Self-assembled short peptides have intrigued scientists due to the convenience of synthesis, good biocompatibility, low toxicity, inherent biodegradability and fast response to change in the physiological environment. Therefore, it is necessary to present a comprehensive summary of the recent advances in the last decade regarding the construction, route of administration and application of self-assembled short peptides based on the knowledge on their unique and specific ability of self-assembly. Herein, we firstly explored the molecular mechanisms of self-assembly of short peptides, such as non-modified amino acids, as well as Fmoc-modified, N-functionalized, and C-functionalized peptides. Next, cell penetration, fusion, and peptide targeting in peptide-based drug delivery were characterized. Then, the common administration routes and the potential pharmaceutical applications (drug delivery, antibacterial activity, stabilizers, imaging agents, and applications in bioengineering) of peptide drugs were respectively summarized. Last but not least, some general conclusions and future perspectives in the relevant fields were briefly listed. Although with certain challenges, great opportunities are offered by self-assembled short peptides to the fascinating area of drug development.

Nanocrystals (NCs), a colloidal dispersion system formulated with stabilizers, have attracted widespread interest due to their ability to effectively improve the oral bioavailability of poorly water-soluble drugs. The stabilizer plays a key role because it can affect the physical stability and even the oral bioavailability of NCs. However, how stabilizers affect the bioavailability of NCs remains unknown. In this study, F68, F127, HPMC, and PVP were each used as a stabilizer to formulate naringenin NCs. The NCs formulated with PVP exhibited excellent release behaviors, cellular uptake, permeability, oral bioavailability, and anti-inflammatory effects. The underlying mechanism is that PVP effectively inhibits the formation of naringenin dimer, which in turn improves the physical stability of the supersaturated solution generated when NC is dissolved. This finding provides insights into the effects of stabilizers on the in vivo performances of NCs and supplies valuable knowledge for the development of poorly water-soluble drugs.

Nanocrystals (NCs) have been widely recognized as an available policy for the formulation of long-acting injections for insoluble drugs. Stabilizers are extremely important for the physical stability of NCs because they can reduce the surface free energy of the system. However, whether stabilizers can affect the in vivo performances of long-acting injectable NCs is unclear. In this study, three celecoxib (CXB) NCs formulated with different stabilizers (PVP K17, TPGS, and F68) were successfully developed by the wet milling method. Among the formulations, CXB-NCs/PVP K17 had a lower dissolution rate. More importantly, CXB-NCs/PVP K17 did not show burst release after intramuscular (i.m.) injection to rats, and it had a strong analgesic effect. These results showed that the stabilizers played a key role in the in vivo behaviors of long-acting injectable NCs. This strongly suggested that the burst release could be avoided by alteration of stabilizers of NCs by i.m. injection.

In this study, to improve the quality of a live attenuated vaccine for duck viral hepatitis (DHV), the lyophilization of a heat-resistant duck hepatitis virus vaccine was optimized. The optimized heat protectors were made of 10% sucrose, 1.2% pullulan, 0.5% PVP, and 1% arginine, etc., with a titer freeze-drying loss of ≤0.50 Lg. The vaccine product\'s valence measurements demonstrated the following: the vaccine could be stored at 2-8 °C for 18 months with a virus titer loss ≤0.91 Lg; at 37 °C for 10 days with a virus valence loss ≤0.89 Lg; and at 45 °C for 3 days with a virus titer loss ≤0.90 Lg. Regarding safety, no deaths occurred in two-day-old ducklings immunized with a 10 times dose vaccine; their energy, diet, and weight gain were all normal, demonstrating that the DHV heat-resistant vaccines were safe for ducklings and did not cause any immune side effects. Duck viral hepatitis freeze-dried vaccine began to produce antibodies at 7 d after immunization, reached above 5.0 on 14 d, and reached above 7.0 on 21 d, showing a continuous upward trend. This indicates that duck viral hepatitis vaccine has a good immunogen level. The optimization of the freeze-drying process saves costs and also improves the quality of the freeze-drying products, which provides important theoretical and technical support for the further study of vaccine products.

The starch-palmitic acid complex nanoparticles were prepared by Cyperus esculentus starch with enzymatic hydrolysis for different times and then complexed with palmitic acid. The FACE and 13C CP/MAS NMR analysis showed that there were more amylose molecules formed and complexed with palmitic acid when starch was treated by enzymatic hydrolysis for 4 h. With the enzymatic hydrolysis time increasing from 0 h to 4 h, the mean size of starch-palmitic acid complex nanoparticles increased from 500 ± 38.83 nm to 567.2 ± 22.32 nm, the size distribution became more uniform, and the crystallinity increased from 14.99% to 47.72%. The starch-palmitic acid complex nanoparticles could be used as a kind of stabilizers to stabilize Pickering emulsions. Rheological properties and storage stability of Pickering emulsions indicted that starch-palmitic acid complex nanoparticles can better stabilize. The starch-palmitic acid complex nanoparticles could be used as stabilizer of Pickering emulsion and encapsulation of bioactive compounds.

Transthyretin (TTR) is associated with several human amyloid diseases. Various kinetic stabilizers have been developed to inhibit the dissociation of TTR tetramer and the formation of amyloid fibrils. Most of them are bisaryl derivatives, natural flavonoids, crown ethers and carborans. In this review article, we focus on TTR tetramer stabilizers, genetic therapeutic approaches and fibril remodelers. The binding modes of typical bisaryl derivatives, natural flavonoids, crown ethers and carborans are discussed. Based on knowledge of the binding of thyroxine to TTR tetramer, many stabilizers have been screened to dock into the thyroxine binding sites, leading to TTR tetramer stabilization. Particularly, those stabilizers with unique binding profiles have shown great potential in developing the therapeutic management of TTR amyloidogenesis.

The heat-stable live-attenuated classical swine fever virus (CSFV) vaccine is an urgent need in many countries of Asia, Europe and Latin America. In this study, the thermostability of lyophilized live-attenuated CSFV vaccine formulations were investigated using accelerated stability at 37 °C for 10 days. The freeze-dried heat-stable formulation ST16, containing excipient combinations of trehalose, glycine, thiourea and phosphate buffer shows the superior thermostability. Moreover, the lyophilized vaccine with formula ST16 kept loss of viral activity less than 0.5 log10 during 24 months at storage temperatures of 2-8 °C. In thermal study, ST16 stabilized the vaccine within 1.0 log10 loss after storage at up to 25 °C for 6 months and room temperature for 7 months. Even under the harshest storage conditions of 37 °C for 25 days and 45 °C for 2 weeks, the virus titer dropped less than 1.0 log10 using ST16. Besides, it is notable that ST16 excluded gelatin and exogenous proteins, which might cause allergic reactions, thus avoiding immune side effects. The vaccine formulated ST16 proved to be safe and effective when immunized to piglets in vivo. The characteristics of dried vaccines were analyzed by X-ray powder diffraction, residual water measurements, differential scanning calorimetry and it was found that vaccine antigen were preserved in an amorphous matrix with high glass transition temperature above 60 °C and low residual water content below 2%, which made the vaccine more stable during storage.

Conventional cancer therapeutics has enormous toxicity and severe side effects that generate multi-drug resistance. Therefore, an urgent need exists for new alternative therapeutic agents for cancer treatment. Cepharanthin (CEP) has anti-cancer potential but has poor aqueous solubility, which limits its clinical use. Nanosuspensions (NS) are attractive as insoluble drug delivery systems.
In this study, we used D-alpha Tocopherol acid Polyethylene Glycol Succinate (TPGS), Polyvinylpyrrolidone (PVP) VA64, and Croscamellose Sodium (CCS) as stabilizers to produce TPGS-CEP-NS, PVP VA64-CEP-NS, and CCS-CEP-NS by wet-milling technology, and then characterized the NS and evaluated their functional activities in vitro.
CEP Nanosuspensions (CEP-NS) were prepared by the wet-milling method. The prepared NS were characterized by particle size distribution, zeta potential, morphology, surface properties, and molecular interactions. The NS were evaluated for their effects on HepG2 cells in vitro. The evaluations included assessment of cellular cytotoxicity, cellular apoptosis, NS uptake by cells, and mitochondrial membrane potential changes.
CEP-NS showed an appropriate particle size and were physically stable. All CEP-NS exhibited HepG2 enhanced anti-proliferative effects by reducing cell viability, enhanced cellular uptake, induced cellular apoptosis, and mitochondrial membrane potential loss.
CEP-NS may be effective therapeutic agents for the treatment of hepatocellular carcinoma.

Tea saponins (TS), a novel multifunctional stabilizer, were explored to stabilize the nanosuspensions. The purpose of this study was to investigate the effect of TS on the stability and redispersibility of nanosuspensions. In present work, hesperidin (HDN), a poorly soluble drug, was used as a model drug. HDN nanosuspensions (HDN-NS) with particle size of 250-270 nm were prepared by high-speed shearing and high-pressure homogenization. The zeta potential of HDN-NS was -23.16 ± 1.12 mV. Compared with traditional stabilizers, TS were superior in stabilization efficiency at low concentrations. Nanosuspensions freeze-dried powder using TS and lactose as cryoprotectants had good redispersibility, and the average particle size was 266.5 ± 9.0 nm after reconstitution. TS and lactose can effectively prevent the irreversible agglomeration of HDN-NS during freeze-drying. The dissolution was enhanced owing to particle size reduction. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) results showed that HDN nanocrystals were irregularly lumpy. The chemical structure and crystal state of HDN had not significantly changed during production. In conclusion, TS have the potential to stabilize and disperse nanosuspensions and provide a promising strategy for the development of poorly soluble drugs.

The nitrate esters are important components of double-base propellants. Aromatic amines are recommended as the stabilizers to delay the decomposition of nitrate esters and increase their storage time. The decomposition mechanisms of alkyl, alkoxy dinitrate, and poly-fluoride nitrate esters and the stabilizing effect of aromatic amines including new designed phenols are studied at the level of B3LYP/6-31G**. Alkyl and alkoxyl dinitrate esters are likely to be transformed by hydrogen abstraction, which is consistent with that of mononitrate and trinitrate esters. However, for poly-fluoride nitrate esters, NO2 catalyzed self-decomposition is preferred. In addition, comparing with mononitrate and trinitrate esters, the order of their stability is mononitrates > dinitrates > trinitrates. Poly-fluoride nitrate esters have a poorer stability than non-fluorinated nitrate esters. Comparing with parent nitrate esters, the stability of new designed poly-fluoride oxygen-containing nitrate esters is slightly improved. Aromatic amines including new designed phenols are effective stabilizers of nitrate esters, especially when introduced hydroxyl in the para position, can enhance the effects of stabilizers. The rate constants for the decomposition of nitrate esters and the bimolecular reaction between stabilizers and NO2 are calculated by using traditional transition state theory. Graphical abstractComparison between the reaction energy barrier of nitrate esters and stabilizers with NO2.