Assessment of metabolomic and proteomic biomarkers in detection and prognosis of progression of renal function in chronic kidney disease

Chronic kidney disease (CKD) is part of a number of systemic and renal diseases and may reach epidemic proportions over the next decade. Efforts have been made to improve diagnosis and management of CKD. We hypothesised that combining metabolomic and proteomic approaches could generate a more systemic and complete view of the disease mechanisms. To test this approach, we examined samples from a cohort of 49 patients representing different stages of CKD. Urine samples were analysed for proteomic changes using capillary electrophoresis-mass spectrometry and urine and plasma samples for metabolomic changes using different mass spectrometry-based techniques. The training set included 20 CKD patients selected according to their estimated glomerular filtration rate (eGFR) at mild (59.9±16.5 mL/min/1.73 m2; n = 10) or advanced (8.9±4.5 mL/min/1.73 m2; n = 10) CKD and the remaining 29 patients left for the test set. We identified a panel of 76 statistically significant metabolites and peptides that correlated with CKD in the training set. We combined these biomarkers in different classifiers and then performed correlation analyses with eGFR at baseline and follow-up after 2.8±0.8 years in the test set. A solely plasma metabolite biomarker-based classifier significantly correlated with the loss of kidney function in the test set at baseline and follow-up (ρ = −0.8031; p<0.0001 and ρ = −0.6009; p = 0.0019, respectively). Similarly, a urinary metabolite biomarker-based classifier did reveal significant association to kidney function (ρ = −0.6557; p = 0.0001 and ρ = −0.6574; p = 0.0005). A classifier utilising 46 identified urinary peptide biomarkers performed statistically equivalent to the urinary and plasma metabolite classifier (ρ = −0.7752; p<0.0001 and ρ = −0.8400; p<0.0001). The combination of both urinary proteomic and urinary and plasma metabolic biomarkers did not improve the correlation with eGFR. In conclusion, we found excellent association of plasma and urinary metabolites and urinary peptides with kidney function, and disease progression, but no added value in combining the different biomarkers data

Regulation of human renal adenocarcinoma cell growth by retinoic acid and its interactions with epidermal growth factor

Regulation of human renal adenocarcinoma cell growth by retinoic acid and its interactions with epidermal growth factor. Retinoic acid (RA) is a natural derivative of vitamin A which regulates the growth and differentiation of epithelia. We have previously proposed that RA participates in compensatory kidney growth and reported that RA inhibits rat mesangial cell growth. This paper describes the effects of RA on a human renal adenocarcinoma cell line (PAD) under different growth conditions, and its interactions with epidermal growth factor (EGF). PAD cells were shown to express RA receptors α and β by Northern blot analysis. In serum free cultures, addition of RA (10-7 M) markedly increased thymidine incorporation by PAD cells (155 ± 7% mean ± se vs. control in 6 separate experiments; P < 0.0001). RA also caused a significant increase in thymidine incorporation by PAD cells under conditions of rapid growth in serum supplemented medium (115 ± 2% vs. control; P < 0.001). RA by itself was unable to reverse contact inhibition of PAD cell growth (NS vs. control), but it synergistically enhanced the mitogenic effect of EGF on confluent monolayers (110 ± 0.6% vs. EGF alone; P < 0.05). Northern blot analysis demonstrated that PAD cells express EGF receptor mRNA, and this was not significantly modified by the addition of RA. Growth arrested (serum starved) PAD cells expressed RAR-α mRNA which was up-regulated eightfold at three hours following the addition of 10% FCS. Thus, our data show that RA is directly mitogenic for serum starved human renal adenocarcinoma cells and that it exerts complex modulation of cell growth in the presence of EGF and serum components

Is Plasma Proteomics Able to Provide Alternative Paths to Better Understand Hypertension?

International audienceThe history of hypertension research is sweet sour. Huge advances have been marred by the persistence of huge black boxes. The term primary hypertension epitomizes the issue: the underlying causes and pathophysiology of most cases of hypertension remain undefined. Furthermore, guideline panels are unable to agree on desirable target blood pressure values, and it may be the time to think about the cure of hypertension rather than just the control of blood pressure. The quote attributed to Einstein, “Insanity: doing the same thing over and over again and expecting different results” may provide some clues. It is likely that the next large conceptual leaps in our understanding of hypertension are based on the application of a novel technology not previously used for this purpose. In this regard, scientific advances depend to a large extent on technological advances that make them possible.1 Hypothesis-based approaches must rely on current knowledge, and we are aware that this is limited. Systems biology provides a nonbiased approach that recognizes the current limitations of our understanding of hypertension. Gajjala et al2 have used plasma proteomics to identify in a nonbiased manner potential molecular determinants that allowed the development of a model capable to discriminate between hypertensive and normotensive individuals. There are 2 main potential clinical consequences of these studies: the use of the proteomics panel as a biomarker and the identification of putative contributors to the pathophysiology of hypertension. As a biomarker of hypertension, the panel cannot, by definition, outperform a cheap and easy to use, noninvasive approach: measurement of blood pressure. So further studies are needed to explore whether the proteomics model may predict outcomes, response to therapy, define risk categories, or even more important, predict the development of clinical hypertension. In addition, as the authors point out, the identified molecular determinants, corresponding to 15 proteins and 1 amino acid, may be the starting point for further studies to clarify the molecular pathophysiology of hypertension.2 Interestingly, the concentrations of fragments corresponding to 11 proteins and tryptophan were decreased in hypertension, whereas those corresponding to 4 proteins (osteocalcin, PRUNE, RAB13, and sarcolipin) were increased. A bioinformatics analysis could not integrate in a single pathway all the identified features. This may represent the involvement of multiple different pathways, current limitations in understanding the potential interconnections between these features or the presence of red herrings. Moreover, despite the statistical association with hypertension, it is currently unknown whether these features may contribute to the pathophysiology of hypertension or are the consequence of hypertension, its complications, associated comorbidities, or therapy. The identified fragments correspond to proteins diverse in their primary location (intracellular or extracellular), as well as in their known functions (enzymes, ion channels, transcription factors, and others). The authors are correct in avoiding any speculation on the potential relationship or function of these peptides in the hypertension context. The possibilities are too wide at this point. A first step would be to validate the findings in a similar hypertensive population. Functional in vivo studies are then required to assess causality

Vascular calcification in different arterial beds in ex vivo ring culture and in vivo rat model

International audienceVascular calcification is a risk factor for cardiovascular and kidney diseases. Medial calcification may differently affect the arterial tree depending on vessel location and smooth muscle injury. The aim was to map the anatomical distribution of vascular calcifications on different arteries and artery locations, in cultured artery rings (ex vivo) and in a rat model of elastocalcinosis (in vivo). Vascular calcification was assessed histologically (von Kossa staining of the media) and by calcium content measurement. Arteries of different sizes were harvested from untreated rats for ring culture and from the vitamin D 3 -nicotine (VDN) rat model for direct observation. When cultured in pro-calcifying conditions, thoracic aorta exhibited similar calcification from the arch to the diaphragm. Calcification increased in abdominal aorta along with the reduction in cross sectional area. Carotid and renal arteries exhibited similar ex vivo calcification. In VDN rats, calcification was greater in carotid artery than in aorta, and was accompanied by fibrosis and apoptosis. Ex vivo, calcification was increased by the induction of lesions on arteries. Along the vascular tree, calcification of the arterial wall increases with the narrowing of vessels in ex vivo ring culture and in vivo. The observed differences represent local susceptibility of the vessels to the calcifying processes