Creatine kinase in seminal plasma of infertile men: activity and isoenzymes

Creatine as a Promising Component of Paternal Preconception Diet

Male fertility has been declining globally over the past several decades, advancing from a personal issue to a public health problem. Beyond any doubt, a reduction in fertility (often characterized by low sperm count or motility) can severely threaten reproductive health and lifecourse framework in a long-term fashion. Aside from uncovering the currently unknown etiology of modern-day male infertility, the scientific and medical community faces a double burden: finding an efficient biomarker of impaired fertility and exploring any intervention that can act to enhance fertility. A plethora of nutritional compounds have been recognized as possible modulators of semen quality, and specific dietary patterns and nutrients appear to be accompanied by a lower risk of male infertility. Creatine, a conditionally essential nutrient, has caught attention as a male fertility-promoting candidate due to its role in sperm energy metabolism. This mini-review describes the creatine-related bioenergetics of spermatozoa, explores a connection between creatine levels and sperm quality in men, and critically examines available evidence for interventional studies with creatine to affect sperm viability.

A drastic shift in the energetic landscape of toothed whale sperm cells

Mammalian spermatozoa are a notable example of metabolic compartmentalization.¹ Energy in the form of ATP production, vital for motility, capacitation, and fertilization, is subcellularly separated in sperm cells. While glycolysis provides a local, rapid, and low-yielding input of ATP along the flagellum fibrous sheath, oxidative phosphorylation (OXPHOS), far more efficient over a longer time frame, is concentrated in the midpiece mitochondria.² The relative weight of glycolysis and OXPHOS pathways in sperm function is variable among species and sensitive to oxygen and substrate availability.^3-5 Besides partitioning energy production, sperm cell energetics display an additional singularity: the occurrence of sperm-specific gene duplicates and alternative spliced variants, with conserved function but structurally bound to the flagellar fibrous sheath.^6,7 The wider selective forces driving the compartmentalization and adaptability of this energy system in mammalian species remain largely unknown, much like the impact of ecosystem resource availability (e.g., carbohydrates, fatty acids, and proteins) and dietary adaptations in reproductive physiology traits.⁸ Here, we investigated the Cetacea, an iconic group of fully aquatic and carnivorous marine mammals, evolutionarily related to extant terrestrial herbivores.⁹ In this lineage, episodes of profound trait remodeling have been accompanied by clear genomic signatures.^10-14 We show that toothed whales exhibit impaired sperm glycolysis, due to gene and exon erosion, and demonstrate that dolphin spermatozoa motility depends on endogenous fatty acid β-oxidation, but not carbohydrates. Such unique energetic rewiring substantiates the observation of large mitochondria in toothed whale spermatozoa and emphasizes the radical physiological reorganization imposed by the transition to a carbohydrate-depleted marine environment.

Caffeine increased progressive motility of human spermatozoa in normozoospermic and asthenozoospermic semen samples and enhanced activity of seminal creatine kinase

Even though the effect of caffeine on humans' health has been revealed in various research studies, its effect on semen quality has yet to be well explained. Here, we measured the effect of caffeine at 1, 5, 10 and 20 mM on motility of human spermatozoa in normozoospermic and asthenozoospermic semen samples, level of seminal nitric oxide, chelation of seminal calcium ions and activity of seminal creatine kinase. Fifty-one normozoospermic and ten asthenozoospermic semen samples were recruited in this study. Sperm motility was evaluated by Makler counter, and seminal nitric oxide, seminal-free calcium and activity of seminal creatine kinase were measured spectrophotometrically. Caffeine at 10 mM significantly (p < .05) increased progressive motility of spermatozoa in both tested groups. Also, caffeine significantly increased (p < .05) activity of creatine kinase and insignificantly (p > .05) altered nitric oxide and free calcium levels in seminal plasma. In conclusion, progressive motility of human spermatozoa was found to be higher in the presence of caffeine at 10 mM in normozoospermic and asthenozoospermic semen samples; this increase, albeit partially, could be due to increased activity of seminal creatine kinase, but not to increased production of nitric oxide or chelation of free calcium ions.

The role of sperm creatine kinase in the assessment of male fertility

The lack of reliable methods to assess sperm fertilizing potential has been a long-standing problem for infertile couples and for their physicians. The most widely used tests, the measurements of sperm concentrations, motility, velocity and morphology in the ejaculate, are of limited utility. Indeed, following intrauterine insemination, a treatment that compensates for low motile sperm concentrations, there were no significant differences found in semen parameters among those who did or did not achieve pregnancies. Other available assays probing for selected sperm functions, such as membrane integrity, acrosome enzyme activity, bovine cervical mucus penetration test, zona-free hamster oocyte penetration test and sperm binding to various carbohydrates,10–13 have all failed thus far to consistently predict male fertility. It became increasingly obvious that there was a need to identify cellular markers of sperm quality and fertilizing potential.

Creatine kinase activity in human spermatozoa and seminal plasma lacks predictive value for male fertility in in vitro fertilization

OBJECTIVE

To examine the predictive value of creatine kinase in human spermatozoa and seminal plasma from patients treated in an IVF program.

DESIGN

Prospective, blind clinical study.

SETTING

Male infertility clinic.

PATIENT(S)

Seventy-three patients and 32 fathers (age, <45 years).

INTERVENTION(S)

Determination of creatine kinase activity in seminal plasma, washed spermatozoa, and swim-up purified spermatozoa from patients treated in an IVF program.

MAIN OUTCOME MEASURE(S)

Creatine kinase activity in seminal plasma, washed spermatozoa, and swim-up purified spermatozoa.

RESULT(S)

Creatine kinase activity in washed spermatozoa correlated significantly with normal sperm morphology. No significant correlations were found between creatine kinase activity or creatine kinase isoenzyme ratio in seminal plasma, washed spermatozoa, or swim-up purified spermatozoa and success in the IVF program. The percentage of spermatozoa with normal morphology was significantly lower in patients whose sperm did not fertilize than in patients whose sperm did fertilize oocytes and in the control group of proven fathers.

CONCLUSION(S)

Total creatine kinase activity and creatine kinase isoenzyme distribution are not sperm function markers for prediction of male fertility in IVF treatment.

Identification of two distinctly localized mitochondrial creatine kinase isoenzymes in spermatozoa

The creatine kinase (CK) isoenzyme system is essential for motility in rooster and sea urchin sperm. In the present study, biochemical characterization as well as immunofluorescence and confocal laser microscopy with highly specific antibodies against various chicken CK isoenzymes revealed that cytosolic brain-type CK isoenzyme (B-CK) is the only CK isoenzyme in rooster seminal plasma, while three isoenzymes, cytosolic B-CK, sarcomeric mitochondrial CK (Mib-CK), and a variant of ubiquitous Mi-CK (‘Mia-CK variant’), are found in rooster spermatozoa. These three isoenzymes are localized in different regions of the sperm cell. B-CK and Mib-CK were localized along the entire sperm tail and in the mitochondria-rich midpiece, respectively. The ‘Mia-CK variant’, on the other hand, was found predominantly at the head-midpiece boundary, in a non-uniform manner in the midpiece itself and, surprisingly, at the distal end of the sperm tail as well as at the acrosome. Several lines of evidence show that the ‘Mia-CK variant’ shares some characteristics with purified Mia-CK from chicken brain, but also displays distinctive features. This is the first evidence for two different Mi-CK isoenzymes occurring in one cell and, additionally, for the co-expression of Mib-CK and cytosolic brain-type B-CK in the same cell. The relevance of these findings for sperm physiology and energetics is discussed.

Creatine kinase in non-muscle tissues and cells

Over the past years, a concept for creatine kinase function, the 'PCr-circuit' model, has evolved. Based on this concept, multiple functions for the CK/PCr-system have been proposed, such as an energy buffering function, regulatory functions, as well as an energy transport function, mostly based on studies with muscle. While the temporal energy buffering and metabolic regulatory roles of CK are widely accepted, the spatial buffering or energy transport function, that is, the shuttling of PCr and Cr between sites of energy utilization and energy demand, is still being debated. There is, however, much circumstantial evidence, that supports the latter role of CK including the distinct, isoenzyme-specific subcellular localization of CK isoenzymes, the isolation and characterization of functionally coupled in vitro microcompartments of CK with a variety of cellular ATPases, and the observed functional coupling of mitochondrial oxidative phosphorylation with mitochondrial CK. New insight concerning the functions of the CK/PCr-system has been gained from recent M-CK null-mutant transgenic mice and by the investigation of CK localization and function in certain highly specialized non-muscle tissues and cells, such as electrocytes, retina photoreceptor cells, brain cells, kidney, salt glands, myometrium, placenta, pancreas, thymus, thyroid, intestinal brush-border epithelial cells, endothelial cells, cartilage and bone cells, macrophages, blood platelets, tumor and cancer cells. Studies with electric organ, including in vivo 31P-NMR, clearly reveal the buffer function of the CK/PCr-system in electrocytes and additionally corroborate a direct functional coupling of membrane-bound CK to the Na+/K(+)-ATPase. On the other hand, experiments with live sperm and recent in vivo 31P-NMR measurements on brain provide convincing evidence for the transport function of the CK/PCr-system. We report on new findings concerning the isoenzyme-specific cellular localization and subcellular compartmentation of CK isoenzymes in photoreceptor cells, in glial and neuronal cells of the cerebellum and in spermatozoa. Finally, the regulation of CK expression by hormones is discussed, and new developments concerning a connection of CK with malignancy and cancer are illuminated. Most interesting in this respect is the observed upregulation of CK expression by adenoviral oncogenes.

Elevated serum levels of creatine kinase BB in autosomal dominant osteopetrosis type II--a family study

A markedly elevated BB isoenzyme fraction of serum creatine kinase was noted in four male siblings and correlated with typical radiographic findings of autosomal dominant osteopetrosis Type II (ADO Type II). Patients with other sclerosing bone diseases had no elevation of CK-BB. The precision of the electrophoretic mobility patterns and correlation by I-125 tagged radioimmunoassay method confirms that this is CK-BB. We postulate that the dysfunctional and/or immature osteoclasts in ADO are more dependent on CK-BB than on the usual tricarboxylic acid cycle for the production of energy. The correlation of marked elevation of serum CK-BB with radiographic evidence of ADO Type II may prove to be of value as a biologic marker in the early diagnosis of the illness and lead to better understanding of the metabolism of bone.

Phosphocreatine, an intracellular high-energy compound, is found in the extracellular fluid of the seminal vesicles in mice and rats

High levels of phosphocreatine, a compound known to serve as an intracellular energy reserve, were found in the fluid contained in seminal vesicle glands. The concentrations of phosphocreatine in the extracellular fluid in the mouse and rat were found to be 5.6 +/- 1.6 and 2.2 +/- 0.8 mumol/g, respectively, which are higher than the intracellular levels reported for smooth muscles. The creatine concentrations in the seminal vesicular fluid from these two species were 22.8 +/- 3.1 and 13.0 +/- 5.3 mumol/g, respectively. These creatine levels are approximately 100 and 65 times higher than the creatine levels in mammalian blood. Smaller amounts of ATP (phosphocreatine/ATP ratio of 20-40) and traces of ADP were also found. Comparison of the pattern of distribution of macromolecules (proteins and DNA) with the distribution of phosphocreatine between the cells and the fluid of the seminal vesicle indicates that cell lysis did not account for the phosphocreatine in the seminal vesicle fluid. Rather, the available evidence strongly suggests that this high-energy compound is actively secreted. We found that in the testes, the sperm are exposed to the highest known creatine concentration in any mammalian tissue studied. Based on these results and other recent reports, we propose that the extracellular phosphocreatine, ATP, and creatine are involved in sperm metabolism.

The BB-isoenzyme is a major component of creatine kinase in skin blister fluid

We measured levels of creatine kinase and its three isoenzymes in serum and blister fluid from 16 healthy volunteers. The BB-isoenzyme was found to be the predominant form in blister fluid while only the MM isoenzyme was found in serum. The levels of BB-isoenzyme in blister fluid decreased as the blisters aged. The source of BB-isoenzyme in blister fluid is most probably the damaged epidermis.

Enzymatic and electrolytic profiles of human semen

Chemical parameters comprising urea and creatinine nitrogen, cations (Na+, K+, and Ca2+), chloride, phosphorus, protein, cholesterol and enzymes, aminotransferases, alkaline and prostatic acid phosphatases, gamma-glutamyltransferase, creatine kinase, and lactate dehydrogenase were ascertained for semen from groups A (vasectomized), B (oligospermic), and C (normospermic) men, 19 to 55 years of age. Of the parameters, the vasectomized group underwent definite depressions in potassium ion, alkaline phosphatase, aspartate aminotransferase, gamma-glutamyltransferase, and lactate dehydrogenase as compared with the normospermic group; the last three enzymes and, possibly, the urea-creatinine ratio were decreased for the oligospermic group vs. the normospermic men. In the comparison of groups A and B, only the decrements in alanine aminotransferase and lactate dehydrogenase were statistically significant. In corroboration of past reports, CK-BB comprised the main isoenzyme of semen creatine kinase.

Correlation between sperm creatine phosphokinase activity and sperm concentrations in normospermic and oligospermic men

Toward the development of biochemical probes for the assessment of sperm function we have measured the activities of sperm creatine-N-phosphotransferase (CPK). There was a highly significant inverse correlation (P less than 0.001 in all comparisons) between sperm CPK activities and sperm concentrations in specimens of normospermic and oligospermic men with greater than 30 million sperm/ml (0.106 +/- 0.01 SEM, N = 90, expressed as CPK U/100 million sperm), 20-30 million sperm/ml (0.333 +/- 0.07 SEM, N = 30) and 10-20 million sperm/ml (0.583 +/- 0.12 SEM, N = 30) when compared with the CPK values of the less than 10 million/ml specimens (2.242 +/- 0.46 SEM, N = 30). Furthermore, the distribution of CPK activities within these four groups showed that 96%, 67%, 43%, and 4% of the samples, respectively, were in the less than 0.250 CPK U/100 million sperm normal range (mean + 2 SD of the greater than 30 million sperm/ml group). However, there was no relationship between sperm CPK activities and the values of sperm motility (P greater than 0.15) or morphology (P = 0.38) in the samples. The migrated sperm fractions (significantly improved in motility and velocity parameters) showed CPK activities lower than the initial semen specimens (P less than 0.01, N = 150). In fact, in some oligospermic men the CPK activities of the migrated sperm fractions were within the range of normospermic samples.(ABSTRACT TRUNCATED AT 250 WORDS)