Urinary FABP1 is a biomarker for impaired proximal tubular protein reabsorption and is synergistically enhanced by concurrent liver injury

Study of non-alcoholic fatty pancreatic disease among the Egyptian population and the value of serum fatty acid binding protein-1 (FABP-1) as a non-invasive biomarker

BACKGROUND

Non-alcoholic fatty pancreas disease (NAFPD) can be detected using various imaging techniques, but accurately measuring the amount of fat in the pancreas remains difficult. Fatty acid binding protein-1 (FABP-1) is a marker specific to certain tissues and can aid in diagnosing NAFPD. However, this study aimed to investigate the prevalence of NAFPD among obese and non-obese people with and without diabetes mellitus (DM). Additionally, it aimed to evaluate the associated risk factors for NAFPD and the utility of the FABP-1 level as a simple, non-invasive biomarker for diagnosing NAFPD.

METHODS

This study is a prospective cross-sectional study.

RESULTS

Ninety-five patients were enrolled in the study, comprising 35 males and 60 females, with a mean age of 44 years and a standard deviation (SD) of 11 years. However, 26.3 % were morbidly obese, 22.1 % were severely obese, 31.6 % were obese, 12.6 % were overweight, and 7.4 % were normal. Additionally, 35.8 % had diabetes mellitus, while 26.3 % of patients had hypertension. Regarding the ultrasonographic findings, 94.7 % of the patients had fatty liver, with the majority (41.1 %) classified as grade II, followed by 38.9 % classified as grade I, and 14.7 % classified as grade III fatty liver. Among these patients, 78.9 % had fatty pancreas, with 38.9 % classified as grade II, 31.6 % classified as grade I, and 8.4 % classified as grade III fatty pancreas. The median FABP-1 level among patients with fatty pancreas was 3.3 ng/ml, which exhibited a significant fair negative correlation with total bilirubin and a fair, positive correlation with alkaline phosphatase and portal vein diameter. A statistically substantial distinction was observed between the levels of AFABP-1 and the presence or grading of the fatty pancreas (p-value = 0.048 and < 0.001, respectively). Using multivariate analysis, FABP-1 was the only significant predictor of a fatty pancreas. The receiver operating characteristic (ROC) curve analysis indicated that at a cut-off point of FABP-1 of ≤ 3.7, it had a sensitivity of 58 %, specificity of 80 %, positive predictive value (PPV) of 96.6 %, negative predictive value (NPV) of 17 %, and an area under the curve (AUC) of 0.77.

CONCLUSION

NAFPD is becoming an increasingly significant challenge. FABP-1 can potentially be a straightforward and non-invasive predictor of the fatty pancreas.

Echinocystic acid prevents obesity and fatty liver via interacting with FABP1

Long-term high-fat diet (HFD) will lead to obesity and their complications. Echinocystic acid (EA), a triterpene, shows anti-inflammatory and antioxidant effects. We predict that EA supplementation can prevent obesity, diabetes, and nonalcoholic steatohepatitis. To test our hypothesis, we investigated the effects of EA supplementation on mice with HFD-induced obesity in vivo and in vitro by adding EA to the diet of mice and the medium of HepG2 cells, the protein target of EA was analyzed by molecular docking. The results showed that EA ameliorated obesity and inhibited blood triglyceride and liver triglyceride concentrations than those in the HFD groups. The data on molecular docking indicated that FABP1 was a potential target of EA. Further experimental results confirmed that EA affected the triglyceride level by regulating the function of FABP1. This study may provide a new potential inhibitor for FABP1 and a new strategy for the treatment of obesity.

The endocytosis receptor megalin: From bench to bedside

The large (∼600 kDa) endocytosis receptor megalin/low-density lipoprotein receptor-related protein 2 is highly expressed at the apical membrane of proximal tubular epithelial cells (PTECs). Megalin plays an important role in the endocytosis of various ligands via interactions with intracellular adaptor proteins, which mediate the trafficking of megalin in PTECs. Megalin mediates the retrieval of essential substances, including carrier-bound vitamins and elements, and impairment of the endocytic process may result in the loss of those substances. In addition, megalin reabsorbs nephrotoxic substances such as antimicrobial (colistin, vancomycin, and gentamicin) or anticancer (cisplatin) drugs and advanced glycation end product-modified or fatty acid-containing albumin. The megalin-mediated uptake of these nephrotoxic ligands causes metabolic overload in PTECs and leads to kidney injury. Blockade or suppression of the megalin-mediated endocytosis of nephrotoxic substances may represent a novel therapeutic strategy for drug-induced nephrotoxicity or metabolic kidney disease. Megalin reabsorbs urinary biomarker proteins such as albumin, α₁-microglobulin, β₂-microglobulin, and liver-type fatty acid-binding protein; thus, the above-mentioned megalin-targeted therapy may have an effect on the urinary excretion of these biomarkers. We have previously established a sandwich enzyme-linked immunosorbent assay to measure the ectodomain (A-megalin) and full-length (C-megalin) forms of urinary megalin using monoclonal antibodies against the amino- and carboxyl-terminals of megalin, respectively, and reported their clinical usefulness. In addition, there have been reports of patients with novel pathological anti-brush border autoantibodies targeting megalin in the kidney. Even with these breakthroughs in the characterization of megalin, a large number of issues remain to be addressed in future research.

Endogenous markers of kidney function and renal drug clearance processes of filtration, secretion, and reabsorption

The kidneys are responsible for maintaining physiologic homeostasis. The kidneys clear a variety of drugs and other substances through passive (filtration) and active processes that utilize transport proteins. Renal clearance is comprised of the processes of glomerular filtration, tubular secretion, and tubular reabsorption. Endogenous biomarkers, such as creatinine and cystatin C, are routinely used to estimate renal clearance. Understanding the contributing components of renal function and clearance, through the use of biomarkers, is necessary in elucidating the renal pharmacology of drugs and other substances. While exogenous markers of kidney function have been known for decades, several complexities have limited their usage. Several endogenous markers are being evaluated and hold promise to elucidate the individual components of kidney function that represent filtration, secretion, and reabsorption.

Integrated single-cell transcriptomics and proteomics reveal cellular-specific response and microenvironment remodeling in aristolochic acid nephropathy

Aristolochic acid nephropathy (AAN) is characterized by acute proximal tubule necrosis and immune cell infiltration, contributing to the global burden of chronic kidney disease and urothelial cancer. Although the proximal tubule has been defined as the primary target of aristolochic acids I (AAI), the mechanistic underpinning of gross renal deterioration caused by AAI has not been explicitly explained, prohibiting effective therapeutic intervention. To this point, we employed integrated single-cell RNA-Seq, bulk RNA-Seq, and mass spectrometry–based proteomics to analyze the mouse kidney after acute AAI exposure. Our results reveal a dramatic reduction of proximal tubule epithelial cells, associated with apoptotic and inflammatory pathways, indicating permanent damage beyond repair. We found the enriched development pathways in other nephron segments, suggesting activation of reparative programs triggered by AAI. The divergent response may be attributed to the segment-specific distribution of organic anion channels along the nephron, including OAT1 and OAT3. Moreover, we observed dramatic activation and recruitment of cytotoxic T and macrophage M1 cells, highlighting inflammation as a principal contributor to permanent renal injury. Ligand-receptor pairing revealed that critical intercellular crosstalk underpins damage-induced activation of immune cells. These results provide potentially novel insight into the AAI-induced kidney injury and point out possible pathways for future therapeutic intervention.