Washingtonia filifera seed extracts inhibit the islet amyloid polypeptide fibrils formations and α-amylase and α-glucosidase activity

Figures & data

Table 1. IC₅₀ values of the aqueous (AE), ethanolic (EE) and methanolic (ME) extracts from W. filifera collected in the areas of Sousse (S) and Gabès (G) against α-glucosidase and α-amylase.

Extracts	IC50 µg/mL	IC50 µg/mL
	α-glucosidase	α-amylase
EEG	1.54 ± 0.11^a	11.33 ± 1.99^a
EES	0.72 ± 0.41^a	3.73 ± 0.45^b
MEG	0.53 ± 0.014^a	6.75 ± 0.11^b,c
MES	0.88 ± 0.028^a	2.39 ± 0.23^b
AEG	1.63 ± 0.23^a	48.32 ± 1.32^d
AES	0.82 ± 0.085^a	25.82 ± 0.13^d
Acarbose	90 ± 7.3^b	8.04 ± 0.65^a,c

Mean values in the same column having different letters are significantly different (p < 0.05).

Figure 1. Inhibition of α-glucosidase enzyme. Lineweaver–Burk plots analysis of EEG (a) and MEG (b).

Table 2. Enzyme kinetics parameters following α-glucosidase and α-amylase with different W. filifera seed extracts.

	KI µg/mL	KIS µg/mL	Inhibition type
		α-glucosidase
EEG	0.08	–	Competitive
EES	0.22	0.41	Mixed
MEG	0.08	1.8	Mixed
MES	0.03	0.48	Mixed
AEG	0.07	0.41	Mixed
AES	0.31	1.74	Mixed
		α-amylase
EES	–	2.47	Uncompetitive
MES	–	3.66	Uncompetitive

Figure 2. Inhibition of α-amylase enzyme. Lineweaver–Burk plots analysis of EES (a) and MES (b).

Figure 3. Thioflavin T fluorescence emission plot corresponding to β-sheet formation of IAPP in the presence of W. filifera methanolic seeds extract from Sousse.

Figure 4. Congo red and Electron microscopy analyses of the material recovered after ThT analysis. In (a), amyloid exhibiting green birefringence after Congo red staining and (b) long unbranched amyloid fibrils are present in solution of IAPP 40 µg/mL. In (c), no Congophilc material can be detected and in (d) an amorphous material is present in solution containing IAPP 40 µg/mL with MES 200 µg/mL. Samples in a and c are stained with Congo red and samples in b and d are negatively contrasted with 2% Uranyl acetate in 50% ethanol.

Table 3. Binding energies of against IAPP, α-amylase and α-glucosidase.

	IAPP	α-amylase	α-glucosidase
Catechin	−6.9 kcal/mol	−7.1 kcal/mol	−8.1 kcal/mol
Protocatechuic acid	−4.9 kcal/mol	−5.5 kcal/mol	−5.3 kcal/mol
p-Hydroxybenzoic acid	−4.5 kcal/mol	−5.2 kcal/mol	−5.2 kcal/mol
B type Procyanidin dimer	−7.8 kcal/mol	−8.5 kcal/mol	−4.9 kcal/mol

Table 4. Physicochemical properties of bioactive compounds in the investigated extracts.

	Molecular formula	Molecular Weight (g/mol)	Rotatable bonds	H-bond acceptor atoms	H-bond donor atoms	Polar surface area (Å^2)	LogPo/w	Water solubility
Catechin	C15H14O6	290.27	1	6	5	110.38	0.85	Soluble
Epicatechin	C15H14O6	290.27	1	6	5	110.38	0.85	Soluble
Protocatechuic acid	C7H6O4	154.12	1	4	3	77.76	0.65	Soluble
p-Hydroxybenzoic acid	C7H6O3	138.12	1	3	2	57.53	1.05	Soluble
Procyanidin B-type	C30H26O12	578.52	3	12	10	220.76	1.37	Soluble
Procyanidin A-type	C30H24O12	576.50	2	12	9	209.76	1.61	Moderately
Quercetin-3-O-glucoside	C21H20O12	464.38	4	12	8	210.51	−0.27	Soluble
Dihydrokaempferol 7-glucoside	C21H22O11	450.39	4	11	7	186.37	−0.48	Soluble