Metabolic acidosis: separation methods and biological relevance of organic acids and lactic acid enantiomers

Semiconducting polymer dots based l-lactate sensor by enzymatic cascade reaction system

BACKGROUND

l-lactate detection is important for not only assessing exercise intensity, optimizing training regimens, and identifying the lactate threshold in athletes, but also for diagnosing conditions like L-lactateosis, monitoring tissue hypoxia, and guiding critical care decisions. Moreover, l-lactate has been utilized as a biomarker to represent the state of human health. However, the sensitivity of the present l-lactate detection technique is inadequate.

RESULTS

Here, we reported a sensitive ratiometric fluorescent probe for l-lactate detection based on platinum octaethylporphyrin (PtOEP) doped semiconducting polymer dots (Pdots-Pt) with enzymatic cascade reaction. With the help of an enzyme cascade reaction, the l-lactate was continuously oxidized to pyruvic and then reduced back to l-lactate for the next cycle. During this process, oxygen and NADH were continuously consumed, which increased the red fluorescence of Pdots-Pt that responded to the changes of oxygen concentration and decreased the blue fluorescence of NADH at the same time. By comparing the fluorescence intensities at these two different wavelengths, the concentration of l-lactate was accurately measured. With the optimal conditions, the probes showed two linear detection ranges from 0.5 nM to 5.0 μM and 5.0 μM-50.0 μM for l-lactate detection. The limit of detection was calculated to be 0.18 nM by 3σ/slope method. Finally, the method shows good detection performance of l-lactate in both bovine serum and artificial serum samples, indicating its potential usage for the selective analysis of l-lactate for health monitoring and disease diagnosis.

SIGNIFICANCE

The successful application of the sensing system in the complex biological sample (bovine serum and artificial serum samples) demonstrated that this method could be used for sensitive l-lactate detection in practical clinical applications. This detection system provided an extremely low detection limit, which was several orders of magnitude lower than methods proposed in other literatures.

Serum D-lactate, a novel serological biomarker, is promising for the diagnosis of periprosthetic joint infection

Background

Although many markers are used for diagnosis of periprosthetic joint infection (PJI), serological screening and diagnosis for PJI are still challenging. We evaluated the performance of serum D-lactate and compared it with ESR, coagulation-related biomarkers and synovial D-lactate for the diagnosis of PJI.

Methods

Consecutive patients with preoperative blood and intraoperative joint aspiration of a prosthetic hip or knee joint before revision arthroplasty were prospectively included. The diagnosis of PJI was based on the criteria of the Musculoskeletal Infection Society, and the diagnostic values of markers were estimated based on receiver operating characteristic (ROC) curves by maximizing sensitivity and specificity using optimal cutoff values.

Results

Of 52 patients, 26 (50%) were diagnosed with PJI, and 26 (50%) were diagnosed with aseptic failure. ROC curves showed that serum D-lactate, fibrinogen (FIB) and ESR had equal areas under the curve (AUCs) of 0.80, followed by D-dimer and fibrin degradation product, which had AUCs of 0.67 and 0.69, respectively. Serum D-lactate had the highest sensitivity of 88.46% at the optimal threshold of 1.14 mmol/L, followed by FIB and ESR, with sensitivities of 80.77% and 73.08%, respectively, while there were no significant differences in specificity (73.08%, 73.08% and 76.92%, respectively).

Conclusion

Serum D-lactate showed similar performance to FIB and ESR for diagnosis of PJI. The advantages of serum D-lactate are pathogen-specific, highly sensitive, minimally invasive and rapidly available making serum D-lactate useful as a point-of-care screening test for PJI.

Enantioselective metabolomics by liquid chromatography-mass spectrometry

Metabolomics strives to capture the entirety of the metabolites in a biological system by comprehensive analysis, often by liquid chromatography hyphenated to mass spectrometry. A particular challenge thereby is the differentiation of structural isomers. Common achiral targeted and untargeted assays do not distinguish between enantiomers. This may lead to information loss. An increasing number of publications demonstrate that the enantiomeric ratio of certain metabolites can be meaningful biomarkers of certain diseases emphasizing the importance of introducing enantioselective analytical procedures in metabolomics. In this work, the state-of-the-art in the field of LC-MS based metabolomics is summarized with focus on developments in the recent decade. Methodologies, tagging strategies, workflows and general concepts are outlined. Selected biological applications in which enantioselective metabolomics has documented its usefulness are briefly discussed. In general, targeted enantioselective metabolomics assays are often based on a direct approach using chiral stationary phases (CSP) with polysaccharide derivatives, macrocyclic antibiotics, chiral crown ethers, chiral ion exchangers, donor-acceptor phases as chiral selectors. Rarely, these targeted assays focus on more than 20 analytes and usually are restricted to a certain metabolite class. In a variety of cases, pre-column derivatization of metabolites has been performed, especially for amino acids, to improve separation and detection sensitivity. Triple quadrupole instruments are the detection methods of first choice in targeted assays. Here, issues like matrix effect, absence of blank matrix impair accuracy of results. In selected applications, multiple heart cutting 2D-LC (RP followed by chiral separation) has been pursued to overcome this problem and alleviate bias due to interferences. Non-targeted assays, on the other hand, are based on indirect approach involving tagging with a chiral derivatizing agent (CDA). Besides classical CDAs numerous innovative reagents and workflows have been proposed and are discussed. Thereby, a critical issue for the accuracy is often neglected, viz. the validation of the enantiomeric impurity in the CDA. The majority of applications focus on amino acids, hydroxy acids, oxidized fatty acids and oxylipins. Some potential clinical applications are highlighted.

Abomasal infusion of corn starch and β-hydroxybutyrate in early-lactation Holstein-Friesian dairy cows to induce hindgut and metabolic acidosis

The objectives of this study were to induce hindgut and metabolic acidosis via abomasal infusion of corn starch and β-hydroxybutyrate (BHB), respectively, and to determine the effects of these physiological states in early-lactation dairy cows. In a 6 × 6 Latin square design, 6 rumen-fistulated Holstein-Friesian dairy cows (66 ± 18 d in milk) were subjected to 5 d of continuous abomasal infusion treatments followed by 2 d of rest. The abomasal infusion treatments followed a 3 × 2 factorial design, with 3 levels of corn starch and 2 levels of BHB. The infusions were water as control, 1.5 kg of corn starch/d, 3.0 kg of corn starch/d, 8.0 mol BHB/d, 1.5 kg of corn starch/d + 8.0 mol BHB/d, or 3.0 kg of corn starch/d + 8.0 mol BHB/d. A total mixed ration consisting of 35.0% grass silage, 37.4% corn silage, and 27.6% concentrate (on a dry matter basis) was fed at 90% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to facilitate determination of energy and N balance. Fecal pH decreased with each level of corn starch infused into the abomasum and was 6.49, 6.00, and 5.15 with 0.0, 1.5, and 3.0 kg of corn starch/d, respectively, suggesting that hindgut acidosis was induced with corn starch infusion. No systemic inflammatory response was observed and the permeability of the intestine or hindgut epithelium was not affected by the more acidic conditions. This induced hindgut acidosis was associated with decreased digestibility of nutrients, except for crude fat and NDF, which were not affected. Induced hindgut acidosis did not affect milk production and composition and energy balance, but increased milk N efficiency. Abomasal infusion of BHB resulted in a compensated metabolic acidosis, which was characterized by a clear disturbance of acid-base status (i.e., decreased blood total CO₂, HCO₃, and base excess, and a tendency for decreased urinary pH), whereas blood pH remained within a physiologically normal range. Abomasal infusion of BHB resulted in increased concentrations of BHB in milk and plasma, but both remained well below the critical threshold values for subclinical ketosis. Induced compensated metabolic acidosis, as a result of abomasally infused BHB, increased energy retained as body fat, did not affect milk production and composition or inflammatory response, but increased intestinal permeability.

Effect of sugar metabolite methylglyoxal on equine lamellar explants: An ex vivo model of laminitis

Laminitis is one of the most devastating diseases in equine medicine, and although several etiopathogenetic mechanisms have been proposed, few clear answers have been identified to date. Several lines of evidence point towards its underlying pathology as being metabolism-related. In the carbonyl stress pathway, sugars are converted to methylglyoxal (MG)-a highly reactive α-oxoaldehyde, mainly derived during glycolysis in eukaryotic cells from the triose phosphates: D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. One common hypothesis is that MG could be synthesized during the digestive process in horses, and excessive levels absorbed into peripheral blood could be delivered to the foot and lead to alterations in the hoof lamellar structure. In the present study, employing an ex vivo experimental design, different concentrations of MG were applied to hoof explants (HE), which were then incubated and maintained in a specific medium for 24 and 48 h. Macroscopic and histological analyses and a separation force test were performed at 24 and 48 h post-MG application. Gene expression levels of matrix metalloproteinase (MMP)-2 and -14 and tissue inhibitor of metalloproteinase (TIMP)-2 were also measured at each time point for all experimental conditions. High concentrations of MG induced macroscopic and histological changes mimicking laminitis. The separation force test revealed that hoof tissue samples incubated for 24 h in a high concentration of MG, or with lower doses but for a longer period (48 h), demonstrated significant weaknesses, and samples were easily separated. All results support that high levels of MG could induce irreversible damage in HEs, mimicking laminitis in an ex vivo model.

Long distance running - Can bioprofiling predict success in endurance athletes?

The TransEuropeFootRace (TEFR) was one of the most extreme multistage competitions worldwide. The ultramarathon took the runners over a distance of 4487 km, from Bari, Italy, to the North Cape, Norway, in 64 days. The participating ultra-long-distance runners had to complete almost two marathons per day (~70 km). The race was accompanied by a research team analysing adaptations of different organ systems of the human body that were exposed to a chronic lack of regeneration time. Here, we analyzed runner's urine using mass spectrometric profiling of thousands of low-molecular weight compounds. The results indicated that pre-race molecular factors can predict finishers and separate them from nonfinishers already before the race. These observations were related to the training volume as finishers ran about twice as many kilometers per week before TEFR than nonfinishers, thus apparently achieving a higher performance level and resistance against overuse. While this hypothesis needs to be validated in future long-distance races, the bioprofiling experiments suggest that the competition readiness of the runners is measurable and might be adjustable.

Validation and Application of a Derivatization-Free RP-HPLC-DAD Method for the Determination of Low Molecular Weight Salivary Metabolites

Saliva is an interesting, non-conventional, valuable diagnostic fluid. It can be collected using standardized sampling device; thus, its sampling is easy and non-invasive, it contains a variety of organic metabolites that reflect blood composition. The aim of this study was to validate a user-friendly method for the simultaneous determination of low molecular weight metabolites in saliva. We have optimized and validated a high throughput, direct, low-cost reversed phase liquid chromatographic method with diode array detection method without any pre- or post-column derivatization. We indexed salivary biomolecules in 35 whole non-stimulated saliva samples collected in 8 individuals in different days, including organic acids and amino acids and other carbonyl compounds. Among these, 16 whole saliva samples were collected by a single individual over three weeks before, during and after treatment with antibiotic in order to investigate the dynamics of metabolites. The concentrations of the metabolites were compared with the literature data. The multianalyte method here proposed requires a minimal sample handling and it is cost-effectiveness as it makes possible to analyze a high number of samples with basic instrumentation. The identification and quantitation of salivary metabolites may allow the definition of potential biomarkers for non-invasive "personal monitoring" during drug treatments, work out, or life habits over time.

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.

pH-mediated inhibition of a bumble bee parasite by an intestinal symbiont

Gut symbionts can augment resistance to pathogens by stimulating host-immune responses, competing for space and nutrients, or producing antimicrobial metabolites. Gut microbiota of social bees, which pollinate many crops and wildflowers, protect hosts against diverse infections and might counteract pathogen-related bee declines. Bumble bee gut microbiota, and specifically abundance of Lactobacillus 'Firm-5' bacteria, can enhance resistance to the trypanosomatid parasite Crithidia bombi. However, the mechanism underlying this effect remains unknown. We hypothesized that the Firm-5 bacterium Lactobacillus bombicola, which produces lactic acid, inhibits C. bombi via pH-mediated effects. Consistent with our hypothesis, L. bombicola spent medium inhibited C. bombi growth via reduction in pH that was both necessary and sufficient for inhibition. Inhibition of all parasite strains occurred within the pH range documented in honey bees, though sensitivity to acidity varied among strains. Spent medium was slightly more potent than HCl, d- and l-lactic acids for a given pH, suggesting that other metabolites also contribute to inhibition. Results implicate symbiont-mediated reduction in gut pH as a key determinant of trypanosomatid infection in bees. Future investigation into in vivo effects of gut microbiota on pH and infection intensity would test the relevance of these findings for bees threatened by trypanosomatids.

Clinical use of plasma lactate concentration. Part 1: Physiology, pathophysiology, and measurement

OBJECTIVE

To review the current literature with respect to the physiology, pathophysiology, and measurement of lactate.

DATA SOURCES

Data were sourced from veterinary and human clinical trials, retrospective studies, experimental studies, and review articles. Articles were retrieved without date restrictions and were sourced primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Lactate is an important energy storage molecule, the production of which preserves cellular energy production and mitigates the acidosis from ATP hydrolysis. Although the most common cause of hyperlactatemia is inadequate tissue oxygen delivery, hyperlactatemia can, and does occur in the face of apparently adequate oxygen supply. At a cellular level, the pathogenesis of hyperlactatemia varies widely depending on the underlying cause. Microcirculatory dysfunction, mitochondrial dysfunction, and epinephrine-mediated stimulation of Na⁺ -K⁺ -ATPase pumps are likely important contributors to hyperlactatemia in critically ill patients. Ultimately, hyperlactatemia is a marker of altered cellular bioenergetics.

CONCLUSION

The etiology of hyperlactatemia is complex and multifactorial. Understanding the relevant pathophysiology is helpful when characterizing hyperlactatemia in clinical patients.

Metabolomic findings in sepsis as a damage of host-microbial metabolism integration

Metabolomics globally evaluates the totality of the endogenous metabolites in patient's body, at the same time reflecting gene function, enzyme activity and degree of organ dysfunction in sepsis. The authors performed the analysis of the main chemical classes of low molecular weight compounds (amino acids, polyols, fatty acids, hydroxy acids, amines, nucleotides and their derivatives) that quantitatively distinguish patients with sepsis from healthy ones. The following keywords were used to find papers published in the Scopus and Web of Science databases from 2008 to 2015: (marker OR biomarker) AND (sepsis OR critical ill OR pneumonia OR hypoxia). Key words for the search were the following: metabolomics, metabolic profiling, sepsis, metabolism, biomarkers, critically ill patients, multiple organ failure. Several metabolomic findings in sepsis are still waiting for an explanation. When assessing metabolomic analysis results in patients with sepsis we should take into account the intervention of microbial metabolism. Among the low molecular weight compounds detected in septic patient blood, a special attention should be paid to the molecules which could be attributed to "common metabolites" of man and bacteria. The genomic region overlap and the production of enzymes which are similar in function and final products could be a possible reason for this phenomenon. For example, microbial biodegradation products of aromatic compounds are increased many times in blood of patients with sepsis. On the one hand, it shows a high metabolic activity of the bacteria. On the other hand, these molecules are intermediates in the metabolism of aromatic amino acids such as tyrosine and phenylalanine in human body. It is important that there are many clinical studies, which confirmed the diagnostic and prognostic significance of series of aromatic metabolites, including those with intrinsic biological activity. We can't exclude the presence of signaling pathways, cell receptors, transmembrane transporters and others which are common for a human and bacteria and their direct participation in mechanisms of organ dysfunction and hypotension in sepsis. Thus, today, we should not limit ourselves studying eukaryotic cells while searching for new molecular mechanisms of sepsis-associated organ failure and septic shock. We should take into account and simulate in the experiments the changes of a human internal environment, which occur during the radical microbiome "restructuring" in critically ill patients. This approach opens up new prospects for an objective monitoring of diseases, carrying out an assessment of the integral metabolic profile in a given time on common metabolites (particularly aromatic), and in future will provide new targets for therapeutic effects.

d(-) Lactic Acid-Induced Adhesion of Bovine Neutrophils onto Endothelial Cells Is Dependent on Neutrophils Extracellular Traps Formation and CD11b Expression

Bovine ruminal acidosis is of economic importance as it contributes to reduced milk and meat production. This phenomenon is mainly attributed to an overload of highly fermentable carbohydrate, resulting in increased d(−) lactic acid levels in serum and plasma. Ruminal acidosis correlates with elevated acute phase proteins in blood, along with neutrophil activation and infiltration into various tissues leading to laminitis and aseptic polysynovitis. Previous studies in bovine neutrophils indicated that d(−) lactic acid decreased expression of L-selectin and increased expression of CD11b to concentrations higher than 6 mM, suggesting a potential role in neutrophil adhesion onto endothelia. The two aims of this study were to evaluate whether d(−) lactic acid influenced neutrophil and endothelial adhesion and to trigger neutrophil extracellular trap (NET) production (NETosis) in exposed neutrophils. Exposure of bovine neutrophils to 5 mM d(−) lactic acid elevated NET release compared to unstimulated neutrophil negative controls. Moreover, this NET contains CD11b and histone H₄ citrullinated, the latter was dependent on PAD4 activation, a critical enzyme in DNA decondensation and NETosis. Furthermore, NET formation was dependent on d(−) lactic acid plasma membrane transport through monocarboxylate transporter 1 (MCT1). d(−) lactic acid enhanced neutrophil adhesion onto endothelial sheets as demonstrated by in vitro neutrophil adhesion assays under continuous physiological flow conditions, indicating that cell adhesion was a NET- and a CD11b/ICAM-1-dependent process. Finally, d(−) lactic acid was demonstrated for the first time to trigger NETosis in a PAD4- and MCT1-dependent manner. Thus, d(−) lactic acid-mediated neutrophil activation may contribute to neutrophil-derived pro-inflammatory processes, such as aseptic laminitis and/or polysynovitis in animals suffering acute ruminal acidosis.

Potentiometric sensor for non invasive lactate determination in human sweat

The present work describes a non invasive lactate sensing in sweat during workout. The sensing system is based on a non-equilibrium potentiometric measure performed using disposable, chemically modified, screen printed carbon electrodes (SPCEs) that can be wetted with sweat during the exercise. The potentiometric signal, which is proportional to lactate concentration in sweat, is produced by a redox reaction activated by UV radiation, as opposed to the enzymatic reaction employed in traditional, blood-based measuring devices. The sensing system exhibits chemical selectivity toward lactate with linearity from 1 mM up to 180 mM. The dynamic linear range is suitable for measurement of lactate in sweat, which is more than 10 times concentrated than hematic lactate and reaches more than 100 mM in sweat during workout. The noninvasive measure can be repeated many times during exercise and during the recovery time in order to get personal information on the physiological and training status as well as on the physical performance. The device was successfully applied to several human subjects for the measurement of sweat lactate during prolonged cycling exercise. During the exercise sweat was simultaneously sampled on filter paper and extracted in water, and the lactate was determined by HPLC for method validation. The lactate concentration changes during the exercise reflected the intensity of physical effort. This method has perspectives in many sport disciplines as well as in health care and biomedical area.

Analysis of short-chain fatty acids in human feces: A scoping review

Short-chain fatty acids (SCFAs) play a crucial role in maintaining homeostasis in humans, therefore the importance of a good and reliable SCFAs analytical detection has raised a lot in the past few years. The aim of this scoping review is to show the trends in the development of different methods of SCFAs analysis in feces, based on the literature published in the last eleven years in all major indexing databases. The search criteria included analytical quantification techniques of SCFAs in different human clinical and in vivo studies. SCFAs analysis is still predominantly performed using gas chromatography (GC), followed by high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and capillary electrophoresis (CE). Performances, drawbacks and advantages of these methods are discussed, especially in the light of choosing a proper pretreatment, as feces is a complex biological material. Further optimization to develop a simple, cost effective and robust method for routine use is needed.

Chiral separation of short chain aliphatic hydroxycarboxylic acids on cinchonan carbamate-based weak chiral anion exchangers and zwitterionic chiral ion exchangers

Chiral short chain aliphatic hydrocarboxylic acids (HCAs) are common compounds being part of different biological processes. In order to control and understand these processes is of pivotal importance to determine the identity of the involved enantiomer or their enantiomeric ratio. In this study the capacity of quinine- and quinidine-derived chiral stationary phases to perform the enantioseparation of eight chiral HCAs (tartaric acid, isocitric acid, malic acid, glyceric acid, 2-hydroxyglutaric acid, 2-hydroxybutyric acid, lactic acid and 3-hydroxybutyric acid) was evaluated. MS-compatible conditions consisting of ACN/MeOH mixtures as eluents with formic acid, acetic acid and/or their ammonium salts as additives, temperatures between 10 and 25°C (except for -20°C for 3-hydroxybutyric acid) and a flow rate of 1.00mL/min yielded full baseline resolution for all studied HCAs. Elution order for the HCA enantiomers was determined revealing different behaviors between the studied compounds.

Long-Term Supplementation with Chromium Malate Improves Short Chain Fatty Acid Content in Sprague-Dawley Rats

Our previous study showed that chromium malate improved the composition of intestinal flora, glycometabolism, glycometabolism-related enzymes, and lipid metabolism in type 2 diabetes mellitus (T2DM) rats. The present study was designed to evaluate the effect of chromium malate with long-term supplementation on short chain fatty acid (SCFA) content in Sprague-Dawley rats. The samples were analyzed by gas chromatography with high linearity (R ² ≥ 0.9995), low quantification limit (0.011-0.070 mM), and satisfactory recoveries. The method was simple and environmentally friendly. The acetic content in cecum of 3-month control group was significantly higher than that of 1-year control group. When compared with 1-year control group, chromium malate (at a dose of 20.0 μg Cr/kg bw) could significantly increase acetic, propionic, i-butyric butyric, butyric, i-valeric, valeric, and n-caproic levels. The acetic, propionic, i-butyric, valeric, and n-caproic contents of 1-year chromium malate group (at a dose of 20.0 μg Cr/kg bw) had a significant improvement when compared with 1-year chromium picolinate group. Acetic, propionic, and butyric contained approximately 91.65 % of the total SCFAs in 1-year group. The results indicated that the improvement of chromium malate on short chain fatty acid content change was better than that of chromium picolinate.

Lactic Acid Determination in Human Plasma Using Ultrasound-Assisted Emulsification Microextraction Followed by Gas Chromatography

A rapid, sensitive, and accurate analytical method was developed for determination of lactic acid (LA) in human plasma to monitor lactic acidosis. This method was based on an ultrasound-assisted emulsification microextraction (USAEME) method followed by gas chromatography with flame ionization detection (GC–FID). Derivatization of LA was carried out by a low density alcoholic solvent which performs both as an extraction solvent and derivatization agent, simultaneously. In this procedure, 100 μL of binary mixtures of pentan-1-ol with toluene (70 : 30, v/v %) was slowly injected into a 10 mL acidified aqueous sample of LA placed into an ultrasonic water bath. The resulting emulsion was centrifuged and after derivatization, 2 μL of organic phase was analysed by GC–FID. The effective variables were evaluated to optimize the efficiency of USAEME. Under the optimum conditions, good linearity in the range of 0.06–7.77 mmol L–1 was obtained with a correlation coefficient (R2) of 0.991 and a limit of detection (LOD) of 0.04 mmol L–1 for water samples. The inter-day and intra-day repeatability of the proposed method in human plasma were evaluated in terms of the relative standard deviation (RSD %) and were found to be <10 %. The results revealed that the USAEME–GC–FID method can be applied successfully for determination of LA in human plasma samples with satisfactory accuracy and precision.

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.

Capillary electrophoresis for monitoring bioprocesses

Chemical characterization and monitoring of fermentation broths and cell culture media provide significant information on the changes occurring within these complex and dynamic systems. Analytical methods based on CE in capillaries and microchips are attractive for integration in instrumental tools to obtain this critical data, improving the understanding and control of bioprocesses. In this review, the use of CE for chemical characterization and monitoring fermentations is discussed, organized by analyte class, including organic acids, pharmaceuticals, proteins, sugars, amino acids, and metabolites published between 1992 and October 2012. A section is dedicated to the roles CE plays throughout the wine making process, where applications range from characterization and increase in fundamental understanding of the fermentation to forensic applications, verifying the authenticity of the wine.

Faecal D/L lactate ratio is a metabolic signature of microbiota imbalance in patients with short bowel syndrome

Our objective was to understand the functional link between the composition of faecal microbiota and the clinical characteristics of adults with short bowel syndrome (SBS).

Sixteen patients suffering from type II SBS were included in the study. They displayed a total oral intake of 2661±1005 Kcal/day with superior sugar absorption (83±12%) than protein (42±13%) or fat (39±26%). These patients displayed a marked dysbiosis in faecal microbiota, with a predominance of Lactobacillus/Leuconostoc group, while Clostridium and Bacteroides were under-represented. Each patient exhibited a diverse lactic acid bacteria composition (L. delbrueckii subsp. bulgaricus, L. crispatus, L. gasseri, L. johnsonii, L. reuteri, L. mucosae), displaying specific D and L-lactate production profiles in vitro. Of 16 patients, 9/16 (56%) accumulated lactates in their faecal samples, from 2 to 110 mM of D-lactate and from 2 to 80 mM of L-lactate. The presence of lactates in faeces (56% patients) was used to define the Lactate-accumulator group (LA), while absence of faecal lactates (44% patients) defines the Non lactate-accumulator group (NLA). The LA group had a lower plasma HCO3⁻ concentration (17.1±2.8 mM) than the NLA group (22.8±4.6 mM), indicating that LA and NLA groups are clinically relevant sub–types. Two patients, belonging to the LA group and who particularly accumulated faecal D-lactate, were at risk of D-encephalopathic reactions. Furthermore, all patients of the NLA group and those accumulating preferentially L isoform in the LA group had never developed D-acidosis. The D/L faecal lactate ratio seems to be the most relevant index for a higher D- encephalopathy risk, rather than D- and L-lactate faecal concentrations per se. Testing criteria that take into account HCO3⁻ value, total faecal lactate and the faecal D/L lactate ratio may become useful tools for identifying SBS patients at risk for D-encephalopathy.

Online enzyme discrimination and determination of substrate enantiomers based on electrophoretically mediated microanalysis

We proposed the first application of an electrophoretically mediated microanalysis (EMMA) method for fast online discrimination and determination of substrate enantiomers, which was achieved by just one EMMA assay. Lactate dehydrogenase (LDH)-catalyzed reaction was studied to evaluate the feasibility and performance of the presented method. The L- and D-LDH chiral enzymatic reactions, which are highly stereoselective to the lactate enantiomers, were initiated successively in one capillary, and the corresponding products, nicotinamide adenine dinucleotide (NADH), were online discriminated and detected by UV absorption. Excellent linear dependence of the two NADH peak intensities on the concentration of the corresponding lactate enantiomers was obtained within a wide range of 0.1-10 mM. The limit of detection was 26 μM for D-lactate and 49 μM for L-lactate (S/N = 3). Good repeatability of online chiral discrimination was demonstrated with relative standard deviation (RSD) < 6.3% for NADH peak height and RSD < 1.5% for migration time (n = 5). K(m) values for L- and D-lactate were measured and were consistent with those of the off-line enzyme assays. The presented method was successfully applied to determine the L-/D-lactate in several yogurt and wine samples. Our study shows a new application of the EMMA method utilizing high stereoselectivity of enzymes for fast online chiral analysis.

Antibody-based multiplex analysis of structurally closely related chiral molecules

Four class-specific and stereoselective antibodies were labeled with different fluorophores to enable simultaneous quantification of the enantiomers of phenylalanine and phenyllactic acid. Using fluorescence immunoassays and microarrays, sensitive detection of each analyte was possible even in the presence of a large excess of the other structurally similar molecules.

The impact of the level of the intestinal short chain Fatty acids in inflammatory bowel disease patients versus healthy subjects

The aim of this study was to determine the changes of short chain fatty acids (SCFAs) in faeces of inflammatory bowel disease (IBD) patients compared to healthy subjects. SCFAs such as pyruvic, lactic, formic, acetic, propionic, isobutyric and butyric acids were analyzed by using high performance liquid chromatography (HPLC). This study showed that the level of acetic, 162.0 µmol/g wet faeces, butyric, 86.9 µmol/g wet faeces, and propionic acids, 65.6 µmol/g wet faeces, decreased remarkably in IBD faecal samples when compared with that of healthy individuals, 209.7, 176.0, and 93.3 µmol/g wet faeces respectively. On the contrary, lactic and pyruvic acids showed higher levels in faecal samples of IBD than in healthy subjects. In the context of butyric acid level, this study also found that the molar ratio of butyric acid was higher than propionic acid in both faecal samples. This might be due to the high intake of starch from rice among Malaysian population. It was concluded that the level of SCFAs differ remarkably between faecal samples in healthy subjects and that in IBD patients providing evidence that SCFAs more likely play an important role in the pathogenesis of IBD.

Treatment of calf diarrhea: intravenous fluid therapy

Severely dehydrated calves that are unable to suckle need intravenous fluids for effective resuscitation. Intravenous fluid therapy is also indicated for sick calves without obvious dehydration, such as calves with strong ion acidosis, ruminal acidosis (rumen drinkers), severe pneumonia, septicemia, or hypothermia. This article presents an updated overview of intravenous fluid therapy for calves, recent insights into the development of metabolic acidosis in young calves resulting from accumulation of D-lactate, a simplified algorithm for intravenous fluid therapy, and a procedure for ear vein catheterization under field conditions.

Determination of lactic acid enantiomers in human urine by high-performance immunoaffinity LC-MS

In this study, a monoclonal anti-d-hydroxy acid antibody was used as chiral selector for chromatographic enantiomer separation and quantification of lactic acid contained in human urine samples. The immunoaffinity column was directly coupled to an electrospray ionization mass spectrometer for detection. Separations were performed at room temperature and under isocratic conditions using ammonium bicarbonate buffer (pH 7.8; 10 mM) as mobile phase. No elaborate sample preparation or analyte derivatization was required and individual runs were completed in less than 10 min.

Simultaneous clinical monitoring of lactic acid, pyruvic acid and ketone bodies in plasma as methoxime/tert-butyldimethylsilyl derivatives by gas chromatography-mass spectrometry in selected ion monitoring mode

Simultaneous determination of lactic acid, pyruvic acid, 3-hydroxybutyric acid and acetoacetic acid for clinical monitoring of lactic acidosis and ketone body formation in human plasma (20 microL) was performed by gas chromatography-mass spectrometry in selected ion monitoring (SIM) mode after generating methoxime/tert-butyldimethylsilyl derivatives. All of the targeted carboxylic acids were detected by characteristic fragment ions, which permitted sensitive and selective identification in the presence of co-extracted free fatty acids and other acidic metabolites at much higher levels. The method was linear (r>or=0.9991), reproducible (% relative standard deviation=1.2-5.8), and accurate (% relative error=-7.2-7.6), with detection limits of 0.05-1.7 ng/mL. This rapid, accurate and selective method using minimal plasma samples (20 microL) is useful in the clinical monitoring of lactic acidosis and ketone body formation in plasma.

Analytical investigation: assay of D-lactate in diabetic plasma and urine

OBJECTIVE

In this study we developed a 96-micro plate enzymatic assay for D-lactate in plasma and urine.

METHODS

D-lactate was assayed enzymatically with a UV-spectrophotometer in plasma from 38 and in urine from 37 diabetics and from 42 non-diabetic controls.

RESULTS

The within-run coefficients of variations (CV) were 2.6% for plasma and 5.7% for urine. The between run CVs were 6.8% for plasma and 6.7% for urine. The mean recovery with standard deviation (S.D.) was 107.4+/-7.3% for plasma and 100.1%+/-6.7% for urine. The plasma D-lactate in diabetics were (mean+/-S.D.) 39.6+/-23.7 microM. We found significant difference between the urinary d-lactate in controls and diabetics (18.2+/-12.0 vs. 35.9+/-24.2 microM/mM creatinine, p<0.0001).

CONCLUSIONS

The assay proved reliable with acceptable precision and recovery. Results suggest that diabetics have elevated urinary and plasma D-lactate as compared to controls.

Enantiomer separation of alpha-hydroxy acids in high-performance immunoaffinity chromatography

In this study, a monoclonal anti-d-hydroxy acid antibody was immobilized onto a synthetic high-flow-through chromatographic support material to produce a chiral stationary phase suitable for enantiomer separation of free alpha-hydroxy acids. Chiral separation of several aliphatic and aromatic members of this class of compounds was achieved in HPLC under mild isocratic buffer conditions using phosphate buffered saline, pH 7.4, as mobile phase. Due to the high degree of stereoselectivity exhibited by the immobilized antibody, in all cases the l-enantiomer eluted with the void volume, while the d-enantiomer was retained and eluted second. The effect of the mobile phase parameters flow rate, temperature, pH, and ionic strength on the enantiomer separation of the model analyte mandelic acid was investigated. While it was found that variations in the flow rate did not change the retention factor k2, dramatic effects on the interaction between the immobilized antibody and d-mandelic acid were observed when any of the other mobile phase parameters were modulated.

Changes in urinary level and configuration ratio of d-lactic acid in patients with short bowel syndrome

The present study showed that the D-lactic acid configuration ratio in the urine rose earlier than that in blood or the urinary or blood D-lactic acid levels upon disease onset, and that the D-lactic acid measurement in urine is more sensitive and useful than that in blood. As this result, a prediction of a D-lactic acidosis may be possible. To simplify the procedure for detecting D-lactic acid, we first showed a correlation between the D-lactic acid configuration ratio in urine and blood, indicating urine could be used. To separate the optical isomers of lactic acid, we simplified our previous procedure. For chiral recognition, we chose O-acetyl-(-)-menthylation and analyzed the samples under GC/MS by capillary gas chromatography on a DB-5 MS column. This procedure is less sensitive than the former method, but it is faster and simpler, requiring only one derivatization step. This method may be useful for predicting D-lactic acidosis in patients with short bowel syndrome.

High performance liquid chromatography–tandem mass spectrometry (HPLC/MS/MS) assay for chiral separation of lactic acid enantiomers in urine using a teicoplanin based stationary phase

A novel method for the separation and simultaneous determination of urinary D- and L-lactic acid enantiomers by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS) is presented. The chiral separation was optimized on a Chirobiotic teicoplanin aglyocone (TAG) column. Most interestingly, the addition of water in small volume fraction to the polar organic mobile phase was found to significantly improve the chromatography. Calibration curves were linear (r2>0.9950) over the range 3-1000 mg/L for L-lactic acid and 0.5-160.8 mg/L for D-lactic acid. The limit of detection (LOD) (S/N=3) and limit of quantification (LOQ) (S/N=10) were determined experimentally (n=3) to be 0.2 and 0.5mg/L for L-lactic acid and 0.4 and 1.3 mg/L for D-lactic acid, respectively. The normal patient range of L-lactic acid was 1-20 microg/mg creatinine with an elevated value of 85 microg/mg creatinine. For D-lactic acid, the range of normal values were between 0 and 5 microg/mg creatinine with an elevated value of 40 microg/mg creatinine. Finally, the validated method allows for rapid analysis with a total run time of 7.5 min.

Automated no-carrier-added synthesis of [1-11C]-labeled d- and l-enantiomers of lactic acid

The first purely chemical method for automated no-carrier-added synthesis of [1-(11)C]-labeled d(R)- and l(S)-2-hydroxypropanoic acid (lactic acid) was developed for experimental neurophysiology studies and position emission tomography (PET) diagnosis. Starting from sodium 1-hydroxyethanesulfonate and [(11)C]HCN (trapped as [(11)C]KCN) the intermediate dl-(R,S)-[1-(11)C]-2-hydroxypropanenitrile was prepared. Its rapid acid hydrolysis gave dl-(R,S)-[1-(11)C]lactic acid, which was isolated by preparative reversed phase HPLC and automatically injected on a second preparative C(18) HPLC column coated with a chiral selector, where both [1-(11)C]lactic acid enantiomers were separated by chiral ligand-exchange chromatography. Two novel chiral selectors for HPLC enantiomeric separation of alpha-hydroxy acids, namely d(R)- or l(S)-2-amino-3-methyl-3-(5-phenylpentylsulfanyl)-butanoic acid were utilized for the preparative HPLC separation of the [1-(11)C]lactic acid enantiomers. The preparation of the selectors and the coating procedure for the manufacturing of the preparative chiral HPLC columns are described. A highly efficient trap for [(11)C]HCN is presented. The whole radiosynthesis is automated, takes about 45 min and leads to more than 80% decay corrected overall radiochemical yield of each enantiomer (up to 2.5 GBq) with over 99% radiochemical, chemical and enantiomeric purity. The specific activity at the end of the synthesis is about 400 GBq/micromol.

Application of optical isomer analysis by diastereomer derivatization GC/MS to determine the condition of patients with short bowel syndrome

To establish a method for separating the optical isomers of lactic acid, we modified the derivatization steps in our procedure for urinary mass-screening for inborn errors of metabolism. For chiral recognition, we chose O-trifluoroacetyl-(-)-menthylation derivatization instead of our previous method, trimethylsilyl derivatization, and the samples were then analyzed under GC/MS by capillary gas chromatography on a DB-5MS column. This method can be used to follow-up the condition of a patient with short bowel syndrome and to prevent onset and/or seizure. d-Lactic acid was also isolated from the urine of healthy controls as one of the main peaks in the chromatogram.

D-lactate in human and ruminant metabolism

D-lactate is normally present in the blood of mammals at nanomolar concentrations due to methylglyoxal metabolism; millimolar d-lactate concentrations can arise due to excess gastrointestinal microbial production. Grain overload in ruminants, short-bowel syndrome in humans, and diarrhea in calves can all result in profound D-lactic acidemia, with remarkably similar neurological manifestations. In the past, D-lactate was thought to be excreted mainly in the urine, and metabolized slowly by the enzyme d-alpha-hydroxy acid dehydrogenase. More recent studies reported that mammals have a relatively high capacity for D-lactate metabolism and identified a putative mammalian D-lactate dehydrogenase. A growing body of literature is also emerging describing subclinical elevation of D-lactate as an indicator of sepsis and trauma. This article describes advances in the understanding of D-lactate metabolism, D-lactic acidosis in ruminants and humans, and subclinical elevation of d-lactate.