title: Characterization of inhibitors of postprandial hyperglycemia from the leaves of Nerium indicum.
abstract: Nerium indicum is an India-Pakistan-originated shrub belonging to the oleander family. The ingestion of leaves of N. indicum before a meal is known to effect the lowering of postprandial glucose levels in Type II diabetic patients and this plant is now used as a folk remedy for Type II diabetes in some regions of Pakistan. In the present study, the hot-water extract of N. indicum leaves was found to reduce the postprandial rise in the blood glucose when maltose or sucrose was loaded in rats. It was also found that the extract strongly inhibited alpha-glucosidase, suggesting that the suppression of the postprandial rise in the blood glucose is due to the occurrence of some inhibitors of alpha-glucosidase in the leaves. We, therefore, tried to isolate the active principles from the leaf extract, using alpha-glucosidase-inhibitory activity as the index. Employing Sephadex G-15, silica gel and reversed-phase HPLC, we isolated two active compounds. The UV, mass and NMR spectrometric analyses established that the chemical structures of these compounds are 3-O-caffeoylquinic acid (chlorogenic acid) and its structural isomer, 5-O-caffeoylquinic acid. Both compounds were shown to inhibit alpha-glucosidases in a non-competitive manner. The authentic chlorogenic acid was found to suppress the postprandial rise in the blood glucose in rats and also inhibited the absorption of the glucose moiety from maltose and glucose in the everted gut sac system prepared from rat intestine. These results demonstrate that chlorogenic acid is one of the major anti-hyperglycemic principles present in the leaves of N. indicum. Furthermore, among polyphenol compounds tested, quercetin and catechins were shown to have strong inhibitory activity against alpha-glucosidase.
authors.affiliation: Department of Nutritional Science, Okayama Prefectural University, Soja, Okayama 719-1197, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Ishikawa
authors.forename: Hiromi
authors.initials: H
authors.lastname: Yamashita
authors.forename: Miki
authors.initials: M
authors.lastname: Hiemori
authors.forename: Eiko
authors.initials: E
authors.lastname: Inagaki
authors.forename: Masumi
authors.initials: M
authors.lastname: Kimoto
authors.forename: Masahiko
authors.initials: M
authors.lastname: Okamoto
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tsuji
authors.forename: Allah Nawaz
authors.initials: AN
authors.lastname: Memon
authors.forename: Alli
authors.initials: A
authors.lastname: Mohammadio
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Natori
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000187:drug effects; D002726:Chlorogenic Acid / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006943:Hyperglycemia / Q000517:prevention & control*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D008320:Maltose / Q000008:administration & dosage; D013058:Mass Spectrometry / Q000379:methods; D030007:Nerium / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology; D018515:Plant Leaves / Q000737:chemistry*; D019518:Postprandial Period; D051381:Rats; D017207:Rats, Sprague-Dawley; D013395:Sucrose / Q000008:administration & dosage; D013997:Time Factors; D000520:alpha-Glucosidases / Q000187:drug effects
chemical_list: D001786:Blood Glucose; D010936:Plant Extracts; D002726:Chlorogenic Acid; D013395:Sucrose; D008320:Maltose; D000520:alpha-Glucosidases