Preparation of exendin-4/PTD mixtures

To evaluate the nasal pharmacokinetic (PK) profile of exendin-4 in rats, we simply mixed it with the PTD (1:2 molar ratio) (Bae et al., 2018). One hundred microliters of exendin-4 (200 µM) were mixed with 100 µL of PTD (400 µM) in 10 mM phosphate buffer (pH 6.4). To evaluate biological activities of exendin-4 in type 2 db/db mice, exendin-4 (10 μM) was mixed with PTD (20 μM) in 10 mM phosphate buffer (pH 6.4) for nasal administration. The exendin-4/PTD mixtures were visually inspected to confirm cloudiness (turbidity) and precipitation. All exendin-4/PTD mixtures were clear.