Lactate: The Fallacy of Oversimplification

Almost a quarter of a millennium after the discovery of an acidic substance in sour milk by Swedish chemist Carl Wilhelm Scheele and more than 100 years after the demonstration of a tight connection between this lactic acid and tissue hypoxia in shock, we are still surrounded by false beliefs and misunderstandings regarding this fascinating molecule. Common perceptions of lactate, the conjugate base of lactic acid, as a plain waste product of anaerobic metabolism and a marker of cellular distress could not be further from the truth. Lactate is formed and utilized continuously by our cells, even under fully aerobic conditions, in large quantities, and although marked hyperlactatemia is always a red flag in our patients, not all these conditions are life-threatening and vice versa-not all critically ill patients have hyperlactatemia. Lactate also does not promote acidosis by itself; it is not toxic, nor is it a metabolic renegade. On the contrary, it has many beneficial properties, and an interpretation of hyperlactatemia might be trickier than we tend to think. The aim of this article is to debunk some of the deeply rooted myths regarding this fascinating molecule.

Functions and mechanisms of lactylation in carcinogenesis and immunosuppression

As critical executors regulating many cellular operations, proteins determine whether living activities can be performed in an orderly and efficient manner. Precursor proteins are inert and must be modified posttranslationally to enable a wide range of protein types and functions. Protein posttranslational modifications (PTMs) are well recognized as being directly associated with carcinogenesis and immune modulation and have emerged as important targets for cancer detection and treatment. Lactylation (Kla), a novel PTM associated with cellular metabolism found in a wide range of cells, interacts with both histone and nonhistone proteins. Unlike other epigenetic changes, Kla has been linked to poor tumor prognosis in all current studies. Histone Kla can affect gene expression in tumors and immunological cells, thereby promoting malignancy and immunosuppression. Nonhistone proteins can also regulate tumor progression and treatment resistance through Kla. In this review, we aimed to summarize the role of Kla in the onset and progression of cancers, metabolic reprogramming, immunosuppression, and intestinal flora regulation to identify new molecular targets for cancer therapy and provide a new direction for combined targeted therapy and immunotherapy.

A d,l-lactate biosensor based on allosteric transcription factor LldR and amplified luminescent proximity homogeneous assay

Lactate, a hydroxycarboxylic acid commercially produced by microbial fermentation, is widely applied in diverse industrial fields. Lactate exists in two stereoisomeric forms (d-lactate and l-lactate). d-Lactate and l-lactate are often simultaneously present in many biological samples. Therefore, a biosensor able to detect both d- and l-lactate is required but previously unavailable. Herein, an allosteric transcription factor LldR from Pseudomonas aeruginosa PAO1, which responds to both d-lactate and l-lactate, was combined with amplified luminescent proximity homogeneous assay technology to develop a d,l-lactate biosensor. The proposed biosensor was optimized by mutation of DNA sequence in binding site of LldR. The optimized biosensor B_Lac-6 can accurately detect the concentration of lactate independent on ratio of the two isomers in pending test samples. The biosensor was also tentatively used in quantitative analysis of d-lactate, l-lactate, or d,l-lactate in fermentation samples produced by three recombinant strains of Klebsiella oxytoca. With its desirable properties, the biosensor B_Lac-6 may be a potential choice for monitoring the concentration of lactate during industrial fermentation.

Novel Strategy for Untargeted Chiral Metabolomics using Liquid Chromatography-High Resolution Tandem Mass Spectrometry

Stereospecific recognition of metabolites plays a significant role in the detection of potential disease biomarkers thereby providing new insights in diagnosis and prognosis. D-Hdroxy/amino acids are recognized as potential biomarkers in several metabolic disorders. Despite continuous advances in metabolomics technologies, the simultaneous measurement of different classes of enantiomeric metabolites in a single analytical run remains challenging. Here, we develop a novel strategy for untargeted chiral metabolomics of hydroxy/amine groups (-OH/-NH₂) containing metabolites, including all hydroxy acids (HAs) and amino acids (AAs), by chiral derivatization coupled with liquid chromatography-high resolution tandem mass spectrometry (LC-HR-MS/MS). Diacetyl-tartaric anhydride (DATAN) was used for the simultaneous derivatization of-OH/-NH₂ containing metabolites as well as the resulting diastereomers, and all the derivatized metabolites were resolved in a single analytical run. Data independent MS/MS acquisition (DIA) was applied to positively identify DATAN-labeled metabolites based on reagent specific diagnostic fragment ions. We discriminated chiral from achiral metabolites based on the reversal of elution order of D and L isomers derivatized with the enantiomeric pair (±) of DATAN in an untargeted manner. Using the developed strategy, a library of 301 standards that consisted of 214 chiral and 87 achiral metabolites were separated and detected in a single analytical run. This approach was then applied to investigate the enantioselective metabolic profile of the bone marrow (BM) and peripheral blood (PB) plasma samples from patients with acute myeloid leukemia (AML) at diagnosis and following completion of the induction phase of chemotherapeutic treatment. The sensitivity and selectivity of the developed method enabled the detection of trace levels of the D-enantiomer of HAs and AAs in primary plasma patient samples. Several of these metabolites were significantly altered in response to chemotherapy. The developed LC-HR-MS method entails a valuable step forward in chiral metabolomics.

Quantitative Evaluation of D-Lactate Pathophysiology: New Insights into the Mechanisms Involved and the Many Areas in Need of Further Investigation

In contrast to L-lactate, D-lactate is produced in minimal quantities by human cells, and the plasma D-lactate concentration normally is maintained at a concentration of only about 0.01 mM. However, in short bowel syndrome, colonic bacterial production of D-lactate may lead to plasma concentrations >3mM with accompanying acidosis and neurological symptoms - a syndrome known as D-lactic acidosis. Minor increases in plasma D-lactate have been observed in various gastrointestinal conditions such as ischemia, appendicitis and Crohn's disease, a finding touted to have diagnostic utility. The novel aspect of this review paper is the application of numerical values to the processes involved in D-lactate homeostasis that previously have been described only in qualitative terms. This approach provides a number of new insights into normal and disordered production, catabolism and excretion of D-lactate, and identifies multiple gaps in our understanding of D-lactate physiology that should be amenable to relatively simple investigative study.

d-Lactate electrochemical biosensor prepared by immobilization of thermostable dye-linked d-lactate dehydrogenase from Candidatus Caldiarchaeum subterraneum

A stable d-lactate electrochemical sensing system was developed using a dye-linked d-lactate dehydrogenase (Dye-DLDH) from an uncultivated thermophilic archaeon, Candidatus Caldiarchaeum subterraneum. To develop the system, the putative gene encoding the Dye-DLDH from Ca. Caldiarchaeum subterraneum was overexpressed in Escherichia coli, and the expressed product was purified. The recombinant enzyme was a highly thermostable Dye-DLDH that retained full activity after incubation for 10 min at 70°C. The electrode for detection of d-lactate was prepared by immobilizing the thermostable Dye-DLDH and multi-walled carbon nanotube (MWCNT) within Nafion membrane. The electrocatalytic response of the electrode was clearly observed upon exposure to d-lactate. The electrode response to d-lactate was linear within the concentration range of 0.03-2.5 mM, and it showed little reduction in responsiveness after 50 days. This is the first report describing a d-lactate sensing system using a thermostable Dye-DLDH.

D-lactic acidosis in humans: systematic literature review

BACKGROUND

D-lactic acidosis is an uncommon and challenging form of metabolic acidosis that may develop in short bowel syndrome. It has been documented exclusively in case reports and small case series.

METHODS

We performed a review of the literature in the National Library of Medicine and Excerpta Medica databases.

RESULTS

We identified 84 original reports published between 1977 and 2017. D-lactic acidosis was observed in 98 individuals ranging in age from 7 months to 86 years with short bowel syndrome. The clinical presentation included Kussmaul breathing, confusion, slurred speech, and gait disturbances. Furthermore, among 99 consecutive patients with short bowel syndrome, 21 reported having episodes with symptoms consistent with D-lactic acidosis. In addition, D-lactic acid might also contribute to acidosis in diabetes mellitus. Finally, abnormally high D-lactic acid was documented after administration or ingestion of large amounts of propylene glycol, as paraneoplastic phenomenon and perhaps also in a so far poorly characterized inherited inborn error of metabolism.

CONCLUSIONS

In humans with short bowel syndrome (or carbohydrate malabsorption), D-lactic acidosis is likely rather common and under-recognized. This condition should be included in the differential diagnosis of unexplained high-gap metabolic acidosis where the anion causing the acidosis is not known. Furthermore, diabetic acidosis might be caused by accumulation of both ketone bodies and D-lactic acid. Finally, there are endogenous sources of D-lactic acid in subjects with propylene glycol intoxication.

The Liver Circadian Clock Modulates Biochemical and Physiological Responses to Metformin

Metformin is widely used in the treatment of type 2 diabetes to lower blood glucose. Although metformin is a relatively safe and effective drug, its clinical efficacy is variable and under certain circumstances it may contribute to life-threatening lactic acidosis. Thus, additional understanding of metformin pharmacokinetics and pharmacodynamics could provide important information regarding therapeutic use of this widely prescribed drug. Here we report a significant effect of time of day on acute blood glucose reduction in response to metformin administration and on blood lactate levels in healthy mice. Furthermore, we demonstrate that while metformin transport into hepatocytes is unaltered by time of day, the kinetics of metformin-induced activation of AMP-activated protein kinase (AMPK) in the liver are remarkably altered with circadian time. Liver-specific ablation of Bmal1 expression alters metformin induction of AMPK and blood glucose response but does not completely abolish time of day differences. Together, these data demonstrate that circadian rhythms affect the biological responses to metformin in a complex manner.

Examining clinical similarities between myalgic encephalomyelitis/chronic fatigue syndrome and D-lactic acidosis: a systematic review

BACKGROUND

The pursuit for clarity in diagnostic and treatment pathways for the complex, chronic condition of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) continues. This systematic review raises a novel question to explore possible overlapping aetiology in two distinct conditions. Similar neurocognitive symptoms and evidence of D-lactate producing bacteria in ME/CFS raise questions about shared mechanisms with the acute condition of D-lactic acidosis (D-la).

METHODS

D-la case reports published between 1965 and March 2016 were reviewed for episodes describing both neurological symptoms and high D-lactate levels. Fifty-nine D-la episodes were included in the qualitative synthesis comparing D-la symptoms with ME/CFS diagnostic criteria. A narrative review of D-la mechanisms and relevance for ME/CFS was provided.

RESULTS

The majority of neurological disturbances reported in D-la episodes overlapped with ME/CFS symptoms. Of these, the most frequently reported D-la symptoms were motor disturbances that appear more prominent during severe presentations of ME/CFS. Both patient groups shared a history of gastrointestinal abnormalities and evidence of bacterial dysbiosis, although only preliminary evidence supported the role of lactate-producing bacteria in ME/CFS.

LIMITATIONS

Interpretation of results are constrained by both the breadth of symptoms included in ME/CFS diagnostic criteria and the conservative methodology used for D-la symptom classification. Several pathophysiological mechanisms in ME/CFS were not examined.

CONCLUSIONS

Shared symptomatology and underlying microbiota-gut-brain interactions raise the possibility of a continuum of acute (D-la) versus chronic (ME/CFS) presentations related to D-lactate absorption. Measurement of D-lactate in ME/CFS is needed to effectively evaluate whether subclinical D-lactate levels affect neurological symptoms in this clinical population.

Practical Guide to Intestinal Rehabilitation for Postresection Intestinal Failure: A Case Study

After massive small-intestinal resection or combined small-intestinal and colonic resection, diarrhea with resulting dehydration, electrolyte abnormalities, and malnutrition occur. Many patients become dependent on IV fluids and nutrition. An adaptation process manifested clinically by decreased diarrhea and improved nutrient absorption according to decreased parenteral nutrition and fluid requirements has been noted to occur over time. In some patients, adaptation is inadequate and may require special techniques to enhance and augment this process. This is a case of a 52-year-old woman who experienced increased stoma output 1 week after major intestinal resection, resulting in dehydration. She required IV fluids in order to maintain hydration. After the initiation of an intestinal rehabilitation program, which included modified diet, soluble fiber, oral rehydration solution (ORS), and medications, IV fluids were successfully weaned off in 3 months. She continues not to receive IV fluids and continues to follow the intestinal rehabilitation plan.

A reassessment of the PROPATRIA study and its implications for probiotic therapy

The PROPATRIA (Probiotics in Pancreatitis Trial) study was a multicenter, double-blind, placebo-controlled clinical trial that aimed to reduce infectious complications in patients with predicted severe acute pancreatitis by the enteral use of a multispecies probiotic preparation. An unprecedented 24 of 152 patients (16%) in the group receiving probiotics died versus 9 of 144 (6%) in the placebo group. This high mortality rate in the probiotic-treated group contrasts strongly with observations from a previous smaller study and from our observations regarding the effects of abundant intestinal lactobacilli in patients with short small bowel (SSB) syndrome. We argue here that a lethal combination of mainly proteolytic pancreas enzymes and probiotic therapy resulted in the high mortality rate of the PROPATRIA trial and that elevated levels of lactic acid produced by bacterial fermentation of carbohydrates were a key contributing factor. We suggest that probiotic therapy may not be counter-indicated for the prevention of secondary infections associated with acute pancreatitis, provided that future clinical studies (i) start probiotic therapy immediately after first onset of disease symptoms, (ii) limit the supply of fermentable carbohydrates, (iii) prevent bacterial (over)growth of patient's own intestinal flora and (iv) massively increase the dose of probiotic bacteria.

Solid state fermentation with lactic acid bacteria to improve the nutritional quality of lupin and soya bean

BACKGROUND

The ability of bacteriocin-like inhibitory substance (BLIS)-producing lactic acid bacteria (LAB) to degrade biogenic amines as well as to produce L(+) and D(-)-lactic acid during solid state fermentation (SSF) of lupin and soya bean was investigated. In addition, the protein digestibility and formation of organic acids during SSF of legume were investigated.

RESULTS

Protein digestibility of fermented lupin and soya bean was found higher on average by 18.3% and 15.9%, respectively, compared to untreated samples. Tested LAB produced mainly L-lactic acid in soya bean and lupin (D/L ratio 0.38-0.42 and 0.35-0.54, respectively), while spontaneous fermentation gave almost equal amounts of both lactic acid isomers (D/L ratio 0.82-0.98 and 0.92, respectively). Tested LAB strains were able to degrade phenylethylamine, spermine and spermidine, whereas they were able to produce putrescine, histamine and tyramine.

CONCLUSIONS

SSF improved lupin and soya bean protein digestibility. BLIS-producing LAB in lupin and soya bean medium produced a mixture of D- and L-lactic acid with a major excess of the latter isomer. Most toxic histamine and tyramine in fermented lupin and soya bean were found at levels lower those causing adverse health effects. Selection of biogenic amines non-producing bacteria is essential in the food industry to avoid the risk of amine formation.

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.

A Randomized Double Blind Controlled Safety Trial Evaluating d-Lactic Acid Production in Healthy Infants Fed a Lactobacillus reuteri-containing Formula

BACKGROUND

d-Lactic acidosis in infants fed lactic acid bacteria-containing products is a concern.

METHODS

The primary objective of this non-inferiority trial was to compare urinary d-lactic acid concentrations during the first 28 days of life in infants fed formula containing Lactobacillus reuteri (1.2 × 10⁶ colony forming units (CFU)/ml) with those fed a control formula. The non-inferiority margin was set at a two-fold increase in d-lactic acid (0.7 mmol/mol creatinine, log-transformed). Healthy term infants in Greece were enrolled between birth and 72 hours of age, and block randomized to a probiotic (N = 44) or control (N = 44) group. They were exclusively fed their formulae until 28 days of age and followed up at 7, 14, 28, 112, and 168 ± 3 days. Anthropometric measurements were taken at each visit and tolerance recorded until 112 days. Urine was collected before study formula intake and at all visits up to 112 days and blood at 14 days.

RESULTS

d-Lactic acid concentration in the probiotic group was below the non-inferiority margin at 28 days: treatment effect −0.03 (95% confidence interval [CI]: [−0.48 to 0.41]) mmol/mol creatinine but was above the non-inferiority margin at 7 and 14 days—treatment effect 0.50 (95% CI: [0.05–0.96]) mmol/mol creatinine and 0.45 (95% CI: [0.00–0.90]) mmol/mol creatinine, respectively. Blood acid excess and pH, anthropometry, tolerance, and adverse events (AEs) were not significantly different between groups.

CONCLUSION

Intake of L. reuteri-containing formula was safe and did not cause an increase in d-lactic acid beyond two weeks.

Behavior of lactobacilli isolated from fermented slurry (ben-saalga) in gnotobiotic rats

Most bacterial strains, which have been studied so far for their probiotic functions, are extensively used by manufacturers in developed countries. In our work, we sought to study a mix (called BSL) comprising three strains belonging to Lactobacillus fermentum, L. paraplantarum and L. salivarius, that were isolated from a traditional African pearl millet based fermented slurry. Our objective was to study this BSL cocktail in gnotobiotic rats, to evaluate their survival and their behavior in the digestive tract conditions. After a single oral inoculation of germfree rats with BSL, the species established stably in the digestive tract with the following hierarchy of abundance: L. salivarius> L. plantarum> L. fermentum. BSL cocktail was metabolically active since it produced 50 mM lactate and it expressed genes involved in binding mechanism in the caecum. Furthermore, the global morphology of the colon epithelium was not disturbed by the BSL cocktail. BSL cocktail did not modify mucus content and host mucus-related genes (MUC1, MUC2, MUC3 or resistin-like molecule β). The cocktail of lactobacilli enhanced the proliferating cell nuclear antigen (PCNA) at a level comparable to what was observed in conventional rats. PCNA was involved in proliferation and DNA repair, but the presence of the cocktail did not provoke proliferative events (with Ki67 as indicator), so we suppose BSL may help gut preservation. This work is the first step towards the selection of strains that are derived from traditional fermented food to formulate new probiotic mixture.

Short bowel syndrome in the NICU

Short bowel syndrome (SBS) is the most common cause of intestinal failure in infants. In neonates and young infants, necrotizing enterocolitis, gastroschisis, intestinal atresia, and intestinal malrotation/volvulus are the leading causes of SBS. Following an acute postsurgical phase, the residual gastrointestinal tract adapts with reorganization of the crypt-villus histoarchitecture and functional changes in nutrient absorption and motility. A cohesive, multidisciplinary approach can allow most neonates with SBS to transition to full enteral feeds and achieve normal growth and development. In this article, the clinical features, management, complications, and prognostic factors in SBS are reviewed.

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.

Self-priming compartmentalization digital LAMP for point-of-care

Digital nucleic acid amplification provides unprecedented opportunities for absolute nucleic acid quantification by counting of single molecules. This technique is useful for molecular genetic analysis in cancer, stem cell, bacterial, non-invasive prenatal diagnosis in which many biologists are interested. This paper describes a self-priming compartmentalization (SPC) microfluidic chip platform for performing digital loop-mediated amplification (LAMP). The energy for the pumping is pre-stored in the degassed bulk PDMS by exploiting the high gas solubility of PDMS; therefore, no additional structures other than channels and reservoirs are required. The sample and oil are sequentially sucked into the channels, and the pressure difference of gas dissolved in PDMS allows sample self-compartmentalization without the need for further chip manipulation such as with pneumatic microvalves and control systems, and so on. The SPC digital LAMP chip can be used like a 384-well plate, so, the world-to-chip fluidic interconnections are avoided. The microfluidic chip contains 4 separate panels, each panel contains 1200 independent 6 nL chambers and can be used to detect 4 samples simultaneously. Digital LAMP on the microfluidic chip was tested quantitatively by using β-actin DNA from humans. The self-priming compartmentalization behavior is roughly predictable using a two-dimensional model. The uniformity of compartmentalization was analyzed by fluorescent intensity and fraction of volume. The results showed that the feasibility and flexibility of the microfluidic chip platform for amplifying single nucleic acid molecules in different chambers made by diluting and distributing sample solutions. The SPC chip has the potential to meet the requirements of a general laboratory: power-free, valve-free, operating at isothermal temperature, inexpensive, sensitive, economizing labour time and reagents. The disposable analytical devices with appropriate air-tight packaging should be useful for point-of-care, and enabling it to become one of the common tools for biology research, especially, in point-of-care testing.

Digital isothermal quantification of nucleic acids via simultaneous chemical initiation of recombinase polymerase amplification reactions on SlipChip

In this paper, digital quantitative detection of nucleic acids was achieved at the single-molecule level by chemical initiation of over one thousand sequence-specific, nanoliter isothermal amplification reactions in parallel. Digital polymerase chain reaction (digital PCR), a method used for quantification of nucleic acids, counts the presence or absence of amplification of individual molecules. However, it still requires temperature cycling, which is undesirable under resource-limited conditions. This makes isothermal methods for nucleic acid amplification, such as recombinase polymerase amplification (RPA), more attractive. A microfluidic digital RPA SlipChip is described here for simultaneous initiation of over one thousand nL-scale RPA reactions by adding a chemical initiator to each reaction compartment with a simple slipping step after instrument-free pipet loading. Two designs of the SlipChip, two-step slipping and one-step slipping, were validated using digital RPA. By using the digital RPA SlipChip, false-positive results from preinitiation of the RPA amplification reaction before incubation were eliminated. End point fluorescence readout was used for "yes or no" digital quantification. The performance of digital RPA in a SlipChip was validated by amplifying and counting single molecules of the target nucleic acid, methicillin-resistant Staphylococcus aureus (MRSA) genomic DNA. The digital RPA on SlipChip was also tolerant to fluctuations of the incubation temperature (37-42 °C), and its performance was comparable to digital PCR on the same SlipChip design. The digital RPA SlipChip provides a simple method to quantify nucleic acids without requiring thermal cycling or kinetic measurements, with potential applications in diagnostics and environmental monitoring under resource-limited settings. The ability to initiate thousands of chemical reactions in parallel on the nanoliter scale using solvent-resistant glass devices is likely to be useful for a broader range of applications.

Digital PCR on a SlipChip

This paper describes a SlipChip to perform digital PCR in a very simple and inexpensive format. The fluidic path for introducing the sample combined with the PCR mixture was formed using elongated wells in the two plates of the SlipChip designed to overlap during sample loading. This fluidic path was broken up by simple slipping of the two plates that removed the overlap among wells and brought each well in contact with a reservoir preloaded with oil to generate 1280 reaction compartments (2.6 nL each) simultaneously. After thermal cycling, end-point fluorescence intensity was used to detect the presence of nucleic acid. Digital PCR on the SlipChip was tested quantitatively by using Staphylococcus aureus genomic DNA. As the concentration of the template DNA in the reaction mixture was diluted, the fraction of positive wells decreased as expected from the statistical analysis. No cross-contamination was observed during the experiments. At the extremes of the dynamic range of digital PCR the standard confidence interval determined using a normal approximation of the binomial distribution is not satisfactory. Therefore, statistical analysis based on the score method was used to establish these confidence intervals. The SlipChip provides a simple strategy to count nucleic acids by using PCR. It may find applications in research applications such as single cell analysis, prenatal diagnostics, and point-of-care diagnostics. SlipChip would become valuable for diagnostics, including applications in resource-limited areas after integration with isothermal nucleic acid amplification technologies and visual readout.

Nanoliter multiplex PCR arrays on a SlipChip

The SlipChip platform was tested to perform high-throughput nanoliter multiplex PCR. The advantages of using the SlipChip platform for multiplex PCR include the ability to preload arrays of dry primers, instrument-free sample manipulation, small sample volume, and high-throughput capacity. The SlipChip was designed to preload one primer pair per reaction compartment and to screen up to 384 different primer pairs with less than 30 nanoliters of sample per reaction compartment. Both a 40-well and a 384-well design of the SlipChip were tested for multiplex PCR. In the geometries used here, the sample fluid was spontaneously compartmentalized into discrete volumes even before slipping of the two plates of the SlipChip, but slipping introduced additional capabilities that made devices more robust and versatile. The wells of this SlipChip were designed to overcome potential problems associated with thermal expansion. By using circular wells filled with oil and overlapping them with square wells filled with the aqueous PCR mixture, a droplet of aqueous PCR mixture was always surrounded by the lubricating fluid. In this design, during heating and thermal expansion, only oil was expelled from the compartment and leaking of the aqueous solution was prevented. Both 40-well and 384-well devices were found to be free from cross-contamination, and end point fluorescence detection provided reliable readout. Multiple samples could also be screened on the same SlipChip simultaneously. Multiplex PCR was validated on the 384-well SlipChip with 20 different primer pairs to identify 16 bacterial and fungal species commonly presented in blood infections. The SlipChip correctly identified five different bacterial or fungal species in separate experiments. In addition, the presence of the resistance gene mecA in methicillin resistant Staphylococcus aureus (MRSA) was identified. The SlipChip will be useful for applications involving PCR arrays and lays the foundation for new strategies for diagnostics, point-of-care devices, and immobilization-based arrays.

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.

D-Lactic acid-induced neurotoxicity in a calf model

Lactic acidosis (DAC) occurs as a complication of short-bowel syndrome in humans and in a variety of other gastrointestinal disorders in monogastrics and ruminants. DAC is associated with signs of impaired central nervous system (CNS) function including ataxia and coma. The objective of this experiment was to determine whether either acidification of nervous tissue or d-lactic acid is responsible for decreased neurological function. Eight Holstein calves (32 +/- 11 days, 70 +/- 10 kg) were surgically catheterized with indwelling intravenous jugular and atlanto-occipital space cerebrospinal fluid (CSF) catheters and infused for 6 h in random order with isomolar dl-lactic acid (dl-LA), l-lactic acid (l-LA), hydrochloric acid (HCl), or saline. dl-LA induced ataxia after 4 h of infusion and produced the greatest obtunding of CNS function (at 7 h, score 8.0 +/- 0.4), whereas the other infusions caused neither ataxia nor scores over 1.5 (P < 0.01 from dl-LA). dl-LA induced significantly less acidemia than HCl (at 6 h pH 7.13 +/- 0.06 and 7.00 +/- 0.04, base excess -16 +/- 1 and -23 +/- 3 mmol/l, bicarbonate 11 +/- 1 and 8 +/- 1 mmol/l respectively, all P < 0.01) but greater than l-LA and saline (P < 0.01). CSF changes followed a similar but less pronounced pattern. Although HCl infusion produced a severe acidemia and CSF acidosis, only minor effects on neurological function were evident suggesting that d-lactate has a direct neurotoxic effect that is independent of acidosis. Conversely, l-LA produced only minor neurological changes.

Nutritional management of infants with short bowel syndrome

The prevalence of short bowel syndrome appears to be increasing because of more aggressive surgical and medical approaches to the management of neonatal intraabdominal catastrophies. Hence, a large cohort of neonates with intestinal failure occupies neonatal intensive care units, requiring chronic total parenteral nutrition (TPN) in hopes that the residual bowel will adapt, thereby permitting weaning of TPN. Alternatively, when there is no hope for adaptation, these infants are maintained on TPN in hopes that they will grow to a size and state of general health satisfactory for either isolated intestinal transplant when liver function is preserved or combined liver-intestinal transplantation when the liver is irreparably damaged. Thus, it is imperative to provide enough parenteral nutrition to facilitate growth while minimizing TPN constituents predisposing to liver damage. Liver disease associated with intestinal failure (IFALD) seems to occur due to a variety of host factors combined with deleterious components of TPN. Host factors include an immature bile secretory mechanism, bile stasis due to fasting, and repeated septic episodes resulting in endotoxemia. Many constituents of TPN are associated with liver damage. Excessive glucose may result in fatty liver and/or hepatic fibrosis, excessive protein may lead to reduced bile flow, and phytosterols present in intravenous lipid may produce direct oxidant damage to the liver or may impede cholesterol synthesis and subsequent bile acid synthesis. Parenteral strategies employed to minimize TPN damage include reducing glucose infusion rates, reducing parenteral protein load, and reducing parenteral lipid load. Furthermore, preliminary studies suggest that fish oil-based lipid solutions may have a salutary effect on IFALD. Ultimately, provision of enteral nutrition is imperative for preventing or reversing IFALD as well as facilitating bowel adaptation. While studies of trophic hormones are ongoing, the most reliable current method to facilitate adaptation is to provide enteral nutrition. Continuous enteral feeding remains the mainstay of enteral nutrition support.

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.

Arguments for a lower carbohydrate-higher fat diet in patients with a short small bowel

Short small bowel patients suffer from malabsorption due to a strongly reduced small bowel surface. These patients usually get a high caloric high carbohydrate-low fat diet at oral or enteral feeding. At several points our studies demonstrate that the effect of this formula is doubtful. In these patients the intestinal flora has strongly been changed and even become characteristic due to abundant presence of lactobacilli (up to nearly 100%). In many patients with a high carbohydrate-low fat diet these bacteria both produce massive amounts of d-lactic acid and gaseous CO2, and they destroy the primary bile acids that are necessary for uptake of lipids. Thus, they cause (i) an increased risk of D-lactic acidosis and D-lactic acid-associated encephalopathy, (ii) flatulence, abdominal pain and non-infectious diarrhoea, and (iii) low uptake of fat and lipophilic vitamins. It is argued that by gradually converting the diet to a low carbohydrate-high fat diet growth of the characteristic lactobacilli can be strongly reduced and so also the mentioned inconveniences.

Lactic acidosis: from sour milk to septic shock

Lactic acidosis is frequently encountered in the intensive care unit. It occurs when there is an imbalance between production and clearance of lactate. Although lactic acidosis is often associated with a high anion gap and is generally defined as a lactate level >5 mmol/L and a serum pH <7.35, the presence of hypoalbuminemia may mask the anion gap and concomitant alkalosis may raise the pH. The causes of lactic acidosis are traditionally divided into impaired tissue oxygenation (Type A) and disorders in which tissue oxygenation is maintained (Type B). Lactate level is often used as a prognostic indicator and may be predictive of a favorable outcome if it normalizes within 48 hours. The routine measurement of serum lactate, however, should not determine therapeutic interventions. Unfortunately, treatment options remain limited and should be aimed at discontinuation of any offending drugs, treatment of the underlying pathology, and maintenance of organ perfusion. The mainstay of therapy of lactic acidosis remains prevention.

Yeast mediates lactic acidosis suppression after antibiotic cocktail treatment in short small bowel?

During acidotic periods in a girl with a short small bowel, very high D-lactic acid concentrations were measured in blood and urine; the patient's characteristic faecal flora contained mainly lactobacilli, and during antibiotic cocktail treatment also many yeasts. In this case report we sought to understand the beneficial effect of the antibiotic cocktail. Microbiological analysis was performed in faecal samples. Total lactic acid in serum and urine was studied using capillary gas chromatography-mass spectrometry, and D- and L-lactic acid in serum and urine by enzymatic assay. The results were coupled to patient's condition. Antibiotic cocktail therapy reduced the acidosis-associated symptoms, faecal lactobacilli and D-lactic acid production, but simultaneously the antibiotic therapy strongly increased the percentage of yeast in the faecal flora. Four to six weeks after each course of treatment the percentage of yeast decreased, whereas the percentage of intestinal lactobacilli increased; D-lactic acid also simultaneously increased in blood and urine. The patient felt well and showed a high percentage of intestinal yeast, but she often suffered from acidosis owing to a high percentage of lactobacilli. The yeast was identified as the pathogenic Candida glabrata. From the mentioned data together with data from the literature it was concluded that during several weeks the selected pathogenic yeast, C. glabrata, acted as a microbiological and metabolic buffer. Shortly after the course of antibiotic treatment this intestinal yeast strongly competed with the intestinal lactobacilli and thus prevented renewed rapid growth, massive D-lactic acid production from glucose and consequently also D-lactic acid-associated acidosis. The emergence of this yeast led us to consider probiotic lactobacilli or yeast for therapeutic use. The lack of knowledge regarding bile acid-deconjugating activity in both lactobacilli and probiotic yeast means that a final recommendation is not yet possible.

Preventive and curative effects of probiotics in atopic patients

Normally, the transport of allergens through the intestinal epithelia to the blood is limited. It is hypothesised that if these compounds arrive in the blood circulation, they must percolate through the epithelial cell layer. Thus, food allergy (and thus atopic eczema) implies an increased intercellular leakage of the gut wall. Such increased intercellular leakage is thought to be caused by a slightly changed cellular morphology due to a slight cytopathologic effect because of both a limited decay of the cytoskeleton and a slightly reduced turgor. These events may be due to a reduced production of intracellular metabolic energy in the epithelial cells due to an increased concentration of familiar, frequently occurring, potentially toxic bacterial metabolites, i.e., d-lactic acid and/or ethanol. In this hypothesis we suggest that adequate probiotics can (i) prevent the increased characteristic intestinal permeability of children with atopic eczema and food allergy, (ii) can thus prevent the uptake of allergens, and (iii) finally can prevent the expression of the atopic constitution. The use of adequate probiotic lactobacilli, i.e., homolactic and/or facultatively heterolactic l-lactic acid-producing lactobacilli, reduces the intestinal amounts of the bacterial, toxic metabolites, d-lactic acid and ethanol by fermentative production of merely the non-toxic l-lactic acid from glucose. Thus, it is thought that beneficial probiotic micro-organisms promote gut barrier function and both undo and prevent unfavourable intestinal micro-ecological alterations in allergic individuals.

Simultaneous determination of l- and d-lactic acid in plasma by capillary electrophoresis

A novel method for simultaneous determination of d- and l-lactic acids in plasma was presented by capillary electrophoresis with photodiode array detection at 195nm. The separation was performed in an uncoated fused-silica capillary. The parameters influencing the resolution and the migration time of lactic acids were optimized. When 150mM phosphate-Tris buffer (pH 7.0) consisting of 220mM 2-hydroxypropyl-beta-cyclodextrin and 0.2mM tetradecyltrimethylammonium bromide was utilized as the running buffer, highly effective chiral separation of d- and l-lactic acids was achieved at about 42min at an effective voltage of -25kV. The resolution of lactic acid enantiomers was >/=1.25. The limits of detection of d- and l-lactic acids in standard solution without any pretreatment were 80 and 50muM (S/N=3), respectively. Sample pretreatment was preceded by protein-removal procedure with acetonitrile. With a pre-concentration procedure by 10 times, the limits of detection of d- and l-lactic acids were 20 and 15muM (S/N=10), respectively. The satisfactory analytical performance of the proposed method was validated.

53-years-old with mental status changes

D-lactic acidosis, a complication of short bowel syndrome, presents with a variety of neurological symptoms and metabolic acidosis. Treatment is hydration, replacement of nutritional deficiency replacement, and selective antibiotics. Prevention entails complex carbohydrate diet and vitamin and mineral supplements.

D-lactic acidosis in short-bowel syndrome managed with antibiotics and probiotics

D-lactic acidosis sometimes occurs in malabsorbed patients with short-bowel syndrome and is characterized by recurrent episodes of encephalopathy and metabolic acidosis. The characteristic neurologic abnormalities and the presence of metabolic acidosis raises a diagnostic suspicion, and the diagnosis is made when the serum level of D-lactic acid is greater than 3 mmol/L. Standard treatment consists of restricting oral carbohydrates or fasting, correction of metabolic acidosis, and a long-term suppression of pathogenic floras with antibiotics. The authors present a case of D-lactic acidosis in a 22-year-old patient with short-bowel syndrome, to whom intestinal bacterial agents (probiotics) were given in addition to oral kanamycin. Recolonization of the intestine with nonpathogenic floras should be a long-term treatment for D-lactic acidosis.

Enantiomeric determination of L- and D-lactic acid in human cerebrospinal fluid by chiral ligand exchange high-performance liquid chromatography

Enantiomeric determination of L- and D-lactate in human cerebrospinal fluid (CSF) was achieved by HPLC on a chiral stationary phase with UV detection. Samples were submitted to a solid-phase extraction procedure using Oasis HLB Plus Extraction Cartridge and L- and D-lactate in the extract were separated by Shodex ORpac CRX-453 B column, a ligand exchange column for chiral separation, using a mobile phase containing copper (II) ion. L- and D-lactate were determined in 25 min. Intra-assay precision in CSF was 4.98% (mean 1.85 mmol/L) for L-lactate and 10.1% (mean 4.96 micromol/L) for D-lactate (n = 5). Detection limits were between 1.0 (L-lactate) and 1.5 (D-lactate) pmol. The mean values (n = 3) of analytical recovery for L- and D-lactate were 95% and 107%, respectively. The mean +/- SD of concentrations of L- and D-lactate in CSF (n = 20) were 1.52 +/- 0.54 mmol/L and 10.98 +/- 5.15 micromol/L, respectively.

Assay of D-lactate in urine of infants and children with reference values taking into account data below detection limit

Accumulation of D-lactic acid produced by intestinal bacteria such as streptococci and lactobacilli has been extensively studied in ruminants [1-4]. In humans an increased production of D-lactate by intestinal bacteria under pathological conditions such as the short bowel syndrome can cause metabolic acidosis [5-8]. Since the lactate assays routinely used only measure L-lactate we developed a sensitive method of D-lactate quantification and established reference values in spot urines of infants and children (0 to 4 years of age). The enzymatic method with fluorimetric quantification of NADH is linear up to 2 mmol/l. It has a detection limit of 3.4 micromol/l. Among structurally related organic acids an interference was found only for L-lactate and DL-2-hydroxybutyrate at concentrations which are way beyond their physiological excretion. One hundred and sixty five spot urines of healthy Swiss (S), Austrian (A), German (G) and Chilean (CHI) infants aged from 0 to 4 years were analyzed. The distribution of the data is close to a lognormal one. Values below the detection limit were simulated and age groups were formed. In all populations D-lactate excretion was found highest during the first year of life; it declines with age during infancy and remains stable from 2.5 to 4 years of age. We show that D-lactate is excreted physiologically by healthy infants and children below 4 years of age and present reference values for D-lactate excretion which show some differences between the populations tested.

Lactobacilli and acidosis in children with short small bowel

BACKGROUND

In patients with a short small bowel, D-lactic acidemia and D-lactic aciduria are caused by intestinal lactobacilli. The purpose of this study was to obtain a detailed picture of the metabolic acidosis in young children with short small bowel.

METHODS

Feces, blood, and urine of children with short small bowel and acidosis were studied microbiologically and/or biochemically.

RESULTS

Previous findings were confirmed that more than 60% of the fecal flora of patients with small short bowel, who are not receiving antibiotics, consists of lactic acid-producing lactobacilli. In blood, D-lactic acid was the most prominent metabolite: the highest serum D-lactate (15.5 mmol/l) was observed in a sample taken immediately after the onset of hyperventilation. The highest D-lactate excretion was in urine collected some hours after the onset of hyperventilation, and amounted to 59 mol/mol creatinine. Acidosis in the patients with short small bowel was related to strongly increased serum D-lactate and anion gap and to strongly decreased serum bicarbonate and pH.

CONCLUSION

In children with small short bowel and acidosis, the common intestinal flora of mainly lactobacilli abundantly produces D-lactic acid from easily fermentable carbohydrates. Thus, these bacteria directly cause shifts of bicarbonate, pH, and base excess and indirectly cause shifts of the anion gap, as well as hyperventilation. These kinetic parameters are strongly associated.

D-Lactate dehydrogenase gene (ldhD) inactivation and resulting metabolic effects in the Lactobacillus johnsonii strains La1 and N312

Lactobacillus johnsonii La1, a probiotic bacterium with demonstrated health effects, grows in milk, where it ferments lactose to D- and L-lactate in a 60:40% ratio. The D-lactate dehydrogenase (D-LDH) gene (ldhD) of this strain was isolated, and an in vitro-truncated copy of that gene was used to inactivate the genomic copy in two strains, La1 and N312, by gene replacement. For that, an 8-bp deletion was generated within the cloned ldhD gene to inactivate its function. The plasmid containing the altered ldhD was transferred to L. johnsonii via conjugative comobilization with Lactococcus lactis carrying pAMbeta1. Crossover integrations of the plasmid at the genomic ldhD site were selected, and appropriate resolution of the cointegrate structures resulted in mutants that had lost the plasmid and in which the original ldhD was replaced by the truncated copy. These mutants completely lacked D-LDH activity. Nevertheless, the lower remaining L-LDH activity of the cells was sufficient to reroute most of the accumulating pyruvate to L-lactate. Only a marginal increase in production of the secondary end products acetaldehyde, diacetyl, and acetoin was observed. It can be concluded that in L. johnsonii D- and L-LDH are present in substantial excess for their role to eliminate pyruvate and regenerate NAD(+) and that accumulated pyruvate is therefore not easily redirected in high amounts to secondary metabolic routes.

Enantiomeric determination of D- and L-lactate in rat serum using high-performance liquid chromatography with a cellulose-type chiral stationary phase and fluorescence detection

A method is described for the quantitative determination of d- and L-lactate in 10 microl of rat serum, which includes fluorescence derivatization of D- and L-lactate with 4-(N, N-dimethylaminosulfonyl)-7-piperazino-2,1,3- benzoxadiazole (DBD-PZ) followed by O-acetylation. The derivatives are separated by HPLC on an octadecylsilica, and, via column switching, on a cellulose-type chiral column. Levulinic acid was used as the internal standard. The enantiomers of lactate were separated with the separation factor (alpha) of 1.27 and the resolution (Rs) of 2.72, while the linearity for the detection was over the range of 10 nmol/ml to 20 micromol/ml (r = 0.999). Interday precision values for D-lactate in rat serum were 5.8, 5.3, and 4.1% for 10, 100, and 1000 nmol/ml, and accuracy values were 109.6, 98.2, and 103.1%, respectively (n = 5). The reduction of d-lactate concentration in rat serum by fasting was observed with the method.