Stabilization of Deformable Nanovesicles Based on Insulin-Phospholipid Complex by Freeze-Drying

Abstract

Deformable nanovesicles have been extensively investigated due to their excellent ability to penetrate biological barriers. However, suffering from serious physical and chemical instabilities, the wide use of deformable nanovesicles in medical applications is still limited. Moreover, far less work has been done to pursue the lyophilization of deformable nanovesicles. Here, we aimed to obtain stable deformable nanovesicles via freeze-drying technology and to uncover the underlying protection mechanisms. Firstly, the density of nanovesicles before freeze-drying, the effect of different kinds of cryoprotectants, and the types of different reconstituted solvents after lyophilization were investigated in detail to obtain stable deformable nanovesicles based on insulin-phospholipid complex (IPC-DNVs). To further investigate the underlying protection mechanisms, we performed a variety of analyses. We found that deformable nanovesicles at a low density containing 8% lactose and trehalose in a ratio of 1:4 (8%-L-T) have a spherical shape, smooth surface morphology in the lyophilized state, a whorl-like structure, high entrapment efficiency, and deformability after reconstitution. Importantly, the integrity of IPC, as well as the secondary structure of insulin, were well protected. Accelerated stability studies demonstrated that 8%-L-T remained highly stable during storage for 6 months at 25 °C. Based on in vivo results, lyophilized IPC-DNVs retained their bioactivity and had good efficacy. Given the convenience of preparation and long term stability, the use of combined cryoprotectants in a proper ratio to protect stable nanovesicles indicates strong potential for industrial production.

Development, Characterization, and Ex Vivo Assessment of Elastic Liposomes for Enhancing the Buccal Delivery of Insulin

“…Therefore, specific nanocarrier vesicles, surface-modified liposomes, or ultra-deformable liposomes are required to enhance the permeability of peptide drugs across alternative routes [ 19 , 20 ]. Recently, the use of ultra-deformable liposomes has gained popularity, owing to the special characteristics of the carrier system, that is, being able to squeeze and penetrate through the membrane barrier prior to releasing the drug into the systemic circulation [ 21 ]. These liposomes are also referred to as flexible vesicles or elastic liposomes.…”

“…Owing to the presence of edge activators, such as Tween 80, Tween 20, Span 80, Span 20, and bile salts, these elastic liposomes can undergo deformation and reformation during penetration across biomembranes [ 22 , 23 ]. In addition, bile salts are bioinspired and biomimetic edge activators, that is, they can destabilize the lipid bilayers of the vesicular system [ 21 , 24 ]. Recently, several approaches have been studied using bile salts to facilitate the transportation of peptides across the buccal membrane [ 5 , 8 ].…”

Factors affecting the buccal delivery of deformable nanovesicles based on insulin–phospholipid complex: an in vivo investigation

“…In this study, a series of IPC-DNVs (Xu et al., 2018 ) and lyophilized IPC-DNVs (Xu et al., 2019 ), were prepared to study the factors that influence buccal drug delivery. In our initial design, we considered obtaining IPC-DNVs, with different drug concentrations and sizes, by changing the hydration volume and ultrasonic power or time, respectively.…”

“…To obtain IPC-DNVs with different drug concentrations and sizes, lyophilized IPC-DNVs were prepared using the freeze-drying technology, as described in our previous study (Xu et al., 2019 ). Briefly, 8% cryoprotectant (lactose and trehalose in a 1:4 ratio) was dissolved in PBS, and 0.5 mL solution of IPC-DNVs was diluted to 1 mL with PBS.…”

“…Additionally, freeze-drying technology was used to fabricate lyophilized IPC-DNVs, using lactose and trehalose (1:4) as the protective agents. The freeze-dried sample could be stored under 25 °C for more than 6 months and had a relative pharmacological bioavailability of 14.49% (Xu et al., 2019 ). In this study, we aimed to evaluate the buccal delivery characteristics of IPC-DNVs in vivo and provide support for dosage form design and administration methods for buccal delivery system of DNVs.…”