Lysozyme in seminal fluid of healthy males and patients with prostatitis and in tissues of the male uro-genital tract

Antimicrobial peptides and proteins as alternative antibiotics for porcine semen preservation

BACKGROUND

Antimicrobial resistance (AMR) is nowadays a major emerging challenge for public health worldwide. The over- and misuse of antibiotics, including those for cell culture, are promoting AMR while also encouraging the research and employment of alternative drugs. The addition of antibiotics to the cell media is strongly recommended in sperm preservation, being gentamicin the most used for boar semen. Because of its continued use, several bacterial strains present in boar semen have developed resistance to this antibiotic. Antimicrobial peptides and proteins (AMPPs) are promising candidates as alternative antibiotics because their mechanism of action is less likely to promote AMR. In the present study, we tested two AMPPs (lysozyme and nisin; 50 and 500 µg/mL) as possible substitutes of gentamicin for boar semen preservation up to 48 h of storage.

RESULTS

We found that both AMPPs improved sperm plasma membrane and acrosome integrity during semen storage. The highest concentration tested for lysozyme also kept the remaining sperm parameters unaltered, at 48 h of semen storage, and reduced the bacterial load at comparable levels of the samples supplemented with gentamicin (p > 0.05). On the other hand, while nisin (500 µg/mL) reduced the total Enterobacteriaceae counts, it also decreased the rapid and progressive sperm population and the seminal oxidation-reduction potential (p < 0.05).

CONCLUSIONS

The protective effect of lysozyme on sperm function together with its antimicrobial activity and inborn presence in body fluids, including semen and cervical mucus, makes this enzyme a promising antimicrobial agent for boar semen preservation.

Structural, Functional and Phylogenetic Analysis of Sperm Lysozyme-Like Proteins

Sperm lysozyme-like proteins belonging to c-type lysozyme family evolved in multiple forms. Lysozyme-like proteins, viz., LYZL2, LYZL3 or SLLP1, LYZL4, LYZL5 and LYZL6 are expressed in the testis of mammals. Not all members of LYZL family have been uniformly and unambiguously identified in the genome and proteome of mammals. Some studies suggested a role of SLLP1 and LYZL4 in fertilization; however, the function of other LYZL proteins is unknown. We identified all known forms of LYZL proteins in buffalo sperm by LC-MS/MS. Cloning and sequence analysis of the Lyzl cDNA showed 38-50% identity at amino acid level among the buffalo LYZL paralogs, complete conservation of eight cysteines and other signature sequences of c-type lysozyme family. Catalytic residues in SLLP1, LYZL4 and LYZL5 have undergone replacement. The substrate binding residues showed significant variation in LYZL proteins. Residues at sites 62, 101, 114 in LYZL4; 101 in SLLP1; 37, 62, and 101 in LYZL6 were more variable among diverse species. Sites 63 and 108 occupied by tryptophan were least tolerant to variation. Site 37 also showed lower tolerance to substitution in SLLP1, LYZL4 and LYZL5, but more variable in non-testicular lysozymes. Models of LYZL proteins were created by homology modeling and the substrate binding pockets were analyzed in term of binding energies and contacting residues of LYZL proteins with tri-N-acetylglucosamine (NAG)3 in the A-B-C and B-C-D binding mode. Except LYZL6, LYZL proteins did not show significant difference in binding energies in comparison to hen egg white lysozyme in the A-B-C mode. (NAG)3 binding energy in the B-C-D mode was higher by 1.3-2.2 kcal/mol than in A-B-C mode. Structural analysis indicated that (NAG)3 was involved in making more extensive interactions including hydrogen bonding with LYZL proteins in B-C-D mode than in A-B-C mode. Despite large sequence divergence among themselves and with respect to c-type lysozymes, substrate binding residues as well as hydrogen bonding network between (NAG)3 and proteins were mostly conserved. LYZL5 in buffalo and other mammalian species contained additional 10-12 amino acid sequence at c-terminal that matched with ankyrin repeat domain-containing protein 27. Phylogenetic analysis indicated LYZL2 to be most ancient among all the LYZL proteins and that the evolution of LYZL proteins occurred through several gene duplications preceding the speciation of mammals from other vertebrates as distant as reptiles and amphibians.

The major bactericidal activity of human seminal plasma is zinc-dependent and derived from fragmentation of the semenogelins

One of the major roles of seminal plasma is to provide antimicrobial protection for the spermatozoa in the female reproductive tract. We found that the bactericidal activity of seminal plasma was highest after resolution of the seminal clot and that this antibacterial activity subsequently became greatly diminished. The antibacterial activity was derived from peptides generated by fragmentation of the semenogelins while the semenogelin holoproteins displayed no antibacterial activity. After ejaculation the semenogelin-derived peptides were fragmented to smaller and smaller fragments over time and thereby lost antibacterial activity. This paralleled the loss of antibacterial activity of whole seminal plasma both in vitro and after sexual intercourse. Moreover, the antibacterial activity of the semenogelin-derived peptides generated in seminal plasma was strictly zinc-dependent both at neutral and low pH. These data provide novel roles for the resolution of seminal clots and for the high zinc concentration in human seminal plasma.

The antibacterial chemokine MIG/CXCL9 is constitutively expressed in epithelial cells of the male urogenital tract and is present in seminal plasma

The integrity of the urogenital tract against potentially invasive pathogens is important for the health of the individual, fertilization, and continuance of species. Antibiotic peptides with broad antimicrobial activity, among them chemokines, are part of the innate immune system. We investigated the presence of the antibacterial interferon (IFN)-dependent CXC chemokines, MIG/CXCL9, IP-10/CXCL10, and I-TAC/CXCL11, in the human male reproductive system. MIG/CXCL9 was detected at 25.0 nM (range 8.1-40.6 nM; n = 14), whereas IP-10/CXCL10 and I-TAC/CXCL11 were detected at lower levels (mean 1.8 nM, range 0.3-5.8 nM and mean 0.6, 0.2-1.6 nM, respectively) in seminal plasma of fertile donors. The levels of MIG/CXCL9 are more than 300-fold higher than those previously reported in blood plasma. In vasectomized donors, significantly lower levels of MIG/CXCL9 (mean 14.7 nM, range 6.6-21.8) were found, suggesting that the testis and epididymis, in addition to the prostate, significantly contribute to the MIG/CXCL9 content of seminal plasma. Strong expression of MIG/CXCL9 was found in the epithelium of testis, epididymis, and prostate, as detected by immunohistochemistry. MIG/CXCL9 at concentrations in the order of those found in seminal plasma possessed antibacterial activity against the urogenital pathogen Neisseria gonorrhoeae. The relatively high levels of MIG/CXCL9 in seminal plasma point to roles for this chemokine in both host defense of the male urogenital tract and during fertilization.

Involvement of Semenogelin-Derived Peptides in the Antibacterial Activity of Human Seminal Plasma1

Mechanisms for protecting spermatozoa, and the testes that produce them, from infection are essential, given the importance of these cells and organs for the fertility of the individual and perpetuation of the species. This is borne out by the publication of numerous papers on this subject over the last 50 years. We extended our work and that of others on the anti-infectious defense system of the male genital tract, using a new strategy for the direct identification of antibacterial molecules in human seminal plasma. We subjected a liquefied seminal plasma cationic fraction to reversed-phase HPLC, monitored microbicidal activity by gel overlay and radial diffusion assays, and identified the proteins and/or peptides present in each active fraction by mass spectrometry. In addition to proteins with known potent microbicidal activity--phospholipase A2, lactoferrin, and lysozyme--we also found that peptides produced by cleavage of semenogelin I, the predominant human semen coagulum protein, had high levels of antibacterial activity.

Viscosity of human seminal fluid: role of lysozyme

The aim of this research was to evaluate the role of lysozyme in the phenomenon of seminal hyper-viscosity. The enzyme was determined in 142 samples of seminal plasma either leucospermic or not, with or without active macrophages classified according to their consistency (normal or high). The kinetic method with Micrococcus lysodeikticus as substrate was employed. No difference was found in enzymatic concentration expressed in nmol/L of enzymatic protein (mean +/- 2 SEM) on comparing normal and high seminal consistency groups, while differences proved highly significant in batches either leucospermic or not (n = 44, 197.2 +/- 51.3 vs. n = 98, 108.3 +/- 12.8; p < .0005). On subdividing the normal and high-consistency groups according to the count of polymorphonuclear leucocytes and the macrophagic responses, differences were also significant (p < .005 in both cases). Lysozyme concentration increases in presence of leucospermic reaction. In vitro lysozyme addition showed no significant effect on samples with high consistency. The results indicate that lysozyme plays no direct role in the phenomenon of seminal hyperviscosity, although its deficiency in cases of chronic infections may prove a factor aggravating the clinical picture.

Study of the accuracy of physical and biochemical markers in semen to detect infectious dysfunction of the accessory sex glands

Infection of the male accessory sex glands may result in impaired secretory function and alteration of the composition of seminal plasma. Using receiver operating characteristic curves and accuracy tests, the power of several biochemical and physical markers was evaluated for their ability to discriminate between semen of infected and noninfected infertile men. The total output of citric acid had the strongest discriminating power, followed by acid phosphatase and gamma-glutamyltranspeptidase. Measurement of the concentration of fructose was found to be nondiscriminatory.

The occurrence of immunoglobulin E in Human seminal plasma

The presence of IgE in human seminal plasma has been explored using two different radioimmunoassay methods. Samples were obtained from 84 patients under investigation for involuntary infertility. Low levels were recorded in seminal plasma (less than 0.05-805 kIU/1) together with a wide scatter of serum values (less than 0.5-956 kIU/1). The incidence of detectable seminal plasma IgE was related to high serum IgE values (P less than 0.001; chi 2-test). Among men reporting allergy problems and who has serum IgE levels above 50 kIU/1 detectable semen IgE was seen in 15 out of 18 patients. Sperm agglutination was observed in 18 men of whom 11 had detectable seminal plasma IgE. The question of whether or not seminal plasma IgE is a plasma transudate or is locally produced as well as its possible function in seminal plasma is discussed.

Infertility and genitourinary infection

There is a vast amount of evidence linking the presence of genitourinary infection with infertility. Infection in either partner can result in specific effects on sperm function, accessory sexual gland dysfunction, and the induction of immunologic responses in either partner. Careful investigation for infection should be undertaken in every couple with the complaint of infertility. Treatment needs to be individualized in each instance.

Search for uro-genital tract infections in patients with symptoms of prostatitis. Studies on aerobic and strictly anaerobic bacteria, mycoplasmas, fungi, trichomonads and viruses

Seventy-nine patients with symptoms of nonacute prostatitis and 20 healthy volunteers were examined for uro-genital tract infection with bacteria, mycoplasmas, fungi, trichomonads and viruses. No differences in the results of the bacterial cultures were found between the patients and the controls. In only a few cases were established urinary tract pathogens found, but in no instance were these findings reproducible in later specimens. The cultures of the expressed prostatic fluids and the samples of semen gave no information of the occurrence of bacteria over and above that obtainable from examination of the urethral specimens. Significant bacteriuria was not found in any of the patients. Though Neisseria gonorrhoeae could not be isolated from any of the subjects, immunofluorescent studies revealed such organisms in seminal fluid in 8% of the patients. Nine of the patients had 1 to 3 years been considered successfully treated for gonorrhoea. Five of these nine patients were still found to harbour gonococci, as judged from the immunofluorescent studies. Corynebacterium vaginale was recovered in an equally low frequency (5%) from the patients and the volunteers. There was no significant difference in the incidence of T-mycoplasmas between the patients (46%) and the controls (35%), while Mycoplasma hominis was only found in the patients (10%). Trichomonas vaginalis could not be detected in wet smears of expressed prostatic fluid in any of the subjects, but could be cultured from one such specimen. Metacycline treatment (performed according the double blind cross-over technique) was studied for effects on the bacterial flora. In about 10% of the patients, an earlier not observed relative dominance of gram-negative rods was found on the cultures made after the therapy. Candida albicans was only isolated from the patients. It was found more often after (24%) than before the (15%) treatment. Complement-fixing antibodies to N. gonorrhoeae, cytomegalovirus and Chlamydia were found in 10, 19, and 33% of the patients, respectively. The corresponding figures for the healthy males were 0, 20 and 5%.

Antimicrobial activity of human seminal fluid

The antibacterial, antifungal and antimycoplasmal activity of human semen was studied. Gram-positive aerobic bacterial species i.e. staphylococci, but not gram-negative aerobic bacteria, were inhibited by seminal fluid in vitro. Neither were anaerobic gram-positive or gram-negative bacteria, nor Candida or Mycoplasma inhibited. Semen of healthy males had a higher antibacterial effect on S. albus than that of patients with symptoms of chronic prostatitis. There was a positive correlation between the antibacterial power of the semen of the patients studied and their content of zinc and magnesium, while no correlation was found with fructose and lysozyme or the number of spermatozoa in any of the groups. A positive correlation was found between the antibacterial capacity and the volume of the ejaculate in the patients but not among the controls. The antibacterial substance(s) was dialysable, ether-extractable, resistant to boiling and partly to storage at room temperature. The addition of EDTA, tranexamic acid and ammonium reineckate to semen did not influence the antibacterial effect, which was, however, slightly inhibited by sodium polyanethol sulphonate. The nature of possible antibacterial substances in semen is discussed.

Effect of metacycline treatment on non-acute prostatitis

Sixty-nine patients with symptoms of non-acute prostatitis were treated with metacycline and placebo according to the double-blind crossover technique. The patients reported improvement significantly more often after metacycline than after placebo treatment. But no difference was found between metacycline and placebo in respect of the palpatory findings or the number, morphology and motility of spermatozoa, the number of white blood cells in expressed prostatitic fluid, the zinc, magnesium or fructose content or antibacterial activity of seminal fluid. The lysozyme level in seminal fluid was significantly more often reduced after treatment with metacycline than after placebo. "Therapeutic" concentrations of metacycline were demonstrable in expressed prostatitic fluid specimens collected three hours after intake of the dose prescribed. The majority of patients harbouring Neisseria gonorrhoeae or Mycoplasma hominis were improved after the antibiotic treatment and the organism was no longer demonstrable. No undesirable effects of the treatment with metacycline were observed.