Urine protein concentration estimation for biomarker discovery

Tailored protein corona behavior in titanium dioxide nanosheet fluorescence biosensor for protein quantification assays

The spontaneous adsorption of proteins onto nanoparticles, known as the protein corona, provides a unique perspective for designing protein-sensing biosensors. This study proposes a tailored protein corona method mediated by Tween-20 and develops a reverse-capture approach for protein quantification assays. The protein-coated microplate captures titanium dioxide nanosheets (TiO2-NS) in a phosphate buffer containing Tween-20 and generates fluorescence signals via the photocatalytic reduction of resazurin to resorufin, thereby indicating the amount of protein. The linear range of the current assay was 0.5-5 ng/mL, and the limit of detection (LOD) was 0.28 ng/mL, which is 100-1000 times more sensitive than the classical colorimetric methods. This method is suitable for the determination of proteins in artificial urine and has broad potential for practical applications.

Urinary cathepsin L is predictive of changes in albuminuria and correlates with glucosepane in patients with type 2 diabetes in a closed-cohort study

AIMS

Cathepsin D (CTSD) and L (CTSL) are lysosomal proteases which degrade and detoxify advanced glycation end product (AGE)-modified proteins which are predictive of the development of diabetic nephropathy. We aimed to quantify cathepsin levels in urine from patients with type 2 diabetes and to relate these to the amount of urinary free AGEs at baseline and with kidney function after four years of follow-up in this closed cohort study.

METHODS

We established and validated a LC MS/MS method for the quantification of CTSD and CTSL in urine. Patients with type 2 diabetes were screened for diabetic kidney disease and 141 patients were seen at baseline and after four years. CTSD and CTSL and free AGEs were quantified in urine by LC MS/MS at baseline in these patients.

RESULTS

The detection limit of CTSD and CTSL in urine was 2.4 ng/l and 19.1 ng/l, respectively. CTSD (p < 0.0001, r = 0.555) and CTSL (p < 0.0001, r = 0.608) correlated positively with albuminuria at time of recruitment. In addition levels of the proteases but not albuminuria correlated with urinary levels of the major cross-linking AGE glucosepane (CTSD: p = 0.012, r = 0.225; CTSL: p < 0.001, r = 0.376). A strong non-linear association between CTSD (r = 0.568), CTSL (r = 0.588) and change in albuminuria over four years was present. High levels of CTSL (p = 0.007, beta = -0.366) were associated with an improvement of albuminuria after four years.

CONCLUSIONS

A sensitive LC MS/MS assay for the quantification of CTSD and CTSL in urine was established. High CTSL baseline levels were associated with an improvement in albuminuria at follow-up. An increased excretion and thus detoxification of the free form of the pathogenic cross-linking AGE glucosepane could explain the positive predictive value of high CTSL levels on albuminuria.

Flavonoids interference in common protein assays: Effect of position and degree of hydroxyl substitution

Flavonoids interfere with colorimetric protein assays in a concentration- and structure-dependent manner. Degree (≥3) and position (C₃) of -OH substitution was associated with intensified interference (p < 0.05). Significant overestimation of protein (~3-5 folds) could occur at higher flavonoid concentrations (>5 μM) and is particularly evident at lower protein concentrations (25-250 μg/ml). Since, healthy human urinary protein (<200 μg/ml) and flavonoids urinary excretion (0.5-2 μg/ml) levels fall in this range, overestimation of protein concentration with flavonoids consumption in diet, including natural supplements, remains relevant issue for diagnostic and research labs. Protein precipitation by acetone to remove interfering flavonoid successfully resolves the problem.

Cetuximab enhanced the efficacy of chemotherapeutic agent in ABCB1/P-glycoprotein-overexpressing cancer cells

The overexpression of ATP-binding cassette (ABC) transporters is closely associated with the development of multidrug resistance (MDR) in certain types of cancer, which represents a formidable obstacle to the successful cancer chemotherapy. Here, we investigated that cetuximab, an EGFR monoclonal antibody, reversed the chemoresistance mediated by ABCB1, ABCG2 or ABCC1. Our results showed that cetuximab significantly enhanced the cytotoxicity of ABCB1 substrate agent in ABCB1-overexpressing MDR cells but had no effect in their parental drug sensitive cells and ABCC1, ABCG2 overexpressing cells. Furthermore, cetuximab markedly increased intracellular accumulation of doxorubicin (DOX) and rhodamine 123 (Rho 123) in ABCB1-overexpressing MDR cancer cells in a concentration-dependent manner. Cetuximab stimulated the ATPase activity but did not alter the expression level of ABCB1 or block phosphorylation of AKT and ERK. Interestingly, cetuximab decreased the cell membrane fluidity which was known to decrease the function of ABCB1. Our findings advocate further clinical investigation of combination chemotherapy of cetuximab and conventional chemotherapeutic drugs in ABCB1 overexpressing cancer patients.

Comparative Analysis of Urinary Total Proteins by Bicinchoninic Acid and Pyrogallol Red Molybdate Methods

BACKGROUND

The concentration of total proteins in urine is a good index of renal function, but its determination is found to be unreliable. The pyrogallol red molybdate (PRM) method for urine total proteins is being widely used in most of the hospitals because of its high sensitivity, better precision and its practicability. Bicinchoninic acid method (BCA) is also used for protein estimation and there have been no studies comparing this method with the PRM method in human urine samples. BCA method overestimates the urinary protein concentration in the presence of interfering substances. After removing the interfering substances present in the human urine samples the results of BCA method were compared with the PRM method.

AIM

The purpose of the study is to identify whether the results of urine total proteins by BCA method are comparable to PRM method and can be used as an alternative to the PRM method.

SETTING AND DESIGN

This is a cross-sectional study done on fresh urine specimens from the hospital laboratory, covering a wide range of protein concentrations.

MATERIAL AND METHODS

Fresh urine specimens covering a wide range of protein concentrations (urine dipstick: nil, trace, 1+, 2+ and ≥ 3+) of 36 patients were analysed by both the methods.

STATISTICAL ANALYSIS

Imprecision was determined by repeated analysis study and Inaccuracy was assessed by comparing the results of the patient's urine samples by both the methods using correlation plots, Bland and Altman, and Passing and Bablok regression analyses.

RESULTS

The coefficient of variation and mean (SD) for the BCA method were 4.6% and 799.1 (882.5) mg/L and for the PRM method were 5.1% and 802.1 (911.9) mg/L. The Pearson correlation coefficient, r was 0.93 (p < 0.0001). Method agreement studies showed no significant constant and proportional bias between both the methods.

CONCLUSION

In urine which is subjected to removal of interfering substances, the BCA results are comparable to PRM method.