Stimulation of Tendon Healing With Delayed Dexamethasone Treatment Is Modified by the Microbiome

Abstract

Background: The immune system reflects the microbiome (microbiota). Modulation of the immune system during early tendon remodeling by dexamethasone treatment can improve rat Achilles tendon healing. The authors tested whether changes in the microbiota could influence the effect of dexamethasone treatment. Hypothesis: A change in microbiome would influence the response to dexamethasone on regenerate remodeling, specifically tendon material properties (peak stress). Study Design: Controlled laboratory study. Methods: Specific opportunist and pathogen-free female rats were housed separately (n = 41) or together with specific pathogen-free rats carrying opportunistic microbes such as Staphylococcus aureus (n = 41). After 6 weeks, all co-housed rats appeared healthy but now carried S aureus. Changes in the gut bacterial flora were tested by API and RapID biochemical tests. All rats (clean and contaminated) underwent Achilles tendon transection under aseptic conditions. Flow cytometry was performed 8 days postoperatively on tendon tissue. Sixty rats received subcutaneous dexamethasone or saline injections on days 5 through 9 after transection. The tendons were tested mechanically on day 12. The predetermined primary outcome was the interaction between contamination and dexamethasone regarding peak stress, tested by 2-way analysis of variance. Results: Dexamethasone increased peak stress in all groups but more in contaminated rats (105%) than in clean rats (53%) (interaction, P = .018). A similar interaction was found for an estimate of elastic modulus ( P = .021). Furthermore, dexamethasone treatment reduced transverse area but had small effects on peak force and stiffness. In rats treated with saline only, contamination reduced peak stress by 16% ( P = .04) and elastic modulus by 35% ( P = .004). Contamination led to changes in the gut bacterial flora and higher levels of T cells (CD3+CD4+) in the healing tendon ( P < .05). Conclusion: Changes in the microbiome influence tendon healing and enhance the positive effects of dexamethasone treatment during the early remodeling phase of tendon healing. Clinical Relevance: The positive effect of dexamethasone on early tendon remodeling in rats is strikingly strong. If similar effects could be shown in humans, immune modulation by a few days of systemic corticosteroids, or more specific compounds, could open new approaches to rehabilitation after tendon injury.

Response to mechanical loading in rat Achilles tendon healing is influenced by the microbiome

“…6 weeks of co-housing lead to higher levels of Staphylococcus aureus and Escherichia coli in the gut microbiota of the contaminated SOPF rats compared to the clean SOPF rats, where the levels of these bacteria were below the detectable limits. However, the total amount of bacteria was higher in the clean rats in comparison to the contaminated rats, including higher levels of gram-positive bacteria (Staphylococcus spp and Enterococcus spp) as previously described [1] ( Table 1).…”

“…Furthermore, the controls showed a different response between the clean and contaminated animals where contaminated rats had considerably decreased peak stress and estimate of elastic modulus [1]. One difference in the set-up between our new study and this previous one is the duration of tendon healing.…”

“…Recent data show that changes in the gut microbiota can alter the levels of CD4 + and CD3+ T cells within the tendon callus [1]. Furthermore, changes in the microbiome can influence the response to different immunomodulatory treatments, such as local PRP injections or systemic corticosteroid treatment, during tendon healing [1,3]. To the best of our knowledge, these two studies are the first to confirm a connection between the microbiome and tendon healing outcomes.…”

“…Tendon healing is dependent on the immune system [1] which has a profound effect on the strength of the tendon callus [2,3]. The immune system, and particularly T cells, changes in response to alterations in the microbial environment in the gut and skin [4,5].…”

“…To the extent that T cells play a role in tendon healing, microbial changes in the gut can indirectly influence this healing. Recent data show that changes in the gut microbiota can alter the levels of CD4 + and CD3+ T cells within the tendon callus [1]. Furthermore, changes in the microbiome can influence the response to different immunomodulatory treatments, such as local PRP injections or systemic corticosteroid treatment, during tendon healing [1,3].…”