Vitamin D-binding protein as a biomarker of active disease in acute intermittent porphyria

Murine models of the human porphyrias: Contributions toward understanding disease pathogenesis and the development of new therapies

Mouse models of the human porphyrias have proven useful for investigations of disease pathogenesis and to facilitate the development of new therapeutic approaches. To date, mouse models have been generated for all major porphyrias, with the exception of X-linked protoporphyria (XLP) and the ultra rare 5-aminolevulinic acid dehydratase deficient porphyria (ADP). Mouse models have been generated for the three autosomal dominant acute hepatic porphyrias, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). The AIP mice, in particular, provide a useful investigative model as they have been shown to have acute biochemical attacks when induced with the prototypic porphyrinogenic drug, phenobarbital. In addition to providing important insights into the disease pathogenesis of the neurological impairment in AIP, these mice have been valuable for preclinical evaluation of liver-targeted gene therapy and RNAi-mediated approaches. Mice with severe HMBS deficiency, which clinically and biochemically mimic the early-onset homozygous dominant AIP (HD-AIP) patients, have been generated and were used to elucidate the striking phenotypic differences between AIP and HD-AIP. Mice modeling the hepatocutaneous porphyria, porphyria cutanea tarda (PCT), made possible the identification of the iron-dependent inhibitory mechanism of uroporphyrinogen decarboxylase (UROD) that leads to symptomatic PCT. Mouse models for the two autosomal recessive erythropoietic porphyrias, congenital erythropoietic porphyria (CEP) and erythropoeitic protoporphyria (EPP), recapitulate many of the clinical and biochemical features of the severe human diseases and have been particularly useful for evaluation of bone marrow transplantation and hematopoietic stem cell (HSC)-based gene therapy approaches. The EPP mice have also provided valuable insights into the underlying pathogenesis of EPP-induced liver damage and anemia.

Multicentric study of the effect of pre-analytical variables in the quality of plasma samples stored in biobanks using different complementary proteomic methods

Analytical proteomics has experienced exponential progress in the last decade and can be expected to lead research studies on diagnostic and therapeutic biomarkers in the near future. Because the development of this type of analysis requires the use of a large number of human samples with a minimum of quality requirements, our objective was to identify appropriate indicators for quality control of plasma samples stored in biobanks for research in proteomics. To accomplish this, plasma samples from 100 healthy donors were obtained and processed according to the pre-analytical variables of: a) time delay for the first centrifugation of the original blood sample (4 or 24h) and b) number of freeze/thaw cycles (1, 2 or 3) of the processed plasma samples. The analyses of samples were performed by different and complementary methods such as SPE MALDI-TOF, DIGE, shotgun (iTRAQ, nLC MALDI TOF/TOF) and targeted nLC MS/MS proteomic techniques (SRM). In general, because the distribution of proteins in all samples was found to be very similar, the results shown that delayed processing of blood samples and the number of freeze/thaw cycles has little or no effect on the integrity of proteins in the plasma samples.

SIGNIFICANCE

The results of the present work indicate that blood proteins in plasma are broadly insensitive to such preanalytical variables as delayed processing or freeze/thaw cycles when analyzed at the peptide level. Although there are other studies related to protein stability of clinical samples with similar results, what is remarkable about our work is the large number of plasma samples examined and that our analyses assessed protein integrity by combining a wide set of complementary proteomic approaches performed at different proteomic platform participating laboratories that all yielded similar results. We believe our study is the most comprehensive performed to date to determine the changes in proteins induced by delayed sample processing and plasma freeze/thaw cycles.