Effects of tuber storage protein of yam (Dioscorea alata cv. Tainong No. 1) and its peptic hydrolyzates on spontaneously hypertensive rats

Abstract

Yam storage protein (YSP) was purified from tubers of Dioscorea alata L. Tainong No. 1 (TN1) to homogeneity by DE-52 ion-exchange chromatography. The short-term (24 h) and long-term (25 days) antihypertensive effects of YSP-TN1 and its peptic hydrolyzates (PH-TN1) were measured in spontaneously hypertensive rats (SHRs). For 24-h antihypertensive measurements, SHRs (age 10 weeks, body weight from 240 to 250 g) were administered orally once (YSP-TN1 and PH-TN1, 40 mg kg −1 SHR) to measure the mean blood pressure (MBP), systolic blood pressure (SBP) and diastolic blood pressure (DBP). For a long-term antihypertensive measurement, SHRs (age 12 weeks, body weight from 250 to 270 g) were administered orally once a day for 25 days (YSP-TN1, 40 mg kg −1 SHR) to measure SBP, DBP and MBP. Captopril (10 or 15 mg kg −1 SHR) was used as a positive control. It was found that short-term administration of 40 mg kg −1 SHR of YSP-TN1 and PH-TN1 effectively lowered SHRs' MBP, SBP and DBP (For YSP-TN1, the lowest blood pressure was reached in the fourth hour and for PH-TN1 in the eighth hour). The lasting effects of PH-TN1 on reduced SHRs' BP were better than those of YSP-TN1 for one oral administration. For oral administration of 40 mg YSP-TN1 kg −1 SHR, the reduced MBP was 21.5 mmHg, which was comparable to 25.2 mmHg (the fourth hour) of 10 mg captopril kg −1 SHR oral administration. For oral administration of 40 mg PH-TN1 kg −1 SHR, the reduced MBP was 33.7 mmHg, comparable to 38.4 mmHg (the fourth hour) of 15 mg captopril kg −1 SHR. For long-term 25-day oral administration of 40 mg YSP-TN1 kg −1 SHR once a day, it was found that a feeding trial of YSP-TN1 effectively lowered SHRs' SBP, DBP and MBP. The greatest reduction in SHRs' blood pressure was reached on the ninth day, for the reduced SBP, 27.7 mmHg; for the reduced DBP, 28.3 mmHg; and for the reduced MBP, 27.5 mmHg.Keywords: antihypertension; diastolic blood pressure (DBP); means of blood pressure (MBP); peptic hydrolyzates; systolic blood pressure (SBP); spontaneously hypertensive rat (SHR); storage protein; yam INTRODUCTIONSeveral peptide-derived angiotensin-convertingenzyme (ACE) inhibitors have been used in the animal model of spontaneously hypertensive rats (SHRs) to evaluate the antihypertensive effects. [1][2][3][4][5][6][7][8][9][10][11] pointed out that three dipeptides, including AW (IC 50 = 18.8 µmol L −1 ), VW (IC 50 = 3.3 µmol L −1 ) and LW (IC 50 = 23.6 µmol L −1 ), were potential ACE inhibitory peptides. However, none of them were able effectively to reduce the blood pressure of SHRs in animal models. Fujita et al. 3 also found that the octapeptides of FFGRCVSP (IC 50 = 0.4 µmol L −1 ) and ERKIKVYL (IC 50 = 1.2 µmol L −1 ) were potent ACE inhibitors, but none of them were effective in animal models to reduce the blood pressure of SHRs.

Antihypertensive Properties of Plant Protein Derived Peptides

“…Among the tuber proteins, the in vivo antihypertensive effects of yam (Dioscorea alata) tuber proteins are the most studied. Lin and co-workers [122] purified storage proteins, dioscorins from yam tubers, that were digested with pepsin and evaluated for their antihypertensive effects in SHR. The maximum effect after single oral administration was observed after 4 h with the dioscorin isolate and after 8 h with the peptic hydrolysate, while the antihypertensive effect of the peptic digest was more pronounced (-33.7 mmHg Mean arterial pressure, MAP) and less transient than that of the dioscorin isolate (-21.5 mmHg MAP).…”

Effects of Different Types of Yam (Dioscorea alata) Products on the Blood Pressure of Spontaneously Hypertensive Rats

“…After being washed and peeled, the tubers were cut into pieces for storage protein purification, as described in previous reports. [11][12][13][14][15]17,18) The yam tubers were homogenized with 4 volumes (W/V) of 50 mM Tris-HCl buffer (pH 8.3). After centrifugation at 12;500 g for 30 min, the supernatants were saved and loaded directly onto a DE-52 ion exchange column.…”

“…The effects of orally-administered PYP-related and LYP-related products by feeding tube (2:0 Â 80 mm) on the blood pressure of SHRs were determined. 12,16,24,25) All the animal experimental procedures followed published guidelines.…”

“…The effects of orally-administered PYP-related and LYP-related products by feeding tube (2:0 Â 80 mm) on the blood pressure of SHRs were determined. 12,16,24,25) All the animal experimental procedures followed published guidelines.26) The male SHRs (8 weeks of age, National Laboratory Animal Center, Taipei, Taiwan) were housed individually in steel cages kept at 24 C under a 12-h light-dark cycle, and had free acess to a standard mouse/rat chow (Prolab Ò RMH2500, 5P14 Diet, PMI Nutrition International, Brentwood, MO) and water. The SHRs were randomly divided into control and sample treatments for blood pressure determinations (six rats per group).…”

“…We have reported that the purified storage protein, dioscorin, from yam tubers exhibited ACE inhibitory activity, 11) antihypertensive effects on SHRs, 12) antioxidant activity, 13,14) and immunomodulatory activity. 15) The results of our recent feeding trial revealed that instant food containing lyophilized yam powders had regulating effects on human blood pressure.…”