Molecular features and immunological properties of lactate dehydrogenase C4 isozymes from mouse and rat testes

Latheef S, Sharun K, Khurana SK, K. A, Tiwari R, Bhatt P, K. V, Chaicumpa W. Role of Antisperm Antibodies in Infertility, Pregnancy, and Potential forContraceptive and Antifertility Vaccine Designs: Research Progress and Pioneering Vision

Sperm of humans, non-human primates, and other mammalian subjects is considered to be antigenic. The effect of changes in autoimmunity on reproductive cells such as spermatozoa and oocytes play a critical but indistinct role in fertility. Antisperm antibodies (ASAs) are invariably present in both females and males. However, the degree of ASA occurrence may vary according to individual and gender. Although the extent of infertility due to ASAs alone is yet to be determined, it has been found in almost 9-12% of patients who are infertile due to different causes. Postcoital presence of spermatozoa in the reproductive tract of women is not a contributory factor in ASA generation. However, ASA generation may be induced by trauma to the vaginal mucosa, or by anal or oral sex resulting in the deposition of sperm inside the digestive tract. It is strongly believed that, in humans and other species, at least some antibodies may bind to sperm antigens, causing infertility. This form of infertility is termed as immunological infertility, which may be accompanied by impairment of fertility, even in individuals with normozoospermia. Researchers target ASAs for two major reasons: (i) to elucidate the association between ASAs and infertility, the reason ASAs causes infertility, and the mechanism underlying ASA-mediated infertility; and (ii) to assess the potential of ASAs as a contraceptive in humans in case ASAs influences infertility. Therefore, this review explores the potential application of ASAs in the development of anti-spermatozoa vaccines for contraceptive purposes. The usefulness of ASAs for diagnosing obstructive azoospermia, salpingitis, and oligoasthenoteratozoospermia has been reviewed extensively. Important patents pertaining to potential candidates for spermatozoa-derived vaccines that may be utilized as contraceptives are discussed in depth. Antifertility vaccines, as well as treatments for ASA-related infertility, are also highlighted. This review will address many unresolved issues regarding mechanisms involving ASAs in the diagnosis, as well as prognoses, of male infertility. More documented scientific reports are cited to support the mechanisms underlying the potential role of ASA in infertility. The usefulness of sperm antigens or ASAs (recombinant) in human and wild or captive animal contraceptive vaccines has been revealed through research but is yet to be validated via clinical testing.

Male contraception: another Holy Grail

The idea that men should participate in family planning by playing an active role in contraception has become more acceptable in recent years. Up to the present the condom and vasectomy have been the main methods of male contraception. There have been and continue to be efforts to develop an acceptable hormonal contraceptive involving testosterone (T) suppression. However the off target affects, delivery of the analogs and the need for T replacement have proven difficult obstacles to this technology. Research into the development of non-hormonal contraception for men is progressing in several laboratories and this will be the subject of the present review. A number of promising targets for the male pill are being investigated. These involve disruption of spermatogenesis by compromising the integrity of the germinal epithelium, interfering with sperm production at the level of meiosis, attacking specific sperm proteins to disrupt fertilizing ability, or interfering with the assembly of seminal fluid components required by ejaculated sperm for acquisition of motility. Blocking contractility of the vas deferens smooth muscle vasculature to prevent ejaculation is a unique approach that prevents sperm from reaching the egg. We shall note the lack of interest by big pharma with most of the support for male contraception provided by the NIH.

Expression of the gene for mouse lactate dehydrogenase C (Ldhc) is required for male fertility

The lactate dehydrogenase (LDH) protein family members characteristically are distributed in tissue- and cell type-specific patterns and serve as the terminal enzyme of glycolysis, catalyzing reversible oxidation reduction between pyruvate and lactate. They are present as tetramers, and one family member, LDHC, is abundant in spermatocytes, spermatids, and sperm, but also is found in modest amounts in oocytes. We disrupted the Ldhc gene to determine whether LDHC is required for spermatogenesis, oogenesis, and/or sperm and egg function. The targeted disruption of Ldhc severely impaired fertility in male Ldhc(-/-) mice but not in female Ldhc(-/-) mice. Testis and sperm morphology and sperm production appeared to be normal. However, total LDH enzymatic activity was considerably lower in Ldhc(-/-) sperm than in wild type sperm, indicating that the LDHC homotetramer (LDH-C(4)) is responsible for most of the LDH activity in sperm. Although initially motile when isolated, there was a more rapid reduction in the level of ATP and in motility in Ldhc(-)(/-) sperm than in wild-type sperm. Moreover, Ldhc(-/-) sperm did not acquire hyperactivated motility, were unable to penetrate the zona pellucida in vitro, and failed to undergo the phosphorylation events characteristic of capacitation. These studies showed that LDHC plays an essential role in maintenance of the processes of glycolysis and ATP production in the flagellum that are required for male fertility and sperm function.

Diagnosis of malaria by detection of plasmodial lactate dehydrogenase with an immunodot enzyme assay

We have previously demonstrated, using polyclonal and monoclonal antibodies, that the lactate dehydrogenase (LDH) of malaria parasites is immunologically distinct from the host enzyme. The polyclonal antibodies, produced against the affinity purified plasmodial LDH (pLDH) in rabbits, showed specificity to LDH of malaria parasites. In the present study, these anti-pLDH polyclonal antibodies were used to develop an immunodiagnostic test (immunodot enzyme assay of plasmodial LDH) based on the detection of parasite LDH in patient blood. The immunodot enzyme assay of plasmodial LDH was evaluated using blood samples from patients with malaria or other infections. Out of 502 microscopically positive malaria blood samples, 497 blood samples showed positive immunodot assays of pLDH while all the 423 microscopically negative cases were found negative by our test. The blood samples from other infections and non-endemic controls were negative by the immunodot enzyme assay of pLDH. This LDH based test was also found negative in blood samples of cured patients 7 days after chloroquine treatment. The test is simple to perform, can be read visually, econimal, highly specific with a sensitivity of approximately 99% and is thus suitable for accurate diagnosis of malaria in field conditions.

RT-PCR amplification of a Rhizopus oryzae lactate dehydrogenase gene fragment

No amino acid or DNA sequence information in sequence databases was found for a fungal lactate dehydrogenase (LDH) isozyme. Highly conserved regions in the lactate dehydrogenase enzymes of all taxonomies are found to be betaalphabeta nucleotide binding and substrate binding sites, also catalysis/active site. The conserved regions were selected as PCR primer target regions. The degenerate primers were designed according to the codon usage, determined by analyzing a number of different genes of Rhizopus species. A fragment of the gene (ldh), coding for approximately 72% of the lactate dehydrogenase enzyme from Rhizopus oryzae, was amplified using degenerate primers by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR). The size of the amplified fragment containing betaalphabeta nucleotide binding site, substrate binding site and catalysis/active site is found to be about 700 bp. The reported degenerate PCR primers and the amplification conditions may lead to the cloning of the lactate dehydrogenase gene of R. oryzae, which is an important organism due to its utilization in lactic acid and enzyme productions in industrial scales.

Changes in testicular lactate dehydrogenases of the rat (Rattus norvegicus) during growth and development

1. We have quantified lactate dehydrogenase (LDH) A, B and C enzyme levels during the first twelve weeks of life in rat testes. 2. Proteins were electrophoresed under non-denaturing conditions, isoenzymes identified by activity staining and quantified by densitometry scanning. 3. LDH A declined 2-3-fold during testes growth, changing from the most to the least abundant isoenzyme form. LDH B remained fairly constant, and LDH C increased from undetectable levels at birth to become the most abundant of the three polypeptides from week 3 onwards.

The cDNA and protein sequences of mouse lactate dehydrogenase B. Molecular evolution of vertebrate lactate dehydrogenase genes A (muscle), B (heart) and C (testis)

Mouse lactate dehydrogenase-B cDNAs were isolated from cDNA libraries of macrophage (ICR strain) and thymus (F1 hybrid of C57BL/6 and CBA strains), and their nucleotide sequences determined. The lactate dehydrogenase-B cDNA insert of thymus clone mB188 consists of the protein-coding sequence (1002 nucleotides), the 5' (46 nucleotides) and 3' (190 nucleotides) non-coding regions, and poly(A) tail (19 nucleotides), while macrophage clone mB168 contains a partial lactate dehydrogenase cDNA insert from codon no. 55 to the poly(A) tail. Seven silent nucleotide substitutions at codon no. 142, 143, 186, 187, 241, 285 and 292, as well as a single nucleotide change in the 3' non-coding region, were found between these different strains of mice. The predicted sequence of 333 amino acids, excluding initiation methionine, was confirmed by sequencing and/or compositional analyses of a total of 103 (31%) amino acids from tryptic peptides of mouse lactate dehydrogenase-B protein. The nucleotide sequence of the mouse coding region for lactate dehydrogenase B shows 86% identity with that of the human isoenzyme, and only eight of the 139 nucleotide differences resulted in amino acid substitutions at residues 10, 13, 14, 17, 52, 132, 236 and 317. The rates of nucleotide substitutions at synonymous and nonsynonymous sites in the mammalian lactate dehydrogenase genes are calculated. The rates of synonymous substitutions for lactate dehydrogenase genes A (muscle) and B (heart) are considerably higher than the average rate computed from human and rodent genes. The rates of nonsynonymous substitutions for lactate dehydrogenase genes A (muscle) and B (heart), particularly the latter, are highly conservative. The rates of synonymous and nonsynonymous substitutions for the lactate dehydrogenase-C gene are about the same as the average rates for mammalian genes. A phylogenetic tree of vertebrate lactate dehydrogenase protein sequences is constructed. In agreement with the previous results, this analysis further indicates that lactate dehydrogenase-C gene branched off earlier than did lactate dehydrogenase-A and lactate dehydrogenase-B genes.

Stage-specific expression of the lactate dehydrogenase-X gene in adult and developing mouse testes

Lactate dehydrogenase-X (LDH-X), a glycolytic enzyme found only in mammalian testes and spermatozoa, is encoded by a single gene (Ldh-x) in the mouse haploid genome. Several studies have demonstrated that LDH-X is associated with germ cells at specific stages of development. We have examined the expression of the Ldh-x gene during mouse spermatogenesis and testis maturation using in situ mRNA hybridization and immunocytochemistry. The results showed that transcription and translation of the Ldh-x gene are initiated at the pachytene stage of germ cell differentiation. However, although the amount of LDH-X protein increased as the germ cells progressed to maturation, its mRNA level was greatly decreased. These observations were confirmed by Northern analysis of total RNA derived from fractionated spermatogenic cells and developing testes. Furthermore, Northern studies also indicated two sizes of Ldh-x transcripts among different populations of spermatogenic cells in mature mouse testis.

Human testicular lactate dehydrogenase-C gene is interrupted by six introns at positions homologous to those of LDH-A (muscle) and LDH-B (heart) genes

Human genomic clones containing parts of testis-specific lactate dehydrogenase-C gene of approximately 40 kilobases in length were isolated and characterized. The protein-coding sequence of human LDH-C gene is interrupted by six introns at positions homologous to those of mammalian LDH-A (muscle) and LDH-B (heart) genes, and exhibits 21%, 24% and 34% nucleotide differences with those of mouse LDH-C, human LDH-A and LDH-B genes, respectively.

Inhibition of the reactivation of acid-dissociated lactate dehydrogenase isoenzymes by their aminoterminal CNBr fragments

The catalytic activity of lactate dehydrogenase isoenzymes (LDH) depends on their tetrameric structure. Stabilization of this quaternary structure is achieved by interaction of the N-terminal part of one subunit with the C-terminal region of the other subunit. The N-terminal peptides from pig M-LDH and H-LDH which are responsible for this stabilization were obtained by CNBr-fragmentation and purification on reversed-phase HPLC. The effect of these peptides on the formation of the quaternary structure of LDH-isoenzymes was investigated by monitoring the reconstitution of the catalytic activity after acid-dissociation. Low concentrations of the N-terminal peptides led to an increased, and high concentrations to a decreased yield of reconstituted LDH activity. The effects of these two peptides were isoenzyme specific. The 32 residue peptide derived from M-LDH showed the highest effect when tested with M-LDH as target enzyme but only a poor effect with H-LDH. On the other side the 33 residue peptide generated from H-LDH showed a moderate effect with both isoenzymes. The effects of the N-terminal LDH peptides are antagonized by the coenzymes NAD+ and NADH. The most significant influence was observed with NAD+ in the M-LDH peptide-M-LDH enzyme system. Comparison of the properties of the reactivation antagonists isolated from human origin with the N-terminal CNBr-peptides of LDH revealed identity in all essential properties, suggesting that the former peptides are generated by degradation of LDH.

Inhibition of lactate dehydrogenase-X by imino-derivatives of gossypol:structure activity relationship

Six imino-derivatives (II, III, IV, V, VI, VII) of gossypol (I) have been synthesized, and their effects were evaluated on the purified mouse lactate dehydrogenase-X. Three of these derivatives (V, VI, VII) with aldehyde groups substituted with hydrophobic functionalities showed equivalent or more inhibitory effects on lactate dehydrogenase-X than gossypol, whereas three other derivatives (II, III, IV) with aldehyde groups substituted with hydrophilic functional groups lost the ability to inhibit lactate dehydrogenase-X. It is suggested that two aldehyde groups of gossypol are not essential to inhibit lactate dehydrogenase-X. Furthermore, the hydrophobic property of the gossypol molecule seems to play a more important role in inhibiting lactate dehydrogenase-X. Therefore, lactate dehydrogenase-X inhibition by gossypol may not be associated with its antifertility mechanism, because the aldehyde group of gossypol is known to be required for its antifertility effect.

Kinetic characterization of the inhibition of purified cynomolgus monkey lactate dehydrogenase isozymes by gossypol

This report describes the results of the first step in a sequence of experiments designed to test the hypothesis that the sperm-specific isozyme of lactate dehydrogenase (LDH-C4), is a site of action of the potential male contraceptive agent gossypol. Cynomolgus monkey LDH-A4, LDH-B4 and LDH-C4 were purified and kinetically characterized. LDH-A4 and LDH-B4 exhibited "linear mixed-type" inhibition by gossypol with both lactate and pyruvate as variable substrates. LDH-C4 also exhibited "linear mixed-type" inhibition with lactate as substrate. However, the C4 isozyme exhibited "parabolic mixed-type" inhibition by gossypol and substrate inhibition with pyruvate as substrate, the latter due to abortive complex formation. Of the three isozymes, LDH-C4 exhibited the lowest apparent Km for pyruvate and the highest apparent Km for lactate. The LDH-C4 form was found to be the most sensitive isozyme to gossypol inhibition, since it had the lowest apparent Ki values for gossypol inhibition. The effect of gossypol on coenzyme binding to LDH-C4 was examined and gossypol binding was found to inhibit binding and release of NADH but not NAD+, an effect possibly due to its interaction with the more hydrophobic loop region of LDH-C4.

Monkey lactate dehydrogenase-C4 as a model for the interaction of enzymes with gossypol

Lactate dehydrogenase-C4 (LDH-C4) plays a central role in the metabolism of spermatogenic and mature sperm cells as well as being an enzyme which is inhibited by gossypol, a male contraceptive. Racemic and (+)-gossypol have equivalent potency as inhibitors of LDH-C4 purified from ejaculated sperm of cynomolgus monkeys. Analogues of gossypol (gossypol-glycine ester Schiff's base, 6,6-dimethoxygossypol and ethyl gossypol) have quantitatively similar inhibitory effects of LDH-C4 activity; apogossypol hexaacetate, however, has no inhibitory effect. Other effective inhibitors of LDH-C4 are antimycin, naphthoquinones and lithocholic acid. LDH-C4 may serve as a model for understanding gossypol binding domains and contraceptive action.

Antigens of Plasmodium falciparum blood stages with clinical interest cloned and expressed in E. coli

The human malaria parasite,Plasmodium falciparum, is currently being actively studied by molecular biologists. It is hoped that the use of recombinant DNA techniques in this area will give new insights into the biology of the organism and, at the same time, provide new approaches to diagnosis and vaccine development.

Our own studies employ the blood stages of the parasite and cover three main areas: enzymes of importance in parasite metabolism; antigens of potential use in a subunit vaccine; and repetitive DNA as a probe able to distinguish genetically different isolates ofP. falciparumand as a species-specific diagnostic tool in human and mosquito infections.

Protein structure and gene organization of mouse lactate dehydrogenase-A isozyme

The complete covalent structure of the 331 amino acids of mouse lactate dehydrogenase (LDH) A4 isozyme has been determined by sequence analyses of both the protein and the genomic DNA. The mouse LDH-A gene spans a length of at least 7000 bases from the translation initiation codon ATG to the end of the 3' untranslated region, and it contains six introns that interrupt the protein-coding sequence. The relationships between the exon-intron organization of LDH-A gene and the structural-functional domains of the protein are discussed.

Antigenic domains of the sperm-specific lactate dehydrogenase C4 isozyme

Lactate dehydrogenase C4 (LDH-C4) is an antigenic protein that occurs only in spermatozoa and the mature testis. The antibody-combining sites of this enzyme were mapped by measuring the binding of anti-LDH-C4 by isolated peptides. Pure mouse LDH-C4 was digested with trypsin, and the resulting fragments were fractionated by reverse-phase high-pressure liquid chromatography. Rabbit anti-mouse LDH-C4 bound to 13 pure peptides. Amino acid compositions and partial or complete sequencing by the Edman degradation was used to identify eight of these fragments in the complete structure of the molecule. The relationship between structure and antigenicity of these peptides is discussed in detail. These data fit best to the domain model of protein antigenicity. This antigenic map of LDH-C4 will be useful in the design of a synthetic contraceptive vaccine.

Nucleotide sequences of the cDNA and an intronless pseudogene for human lactate dehydrogenase-A isozyme

Eight cDNA clones for lactate dehydrogenase-A isozyme (LDH-A) were isolated from a human fibroblast cDNA library, characterized, and no sequence heterogeneity was found. Four cDNA clones appear to contain nearly full-length cDNA inserts and the complete nucleotide sequence of 1710 base pairs consists of the protein-coding sequence (999 base pairs), the 5' (97 base pairs) and 3' (565 base pairs) untranslated regions and poly(dA) tail (49 base pairs). The predicted amino acid sequence of the human LDH-A polypeptide shows 92% homology (27 differences out of 331 amino acids compared) with that of the pig LDH-A subunit determined by direct protein sequencing [Kiltz et al. (1977) Hoppe-Seyler's Z. Physiol. Chem. 358, 123-127]. Human genomic clones containing an LDH-A pseudogene were isolated and the nucleotide sequence of 1635 base pairs from an intronless pseudogene was determined. The presence of two termination codons, two deletions of three nucleotides each and the replacement of three arginine residues at the active site (nos 98, 105 and 168) by other amino acids renders its coding region incapable of producing a functional LDH-A protein. A comparison between human LDH-A cDNA and the pseudogene sequences reveals 12.9% differences (114 transitions, 65 transversions and 36 deletions/insertions). Further, only four out of the 25 dCpdG dinucleotides present in the cDNA sequence remain unchanged, although the sequences possess 87.1% homology.

An evaluation of heterologous antibodies to lactate dehydrogenase-C in the detection of mutations

We report that we are unable to repeat consistently the results published by Ansari et al. (1980) using antibodies to detect mutations in lactate dehydrogenase-C (LDH-C, previously called LDH-X) directly in sperm of mice exposed to the mutagen procarbazine. The approach made use of the interspecies differences in the antigenic sites between the LDH-C of the rat and mouse in sperm. The visualization of mutations in mouse LDH-C was based on the detection of alterations in antigenic sites of mouse LDH-C such that mouse sperm would bind the antibody that was specific for rat LDH-C (presumptive mutants); the antibody was termed specific when it immunofluorescently labeled rat sperm but not mouse sperm. The original work reported increases in the frequency of occurrence of mouse sperm that would bind rat-specific antibody from mice treated with procarbazine as compared control mice; a single absorbed antiserum was used throughout the experiments. In this study, we found that there is too much variation in the frequency of mouse sperm that react with rabbit antibodies to purified rat LDH-C for the system to be useful in mutagenesis studies. The fundamental criterion of antibody specificity was maintained as in the original work. The frequency of labeled mouse sperm depended on the absorption of the antibody on mouse proteins, indicating that the factors denoting a presumptive mutant were associated with the mouse proteins. In some experiments, the frequency of labeled mouse sperm was higher among sperm from procarbazine-treated mice than among sperm from control mice. This increase, however, was not consistently reproducible. After extensive absorption of the antibody on mouse proteins, no presumptive mutants were observed in sperm from treated and control animals; these antibodies continued to immunofluorescently label rat sperm. The absence of presumptive mutants with highly absorbed antibody suggests that natural variation between species may not be appropriate as markers for the detection of mutations without a thorough knowledge of the number of independent events at the DNA level required to produce a change in antigenic recognition.

Kinetics of gossypol inhibition of bovine lactate dehydrogenase X

Gossypol, a polyphenolic binaphthalene dialdehyde isolated from cotton meal is a potent inhibitor of lactate dehydrogenase-X purified from bovine testis. For the conversion of pyruvate to lactate the IC50 for gossypol is 200 microM for the reverse reaction the IC50 is 12 microM. Gossypol is a competitive inhibitor of NADH, Ki = 30 microM (Km = 17 microM), and NAD+, Ki = 6 microM (Km = 130 microM), and noncompetitive for pyruvate, Ki = 220 microM (Km = 224 microM), and lactate, Ki = 52 microM (Km = 5.6 mM).