(147) Aging and Fertility: L-Homocysteine and Methyloctadecanoyl-CoA as Key Discriminators of Metabolic Aging in Human Spermatozoa.

Md S. Khan^1,2; Ishfaq A. Sheikh¹; Taha A. A. Hamoda³; Mohammad Imran Khan⁴; Arif Mohammed⁵; Abrar Ahmad²; Erdogan Memili⁶; Mohd A. Beg1,*

¹King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia.

²Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia.

³Department of Urology, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia.

⁴Research Center, King Faisal Specialist Hospital & Research Center, Jeddah, Saudi Arabia.

⁵Department of Biological Sciences, College of Science, University of Jeddah, Jeddah, Saudi Arabia.

⁶Cooperative Agricultural Research Center, College of Agriculture and Human Sciences, Prairie View A&M University, Prairie View, TX, United States.

*Correspondence: E-mail: mabeg51@gmail.com ; Tel: +966-552822451.

Abstract Text:

Advancing age is a significant contributor to fertility decline in men. Aging is an evolving challenge for reproductive health, considering the global trends towards delayed parenthood and older couples increasingly seeking fertility interventions. However, the progress in this area is constrained by a limited understanding of the molecular mechanisms underlying sperm dysfunction with age. This study involved a comprehensive metabolomic profiling of spermatozoa from healthy, fertile Saudi men categorized into three age groups: young adult (21–30 years; n = 6), late adult (31–40 years; n = 7), and advanced age (41–51 years; n = 5). Gradient purified spermatozoa were analyzed using LC-MS/MS. The metabolite data were processed using XCMS and annotated using the Human Metabolome Database. Statistical and functional analyses were performed using MetaboAnalyst-Pro. Across all samples, 380 metabolites were identified, with 164 showing statistically significant differences (P < 0.05) among age groups. Multivariate analyses including principal component analysis, partial least squares discriminant analysis, and random forest classification demonstrated distinctly separated clustering patterns, particularly between the young adult group and advanced age group, highlighting distinct age-associated alterations in the sperm metabolome. Notably, L-homocysteine was nearly undetectable in all spermatozoa samples from the advanced age group, contrasting with its high abundance in young adult group. Whereas methyloctadecanoyl-CoA was markedly elevated in the advanced age group contrasting with nearly no detection in the young adult group suggesting the potential of these metabolites as discriminative metabolic markers of sperm aging. L-homocysteine, a sulfur-containing amino acid from methionine metabolism, is critical for redox balance and methylation. As a precursor to cysteine via the transsulfuration pathway, L-homocysteine is essential for glutathione synthesis, and its depletion may impair antioxidant defenses, increase oxidative stress, and disrupt mitochondrial function. Furthermore, the depletion of L-homocysteine could disrupt methylation-dependent control of gene expression, affecting processes such as cell growth and differentiation. Methyloctadecanoyl-CoA is a long-chain acyl-CoA derived from fatty acid metabolism and functions as a key intermediate in lipid metabolism. Acyl-CoAs have roles in β-oxidation in mitochondria and peroxisomes, as well as the synthesis of complex lipids such as phospholipids and cholesteryl esters. Beyond energy metabolism, acyl-CoAs contribute to diverse cellular processes including post-translational protein acylation, enzymatic regulation, intracellular trafficking, and membrane dynamics.  The functional implications of this age-related accumulation of methyloctadecanoyl-CoA remain unclear, however, excessive acyl-CoA levels have been associated with lipotoxicity and impaired cellular function. Collectively, these findings implicate altered L-homocysteine metabolism and increased methyloctadecanoyl-CoA abundance in the pathophysiology of age-related sperm dysfunction and underscore their potential as biomarkers of male reproductive aging warranting further investigation.

Acknowledgments: The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia for funding this research work through project number 1132.