142 Metabolomic analysis of fresh and frozen bovine seminal plasma: A preliminary study

Sperm cryopreservation is essential for assisted reproduction; however, freezing induces biochemical and physical damage to the sperm membrane structures, negatively affecting sperm fertilising ability (Castro et al. 2006 J. Anim. Sci. Biotechnol. 5, 1-9). Metabolomics is the study of small molecules, commonly known as metabolites, which play essential roles in biological systems. Emerging research in the field of metabolomics showed a potential role in identifying male fertility biomarkers (Bieniek et al. 2016 Asian J. Androl. 18, 426-433). Metabolites present in the seminal plasma play several roles related to sperm motility, sperm membrane protection from oxidative stress, and regulation of metabolic activity (Therien et al. 1995 Biol. Reprod. 52, 1372-1379). However, the extent of metabolite changes in seminal plasma during cryopreservation is still not well known. Therefore, the aim of this study was to evaluate the differences of the seminal plasma metabolites between fresh and frozen bovine sperm. Four ejaculates from eight Holstein (Bos taurus) bulls (4-6 years age) maintained at an authorised national semen collection center (Centro Tori Chiacchierini, Civitella D’Arna, Italy) under uniform management conditions were collected weekly using an artificial vagina (IMV Technologies). Each ejaculate was split into two aliquots (one fresh and one frozen) at −20°C for at least 2h. Seminal plasma from fresh (immediately) and frozen-thawed semen was separated from sperm by centrifugation (1600×g for 10min), and supernatants were then transferred to a 2-mL tube and stored at −80°C until use. After methanol extraction of metabolites, samples were centrifuged at 6400×g for 30min at 4°C, and supernatants were analysed using a liquid chromatography-mass spectrometry (LC-MS; Agilent 1260 HPLC; Agilent Technologies) system with an autosampler and a binary pump coupled to an Agilent Q-TOF 6540 (Agilent Technologies). Univariate analyses of the data were performed using bioinformatics approaches. The differences between fresh and frozen seminal plasma samples were analysed using a paired Student's t-test. Twenty-three metabolites were found in both fresh and frozen seminal plasma samples, out of which eight were significantly different (P<0.05) between the two groups; among these, hypotaurine, ceramide, and isoindoline were identified. In particular, hypotaurine and ceramide were downregulated, whereas isoindoline was upregulated in fresh samples compared with frozen samples. To the best of our knowledge, this is the first study to identify seminal plasma metabolites in fresh and frozen samples by using LC-MS. In order to ensure the reliability and accuracy of results, the validation of the method used in the analysis of biosamples is still in progress, as is the evaluation of the metabolic profile in sperm cells. In conclusion, the results of this study suggest that LC-MS can be a promising screening tool to detect metabolites potentially associated with bull fertility.

Factors affecting the production of Trichoderma harzianum secondary metabolites during the interaction with different plant pathogens

AIMS

Strains of Trichoderma spp. produce numerous bioactive secondary metabolites. The in vitro production and antibiotic activities of the major compounds synthesized by Trichoderma harzianum strains T22 and T39 against Leptosphaeria maculans, Phytophthora cinnamomi and Botrytis cinerea were evaluated. Moreover, the eliciting effect of viable or nonviable biomasses of Rhizoctonia solani, Pythium ultimum or B. cinerea on the in vitro production of these metabolites was also investigated.

METHODS AND RESULTS

T22azaphilone, 1-hydroxy-3-methyl-anthraquinone, 1,8-dihydroxy-3-methyl-anthraquinone, T39butenolide, harzianolide, harzianopyridone were purified, characterized and used as standards. In antifungal assays, T22azaphilone and harzianopyridone inhibited the growth of the pathogens tested even at low doses (1-10 microg per plug), while high concentrations of T39butenolide and harzianolide were needed (>100 microg per plug) for inhibition. The in vitro accumulation of these metabolites was quantified by LC/MS. T22azaphilone production was not enhanced by the presence of the tested pathogens, despite its antibiotic activity. On the other hand, the anthraquinones, which showed no pathogen inhibition, were stimulated by the presence of P. ultimum. The production of T39butenolide was significantly enhanced by co-cultivation with R. solani or B. cinerea. Similarly, viable and nonviable biomasses of R. solani or B. cinerea increased the accumulation of harzianopyridone. Finally, harzianolide was not detected in any of the interactions examined.

CONCLUSIONS

The secondary metabolites analysed in this study showed different levels of antibiotic activity. Their production in vitro varied in relation to: (i) the specific compound; (ii) the phytopathogen used for the elicitation; (iii) the viability of the elicitor; and (iv) the balance between elicited biosynthesis and biotransformation rates.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of cultures of phytopathogens to enhance yields of Trichoderma metabolites could improve the production and application of novel biopesticides and biofertilizers based on the active compounds instead of the living microbe. This could have a significant beneficial impact on the management of diseases in crop plants.

Major secondary metabolites produced by two commercial Trichoderma strains active against different phytopathogens

AIMS

Trichoderma harzianum strains T22 and T39 are two micro-organisms used as active agents in a variety of commercial biopesticides and biofertilizers and widely applied amongst field and greenhouse crops. The production, isolation, biological and chemical characterization of the main secondary metabolites produced by these strains are investigated.

METHODS AND RESULTS

Of the three major compounds produced by strain T22, one is a new azaphilone that shows marked in vitro inhibition of Rhizoctonia solani, Pythium ultimum and Gaeumannomyces graminis var. tritici. In turn, filtrates from strain T39 were demonstrated to contain two compounds previously isolated from other T. harzianum strains and a new butenolide. The production of the isolated metabolites was also monitored by liquid chromatography/mass spectrometry during in vitro interaction with R. solani.

CONCLUSIONS

This paper reports the isolation and characterization of the main secondary metabolites obtained from culture filtrates of two T. harzianum strains and their production during antagonistic interaction with the pathogen R. solani.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first work on secondary metabolites produced by the commercially applied strains T22 and T39. Our results provide a better understanding of the metabolism of these fungi, which are both widely used as biopesticides and/or biofertilizers in biocontrol.

Development of a stable isotope dilution assay for an accurate quantification of protein-bound N(epsilon)-(1-deoxy-D-fructos-1-yl)-L-lysine using a (13)C-labeled internal standard

Syntheses of the labeled Amadori compound [(13)C(6)]-N(epsilon)-(1-deoxy-D-fructos-1-yl)-L-lysine ([(13)C(6)]-DFLys) and the labeled glycated tetrapeptide Ala-[(13)C(6)]-DFLys-Leu-Gly are presented. The compounds were used in the development of stable isotope dilution assays for the quantification of the degree of glycosylation of bovine serum albumin treated for 20 min at 95 degrees C in the presence of glucose. The experiments revealed that the use of the labeled standards in combination with LC/MS allowed the exact quantification of protein-bound DFLys with the high recovery rate of 95% (at a spike level of 150 nmol/mg of protein) and a low detection limit of 5 nmol/mg of protein. The data revealed, however, that DFLys is significantly degraded during the enzymic hydrolysis of the protein backbone generally needed in the quantification procedure and, furthermore, incomplete digestion of the protein was observed. Both sources of errors were clearly overcome by using in particular the labeled peptide as the internal standard.

Convenient synthesis of lactuloselysine and its use for LC-MS analysis in milk-like model systems

The synthesis of the Amadori product lactuloselysine [N(epsilon)-(1-deoxy-D-lactulosyl-1)-L-lysine] was obtained starting from FMOC-lysine-OH (N(alpha)-9-fluorenylmethoxy-carbonyl-N(epsilon)H(2)-L-lysine-OH) and lactose. Compound identity was confirmed by MALDI-ToF, electrospray, and NMR analysis. A selective LC-MS procedure which allowed the detection of lactuloselysine up to 10 ng mL(-)(1) was set up and used to follow the formation of the compound in a lactose-lysine model system; quantification of this molecule after complete enzymatic hydrolysis of whey-proteins from milk samples was also performed.