Rodents respond to a chronic high-fat diet (HFD) in two ways: some readily become obese (obesity prone, OP) and others do not (obesity resistant, OR). Although several hypotheses have been proposed, the mechanisms underlying the inter-individual susceptibility to diet-induced obesity remain to be fully defined. In the present study, two-dimensional gel electrophoresis (2-DE) combined with matrix-assisted laser desorption ionisation time-of-flight MS was carried out for identification of differentially expressed liver proteins in OP and OR rats fed a HFD, in an attempt to discover marker proteins involved in susceptibility and/or resistance to obesity in rat liver. The 2-DE analysis demonstrated that forty spots from 380 visualised spots were differentially regulated between the groups. Among these forty spots, twelve were differentially expressed proteins between OP and OR rats, reaching statistical significance. Of these, five proteins have already been linked to obesity; however, seven proteins involved in obesity susceptibility or resistance were identified for the first time in the present study. In order to validate the proteomic results and gain insight into the metabolic changes between the OP and OR groups, we further confirmed the expression pattern of some proteins of interest by Western blot analysis. Combined results of proteomic analysis with Western blot analysis revealed that reduced lipogenesis and increased fat oxidation were achieved in the livers of OR rats. In conclusion, the present proteomic study is an important advance over the previous steps required for identification of OP and OR rats, and should prove valuable in the search for the pathogenesis of obesity in humans.

Proteins of the piroplasms of Theileria sergenti, T. buffeli and T. orientalis were analysed by two-dimensional polyacrylamide gel electrophoresis. Protein spot patterns of T. buffeli and T. orientalis were identical except for a few minor proteins, whereas spot patterns of two T. sergenti stocks were differentiated from those of T. buffeli and T. orientalis by a characteristic set of proteins including a major protein of molecular weight 33–34 kDa. This result indicates that Japanese T. sergenti can be phenotypically distinguishable from European and Australia Theileria species; T. orientalis and T. buffeli.

Sodium fluoride (NaF) is an anion that has been previously shown to block the moulting process of Ascaris suum larvae. This study describes moulting and development-specific protein expression profiles of A. suum lung-stage L3 (AsLL3) following NaF exposure. AsLL3s cultured in the presence or absence of NaF were prepared for protein analysis using two-dimensional (2D) electrophoresis. NaF exposure inhibited at least 22 proteins in AsLL3 compared with moulted larvae (i.e. AsLL4). A further comparison of AsLL4 with those of pre-cultured AsLL3 and NaF-exposed AsLL3 revealed 8 stage-specifically and 4 over-expressed proteins. Immunoblot analysis revealed an inhibition by NaF of 19 immunoreactive proteins. Enzyme assay and immunochemical data showed an inhibition of the moulting-specific inorganic pyrophosphatase activity by 41% and a decreased expression in NaF-treated larvae, indicating its significance in the moulting process. A protein spot associated with NaF inhibition was isolated and identified by peptide mass spectrometry and bioinformatics approaches to be a member of 3–hydroxyacyl–CoA dehydrogenase/short-chain dehydrogenase enzyme families. These results have implications for the identification of proteins specific to the moulting process as potential chemotherapeutic targets.

The global profiling of the whole protein complement of the genome expressed in a particular cell or organ, or in plasma or serum, makes it possible to identify biomarkers that respond to alterations in diet or to treatment, and that may have predictive value for the modelling of biological processes. Proteomics has not yet been applied on a large scale in nutritional studies, yet it has advantages over transcriptome profiling techniques in that it directly assesses the entities that carry out the biological functions. The present review summarizes the different approaches in proteomics research, with special emphasis on the current technical ‘workhorses’: two-dimensional (2D)-PAGE with immobilized pH gradients and protein identification by MS. Using a work-flow approach, we provide information and advice on sample handling and preparation, protein solubilization and pre-fractionation, protein separation by 2D-PAGE, detection and quantification via computer-assisted analysis of gels, and protein identification and characterization techniques by means of MS. Examples from nutritional studies employing proteomics are provided to demonstrate not only the advantages but also the limitations of current proteome analysis platforms.

The high dietary protein requirements of salmonid fish are met with fishmeal-based feed in commercial aquaculture. The sustainability of this practice is questionable and, therefore, the feasibility of substituting fishmeal with plant-based products needs to be investigated. We investigated growth and metabolism in rainbow trout (Oncorhynchus mykiss) fed a diet composed of a mixture of plant proteins compared with those fed a fishmeal-based diet. Using two-dimensional gel electrophoresis of liver protein extracts, we showed that the liver protein profile changed in response to the alteration in the diet. A number of metabolic pathways were identified as sensitive to the protein source substitution. These included pathways involved in primary energy generation, maintenance of reducing potential, bile acid synthesis, and transport and cellular protein degradation. Interestingly, the pathways shown to be affected in the present study were somewhat different from those identified in our previous work with soyabean-based-protein replacement of fishmeal, with the effects on the abundance of several stress response proteins notably absent. We conclude, therefore, that the metabolic effects of plant protein replacement in aquaculture feed varies with plant-protein source.

Two-dimensional gel electrophoresis was used to compare the protein profiles of two geographically isolated populations of the tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) in Kenya. Most of the protein spots were common to both populations, but a number were specific to each population. Since proteins are encoded by genes, the presence of population-specific proteins suggests that there may be genetic differences between the two populations. It is proposed that some of these population-specific proteins might be related to the differences in susceptibility of the ticks to Tlwileria pnrva infection.