Biological variation, reference change values and index of individuality of GDF-15

Growth Differentiation Factor-15 as a Potential Biomarker for Renal Involvement in POEMS Syndrome

Introduction

Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome is a rare plasma cell dyscrasia. Growth differentiation factor-15 (GDF-15) is related with renal function, but few studies have focused on it in renal impairment of POEMS syndrome.

Objective

To evaluate the potential of circulating GDF-15 concentration as a biomarker for renal function in POEMS syndrome.

Methods

150 Chinese patients, diagnosed with POMES syndrome, were enrolled and divided into three subgroups according to their chemotherapy stage. All the patients' medical records were retrospectively analyzed and plasma VEGF and GDF-15 were measured using ELISA kits. Treatment-naïve patients were followed up for 13±6 months.

Results

Plasma GDF-15 concentration positively correlated with serum creatinine (r=0.4048; P<0.0001), blood urea nitrogen (r=0.3302; P<0.0001), risk stratification (r=0.3949; P<0.0001), while negatively correlating with eGFR (r=-0.5057; P<0.0001) and albumin (r=-0.3800; P=0.0014). GDF-15>547.8 pg/mL provided an AUC of 0.8541 in diagnosing renal impairment (eGFR<60mL/min/1.73m2) in POEMS syndrome. With a prevalence of renal impairment of 16.7%, GDF-15>547.8 pg/mL showed a prominent NPV (94.9%) for the diagnosis of renal impairment in POEMS syndrome. Moreover, treatment-naïve patients with serous effusion had higher plasma GDF-15 concentration (P=0.0004) and lower eGFR (P=0.0001) than those without serous effusion. Noteworthy, baseline GDF-15 was positively correlated with ΔeGFR (r=0.4694, P=0.0044).

Conclusion

Circulating GDF-15 concentration is associated with serous effusion, renal function and risk stratification, while a plasma GDF-15 < 547.8 pg /mL can help rule out renal impairment in POEMS syndrome. Baseline plasma GDF-15 is associated with renal remission after chemotherapy.

Defining Biological Variability, Analytical Precision and Quantitative Biophysiochemical Characterization of Human Urinary Extracellular Vesicles

The magnitude of combined analytical errors of urinary extracellular vesicle (uEV) preparation and measurement techniques (CVA) has not been thoroughly investigated to determine whether it exceeds biological variations. We utilized technical replicates of human urine to assess the repeatability of uEV concentration and size measurements by nanoparticle tracking analysis (NTA) following differential velocity centrifugation (DC), silicon carbide, or polyethylene glycol uEV isolation methods. The DC method attained the highest precision. Consequently, DC-derived uEV size, most abundant protein levels, and optical redox ratio (ORR) were further assessed by dynamic light scattering (DLS), immunoblotting or multi-photon (SLAM) microscopy. Procedural errors primarily affected uEV counting and uEV-associated protein quantification, while instrumental errors contributed most to the total variability of NTA- and DLS-mediated uEV sizing processes. The intra-individual variability (CVI) of uEV counts assessed by NTA was smaller than inter-individual variability (CVG), resulting in an estimated index of individuality IOI < 0.6, suggesting that personalized reference interval (RI) is more suitable for interpretation of changes in subject's test results. Population-based RI was more appropriate for ORR (IOI > 1.4). The analytical performance of DC-NTA and DC-SLAM techniques met optimal CVA < 0.5 × CVI criteria, indicating their suitability for further testing in clinical laboratory settings.

Role and Mechanism of Growth Differentiation Factor 15 in Chronic Kidney Disease

GDF-15 is an essential member of the transforming growth factor-beta superfamily. Its functions mainly involve in tissue injury, inflammation, fibrosis, regulation of appetite and weight, development of tumor, and cardiovascular disease. GDF-15 is involved in various signaling pathways, such as MAPK pathway, PI3K/AKT pathway, STAT3 pathway, RET pathway, and SMAD pathway. In addition, several factors such as p53, ROS, and TNF-α participate the regulation of GDF-15. However, the specific mechanism of these factors regulating GDF-15 is still unclear and more research is needed to explore them. GDF-15 mainly improves the function of kidneys in CKD and plays an important role in the prediction of CKD progression and cardiovascular complications. In addition, the role of GDF-15 in the kidney may be related to the SMAD and MAPK pathways. However, the specific mechanism of these pathways remains unclear. Accordingly, more research on the specific mechanism of GDF-15 affecting kidney disease is needed in the future. In conclusion, GDF-15 may be a therapeutic target for kidney disease.

Biological Variation Estimates for Plasma Copeptin and Clinical Implications

BACKGROUND

Plasma copeptin measurement is useful for the differential diagnoses of polyuria-polydipsia syndrome. It has also been proposed as a prognostic marker for cardiovascular diseases. However, limited information is available about the within- (CVI) and between-subject (CVG) biological variation (BV). This study presents BV estimates for copeptin in healthy individuals.

METHODS

Samples were collected weekly from 41 healthy subjects over 5 weeks and analyzed using the BRAHMS Copeptin proAVP KRYPTOR assay after at least 8 h of food and fluid abstinence. Outlier detection, variance homogeneity, and trend analysis were performed followed by CV-ANOVA for BV and analytical variation (CVA) estimation with 95% confidence intervals. Reference change values (RCVs), index of individuality (II), and analytical performance specification (APS) were also calculated.

RESULTS

The analysis included 178 results from 20 males and 202 values from 21 females. Copeptin concentrations were significantly higher in males than in females (mean 8.5 vs 5.2 pmol/L, P < 0.0001). CVI estimates were 18.0% (95% CI, 15.4%-21.6%) and 19.0% (95% CI, 16.4%-22.6%), for males and females, respectively; RCVs were -35% (decreasing value) and 54% (increasing value). There was marked individuality for copeptin. No result exceeded the diagnostic threshold (>21.4 pmol/L) for arginine vasopressin resistance.

CONCLUSIONS

The availability of BV data allows for refined APS and associated II, and RCVs applicable as aids in the serial monitoring of patients with specific diseases such as heart failure. The BV estimates are only applicable in subjects who abstained from oral intake due to the rapid and marked effects of fluids on copeptin physiology.

Emerging Biomarkers in the Laboratory and in Practice: A Novel Approach to Diagnosing Heart Failure in Diabetes

The Biomarkers for the Diagnosis of Heart Failure in Diabetes webinar was hosted by Diabetes Technology Society on September 20, 2023, with the objective to review current evidence and management practices of biomarker screening for heart failure in people with diabetes. The webinar discussed (1) the four stages of heart failure, (2) diabetes and heart failure, (3) natriuretic peptide and troponin for diagnosing heart failure in diabetes, (4) emerging composite and investigational biomarkers for diagnosing heart failure, and (5) prevention of heart failure progression. Experts in heart failure from the fields of clinical chemistry, cardiology, and diabetology presented data about the importance of screening for heart failure as an often-unnoticed complication of people with type 1 and type 2 diabetes.

Specifications of qPCR based epigenetic immune cell quantification

OBJECTIVES

Immune monitoring is an important aspect in diagnostics and clinical trials for patients with compromised immune systems. Flow cytometry is the standard method for immune cell counting but faces limitations. Best practice guidelines are available, but lack of standardization complicates compliance with e.g., in vitro diagnostic regulations. Limited sample availability forces immune monitoring to predominantly use population-based reference intervals. Epigenetic qPCR has evolved as alternative with broad applicability and low logistical demands. Analytical performance specifications (APS) have been defined for qPCR in several regulated fields including testing of genetically modified organisms or vector-shedding.

METHODS

APS were characterized using five epigenetic qPCR-based assays quantifying CD3+, CD4+, CD8+ T, B and NK cells in light of regulatory requirements.

RESULTS

Epigenetic qPCR meets all specifications including bias, variability, linearity, ruggedness and sample stability as suggested by pertinent guidelines and regulations. The assays were subsequently applied to capillary blood from 25 normal donors over a 28-day period. Index of individuality (IoI) and reference change values were determined to evaluate potential diagnostic gains of individual reference intervals. Analysis of the IoI suggests benefits for individual over population-based references. Reference change values (RCVs) show that changes of approx. Fifty percent from prior measurement are suggestive for clinically relevant changes in any of the 5 cell types.

CONCLUSIONS

The demonstrated precision, long-term stability and obtained RCVs render epigenetic cell counting a promising tool for immune monitoring in clinical trials and diagnosis.

Growth differentiation factor 15 and cardiovascular risk: individual patient meta-analysis

AIMS

Levels of growth differentiation factor 15 (GDF-15), a cytokine secreted in response to cellular stress and inflammation, have been associated with multiple types of cardiovascular (CV) events. However, its comparative prognostic performance across different presentations of atherosclerotic cardiovascular disease (ASCVD) remains unknown.

METHODS AND RESULTS

An individual patient meta-analysis was performed using data pooled from eight trials including 53 486 patients. Baseline GDF-15 concentration was analyzed as a continuous variable and using established cutpoints (<1200 ng/L, 1200-1800 ng/L, > 1800 ng/L) to evaluate its prognostic performance for CV death/hospitalization for heart failure (HHF), major adverse cardiovascular events (MACE), and their components using Cox models adjusted for clinical variables and established CV biomarkers. Analyses were further stratified on ASCVD status: acute coronary syndrome (ACS), stabilized after recent ACS, and stable ASCVD. Overall, higher GDF-15 concentration was significantly and independently associated with an increased rate of CV death/HHF and MACE (P < 0.001 for each). However, while GDF-15 showed a robust and consistent independent association with CV death and HHF across all presentations of ASCVD, its prognostic association with future myocardial infarction (MI) and stroke only remained significant in patients stabilized after recent ACS or with stable ASCVD [hazard ratio (HR): 1.24, 95% confidence interval (CI): 1.17-1.31 and HR: 1.16, 95% CI: 1.05-1.28 for MI and stroke, respectively] and not in ACS (HR: 0.98, 95% CI: 0.90-1.06 and HR: 0.87, 95% CI: 0.39-1.92, respectively).

CONCLUSION

Growth differentiation factor 15 consistently adds prognostic information for CV death and HHF across the spectrum of ASCVD. GDF-15 also adds prognostic information for MI and stroke beyond clinical risk factors and cardiac biomarkers but not in the setting of ACS.