Lip Yong Chung

Synergistic antimicrobial activity between pentacyclic triterpenoids and antibiotics against Staphylococcus aureus strains

BackgroundThere has been considerable effort to discover plant-derived antibacterials against methicillin-resistant strains of Staphylococcus aureus (MRSA) which have developed resistance to most existing antibiotics, including the last line of defence, vancomycin. Pentacyclic triterpenoid, a biologically diverse plant-derived natural product, has been reported to show anti-staphylococcal activities. The objective of this study is to evaluate the interaction between three pentacyclic triterpenoid and standard antibiotics (methicillin and vancomycin) against reference strains of Staphylococcus aureus.Methods and ResultsThe activity of the standard antibiotics and compounds on reference methicillin-sensitive and resistant strains of S. aureus were determined using the macrodilution broth method. The minimum inhibitory concentration (MIC) of the compounds was compared with that of the standard antibiotics. The interaction between any two antimicrobial agents was estimated by calculating the fractional inhibitory concentration (FIC index) of the combination. The various combinations of antibiotics and compounds reduced the MIC to a range of 0.05 to 50%.ConclusionPentacyclic triterpenoids have shown anti-staphylococcal activities and although individually weaker than common antibiotics produced from bacteria and fungi, synergistically these compounds may use different mechanism of action or pathways to exert their antimicrobial effects, as implicated in the lowered MICs. Therefore, the use of current antibiotics could be maintained in their combination with plant-derived antibacterial agents as a therapeutic option in the treatment of S. aureus infections.

Antimicrobial activities of Malaysian plant species

Antimicrobial activities against reference Gram-positive (Staphylococcus aureus, Enterococcus faecalis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria and Candida albicans were tested on 191 plant extracts obtained from more than 30 families of plants found in the state of Sabah, Malaysia. The plant extracts were tested by a disk-diffusion technique in which antimicrobial activity was evaluated based on the ability of the plant extracts to diffuse through agar to affect the target organisms. The extracts of Callicarpa erioclona Schau. (Verbenaceae), Callicarpa farinosa Roxb. (Verbenaceae), Sphonodesma friflora Wright (Verbenaceae), and Homalium panayanum F. Villar (Flacourticeae) exhibited antimicrobial properties worthy of further investigation.

Assessing biocompatibility of graphene oxide-based nanocarriers: A review

Graphene oxide (GO)-based nanocarriers have been frequently studied due to their high drug loading capacity. However, the unsatisfactory biocompatibility of these GO-based nanocarriers hampers their use in clinical settings. This review discusses how each of the physicochemical characteristics (e.g., size, surface area, surface properties, number of layers and particulate states) and surface coatings on GO affect its in vitro and in vivo nanotoxicity. We provide an overview on the effect of GO properties on interactions with cells such as red blood cells, macrophages and cell lines, and experimental organisms including rodents, rabbits and Zebrafish, offering some guidelines for development of safe GO-based nanocarriers. We conclude the paper by outlining the challenges involving GO-based formulations and future perspectives of this research in the biomedical field.

In Vivo Studies of Nanostructure-Based Photosensitizers for Photodynamic Cancer Therapy

Animal models, particularly rodents, are major translational models for evaluating novel anticancer therapeutics. In this review, different types of nanostructure-based photosensitizers that have advanced into the in vivo evaluation stage for the photodynamic therapy (PDT) of cancer are described. This article focuses on the in vivo efficacies of the nanostructures as delivery agents and as energy transducers for photosensitizers in animal models. These materials are useful in overcoming solubility issues, lack of tumor specificity, and access to tumors deep in healthy tissue. At the end of this article, the opportunities made possible by these multiplexed nanostructure-based systems are summarized, as well as the considerable challenges associated with obtaining regulatory approval for such materials. The following questions are also addressed: (1) Is there a pressing demand for more nanoparticle materials? (2) What is the prognosis for regulatory approval of nanoparticles to be used in the clinic?

Are free radicals and not quinones the haptenic species derived from urushiols and other contact allergenic mono- and dihydric alkylbenzenes? The significance of NADH, glutathione, and redox cycling in the skin

SummaryThe induction of allergic contact dermatitis to urushiols from poison ivy and related plants is generally believed to involve an initial oxidation event by which a protein-reactive quinone is formed. However, this does not readily account for the contact allergenicity of closely related mono- and dihydric alkylbenzenes such as the alkylphenols and alkylresorcinols which are not so easily oxidised to quinones in vitro. When the redox processes known to occur in living tissues are taken into consideration, a more plausible unifying mechanism involving the formation of protein-reactive radical species becomes apparent. Experiments described here examine the autoxidation of p-benzoquinone and various mono- and dihydric benzenes and alkylbenzenes, and their reactions with the diphenylpicrylhydrazyl radical, cysteine, glutathione, and NADH. We have also demonstrated that administration to mice of 2-oxo-4-thiazolidine carboxylate, a compound known to elevate intracellular glutathione levels, inhibits the irritancy and sensitising activity of 3-pentadecylphenol. This work suggests that redox cycling in the skin following penetration of allergenic mono- and dihydric alkylbenzenes initially depletes local levels of endogenous reducing equivalents such as glutathione and NADH; once depleted, further cycling results in the uncontrolled generation of radical species which may reasonably be expected to exhibit protein reactivity.

Biocompatibility of Wound Management Products: A Study of the Effects of Various Polysaccharides on Murine L929 Fibroblast Proliferation and Macrophage Respiratory Burst

Abstract— An in‐vitro screening method to examine the biocompatibility of materials used in wound management has been evaluated. This involved the use of a macrophage respiratory‐burst assay and a fibroblast proliferation assay to represent respectively the inflammatory and the granulation phases in wound healing. Standard polysaccharides (calcium and sodium alginates, i‐carrageenan, chitin, chitosan lactate, chondroitin sulphate and pectic acid) were used as test compounds. None of the polysaccharide samples caused a significant increase in L929 fibroblast cell numbers relative to control after 6 days incubation. The overall effect of exposure of the fibroblast cultures to the alginates, carrageenan and chondroitin sulphate was an extension of lag phase followed by an enhanced rate of cell proliferation in the logarithmic phase. Only calcium and sodium alginates and chondroitin sulphate enhanced the respiratory burst activity of murine macrophages; i‐carrageenan and chitosan lactate were markedly inhibitory. The results suggest that a macrophage activity assay should be included as part of an in‐vitro screening program to evaluate the biocompatibility of wound management materials and to detect intrinsic biological activity.

Improved photodynamic efficacy of Zn(II) phthalocyanines via glycerol substitution.

Phthalocyanines are excellent photosensitizers for photodynamic therapy as they have strong absorbance in the near infra-red region which is most relevant for in vivo activation in deeper tissular regions. However, most phthalocyanines present two major challenges, ie, a strong tendency to aggregate and low water-solubility, limiting their effective usage clinically. In the present study, we evaluated the potential enhancement capability of glycerol substitution on the photodynamic properties of zinc (II) phthalocyanines (ZnPc). Three glycerol substituted ZnPc, 1–3, (tetra peripherally, tetra non-peripherally and mono iodinated tri non-peripherally respectively) were evaluated in terms of their spectroscopic properties, rate of singlet oxygen generation, partition coefficient (log P), intracellular uptake, photo-induced cytotoxicity and vascular occlusion efficiency. Tetrasulfonated ZnPc (ZnPcS4) was included as a reference compound. Here, we showed that 1–3 exhibited 10–100 nm red-shifted absorption peaks with higher molar absorptivity, and at least two-fold greater singlet oxygen generation rates compared to ZnPcS4. Meanwhile, phthalocyanines 1 and 2 showed more hydrophilic log P values than 3 consistent with the number of glycerol attachments but 3 was most readily taken up by cells compared to the rest. Both phthalocyanines 2 and 3 exhibited potent phototoxicity against MCF-7, HCT-116 and HSC-2 cancer cell-lines with IC50 ranging 2.8–3.2 µM and 0.04–0.06 µM respectively, while 1 and ZnPcS4 (up to 100 µM) failed to yield determinable IC50 values. In terms of vascular occlusion efficiency, phthalocyanine 3 showed better effects than 2 by causing total occlusion of vessels with diameter <70 µm of the chorioallantoic membrane. Meanwhile, no detectable vascular occlusion was observed for ZnPcS4 with treatment under similar experimental conditions. These findings provide evidence that glycerol substitution, in particular in structures 2 and 3, is able to improve the photodynamic properties of ZnPc.

A study of hydrogen peroxide generation by, and antioxidant activity of, Granuflex™ (DuoDERM™) Hydrocolloid Granules and some other hydrogel/hydrocolloid wound management materials

Summary The effect of Granuflex™ Hydrocolloid Granules (0.0l–0.50% w/v) on the rate of proliferation of murine (L929) fibroblasts was examined. The dose–response curve showed a significant (P<0.02) pro‐proliferant effect at 0.05%, and a significant (P<0.02) antiproliferant effect at 0.50%, mirroring the dose–response curve produced by hydrogen peroxide in the concentration range 10−9–10−4 mol/l. The antiproliferant effect at 0.20% w/v was abolished by catalase, suggesting that the biological activity of Granuflex was mediated by the in situ generation of hydrogen peroxide. Formation of hydrogen peroxide by Granuflex was confirmed by performing the scopoletinhorseradish peroxidase assay in the presence and absence of catalase. The total concentration of hydrogen peroxide detected was about 8 × 10−6 mol/1 (using 0.5% w/v Granuflex) after 48 h at 37°C. In contrast, when hydrogen peroxide itself was added to L929 cultures, a similar antiproliferant activity was observed at concentrations between 10−4 and 10−5 mol/l. These results suggested that Granuflex was undergoing autoxidation in the culture medium, and hence that it might possess antioxidant activity. In assays for antioxidant activity using 1,l‐diphenyl‐2‐picrylhydrazyI (DPPH), Granuflex, and two other hydrocolloid dressings (Comfeel® Powder and Bard® Absorption Dressing) showed significant ability to reduce DPPH to DPPH2. These three dressings also displayed superoxide scavenging activity in a nitroblue tetrazolium reduction assay. We conclude that, in addition to providing a moist wound‐healing environment. Granuflex and certain other hydrocolloids might contribute to the establishment and maintenance of the reducing environment necessary for energy production and hence cell division. The release of hydrogen peroxide into the wound environment couid conceivably contribute both to the inflammation phase of wound healing and to fibroblast proliferation and hence the granulation phase.

Biochemical responses of skin to allergenic and non-allergenic nitrohalobenzenes

Using a selection of ‘classic’ haptens (dinitrohalobenzenes and picryl chloride) and related nonsensitizing analogous, we examined changes in levels of glutathione (GSH) and glutathione disulphide (GSSG) in mouse skin 12 h after their epicutaneous application. We observed that elevation of GSSG levels and/or depletion of GSH levels correlated well with contact allergenic potential. Non-sensitizing analogous failed to perturb GSH/GSSG status. In vitro assays using mouse skin and rat liver microsomal preparations indicated that only the allergenic nitrohalobenzenes initiated NADPH-dependent oxygen utilization, with the activity falling off in the order picryl chloride ≫ DNIB > DNBB > DNCB > DNFB. In addition, an examination of the colour of mouse skin homogenates ex vivo after application of the dinitrohalobenzenes showed significant yellowing (consistent with aromatic nucleophilic substitution) only with DNFB. Our results indicate that, while an aromatic nucleophilic substitution reaction with skin protein can possibly account for the allergenicity of DNFB, it does not seem to occur with DNCB, DNBB or DNIB. These may instead behave mainly as prohaptens which are activated enzymically by NADPH-dependent reductase (s) within the skin, with the concomitant generation of superoxide and hydrogen peroxide, to form potentially protein-reactive free radical and other metabolites. Picryl chloride appears capable of both conjugating directly with proteins by aromatic nucleophilic substitution and undergoing NADPH-dependent metabolism to other potentially protein-reactive metabolites.

Synthesis, Characterization, X-ray crystallography, acetyl cholinesterase inhibition and antioxidant activities of some novel ketone derivatives of gallic hydrazide-derived schiff bases

Alzheimer’s disease (AD) is the most common form of dementia among older people and the pathogenesis of this disease is associated with oxidative stress. Acetylcholinesterase inhibitors with antioxidant activities are considered potential treatments for AD. Some novel ketone derivatives of gallic hydrazide-derived Schiff bases were synthesized and examined for their antioxidant activities and in vitro and in silico acetyl cholinesterase inhibition. The compounds were characterized using spectroscopy and X-ray crystallography. The ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays revealed that all the compounds have strong antioxidant activities. N-(1-(5-bromo-2-hydroxyphenyl)-ethylidene)-3,4,5-trihydroxybenzohydrazide (2) was the most potent inhibitor of human acetyl cholinesterase, giving an inhibition rate of 77% at 100 μM. Molecular docking simulation of the ligand-enzyme complex suggested that the ligand may be positioned in the enzyme’s active-site gorge, interacting with residues in the peripheral anionic subsite (PAS) and acyl binding pocket (ABP). The current work warrants further preclinical studies to assess the potential for these novel compounds for the treatment of AD.