Table 1.

Literature review summary

Study	Animal model	OA inducing method	Intervention	OA assessment method	Microbiome Assessment	Conclusion
Collins et al., 2015 [43]	Rats (male)	High fat/high sucrose diet for 28 weeks. (40% energy from fat and 45% from sucrose)	N/A	Cartilage histological evaluation (Modified Mankin scores), synovial and sub-chondral bone assessment (OARSI), serum and synovial fluid biomarkers analysis	Fecal sample 16s sequencing	Higher Mankin scores, and higher level of serum LPS in obese animals. -->Lactobacillus species and Methanobrevibacter spp. abundance correlated with Mankin scores.
Huang et al., 2016 [44]	Humans (male and female)	N/A	N/A	Knee Radiography, Etarfolatide SPECT/CT scans, serum and synovial fluid biomarker analysis, WOMAC questionnaire, NHANES-I pain scores	N/A	Serum LPS and LBP levels were associated with an increased abundance of activated macrophages in the knee joint capsule and synovium; they were also associated with osteophyte formation, knee joint space narrowing, and WOMAC scores.
Ulici et al., 2018 [45▪]	Germ Free Mice (male)	DMM surgery	N/A	Histologic cartilage evaluation (ACS scores), osteophyte and synovial membrane evaluation	Fecal samples 16s sequencing	Reduced ACS scores in germ free mice compared to the control group. Differences in abundance of microbes detected in high and low ACS mice.
Schott et al., 2018 [13▪▪]	Mice (male)	High fat diet induced obesity (60% kcal from fat for 12 weeks) and DMM surgery	Oligofructose (prebiotic)	Cartilage histological evaluation (OARSI scores), IHC and IF of cartilage and synovium, PAST cells flow cytometry, Micro CT scan of mineralized meniscus, serum biomarkers analysis	Fecal samples 16s sequencing	Prebiotic supplementation reduced OA severity observed in HFD mice. Bifidobacterium pseudolongum abundance increased with prebiotic treatment; its levels were inversely related to the OA severity, systemic, and colon inflammation.
Guss et al., 2019 [47]	Mice (male)	Metabolic disorder (TLR5KO), High fat diet induced obesity (60% energy from fat)	Tibial mechanical loading (2 weeks or 6 weeks)	Cartilage histological evaluation (OARSI scores and Modified Mankin scores), Micro CT evaluation of the subchondral bone trabecular architecture, serum biomarker analysis	Fecal samples 16s sequencing	Long term (6 weeks) mechanical loading is necessary to induce OA. Mild metabolic disorder is not sufficient to develop severe OA. Disturbing metabolic disorder with antibiotics reduces OA severity.
Rios et al., 2019 [49▪▪]	Rats (male)	High fat/high sucrose diet for 28 weeks (20% energy from fat, 50% from sucrose)	Prebiotic fibers supplementation and exercise (12 weeks)	Cartilage histological evaluation (Modified Mankin scores), synovial and sub-chondral bone assessment (OARSI), serum and synovial fluid biomarker analysis	Cecal matter 16s sequencing	Prebiotic fibers, exercise, and the combination of both prevented OA development. Prebiotic treatment increased Bifidobacterium and Roseburia; they decreased Closteridium leptum and Akkemansia muciniphila.
Henrotin et al., 2019 [50▪]	Dunkin Hartley Guinea pigs (male)	Spontaneous development	Lyophilized inactivated culture from Bifidobacteri-um longum CBi0703 (12 weeks)	Cartilage histological evaluation (OARSI scores), serum biomarkers analysis	N/A	B. longum oral administration decreased cartilage damage and decreased type II collagen degradation.

Studies investigating the connection between osteoarthritis development and the gut microbiome in rodent models of osteoarthritis are enumerated. Relevant studies were identified through a PubMed search for articles in English published in peer-reviewed journals. We used multiple search terms capturing osteoarthritis, joint, cartilage, gut microbiome and microbiota. Articles selected were reviewed by all coauthors for final inclusion. ACS, articular cartilage structure; CT, computed tomography; HFD, high-fat diet; IF, immunofluorescence; IHC, immunohistochemistry; LBP, LPS binding protein; LPS, lipopolysaccharides; OA, osteoarthritis; SPECT, single-photon emission computerized tomography.