Enzymic and non-enzymic hydrolysis of a polymeric prodrug: Hydrocortisone esters of hyaluronic acid

Hyaluronan-colistin conjugates: Synthesis, characterization, and prospects for medical applications

The development of nanotechnology-based antibiotic delivery systems (nanoantibiotics) is an important challenge in the effort to combat microbial multidrug resistance. These systems have improved biopharmaceutical characteristics by increasing local bioavailability and reducing systemic toxicity and the number and frequency of drug side effects. Conjugation of low -molecular -weight antibacterial agents with natural polysaccharides is an effective strategy for developing optimal targeted delivery systems with programmed release and reduced cytotoxicity. This study describes the synthesis of conjugates of colistin (CT) and hyaluronic acid (HA) using carbodiimide chemistry to conjugate the amino groups of CT with the carboxyl groups of HA. The obtained polysaccharide carriers had a degree of substitution (DS) with CT molecules of 3-10 %, and the CT content was 129-377 μg/mg. The size of the fabricated particles was 300-600 nm; in addition, there were conjugates in the form of single macromolecules (30-50 nm). The ζ-potential of developed systems was about -20 mV. In vitro release studies at pH 7.4 and pH 5.2 showed slow hydrolysis of amide bonds, with a CT release of 1-5 % after 24 h. The conjugates retained antimicrobial activity depending on the DS: at DS 8 %, the minimum inhibitory concentration (MIC) of the conjugate corresponded to the MIC of free CT. The resulting systems also reduced CT nephrotoxicity by 20-50 %. These new conjugates of CT with HA are promising for the development of nanodrugs for safe and effective antimicrobial therapy.

Hydrolysis-Sensitive Dithiolethione Prodrug Micelles

Prodrug micelles carrying 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADT-OH), a compound possessing chemopreventive properties, are prepared from amphiphilic block copolymers linking ADT-OH via an ester bond using glycine (PAM-PGlyADT) and isoleucine linkers (PAM-PIleADT). The release of ADT-OH from the PAM-PIleADT micelles is much slower than the PAM-PGlyADT micelles. The PAM-PGlyADT micelles show comparable toxicity with ADT-OH in different cancer cell lines, whereas the PAM-PIleADT micelles are not toxic up to 400 µM. This ADT-ester prodrug micelle approach enables to modulate the release rate of ADT-OH and thus might find application in cancer therapy and prevention.

Multimonth controlled small molecule release from biodegradable thin films

Long-term, localized delivery of small molecules from a biodegradable thin film is challenging owing to their low molecular weight and poor charge density. Accomplishing highly extended controlled release can facilitate high therapeutic levels in specific regions of the body while significantly reducing the toxicity to vital organs typically caused by systemic administration and decreasing the need for medical intervention because of its long-lasting release. Also important is the ability to achieve high drug loadings in thin film coatings to allow incorporation of significant drug amounts on implant surfaces. Here we report a sustained release formulation for small molecules based on a soluble charged polymer-drug conjugate that is immobilized into nanoscale, conformal, layer-by-layer assembled films applicable to a variety of substrate surfaces. We measured a highly predictable sustained drug release from a polymer thin film coating of 0.5-2.7 μm that continued for more than 14 mo with physiologically relevant drug concentrations, providing an important drug delivery advance. We demonstrated this effect with a potent small molecule nonsteroidal anti-inflammatory drug, diclofenac, because this drug can be used to address chronic pain, osteoarthritis, and a range of other critical medical issues.

Kinetics of the acidic and enzymatic hydrolysis of benazepril HCl studied by LC

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for the kinetic investigation of the chemical and enzymatic hydrolysis of benazepril hydrochloride. Kinetic studies on the acidic hydrolysis of benazepril hydrochloride were carried out in 0.1 M hydrochloric acid solution at 50, 53, 58 and 63 degrees C. Benazepril hydrochloride appeared stable in a pH 7.4 phosphate buffered solution at 37 degrees C and showed susceptibility to undergoing in vitro enzymatic hydrolysis with porcine liver esterase (PLE) in a pH 7.4 buffered solution at 37 degrees C. Benazeprilat appeared to be the major degradation product in both (chemical and enzymatic) studies of hydrolysis. Statistical evaluation of the proposed HPLC methods revealed their good linearity and reproducibility. Relative standard deviation (R.S.D.) was less than 4.76, while detection limits for benazepril hydrochloride and benazeprilat were 13.0 x 10(-7) and 9.0 x 10(-7) M, respectively. Treatment of the kinetic data of the acidic hydrolysis was carried out by non-linear regression analysis and k values were determined. The kinetic parameters of the enzymatic hydrolysis were determined by non-linear regression analysis of the data using the equation of Michaelis-Menten.

Controlled chemical modification of hyaluronic acid: synthesis, applications, and biodegradation of hydrazide derivatives

Controlled modification of the carboxylic acid moieties of hyaluronic acid with mono- and polyfunctional hydrazides leads to biochemical probes, biopolymers with altered physical and chemical properties, tethered drugs for controlled release, and crosslinked hydrogels as biocompatible scaffoldings for tissue engineering. Methods for polyhydrazide synthesis, for prodrug preparation, for hydrogel crosslinking, and for monitoring biodegradation are described.

A continuous fluorimetric method to monitor the enzymatic hydrolysis of medicinal esters

This paper describes a new spectrofluorimetric assay for continuously monitoring the enzymatic hydrolysis of medicinal esters. The procedure is based on the stoichiometric quantity of protons generated by the hydrolysis of the substrate, which produces changes in the fluorescence of a pH-sensitive dye. The pH indicator, 2', 7'-bis(car-boxyethyl)-5(6)-carboxyfluorescein, was selected due to its favourable pKa for studies under physiological conditions. Moreover, the presence of a domain in the spectra (< 442 nm) where fluorescence intensities are independent of pH allows measurements of wavelength ratios that cancel artifacts and lower sample-to-sample variability. The indicator did not affect the catalytic activity of purified hog liver carboxylesterase or human serum albumin. This assay is easy to perform and appears to be especially useful for studying enzymatic reactions with half-lives of the order of minutes or hours.

Antioxidant effects of hyaluronan and its alpha-methyl-prednisolone derivative in chondrocyte and cartilage cultures

OBJECTIVE

To compare hyaluronan and its alpha-methyl prednisolone derivative (HYC-141) with respect to their potential to directly cause tissue damage and to protect tissues from attack by reactive oxygen species.

METHODS

Cartilage samples and chondrocytes were isolated from 15-day chick embryos and were exposed to enzyme-based and activated inflammatory cell-free radical generating systems in the presence of varying concentrations of alpha-methyl prednisolone, hyaluronan, and HYC-141. Tissue and cell vitality was measured by determining the incorporation of radioactive sulphate into newly synthesized glycosaminoglycans.

RESULTS

Only alpha-methyl prednisolone caused a significant decrease in biosynthetic activity. All the tested substances were capable, to some extent, of protecting tissues and cells from damage by reactive oxygen species; HYC-141 demonstrated the greatest protective effect.

CONCLUSION

These data suggest that HYC-141 may possess certain advantages over the individual component molecules in the local treatment of arthropathies.