Microemulsions as topical delivery vehicles for the anti-melanoma prodrug, temozolomide hexyl ester (TMZA-HE)

A prodrug, temozolomide acid hexyl ester (TMZA-HE), was identified as a skin-deliverable congener for temozolomide (TMZ) to treat skin cancers. Poor solubility and instability of TMZA-HE rendered a serious challenge for formulation of a topical preparation. Microemulsions (ME) were chosen as a potential vehicle for TMZA-HE topical preparations. ME systems were constructed with either oleic acid (OA) or isopropyl myristate (IPM) as the oil phase and tocopheryl (vitamin E) polyethylene glycol 1000 succinate (VE-TPGS) as a surfactant. Topical formulations of OA and IPM ME systems demonstrated beneficial solubilising ability and provided a stable environment for the prodrug, TMZA-HE. Significant differences between the microstructures of OA and IPM ME systems were revealed by freeze fracture electron microscopy (FFEM) and different loading abilities and permeation potencies between the two systems were also identified. In permeation studies, IPM ME systems, with inclusion of isopropyl alcohol (IPA) as a co-surfactant, significantly increased TMZA-HE permeation through silicon membranes and rat skin resulting in less drug retention within the skin, while OA ME systems demonstrated higher solubilising ability and a higher concentration of TMZA-HE retained within the skin. Therefore IPM ME systems are promising for transdermal delivery of TMZA-HE and OA ME systems may be a suitable choice for a topical formulation of TMZA-HE. © 2007 The Authors.

Development and growth of the lichen Rhizocarpon geographicum

The development of new areolae on the marginal hypothallus of the lichen Rhizocarpon geographicum (L.) DC was studied after complete or partial removal of the central areolae. New areolae developed slowly on the isolated hypothalli over two years. Development was similar when the areolae were completely removed and when the central areolae were separated from the marginal hypothallus by ‘moats’ 2 to 5 mm in width. However, in intact thalli, the marginal areolae developed rapidly during Jan. – June 1986 but showed periods of retreat from the margin during Oct. - Dec. 1985 and July – Sept. 1986. These results suggested that primary areolae may develop from free-living algal cells trapped by the hypothallus while secondary areolae may develop from zoospores produced by the thallus. Complete removal of the areolae resulted in no measurable radial growth of the marginal hypothallus over 18 months. Removal of the central areolae to within 1 and 2 mm of the hypothallus significantly reduced growth. These results suggest that the areolae may supply the hypothallus with carbon for growth. When the marginal hypothallus was experimentally removed a new hypothallus developed within one year. Regeneration occurred initially by retreat of the marginal areolae and later by new hyphal growth. The concentration of ribitol, arabitol and mannitol was measured in the areolae and marginal hypothallus on four occasions in 1985/6 in a population growing on a steep south facing rock surface. The three carbohydrates were present in significantly higher concentration in the areolae than in the hypothallus. Hence, the slow growth of this species may result from inhibited transport of carbohydrate from areolae to hypothallus.

Time controlled photo-oxidation of polyolefins by polymer bound additives

A variety of iron compounds containing vinyl or thiol functional groups (used as photoactivators) have been synthesised and some of these were successfully bound to both polyethylene and polypropylene backbones during processing in the presence of peroxide and interlinking agent. Concentrates (masterbatches) of the photoactivators in PP and PE were prepared and the pro-oxidant effect of the diluted masterbatches in absence and presence of an antioxidant was evaluated. An antioxidant photoactivator (FeDNC ) was found to sensitise the photoactivity of pro-oxidants (Metone A / Metone M) whereas an antioxidant (ZnDNC) was found to stabilise the polymer (PP and PE) containing both of these combinations. It was observed that the lower concentration of FeDNC sensitises the stability of the polymer containing very small concentration of NiDNC whereas higher concentration of FeDNC stabilises the polymer (LDPE) containing same amount of NiDNC compared to FeDNC alone. The photostability of unstabilised PP containing FeAc could be varied by varying the concentration of ZnDEC. Both the induction period and the UV - life time of the polymer increased by increasing concentration of ZnDEC. It is suggested that ligand exchange reaction may take place between FeAc and ZnDNC. A polymer bound UV stabiliser (HAEB) and a thermal stabiliser (DBBA) were used with a non extractable photoactivator (FeAc) in PP. Small concentrations of the stabilisers (HAEB and DBBA) in combination with the photoactivator (FeAc) sensitise the polymer. The antioxidant present in commercial polymer (LDPE and PP) was found to be of a hindered phenol type, which was found to antagonise with ZnDNC when used in combination with the photoactivators.

Chemical and physical methods of enhancing the percutaneous absorption of antimicrobial agents

Contrary to previously held beliefs, it is now known that bacteria exist not only on the surface of the skin but they are also distributed at varying depths beneath the skin surface. Hence, in order to sterilise the skin, antimicrobial agents are required to penetrate across the skin and eliminate the bacteria residing at all depths. Chlorhexidine is an antimicrobial agent with the widest use for skin sterilisation. However, due to its poor permeation rate across the skin, sterilisation of the skin cannot be achieved and, therefore, the remaining bacteria can act as a source of infection during an operation or insertion of catheters. The underlying theme of this study is to enhance the permeation of this antimicrobial agent in the skin by employing chemical (enhancers and supersaturated systems) or physical (iontophoresis) techniques. The hydrochloride salt of chlorhexidine (CHX), a poorly soluble salt, was used throughout this study. The effect of ionisation on in vitro permeation rate across the excised human epidennis was investigated using Franz-type diffusion cells. Saturated solutions of CHX were used as donor and the variable studied was vehicle pH. Permeation rate was increased with increasing vehicle pH. The pH effect was not related to the level of ionisation of the drug. The effect of donor vehicle was also studied using saturated solutions of CHX in 10% and 20% ethanol as the donor solutions. Permeation of CHX was enhanced by increasing the concentration of ethanol which could be due to the higher concentration of CHX in the donor phase and the effect of ethanol itself on the membrane. The interplay between drug diffusion and enhancer pretreatment of the epidennis was studied. Pretreatment of the membrane with 10% Azone/PG demonstrated the highest diffusion rate followed by 10% olcic acid/PG pretreatment compared to other pretreatment regimens (ethanol, dimethyl sulfoxide (DMSO), propylene glycol (PG), sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DT AB). Differential Scanning Calorimetry (DSC) was also employed to study the mode of action of these enhancers. The potential of supersaturated solutions in enhancing percutaneous absorption of CHX was investigated. Various anti-nucleating polymers were screened in order to establish the most effective agent. Polyvinylpyrrolidone (PVP, K30) was found to be a better candidate than its lower molecular weight counterpart (K25) and hydroxypropyl methyleellulose (HPMC). The permeation studies showed an increase in diffusion rate by increasing the degree of saturation. Iontophoresis is a physical means of transdemal drug delivery enhancement that causes an increased penetration of molecules into or through the skin by the application of an electric field. This technique was employed in conjunction with chemical enhancers to assess the effect on CHX permeation across the human epidermis. An improved transport of CHX, which was pH dependant was observed upon application of the current. Combined use of iontophoresis and chemical enhancers further increased the CHX transport indicating a synergistic effect. Pretreatment of the membrane with 10% Azone/PG demonstrated the greatest effect.

The role of insulin and the insulin-like growth factors in the proliferation of the rat thymic lymphocyte

Concanavalin A, provoked a 35-fold increase in the rate of proliferation of rat thymocytes. Insulin (10-6M), and insulin-like growth factor I (10-10M) approximately doubled the rate of DNA synthesis. Both of these structurally related molecules acted through the type I insulin-like growth factor receptor. The sequential addition of Concanavalin A and insulin, promoted a much greater proliferative response than to either of the two agonists alone. Insulin also increased the uptake of glucose and amino acids by the cells. Glucose uptake was enhanced at insulin concentrations of 10-6M and 10-10M. Amino acid uptake was more strongly affected at the higher concentration. Insulin-like growth factor I (10-11M) also enhanced amino acid uptake. The effects of insulin on metabolism were mediated by both insulin and type I insulin-like growth factor receptors. These effects were greatly enhanced after a pre-treatment with Concanavalin A. Concanavalin A provided a primary mitogenic signal to the cells. Amongst the responses was an increased expression of insulin and/or type I insulin-like growth factor receptors. The consequent enhanced cellular sensitivity to these agonists, enabled them to facilitate the passage of the cells through the cell cycle by: i) providing a secondary mitogenic signal, and ii) promoting the uptake of raw materials and energy substrates. The initiation of DNA synthesis and passage through the cell cycle was thus punctuated by the sequential expression of various cell surface receptors. This regulated cellular sensitivity, enabling them to react in a precisely orchestrated fashion to hormones and other molecules in their environment. The intracellular mechanism of insulin action remains an enigma. Although the presence of extracellular calcium was essential for insulin stimulation of amino acid uptake and DNA synthesis, the cation did not subserve a direct mediator function. Insulin promoted an increase in intracellular pH, which was mediated by the Na+/H+ antiport. Other mechanisms were probably also involved in mediating the full cellular response to insulin.

Concentration of the UK stock market

During 1999 and 2000 a large number of articles appeared in the financial press which argued that the concentration of the FTSE 100 had increased. Many of these reports suggested that stock market volatility in the UK had risen, because the concentration of its stock markets had increased. This study undertakes a comprehensive measurement of stock market concentration using the FTSE 100 index. We find that during 1999, 2000 and 2001 stock market concentration was noticeably higher than at any other time since the index was introduced. When we measure the volatility of the FTSE 100 index we do not find an association between concentration and its volatility. When we examine the variances and covariance’s of the FTSE 100 constituents we find that security volatility appears to be positively related to concentration changes but concentration and the size of security covariances appear to be negatively related. We simulate the variance of four versions of the FTSE 100 index; in each version of the index the weighting structure reflects either an equally weighted index, or one with levels of low, intermediate or high concentration. We find that moving from low to high concentration has very little impact on the volatility of the index. To complete the study we estimate the minimum variance portfolio for the FTSE 100, we then compare concentration levels of this index to those formed on the basis of market weighting. We find that realised FTSE index weightings are higher than for the minimum variance index.

Protein interactions studied by SAXS:effect of ionic strength and protein concentration for BSA in aqueous solutions

We have studied a series of samples of bovine serum albumin (BSA) solutions with protein concentration, c, ranging from 2 to 500 mg/mL and ionic strength, I, from 0 to 2 M by small-angle X-ray scattering (SAXS). The scattering intensity distribution was compared to simulations using an oblate ellipsoid form factor with radii of 17 x 42 x 42 A, combined with either a screened Coulomb, repulsive structure factor, S-SC(q), or an attractive square-well structure factor, S-SW(q). At pH = 7, BSA is negatively charged. At low ionic strength, I <0.3 M, the total interaction exhibits a decrease of the repulsive interaction when compared to the salt-free solution, as the net surface charge is screened, and the data can be fitted by assuming an ellipsoid form factor and screened Coulomb interaction. At moderate ionic strength (0.3-0.5 M), the interaction is rather weak, and a hard-sphere structure factor has been used to simulate the data with a higher volume fraction. Upon further increase of the ionic strength (I >= 1.0 M), the overall interaction potential was dominated by an additional attractive potential, and the data could be successfully fitted by an ellipsoid form factor and a square-well potential model. The fit parameters, well depth and well width, indicate that the attractive potential caused by a high salt concentration is weak and long-ranged. Although the long-range, attractive potential dominated the protein interaction, no gelation or precipitation was observed in any of the samples. This is explained by the increase of a short-range, repulsive interaction between protein molecules by forming a hydration layer with increasing salt concentration. The competition between long-range, attractive and short-range, repulsive interactions accounted for the stability of concentrated BSA solution at high ionic strength.