PTM-Fetuin-A: A Novel Biomarker for Early Detection of Diabetic Kidney Disease

Chronic Kidney Disease (CKD) is a significant public health issue with a rising prevalence globally. Diabetic kidney disease (DKD), a leading cause of CKD, necessitates improved biomarkers for early detection and effective management. Traditional markers such as serum creatinine, estimated glomerular filtration rate (eGFR), and albuminuria have notable limitations in sensitivity and specificity, especially for early detection. Fetuin-A, specifically its post-translationally modified form (PTM-Fetuin-A), has emerged as a potential novel biomarker for DKD. This study evaluates PTM-Fetuin-A in a cohort of Bulgarian patients with type 1 and type 2 diabetes, assessing its correlation with traditional markers such as albuminuria and eGFR. Significant correlations were observed between PTM-Fetuin-A and these indicators (e.g., Pearson’s r = 0.447, p = 0.025 for albuminuria), highlighting its ability to detect early kidney function decline. Furthermore, PTM-Fetuin-A demonstrated potential as a non-invasive tool for identifying normoalbuminuric DKD, addressing gaps left by conventional biomarkers. By offering additional prognostic value, PTM-Fetuin-A could improve the early diagnosis and clinical management of diabetic patients, reducing the burden of CKD.

Chronic Kidney Disease (CKD) is a significant public health problem worldwide, with an increasing prevalence often described as a global pandemic. CKD affects approximately 10% of the global population, causing substantial morbidity and mortality, especially among individuals with comorbidities such as diabetes and hypertension [1,2]. Its progression frequently leads to End-Stage Renal Disease (ESRD), which necessitates dialysis or kidney transplantation—both resource-intensive treatments that impose a considerable burden on healthcare systems. Additionally, CKD has a profound economic impact, with high healthcare costs stemming from the treatment of advanced stages and associated complications [2].

Diabetic Kidney Disease (DKD), a prevalent complication of diabetes mellitus, is the leading cause of CKD and accounts for nearly half of all ESRD cases [3,4]. The global rise in diabetes incidence underscores the critical need for early identification and effective strategies to slow DKD progression and reduce the associated healthcare burden.

Currently, kidney function assessment in diabetic patients primarily relies on traditional biomarkers such as serum creatinine, estimated glomerular filtration rate (eGFR), and albuminuria. However, these markers have limitations in detecting early renal changes, particularly in normoalbuminuric patients, and their sensitivity and specificity are influenced by factors such as age, sex, and muscle mass [5,6]. Therefore, there is an urgent need for novel biomarkers capable of providing earlier and more accurate detection of kidney dysfunction, especially in diabetic patients at high risk of progression to ESRD.

Traditional biomarkers used for monitoring kidney function each have significant limitations that reduce their effectiveness, particularly in the early detection of DKD. Serum creatinine, one of the most widely used markers, is affected by factors such as muscle mass, age, and sex, making it an imperfect indicator of kidney health. Creatinine has a “blind spot area” in early kidney damage due to tubular secretion, meaning its levels may not rise until substantial kidney damage has occurred, limiting its utility for early detection [6]. Estimated glomerular filtration rate (eGFR), derived from serum creatinine levels, provides a general estimate of kidney function but is subject to similar confounding factors that impact creatinine levels, such as variations in muscle mass and ethnicity. Additionally, eGFR is calculated using formulas such as the Modification of Diet in Renal Disease (MDRD) equation or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, both of which have limitations in accuracy for certain populations, including those with extremes in body mass or age [7].

Albuminuria, which measures the presence of albumin in the urine, is another commonly used marker for assessing kidney damage. It is more sensitive than serum creatinine for detecting early kidney damage, particularly in diabetic patients. However, not all patients with ongoing DKD will have elevated levels of albumin in their urine. This condition, known as normoalbuminuric DKD, complicates the early diagnosis and risk stratification of patients, as albuminuria alone may fail to capture early pathophysiological changes in the kidney [8]. Furthermore, albuminuria can be influenced by factors such as hydration status, exercise, and infection, which can lead to variability in measurements and reduce its reliability as a standalone marker.

Given these limitations, there is a critical need for more specific and sensitive biomarkers that can accurately reflect early kidney damage and predict disease progression. Such biomarkers would ideally detect subtle renal changes before significant structural damage occurs, allowing for timely intervention and improved patient outcomes [9,10].

The role of Fetuin-A in chronic kidney disease

Fetuin-A, also known as alpha-2-Heremans-Schmid glycoprotein (AHSG), is primarily synthesized in the liver and released into circulation, playing a role in processes such as calcium regulation, inhibition of ectopic calcification, and modulation of insulin signaling pathways [9,10]. Elevated levels of fetuin-A are linked to insulin resistance, metabolic syndrome, and cardiovascular risk, which are common comorbidities in diabetes and CKD [11-13].

Post-translationally modified fetuin-A (PTM-Fetuin-A) has emerged as a promising biomarker for early detection of renal dysfunction, particularly in patients with diabetes. PTM-Fetuin-A is a modified form of the protein that reflects underlying molecular changes associated with kidney injury and inflammation. Recent studies have demonstrated that PTM-Fetuin-A levels correlate with markers of renal dysfunction, such as albuminuria and eGFR, and may provide additional prognostic value beyond traditional biomarkers [14,15]. The ability of PTM-Fetuin-A to detect early changes in renal function, even in patients with normoalbuminuric DKD, suggests that it could serve as an important tool for improving the early diagnosis and management of diabetic kidney disease.

Musolino, et al. (2024) conducted a pilot study on PTM-Fetuin-A in patients with CKD of both diabetic and non-diabetic etiology, demonstrating that PTM-Fetuin-A levels were significantly elevated in patients with DKD compared to those with other causes of CKD. The authors suggested that PTM-Fetuin-A could be used as a non-invasive biomarker to differentiate between diabetic and non-diabetic CKD, particularly in cases where renal biopsy is not feasible [15]. This finding aligns with earlier work by Kumar Bandi, et al. (2022), who reported a significant correlation between PTM-Fetuin-A and albuminuria, with PTM-Fetuin-A showing superior performance in predicting CKD stages compared to traditional markers like UACR [16].

Studies by Chuanga, et al. (2024) further explored the potential of PTM-Fetuin-A as a biomarker capable of predicting kidney function decline in patients with type 2 diabetes from different ethnic backgrounds. Their findings indicated that high PTM-Fetuin-A levels were associated with a higher risk of renal function decline, independent of other traditional risk factors such as albuminuria, eGFR, and HbA1c levels [17,18]. The additive predictive power of PTM-Fetuin-A over traditional markers suggests that it may be a valuable tool for the early identification of patients at risk for DKD progression.

Based on the existing evidence regarding PTM-Fetuin-A as a potential biomarker, our study aims to further evaluate its role in the early detection and monitoring of diabetic kidney disease. Specifically, we investigated PTM-Fetuin-A levels in a cohort of Bulgarian patients with type 1 and type 2 diabetes, with and without low-grade albuminuria. By comparing PTM-Fetuin-A with traditional markers such as albuminuria and eGFR, we sought to determine its potential as a non-invasive tool for early identification of DKD and to assess its prognostic value in predicting kidney function decline [19,20].

This study was designed as a cross-sectional observational analysis involving 70 patients with diabetes mellitus, both type 1 and type 2. Participants were recruited from a single healthcare center in Bulgaria, and the primary aim was to assess the levels of post-translationally modified fetuin-A (PTM-Fetuin-A) as a biomarker for Diabetic Kidney Disease (DKD). The analysis also compared PTM-Fetuin-A levels with traditional kidney function markers such as albuminuria and estimated glomerular filtration rate (eGFR) to evaluate its potential for early detection and prognostic value in renal function decline.

The participants included 25 individuals with type 1 diabetes and 45 with type 2 diabetes, with an age range of 19 to 88 years and a mean age of 53.5 years. All 70 participants were evaluated at three distinct time points: baseline (V0), the third month (V3), and the sixth month (V6) (Table 1A).

Inclusion criteria

• Confirmed diagnosis of Type 1 or Type 2 diabetes mellitus,
• аge 19–88 years, Presence or absence of low-grade albuminuria
• Not on dialysis or kidney transplantation
• Categorized by diabetes duration: <5 years, 5–10 years, >10 years

Exclusion criteria

• Acute infections or inflammatory conditions
• History of non-diabetic kidney disease
• Use of nephrotoxic medications
• Active malignancy or severe systemic disease

Urine samples were collected from each participant at three distinct time points: baseline (V0), the third month (V3), and the sixth month (V6). The samples were centrifuged and stored at -80°C until analysis. Biomarkers including serum creatinine, albuminuria, eGFR, body mass index (BMI), and ratios such as albumin/creatinine (UACR) and fetuin/creatinine (FCR) were measured at the same intervals. The PTM-Fetuin-A levels were determined using a commercially available enzyme-linked immunosorbent assay (ELISA) kit, following the manufacturer’s instructions. All samples were processed in duplicate to ensure accuracy, and frozen urine samples were analyzed in a single batch to minimize variability.

Statistical analyses were conducted using SPSS software (version 25.0). Descriptive statistics, such as mean values, standard deviations, and ranges, were used to characterize PTM-Fetuin-A, eGFR, and UACR across the different groups and time points. The Mann-Whitney U test was used to compare PTM-Fetuin-A levels between groups where data did not meet the assumptions of normality. One-way ANOVA was performed to compare PTM-Fetuin-A levels between different subgroups, while Pearson’s correlation coefficient and Spearman’s rho were used to explore relationships between PTM-Fetuin-A, eGFR, and UACR. Multiple linear regression was employed to assess the impact of traditional markers (UACR and eGFR) on PTM-Fetuin-A levels over time, with R² and p-values indicating the strength and significance of these relationships.

The assessment of the relationship between PTM-Fetuin-A levels in urine, albuminuria, and CKD progression revealed several significant findings. Notably, a positive correlation was observed between baseline PTM-Fetuin-A levels (V0) and albuminuria levels at six months (V6), with Pearson’s correlation coefficient r = 0.447 and p = 0.025. This indicates that higher initial levels of PTM-Fetuin-A may predict an increase in albuminuria over time (Table 1B).

Comparison between patients with type 1 and type 2 diabetes across different time points (V0, V3, V6) showed no statistically significant differences in PTM-Fetuin-A levels. For instance, at V0, the mean PTM-Fetuin-A level was 4.29 ng/ml in type 1 diabetes patients and 3.36 ng/ml in type 2 diabetes patients, with Mann-Whitney U test results of U = 550 and p = 0.88, indicating no significant difference. These results suggest that while PTM-Fetuin-A levels do not significantly differ between diabetes types, their correlation with albuminuria positions PTM-Fetuin-A as a potential biomarker for tracking disease progression (Table 2).

A significant positive correlation was also observed between the Fetuin/creatinine ratio (FCR) and UACR, as well as between FCR and eGFR, with varying degrees across type 1 and type 2 diabetes and depending on diabetes duration. For example, for V6, a strong correlation was noted between FCR and UACR in patients with a shorter diabetes duration (less than 5 years), with r = 0.599 and p = 0.009. This finding suggests that increased urinary PTM-Fetuin-A levels are closely related to rising albuminuria, which is a key indicator of kidney damage in diabetic nephropathy (Figures 1-3).

The correlation analysis revealed significant relationships between the Fetuin/Creatinine Ratio (F/Ucr), estimated glomerular filtration rate (eGFR), and serum creatinine (SrCr) at specific time points. At baseline (V0), a significant negative correlation was observed between F/Ucr and eGFR (r = -0.499, p = 0.035), suggesting that higher levels of PTM-Fetuin-A relative to creatinine are associated with reduced kidney function. Similarly, a significant positive correlation was found between F/Ucr and SrCr (r = 0.518, p = 0.028), which is consistent with the established inverse relationship between eGFR and SrCr. However, these correlations did not persist at subsequent time points (V3 and V6), indicating a transient nature of the relationships between F/Ucr and these traditional kidney function markers in this short-term study.

In contrast, the correlation between eGFR and SrCr remained strong and consistent across all three-time points (r = -0.721, -0.799, and -0.804 for V0, V3, and V6, respectively; all p < 0.001). This stability highlights the robustness of these traditional markers in reflecting kidney function over time. The lack of persistence in correlations between F/Ucr and other markers suggests that PTM-Fetuin-A may be sensitive to acute or short-term changes in renal function rather than serving as a stable longitudinal biomarker.

In patients with type 2 diabetes, correlation analysis showed negative associations between FCR and eGFR at different time points. For V6, a significant negative correlation was observed with r = -0.736 and p < 0.001, indicating that as eGFR decreases (worsening kidney function), FCR levels increase. This supports the relationship between declining kidney function and increasing PTM-Fetuin-A levels.

In patients with a diabetes duration of less than 5 years, a significant negative correlation was found between FCR and eGFR at V0 (r = -0.499, p = 0.035), suggesting that PTM-Fetuin-A may serve as a sensitive marker for worsening kidney function in the early stages of the disease. For patients with diabetes duration over 10 years, the correlations between FCR and eGFR were weaker or absent. For example, no significant correlation was found for V0 eGFR and FCR (r = -0.165, p = 0.432), suggesting that in prolonged kidney damage, other factors may have a greater impact on disease progression (Table 3).

These findings suggest that PTM-Fetuin-A, as represented by F/Ucr, may have potential as a short-term indicator of kidney function. However, its utility as a reliable, long-term biomarker requires further investigation in extended longitudinal studies. In contrast, the consistent relationship between eGFR and SrCr underscores their reliability as indicators of renal function and progression of kidney disease.

Our findings align with previous studies that highlight the potential of PTM-Fetuin-A as a biomarker for early detection of diabetic kidney disease (DKD). The positive correlation between baseline PTM-Fetuin-A levels and subsequent albuminuria levels supports the hypothesis that PTM-Fetuin-A can serve as an early predictor of kidney function decline. This is consistent with Musolino, et al. (2024), who also reported elevated PTM-Fetuin-A levels in patients with DKD compared to those with non-diabetic CKD, suggesting its utility as a non-invasive biomarker for monitoring renal health [17,21].

Moreover, the strong correlation observed between the FetuinA/creatinine ratio (FCR) and UACR in patients with a shorter diabetes duration mirrors findings by Kumar Bandi, et al. (2022), who demonstrated the similar performance of PTM-Fetuin-A to traditional markers like UACR in predicting CKD stages [22,23]. These results indicate that PTM-Fetuin-A not only correlates well with established markers of kidney damage but may also offer additional prognostic value, particularly in early-stage disease.

Interestingly, our study found no significant differences in PTM-Fetuin-A levels between patients with type 1 and type 2 diabetes, similar to the findings by Chuanga, et al. (2024), who observed high PTM-Fetuin-A levels across different ethnic backgrounds without significant variation between diabetes types [19,24]. This suggests that PTM-Fetuin-A levels may be influenced more by the presence of kidney damage rather than by the type of diabetes itself.

Our correlation analysis between FCR and eGFR further supports the potential role of PTM-Fetuin-A in monitoring kidney function decline. The significant negative correlation between FCR and eGFR in type 2 diabetes patients indicates that as kidney function declines, PTM-Fetuin-A levels increase, which is in line with the general understanding of biomarkers that reflect worsening renal function. This observation adds to the growing body of evidence suggesting that PTM-Fetuin-A could be a reliable indicator of kidney health, particularly in the context of diabetic nephropathy.

However, it is important to note that in patients with longer diabetes duration (over 10 years), the correlations between FCR and eGFR were weaker or absent. This finding suggests that PTM-Fetuin-A may be more effective as a biomarker in the earlier stages of diabetes-related kidney damage, whereas other factors may play a more dominant role in long-standing disease progression. This highlights the need for a multimodal approach in the assessment of CKD progression, particularly in advanced cases.

In conclusion, our study supports the use of PTM-Fetuin-A as a promising biomarker for early detection and monitoring of DKD. By offering additional prognostic value beyond traditional markers like albuminuria and eGFR, PTM-Fetuin-A could improve the management of patients with diabetes, particularly those at risk of rapid kidney function decline.

In summary, this study provides evidence supporting the potential of PTM-Fetuin-A as an effective biomarker for the early detection and monitoring of diabetic kidney disease (DKD). The significant correlations between PTM-Fetuin-A, albuminuria, and kidney function highlight its value beyond traditional markers like serum creatinine and eGFR, particularly in early disease stages. While our findings align with previous research, they also underscore the need for further studies to confirm the utility of PTM-Fetuin-A in different populations and to explore its role in more advanced cases of CKD. The use of PTM-Fetuin-A in clinical practice could help improve early diagnosis and management of DKD, ultimately reducing the burden of chronic kidney disease among diabetic patients.

Disclaimer (Artificial intelligence)

The author(s) hereby declare that generative AI technologies, such as Large Language Models (e.g., ChatGPT), were utilized during the writing or editing process of this manuscript. The specific details of AI usage, including the name, version, model, source, and input prompts provided to the AI, are transparently outlined below.

Details of AI usage

1. Name and source of technology: OpenAI ChatGPT, GPT-4, December 2024 version.
2. Purpose of use: Translation of the manuscript into English for enhanced terminological accuracy, given that English is not the author’s native language.
3. Input prompts: Text provided to the AI included original content in Bulgarian for translation, along with clarifications on preferred terminology to ensure scientific accuracy and readability.

The author(s) take full responsibility for verifying and ensuring the accuracy, validity, and originality of the content produced through the assistance of AI technology.

Ethical approval

The study was reviewed and approved by the Ethics Committee of the Bulgarian Society of Nephrology.

Patient Consent

All participants provided written informed consent before inclusion in the study. Confidentiality and data protection measures were strictly followed.

Compliance with institutional guidelines

The study adhered to the ethical principles outlined in the Declaration of Helsinki and followed standard clinical and laboratory practices.

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