Serum amyloid P component: a new biomarker for low sperm concentration?

Serum amyloid P component (SAP) is present in seminal plasma, on spermatozoa, and in different tissues of the male reproductive tract, but its function is not known. The aims of this study were to determine if the concentration of SAP in seminal plasma is associated with commonly assessed semen parameters and to investigate if SAP could be a new, indirect biomarker for these parameters. In a cross-sectional study of 203 young volunteers, the concentration of SAP in seminal plasma was measured with a in-house developed enzyme-linked immunosorbent assay. Scatter plots, Pearson's correlation coefficients (r), and linear regression models were produced, and SAP showed a statistically significant correlation with sperm concentration (r = 0.75), sperm number (r = 0.68), semen volume (r = -0.19), progressive sperm motility (r = 0.24), and sperm immotility (r = -0.20). When the study group was dichotomized, SAP could be used to discriminate samples with a sperm concentration < or ≥5 × 106 ml-1, 15 × 106 ml-1, or 40 × 106 ml-1, and in receiver operating characteristic curves, the corresponding areas under the curves were 0.97, 0.93, and 0.82, respectively, with P < 0.001 for all three cutoff values studied. The concentration of SAP in seminal plasma showed a strong, positive correlation with the concentration of spermatozoa in semen. SAP may be used as a new indirect potential biomarker for sperm concentration in fresh and in frozen, stored samples. In addition, it is envisaged that the assay could be developed into a home fertility test to differentiate between a low and a normal sperm concentration.

Determination of serum amyloid P component in seminal plasma and correlations with serum hormone levels in young, healthy men.

Serum amyloid P component (SAP) belongs to the pentraxin family of proteins. SAP is evolutionary conserved, and involved in amyloidosis, innate immunity, inflammation, and apoptosis. We have previously described SAP in the male reproductive tract, where it occurs in seminal fluid, on spermatozoa, and in epididymal, seminal vesicle, and prostate tissue. In the present investigation, our aim was to characterize SAP in male reproduction. In short, we developed and evaluated an immunoassay, analysed the concentration of SAP in seminal plasma and serum in samples from healthy men (N = 203), and studied hormonal regulation. SAP in seminal plasma showed a positively skewed distribution and a median concentration of 1.01 mg/L (inter quartile range [IQR] 0.56-1.65 mg/L). SAP in serum had a Gaussian distribution and a median concentration of 40.5 mg/L (IQR 34.2-49.2 mg/L). Furthermore, SAP concentrations in seminal plasma were not correlated with serum concentrations of SAP, testosterone, sex hormone-binding globulin (SHBG), the testosterone/SHBG ratio, inhibin B, or estradiol. Only a weak negative correlation was found between seminal plasma SAP and serum levels of follicle-stimulating hormone (FSH) (Spearman's rho -0.159; p = 0.023) and luteinizing hormone (LH) (Spearman's rho -0.162; p = 0.021). In conclusion, all men investigated had measurable SAP levels in seminal plasma and in serum. SAP concentrations were 40 times lower in seminal fluid than in serum, and there was no correlation between those two variables. It seems that hormonal regulation is not the major pathway regulating seminal plasma SAP, and seminal plasma SAP and serum SAP are not co-regulated.

The pentraxin serum amyloid P component is found in the male genital tract and attached to spermatozoa.

Serum amyloid P component (SAP) belongs to the pentraxin family of proteins, members of which are characterized by radial pentameric structure and calcium-dependent ligand binding. SAP is present in all types of amyloidosis and has been shown to bind to several ligands, but the physiological function of this protein has not been fully elucidated. The present study identified and characterized SAP in human semen and immunolocalized it to the male reproductive tract. SAP was also detected in seminal plasma by immunoblotting and purification by affinity chromatography followed by mass spectrometry. According to electroimmunoassay, the concentration of SAP in semen is approximately 2 mg/L, and flow cytometry revealed SAP attached to the surface of spermatozoa. Moreover, immunohistochemistry showed positive staining of spermatozoa, subsets of epithelial cells, and the stroma of accessory male genital glands and testis. Presence of mRNA supports local production of SAP, as shown with reverse transcription polymerase chain reaction. We identified SAP in a new setting - the human male reproductive system. SAP was detected on ejaculated spermatozoa, in seminal plasma and in tissue sections from the male reproductive tract. Further functional studies are needed to explain the role of SAP in human reproduction.