Biochemistry, Lactate Dehydrogenase (LDH)

Article Author:
Aisha Farhana
Article Editor:
Sarah Lappin
Updated:
5/17/2020 11:03:50 AM
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Biochemistry, Lactate Dehydrogenase (LDH)

Introduction

Lactate dehydrogenase (LDH) is an important enzyme of the anaerobic metabolic pathway. It belongs to the class of oxidoreductases, with an enzyme commission number EC 1.1.1.27. The function of the enzyme is to catalyze the reversible conversion of lactate to pyruvate with the reduction of NAD+ to NADH and vice versa.[1] The enzyme is present in a variety of organisms, that include plants and animals. It is ubiquitously present in all tissues and serves as an important checkpoint of gluconeogenesis and DNA metabolism. A species-wide analysis of LDH demonstrates its well-preserved structure with only a few changes in the amino acid sequence across species.[2] The structural similarity with slight amino acid changes provides a logical platform for designing functional molecules to modulate the catalytic potential and expression of the enzyme. In this article, we will focus our attention on the biochemical function, testing methods, and clinical relevance of the LDH enzyme. 

Issues of Concern

Lactate dehydrogenase is an enzyme that is present in almost all body tissues. Conditions that can cause increased LDH in the blood may include liver disease, anemia, heart attack, bone fractures, muscle trauma, cancers, and infections such as encephalitis, meningitis, encephalitis, and HIV. LDH is also a non-specific marker of tissue turnover, which is a normal metabolic process. Many cancers cause a general increase in LDH levels or an increase in one of its isozymes. Thus it can be a non-specific tumor marker not useful in identifying the type of cancer. Because LDH is non-specific and routine isozyme measurement is usually unavailable in clinical laboratories, LDH measurements provide incomplete information, and alternate assays such as CK for muscle, ALT for liver, troponin for heart diseases, etc. are needed.

Additionally, LDH activity is affected by hemolysis of the blood sample. Since RBC contain their own LDH protein, hemolysis causes an artifactual increase leading to false-positive high results. Besides, any cellular necrosis can result in increased serum concentration, and its ubiquitous distribution throughout tissues confers a severe handicap to its wider clinical utility as a biomarker.

Cellular

LDH is a cytoplasmic enzyme that is present in almost all tissues but at high concentrations in muscle, liver, and kidney. Red blood cells also contain moderate concentrations of this enzyme. LDH exhibits five isomeric forms assembled in tetramers of either of the two types of subunits, namely muscle (M) and heart (H). The isoforms called isozymes are named as LDH-1 through LDH-5, each showing differential expression in different tissues.[3] This differential expression of LDH is the basis of its importance as a clinical diagnostic marker. Isozyme LDH-1 has four heart subunits (4H) and is the major isozyme present in the heart tissue. Isozyme LDH-2 has three heart and one muscle subunit (3H1M) and is the major isozyme of the reticuloendothelial system and RBC. The LDH-3 isozyme consists of two heart and two muscle subunits (2H2M) and is the major isozyme of the lungs. Isozyme LDH-4 has one heart and three muscle subunits (1H3M) and is the primary isozyme present in the kidneys. The LDH-5 isozyme has four muscle subunits (4M) and has significant expression in liver and skeletal muscle.[4][5] These five isoforms, although catalyzing the same overall reaction, differ in their affinity to the substrate, inhibition concentration, isoelectric point, and electrophoretic mobility. These five isoforms can be visualized in the active state using LDH zymography.

Though LDH is predominantly a cytoplasmic enzyme, its mitochondrial presence in also demonstrated by various studies. The presence of a mitochondrial L-lactate dehydrogenase (mL-LDH) was confirmed in yeast, plant, and animals.[6] L-lactate, which is the substrate for mL-LDH, is transported to the mitochondria through L-lactate/H symporter and the L-lactate/pyruvate and L-lactate/oxaloacetate antiporters. Subsequently, mL-LDH facilitates the oxidation of L-lactate to pyruvate in the mitochondrial matrix.[7] Many cancer cells reprogram the mitochondrial processes to fulfill their higher demands for energy. Glycolysis becomes elevated in cancer cells, and hence, mL-LDH may be a player in the accelerating oxidative phosphorylation.[8]

Molecular

The genes that encode LDH are LDHA, LDHB, LDHC, and LDHD. LDHA, LDHB, and LDHC encode for L-isomers of the enzyme, whereas LDHD encodes the  D-isomer. The L-isomers use and produce L-lactate, which is the major enantiomeric form of lactate present in the vertebrates. The gene that encodes the LDHA form of the enzyme is located on chromosome 11p15.4 and is transcribed into a 332 amino acid protein. The LDHB gene is located on chromosome 12p12.1 and encodes a protein of 334 amino acids. The isozyme forms of Lactate dehydrogenase enzymes, LDH-1 through LDH-5 are translational products of two genes LDHA and LDHB gene [9]. The two genes provide instructions for making the lactate dehydrogenase-A and lactate dehydrogenase-B subunits of the lactate dehydrogenase enzyme. There are five different forms of LDH, each made up of four subunits. Various combinations of the protein products of lactate dehydrogenase-A subunits and lactate dehydrogenase-B subunits produced from a different gene) make up the different forms of the enzyme.[4]

In the mammalian system, two more subunits, LDHC and LDHBx, are also included to form LDH tetramer. The LDHC gene encodes LDHC protein that is specific to the testes, while the LDHBx gene encodes the LDHBx protein specific to the peroxisome.[10] LDHBx is the readthrough form of the LDHB gene. LDHBx is generated by translation of the LDHB mRNA, where the stop codon is read as encoding an amino acid. Consequently, translation proceeds to the next stop codon, which adds seven amino acid residues encoding the peroxisomal targeting signal to the normal LDH-H protein so that LDHBx is imported into the peroxisome.[11] The secondary structure of LDH comprises of 40% alpha helices and 23% beta-sheets; this makes LDH as mixed beta-alpha-beta, with parallel beta sheets as the main component of the protein structure.[12]

The active site of the enzyme is located in its substrate-binding pocket and contains catalytically important His-193 as well as Asp-168, Arg-171, Thr-246, and Arg-106. His-193 is the active amino acids present in the active site of humans as well as other species of the animal kingdom. All the LDH isozymes are structurally very similar; however, each one has distinct kinetic properties resulting from the differences in the charged amino acids flanking the active site [2][13].

The two different subunits of LDH (the M subunit and H subunit of LDH) both maintain the same active site structure and amino acids that participate in the reaction. In the tertiary structure, the alanine of the M-chain is replaced with glutamine in the H-chain. Alanine is a nonpolar and small molecular weight amino acid, while glutamine is a positively charged amino acid. This chemistry provides different biochemical properties to the two subunits. Hence, the H subunit can bind faster but has fivefold reduced catalytic activity as compared to the M-subunit. LDHA subunit carries a net charge of -6 and exhibits a higher affinity towards pyruvate, thus converting pyruvate to lactate and  NADH to NAD+. On the other hand, LDHB has a net charge of +1 and demonstrates a higher affinity towards lactate, resulting in a preferential conversion of lactate to pyruvate and NAD+ to NADH.[4]

LDH is inherent in maintaining homeostasis when there is a lack of oxygen. Oxygen levels in the muscle tissues drop quickly upon heavy exercise. Since oxygen is typically the final electron acceptor of the electron transport chain (ETC), the chain halts along with ATP synthase. Nonetheless, muscle cells continue to function by creating ATP through NAD+. LDH produces lactic acid as an end product through a fermentation reaction. In the process, LDH removes electrons from NADH and makes NAD+, which is channelized in the glycolysis pathway to create ATP.[1] Though this process creates less ATP as compared to the ETC, it allows the cell to carry out its physiological and biochemical functions in the absence of oxygen.

Function

Lactate Dehydrogenase is one of the H transfer (oxidoreductase) enzymes, which catalyzes the reversible conversion of pyruvate to lactate using NADH.  Basically, the enzyme is involved in the anaerobic metabolism of glucose when oxygen is absent or in limited supply.[14]

  • Pyruvate + NADH + H+ ­--> Lactate + NAD+

When cells become exposed to anaerobic or hypoxic conditions, the production of ATP by oxidative phosphorylation becomes disrupted. This process demands cells to produce energy by alternate metabolism. Consequently, LDH is upregulated in such conditions to cater to the need for energy production. However, lactate produced during anaerobic conversion of glucose meets a dead end in metabolism. It cannot undergo further metabolism in any tissue except the liver. Hence, lactate is released in the blood and transported to the liver, where LDH performs the reverse reaction of converting lactate to pyruvate through the Cori cycle.[6]

During exercise, when muscles exhaust the oxygen, pyruvate gets catalyzed into lactic acid by the lactate dehydrogenase enzyme. In erythrocytes also pyruvate is not further metabolized due to the absence of mitochondria but remains within the cytoplasm, finally converting to lactate. In this reaction, NADH oxidizes to NAD+. The availability of high intracellular concentrations of NAD is necessary to carry out the preparatory phase of glycolysis. The net ATP production of anaerobic glycolysis is only 2 ATP per glucose molecule as compared to oxidative phosphorylation, which produces 36 ATP per glucose molecule. LDH can also catalyze the dehydrogenation of 2-hydroxybutyrate, but it is the less preferred substrate for LDH than lactate.[14]

The subunit composition of the LDH enzyme (H and M subunits) varies among tissues (mentioned previously in the 'cellular' section). This variation is due to the difference in the metabolic rates, energy needs, and function of the tissues, which reflects in their LDHA: LDHB ratio. Almost 40% of lactate in the circulation is released from the skeletal muscle. This lactate is further absorbed mostly by the liver and kidney, where it undergoes oxidation for the synthesis of glucose. In the brain, about 10% of the lactate oxidizes to fuel 8% of cerebral energy needs during resting conditions, and the remaining lactate is released in circulation.[14][15] However, hyperlactatemia and physical exertion can lead to the uptake of lactate, which supports 60% of brain metabolism, with the contribution of cerebral lactate oxidation only up to 33%.

In cancer cells, the function of LDH, specifically LDHA, is modified as compared to the normal cells. Cancer cells employ LDH to increase their aerobic metabolism (glycolysis and ATP production, and lactate production) even in the presence of oxygen. This process is known as the Warburg effect. The abnormal cancer cells benefit from switching to anaerobic metabolic phenotype by avoiding the generation of oxidative stress by the ETC. Additionally, the cancer cells also gain access to the metabolic intermediates of the tricarboxylic acid cycle, generated through glucose and pyruvate, to synthesize lipids and nucleic acid for rapid cell proliferation.[16][17]

Mechanism

LDH catalyzes the synchronized inter-conversion of pyruvate to lactate and NADH to NAD+ and increases the speed of reaction by 14 times. The chemical reaction proceeds by transferring a hydride ion from NADH to pyruvate at its C2 carbon. The molecular mechanism involves the binding of NADH to the enzymes as a first step. Many residues at the active site are involved in this binding. Once NADH is bound, it facilitates the binding of lactate, through an interaction between the NADH ring and the LDH residues. Transfer of a hydride quickly occurs in both directions forming two tertiary complexes, namely,  LDH-NAD+-lactate and LDH-NADH-pyruvate.[18] Subsequently, pyruvate Is dissociated from the enzyme first, and then NAD+ is released. The rate of dissociation of NADH  and NAD+ proves to be the rate-limiting step in this reaction, and the final conversion of pyruvate to lactate leading to the regeneration of NAD+ is thermodynamically favored in the reaction.[19]

Enzyme regulation: LDH  activity is dependant on the metabolic switch to anaerobic respiration. LDH is modulated by three types of regulations, namely, allosteric modulation, substrate-level regulation, and transcriptional regulation. The relative availability and concentration of substrates regulate the activity of LDH. The enzyme becomes more active during extreme muscular activity when there is an increase in substrates. The demand for ATP compared to aerobic ATP supply causes the accumulation of ADP, AMP, and Pi. Glycolytic flux leads to the production of pyruvate that exceeds the metabolic capacity of pyruvate dehydrogenase and other shuttle enzymes that metabolize pyruvate. This process channelizes the flux of pyruvate and NAD+ through LDH, subsequently generating lactate and NADH.[20]

In conditions of increased NADH/NAD+ ratio, as usually happens in individuals who drink, high concentrations of ethanol lead to the production of high concentrations of lactate and NADH, and thus the depletion of NAD+. This reaction subsequently leads to pyruvate conversion to lactate linked to the regeneration of NAD+. Thus, the high NADH/NAD+ ratio shifts the LDH equilibrium towards lactate.[20]

Testing

LDH assays can measure the amount of LDH present in the serum that has leaked from the tissues upon damage. The catalytic property of LDH leading to reversible oxidation of L-lactate to pyruvate, mediated by the hydrogen acceptor, NAD+, is harnessed as a basis of the measurement of LDH activity. The clinical diagnostic laboratories assess the rate of production of NADH that changes the optical density of the sample measured spectrophotometrically at 340 nm. The conversion of pyruvate to lactate or reverse reaction of oxidation of L-lactate to pyruvate can be monitored spectrophotometrically. LDH activity is measurable in various samples such as plasma, serum, tissue, cells, and in the culture medium for research purposes. It requires handling care when serum and plasma are used as samples because hemolysis can cause an artefactual increase in the enzyme levels due to its release from ruptured erythrocytes. 

Typically, the normal range of LDH is between 140 to 280 U/L. However, the clinical interpretation depends upon the signs and symptoms of the patient. The serum usually has a higher level of LDH as compared with plasma because of LDH release during clotting. The LDH activity also increases during strenuous exercise to generate lactic acid under normal physiological conditions.[21] LDH test is affected by drugs and medications, which could interfere with accurate testing for LDH. The presence of high concentrations of vitamin C may lead to low LDH levels readout. On the other hand, the presence of anesthetics, aspirin, alcohols, and certain narcotics, and procainamide may increase the LDH levels. The LDH test may only show an elevated concentration of one or more types of isozymes. Liver diseases, kidney diseases, muscle injury, trauma, heart attack, certain infectious diseases, pancreatitis, cancer, and anemia are some of the health conditions that can lead to a rise in serum LDH levels. Furthermore, the concentration of LDH varies with age, infants and young children usually have much higher normal levels of LDH levels as compared to older children and adults. Newborns have a normal range of 135 to 750 U/L (units/L), children up to 12 months have 180 to 435 U/L and above 18 years of age have a normal range of 122 to 222 U/L (as indicated by Mayo Clinic Labs).

Besides testing the concentration of LDH in samples, LDH isozymes testing also helps to assess the type, location, and severity of tissue damage.  LDH is a tetrameric enzyme made of H and M subunits. The assembly of the enzymes occurs in a defined ratio through a tissue-specific synthesis of subunits, hence providing tissue specificity, i.e., heart-specific LDH (LDH-1) preferentially synthesizes all four H subunits, while liver LDH (LDH-5)  is exclusively made of all M-subunits. Similarly, other tissues synthesize the subunits in a specified ratio. LDH isozyme testing identifies the isozymes as LDH 1 to 5 based on the electrophoretic mobility shift. The different subunit composition imparts a difference in the net charges and hence different migration in an electric field. A good separation pattern of LDH isozymes is obtained in a buffer of pH of 8.6. In a typical LDH isozyme electrophoretic pattern, LDH-1 moves as a fast band, followed by LDH-2, LDH-3, LDH-4, and LDH-5 being the slowest band. The normal serum percentage of LDH-1 (4H) is 30.4 to 36.4%, LDH-2 (3H1M) is 30.4 to 36.4%, LDH-3 (2H2M) is 19.2 to 24.8%, LDH-4 (1H3M) is 9.6 to 15.6%, and LDH-5 (4M) is 5.5 to 12.7%.

Pathophysiology

The quantification of LDH is of clinical interest as a serum concentration of LDH isozymes reflect tissue-specific pathological conditions. Hence, LDH can be used as a marker for diverse tissue injuries owing to its isozyme form, and its ubiquitous presence. Upon tissue damage, the cells release LDH in the bloodstream. Depending upon the type of tissue injury, the enzyme can remain elevated for up to 7 days in the bloodstream. The elevated LDH in serum as a result of organ destruction occurs due to significant cell death that results in loss of cytoplasm. Causes of tissue damage can be diseases such as acute myocardial infarction, anemia, pulmonary embolism, hepatitis, acute renal failure, etc.[22] LDH can be used as a satisfactory marker for the staging of a disease (S-classification), monitor prognosis or response to treatment, and to evaluate body fluids other than blood. The decrease in LDH levels during treatment is indicative of better prognosis and/or good response to treatment in conditions such as acute myocardial infarction or liver injury. In acute myocardial infarction, LDH-1 isozyme remains elevated from the second day to up to the 4th day. Similarly, in liver injury, LDH-5 is elevated. A significant increase in LDH-5 higher than LDH-4 is a marker of hepatocellular injuries such as hepatitis or cirrhosis.

LDH increases during effusion in serous body fluids such as pericardial and peritoneal fluids. Hence, it serves to characterize effusion. In cerebrospinal fluid, LDH increases in bacterial meningitis, while it is observed to be normal in viral meningitis. The ratio of fluid LDH compared to the upper limit of normal serum LDH (> 0.6) indicates an inflammatory process, and hence exudate.[23]

There is a marked increase in LDH during intracranial hemorrhage. More than 40 U/L increase above the normal levels is observed in the central nervous system lymphoma, leukemia, and metastatic carcinoma. Elevated levels of more than one isoenzyme may be indicative of more than one cause of tissue damage, e.g., in conditions where pneumonia may also be associated with a heart attack. Very levels of LDH appear to correlate with severe disease or multiple organ failure.

LDH is the only serum biomarker useful for assessing metastatic melanomas.[24] In malignancy, the growth of tumor cells consumes oxygen more than the supply; thus, hypoxia is quite common. The growing tumors undergo LDH mediated energy production to fulfill the demand of fast cellular growth.[25] Hence, LDH is an established marker of metastases, especially in the liver. It is also a crucial single prognostic factor since patients with high LDH have reduced survival rates. Besides, LDH levels serve to predict incidences metastasis in uveal melanoma.[26] LDH has a good correlation with tyrosine kinase expression in tumors.[27]

This enzyme also constitutes a potential therapeutic target for diseases such as malaria and cancer. The LDH isoform expressed by Plasmodium falciparum, the malarial parasite, is a crucial enzyme for the generation of energy in the parasite. Since these malarial parasites lack a tricarboxylic acid cycle for ATP formation, anaerobic glycolysis serves as a source of energy.[28] The inhibitors of Plasmodium falciparum LDH would only be directed towards the parasite and would selectively kill the parasite.

Most invasive tumors undergo a metabolic switching (Warburg effect) from oxidative phosphorylation to higher anaerobic glycolysis. This switch occurs through upregulation of the LDH-5 (also called LDH-A), the isoform normally present in muscles and the liver.[22] Hence, inhibition of LDH-5 can specifically target the site of tumor progression and invasiveness. An analog, N-hydroyxindole class LDH inhibitors are also tested effectively as anticancer agents.[29][30] Many clinical trials and translational data demonstrated that targeting LDHA genes or its protein product LDH-5 may be harnessed as a metabolic treatment of cancer.[31][28]

Researchers have conducted clinical trials in melanoma patients with low LDH, and treatment with Ipilimumab showed higher efficacy when treatment started with low baseline LDH.[32][33] Another trial using a combination of Bcl2 antisense oligonucleotide plus dacarbazine also showed efficacy in patients with low baseline LDH.[34] Thus, the overall importance of LDH as a tumor marker becomes masked because of its low sensitivity and specificity.[35] High LDL levels are usually associated with advanced stages of cancer.[36]

The deficiency of enzyme LDH is very rare, and not much data is available for its prevalence. This deficiency can result from either the mutations in the LDHA gene or the LDHB gene leading to a deficiency in LDH-A (M- subunit protein) and LDH-B (H-subunit protein) proteins, respectively.[37] LDHA gene mutations result in the formation of an abnormal M subunit protein. This protein subunit cannot bind to other subunits to form the LDH enzyme.

LDHA gene mutation mostly affects skeletal muscles, because skeletal LDH has all M-subunits. However, a lack of functional subunit reduces the amount of enzyme formed in all other tissues as well. This chemistry results in an ineffective breakdown of glycogen. Hence, LDHA gene deficiency is also called glycogen storage disease XI. The unavailability of sufficient energy, especially to the muscle cells, causes muscle weakness and breakdown of muscle tissue (rhabdomyolysis).[38] The effect is more pronounced during strenuous activities, and muscle tissue destruction releases protein myoglobin. This protein is processed in the kidneys and released in the urine, causing myoglobinuria. The high accumulation of myoglobin protein can damage the kidneys, which can also lead to kidney failure. In some patients with LDHA deficiency causes skin rashes of varying severity.[39]

On the other hand, LDHB gene mutations affect the heart muscle primarily because the heart LDH is made of all four H-subunits. In cardiac muscle, the involuntary muscle movement is fueled by the conversion of lactate to pyruvate through the LDH enzyme. Such conditions lead to a reduced LDH activity in cardiac muscle of patients with LDHB deficiency. Interestingly, no visible phenotype, signs, or symptoms are observed in such patients. Both LDHA and LDHB gene mutations have shown relevance in tumorigenesis.[40]

Clinical Significance

LDH serves as a general indicator of acute and chronic diseases. Elevation in serum LDH activity follows isoenzyme patterns that are characteristic of various diseases.

  • LDH increase can serve as a prognostic marker of cancer progression for different types of cancer. LDH also serves as one of the important diagnostic markers of cutaneous lymphoma. The concentration of LDH-5 is demonstrated as a predictor of radiotherapy and chemotherapy response in cancer patients. LDH is useful in evaluating metastatic cancer patients. Contrarily, LDH-5 serves as a marker for radio-sensitization.
  • The enzymes can function to monitor progressive conditions such as muscular dystrophy or HIV infection.
  • In sports medicine, LDH potentially indicates muscle response to training, with an increase in skeletal and cardiac muscles after 3-5 hours of training.
  • If LDH-1 is found to be greater than LDH-2, it indicates myocardial infarction, with a ‘flipped’ ratio of LDH-1/LDH-2 greater than 1. The increase in LDH persists for approximately ten days. It increases at 12 hours and peaks at 24-48 hours. A very high level thus indicates acute myocardial infarction.
  • Greater than 50 times increase in LDH-1 and LDH-2  indicate megaloblastic anemia.
  • Increased LDH-5 in serum is a marker for muscular dystrophy.
  • A ten times increase in serum LDH indicates toxic hepatitis with jaundice.
  • An increase in LDH-3 is associated with the massive destruction of platelets as in pulmonary embolism.
  • LDH is used to assess the nature, or pathological accumulation of pleural, peritoneal, or pericardial fluids. Serum LDH, compared to serous fluid LDH, helps in distinguishing exudate from transudate effusions.
  • In patients with non-seminomatous testicular cancer LDH is used as a staging (S classification) marker.
  • Abnormally low levels of LDH are very rare and usually not considered harmful.

References

[1] Schumann G,Bonora R,Ceriotti F,Clerc-Renaud P,Ferrero CA,Férard G,Franck PF,Gella FJ,Hoelzel W,Jørgensen PJ,Kanno T,Kessner A,Klauke R,Kristiansen N,Lessinger JM,Linsinger TP,Misaki H,Panteghini M,Pauwels J,Schimmel HG,Vialle A,Weidemann G,Siekmann L, IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C. Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase. Clinical chemistry and laboratory medicine. 2002 Jun;     [PubMed PMID: 12211663]
[2] Holmes RS,Goldberg E, Computational analyses of mammalian lactate dehydrogenases: human, mouse, opossum and platypus LDHs. Computational biology and chemistry. 2009 Oct;     [PubMed PMID: 19679512]
[3] Drent M,Cobben NA,Henderson RF,Wouters EF,van Dieijen-Visser M, Usefulness of lactate dehydrogenase and its isoenzymes as indicators of lung damage or inflammation. The European respiratory journal. 1996 Aug;     [PubMed PMID: 8866602]
[4] Read JA,Winter VJ,Eszes CM,Sessions RB,Brady RL, Structural basis for altered activity of M- and H-isozyme forms of human lactate dehydrogenase. Proteins. 2001 May 1;     [PubMed PMID: 11276087]
[5] Khan AA,Allemailem KS,Alhumaydhi FA,Gowder SJT,Rahmani AH, The Biochemical and Clinical Perspectives of Lactate Dehydrogenase: An Enzyme of Active Metabolism. Endocrine, metabolic     [PubMed PMID: 31886754]
[6] Passarella S,Schurr A, l-Lactate Transport and Metabolism in Mitochondria of Hep G2 Cells-The Cori Cycle Revisited. Frontiers in oncology. 2018;     [PubMed PMID: 29740537]
[7] Liang X,Liu L,Fu T,Zhou Q,Zhou D,Xiao L,Liu J,Kong Y,Xie H,Yi F,Lai L,Vega RB,Kelly DP,Smith SR,Gan Z, Exercise Inducible Lactate Dehydrogenase B Regulates Mitochondrial Function in Skeletal Muscle. The Journal of biological chemistry. 2016 Dec 2;     [PubMed PMID: 27738103]
[8] de Bari L,Atlante A, Including the mitochondrial metabolism of L-lactate in cancer metabolic reprogramming. Cellular and molecular life sciences : CMLS. 2018 Aug;     [PubMed PMID: 29728715]
[9] Laughton JD,Charnay Y,Belloir B,Pellerin L,Magistretti PJ,Bouras C, Differential messenger RNA distribution of lactate dehydrogenase LDH-1 and LDH-5 isoforms in the rat brain. Neuroscience. 2000;     [PubMed PMID: 10717443]
[10] Markert CL,Shaklee JB,Whitt GS, Evolution of a gene. Multiple genes for LDH isozymes provide a model of the evolution of gene structure, function and regulation. Science (New York, N.Y.). 1975 Jul 11;     [PubMed PMID: 1138367]
[11] Schueren F,Lingner T,George R,Hofhuis J,Dickel C,Gärtner J,Thoms S, Peroxisomal lactate dehydrogenase is generated by translational readthrough in mammals. eLife. 2014 Sep 23;     [PubMed PMID: 25247702]
[12] Auerbach G,Ostendorp R,Prade L,Korndörfer I,Dams T,Huber R,Jaenicke R, Lactate dehydrogenase from the hyperthermophilic bacterium thermotoga maritima: the crystal structure at 2.1 A resolution reveals strategies for intrinsic protein stabilization. Structure (London, England : 1993). 1998 Jun 15;     [PubMed PMID: 9655830]
[13] Eventoff W,Rossmann MG,Taylor SS,Torff HJ,Meyer H,Keil W,Kiltz HH, Structural adaptations of lactate dehydrogenase isozymes. Proceedings of the National Academy of Sciences of the United States of America. 1977 Jul;     [PubMed PMID: 197516]
[14] Adeva-Andany M,López-Ojén M,Funcasta-Calderón R,Ameneiros-Rodríguez E,Donapetry-García C,Vila-Altesor M,Rodríguez-Seijas J, Comprehensive review on lactate metabolism in human health. Mitochondrion. 2014 Jul;     [PubMed PMID: 24929216]
[15] Overgaard M,Rasmussen P,Bohm AM,Seifert T,Brassard P,Zaar M,Homann P,Evans KA,Nielsen HB,Secher NH, Hypoxia and exercise provoke both lactate release and lactate oxidation by the human brain. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2012 Jul;     [PubMed PMID: 22441982]
[16] Liberti MV,Locasale JW, The Warburg Effect: How Does it Benefit Cancer Cells? Trends in biochemical sciences. 2016 Mar;     [PubMed PMID: 26778478]
[17] Al Bawab AQ,Zihlif M,Jarrar Y,Saleh A, Continuous Hypoxia and Glucose Metabolism, The Effects on Genes Expression in Mcf7 Breast Cancer Cell Line. Endocrine, metabolic     [PubMed PMID: 32370732]
[18] Shi Y,Pinto BM, Human lactate dehydrogenase a inhibitors: a molecular dynamics investigation. PloS one. 2014;     [PubMed PMID: 24466056]
[19] Spriet LL,Howlett RA,Heigenhauser GJ, An enzymatic approach to lactate production in human skeletal muscle during exercise. Medicine and science in sports and exercise. 2000 Apr;     [PubMed PMID: 10776894]
[20] Valvona CJ,Fillmore HL,Nunn PB,Pilkington GJ, The Regulation and Function of Lactate Dehydrogenase A: Therapeutic Potential in Brain Tumor. Brain pathology (Zurich, Switzerland). 2016 Jan;     [PubMed PMID: 26269128]
[21] Tokinoya K,Ishikura K,Yoshida Y,Ra SG,Sugasawa T,Aoyagi A,Nabekura Y,Takekoshi K,Ohmori H, LDH isoenzyme 5 is an index of early onset muscle soreness (EOMS) during prolonged running. The Journal of sports medicine and physical fitness. 2020 Apr 6;     [PubMed PMID: 32253893]
[22] Feng Y,Xiong Y,Qiao T,Li X,Jia L,Han Y, Lactate dehydrogenase A: A key player in carcinogenesis and potential target in cancer therapy. Cancer medicine. 2018 Dec;     [PubMed PMID: 30403008]
[23] Mercer RM,Corcoran JP,Porcel JM,Rahman NM,Psallidas I, Interpreting pleural fluid results . Clinical medicine (London, England). 2019 May;     [PubMed PMID: 31092513]
[24] Jurisic V,Radenkovic S,Konjevic G, The Actual Role of LDH as Tumor Marker, Biochemical and Clinical Aspects. Advances in experimental medicine and biology. 2015;     [PubMed PMID: 26530363]
[25] Mishra D,Banerjee D, Lactate Dehydrogenases as Metabolic Links between Tumor and Stroma in the Tumor Microenvironment. Cancers. 2019 May 29;     [PubMed PMID: 31146503]
[26] Gallo M,Sapio L,Spina A,Naviglio D,Calogero A,Naviglio S, Lactic dehydrogenase and cancer: an overview. Frontiers in bioscience (Landmark edition). 2015 Jun 1;     [PubMed PMID: 25961554]
[27] Liu J,Chen G,Liu Z,Liu S,Cai Z,You P,Ke Y,Lai L,Huang Y,Gao H,Zhao L,Pelicano H,Huang P,McKeehan WL,Wu CL,Wang C,Zhong W,Wang F, Aberrant FGFR Tyrosine Kinase Signaling Enhances the Warburg Effect by Reprogramming LDH Isoform Expression and Activity in Prostate Cancer. Cancer research. 2018 Aug 15     [PubMed PMID: 29891507]
[28] Granchi C,Bertini S,Macchia M,Minutolo F, Inhibitors of lactate dehydrogenase isoforms and their therapeutic potentials. Current medicinal chemistry. 2010;     [PubMed PMID: 20088761]
[29] Di Bussolo V,Calvaresi EC,Granchi C,Del Bino L,Frau I,Lang MC,Tuccinardi T,Macchia M,Martinelli A,Hergenrother PJ,Minutolo F, Synthesis and biological evaluation of non-glucose glycoconjugated {i}N{/i}-hydroyxindole class LDH inhibitors as anticancer agents. RSC advances. 2015;     [PubMed PMID: 26167277]
[30] Urbańska K,Orzechowski A, Unappreciated Role of LDHA and LDHB to Control Apoptosis and Autophagy in Tumor Cells. International journal of molecular sciences. 2019 Apr 27;     [PubMed PMID: 31035592]
[31] Augoff K,Hryniewicz-Jankowska A,Tabola R, Lactate dehydrogenase 5: an old friend and a new hope in the war on cancer. Cancer letters. 2015 Mar 1;     [PubMed PMID: 25528630]
[32] Martens A,Wistuba-Hamprecht K,Geukes Foppen M,Yuan J,Postow MA,Wong P,Romano E,Khammari A,Dreno B,Capone M,Ascierto PA,Di Giacomo AM,Maio M,Schilling B,Sucker A,Schadendorf D,Hassel JC,Eigentler TK,Martus P,Wolchok JD,Blank C,Pawelec G,Garbe C,Weide B, Baseline Peripheral Blood Biomarkers Associated with Clinical Outcome of Advanced Melanoma Patients Treated with Ipilimumab. Clinical cancer research : an official journal of the American Association for Cancer Research. 2016 Jun 15;     [PubMed PMID: 26787752]
[33] Weide B,Martens A,Hassel JC,Berking C,Postow MA,Bisschop K,Simeone E,Mangana J,Schilling B,Di Giacomo AM,Brenner N,Kähler K,Heinzerling L,Gutzmer R,Bender A,Gebhardt C,Romano E,Meier F,Martus P,Maio M,Blank C,Schadendorf D,Dummer R,Ascierto PA,Hospers G,Garbe C,Wolchok JD, Baseline Biomarkers for Outcome of Melanoma Patients Treated with Pembrolizumab. Clinical cancer research : an official journal of the American Association for Cancer Research. 2016 Nov 15;     [PubMed PMID: 27185375]
[34] Bedikian AY,Millward M,Pehamberger H,Conry R,Gore M,Trefzer U,Pavlick AC,DeConti R,Hersh EM,Hersey P,Kirkwood JM,Haluska FG, Bcl-2 antisense (oblimersen sodium) plus dacarbazine in patients with advanced melanoma: the Oblimersen Melanoma Study Group. Journal of clinical oncology : official journal of the American Society of Clinical Oncology. 2006 Oct 10;     [PubMed PMID: 16966688]
[35] Smylie MG, Use of immuno-oncology in melanoma. Current oncology (Toronto, Ont.). 2020 Apr;     [PubMed PMID: 32368174]
[36] Yao Y,Wang H,Li B, LDH5 overexpression is associated with poor survival in patients with solid tumors: a meta-analysis. Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine. 2014 Jul;     [PubMed PMID: 24744144]
[37] Monroe GR,van Eerde AM,Tessadori F,Duran KJ,Savelberg SMC,van Alfen JC,Terhal PA,van der Crabben SN,Lichtenbelt KD,Fuchs SA,Gerrits J,van Roosmalen MJ,van Gassen KL,van Aalderen M,Koot BG,Oostendorp M,Duran M,Visser G,de Koning TJ,Calì F,Bosco P,Geleijns K,de Sain-van der Velden MGM,Knoers NV,Bakkers J,Verhoeven-Duif NM,van Haaften G,Jans JJ, Identification of human D lactate dehydrogenase deficiency. Nature communications. 2019 Apr 1;     [PubMed PMID: 30931947]
[38] Lee BJ,Zand L,Manek NJ,Hsiao LL,Babovic-Vuksanovic D,Wylam ME,Qian Q, Physical therapy-induced rhabdomyolysis and acute kidney injury associated with reduced activity of muscle lactate dehydrogenase A. Arthritis care     [PubMed PMID: 22127970]
[39] Lund AM,Christensen E,Skovby F, [Diagnosis and acute treatment of inborn metabolic diseases in infants]. Ugeskrift for laeger. 2002 Nov 25;     [PubMed PMID: 12523004]
[40] Walenta S,Mueller-Klieser WF, Lactate: mirror and motor of tumor malignancy. Seminars in radiation oncology. 2004 Jul;     [PubMed PMID: 15254870]