Isolation and identification of N-terminally extended forms of 5-oxoprolylglutamylprolinamide (Glp-Glu-Pro-NH2), a thyrotropin-releasing-hormone (TRH)-like peptide present in human semen

TRH-like peptides

TRH-like peptides are characterized by substitution of basic amino acid histidine (related to authentic TRH) with neutral or acidic amino acid, like glutamic acid, phenylalanine, glutamine, tyrosine, leucin, valin, aspartic acid and asparagine. The presence of extrahypothalamic TRH-like peptides was reported in peripheral tissues including gastrointestinal tract, placenta, neural tissues, male reproductive system and certain endocrine tissues. Work deals with the biological function of TRH-like peptides in different parts of organisms where various mechanisms may serve for realisation of biological function of TRH-like peptides as negative feedback to the pituitary exerted by the TRH-like peptides, the role of pEEPam such as fertilization-promoting peptide, the mechanism influencing the proliferative ability of prostatic tissues, the neuroprotective and antidepressant function of TRH-like peptides in brain and the regulation of thyroid status by TRH-like peptides.

Gonadins, a novel family of glutamyl-tripeptide amides present in the testis with activity in the hypophyseal–gonadal axis

Here we present a new family of endogenous peptides identified in rat testis with structure of glutamyl-tripeptide amides which are also present in plasma. These peptides have different activities in the hypophyseal-gonadal axis. Evidences showing the endocrine activities of some of the peptides are presented. In this communication we demonstrate the presence of peptides with a common structure Glu-X-Pro amide, where X can be one of the following amino acids: glutamic acid, glutamine, aspartic acid, asparagine, phenylalanine or tyrosine. These peptides have been identified by a series of chromatographies and by mass spectrometry. Some of the peptides where tested for its biological activity observing that subcutaneous administration of the peptides Glu-Glu-Pro amide, Glu-Gln-Pro amide and Glu-Phe-Pro amide were able to reduce plasma levels of testosterone and luteinizing hormone (LH) without modification of the levels of follicle stimulating hormone (FSH). The peptide Glu-Asp-Pro amide, however, produced an increase in the levels of testosterone without modifying LH or FSH levels. It is proposed that the glutamyl-tripeptide amides that reduce the levels of testosterone and LH are released from the testis and act in the pituitary via circulation in an endocrine manner. The specific inhibition of LH release is similar to that produced by inhibin on FSH release. On the other hand the peptide that increases the levels of testosterone is produced in the testis and seems to act directly in the testis in a paracrine or autocrine manner. It is proposed here a new mechanism of regulation of hypophyseal-gonadal axis, a negative feedback exerted by the glutamyl-tripeptide amides in the pituitary. Also it is proposed the generic name of gonadins for the novel family of glutamyl-tripeptide amides. We suggest that gonadins could be used in the future as drugs for treatment of different endocrine disorders, hormone-dependent cancer and as contraceptives.

A comprehensive characterization of the peptide and protein constituents of human seminal fluid

BACKGROUND

Knowledge of the peptide and protein components of seminal fluid and their role in prostate diseases including benign prostatic hyperplasia and prostate carcinoma is scant. We have undertaken a proteomic analysis of semen as a forerunner to identifying sensitive and specific diagnostic markers of prostatic diseases; to aid in improved therapeutic intervention; and, to enhance our understanding of prostate health and disease.

METHODS

Peptide and protein components of pooled human seminal fluid (n = 5) were separated by gel electrophoresis (1D and 2D) and identified by either matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) or capillary liquid chromatography tandem mass spectrometry (LC-MS/MS).

RESULTS

Analysis by two-dimensional electrophoresis (2DE) established that there were multiple post-translational variants of the majority of the proteins. Hormones, growth factors and bioactive peptides were detected and identified.

CONCLUSIONS

We have identified over 100 protein and peptide components of normal human seminal fluid.

Characterization of a circulating N-extended form of the thyrotropin-releasing hormone-like peptide pGlu-Glu-Pro amide in human plasma

The TRH-like peptides pGlu-Glu-Pro amide, pGlu-Phe-Pro amide, and pGlu-Gln-Pro amide were isolated and identified some years ago, and these peptides have been proven to be present in many tissues and fluids. The presence of TRH-like immunoreactivity distinct from TRH in blood has been observed previously. In the present study, the presence of N-extended forms of TRH-like peptides in plasma has been investigated. Peripheral blood samples of human, rat, and rabbit were obtained and plasma was extracted. The peptides were separated in several steps of chromatography, including gel filtration, cation and anion exchange, and HPLC. The concentrations of the TRH-like peptides in the column fractions were measured by RIA with TRH antibody. The N-extended forms of TRH-like peptides were determined by RIA after trypsin digestion. In human plasma it was observed an N-extended form of TRH-like peptides in substantial concentration. After trypsin and heating, the N-extended forms of TRH-like peptides were rechromatographed on Sephadex G-50. This showed that the TRH-like peptides released have a similar size to TRH. The peptides were then separated by cation exchange chromatography, and the major fraction was unretained, indicating a neutral or acidic nature. Part of the unretained fraction was then chromatographed on anion exchange column in which the major fraction was retained, demonstrating the acidic nature of the peptides. Similar results have been observed in rat and rabbit. The other part of the unretained fraction from cation exchange chromatography of human plasma was purified on HPLC. The results demonstrated that the major component observed by HPLC cochromatographed with synthetic pGlu-Glu-Pro amide. This study represents the first demonstration of a circulating N-extended form of any TRH-like peptide.

Molecular cloning in the marmoset shows that semenogelin is not the precursor of the TRH-like peptide pGlu-Glu-Pro amide

Two peptides with similar structures to thyrotropin-releasing hormone (TRH), pGlu-Glu-Pro amide and pGlu-Phe-Pro amide, have been identified in human seminal fluid and it has been shown that one of these peptides, pGlu-Glu-Pro amide, has the ability to increase the capacitation of sperm cells, consistent with a role in fertility. In order to select a species in which there is a high degree of expression of the genes that code for 'TRH-like' peptides, we have determined the levels of these peptides in the prostate, pancreas and thyroid of a range of species including rat, rabbit, ox, marmoset, macaque and man. The peptides were extracted from the tissues and purified before determination by RIA with TRH antibody. In addition, trypsin digestion and TRH RIA was used to investigate the presence of N-extended forms. The highest concentrations of TRH-immunoreactive peptides were found in the tissues of the marmoset, Callithrix jacchus. Ion-exchange chromatography demonstrated that marmoset thyroid contained principally authentic TRH, the pancreas contained both TRH and TRH-like peptides while the prostate contained TRH-like peptides alone. Further purification by HPLC showed that the main TRH-immunoreactive peptide in marmoset prostate was pGlu-Glu-Pro amide and a second component was identified as pGlu-Phe-Pro amide. The results indicate that the biosynthesis of these peptides could be studied to advantage in the marmoset. The biosynthetic precursors of the TRH-like peptides have not been identified. To examine whether pGlu-Glu-Pro amide might originate from semenogelin, we determined the sequence of semenogelin in the marmoset. It exhibited a high degree of homology with human semenogelin-I, but in place of the Lys-Gln-Glu-Pro sequence that might give rise to pGlu-Glu-Pro amide, marmoset semenogelin possessed the sequence Ser-Gln-Asp-Gln which cannot serve as a precursor for a TRH-like peptide. Further evidence was obtained by Northern blot analysis of a range of marmoset tissues. The results showed that semenogelin is not present in marmoset prostate. It is concluded that pGlu-Glu-Pro amide originates from a precursor distinct from semenogelin, both in marmoset and in man.