibitor with the inhibitory ratio of catechin Wrat, following a signiˆcant suppression 1 W5400 lower than that of acarbose (Fig. 1).
Although their experimental results might be correctwithin the conventional baker's yeast AGH inhibito-ry assay system, the fact that the BGL in SD ratadministered luteolin was not suppressed (Fig. 2)supported the validity of the in vitro results from ourproposed i AGH assay system (Fig. 1).
In conclusion, it was found that luteolin did not possess an in vivo suppression eŠect on glucoseproduction from carbohydrates through AGH inhi-bition in the gut.
Part of this work was supported by a Grand-in Aid for Scientiˆc Research on Priority Areas from the EŠects of Luteolin on Blood Glucose Levels after Single Ministry of Education, Science, and Culture of Oral Administration of 2 g Wkg Maltose in SD Rats.
One ml of 100 (#) and 200 mg Wkg ($) luteolin was given to male 7-week-old SD rats. Acarbose () with the dose of3 mg Wkg was used as a positive control. After 5 min, 1 ml of 2 g Wkg of maltose solution was administered to each rat. Con- trol rats () were administered the same volume of substrate so- Watanabe, J., Kawabata, J., Kurihara, H., and Niki, lution without ‰avonoid. At each time to 120 min, about 20 ml R., Isolation and identiˆcation of a-glucosidase of blood samples were collected from the tail vein, the blood inhibitors from Tochu-cha. Biosci. Biotechnol.
glucose level was immediately measured by a disposable glucose sensor. Data are the mean (mg Wdl)±SEM. The signiˆcant diŠer- Honda, M. and Hara, Y., Inhibition of rat small ence versus control was examined with an unpaired Student's t-test (n intestinal sucrase and a-glucosidase activities by tea polyphenols. Biosci. Biotechnol. Biochem., 57,123–124 (1993).
Toeller, M., a-Glucosidase inhibitors in diabetes: of insulin secretion after administering 4 g of e‹cacy in NIDDM subjects. Eur. J. Clin. Invest., sucrose Wrat in Wistar rats. Catechins were also in- volved in an alternative function with respect to the Kobayashi, Y., Suzuki, M., Satsu, H., Arai, S., inhibition of transport activity of glucose transporter Hara, Y., Suzuki, K., Miyamoto, Y., and Shimizu, at the mucosal brush border membrane.4) Thus, both M., Green tea polyphenols inhibit the sodium-depen- functions of catechins would be presumable for dent glucose transporter of intestinal epithelial cellsby a competitive mechanism. J. Agric. Food Chem., preventing the hyperglycemia eŠect. In the case of ‰avone and ‰avonol, however, no potent anti-hyper- Matsui, T., Ueda, T., Oki, T., Sugita, K., Terahara, glycemia eŠects through the inhibition of AGH were N., and Matsumoto, K., a-Glucosidase inhibitory observed in the i AGH inhibitory assay (Fig. 1) and in action of natural acylated anthocyanins. 1. Survey of vivo SD rat study (Fig. 2). Even an excessive dose natural pigments with potent inhibitory activity. J.
(200 mg Wkg) of luteolin that showed a weak iAGH Agric. Food Chem., 49, 1948–1951 (2001).
(maltase) inhibitory activity (IC50; 2.3 mM) did not Matsui, T., Ueda, T., Oki, T., Sugita, K., Terahara, aŠect the in vivo BGL. These ˆndings strongly N., and Matsumoto, K., a-Glucosidase inhibitory demonstrated that the ‰avonoids used in this study action of natural acylated anthocyanins. 2. a-Glucosi- had poor ability to delay or inhibit the production of dase inhibition by isolated acylated anthocyanins. J.
glucose from carbohydrates in the gut.
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Wang, H., Nair, M. G., Strasburg, G. M., Booren, Contrary to our negative results against AGH inhi- A. M., and Gray, J. I., Antioxidant polyphenols bition by ‰avonoids, Kim et al.13) reported the potent from tart cherries ( Prunus cerasus). J. Agric. Food in vitro eŠectiveness of luteolin on the inhibition of AGH and a-amylase rather than acarbose as a ther- Peterson, J. and Dwyer, J., Flavonoids-dietary apeutic drug. However, we thought that they ob- occurrence and biochemical activity. Nutr. Res., 18, tained erroneous results, because AGH inhibitory action varied with its origins14) and the extent to Miyake, Y., Kuzuya, K., Ueno, C., Katayama, N., which AGH was inhibited was largely in‰uenced by Hayakawa, T., Tsuge, H., and Osawa, T., Suppres- its membrane-bound state or not,11) as we have sive eŠect of components in lemon juice on blood already reported in our previous papers. As a result pressure in spontaneously hypertensive rats. Food of i AGH assay of luteolin, the magnitude of maltase Sci. Technol. Int. Tokyo, 4, 29–32 (1998).
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H., and Hara, Y., Reduction of blood glucose levels

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