# Red Algae Alters Expression of Inflammatory Pathways in an Osteoarthritis In Vitro Co-Culture

## TL;DR

This study shows that red algae can reduce inflammation in an osteoarthritis cell model, offering a potential natural treatment alternative.

## Contribution

The paper introduces a novel in vitro co-culture model and demonstrates red algae's effect on reducing inflammatory gene expression in OA.

## Key findings

- The co-culture model remained viable for at least seven days under inflammatory conditions.
- Litho reduced expression of inflammatory genes like IL-1β, IL-6, PTGS2, and C1qTNF2.
- Litho treatment ameliorated the IL-1β-induced reduction in C1qTNF2 confirmed by ddPCR.

## Abstract

Background/Objectives: Osteoarthritis (OA) is one of the most prevalent chronic conditions and significantly contributes to local and global disease burden. Common pharmaceuticals that are used to treat OA cause significant side effects, thus non-pharmaceutical bioactive alternatives have been developed that can impact OA symptoms without severe side-effects. One such alternative is the Red Algae Lithothamnion species (Litho). However, there is little mechanistic knowledge of its potential to effect OA gene expression, and a human in vitro model using commercially available cell lines to test its effectiveness has yet to be developed. Methods: Human osteoblast (hFOB 1.19. CRL-11372) and chondrocyte (C28/I2) cell lines were co-cultured indirectly using transwells. IL1-β was used to induce an inflammatory state and gene expression profiles following treatment were the primary outcome. Conclusions: Results indicated that the model was physiologically relevant, remained viable over at least seven days, untreated or following induction of an inflammatory state while maintaining hFOB 1.19. and C28/I2 cell phenotypic characteristics. Following treatment, Litho reduced the expression of inflammatory and pain associated genes, most notably IL-1β, IL-6, PTGS2 (COX-2) and C1qTNF2 (CTRP2). Confirmatory analysis with droplet digital PCR (ddPCR) revealed that Il-1β induced a significant reduction in C1qTNF2 at 7 days which was ameliorated with Litho treatment. These data present a novel and replicable co-culture model of inflammatory OA that can be used to investigate bioactive nutraceuticals. For the first time, this model demonstrated a reduction in C1qTNF2 expression that was mitigated by Red Algae Lithothamnion species.