The fatty acid composition of the major phosphoglycerides of ram and human spermatozoa

PUFA-rich phospholipid classes and subclasses of ram spermatozoa are unevenly affected by cryopreservation with a soybean lecithin-based extender

Cryopreservation is known to affect spermatozoa structure and function. Ram sperm are among the most highly sensitive mammalian gametes to freezing, due to their lipid composition, which limit their efficiency in artificial insemination programs. The aim of this study was to investigate the effects of cryopreservation with a chemically defined soybean lecithin-based extender on ram spermatozoa functionality on the one hand, and quantifiable changes in lipid and fatty acid profile on the other. Freeze-thawing decreased sperm quality, as indicated by post-thaw parameters related to membrane integrity, mitochondrial viability and sperm motility. The most relevant lipid change after cryopreservation was a remarkable loss of all glycerophospholipids containing 22:6n-3. Species of sphingomyelin with very long chain polyunsaturated fatty acids (VLC-PUFA), that are exclusively located in the sperm head, where responsible of its reduction after cryostorage. Freezing caused a reduction in mitochondrial function, which was confirmed by significantly decreased of mitochondrial membrane potential and by the generation of 4-HNE. Mitochondria damage was accompanied by a loss in cardiolipin with 18:2n-6 and phosphatidylethanolamine with 20:4n-6, two well-known lipids that are critical components for mitochondrial membrane functionality. Loss of sterols after cryopreservation occurred along with a decrease in the order of sperm membrane lipids. Our research provides new insights on deleterious effects of cryopreservation on PUFA-rich phospholipids of ram sperm and highlight their importance as biomarkers of ultrastructural, biochemical and functional damage that ram spermatozoa undergo after freezing-thawing.

Plasma and acrosomal membrane lipid content of saltwater crocodile spermatozoa

This study describes the chemical lipid composition of the sperm plasma and acrosomal membranes of the saltwater crocodile Crocodylus porosus with the aim of providing new insights into sperm physiology, particularly that associated with their preservation ex vivo . The specific fatty acid composition of the sperm plasma and acrosomal membranes is documented. The mean (±s.d.) ratio of unsaturated to saturated membrane fatty acids within the plasma membrane was 2.57±0.50, and was determined to be higher than a similar analysis of the lipids found in the acrosomal membrane (0.70±0.10). The saltwater crocodile sperm plasma membrane also contained remarkably high levels of cholesterol (mean (±s.d.) 40.7±4.5 nmol per 106 sperm cells) compared with the spermatozoa of other amniote species that have so far been documented. We suggest that this high cholesterol content could be conferring stability to the crocodile sperm membrane, allowing it to tolerate extreme osmotic fluxes and rapid changes in temperature. Our descriptive analysis now provides those interested in reptile and comparative sperm physiology an improved baseline database for interpreting biochemical changes associated with preservation pathology (e.g. cold shock and cryoinjury), epididymal sperm maturation and capacitation/acrosome reaction.

Structural determinants of the packing and electrostatic behavior of unsaturated phosphoglycerides

Docosahexaenoic acid-containing phosphoglycerides accumulate preferentially in membranes of the retina, brain, and spermatozoa, but the functional significance of this largely remains to be determined. Previously we compared the physical properties of homogeneous monolayers of these and other phosphoglyceride species to obtain insights into their physiological roles. Particularly noteworthy were the unusually low dipole moments of species having sn-2-docosahexaenoyl chains. In this study, we have investigated the electrostatic and lateral packing properties of related phosphoglycerides and found that: 1), The dipole moment-lowering effect of the docosahexaenoyl group arises from its having a Z double bond at chain position n-3. 2), The large dipole moment-lowering effects at sn-1 of an ether bond to an alkyl or a 1Z alkenyl chain and that of a sn-2-esterified n-3 fatty acid are additive. 3), The 1Z double bond in an alkenyl chain lowers the molecular area of a phosphoglyceride and, concomitantly, makes it less compressible. 4), Ethanolamine-containing phosphoglycerides are generally less compressible than their corresponding choline analogs. Our data showing that relatively small lipid structural changes markedly alter lipid physical properties in fluid phases underscores the need to study the function of peripheral and integral membrane proteins in the presence of appropriate lipid species.

Chronic pelvic pain syndrome/chronic prostatitis affect the acrosome reaction in human spermatozoa

Male genital tract inflammations constitute an important factor of male subfertility in which different mediators are discussed damaging sperm membranes. As acrosome reaction (AR) is ultimately a membrane function, this study aimed at investigating the effects of the chronic pelvic pain syndrome on AR. In a total of 56 patients with chronic pelvic pain syndrome NIH IIIA and NIH IIIB, AR, concentration of leucocytes in ejaculate and urine after prostate massage, sperm concentration, motility, vitality and morphology were determined. The control group (n = 95) consisted of patients with normozoospermia and proven absence of signs of inflammation. Compared to the control, both patients groups showed poorer sperm morphology (P < 0.0001) and sperm concentration (P < 0.002). In addition, while maximum AR was not affected, inducibility of AR was significantly lower (P < 0.004) and spontaneous AR increased (P < 0.02). Our data clearly demonstrate a significant influence of the inflammation on acrosomal functionality, which could be mediated by inflammatory mediators like ROS.

Brownian dynamics simulation of the unsaturated lipidic molecules oleic and docosahexaenoic acid confined in a cellular membrane

A Brownian dynamics (BD) simulation of two unsaturated molecules, oleic and docosahexaenoic acid, in an environment that reproduces a cellular membrane, is presented. The results of the simulations, performed using mean-field potentials, were calibrated with experimental results obtained for oleic acid in a cellular membrane. The agreement between simulation and experimental results is excellent which validates subsequent simulation outcome for docosahexaenoic acid. This molecule is a major component of several cellular membranes thought to be involved in specific biological functions that require conformational changes of membrane components. The results for docosahexaenoic acid indicate that it is minimally influenced by temperature changes and that it presents great conformational variability.

Scavenging effect of N-acetyl-L-cysteine against reactive oxygen species in human semen: a possible therapeutic modality for male factor infertility?

A new approach to reduce the level of reactive oxygen species (ROS) in human semen by using N-acetyl-L-cysteine (NAC) was evaluated. Semen samples were incubated with or without NAC (1.0 mg ml-1) at room temperature. The chemiluminescent signal of the oxidation of luminol was detected by means of an MTP reader after 0, 20, 40, 60 and 120 min, respectively, using 200 microM luminol. In addition, the dose-dependent action of NAC (0.1, 1.0 and 5.0 mg ml-1) and the influence of NAC on functional sperm parameters (motility and acrosome reaction) were studied. ROS levels decreased significantly after 20 min incubation with NAC. This reduction was greater in the high ROS group (> 30000 counts/10(7) viable sperm at t = 0) than in the low ROS group (< 30000). In addition, a marked dose-dependence of NAC was observed. Concerning sperm function, total sperm motility improved after incubation with NAC, but no significant change was observed with respect to the acrosome reaction. NAC (at concentrations of 1.0 mg ml-1) significantly reduced ROS in human semen and showed the possibility of improving impaired sperm function. After further testing NAC might be useful for the treatment of male infertility patients.

Antisperm antibody binding to human sperm inhibits capacitation induced changes in the levels of plasma membrane sterols

PROBLEM

Human spermatozoa express mannose ligand receptors (MLRs) over the entire head when incubated under conditions that promote loss of free cholesterol. Binding of IgA, IgG, and/or IgM head-directed anti-sperm antibodies (ASAs) to freshly isolated sperm blocks MLR expression in a dose dependent manner.

METHODS

Comparison of Western blots of immunoprecipitated glycoproteins from fresh sperm exposed to ASAs from women with those of sperm membrane proteins isolated from capacitated sperm probed with a goat anti-human macrophage MLR antiserum showed that ASAs do not react with human sperm MLRs of 48 and 61 kd apparent molecular weight.

RESULTS

The direct effect of ASA binding was to increase membrane free cholesterol content which remained greater than 0.005 mumol/10(9) sperm after 18 h incubations, whereas the sterol content of controls decreased to less than 0.001 mumol/10(9) sperm. Cholesterol addition to sperm inhibited MLR expression in a manner analogous to ASA binding, while increasing temperatures up to the crystalline/liquid-crystalline phase transition for sperm membranes; less than 45 degrees C failed to promote the appearance of MLRs on the surface of fresh sperm.

CONCLUSIONS

We conclude that ASA effects on membrane cholesterol content prevent the membrane fluidity changes needed for MLR expression.

Spectrophotometric phosphate assay in human seminal plasma. A technique for the determination of glycerol-3-phosphorylcholine secretion

Glycerol-3-phosphorylcholine (GLY-3-PrC) has a role in determining the epididymal environment, but its function is not yet completely clear. This lack of knowledge might be partially due to the limitations of techniques currently employed in the GLY-3-PrC determination. In this paper we have studied and adjusted to human seminal plasma a spectrophotometric assay initially devised for bull and rabbit ejaculates. By means of column-chromatography and solvent extraction the specific interferences (up to 30%) present in human ejaculate, probably due to phosphatidylcholine, were avoided. The technique is precise, simple, cheap and shows GLY-3-PrC recovery higher than 90%.

Diffusion and regionalization in membranes of maturing ram spermatozoa

An essential feature of the "fluid mosaic model" (Singer, S. J., and G. L. Nicolson , 1972, Science (Wash. DC)., 175:720-731) of the cell plasma membrane is the ability of membrane lipids and proteins to diffuse laterally in the plane of the membrane. Mammalian sperm are capable of overcoming free random diffusion and restricting specific membrane components, both lipid and protein, to defined regions of the sperm's surface. The patterns of these regionalizations evolve with the processes of sperm differentiation: spermatogenesis, epididymal maturation, and capacitation. We have used the technique of fluorescence recovery after photobleaching to measure the diffusion of the lipid analogue 1,1'- dihexadecyl 3,3,3',3'- tetramethylindocarbocyanine perchlorate ( C16dil ) on the different morphological regions of testicular and ejaculated ram spermatozoa. We have found: (a) that the major morphologically distinct regions (head, midpiece, and tail) of the plasma membrane of both testicular and ejaculated spermatozoa are also physically distinct as measured by C16dil diffusibility; (b) that despite regional differences in diffusibility there is exchange of this lipid analogue by lateral diffusion between the major morphological regions of the plasma membrane; and (c) that epididymal maturation results in changes in C16dil diffusibility in the different regions of the sperm plasma membrane. In particular, the plasma membranes of the anterior and posterior heads become physically distinct.

Analysis of phospholipids in human semen by high-performance liquid chromatography

A sensitive method for the separation of phospholipids by a high-performance liquid chromatographic procedure is described. The chromatographic separation was achieved on a 25-cm column packed with Bio-Sil HP-10 coupled with a pre-column packed with Si-100 Polyol. Phosphatidylinositol, phosphatidylglycerol, cardiolipin, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, lysophosphatidylethanolamine and lysophosphatidylcholine were completely separated and quantitated. The eluted phospholipids were monitored at 203 nm. The method was shown to be applicable to the analysis of phospholipids from human semen.

Peroxidative breakdown of phospholipids in human spermatozoa, spermicidal properties of fatty acid peroxides, and protective action of seminal plasma

Aerobic incubation of human spermatozoa in the presence of catalytic amounts of ascorbate and ferrous ion results in rapid peroxidative breakdown of sperm phospholipids and fatty acids; most strongly affected are phosphatidyl ethanolamine, ethanolamine plasmalogen, and docosahexanoic acid. Both peroxidation of the endogenous sperm phospholipid and the concurrent loss of motility can be fully prevented, but not reversed, by an "antiperoxidant" factor present in human seminal plasma. Exogenously applied lipid peroxides are powerfully spermicidal. Washed human spermatozoa, at a concentration normally present in semen, treated with as little as 30 nmoles of lipid peroxide/ml become irreversibly immotile within a few minutes. The antiperoxidant factor present in human seminal plasma effectively counteracts the toxic effect of exogenous peroxidized fatty acids upon human spermatozoa, but is unable to restore motility lost by lipid peroxide action.

Linolenic acid deficiency

Linolenic acid deficiency has not been demonstrated clearly in warm blooded animals, yet circumstantial evidence suggests that n-3 fatty acids may have functions in these animals. The fact that several species of fish definitely require dietary n-3 fatty acids indicates that n-3 fatty acids have important and specific functions in these animals and suggests that such functions may also be present in warm blooded animals. It is also true that n-3 fatty acid distribution in tissues of birds and mammals appears to be under strict metabolic control, and that this complex metabolic control mechanism apparently has survived evolutionary pressure for a very long time. So far, attempts to produce linolenic acid deficiency in mammals have not revealed an absolute requirement for n-3 fatty acids. If functions for n-3 fatty acids do exist in warm blooded animals, it seems probable that they may be located in the cerebral cortex or in the retina, because these tissues normally contain high concentrations of n-3 fatty acids.