The analgesic efficacy of intra-articular acetaminophen in an experimental model of carrageenan-induced arthritis

Carrageenan and TLR4 Crosstalk: A Comprehensive Review of Inflammatory Responses in Animal Models

Carrageenan, a naturally occurring polysaccharide derived from red seaweed, has been utilized extensively in the food industry as a stabilizer, thickener, and emulsifier due to its unique gel-forming properties. This versatile compound exists in various forms, including kappa, iota, and lambda, each with distinct characteristics suitable for different applications. Its widespread use as a food additive has raised concerns regarding its safety, particularly its potential inflammatory effects on the gastrointestinal tract. While carrageenan has been deemed safe for consumption by regulatory agencies in small amounts, studies have suggested its association with intestinal inflammation and gastrointestinal disturbances, particularly in susceptible individuals. Animal models, including rodents and non-human primates, have been employed to investigate the inflammatory response induced by carrageenan ingestion. These models have provided valuable insights into the molecular mechanisms underlying its pro-inflammatory properties. At the molecular level, carrageenan is believed to trigger inflammation by activating toll-like receptor 4 (TLR4) signaling pathways, leading to the production of pro-inflammatory cytokines and the recruitment of immune cells to the site of exposure. Furthermore, carrageenan-induced inflammation may disrupt the intestinal barrier function, facilitating the translocation of luminal antigens and exacerbating immune responses. This review provides a comprehensive examination of the current understanding of carrageenan's role in inflammation, encompassing its diverse applications in the food industry, safety concerns, experimental findings from animal models, and molecular mechanisms underlying its pro-inflammatory effects.

Primary Human Chondrocytes Affected by Cigarette Smoke-Therapeutic Challenges

Although several researchers have attested deleterious effects of smoking to the musculoskeletal system, the association between smoking and the onset of osteoarthritis (OA) remains unclear. Here, we investigate the effect of cigarette smoke extract (CSE) on primary human chondrocytes. The present study demonstrates that physiological concentrations of CSE (0.1%-10%) inhibit the viability, proliferation, and matrix formation of chondrocytes in a dose- and time-dependent manner. Significant amounts of free radicals were generated by 10% of CSE and led to cell death. A clinical dosage (4 mg/mL) of dexamethasone (Dex) showed toxic effects on chondrocytes, and the long-time treatment by lower doses (4-400 μg/mL) induced hypertrophic changes in the chondrocytes. To substitute Dex, diclofenac (Dic, 1 μg/mL) and acetaminophen (Ace, 10 μg/mL) were tested and did not worsen the metabolic activity of CSE-exposed chondrocytes. Hyaluronic acid (HA, 5 mg/mL) combined with Dic or Ace significantly inhibited the oxidative stress and enhanced the viability and matrix formation of CSE-exposed chondrocytes. This study shows for the first time that CSE mediates the disruption of cartilage through inducing cell death by increasing oxidative stress, and that this effect is fortified by Dex. The deleterious effects of CSE on chondrocytes could be reversed by treatment with HA combined with first-line analgesic/anti-inflammatory agents.

Contributions of peripheral, spinal, and supraspinal actions to analgesia

Pain signaling involves several main compartments that can be considered as potential sites for analgesic drug actions. When drugs are given systemically, they can act at spinal, supraspinal and peripheral sites, and several methods have been developed for identifying where they act. These include (1) localized delivery of drugs to specific sites (via intracerebral, intrathecal, and intraplantar injections), (2) systemic delivery of drugs with localized delivery of antagonists for the receptor on which the drug acts or for a system recruited by the drug, (3) use of peripherally restricted analogs, and (4) use of conditional knockout technology to selectively deplete receptors on nociceptors. Delivery of drugs simultaneously to several sites (spinal/supraspinal, peripheral/spinal, and peripheral/supraspinal) reveals "self-synergy" between sites for some agents. Knowledge of peripheral contributions to drug actions is important because of the potential to develop peripherally restricted analgesics (with a diminished side effect profile due to not entering the central nervous system), the potential to deliver drugs peripherally (e.g. topically) to act on sensory nerve endings and adjacent tissue (with a diminished side effect profile due to limited systemic absorption), and the potential to use combinations of topical and oral drug regimens to obtain improved pain relief (without increasing the side effect burden). This review considers methods used for compartmental analysis, and results of such site analysis for several major classes of analgesic drugs that are in current use.