Estimating the level of carbamoylated plasma non-high-density lipoproteins using infrared spectroscopy

Background: The increased cardiovascular morbidity and mortality observed in chronic kidney disease (CKD) patients can be partly explained by the presence of carbamoylated lipoproteins. Lipid profiles can be determined with infrared spectroscopy. In this paper, the effects of carbamoylation on spectral changes of non-high-density lipoproteins (non-HDL) were studied. Methods: In the present study, fasting serum samples were obtained from 84 CKD patients (CKD stage 3-5: n = 37 and CKD stage 5d (hemodialysis): n = 47) and from 45 healthy subjects. In vitro carbamoylation of serum lipoproteins from healthy subjects was performed using increasing concentrations of potassium cyanate. Lipoprotein-containing pellets were isolated by precipitation of non-HDL. The amount of carbamoylated serum non-HDL was estimated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, followed by soft independent modelling by class analogy analysis. Results: Carbamoylation resulted in a small increase of the amide I band (1714-1589 cm(-1)) of the infrared spectroscopy (IR) spectrum. A significant difference in the amide II/amide I area under the curves (AUC) ratio was observed between healthy subjects and CKD patients, as well as between the two CKD groups (non-dialysis versus hemodialysis patients). Conclusions: ATR-FTIR spectroscopy can be considered as a novel method to detect non-HDL carbamoylation

Albumin assays and clinical decision-making in nephrotic syndrome patients

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Carbamoylated nail proteins as assessed by near-infrared analysis are associated with load of uremic toxins and mortality in hemodialysis patients

Carbamoylation is an important risk factor for accelerated atherogenesis and mortality in patients undergoing hemodialysis (HD). We intended to explore whether carbamoylation as assessed by near-infrared (NIR) analysis of nail proteins is associated with (a) plasma concentrations of representative uremic toxins and (b) mortality in HD patients. A total of 53 healthy volunteers and 84 consecutive HD patients were enrolled in this cross-sectional cohort study. Standard laboratory methods were used to measure routine parameters, whereas levels of uremic toxins were determined using reversed-phase high-performance liquid chromatography (RP-HPLC). Spectra of distal fingernail clippings were obtained using an Avantes NIR spectrometer and processed using chemometric data analysis. The second derivative of the peak intensity at 1494 nm attributed to N-H amide bands from NH2 of carbamoyl (-CONH2) groups was higher in HD patients than in control subjects (p < 0.0001). Peak intensity levels were associated with age and plasma levels of representative uremic toxins. Cox-regression analysis revealed a significant association with all-cause mortality, even after adjustment for age. In conclusion, our data revealed that carbamoylation as assessed by NIR analysis of nail proteins is associated with plasma concentrations of uremic toxins and also with mortality in HD patients. Further research to explore whether it is a surrogate marker or a hard indicator of mortality risk is warranted

Binding of bromocresol green and bromocresol purple to albumin in hemodialysis patients

BACKGROUND: Colorimetric albumin assays based on binding to bromocresol purple (BCP) and bromocresol green (BCG) yield different results in chronic kidney disease. Altered dye binding of carbamylated albumin has been suggested as a cause. In the present study, a detailed analysis was carried out in which uremic toxins, acute phase proteins and Kt/V, a parameter describing hemodialysis efficiency, were compared with colorimetrically assayed (BCP and BCG) serum albumin. METHODS: Albumin was assayed using immunonephelometry on a BN II nephelometer and colorimetrically based on, respectively, BCP and BCG on a Modular P analyzer. Uremic toxins were assessed using high-performance liquid chromatography. Acute phase proteins (C-reactive protein and α1-acid glycoprotein) and plasma protein α2-macroglobulin were assayed nephelometrically. In parallel, Kt/V was calculated. RESULTS: Sixty-two serum specimens originating from hemodialysis patients were analyzed. Among the uremic toxins investigated, total para-cresyl sulfate (PCS) showed a significant positive correlation with the BCP/BCG ratio. The serum α1-acid glycoprotein concentration correlated negatively with the BCP/BCG ratio. The BCP/BCG ratio showed also a negative correlation with Kt/V. CONCLUSIONS: In renal insufficiency, the BCP/BCG ratio of serum albumin is affected by multiple factors: next to carbamylation, uremic toxins (total PCS) and α1-acid glycoprotein also play a role

Detection and characterization of a biochemical signature associated with diabetic nephropathy using near-infrared spectroscopy on tissue sections

Histological evaluation of renal biopsies is currently the gold standard for acquiring important diagnostic and prognostic information in diabetic nephropathy (DN) patients. Nevertheless, there is an unmet clinical need for new biomarkers that allow earlier diagnosis and risk stratification. As biochemical changes in tissues must precede any symptomatic or morphological expression of a disease, we explored the potential of near-infrared (NIR) spectroscopy in the detection of a biochemical signature associated with DN. Kidney tissue sections were investigated using NIR spectroscopy, followed by principal component analysis and soft independent modelling of class analogy. A biochemical signature indicative of DN was detected, which enabled perfect discrimination between tissue sections with normal histological findings (n = 27) and sections obtained from DN patients (n = 26). Some spectral changes related to carbamoylation and glycation reactions appeared to be similar to the ones obtained in patients with DN. In addition, treatment with the deglycating enzyme fructosamine-3-kinase resulted in partial to pronounced restorations of the spectral pattern. Significant relationships were found between spectral features and laboratory parameters indicative of glycemic and uremic load, such as hemoglobin A1c, urea, creatinine, estimated glomerular filtration rate, and proteinuria. The presented method could be a useful tool to complement histopathological analysis in order to prevent or delay further disease progression, especially in the setting of post-transplant surveillance kidney biopsies

Urinary myeloid IgA Fc alpha receptor (CD89) and transglutaminase-2 as new biomarkers for active IgA nephropathy and henoch-Schönlein purpura nephritis

Background: IgA nephropathy (IgAN) and Henoch-Schönlein purpura nephritis (HSPN) are glomerular diseases that share a common and central pathogenic mechanism. The formation of immune complexes containing IgA1, myeloid IgA Fc alpha receptor (FcαRI/CD89) and transglutaminase-2 (TG2) is observed in both conditions. Therefore, urinary CD89 and TG2 could be potential biomarkers to identify active IgAN/HSPN. Methods: In this multicenter study, 160 patients with IgAN or HSPN were enrolled. Urinary concentrations of CD89 and TG2, as well as some other biochemical parameters, were measured. Results: Urinary CD89 and TG2 were lower in patients with active IgAN/HSPN compared to IgAN/HSPN patients in complete remission (P &lt; 0.001). The CD89xTG2 formula had a high ability to discriminate active from inactive IgAN/HSPN in both situations. : CD89xTG2/proteinuria ratio (AUC: 0.84, P &lt; 0.001, sensitivity: 76%, specificity: 74%) and CD89xTG2/urinary creatinine ratio (AUC: 0.82, P &lt; 0.001, sensitivity: 75%, specificity: 74%). Significant correlations between urinary CD89 and TG2 (r = 0.711, P &lt; 0.001), proteinuria and urinary CD89 (r = -0.585, P &lt; 0.001), and proteinuria and urinary TG2 (r = -0.620, P &lt; 0.001) were observed. Conclusions: Determination of CD89 and TG2 in urine samples can be useful to identify patients with active IgAN/HSPN