Hypothesis

Chronic analgesic use blunts the glucocorticoid‑mediated increase in intestinal ASBT expression, reducing bile acid reabsorption and impairing FXR/TGR5 signaling that normally counters inflammation‑driven metabolic dysfunction.

Mechanistic Basis

Inflammatory pain triggers a homeostatic stress response: glucocorticoids rise and upregulate ileal ASBT by ~1.34‑fold, preserving bile acid pools for FXR and TGR5 activation 3. These receptors stimulate GLP‑1 release, improve glucose tolerance, and promote energy expenditure 4. NSAIDs and opioids inhibit glucocorticoid synthesis or signaling, thereby preventing this compensatory ASBT increase. Consequently, bile acid flux to the distal intestine falls, FXR/TGR5 activity drops, and the anti‑metabolic effects of prolonged IL‑6 and TNF‑α signaling (observed in older adults with pain) are unopposed 1, 2.

Testable Predictions

1. In rodent models of chronic inflammatory pain, co‑administration of a glucocorticoid receptor agonist will restore ASBT mRNA and protein levels despite analgesic treatment, whereas a glucocorticoid antagonist will abolish the analgesic‑induced ASBT suppression.
2. Human subjects using daily NSAIDs for >6 months will show reduced fasting serum bile acid concentrations and lower FXR target gene expression (e.g., FGF19) in ileal biopsies compared with age‑matched controls not on analgesics.
3. Metabolically, analgesic‑treated individuals will exhibit higher HOMA‑IR and lower GLP‑1 response to a mixed‑meal tolerance test, effects that are rescued by exogenous bile acid supplementation (e.g., taurocholic acid) in a crossover trial.

Falsifiability

If longitudinal analgesic use does not alter ASBT expression, bile acid pool size, or FXR/TGR5 downstream signaling, or if correcting bile acid deficiency fails to improve metabolic parameters, the hypothesis would be refuted.