N-Lactoyl Amino Acids: Emerging Biomarkers in Metabolism and Disease.

N-lactoyl amino acids (Lac-AA) form an emerging class of metabolites that have gained significant attention in recent years due to their ubiquitous presence in different biological systems and potential roles in various biochemical processes. This narrative review aims to provide a comprehensive overview of the current understanding of Lac-AA, emphasising their biosynthesis, physiological roles, and potential implications in various diseases. We discuss the discovery of Lac-AA as signalling molecules, and their involvement in exercise-induced appetite suppression, energy metabolism, and other pathways. This review explores the complex relationship between Lac-AA and various pathological conditions, including mitochondrial disorders, type 2 diabetes, phenylketonuria, cancer, and rosacea. We also examine the interplay between Lac-AA and the gut microbiota, as well as their association with metformin treatment. Furthermore, we address the ongoing debate regarding whether Lac-AA are merely reflections of lactate and amino acid levels or independent signalling molecules. This review synthesises the latest research findings, highlights the significance of Lac-AA in metabolic research, and identifies promising avenues for future investigation in this rapidly evolving field.