Critical commentary on "The potential of a site-specific delivery of thiamine hydrochloride as a novel insect repellent exerting long-term protection on human skin: In-vitro, ex-vivo study and clinical assessment".

This letter comments on a recent article by Halawani et al. (10.1016/j.xphs.2021.07.017), which claimed a complex hydrogel formulation of thiamine nanospheres is a topical insect repellent. The authors did not thoroughly review the extensive prior literature on the subject that found no evidence of repellency for thiamine, and the experiment described lacked negative controls. Its results are not conclusive.

The Potential of a Site-Specific Delivery of Thiamine Hydrochloride as a Novel Insect Repellent Exerting Long-Term Protection on Human Skin: In-vitro, Ex-vivo Study and Clinical Assessment.

Thiamine hydrochloride (TH) was thought to exert a good insect repellent activity. The purpose of this work was to develop a formulation that releases TH in sustained regimen on human skin. Long lasting protection against mosquito bites was achieved. Pullulan acetate (PA) was used to prepare TH nanospheres. Optimal system was incorporated in Pluronic® hydrogel. Formulae were tested for in-vitro release and ex-vivo permeation. Complete protection time (CPT) was done adopting Kaplan-Meier survival function for the synthetic repellent (DEET), TH solution and nanospheres in hydrogel. Release profile of TH solution, nanospheres and nanosphere-loaded hydrogel (DG) demonstrated an added effect of DG, where t 1/2 was 11.2 ± 1.4 h. SEM for DG showed homogenous dispersion of nanospheres inside the matrix of the gel. Ex-vivo permeation showed only 0.761 ± 0.04% of TH in hydrogel permeated the skin after 12 h, while 44.98 ± 3.2% permeated when TH solution was applied. Clinical study revealed a significant difference in CPT between TH solution with either DEET or (DG) (p<0.05), and no significant difference between DEET and DG with CPT 400 ± 31 and 360 ± 18 min, respectively (P > 0.05). The high efficacy of TH-loaded hydrogel rendered it a successful alternative for DEET, offering long protection against mosquito bites.

Effect of inhibitors of endocytosis and NF-kB signal pathway on folate-conjugated nanoparticle endocytosis by rat Kupffer cells.

The regular accumulation of nanoparticles in the liver makes them hepatotoxic and decreases the circulation time, thus reducing their therapeutic effect. Resolving this problem will be significant in improving bioavailability and reducing side effects. In this study, we reduced the phagocytosis of epirubicin (EPI)-loaded folic acid-conjugated pullulan acetate (FPA/EPI) nanoparticles by Kupffer cells (KCs) through internalization and nuclear factor kappa B (NF-kB) signal pathway inhibitors, thus allowing development of FPA/EPI nanoparticles as a nanodrug delivery system (NDDS) based on our previous study. FPA/EPI nanoparticles were prepared by the dialysis method. Rat KCs were preincubated with the following individual or compound inhibitors: chlorpromazine (CPZ), nystatin (NY), colchicine (Col), amiloride (AMR), and pyrrolidine dithiocarbamate (PDTC). Dose- and time-dependent cellular uptake effects of inhibitors on FPA/EPI nanoparticles were determined through fluorometry. The cytokine levels of tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1ß), and IL-6 were tested in culture supernatants by bead-based multiplex flow cytometry. The uptake study demonstrated that inhibitors had an obvious inhibitory effect (P<0.05 or P<0.01), with NY, AMR and Col all showing time-dependent inhibitory effects. PDTC + NY had the strongest inhibitory effect, with an uptake rate of 14.62%. The levels of the three proinflammatory cytokines were changed significantly by the compound inhibitors. TNF-α was significantly inhibited (P<0.05 or P<0.01), but IL-1ß and IL-6 showed smaller decreases. These results suggested that clathrin- and caveolae-mediated endocytosis were the main routes via which nanoparticles entered KCs and that the NF-kB signal pathway was very important too. In summary, multiple mechanisms, including clathrin- and caveolae-mediated endocytosis, contribute to cytokine production in macrophages following exposure to folic acid-conjugated pullulan acetate nanoparticles. Thus, the endocytosis inhibition strategy has great potential for improving therapy and reducing toxicity of an NDDS in the treatment of cancer.

Statistical modeling of pullulan production and its application in pullulan acetate nanoparticles synthesis.

This work focused on the optimization of exo-polysaccharide, pullulan production by exploiting cassava bagasse, an agricultural solid waste residue by solid state fermentation and its application in the preparation of pullulan acetate nanoparticles. Statistical approach was investigated to maximize the pullulan production using C/N ratio, initial pH, NaCl and ZnSO4·5H2O. The optimum conditions for maximum yield of pullulan (39.42±0.62mg/gds) were found to be: C/N=25.94, initial pH=5.5 and NaCl=0.55g/L. Using the optimized medium variables, the production of pullulan was investigated in lab scale solid state fermentation. The pullulan produced was characterized by thermo gravimetric and XRD analysis. Also pullulan acetate nanoparticles were synthesized from chemical modification of pullulan and the average particle size of nanoparticles was examined by zeta particle sizer.

Modified pullulan nanoparticles for oral delivery of lopinavir: formulation and pharmacokinetic evaluation.

In this investigation, we report the use of the pullulan acetate, a hydrophobic derivative of pullulan in the formulation of Lopinavir loaded nanoparticles meant for oral delivery. Pullulan was modified to pullulan acetate by acetylation process in the presence of pyridine; acetylation was confirmed by FT-IR and NMR spectra. Lopinavir, an HIV-protease inhibitor was formulated into nanoparticles of pullulan acetate by the well-known emulsion-solvent-evaporation method. The nanoparticles were tested for particle size, entrapment efficiency, in-vitro drug release and stability. Further, extensive pharmacokinetic and tissue distribution studies were performed in Wistar rats. The results showed that, with our method, we could obtain nanoparticles of ∼197 nm, high entrapment efficiency (∼75%) and monodisperse nature (PDI<0.2). Stability data showed that the nanoparticles were stable over a period of 3 months. From the pharmacokinetic study data, we found that the relative bioavailability of Lopinavir from nanoparticles was ∼2 folds higher than the free drug. Moreover, the tissue distribution study showed a higher distribution of Lopinavir loaded nanoparticles to lymphoid organs (liver, spleen and lymph nodes that are also important viral reservoirs in HIV infection). Thus, we conclude that Lopinavir loaded nanoparticle could be a superior alternative approach to free Lopinavir in treating HIV infection.