Weng-Keong Loke

Wound Dressing with Sustained Anti-Microbial Capability

To overcome current limitations in wound dressings for treating mustard-burn induced septic wound injuries, a nonadherent wound dressing with sustained anti-microbial capability has been developed. The wound dressing consists of two layers: the upper layer is a carboxymethyl-chitin hydrogel material, while the lower layer is an anti-microbial impregnated biomaterial. The hydrogel layer acts as a mechanical and microbial barrier, and is capable of absorbing wound exudate. In physiological fluid, the carboxymethylated-chitin hydrogel swells considerably, imbibing up to 4 times its own weight of water and is also highly porous to water vapor. The moisture permeability of the dressing prevents the accumulation of fluid in heavily exudating wounds seen in second-degree burns. The lower layer, fabricated from chitosan acetate foam, is impregnated with chlorhexidine gluconate. From the in vitro release studies, the loading concentration was optimized to deliver sufficient anti-microbial drug into the wound area to sustain the anti-microbial activity for 24 h. The anti-microbial activity of the dressing against Pseudomonas aeruginosa and Staphylococcus aureus was tested using the Bauer-Kirby Disk Diffusion Test.

Wet decontamination‐induced stratum corneum hydration—effects on the skin barrier function to diethylmalonate

Decontamination of chemical agents from the skin uses both dry and wet decontamination processes. Recent studies have shown that wet decontamination frequently results in stratum corneum hydration. To evaluate the hydration effect of wet decontamination on the skin barrier function and hence on the decontamination efficiency, a series of comparative studies were carried out on human skin contaminated with the nerve agent simulant diethylmalonate, using decontamination media having different salinity and surfactants. The results showed that, compared to non‐decontaminated skin, remnant diethylmalonate on decontaminated skin penetrated at an accelerated rate in the immediate 2 h following decontamination. This transient enhancement effect, ranging from 20 to 98%, was depended on the nature of the decontamination media used and was more obvious in skin samples that were decontaminated 1 h post‐exposure. All decontamination media exhibited this effect, with the greatest enhancement observed in the following order: anionic surfactant > cationic surfactant > non‐ionic surfactant > deionized water > 0.9% saline > 9% saline. Copyright

O-substituted derivatives of pralidoxime : Muscarinic properties and protection against soman effects in rats

O-Substituted aldoximes of the cholinesterase reactivator pralidoxime (O-methyl 1, O-benzyl 2, O-propynyl 3 and O-butynyl 4 derivatives) were synthesized and found to exhibit strong binding affinities for muscarinic receptors in rat brain, heart and submandibulary glands. The aldoximes were noncompetitive antagonists of acetylcholine-induced contraction of the guinea pig ileum. A good correlation was observed between binding affinity and pK(B). Weak anticholinesterase activities were observed for these compounds. When given intracerebroventricularly into conscious rats before soman administration (0.9 LD(50), subcutaneously), the aldoximes, like atropine but not pralidoxime, protected against respiratory depression (3,4) and bradycardia (2). No protection against soman-induced pressor effects was noted. The protective effects of these aldoximes may be the outcome of compensatory mechanisms, of which the cholinergic receptor agonist and antagonist properties of these compounds may be important.

Protective actions of des‐aspartate‐angiotensin I in mice model of CEES‐induced lung intoxication

The present study investigated the protective actions of des‐aspartate‐angiotensin I (DAA‐I) in mice that were intranasally administered 2‐chloroethyl ethyl sulfide (CEES), a half sulfur mustard. The protection was dose‐dependent, and an oral dose of 75 mg kg−1 per day administered 18 h post exposure and for the following 13 days, offered maximum protection that increased survival by a third. DAA‐I attenuated the early processes of inflammation seen in the CEES‐inoculated mice. DAA‐I attenuated (i) elevated pulmonary ROS, and gp91‐phox protein of NADPH oxidase, a non phagocytic enzyme that generates superoxide and subsequent ROS; (ii) intercellular adhesion molecule‐1 (ICAM‐1) that is involved in the extravasation of circulating leucocytes; and (iii) myeloperoxidase activity, which is a surrogate enzymatic measurement of neutrophil infiltration. These actions led to improved histological lung structures, and survival of type‐1 pneumocytes. The action of DAA‐I on animal survival was blocked by losartan, a selective angiotensin AT1 receptor blocker, indicting that the AT1 receptor mediates the protection. The presence of elevated PGE2 and PGI2 in lung supernatants of DAA‐I treated CEES‐inoculated mice indicates that the two prostaglandins are involved in signaling the protective actions of DAA‐I. This finding complements earlier studies showing that DAA‐I acts on an indomethacin‐sensitive angiotensin AT1 receptor. The findings of the present study are the first demonstration of an angiotensin peptide as an effective antidote for CEES intoxication. DAA‐I is also an effective therapeutic intervention against CEES that was instituted at 18 h post exposure, and challenges conventional assumptions of limited efficacy with delayed action against alkylating agents. Copyright

Detection of Proteins by On‐Column, Non‐Covalent Labeling with NanoOrange During Capillary Zone Electrophoresis

Abstract To avoid prior derivatization of proteins with fluorescent reagents, on‐column labeling of non‐covalent dye NanoOrange on proteins was evaluated with sodium dodecyl sulfate (SDS) as an additive using laser induced fluorescence (LIF) monitoring in capillary electrophoresis (CE). Performance of NanoOrange in buffer solutions of various pH values was tested. Acidic buffer solution was found to be unsuitable for on‐column NanoOrange labeling. SDS enhanced the fluorescence intensities of basic proteins with high pI values. The fluorescence intensities of protein solutions with or without SDS additives were compared using a fluorescence spectrophotometer. The applicability of on‐column labeling and detection of staphylococcal enterotoxin B was also demonstrated. This on‐column labeling method provides a rapid, direct, widely applicable technique for protein studies.

Des-Aspartate-Angiotensin I Attenuates Mortality of Mice Exposed to Gamma Radiation via a Novel Mechanism of Action.

ACE inhibitors and ARBs (angiotensin receptor blockers) have been shown to attenuate radiation injuries in animal models of lethal gamma irradiation. These two classes of drug act by curtailing the actions of angiotensin II-linked inflammatory pathways that are up-regulated during gamma radiation in organ systems such as the brain, lung, kidney, and bone marrow. ACE inhibitors inhibit ACE and attenuate the formation of angiotensin II from angiotensin I; ARBs block the angiotensin AT1 receptor and attenuate the actions of angiotensin II that are elicited through the receptor. DAA-I (des-aspartate-angiotensin I), an orally active angiotensin peptide, also attenuates the deleterious actions of angiotensin II. It acts as an agonist on the angiotensin AT1 receptor and elicits responses that oppose those of angiotensn II. Thus, DAA-I was investigated for its anticipated radioprotection in gamma irradiated mice. DAA-I administered orally at 800 nmole/kg/day for 30 days post exposure (6.4 Gy) attenuated the death of mice during the 30-day period. The attenuation was blocked by losartan (50 nmole/kg/day, i.p.) that was administered sequential to DAA-I administration. This shows that the radioprotection was mediated via the angiotensin AT1 receptor. Furthermore, the radioprotection correlated to an increase in circulating PGE2 of surviving animals, and this suggests that PGE2 is involved in the radioprotection in DAA-I-treated mice. At the hematopoietic level, DAA-I significantly improved two syndromes of myelosuppression (leucopenia and lymphocytopenia), and mice pre-treated with DAA-I prior to gamma irradiation showed significant improvement in the four myelodysplastic syndromes that were investigated, namely leucopenia, lymphocytopenia, monocytopenia and thrombocytopenia. Based on the known ability of PGE2 to attenuate the loss of functional hematopoietic stem and progenitor cells in radiation injury, we hypothesize that PGE2 mediated the action of DAA-I. DAA-I completely attenuated the increase in circulating level of two inflammatory cytokines, TNFα and IL-6, in irradiated mice; and this shows that DAA-I exerted additional anti-inflammatory actions, which could also have contributed to its radioprotection. These findings show that DAA-I acts via a novel mechanism of action on the angiotensin AT1 receptor to specifically release PGE2, which mediates radioprotection in the gamma irradiated mice.

Des-aspartate-angiotensin I attenuates ICAM-1 formation in hydrogen peroxide-treated L6 skeletal muscle cells and soleus muscle of mice subjected to eccentric exercise.

L6 skeletal muscle cells overexpressed ICAM-1 when treated with H2O2. Maximum effect was observed at 200 μM H2O2. Des-aspartate-angiotensin I (DAA-I) concentration-dependently attenuated the overexpression. Maximum attenuation occurred at 10(-10) M DAA-I. H2O2 activated NFκB and its translocation into the nucleus of L6 muscle cells suggesting that NFκB mediates the H2O2-induced overexpression of ICAM-1. DAA-I inhibited the activation and translocation of NFκB. H2O2 is a major oxidant formed during skeletal muscle contraction and is implicated in oxidative stress and skeletal muscle damage in excessive unaccustomed exercise. The data show that DAA-I has antioxidant action, and its action was further investigated in the soleus muscle of mice subjected to 240 min of eccentric exercise on a rodent treadmill. The eccentric exercise induced superoxide formation and overexpression of ICAM-1 in the soleus muscle of the mice at 3 days post exercise. DAA-I (0.2 nmole/kg/day) administered orally on day 1 (pre-exercise) and 2 days post-exercise attenuated both the ROS formation and ICAM-1 overexpression. Earlier studies show that DAA-I acts as an agonist on the angiotensin AT1 receptor and elicits responses opposing those of angiotensin II. The present and earlier findings support the recent suggestion that angiotensin II is involved in skeletal muscle damage, and curtailment of its actions via ACE inhibitors and losartan protects and improves skeletal muscle damage. These findings open up new avenues for treatment and management of skeletal muscle damage via the interventions of the renin angiotensin system.

Quinuclidinone O-alkynyloximes with muscarinic agonist activity

A series of quinuclidinone O-alkynyloximes (14-19) were synthesized and evaluated in radioligand displacement assays for binding affinities to M1-M3 muscarinic receptors. Radioligand displacement assays were carried out using [3H] oxotremorine-M and [3H] pirenzepine on rat cortical tissue and [3H] N-methylscopolamine on rat heart and submandibulary glands. Two alkynyloximes 15 and 18 had pirenzepine/oxotremorine M ratios which were indicative of muscarinic agonist and partial agonist activity, respectively. They were tested for their mnemonic effects in mice using the swimming escape task and found to attenuate scopolamine induced impairment of the task in mice at 2mg/kg. The results show that the O-alkynyloxime moiety linked to azacycles of appropriate size and rigidity (for example quinuclidine and tropane) is a potentially useful muscarinic pharmacophore that can be exploited for the design of muscarinic agonists.

Retrospective population pharmacokinetic/pharmacodynamic analysis of pyridostigmine, a cholinesterase inhibitor, in Chinese males

Objectives We have characterised the population pharmacokinetics‐pharmacodynamics of pyridostigmine given as pyridostigmine bromide.