Background/Objectives: This study examined whether dexamethasone (Dex) and decanoic acid (DA) exert complementary effects on inflammatory signaling, catabolic gene expression, and peroxisome proliferator-activated receptor gamma (PPARγ) activation in human chondrocytes. Methods: Two donor-specific primary human chondrocyte models, each derived from a single knee donor, were used, in which cells were treated with Dex (≤0.1 µM), DA (≤500 µM), or combinations thereof. Acute Interleukin-1β(IL-1β)-induced PGE₂ release was evaluated in normal donor cells, whereas prolonged transcriptional responses and PPARγ DNA-binding activity were evaluated in OA donor cells. IL-1β-induced prostaglandin E₂ (PGE₂) release was measured by competitive ELISA after 24 h. Glyceraldehyde-3-phosphate dehydrogenase-normalized transcription of Collagen type II alpha 1, Collagen type I alpha 1, Aggrecan, SRY-Box Transcription Factor 9, Runt-Related Transcription Factor 2, and Matrix Metalloproteinase 13 (MMP13) was assessed by qRT-PCR at 7, 10–14, and 20–28 days. In addition, PPARγ DNA-binding activity was measured after 1 week. Interactions were evaluated by Loewe additivity and highest single agent (HSA) analyses. Results: Dex and DA each reduced PGE₂ release, whereas co-treatment increased potency and maximal inhibition, with a Loewe combination index of 0.4 at 1 nM Dex plus 19 µM DA. In the temporal analysis, Dex plus DA showed a positive MMP13 ΔCt difference versus Dex at 10–14 days (2.42 ± 2.14; p = 0.065) and a more consistent difference at 20–28 days (1.11 ± 0.25; p = 0.016). This agreed with fixed-dose HSA findings at 14 and 28 days (ΔHSA ≈ −75 for 0.1 µM Dex plus 100 µM DA versus Dex). Co-treatment was also associated with increased PPARγ activation beyond the HSA reference (ΔHSA ≈ 0.09 for 0.1 µM Dex plus 100–250 µM DA versus Dex). Conclusions: Dex plus DA co-treatment produced complementary effects on acute PGE₂ inhibition, as well as late-onset MMP13 suppression and PPARγ activity in the donor-specific chondrocyte models studied. These hypothesis-generating findings provide an in vitro rationale for future evaluation of this combination as a corticosteroid-sparing strategy.

Critical illnesses such as sepsis, trauma, and multi-organ failure initiate complex molecular cascades that disrupt cellular homeostasis and contribute to poor outcomes. Key among these mediators are Nicotinamide Adenine Dinucleotide (NAD+/NADH), Nitric Oxide (NO), and Hypoxia-Inducible Factor 1-alpha (HIF1α), each playing crucial roles in redox regulation, immune modulation, and tissue adaptation to hypoxia. This review examines the individual and interrelated roles of NAD+, NO, and HIF1α in critically ill patients. We explore how imbalances in NAD+/NADH ratio impair mitochondrial metabolism, how dysregulated NO signaling alters vascular tone and immune responses, and how HIF1α stabilization governs transcriptional programs under hypoxia. By mapping the biochemical crosstalk among these molecules, we identify potential feedback loops that influence inflammation, cellular energetics, and patient outcomes. A central theme is the safety and therapeutic relevance of modulating these mediators, with specific focus on the timing, context, and molecular profile of patients in critical care. Understanding the dynamic interplay among NAD+, NO, and HIF1α offers new opportunities for precision medicine in critical illness. We propose a hypothesis that phase-specific modulation of these pathways—through NAD+ precursors, NO donors/scavengers, or HIF1α stabilizers—could improve outcomes if guided by real-time molecular profiling. Prioritizing patient safety through targeted, biomarker-informed interventions may prevent progression to multi-organ failure and enable more personalized and effective treatments.

Osteoarthritis (OA) is traditionally framed as a degenerative cartilage disease caused by age-related mechanical wear. However, this paradigm does not adequately account for the synovitis, metabolic disturbance, and pain that commonly precede overt structural loss. In this Hypothesis and Theory article, we propose a testable systems model in which OA reflects a failure of interdependent synovial regulatory networks rather than a purely structural endpoint. These networks include: (1) energy-redox imbalance driven by declining NAD+ availability and mitochondrial inefficiency, which may prime synovial inflammation; (2) dysregulated MRP4- and MCT4-dependent efflux, leading to extracellular accumulation of prostaglandins and lactate that may promote nociception and stromal activation; (3) reduced protein phosphatase 2A (PP2A)-mediated signaling restraint, which may permit persistence of NF-κB and MAPK phosphorylation; and (4) impaired lipid mediator class switching, which may limit biosynthesis of specialized pro-resolving mediators such as Maresin-2 and Resolvin D1. We further propose that microtubule organization may function as a mechanometabolic interface linking redox decline, lactate signaling, transporter localization, and impaired mechanosensing. Because current anti-inflammatory therapies largely suppress inflammatory output rather than restore regulatory control, they may provide symptomatic relief without durable disease modification. We therefore outline a regulatory-restoration framework focused on NAD+ -redox alignment, mediator transport, phosphatase tone, and resolution-pathway recovery, while explicitly defining the limitations and falsifiable predictions of the model.

Longevity science has shifted from the pursuit of lifespan extension toward preservation of healthspan, resilience, and functional independence. The hallmarks of aging provide a powerful descriptive structure, but they do not by themselves specify how diverse molecular defects translate into loss of adaptive function. We propose a complementary conceptual framework in which aging is viewed as progressive impairment of biological self-correction: the distributed capacity to sense consequential perturbations, scale an appropriate response, repair or remove damage, terminate the response, and recover or adaptively re-equilibrate while preserving future functional reserve. This framework is not intended to replace homeostasis, homeodynamics, allostasis, physiological reserve, or resilience; rather, it links these established concepts to the molecular machinery that generates dynamic recovery. Correction fidelity is proposed to be measured independently of the hallmarks using stress-response trajectories, including response latency, magnitude of deviation, recovery slope or half-time, integrated deviation, residual deficit, overshoot, biological cost, final functional state, and preservation of subsequent reserve. Importantly, successful recovery need not mean return to a fixed youthful baseline because aging may also shift the physiological setpoint toward a less favorable but actively defended equilibrium. We integrate evolutionary and biodemographic principles with inflammaging, nutrient sensing, NAD+ biology, senescence, autophagy, partial reprogramming, and resilience research, and propose falsifiable predictions for testing whether dynamic recovery adds information beyond chronological age, frailty, and static aging biomarkers.

Objective: Persistent extracellular prostaglandin signaling contributes to synovial inflammation and pain in osteoarthritis (OA), although prostaglandin E2 (PGE2) can also have context-dependent homeostatic functions. Decanoic acid (DA) is a 10-carbon medium-chain fatty acid with reported peroxisome proliferator-activated receptor-modulating and anti-inflammatory activity. Its amphipathic carboxylate structure also made it an exploratory candidate for interaction with the hydrophobic organic-anion binding region of multidrug resistance protein 4 (MRP4/ABCC4). We tested whether DA changes prostaglandin compartmentalization and enhances the effect of very-low-dose dexamethasone (Dex) in interleukin-1β (IL-1β)-stimulated human OA fibroblast-like synoviocytes. Methods: Primary human osteoarthritis fibroblast-like synoviocytes were stimulated with IL-1β and treated with DA, Dex, or their combination. Extracellular and intracellular prostaglandins were quantified by competitive ELISA. MRP4 inhibition was evaluated in inside-out HEK293 membrane vesicles overexpressing human MRP4 using ATP-dependent DHEAS transport, with MK-571 as the positive inhibitor control. Molecular docking and UHPLC-MS lipidomics were also performed. Replicates were independently cultured wells or pellets from the same donor Results: DA reduced extracellular PGE2 and increased intracellular PGE2. With a fixed 0.1 nM Dex background, the fitted DA IC50 changed from 19.42 μM (95% CI, 11.14–32.49 μM) to 8.62 μM (95% CI, 4.69–15.26 μM) with an F -test P = 0.0402, indicating Das ability to potentiate the inhibitory effect of sub-nanomolar DEX. DA also reduced extracellular PGD2 and PGI2. In vesicles, DA inhibited MRP4-mediated DHEAS transport in a concentration-dependent manner (calculated IC50, approximately 33.86 μM), but PGE2 transport was not measured directly. Docking placed DA near the MK-571 reference pose. DA was also associated with increased 17(S)-HDHA and maresin 2 (MaR2). Conclusions: In this single-donor proof-of-concept model, DA altered prostaglandin distribution, inhibited MRP4 probe-substrate transport, and enhanced extracellular prostaglandin suppression in the presence of low-dose Dex. The findings are consistent with, but do not prove, an MRP4-associated contribution to prostaglandin export. The increases in 17(S)-HDHA and MaR2 are associative and do not establish that intracellular PGE2 retention caused resolution signaling. Multi-donor validation, direct PGE2 transport studies, genetic MRP4 experiments, and intra-articular pharmacokinetic and safety studies are required.