Malcolm N. Jones

The biodegradation of surfactants in the environment.

The possible contamination of the environment by surfactants arising from the widespread use of detergent formulations has been reviewed. Two of the major surfactants in current use are the linear alkylbenzene sulphonates (LAS) and the alkyl phenol ethoxylates (APE). These pass into the sewage treatment plants where they are partially aerobically degraded and partially adsorbed to sewage sludge that is applied to land. The biodegradation of these and a range of other surfactants both in wastewater treatment plants and after discharge into natural waters and application to land resulting in sewage sludge amended soils has been considered. Although the application of sewage sludge to soil can result in surfactant levels generally in a range 0 to 3 mg kg(-1), in the aerobic soil environment a surfactant can undergo further degradation so that the risk to the biota in soil is very small, with margins of safety that are often at least 100. In the case of APE, while the surfactants themselves show little toxicity their breakdown products, principally nonyl and octyl phenols adsorb readily to suspended solids and are known to exhibit oestrogen-like properties, possibly linked to a decreasing male sperm count and carcinogenic effects. While there is little serious risk to the environment from commonly used anionic surfactants, cationic surfactants are known to be much more toxic and at present there is a lack of data on the degradation of cationics and their fate in the environment.

Fatty acid chain length determines cholecystokinin secretion and effect on human gastric motility

BACKGROUND & AIMS Fatty acids induce cholecystokinin (CCK) secretion and modify gastric motility, but the chain length requirements for these effects are not known. Nor is it clear whether the effects of fatty acids on gastric motility in humans are CCK mediated or directly exerted. The aim of this study was to determine the role of fatty acyl chain length in CCK secretion and in influencing gastric motility. METHODS Fatty acids were infused into the upper gut in healthy volunteers; plasma CCK was determined by radioimmunoassay. Effects of fatty acids on antral contractility were determined by percutaneous ultrasonography; effects on proximal gastric tone were studied during fundal distention. RESULTS Plasma CCK concentration was consistently and similarly elevated by fatty acids with a chain of 12 carbon atoms or longer, whereas those of 11 or fewer carbon atoms failed to increase plasma CCK. A 12-carbon but not a 10-carbon-long chain fatty acid reduced antral contractile amplitude, an effect that was abolished by loxiglumide (a specific CCK-A receptor antagonist). The 12-carbon fatty acid also reduced proximal gastric tone more than the 10-carbon fatty acid. CONCLUSIONS A highly specific, chain length-sensitive fatty acid recognition system exists in the proximal gut mediating CCK secretion and gastric motility. An additional, probably CCK-independent, effect of fatty acid also regulates proximal gastric tone.

Colloidal properties of humic substances

Abstract Humic substances are structurally complex large to macromolecules which occur in soils and natural waters as a consequence of the breakdown of plant and animal residues by microbial activity. A major portion (approx. 50%) of the earths carbon is in the form of humic materials (fulvic and humic acids). The characterisation of humic substances is a major problem due to their heterogeneity both in terms of structure and size and to their tendency to associate in solutions as their concentration increases. Methods of characterisation of humic materials are reviewed and their interactions with substances such as clay particles, herbicides, pesticides and metallic ions which occur in the natural environment considered. The experimental methods of investigating the binding of metallic ions are also reviewed. There have been several approaches to the molecular modelling of metal ion binding based on the representation of humic molecules as colloidal particles with an associated electrical double layer. The various theoretical models have been described and the relative merits of the approaches compared.

Surfactants in membrane solubilisation

An understanding of the action of many drugs requires a knowledge of how the drug reaches the site of action in a cell. A detailed knowledge of the structure and function of cell membranes is often required to understand the transport of drugs across the plasma membrane. To obtain this information proteins must be isolated. The isolation and characterisation of cell membrane proteins usually requires the solubilisation of the membrane and a method of separation of the various membrane proteins and glycoproteins. The starting point for such an investigation is the choice of a suitable surfactant (detergent) to solubilise the membrane. This review considers the range of surfactants that are available for membrane solubilisation, how surfactants interact with membranes, the part they play in the separation of integral membrane proteins and in the reconstitution of membrane proteins for functional studies. The solubilisation of specific membrane proteins and glycoproteins including the human erythrocyte anion transporter, mitochondrial porin, sarcoplasmic reticulum Ca(2+)-ATPase, the ATPase-active multidrug transporter P-glycoprotein, bacteriorhodopsin and rhodopsin are also discussed.

The surface properties of phospholipid liposome systems and their characterisation

The field of liposome (vesicle) research has expanded considerably over the last 30 years. In physical chemical terms liposomes have many of the characteristics of colloidal particles and their stability is determined in part by the classical surface forces. It is now possible to engineer a wide range of liposomes varying in size, phospholipid composition and surface characteristics. The surfaces of liposomes can be modified by the choice of bilayer lipid as well as by the incorporation and covalent linkage of proteins (e.g. antibodies and sugar binding proteins [lectins]), glycoproteins and synthetic polymers. Much of the impetus for liposome design has come from their potential value as drug delivery systems. The development of technologies for the production of such a range of liposome systems has presented interesting problems in the characterisation of their properties. The review addresses the progress that has been made in characterising the surfaces of different types of liposomes with specific reference to their electrophoretic properties and their interpretation and the physical interactions between liposomal bilayers.

Concentrations and fluxes of dissolved organic carbon in drainage water from an upland peat system

Abstract Measurements were made of the concentrations of total and hydrophilic dissolved organic carbon (DOC) and optical absorbance at 340 nm (A 340 ) in two pools (X and Y) situated in an area of peat on Great Dun Fell, North Pennines, UK, between November 1992 and December 1996. Other chemical data were also collected. Pool X was acid (pH 3.9–5.3) while Pool Y was circumneutral (pH 5.8–6.9). Concentrations of DOC in the two pools displayed similar seasonal variations, ranging from as low as 5 mg L −1 in winter to 20 mg L −1 or more in late summer and early autumn. The ratio of hydrophilic to total DOC also showed a seasonal trend, with the highest values observed during the summer months. During the period to mid-1995, the ratio of A 340 /DOC in both pools was nearly constant, but fell by 50% following a two-month period of drought, during which time the pools were dry, remaining at the lower value throughout the remainder of the sampling period. Through a series of salt addition experiments, estimates of water flow through the pools were made during two separate periods (2 weeks and 3 weeks). The results were consistent with flows calculated using a simple rainfall-runoff model, driven by rainfall inputs, and taking into account the size and slopes of the catchment. Water flow was strongly correlated with rainfall amount and frequency, and the model could therefore be used to estimate flows over the entire sampling period. The flows were combined with concentration data to estimate fluxes of DOC. The fluxes in 1993 and 1994 were similar (15 g m −2 a −1 ) and showed a strong seasonality, with most carbon passing through the pools during the late summer and autumn. In 1995, a year of low rainfall and high temperatures, the flux was only 7.0 g m −2 a −1 , increasing again to 10 g m −2 a −1 in 1996. The results were interpreted in terms of production of dissolvable organic matter within the catchment soils during summer, and export associated with subsequent high rainfall events. The climatic conditions of 1995 appeared to have restricted the soil production of dissolvable organic matter.

Effect of grafted polyethylene glycol (PEG) on the size, encapsulation efficiency and permeability of vesicles

Liposomes have been prepared by the vesicle extrusion method (VETs) from mixtures of dipalmitoylphosphatidylcholine (DPPC), phosphatidylinositol (PI) and dipalmitoylphosphatidylethanolamine with covalently linked poly(ethylene glycol) molecular mass 5000 and 2000 (DPPE-PEG 5000 and DPPE-PEG 2000) covering a range of 0-7.5 mole%. The encapsulation of D-glucose has been studied and found to be markedly dependent on the mole% DPPE-PEG. The permeability of the liposomes to D-glucose has been measured both as a function of temperature and liposome composition. The permeability coefficients for D-glucose increase with mole% DPPE-PEG 5000 and with temperature over the range 25-50 degrees C. The activation energies for glucose permeability range from 90 to 23 kJ mol(-1). The decrease in activation energy with increasing temperature is attributed to an increasing number of bilayer defects as the liposome content of PEG-grafted lipid is increased. The dependence of D-glucose encapsulation as a function of PEG-grafted lipid content is discussed in terms of the conformation of the PEG molecules on the inner surface of the bilayer. For liposomes containing DPPE-PEG 5000 the relative percentage encapsulation of glucose, assuming that the PEG surface layer excludes glucose, is comparable to that predicted from the mushroom and brush conformational models.

Determination of molecular weights of humic substances by analytical (UV scanning) ultracentrifugation

Abstract Samples of peat humic acid (PHA) and surface water humic (WBHA) and fulvic (WBFA) acids have been extracted from Whitray Beck in North Yorkshire, U.K. The molecular weights of the extracts have been investigated by sedimentation equilibrium using an analytical ultracentrifuge equipped with a UV scanning system. The system allows measurements to be made at low concentrations of humic substances, comparable to those existing in natural humic-rich water. A method is described for correcting UV scanning data for changes in the optical properties of the materials with changing molecular weight. Measurements have also been made on reference samples of Suwannee river humic (SRHA) and fulvic (SRFA) acids from the International Humic Substances Society (IHSS). The weight-average molecular weights of the extracted samples range from approximately 2000 to 17000 and follow a series PHA > WBHA > WBFA. Apparent specific volumes of these materials were in a range from 0.45 to 0.58 cm 3 g −1 as measured by digital densimetry. All the samples studied were analysed by gel filtration, but the molecular weights determined by this method based on a globular protein calibration are not in good accord with the absolute determinations by the sedimentation-equilibrium technique. The molecular weight of the SRHA determined by sedimentation equilibrium is in good agreement with that reported by Beckett (1987) et al., based on flow field-flow fractionation.

The Interaction of Phospholipid Liposomes with Bacteria and Their Use in the Delivery of Bactericides

Liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC) incorporating the cationic lipids stearylamine (SA), dimethyldioctadecylammonium bromide (DDAB) and dimethylaminoethane carbamoyl cholesterol (DCchol) and the anionic lipids dipalmitoylphosphatidylglycerol (DPPG) and phosphatidylinositol (PI). Their adsorption to biofilms of skin-associated bacteria (Staphylococcus epidermidis and Proteus vulgaris) and oral bacteria (Streptococcus mutans and sanguis) has been investigated as a function of mole % cationic and anionic lipid. Targeting (adsorption) was most effective for the systems DPPC-chol-SA, DPPC-DPPG and DPPC-PI liposomes to S. epidermidis. The effect of extracellular mucopolysaccharide on targeting was investigated for S. epidermidis biofilms. It was found that targeting increased with the level of extracellular mucopolysaccharide for all liposome compositions studied. The delivery of the oil-soluble bactericide Triclosan and the water soluble bactericide chlorhexidine was studied for a number of liposomal compositions. Superior delivery of both bactericides relative to the free bactericide occurred for DPPC-chol-SA liposomes and for Triclosan delivery by DPPC-DPPG and DPPC-PI liposomes targeted to S. epidermidis at low bactericide concentrations. DPPC-chol-SA liposomes were also effective for delivery of Triclosan to S. sanguis biofilms. Double labelling experiments using [14C]-chlorhexidine and [3H]-DPPC suggested that there was exchange between adsorbed liposomes which had delivered bactericide to the biofilm and those in the bulk solution implying a diffusion mechanism for bactericide delivery.

Aminoglycoside antibiotics induce pH-sensitive activation of the calcium-sensing receptor

The aminoglycoside antibiotic (AGA) neomycin is a known agonist of the extracellular calcium-sensing receptor (CaR). To test whether other AGA drugs stimulate the CaR, we studied the relative effects of four AGAs on intracellular Ca(2+) concentration ([Ca(2+)](i)) using CaR-transfected human embryonic kidney (HEK)-293 cells. Gentamicin, tobramycin, and neomycin evoked dose-dependent increases in [Ca(2+)](i) with EC(50) values of 258, 177, and 43 microM, respectively, in CaR-transfected, but not in non-transfected cells. Kanamycin was ineffective at doses <1mM. Thus, AGAs stimulate the CaR with a rank order of potency that correlates positively with the number of their attached amino groups. The CaR is expressed on the apical surface of renal proximal tubule cells, which is also the site of AGA endocytosis and nephrotoxicity. In the current study, reducing extracellular pH from 7.4 to 6.9, to mimic the luminal pH of the proximal tubule, enhanced the sensitivity of the CaR to tobramycin, suggesting that the AGAs may be more potent CaR agonists in the proximal tubule than elsewhere. This pH effect was not observed when stimulating CaR with the non-ionizable agonist, Gd(3+), suggesting that the enhanced AGA effect is due to increased ionization of the drug. Thus, we show that a number of AGA drugs are capable of CaR activation and that their potency most likely relates to the number of their amino side chains and to their pH-dependent charge characteristics. The contribution of CaR activation to the pharmacological/toxicological effects of these AGAs remains to be determined.