Synthesis and release studies of shikonin-containing microcapsules prepared by the solvent evaporation method

Preparation and Short-Term Aging Properties of Asphalt Modified by Novel Sustained-Release Microcapsules Containing Rejuvenator

Aged asphalt can enormously affect the performance of asphalt pavement and cause serious environmental hazards. Microcapsule-modified asphalt is one of the effective means to improve the anti-aging ability of asphalt. In this work, novel sustained-release microcapsules containing rejuvenator were prepared by the solvent evaporation method. The morphology of the microcapsules was characterized by scanning electron microscopy (SEM). The sustained-release properties of the microcapsules were investigated by static thermogravimetric analysis. The physical properties such as penetration, ductility, softening point, and Brookfield viscosity of the original asphalt and microcapsule-modified asphalt were studied. In addition, the viscoelasticity of the original asphalt and microcapsule-modified asphalt was investigated by means of a dynamic shear rheometer (DSR). The results show that the prepared microcapsules have a smooth surface and a complete encapsulation with an average particle size of 60 μm. After the heating treatment (above 140 °C), a large number of micropores were formed on the shell surface of microcapsules, which provided a structural basis for the sustained-release of rejuvenator. The release rate of the rejuvenator was obviously slowed down by the microcapsules. The aging behavior of sustained-release microcapsules containing rejuvenator-modified asphalt can be greatly improved. The enhanced anti-aging properties of sustained-release microcapsule-modified asphalt are attributed to the functions of the rejuvenator which can be slowly released from the micropores on the microcapsules' surface, after which the light components lost in the original asphalt can be supplemented.

Evaluation of gum mastic (Pistacia lentiscus) as a microencapsulating and matrix forming material for sustained drug release

In this study, a natural gum mastic was evaluated as a microencapsulating and matrix-forming material for sustained drug release. Mastic was characterized for its physicochemical properties. Microparticles were prepared by oil-in-oil solvent evaporation method. Matrix tablets were prepared by wet and melt granulation techniques. Diclofenac sodium (DFS) and diltiazem hydrochloride (DLTZ) were used as model drugs. Mastic produced discrete and spherical microspheres with DLTZ and microcapsules with DFS. Particle size and drug loading of microparticles was in the range of 22–62 µm and 50–87%, respectively. Increase in mastic: drug ratio increased microparticle size, improved drug loading and decreased the drug release rate. Microparticles with gum: drug ratio of 2:1 could sustain DLTZ release up to 12 h and released 57% DFS in 12 h. Mastic produced tablets with acceptable pharmacotechnical properties. A 30% w/w of mastic in tablet could sustain DLTZ release for 5 h from wet granulation, and DFS release for 8 h and 11 h from wet and melt granulation, respectively. Results revealed that a natural gum mastic can be used successfully to formulate matrix tablets and microparticles for sustained drug release.

Shikonin Suppresses NLRP3 and AIM2 Inflammasomes by Direct Inhibition of Caspase-1

Shikonin is a highly lipophilic naphtoquinone found in the roots of Lithospermum erythrorhizon used for its pleiotropic effects in traditional Chinese medicine. Based on its reported antipyretic and anti-inflammatory properties, we investigated whether shikonin suppresses the activation of NLRP3 inflammasome. Inflammasomes are cytosolic protein complexes that serve as scaffolds for recruitment and activation of caspase-1, which, in turn, results in cleavage and secretion of proinflammatory cytokines IL-1β and IL-18. NLRP3 inflammasome activation involves two steps: priming, i.e. the activation of NF-κB pathway, and inflammasome assembly. While shikonin has previously been reported to suppress the priming step, we demonstrated that shikonin also inhibits the second step of inflammasome activation induced by soluble and particulate NLRP3 instigators in primed immortalized murine bone marrow-derived macrophages. Shikonin decreased NLRP3 inflammasome activation in response to nigericin more potently than acetylshikonin. Our results showed that shikonin also inhibits AIM2 inflammasome activation by double stranded DNA. Shikonin inhibited ASC speck formation and caspase-1 activation in murine macrophages and suppressed the activity of isolated caspase-1, demonstrating that it directly targets caspase-1. Complexing shikonin with β-lactoglobulin reduced its toxicity while preserving the inhibitory effect on NLRP3 inflammasome activation, suggesting that shikonin with improved bioavailability might be interesting for therapeutic applications in inflammasome-mediated conditions.

Addition of β-lactoglobulin produces water-soluble shikonin

Shikonin and its ester derivatives belong to a group of secondary metabolites with a wide array of beneficial effects on human health. However, shikonin is principally used in oil-based preparations due to the low solubility of the pigment in aqueous media, and the positive properties of shikonin are not exploited to their full potential. Such low aqueous solubility often results in poor bioavailability, makes shikonin undesirable for oral administration, and restricts its broadened use in the food and pharmaceutical industries. The purpose of this study was to enhance the aqueous solubility of shikonin by the addition of β-lactoglobulin and to characterize the macromolecule-ligand binding interaction by means of spectrophotometry, spectrofluorometry, high-performance liquid chromatography, and mass spectrometry. In the presence of β-lactoglobulin the solubility of shikonin is increased up to 181-fold. One shikonin molecule binds covalently to β-lactoglobulin via Cys(121), whereas the remaining pigment molecules most probably bind to the protein via noncovalent interactions.

Preparation and release studies of alkannin-containing microcapsules

Microcapsules containing the pharmaceutical substance alkannin were prepared by the solvent evaporation method to enhance alkannin stability (reduce photo-oxidation, polymerization), to decrease its hydrophobicity and to control its release rate. The effect of various parameters, such as the type of polymeric matrix, the type of surfactant used for microcapsules preparation and the addition of Pistacia lentiscus resin in the core, on the characteristics of the produced microcapsules and the release rate of alkannin were investigated experimentally. Among the polymers tested for matrix, ethylcellulose of viscosity 46cp was the most successful, while ethylcellulose 10cp gave microcapsules with good morphological characteristics but high release rate. Beeswax resulted in flocculation and P. lentiscus resin with or without colophony as the matrix resulted in compact particles with no pores and much slower release, but did not allow alkannin to release easily from the matrix. Sodium dodecyl sulfate resulted in microcapsules with desirable morphological and physicochemical characteristics, while acacia and tragacanth gums were not indicated as surfactants in alkannin microencapsulation since they gave a high release rate and a great extent of particle size, respectively. The incorporation of Pistacia lentiscus resin in the capsule core increased loading and microencapsulation efficiency. Ethylcellulose of 46cp viscosity with sodium dodecyl sulfate as surfactant had the best characteristics studied for alkannin microencapsulation. Finally, the dissolution rate of alkannin from microcapsules was studied in a simulated intestinal and gastric environment and an external environment. Alkannin-containing microcapsules with improved properties can be used internally and externally as a new drug-delivery system.

Study on the enantiomeric ratio of the pharmaceutical substances alkannin and shikonin

The chiral pair alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity; their enantiomeric ratio does not influence the major biological activity studied hitherto. Nevertheless, in pharmaceutical development and approval of chiral drugs from the Health and Regulatory Authorities, full documentation of methods of analysis of enantiomeric drugs, is required in order to evaluate the enantiomeric purity of starting materials and final products and to control the stability of enantiomers in pharmaceutical formulations under several experimental conditions. In the present study, the enantiomeric ratio of A/S was determined in several commercial samples of alkannin and shikonin and also the proportion of A/S derivatives in several Alkanna root samples, which are all used as active ingredients in pharmaceuticals. Light and air proved not to influence the enantiomeric ratio of A/S on a shikonin commercial sample, and temperature also did not alter the A/S ratio on shikonin and alkannin commercial samples. Microencapsulation of alkannin and shikonin commercial samples in ethylcellulose microspheres and also molecular inclusion of a shikonin commercial sample in beta-hydroxypropyl-cyclodextrin, which are used as drug delivery systems, did not alter the A/S enantiomeric ratio.