Metabolomic Insights into Reprogrammed Caffeine Metabolism in the Hippocampus of Myofascial Pain Syndrome Rats

The objective of this investigation was to examine the histopathological alterations in the rat hippocampus induced by myofascial trigger points (MTrPs), assess hippocampal neuronal excitability by measuring c-fos protein expression, and Non-targeted metabolomics was employed to profile hippocampal metabolite variations and elucidate the pathophysiological mechanisms underlying myofascial pain syndrome (MPS).

Male SD rats were divided into MTrPs group (n=6) and control group (n=6). The MTrPs model was induced through localized blunt impact to the gastrocnemius muscle followed by repetitive eccentric exercise. Successful modeling was confirmed by the presence of palpable taut bands (TBs), along with measurements of mechanical and thermal withdrawal thresholds (MWT and TWL), and electromyographic (EMG) recordings. We assessed hippocampal neuropathological damage using HE and Nissl staining and measured c-fos protein expression to reflect hippocampal neuronal activity. Metabolomics analysis with statistical variable analysis helped distinguish affected individuals from controls.

TB detection, MWT, TWL and EMG confirmed successful model establishment. Pathological evaluation indicated a disorganized structure and neuronal injury in the CA1 region of the hippocampus in MTrPs rats, alongside elevated c-fos protein expression, suggesting heightened neuronal excitation and potential central sensitization. Metabolomic profiling revealed 79 differentially expressed metabolites (VIP > 1, P < 0.05) in MPS rats compared with controls. Further KEGG enrichment analysis demonstrated that 26 of these metabolites were involved in 20 metabolic pathways, with caffeine metabolism being notably affected (P = 0.000444), highlighting its critical role in the pathophysiology of MPS.

MPS causes pathological damage to the hippocampus, and increased c-fos protein expression suggests possible central sensitization in MPS rats. Metabolomics analysis revealed significant hippocampal changes, particularly reduced caffeine metabolism, underscoring potential central mechanisms in MPS. This study enhances our understanding of MPS etiology based on hippocampal pathology and provides potential biological markers.