Development and optimization of thiolated dendrimer as a viable mucoadhesive excipient for the controlled drug delivery: An acyclovir model formulation

In the present study we report the development of novel thiolated dendrimers for mucoadhesive drug delivery. The thiolated dendrimers were synthesized by conjugating PAMAM dendrimer (G3.5)with cysteamine at two different molar ratios, i.e. 1:30 (DCys1) and 1:60 (DCys2). The thiolated dendrimers were further encapsulated with acyclovir (DCys1Ac and DCys2Ac) and the conjugates were characterized for thiol content, drug loading, drug release, and mucoadhesive behavior. The thiolated dendrimer conjugates showed thiol content of 10.56±0.34 and 68.21±1.84 μM/mg of the conjugate for DCys1 and DCys2, respectively. The acyclovir loading was observed to be highest in dendrimer drug conjugate (DAc) compared to other DCys1Ac and DCys2Ac conjugates. The thiolated dendrimers showed sustained release of acyclovir and showed higher mucoadhesion. The in vitro mucoadhesive activity of DCys2Ac was 1.53 and 2.89 fold higher mucoadhesion compared to DCys1Ac and DAc, respectively. These results demonstrated the usefulness of thiolated dendrimers as a mucoadhesive carrier and represent a novel platform for drug delivery.From the Clinical EditorThis study demonstrates the utility of thiolated dendrimers as mucoadhesive carriers as reported in an acyclovir delivery model system.     

Salivary Bicarbonate as a Major Factor in the Prevention of Upper Esophageal Mucosal Injury in Gastroesophageal Reflux Disease

Background

It has been previously demonstrated that the exposure of the lower esophageal mucosa to acid and pepsin results in significant increase in salivary protective factors secretion, mediated by the esophago-salivary reflex. The impact of the upper esophageal mucosal exposure to acid and pepsin on salivary secretory response remains unknown.

Aims

To investigate the rate of salivary protective factors secretion during the upper esophageal mucosal exposure to acid and pepsin and to compare with the corresponding results recorded during the lower esophageal mucosal exposure, in the same group of asymptomatic volunteers.

Methods

The study was conducted in 10 asymptomatic volunteers. Salivary samples were collected during the esophageal mucosal exposure to saline, followed by acid/pepsin and the final saline, using the esophageal perfusion catheter. Salivary bicarbonate and non-bicarbonate buffers were analyzed using TitraLab. Salivary mucin and protein were quantified through PAS and Lowry methodologies, respectively, whereas PE₂ using radioimmunoassay. Statistical analysis was performed using Σ-Stat software.

Results

The rate of salivary bicarbonate secretion was significantly higher (3.1-fold) during the upper versus the lower esophageal mucosal exposure to acid and pepsin (87.5 ± 14.4 vs. 28.0 ± 7.70 μEq/min, p < 0.05). The volumes of saliva, pH, salivary protein, mucin and PE₂ were similar in both esophageal perfusions.

Conclusions

Threefold stronger secretion of salivary bicarbonate could be a major factor protecting the upper esophageal mucosa. This phenomenon may represent an ultimate defense mechanism potentially preventing further complications within the upper esophageal mucosa; however, it needs to be confirmed in patients of gastroesophageal reflux disease.     

A novel vitamin B12-nanosphere conjugate carrier system for peroral delivery of insulin.

In spite of great potential, effective oral delivery of many vitamin B(12)-peptide/protein drug conjugates does not occur due to the limited uptake capacity of the VB(12) transport system, loss of bioactivity of native protein and/or intrinsic factor affinity of VB(12) and liability to GI degradation. In order to overcome these shortcomings in a two pronged way, we have endeavoured to develop a VB(12)-Nanoparticles (NPs) system to enhance the uptake capacity of both NPs and VB(12) transport to deliver orally effective insulin. NPs were prepared using different molecular weight dextrans and epichlorohydrin as cross-linker by an emulsion method. NPs surface was modified with succinic anhydride, and conjugated with amino VB(12) derivatives of carbamate linkage. VB(12) attachment was confirmed by IR, XPS analysis, and was quantified by HPLC (4.0 to 4.4% w/w of NPs). The pre-formed NPs conjugates (Zave=160-250 nm; polydisperse) were loaded with 2, 3 and 4% w/w of insulin, and the entrapment was found to be 45-70%. NPs conjugates were found to protect 65-83% of entrapped insulin against in vitro gut proteases. In vitro release studies exhibit an initial burst followed by diffusion controlled first order kinetics with 75-95% release within 48 h. After oral administration of these carriers (20 IU/kg), a nadir of 70-75% reduction in plasma glucose was found in 5 h, reached basal levels in 8-10 h, and a prolonged second phase was found until 54 h. The % pharmacological availability (PA) of 70 K NPs conjugate containing 2, 3 and 4% w/w insulin was 1.1, 1.9 and 2.6 fold higher, respectively compared to NPs without VB(12); consistent with the hypothesis that uptake was mediated by the vitamin B(12) transport. NPs of 70 K dextran showed 1.4 fold PA compared to 10 K while negligible action was observed with 200 K. The potential utilities of VB(12)-NPs carrier as an oral delivery platform of proteins, especially insulin via dextran-coated particles necessities further elaborate investigations.     

Oxidative stress in pediatric nephrotic syndrome

BACKGROUND: Thiopurine S-methyltransferase (TPMT), which exhibits autosomal codominant polymorphism, plays an important role in the metabolism of thiopurine drugs such as mercaptopurine, thioguanine and azathioprine. Decreased activity of TPMT is associated with severe hematopoietic toxicity after administration of standard doses of these drugs. METHODS: We developed a specific high-performance liquid chromatographic (HPLC) assay for measuring 6-methylmercaptopurine (6-MMP) formed from 6-mercaptopurine (6-MP) in red blood cells (RBC) lysates. The assay was used to study the distribution of TPMT activities in 44 healthy Japanese subjects with different TPMT genotypes. RESULTS: The TPMT activities in the subjects ranged from 17.9 to 37.1 pmol/h/mgHb. The TPMT activity of one subject with TPMT*1/*3C (17.9 pmol/h/mgHb) was 40% lower than the mean value of TPMT activities in 43 subjects with TPMT*1/*1 (29.6+/-4.3 pmol/h/mgHb). CONCLUSIONS: This sensitive and reproducible HPLC assay for determination of TPMT activity in RBC clinical studies has been designed to optimize dosage regimens of thiopurine drugs.