Changes of urinary phospholipids in the chronic kidney disease patients

Bifunctional Ti4+-modified paper for selective extraction or removal of phospholipids and paper spray mass spectrometry for bioanalysis in urine and plasma

BACKGROUND

Phospholipids (PLs) are major constituents of cell membranes, play important roles in cell proliferation and death, as well as in signal transduction, and therefore are relevant biomarkers for different pathologies. On the other hand, when the analysis of small compounds, such as therapeutics in blood is desired, then phospholipids are part of the matrix and cause serious interference during analysis. Currently, both the analysis and removal of PLs from biological samples are limited by extensive sample preparation and instrumental separation.

RESULTS

A fast and simple quantitative Ti4+-modified paper spray tandem mass spectrometric (TiPS-MS/MS) method was established in urine, where the enrichment of phospholipids was achieved, as well as reduction of matrix effects (primarily caused by high salt content) that ultimately led to improved sensitivity and selectivity. The method could achieve a physiologically relevant limit of detection (0.01-0.03 μg mL-1). Also, the usefulness of the Ti4+-modified paper was investigated in the opposite mode, namely for the selective removal of phospholipids from matrices such as plasma. Clonidine is used as model compound, as the detection of this compound is known to suffer from ion suppression by phospholipids. Compared with blank paper spray tandem mass spectrometry, the limit of detection could be improved from 0.3 μg mL-1 to 0.03 μg mL-1 by employing a Ti4+-modified paper on top of the spray tip to capture phospholipids from the sample.

SIGNIFICANCE AND NOVELTY

A novel Ti4+-modified paper was developed to allow for rapid solid-phase extraction of phospholipids from urine or selective removal from plasma, followed by direct paper spray mass spectrometric detection as a fast and convenient sample preparation and analysis combination. The paper properties are based on the Ti4+ metal ion, which can selectively bind phosphate-containing compounds under acidic conditions, and its applicability was demonstrated in relevant biological matrices.

Dynamic modulations of urinary sphingolipid and glycerophospholipid levels in COVID-19 and correlations with COVID-19-associated kidney injuries

Background

Among various complications of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), renal complications, namely COVID-19-associated kidney injuries, are related to the mortality of COVID-19.

Methods

In this retrospective cross-sectional study, we measured the sphingolipids and glycerophospholipids, which have been shown to possess potent biological properties, using liquid chromatography-mass spectrometry in 272 urine samples collected longitudinally from 91 COVID-19 subjects and 95 control subjects without infectious diseases, to elucidate the pathogenesis of COVID-19-associated kidney injuries.

Results

The urinary levels of C18:0, C18:1, C22:0, and C24:0 ceramides, sphingosine, dihydrosphingosine, phosphatidylcholine, lysophosphatidylcholine, lysophosphatidic acid, and phosphatidylglycerol decreased, while those of phosphatidylserine, lysophosphatidylserine, phosphatidylethanolamine, and lysophosphatidylethanolamine increased in patients with mild COVID-19, especially during the early phase (day 1–3), suggesting that these modulations might reflect the direct effects of infection with SARS-CoV-2. Generally, the urinary levels of sphingomyelin, ceramides, sphingosine, dihydrosphingosine, dihydrosphingosine l-phosphate, phosphatidylcholine, lysophosphatidic acid, phosphatidylserine, lysophosphatidylserine, phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylglycerol, lysophosphatidylglycerol, phosphatidylinositol, and lysophosphatidylinositol increased, especially in patients with severe COVID-19 during the later phase, suggesting that their modulations might result from kidney injuries accompanying severe COVID-19.

Conclusions

Considering the biological properties of sphingolipids and glycerophospholipids, an understanding of their urinary modulations in COVID-19 will help us to understand the mechanisms causing COVID-19-associated kidney injuries as well as general acute kidney injuries and may prompt researchers to develop laboratory tests for predicting maximum severity and/or novel reagents to suppress the renal complications of COVID-19.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00880-5.

Lipidomic and Metabolomic Signature of Progression of Chronic Kidney Disease in Patients with Severe Obesity

Severe obesity is a major risk for chronic kidney disease (CKD). Early detection and careful monitoring of renal function are critical for the prevention of CKD during obesity, since biopsies are not performed in patients with CKD and diagnosis is dependent on the assessment of clinical parameters. To explore whether distinct lipid and metabolic signatures in obesity may signify early stages of pathogenesis toward CKD, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-high resolution accurate mass-mass spectrometry (GC-HRAM-MS) analyses were performed in the serum and the urine of severely obese patients with and without CKD. Moreover, the impact of bariatric surgery (BS) in lipid and metabolic signature was also studied, through LC-MS and GC-HRAM-MS analyses in the serum and urine of patients with severe obesity and CKD before and after undergoing BS. Regarding patients with severe obesity and CKD compared to severely obese patients without CKD, serum lipidome analysis revealed significant differences in lipid signature. Furthermore, serum metabolomics profile revealed significant changes in specific amino acids, with isoleucine and tyrosine, increased in CKD patients compared with patients without CKD. LC-MS and GC-HRAM-MS analysis in serum of patients with severe obesity and CKD after BS showed downregulation of levels of triglycerides (TGs) and diglycerides (DGs) as well as a decrease in branched-chain amino acid (BCAA), lysine, threonine, proline, and serine. In addition, BS removed most of the correlations in CKD patients against biochemical parameters related to kidney dysfunction. Concerning urine analysis, hippuric acid, valine and glutamine were significantly decreased in urine from CKD patients after surgery. Interestingly, bariatric surgery did not restore all the lipid species, some of them decreased, hence drawing attention to them as potential targets for early diagnosis or therapeutic intervention. Results obtained in this study would justify the use of comprehensive mass spectrometry-based lipidomics to measure other lipids aside from conventional lipid profiles and to validate possible early markers of risk of CKD in patients with severe obesity.

A narrative review of urinary phospholipids: from biochemical aspect towards clinical application

As a newly emerged discipline, lipidomic studies have focused on the comprehensive characterization and quantification of lipids in a given biological system, which has remarkably advanced in recent years owing to the rapid development of analytical techniques, especially mass spectrometry. Among diverse lipid classes, phospholipids, which have fundamental roles in the formation of cellular membranes, signaling processes, and bioenergetics have gained momentum in several fields of research. The altered composition, concentration, spatial distribution, and metabolism of phospholipids in cells, tissues, and body fluids have been elucidated in various human diseases such as cancer, inflammation, as well as cardiovascular and metabolic disorders. Among the different kinds of phospholipid sources in the human body, urine has not been extensively investigated in recent years owing to the extremely low concentrations of phospholipids and high levels of salts and other contaminants, which can interfere with precise detection. However, with profound advances and rapid expansion in analytical methods, urinary phospholipids have attracted increasing attention in current biomedical research as urine is an easily available source for the discovery of noninvasive biomarkers. In this review, we provide an overview of urinary phospholipids, including their biochemical aspects and clinical applications, aimed at promoting this field of research.

DESI-MSI and METASPACE indicates lipid abnormalities and altered mitochondrial membrane components in diabetic renal proximal tubules

INTRODUCTION

Diabetic kidney disease (DKD) is the most prevalent complication in diabetic patients, which contributes to high morbidity and mortality. Urine and plasma metabolomics studies have been demonstrated to provide valuable insights for DKD. However, limited information on spatial distributions of metabolites in kidney tissues have been reported.

OBJECTIVES

In this work, we employed an ambient desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) coupled to a novel bioinformatics platform (METASPACE) to characterize the metabolome in a mouse model of DKD.

METHODS

DESI-MSI was performed for spatial untargeted metabolomics analysis in kidneys of mouse models (F1 C57BL/6J-Ins2Akita male mice at 17 weeks of age) of type 1 diabetes (T1D, n = 5) and heathy controls (n = 6).

RESULTS

Multivariate analyses (i.e., PCA and PLS-DA (a 2000 permutation test: P < 0.001)) showed clearly separated clusters for the two groups of mice on the basis of 878 measured m/z's in kidney cortical tissues. Specifically, mice with T1D had increased relative abundances of pseudouridine, accumulation of free polyunsaturated fatty acids (PUFAs), and decreased relative abundances of cardiolipins in cortical proximal tubules when compared with healthy controls.

CONCLUSION

Results from the current study support potential key roles of pseudouridine and cardiolipins for maintaining normal RNA structure and normal mitochondrial function, respectively, in cortical proximal tubules with DKD. DESI-MSI technology coupled with METASPACE could serve as powerful new tools to provide insight on fundamental pathways in DKD.

Distribution of plasma oxidised phosphatidylcholines in chronic kidney disease and periodontitis as a co-morbidity

Individuals with chronic kidney disease (CKD) and periodontitis as a co-morbidity have a higher mortality rate than individuals with CKD and no periodontitis. The inflammatory burden associated with both diseases contributes to an increased risk of cardiovascular and all-cause mortality. We previously demonstrated that periodontitis is associated with increasing circulating markers of inflammation and oxidative stress. We propose that inflammatory oxidised phosphocholines may contribute to the increased risk of cardiovascular disease in patients with CKD. However, the analysis of oxidised phospholipids has been limited by a lack of authentic standards for absolute quantification. Here, we have developed a comprehensive quantification liquid chromatography-mass spectrometry-based multiple reaction monitoring method for oxidised phospholipids (including some without available authentic species) that enables us to simultaneously measure twelve oxidised phosphatidylcholine species with high levels of sensitivity and specificity. The standard curves for commercial standards 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphatidylcholine (PGPC); 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphatidylcholine (PONPC), 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphatidylcholine (PAzPC) and 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphatidylcholine (POVPC), were linear with a correlation coefficient greater than 0.99 for all analytes. The method is reproducible, with intra- and inter-day precision <15%, and accuracy within ±5% of nominal values for all analytes. This method has been successfully applied to investigate oxidised phosphatidylcholine in plasma from CKD patients with and without chronic periodontitis and the data that was obtained has been compared to plasma from healthy controls. Comparative analysis demonstrates altered chain fragmented phosphatidylcholine profiles in the plasma samples of patients with CKD and periodontitis as a co-morbidity compared to healthy controls.

Repeated administration of the NSAID meloxicam alters the plasma and urine lipidome

Non-steroidal anti-inflammatories (NSAIDs), such as meloxicam, are the mainstay for treating painful and inflammatory conditions in animals and humans; however, the repeated administration of NSAIDs can cause adverse effects, limiting the long-term administration of these drugs to some patients. The primary aim of this study was to determine the effects of repeated meloxicam administration on the feline plasma and urine lipidome. Cats (n = 12) were treated subcutaneously with either saline solution or 0.3 mg/kg body weight of meloxicam daily for up to 31 days. Plasma and urine lipidome were determined by LC-MS before the first treatment and at 4, 9 and 13 and 17 days after the first administration of meloxicam. The repeated administration of meloxicam altered the feline plasma and urine lipidome as demonstrated by multivariate statistical analysis. The intensities of 94 out of 195 plasma lipids were altered by the repeated administration of meloxicam to cats (p < 0.05). Furthermore, we identified 12 lipids in plasma and 10 lipids in urine that could serve as biomarker candidates for discriminating animals receiving NSAIDs from healthy controls. Expanding our understanding about the effects of NSAIDs in the body could lead to the discovery of mechanism(s) associated with intolerance to NSAIDs.

Urinary Lipidomics: evidence for multiple sources and sexual dimorphism in healthy individuals

Urinary lipidomics may add new valuable biomarkers to the diagnostic armamentarium for early detection of metabolic and kidney diseases. Sources and composition of urinary lipids in healthy individuals, however, have not been investigated in detail. Shotgun lipidomics was used to quantify lipidomic profiles in native urine samples from 16 individuals (eight men, eight women) collected in five fractions over 24 h. All probands were comprehensively characterized by urinary and clinical indices. The mean total urinary lipid concentration per sample was 0.84 μM in men and 1.03 μM in women. We observed significant intra- and interindividual variations of lipid concentrations over time, but failed to detect a clear circadian pattern. Based on quantity and subclass composition it seems very unlikely that plasma serves as major source for the urinary lipidome. Considering lipid metabolites occurring in at least 20% of all samples 38 lipid species from 7 lipid classes were identified. Four phosphatidylserine and one phosphatidylethanolamine ether species (PE-O 36:5) were detectable in almost all urine samples. Sexual dimorphism has been found mainly for phosphatidylcholines and phosphatidylethanolamines. In men and in women urinary lipid species were highly correlated with urinary creatinine and albumin excretion, reflecting glomerular filtration and tubular transport processes. In women, however, lipid species deriving from urinary cells and cellular constituents of the lower genitourinary tract considerably contributed to the urinary lipidome. In conclusion, our study revealed the potential of urinary lipidomics but also the complexity of methodological challenges which have to be overcome for its implementation as a routine diagnostic tool for renal, urological and metabolic diseases.

Lipidomics: new insight into kidney disease

Due to the incidence of type-2 diabetes and hypertension, chronic kidney disease (CKD) has emerged as a major public health problem worldwide. CKD results in premature death from accelerated cardiovascular disease and various other complications. Early detection, careful monitoring of renal function, and response to therapeutic intervention are critical for prevention of CKD progression and its complications. Unfortunately, traditional biomarkers of renal function are insufficiently sensitive or specific to detect early stages of disease when therapeutic intervention is most effective. Therefore, more sensitive biomarkers of kidney disease are needed for early diagnosis, monitoring, and effective treatment. CKD results in profound changes in lipid and lipoprotein metabolism that, in turn, contribute to progression of CKD and its cardiovascular complications. Lipids and lipid-derived metabolites play diverse and critically important roles in the structure and function of cells, tissues, and biofluids. Lipidomics is a branch of metabolomics, which encompasses the global study of lipids and their biologic function in health and disease including identification of biomarkers for diagnosis, prognosis, prevention, and therapeutic response for various diseases. This review summarizes recent developments in lipidomics and its application to various kidney diseases including chronic glomerulonephritis, IgA nephropathy, chronic renal failure, renal cell carcinoma, diabetic nephropathy, and acute renal failure in clinical and experimental research. Analytical technologies, data analysis, as well as currently known metabolic biomarkers of kidney diseases are addressed. Future perspectives and potential limitations of lipidomics are discussed.

Top-down lipidomics of low density lipoprotein reveal altered lipid profiles in advanced chronic kidney disease

This study compared the molecular lipidomic profile of LDL in patients with nondiabetic advanced renal disease and no evidence of CVD to that of age-matched controls, with the hypothesis that it would reveal proatherogenic lipid alterations. LDL was isolated from 10 normocholesterolemic patients with stage 4/5 renal disease and 10 controls, and lipids were analyzed by accurate mass LC/MS. Top-down lipidomics analysis and manual examination of the data identified 352 lipid species, and automated comparative analysis demonstrated alterations in lipid profile in disease. The total lipid and cholesterol content was unchanged, but levels of triacylglycerides and N-acyltaurines were significantly increased, while phosphatidylcholines, plasmenyl ethanolamines, sulfatides, ceramides, and cholesterol sulfate were significantly decreased in chronic kidney disease (CKD) patients. Chemometric analysis of individual lipid species showed very good discrimination of control and disease sample despite the small cohorts and identified individual unsaturated phospholipids and triglycerides mainly responsible for the discrimination. These findings illustrate the point that although the clinical biochemistry parameters may not appear abnormal, there may be important underlying lipidomic changes that contribute to disease pathology. The lipidomic profile of CKD LDL offers potential for new biomarkers and novel insights into lipid metabolism and cardiovascular risk in this disease.