Preparation and evaluation of a self-nanoemulsifying drug delivery system loaded with Akebia saponin D–phospholipid complex

Figures & data

Figure 1 The structure of ASD.

Abbreviation: ASD, Akebia saponin D.

Table 1 Experimental arrangement of formulations

Excipient	Formulation (%, w/w)
	1	2	3	4	5	6
Peceol (Glyceryl monooleate [type 40])	20	20	20	20	20	20
Cremophor^® EL (Polyoxyl 35 castor oil)	52	58.5	62.4	–	–	–
Cremophor^® RH 40 (Polyoxyl 40 hydrogenated castor oil)	–	–	–	52	58.5	62.4
Transcutol HP (Diethylene glycol monoethyl ether)	26	19.5	15.6	26	19.5	15.6
Grade	I	I	I	II	II	II

Table 2 Visual assessment of efficiency of self-emulsification

Grade	Dispersibility and appearance	Time of self-emulsification (minutes)
I	Rapidly forming nanoemulsion which is clear or slightly bluish in appearance	<1
II	Rapidly forming, slightly less clear emulsion which has a bluish white appearance	<2
III	Bright white emulsion (similar to milk in appearance)	<3
IV	Dull, grayish white emulsion with a slight oily appearance that is slow to emulsify	>3
V	Exhibits poor or minimal emulsification with large oil droplets present on the surface	>3

Figure 2 Infrared spectra.

Notes: (A) ASD. (B) Phospholipids. (C) Physical mixture of ASD and phospholipids. (D) APC.

Abbreviations: ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex.

Figure 3 DSC thermograms.

Notes: (A) ASD. (B) Phospholipids. (C) Physical mixture of ASD and phospholipids. (D) APC.

Abbreviations: DSC, differential scanning calorimetry; ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex; Exo, exothermic.

Figure 4 Scanning electron micrographs.

Notes: (A) ASD (×500 magnification). (B) APC (×500 magnification).

Abbreviations: ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex.

Table 3 Solubility of ASD, physical mixture, and APC in water and n-octanol (n=3)

Sample	Solubility in water (mg/mL)	Solubility in n-octanol (mg/mL)
ASD	10.70±0.51	2.38±0.12
Physical mixture	4.36±0.20	2.84±0.36
APC	20.96±1.21	29.58±1.69

Abbreviations: ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex.

Figure 5 Solubility of APC in various carriers.

Notes: (A) Oils. (B) Surfactant and cosurfactant (n=3). PEG 400, Diethylene glycol monoethyl ether, and 1,2-propanediol were tested for surfactant. Polyoxyl 40 hydrogenated castor oil and Polyoxyl 35 castor oil were tested for cosurfactant.

Abbreviations: APC, Akebia saponin D–phospholipid complex; PEG 400, polyethylene glycol 400.

Table 4 Droplet size, polydispersity index, and zeta potential of SNEDDS formulations with different drug loading after dilution with distilled water at a ratio of 1:100

System	Drug loading (%)	Particle size, mean ± SD (nm)a	Percent polydispersity, mean ± SD (%)b	Zeta potential, mean ± SD (mV)
Peceol (Glyceryl monooleate [type 40])/	0	13.6±0.4	3.19	−28.5±1.3
Cremophor^® EL (Polyoxyl 35 castor oil)/	1	38.2±3.2	1.47	−26.2±1.45
Transcutol HP (Diethylene glycol monoethyl ether)/APC	2	84.7±1.1	0.576	−22.9±1.21
	3	120.6±0.6	0.436	−18.6±0.85
	4	148.0±2.7	0.378	−13.7±0.92
	5	256.0±3.1	0.273	−4.9±0.57

Notes:

a Reported as number-weighted size.

b Calculated by the following equation: (polydispersity/[mean hydrodynamic radius]) ×100%. Glyceryl monooleate (type 40)/Polyoxyl 35 castor oil/Diethylene glycol monoethyl ether =1:4.5:4.5 (w/w/w); n=3.

Abbreviations: SNEDDS, self-nanoemulsifying drug delivery system; SD, standard deviation; APC, Akebia saponin D–phospholipid complex.

Figure 6 Pseudoternary phase diagram of the SNEDDS formulation composed of Glyceryl monooleate (type 40), Polyoxyl 35 castor oil, Diethylene glycol monoethyl ether, and APC with a drug loading of 4%.

Abbreviations: SNEDDS, self-nanoemulsifying drug delivery system; APC, Akebia saponin D–phospholipid complex.

Figure 7 Transmission electron microscope image of APC-SNEDDS formulation (×12,000 magnification).

Note: The SNEDDS was composed of Peceol (Glyceryl monooleate [type 40]), Cremophor^® EL (Polyoxyl 35 castor oil), Transcutol HP (Diethylene glycol monoethyl ether), and APC with a drug loading of 4%.

Abbreviations: APC, Akebia saponin D–phospholipid complex; SNEDDS, self-nanoemulsifying drug delivery system.

Table 5 Effects of aqueous phase pH, dilution factor, and heating–cooling cycles on droplet size of APC-SNEDDS (mean ± SD, n=3)

Dilution factor	Water (nm)	pH 1.2 (nm)	pH 6.8 (nm)	After heating–cooling test
50	150.1±3.8	149.6±3.3	147.1±5.1	–
100	148.0±2.7	148.9±4.5	149.7±4.5	148.3±5.2
1,000	147.3±4.1	151.2±4.7	148.3±4.2	–

Abbreviations: APC, Akebia saponin D–phospholipid complex; SNEDDS, self-nanoemulsifying drug delivery system; SD, standard deviation.

Table 6 Bioavailability and pharmacokinetic parameters of ASD after oral administration of ASD, APC, and APC-SNEDDS (mean ± SD, n=6)

Parameter	ASD	APC	APC-SNEDDS
Cmax 1 (ng/mL)	437.2±174.2	342.3±154.2	733.4±203.8*,##
Cmax 2 (ng/mL)	180.5±75.1	549.7±113.5**	985.8±366.6**,#
Tmax 1 (hours)	2.0±1.1	0.195±0.068**	0.195±0.068**
Tmax 2 (hours)	9.8±2.4	8.0±1.1	6.667±0.82*,#
AUC0–36 h (ng·h/mL)	3,019.4±963.5	5,551.1±1,357.4**	13,038.4±5,121.7**,#
AUC0–∞ (ng·h/mL)	3,491.9±1,227.7	5,967.8±1,397.0**	13,528.1±5,468.3**,#
F (%)	–	183.8	431.8

Notes:

* P<0.05 and

** P<0.01 compared with ASD group.

# P<0.05 and

## P<0.01 compared with APC group.

Abbreviations: ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex; SNEDDS, self-nanoemulsifying drug delivery system; SD, standard deviation; C_max, maximum plasma concentration; T_max, time to maximum plasma concentration; AUC, the area under the plasma concentration–time curve; F, relative bioavailability.

Figure 8 Plasma concentration–time profiles of ASD after oral administration of ASD, APC, and APC-SNEDDS formulation at a dose of 90 mg/kg (mean ± SD, n=6).

Abbreviations: ASD, Akebia saponin D; APC, Akebia saponin D–phospholipid complex; SNEDDS, self-nanoemulsifying drug delivery system; SD, standard deviation.

Figure 9 Proposed schematic diagram of APC-SNEDDS dissolved in distilled water.

Abbreviations: APC, Akebia saponin D–phospholipid complex; SNEDDS, self-nanoemulsifying drug delivery system.