Elevated serum phosphate predicts mortality in renal transplant recipients

BACKGROUND.: High serum phosphate has been identified as an important contributor to the vascular calcification seen in patients with chronic kidney disease (Block et al., Am J Kidney Dis 1998; 31: 607). In patients on hemodialysis, elevated serum phosphate levels are an independent predictor of mortality (Block et al., Am J Kidney Dis 1998; 31: 607; Block, Curr Opin Nephrol Hypertens 2001; 10: 741). The aim of this study was to investigate whether an elevated serum phosphate level was an independent predictor of mortality in patients with a renal transplant.
METHODS.: Three hundred seventy-nine asymptomatic renal transplant recipients were recruited between June 2000 and December 2002. Serum phosphate was measured at baseline and prospective follow-up data were collected at a median of 2441 days after enrolment.
RESULTS.: Serum phosphate was significantly higher in those renal transplant recipients who died at follow-up when compared with those who were still alive at follow-up (P<0.001). In Kaplan-Meier analysis, serum phosphate concentration was a significant predictor of mortality (P=0.0001). In multivariate Cox regression analysis, serum phosphate concentration remained a statistically significant predictor of all-cause mortality after adjustment for traditional cardiovascular risk factors, estimated glomerular filtration rate, and high sensitivity C reactive protein (P=0.036) and after adjustment for renal graft failure (P=0.001).
CONCLUSIONS.: The results of this prospective study are the first to show that a higher serum phosphate is a predictor of mortality in patients with a renal transplant and suggest that serum phosphate provides additional, independent, prognostic information to that provided by traditional risk factors in the risk assessment of patients with a renal transplant.

Structural basis of substrate selectivity in the glycerol-3-phosphate: phosphate antiporter GlpT.

Major facilitators represent the largest superfamily of secondary active transporter proteins and catalyze the transport of an enormous variety of small solute molecules across biological membranes. However, individual superfamily members, although they may be architecturally similar, exhibit strict specificity toward the substrates they transport. The structural basis of this specificity is poorly understood. A member of the major facilitator superfamily is the glycerol-3-phosphate (G3P) transporter (GlpT) from the Escherichia coli inner membrane. GlpT is an antiporter that transports G3P into the cell in exchange for inorganic phosphate (Pi). By combining large-scale molecular-dynamics simulations, mutagenesis, substrate-binding affinity, and transport activity assays on GlpT, we were able to identify key amino acid residues that confer substrate specificity upon this protein. Our studies suggest that only a few amino acid residues that line the transporter lumen act as specificity determinants. Whereas R45, K80, H165, and, to a lesser extent Y38, Y42, and Y76 contribute to recognition of both free Pi and the phosphate moiety of G3P, the residues N162, Y266, and Y393 function in recognition of only the glycerol moiety of G3P. It is the latter interactions that give the transporter a higher affinity to G3P over Pi.

The schistosome excretory system: a key to regulation of metabolism, drug excretion and host interaction

There is a gulf between the enormous information content of the various genome projects and the understanding of the life of the parasite in the host. In vitro studies with adult Schistosoma mansoni using several substrates suggest that the excretory system contains both P-glycoproteins and multiresistance proteins. If both these families of protein were active in vivo, they could regulate parasite metabolism and be responsible for the excretion of drugs. During skin penetration, membrane-impermeant molecules of a wide range of molecular weights can be taken into the cercaria and schistosomulum through the nephridiopore, through the surface membrane or through both. We speculate that this uptake process might stimulate novel signalling pathways involved in growth and development.

Effect of the metabolic inhibitor, methimazole on the drug susceptibility of a triclabendazole-resistant isolate of Fasciola hepatica

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) is altered in the presence of a metabolic inhibitor. The flavin monooxygenase system (FMO) was inhibited using methimazole (MTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-sensitive isolates Were used for these experiments. The FMO system was inhibited by a 2-h pre-incubation in methimazole (100 mu M). Flukes were then incubated for I further 22 h in NCTC medium containing either MTZ; MTZ+nicotinamide adenine dinucleotide phosphate (NADPH) (1 nm); MTZ+NADPH+TCBZ (15 mu g/ml); or MTZ+NADPH+triclabendazole sulphoxide (TCBZ.SO) (15 mu g/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed Using scanning electron microscopy'. After treatment with either TCBZ or TCBZ.SO alone, there was greater surface disruption to the triclabendazole-susceptible than -resistant isolate. However, co-incubation with MTZ and TCBZ/TCBZ.SO lead to more severe surface changes to the TCBZ-resistant isolate than with each drug oil its own; this was not seen for the TCBZ-susceptible Cullompton isolate. Results of this study support the concept of altered drug metabolism in TCBZ-Resistant flukes and this process may play a role in the development of drug resistance.

Potentiation of triclabendazole sulphoxide-induced tegumental disruption by methimazole in a triclabendazole-resistant isolate of Fasciola hepatica

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The flavin monooxygenase system (FMO) was inhibited using methimazole (MTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The FMO system was inhibited by a 2-h pre-incubation in methimazole (100 mu M), then incubated for a further 22 h in NCTC medium containing either MTZ; MTZ+nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM); MTZ+NADPH+TCBZ (15 mu g/ml); or MTZ+NADPH+triclabendazole sulphoxide (TCBZ.SO) (15 mu g/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than triclabedazole-resistant isolate. However, co-incubation with MTZ+TCBZ, but more particularly MTZ+TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own, with severe swelling of the basal infolds and mucopolysaccharide masses in the syncytium, accompanied by a reduction in numbers of secretory bodies. The synthesis and production of secretory bodies in the tegumental cells was severely affected as well. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes, and this process may play a role in the development of drug resistance.

Selective small molecule inhibitors of glycogen synthase kinase-3 modulate glycogen metabolism and gene transcription

Background: Glycogen synthase kinase-3 (GSK-8) is a serine/threonine protein kinase, the activity of which is inhibited by a variety of extracellular stimuli including insulin, growth factors, cell specification factors and cell adhesion. Consequently, inhibition of GSK-3 activity has been proposed to play a role in the regulation of numerous signalling pathways that elicit pleiotropic cellular responses. This report describes the identification and characterisation of potent and selective small molecule inhibitors of GSK-3.