Optimized vinpocetine-loaded vitamin E D-α-tocopherol polyethylene glycol 1000 succinate-alpha lipoic acid micelles as a potential transdermal drug delivery system: in vitro and ex vivo studies

Figures & data

Table 1 Independent and dependent variables of VNP-TPGS-ALA transdermal film formulations in Box–Behnken design

Independent variables	Unit	Levels
		−1	0	1
ALA in TPGS (X1)	%	0	15	30
Citral concentration (X2)	%	1	2	3
PG concentration (X3)	%	1	3	5
Dependent variables	Unit	Constraints
		Low	High	Goal
Elongation percent (Y1)	%	5	140	72.5
Initial permeation after 2 hours (Y2)	%	10.24	30.36	20.3
Cumulative permeation after 24 hours (Y3)	%	57.72	97.29	77.5

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.

Table 2 Composition of VNP-TPGS-ALA transdermal film formulations and their observed responses

Runs	X1	X2	X3	Y1*	Y2*	Y3*
	(%)	(%)	(%)	(%)	(%)	(%)
1	15.0	1.0	5.0	125.0	20.89	71.85
2	0.0	2.0	5.0	130.0	22.3	92.15
3	15.0	1.0	1.0	25.0	14.86	66.43
4	15.0	3.0	1.0	5.0	19.67	73.1
5	15.0	2.0	3.0	95.0	17.9	80.89
6	30.0	2.0	1.0	20.0	11.84	64.41
7	15.0	2.0	3.0	90.0	17.72	78.96
8	0.0	1.0	3.0	85.0	21.58	86.65
9	15.0	3.0	5.0	140.0	18.44	89.66
10	0.0	3.0	3.0	110.0	30.36	97.29
11	30.0	1.0	3.0	95.0	10.24	57.72
12	30.0	2.0	5.0	125.0	14.1	64.69
13	15.0	2.0	3.0	95.0	17.67	77.85
14	30.0	3.0	3.0	115.0	12.3	66.21
15	0.0	2.0	1.0	10.0	19.39	88.15

Notes:

* The observed values of Y₁, Y₂, and Y₃ represent the means of three determinations; SDs were <5% of the mean and thus are omitted from the table. X₁: ALA in TPGS; X₂: citral concentration; X₃: PG concentration; Y₁: elongation percent; Y₂: initial permeation after 2 hours; and Y₃: cumulative permeation after 24 hours.

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.

Figure 1 Particle size distribution measured by particle size analyzer (A) and TEM photomicrographs of VNP-TPGS-ALA micelles (B).

Abbreviations: ALA, alpha lipoic acid; TEM, transmission electron microscopy; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.

Figure 2 Ex vivo permeation profile of VNP-TPGS-ALA transdermal patch formulations: F1–F5 (A); F6–F10 (B); and F11–F15 (C).

Abbreviations: ALA, alpha lipoic acid; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.

Figure 3 Standard Pareto charts revealing the significance of the independent variables (X₁, X₂, and X₃) and their combined effects on the investigated dependent variables Y₁ (A), Y₂ (B), and Y₃ (C).

Notes: X₁: ALA in TPGS; X₂: citral concentration; X₃: PG concentration; Y₁: elongation percent; Y₂: initial permeation after 2 hours; and Y₃: cumulative permeation after 24 hours.

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate.

Figure 4 Three-dimensional response surface plots showing the effects of the independent variables X₁ and X₂ at midpoint of X₃ on the investigated dependent variables Y₁ (A and B), Y₂ (C), and Y₃ (D–F).

Notes: X₁: ALA in TPGS; X₂: citral concentration; X₃: PG concentration; Y₁: elongation percent; Y₂: initial permeation after 2 hours; and Y₃: cumulative permeation after 24 hours.

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate; VNP, vinpocetine.

Table 3 Estimated effects of factors and associated P-values for dependent variables (Y₁, Y₂, and Y₃)

Factors	Response
	Y1		Y2		Y3
	Estimated effect	P-value	Estimated effect	P-value	Estimated effect	P-value
X1	5.0	0.4391	−11.2875	0.0015*	−27.8025	0.0001*
X2	10.0	0.1537	3.3	0.1259	10.9025	0.0061*
X3	115.0	0.0000*	2.4925	0.2243	6.565	0.0405*
${\mathrm{X}}_1^2$	5.41667	0.5634	−0.700833	0.8017	−0.175833	0.9621
X1X2	−2.5	0.7784	−3.36	0.2436	−1.075	0.7634
X1X3	−7.5	0.4137	−0.325	0.9033	−1.86	0.6060
${\mathrm{X}}_2^2$	10.4167	0.2878	2.41417	0.4035	−4.35583	0.2708
X2X3	17.5	0.0921	−3.63	0.2128	5.57	0.1604
${\mathrm{X}}_3^2$	−49.5833	0.0024*	−1.01083	0.7182	−3.59083	0.3544
R^2	98.8172		90.8485		97.1272
Adj. R^2	96.6882		74.3758		91.9562
SEE	8.41625		2.54266		3.38154
MAE	4.11111		1.21089		1.69456

Notes:

* Significant effect of factors on individual dependent variables. X₁: ALA in TPGS; X₂: citral concentration; X₃: PG concentration; Y₁: elongation percent; Y₂: initial permeation after 2 hours; Y₃: cumulative permeation after 24 hours. R²: coefficient of determination; Adj. R²: coefficient of determination adjusted for degrees of freedom; MAE: mean absolute error; SEE: standard error of estimate.

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate.

Table 4 Optimal calculated variables and observed, predicted, and residual values for responses

Independent variables	Optimum	Dependent variables	Predicted	Observed	Residual
ALA in TPGS (%)	16.62	Elongation percent (%)	72.5	75.69	3.19
Citral concentration (%)	3.0	Initial permeation after 2 hours (%)	19.98	18.89	1.09
PG concentration (%)	2.18	Cumulative permeation after 24 hours (%)	78.2	74.74	3.46

Abbreviations: ALA, alpha lipoic acid; PG, propylene glycol; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate.

Figure 5 Visualization of skin penetration of the optimized TPGS-ALA-loaded transdermal (left column) and control (right column) films after 0.5, 2, and 4 hours using fluorescence laser microscope (magnification 400×).

Abbreviations: ALA, alpha lipoic acid; TPGS, D-α-tocopherol polyethylene glycol 1000 succinate.