15d-PGJ2

Understanding the metabolic pathways and kinetics of prostaglandins is essential for elucidating their biological functions and therapeutic potential. Prostaglandin D₂ (PGD₂), a somnogen in the brain, undergoes nonenzymatic conversion into J-series prostaglandins, including 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂). PGD₂ is possibly transported by lipocalin-type prostaglandin D synthase (L-PGDS), which may also influence its metabolism. However, the kinetics of PGD₂ metabolism, particularly in the context of the PGD₂-L-PGDS complex, remains poorly understood. In this study, we investigated the effects of L-PGDS on the dehydration reaction of PGD₂ in an aqueous buffer using real-time NMR spectroscopy, complemented by UV-visible absorption spectroscopy. In the absence of L-PGDS, 15d-PGJ₂ was formed over several tens of hours via the transient accumulation of prostaglandin J₂ and 15-deoxy-Δ^12,14-prostaglandin D₂ as intermediates. In contrast, the PGD₂-L-PGDS complex converted to a L-PGDS-15d-PGJ₂ complex, without exhibiting detectable reaction intermediates or byproducts, at a time scale of 3 h. We also determined the crystal structure of the L-PGDS-15d-PGJ₂ complex, demonstrating that the covalent bond is formed between Cys65 of L-PGDS and the carbon atom at the C9 position of 15d-PGJ₂. These results, combined with the fact that L-PGDS is present in excess relative to PGD₂ and 15d-PGJ₂ in the arachnoid membrane, suggest that most PGD₂ exists in the L-PGDS-bound form and that 15d-PGJ₂ generated through dehydration is rapidly and effectively sequestered by L-PGDS. Thus, L-PGDS may function as a scavenger for 15d-PGJ₂, mitigating its potential deleterious effects in the arachnoid membrane. This real-time NMR-based approach provides a useful platform for studying the metabolism behavior of other prostaglandins under physiologically relevant conditions.

Metabolomics was first applied to explore the formation pathway and regulatory factors for advanced glycation end products (AGEs) in preserved egg yolk (PEY) during pickling. Most reactions that contributed to formation of AGEs, including oxidation and/or degradation of matrix/precursors and Maillard reaction, occurred primarily in PEY in early stage, and lipid oxidation occurred prior to protein oxidation. Additionally, the formation of N^ε-carboxymethyl-lysine (CML) in PEY was mainly attributed to glyoxal derived from D-glucuronic acid in early stage based on the correlation between metabolites and AGEs. Reactive oxygen radicals from oxidized lipids also promoted the enrichment of CML and N^ε-carboxymethyl-lysine (CEL). Moreover, during later stage, the accumulation of CEL was enhanced through methylglyoxal from Schiff bases, and acidic compounds could inhibit AGEs via hindering Maillard reaction. This manuscript pioneered the application of metabolomics to reveal the formation pathway of AGEs, and will provide new perspective on AGEs formation in foods.