Fluorimetric determination of d-lactate in urine of normal and diabetic rats by column-switching high-performance liquid chromatography

D-lactate is a promising biomarker for the diagnosis of periprosthetic joint infection

Introduction

Reliable biomarkers for the diagnosis of periprosthetic joint infection (PJI) are of paramount clinical value. To date, synovial fluid leukocyte count is the standard surrogate parameter indicating PJI. As D-lactate is almost solely produced by bacteria, it represents a promising molecule in the diagnostic workflow of PJI evaluation. Therefore, the purpose of this study was to assess the performance of synovial fluid D-lactate for diagnosing PJI of the hip and knee.

Materials and Methods

These are preliminary results of a prospective multicenter study from one academic center. Seventy-two consecutive patients after total hip arthroplasty (THA) or total knee arthroplasty (TKA) were prospectively included. All patients received a joint aspiration in order to rule out or confirm PJI, which was diagnosed according to previously published institutional criteria. Synovial fluid D-lactate was determined spectrophotometrically at 450 nm. Receiver operating characteristic (ROC) analysis was performed to assess the diagnostic performance.

Results

Eighteen patients (25%) were diagnosed with PJI and 54 patients (75%) were classified as aseptic. Synovial fluid D-lactate showed a sensitivity of 90.7% (95% CI: 79.7%-96.9%) and specificity of 83.3% (95% CI: 58.6%-96.4%) at a cut-off of 0.04 mmol/L. The median concentration of D-lactate was significantly higher in patients with PJI than in those with aseptic conditions (0.048 mmol/L, range, 0.026-0.076 mmol/L vs. 0.024 mmol/L, range, 0.003-0.058 mmol/L, p < 0.0001). The predominat microogranisms were staphylococci, followed by streptococci and gram-negative bacteria.

Conclusion

D-lactate bears a strong potential to act as a valuable biomarker for diagnosing PJI of the hip and knee. In our study, a cutoff of 0.04 mmol/L showed a comparable sensitivity to synovial fluid leukocyte count. However, its specificity was higher compared to conventional diagnostic tools. The additional advantages of D-lactate testing are requirement of low synovial fluid volume, short turnaround time and low cost.

Evaluation of the nephrotoxicity and safety of low-dose aristolochic acid, extending to the use of Xixin (Asurum), by determination of methylglyoxal and d-lactate

ETHNOPHARMACOLOGICAL RELEVANCE

Most Aristolochiaceae plants are prohibited due to aristolochic acid nephropathy (AAN), except Xixin (Asarum spp.). Xixin contains trace amounts of aristolochic acid (AA) and is widely used in Traditional Chinese Medicine. Methylglyoxal and d-lactate are regarded as biomarkers for nephrotoxicity.

AIM OF THE STUDY

The use of Xixin (Asarum spp.) is essential and controversial. This study aimed to evaluate tubulointerstitial injury and interstitial renal fibrosis by determining urinary methylglyoxal and d-lactate after withdrawal of low-dose AA in a chronic mouse model.

MATERIALS AND METHODS

C3H/He mice in the AA group (n = 24/group) were given ad libitum access to distilled water containing 3 μg/mL AA (0.5 mg/kg/day) for 56 days and drinking water from days 57 to 84. The severity of tubulointerstitial injury and fibrosis were evaluated using the tubulointerstitial histological score (TIHS) and Masson's trichrome staining. Urinary and serum methylglyoxal were determined by high-performance liquid chromatography (HPLC); urinary d-lactate were determined by column-switching HPLC.

RESULTS

After AA withdrawal, serum methylglyoxal in the AA group increased from day 56 (429.4 ± 48.3 μg/L) to 84 (600.2 ± 99.9 μg/L), and peaked on day 70 (878.3 ± 171.8 μg/L; p < 0.05); TIHS and fibrosis exhibited similar patterns. Urinary methylglyoxal was high on day 56 (3.522 ± 1.061 μg), declined by day 70 (1.583 ± 0.437 μg) and increased by day 84 (2.390 ± 0.130 μg). Moreover, urinary d-lactate was elevated on day 56 (82.10 ± 18.80 μg) and higher from day 70 (201.10 ± 90.82 μg) to 84 (193.28 ± 61.32 μg).

CONCLUSIONS

Methylglyoxal is induced after AA-induced tubulointerstitial injury, so methylglyoxal excretion and metabolism may be a detoxification and repair strategy. A low cumulative AA dose is the key factor that limits tubulointerstitial injury and helps to repair. Thus, AA-containing herbs, especially Xixin, should be used at low doses for short durations (less than one month).

Development of a selective three-dimensional HPLC system for enantiomer discriminated analysis of lactate and 3-hydroxybutyrate in human plasma and urine

For the enantiomer discriminated determination of lactate (LA) and 3-hydroxybutyrate (3HB) in various complicated samples, a three-dimensional HPLC (3D-HPLC) system has been designed and developed by investigating the separation of the target analytes from unknown substances observed in the real target matrices. LA and 3HB were pre-column derivatized with 4-nitro-7-piperazino-2,1,3-benzoxadiazole for the sensitive fluorescence detection and introduced into the 3D-HPLC system composed of reversed-phase, mixed-mode and enantioselective separations. The present method was validated by calibration curves, precision and accuracy using standard solutions and human samples, and sufficient values were obtained. Using the method, the levels of d-LA, l-LA, d-3Hb and l-3HB were determined, and their concentrations were 9.9, 1004.2, 79.7 and 2.1 μM in the human plasma and 16.0, 86.6, 8.7 and 4.8 μM in the human urine, respectively. The present 3D-HPLC system could selectively determine trace amounts of the target hydroxy acid enantiomers without disturbance of the intrinsic interfering substances in complicated matrices and the applications to various disease samples are expected.

Utilizing methylglyoxal and D-lactate in urine to evaluate saikosaponin C treatment in mice with accelerated nephrotoxic serum nephritis

The relationship between methylglyoxal (MGO) and D-lactate during saikosaponin C (SSC) treatment of mice with accelerated nephrotoxic serum (NTS) nephritis was investigated. NTS nephritis was induced by administration of anti-basement membrane antibodies to C57BL/6 mice and three dosages of SSC were administered for 14 days. Proteinuria, blood urea nitrogen, serum creatinine, renal histology, urinary MGO and d-lactate changes were examined. Compared to the NTS control group, the middle dosage (10 mg/kg/day) of SSC significantly alleviated the development of nephritis based on urine protein measurements (34.40 ± 6.85 vs. 17.33 ± 4.79 mg/day, p<0.05). Pathological observation of the glomerular basement membrane (GBM) revealed monocyte infiltration, hypertrophy, and crescents were alleviated, and injury scoring also showed improved efficacy for the middle dose of SSC during nephritis (7.92 ± 1.37 vs. 3.50 ± 1.14, p<0.05). Moreover, the significant decreases in urinary levels of MGO (24.71 ± 3.46 vs. 16.72 ± 2.36 μg/mg, p<0.05) and D-lactate (0.31 ± 0.04 vs. 0.23 ± 0.02 μmol/mg, p<0.05) were consistent with the biochemical and pathological examinations. This study demonstrates that MGO and D-lactate may reflect the extent of damage and the efficacy of SSC in NTS nephritis; further studies are required to enable clinical application.

Methylglyoxal and D-lactate in cisplatin-induced acute kidney injury: Investigation of the potential mechanism via fluorogenic derivatization liquid chromatography-tandem mass spectrometry (FD-LC-MS/MS) proteomic analysis

Nephrotoxicity severely limits the chemotherapeutic efficacy of cisplatin (CDDP). Oxidative stress is associated with CDDP-induced acute kidney injury (AKI). Methylglyoxal (MG) forms advanced glycation end products that elevate oxidative stress. We aimed to explore the role of MG and its metabolite D-lactate and identify the proteins involved in CDDP-induced AKI. Six-week-old female BALB/c mice were intraperitoneally administered CDDP (5 mg/kg/day) for 3 or 5 days. Blood urea nitrogen (42.6 ± 7.4 vs. 18.3 ± 2.5; p < 0.05) and urinary N-acetyl-β-D-glucosaminide (NAG; 4.89 ± 0.61 vs. 2.43 ± 0.31 U/L; p < 0.05) were significantly elevated in the CDDP 5-day group compared to control mice. Histological analysis confirmed AKI was successfully induced. Confocal microscopy revealed TNF-α was significantly increased in the CDDP 5-day group. Fluorogenic derivatized liquid chromatography-tandem mass spectrometry (FD-LC-MS/MS) showed the kidney MG (36.25 ± 1.68 vs. 18.95 ± 2.24 mg/g protein, p < 0.05) and D-lactate (1.78 ± 0.29 vs. 1.12 ± 0.06 mol/g protein, p < 0.05) contents were significantly higher in the CDDP 5-day group than control group. FD-LC-MS/MS proteomics identified 33 and nine altered peaks in the CDDP 3-day group and CDDP 5-day group (vs. control group); of the 35 proteins identified using the MOSCOT database, 11 were antioxidant-related. Western blotting confirmed that superoxide dismutase 1 (SOD-1) and parkinson disease protein 7 (DJ-1) are upregulated and may participate with MG in CDDP-induced AKI. This study demonstrates TNF-α, MG, SOD-1 and DJ-1 play crucial roles in CDDP-induced AKI.

Effect of prednisolone on glyoxalase 1 in an inbred mouse model of aristolochic acid nephropathy using a proteomics method with fluorogenic derivatization-liquid chromatography-tandem mass spectrometry

Prednisolone is involved in glucose homeostasis and has been used for treatment for aristolochic acid (AA) nephropathy (AAN), but its effect on glycolysis in kidney has not yet been clarified. This study aims to investigate the effect in terms of altered proteins after prednisolone treatment in a mice model of AAN using a proteomics technique. The six-week C3H/He female mice were administrated AA (0.5 mg/kg/day) for 56 days. AA+P group mice were then given prednisolone (2 mg/kg/day) via oral gavage for the next 14 days, and AA group mice were fed water instead. The tubulointerstitial damage was improved after prednisolone treatment comparing to that of AA group. Kidney homogenates were harvested to perform the proteomics analysis with fluorogenic derivatization-liquid chromatography-tandem mass spectrometry method (FD-LC-MS/MS). On the other hand, urinary methylglyoxal and D-lactate levels were determined by high performance liquid chromatography with fluorescence detection. There were 47 altered peaks and 39 corresponding proteins on day 14 among the groups, and the glycolysis-related proteins, especially glyoxalase 1 (GLO1), fructose-bisphosphate aldolase B (aldolase B), and triosephosphate isomerase (TPI), decreased in the AA+P group. Meanwhile, prednisolone decreased the urinary amount of methylglyoxal (AA+P: 2.004 ± 0.301 μg vs. AA: 2.741 ± 0.630 μg, p < 0.05), which was accompanied with decrease in urinary amount of D-lactate (AA+P: 54.07 ± 5.45 μmol vs. AA: 86.09 ± 8.44 μmol, p < 0.05). Prednisolone thus alleviated inflammation and interstitial renal fibrosis. The renal protective mechanism might be associated with down-regulation of GLO1 via reducing the contents of methylglyoxal derived from glycolysis. With the aid of proteomics analysis and the determination of methylglyoxal and its metabolite-D-lactate, we have demonstrated for the first time the biochemical efficacy of prednisolone, and urinary methylglyoxal and its metabolite-D-lactate might be potential biomarkers for AAN.

Performance of synovial fluid D-lactate for the diagnosis of periprosthetic joint infection: A prospective observational study

OBJECTIVES

Synovial fluid leukocyte count is the current standard test for diagnosing periprosthetic joint infection (PJI). As D-lactate is almost exclusively produced by bacteria, it represents a useful biomarker for bacterial infection. We evaluated the performance of synovial fluid D-lactate for the diagnosis of PJI and compared it with the synovial fluid leukocyte count.

METHODS

Consecutive patients with joint aspiration of a prosthetic hip, knee or shoulder joint were prospectively included. PJI was diagnosed according to the working criteria of the European Bone and Joint Infection Society (EBJIS). The synovial fluid D-lactate was determined spectrophotometrically at 570 nm, synovial fluid leukocytes were counted by flow cytometry. The receiver operating characteristic (ROC) analysis was performed to assess the diagnostic performance of investigated parameters.

RESULTS

Of 148 patients, 44 (30%) were diagnosed with PJI and 104 (70%) with aseptic failure. For diagnosis of PJI, the sensitivity of synovial fluid D-lactate (at cut-off 1.263 mmol/l) was 86.4% [95% CI, 75.0-95.5%] and the specificity was 80.8% [95% CI, 73.1-88.5%]. The AUCs of D-lactate concentration and leukocyte count were 90.3% [95% CI 85.7-95.0%] and 91.0% [95% CI 85.1-96.8%], respectively (p = 0.8). Virulence of the pathogen did not influence the D-lactate concentration (p = 0.123). The synovial fluid erythrocyte concentration correlated with D-lactate in patients with aseptic failure (ρ = 0.339, p <0.01).

CONCLUSION

Synovial fluid D-lactate showed similar performance to the leukocyte count for diagnosis of PJI. Advantages of D-lactate test are requirement of low synovial fluid volume, short turnaround time and low cost.

Metabolic profiling of metformin treatment for low-level Pb-induced nephrotoxicity in rat urine

Chronic kidney disease is a worldwide problem, and Pb contamination is a potential risk factor. Since current biomarkers are not sensitive for the diagnosis of Pb-induced nephrotoxicity, novel biomarkers are needed. Metformin has both hypoglycaemic effects and reno-protection ability. However, its mechanism of action is unknown. We aimed to discover the early biomarkers for the diagnosis of low-level Pb-induced nephrotoxicity and understand the mechanism of reno-protection of metformin. Male Wistar rats were randomly divided into control, Pb, Pb + ML, Pb + MH and MH groups. Pb (250 ppm) was given daily via drinking water. Metformin (50 or 100 mg/kg/d) was orally administered. Urine was analysed by nuclear magnetic resonance (NMR)-based metabolomics coupled with multivariate statistical analysis, and potential biomarkers were subsequently quantified. The results showed that Pb-induced nephrotoxicity was closely correlated with the elevation of 5-aminolevulinic acid, D-lactate and guanidinoacetic acid in urine. After co-treatment with metformin, 5-aminolevulinic acid and D-lactate were decreased. This is the first demonstration that urinary 5-aminolevulinic acid, D-lactate and guanidinoacetic acid could be early biomarkers of low-level Pb-induced nephrotoxicity in rats. The reno-protection of metformin might be attributable to the reduction of D-lactate excretion.

Enantioselective and simultaneous determination of lactate and 3-hydroxybutyrate in human plasma and urine using a narrow-bore online two-dimensional high-performance liquid chromatography system

For the enantioselective and simultaneous analysis of lactate and 3-hydroxybutyrate, a validated online two-dimensional high-performance liquid chromatography system using 4-nitro-7-piperazino-2,1,3-benzoxadiazole as a fluorescent derivatization reagent has been developed. For the reversed-phase separation in the first dimension, a Capcell Pak C18 ACR column (1.5 × 250 mm, particle size 3 μm) was used, and the target fractions were isolated by their hydrophobicity. In the second dimension, a polysaccharide-coated enantioselective column, Chiralpak AD-H (2.0 × 250 mm, 5 μm), was used. The system was validated by the calibration curve, intraday precision, interday precision, and accuracy using standards and real human samples, and satisfactory results were obtained. The present method was applied to human plasma and urine, and in the plasma, trace amounts of d-lactate (8.4 μM) and l-3-hydroxybutyrate (1.0 μM), besides high levels of l-lactate (860.9 μM) and d-3-hydroxybutyrate (59.4 μM), were successfully determined. In urine, trace levels of d-lactate (3.7 μM), d-3-hydroxybutyrate (2.3 μM), and l-3-hydroxybutyrate (3.3 μM) in addition to a relatively large amount of l-lactate (15.4 μM) were observed. The present online two-dimensional high-performance liquid chromatography system is useful for the simultaneous determination of all the lactate and 3-hydroxybutyrate enantiomers in human physiological fluids, and further clinical applications are ongoing.

Development of an enzymatic assay system of D-lactate using D-lactate dehydrogenase and a UV-LED fluorescent spectrometer

In this study, we aimed to develop a new enzymatic assay system of d-lactate with good precision, accuracy, and sensitivity for the determination of D-lactate concentrations in rat serum. D-Lactate dehydrogenase (D-LDH) was utilized to catalyze D-lactate and NAD(+) to pyruvate and NADH, respectively. The generated NADH was excited by using a 340-nm UV-light-emitting diode (LED), and the fluorescence at 491 nm was detected to determine the concentration of D-lactate in rat serum. The optics, consisting of the sample cuvette, were set on three-dimensional stages to receive the most intensive fluorescence signal into the spectrometer. The optimal conditions of the D-LDH reaction were pH 8.5 and 25 °C for 90 min. The results showed that the new D-lactate assay system had good linearity (R(2)=0.9964) in the calibration range from 5 to 150 μM. Intra-day and inter-day accuracies were in the range of 103.96-109.09% and 102.84-104.59%, respectively, and the intra-day and inter-day precision was 4.28-6.82% and 4.04-12.40%, respectively. Finally, serum D-lactate concentrations determined by the proposed enzymatic assay system were compared with those obtained by a conventional HPLC method. The newly developed D-lactate assay system could detect 10-15 samples in 90 min, whereas the HPLC method could detect only one sample over the same time period.

Chitosan Prevents Gentamicin-Induced Nephrotoxicity via a Carbonyl Stress-Dependent Pathway

Aminoglycosides are widely used to treat infections; however, their applications are limited by nephrotoxicity. With the increase of antibiotic resistance, the use of aminoglycosides is inevitable. Low-molecular-weight chitosan (LMWC) has shown renal protective effects in dialysis patients. However, no study has evaluated LMWC for preventing aminoglycoside-induced nephrotoxicity or determined the mechanisms underlying the renal protective effects. In this study, LMWC (165 or 825 mg/kg/day) or metformin (100 mg/kg/day) was orally administered for 13 days to rats with nephropathy induced by gentamicin (GM), a kind of aminoglycoside (150 mg/kg/day i.p. for 6 days). Both LMCW doses improved renal function. Serum creatinine levels improved in rats treated with 165 and 825 mg/kg/day LMWC (from 2.14 ± 0.74 mg/dL to 1.26 ± 0.46 mg/dL and 0.69 ± 0.12 mg/dL, resp., P < 0.05). Blood urea nitrogen levels were also improved in these rats (from 73.73 ± 21.13 mg/dL to 58.70 ± 22.71 mg/dL and 28.82 ± 3.84 mg/dL, resp., P < 0.05). Additionally, renal tissue morphology improved after LMWC treatment, and accumulation of renal methylglyoxal, a damage factor associated with carbonyl stress, was reversed. These results show that LMWC prevents GM-induced renal toxicity via a carbonyl stress-dependent pathway.

Development and validation of a novel derivatization method for the determination of lactate in urine and saliva by liquid chromatography with UV and fluorescence detection

We developed a novel and straightforward derivatization method for the determination of lactate by reversed phase high-performance liquid chromatography (RP-HPLC) with fluorescence and UV detection in biological matrices as urine and saliva. The derivatization of lactate was achieved employing 9-chloromethyl anthracene (9-CMA) as fluorescence reagent, which has never been previously used to obtain a lactate derivative. Lactate reacts with 9-CMA with high selectivity in a very short time, without requiring extraction procedures from the aqueous solution, and the reaction reaches 70% completion in 30 min. The ester derivative obtained can be easily determined by RP-HPLC with fluorescence detection at 410 nm (λ ex=365 nm) and UV detection at 365 nm. The method was also optimized in order to allow for the simultaneous determination of lactate and creatinine for the application to urine samples. The lactate calibration curve was linear in the investigated range 2 × 10(-4)-3 × 10(-2)mM and the limit of detection, calculated as three times the standard deviation of the blank divided by the calibration curve slope, was 50 nM for both fluorescence and UV detection. Intra-day and inter-day repeatability were lower than 5% and 6%, respectively. The method proposed was successfully applied to the analysis of urine and saliva samples.

Proteome analysis of altered proteins in streptozotocin-induced diabetic rat kidney using the fluorogenic derivatization-liquid chromatography-tandem mass spectrometry method

To find new molecular markers for early diagnosis of diabetic nephropathy, we applied fluorogenic derivatization-liquid chromatography-tandem mass spectrometry to identify the differentially expressed proteins in the kidney of control and streptozotocin-induced diabetic rats. The Sprague-Dawley rats were injected with the sodium citrate buffer or streptozotocin and then killed after 1, 4, 12 and 24 weeks. The results showed that seven proteins were significantly changed after 1 week of injection. Only one protein had significantly changed after 4 weeks of injection. However, after 12 weeks of injection, the number of altered proteins rose to 10. After 24 weeks of injection, 18 proteins had altered significantly. Five common proteins were significantly altered at week 12 and 24 after injection, respectively. Importantly, these proteins appeared prior to microalbuminuria and may serve as new biomarkers that are able to improve early detection of and new drug development for diabetic-related nephropathy.

Determination of lipoprotein lipase activity in post heparin plasma of streptozotocin-induced diabetic rats by high-performance liquid chromatography with fluorescence detection

The activity of lipoprotein lipase (LPL), an enzyme responsible for lipoprotein metabolism, would vary in diseases and metabolic disorders. For determination of LPL activity, a highly sensitive high performance liquid chromatography (HPLC) method using a fluorescent reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was applied to determinate the oleic acid (OA) generated from triolein by LPL activity without multiple solvents extraction step. We studied the optimal conditions of the reaction including the effect of emulsifiers, deproteinizing solvents, and the concentration of bovine serum albumin (BSA). Ten millimolar concentrations of triolein, 5% of BSA, 1% of Gum arabic (GA), and acetonitrile showed the optimum conditions for measuring the LPL activity. The accuracy values for the determination of LPL activity in 10 microL of rat post heparin plasma were 108.73 approximately 114.36%, and the intra- and inter-day precision values were within 1.28% and 2.91%, respectively. The limit of detection was about 4.53 nM (signal-to-noise ratio 3). The proposed method was applied to determination of LPL activity in post heparin plasma of normal and streptozotocininduced diabetic rats associated with 52.3% reduction. The established assay system could be used for determining LPL activity in different physiological and pathological conditions to clarify the relationship between LPL activity and diabetes mellitus.

Development of a column-switching high-performance liquid chromatography for kynurenine enantiomers and its application to a pharmacokinetic study in rat plasma

Kynurenine (KYN), a tryptophan metabolite, is a precursor of kynurenic acid, which is an antagonist of N-methyl-d-aspartate receptor. In this study, an enantiomeric separation of d,l-KYN derivatized with the benzofurazan fluorescence reagent 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) (DBD-d,l-KYN) was first investigated by using a high-performance liquid chromatography (HPLC) with several chiral columns. As a consequence, DBD-d,l-KYN was enantiomerically separated on a cellulose-type chiral column (CHIRALCEL OJ-RH) with a mobile phase of H(2)O/CH(3)CN/MeOH (40/50/10) containing 0.1% acetic acid. Under this condition, the separation factor and resolution were 1.48 and 1.28, respectively. Next, a column-switching HPLC consisting of both octadecylsilica and chiral columns was developed and used to determine both d- and l-KYN enantiomers in 10 microL of rat plasma following the intraperitoneal administration of d,l-KYN to rats (10 mg kg(-1)). The result revealed that the concentration of l-KYN was higher than that of d-KYN, suggesting that d-KYN was eliminated faster than l-KYN.