Validity of the MDRD formula in different patient populations.

<p>* The MDRD formula is not valid in patients on the internal medicine and nephrology ward. For other hospitalized patients it is not tested.</p><p>Validity of the MDRD formula in different patient populations.</p

Validity of the MDRD in specific patient populations.

<p>* Not all parameters were reported in the included articles. Especially when it came to subanalysis of patients with an eGFR < 60 ml/min.1.73m².</p><p>^$ When individual data were available we calculated missing parameters ourselves.</p><p>^<i>≠</i> The MDRD-formula used was not reported. Given the time at which the study was conducted, we assume that the re-expressed MDRD-formula was used.</p><p>Validity of the MDRD in specific patient populations.</p

Flow of study selection.

<p>Flow of study selection.</p

Precision and accuracy.

<p>Source: <a href="http://www.nrcan.gc.ca/minerals-metals/non-destructive-testing/application/2914" target="_blank">http://www.nrcan.gc.ca/minerals-metals/non-destructive-testing/application/2914</a>,</p

Definitions outcome measurements.

<p>* Preferred definition because a relative scale provides a more relevant metric.</p><p>^‡ In some articles the mean percentage difference was called the mean percentage error (MPE).</p><p>^§ Preferred definition of accuracy. We limited our search to P₁₀, P₂₀, P₃₀ and P₅₀.</p><p>Definitions outcome measurements.</p

Determinants of serum creatinine level.

<p>Determinants of serum creatinine level.</p

Optimized Metabolomic Approach to Identify Uremic Solutes in Plasma of Stage 3–4 Chronic Kidney Disease Patients

<div><p>Background</p><p>Chronic kidney disease (CKD) is characterized by the progressive accumulation of various potential toxic solutes. Furthermore, uremic plasma is a complex mixture hampering accurate determination of uremic toxin levels and the identification of novel uremic solutes.</p><p>Methods</p><p>In this study, we applied ¹H-nuclear magnetic resonance (NMR) spectroscopy, following three distinct deproteinization strategies, to determine differences in the plasma metabolic status of stage 3–4 CKD patients and healthy controls. Moreover, the human renal proximal tubule cell line (ciPTEC) was used to study the influence of newly indentified uremic solutes on renal phenotype and functionality.</p><p>Results</p><p>Protein removal via ultrafiltration and acetonitrile precipitation are complementary techniques and both are required to obtain a clear metabolome profile. This new approach, revealed that a total of 14 metabolites were elevated in uremic plasma. In addition to confirming the retention of several previously identified uremic toxins, including p-cresyl sulphate, two novel uremic retentions solutes were detected, namely dimethyl sulphone (DMSO₂) and 2-hydroxyisobutyric acid (2-HIBA). Our results show that these metabolites accumulate in non-dialysis CKD patients from 9±7 µM (control) to 51±29 µM and from 7 (0–9) µM (control) to 32±15 µM, respectively. Furthermore, exposure of ciPTEC to clinically relevant concentrations of both solutes resulted in an increased protein expression of the mesenchymal marker vimentin with more than 10% (p<0.05). Moreover, the loss of epithelial characteristics significantly correlated with a loss of glucuronidation activity (Pearson r = −0.63; p<0.05). In addition, both solutes did not affect cell viability nor mitochondrial activity.</p><p>Conclusions</p><p>This study demonstrates the importance of sample preparation techniques in the identification of uremic retention solutes using ¹H-NMR spectroscopy, and provide insight into the negative impact of DMSO₂ and 2-HIBA on ciPTEC, which could aid in understanding the progressive nature of renal disease.</p></div

¹H resonance assignments and plasma concentrations of uremic solutes in stage 3–4 CKD patients.

<p>Values are shown as mean (C_u) ± SD or range (µM) and maximal uremic concentration (C_max,). ND, not detected; NA, not applicable.</p>a<p>Numbers correspond to peaks in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071199#pone-0071199-g003" target="_blank">Fig. 3</a>.</p>b<p>Hypothetical C_max calculated as C_max = C_u +2 SD, as previously described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071199#pone.0071199-Mutsaers1" target="_blank">[2]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071199#pone.0071199-Vanholder1" target="_blank">[3]</a>.</p>c<p>Data obtained from the Human Metabolome Database (<a href="http://www.hmdb.ca" target="_blank">www.hmdb.ca</a>) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071199#pone.0071199-Wishart1" target="_blank">[42]</a>.</p>d<p>Only detected in one patient.</p

Characteristics of study subjects.

<p>Values are shown as mean ± SD. ND, not determined.</p>a<p>Control metabolite levels were similar as compared to an established database (n = 50) from the Radboud University Nijmegen.</p>b<p>eGFR was calculated using the Modification of Diet in Renal Disease (MDRD) equation (<a href="http://www.nkdep.nih.gov" target="_blank">www.nkdep.nih.gov</a>).</p

Accumulation of uremic solutes.

<p>500 MHz ¹H-NMR spectrum of plasma (ultrafiltrate) from (<b>A</b>) a healthy control and (<b>B</b>) a CKD patient. Insets show 5 regions of interest in greater detail. Metabolite abnormalities: Creatinine (1 and 2), 1-methylhistidine (3), 3-methylhistidine (4), <i>myo</i>-Inositol (5), trimethylamine <i>N</i>-oxide (6), dimethyl sulphone (7), <i>N,N</i>-dimethylglycine (8) and 2-hydroxyisobutyric acid (9).</p