Continuous low-intensity ultrasound attenuates IL-6 and TNFα-induced catabolic effects and repairs chondral fissures in bovine osteochondral explants

BMC Musculoskelet Disord. 2019 May 4;20(1):193. doi: 10.1186/s12891-019-2566-4.


Background: Cartilage repair outcomes are compromised in a pro-inflammatory environment; therefore, the mitigation of pro-inflammatory responses is beneficial. Treatment with continuous low-intensity ultrasound (cLIUS) at the resonant frequency of 5 MHz is proposed for the repair of chondral fissures under pro-inflammatory conditions.

Methods: Bovine osteochondral explants, concentrically incised to create chondral fissures, were maintained under cLIUS (14 kPa (5 MHz, 2.5 Vpp), 20 min, 4 times/day) for a period of 28 days in the presence or absence of cytokines, interleukin-6 (IL-6) or tumor necrosis factor (TNF)α. Outcome assessments included histological and immunohistochemical staining of the explants; and the expression of catabolic and anabolic genes by qRT-PCR in bovine chondrocytes. Cell migration was assessed by scratch assays, and by visualizing migrating cells into the hydrogel core of cartilage-hydrogel constructs.

Results: Both in the presence and absence of cytokines, higher percent apposition along with closure of fissures were noted in cLIUS-stimulated explants as compared to non-cLIUS-stimulated explants on day 14. On day 28, the percent apposition was not significantly different between unstimulated and cLIUS-stimulated explants exposed to cytokines. As compared to non-cLIUS-stimulated controls, on day 28, cLIUS preserved the distribution of proteoglycans and collagen II in explants despite exposure to cytokines. cLIUS enhanced the cell migration irrespective of cytokine treatment. IL-6 or TNFα-induced increases in MMP13 and ADAMTS4 gene expression was rescued by cLIUS stimulation in chondrocytes. Under cLIUS, TNFα-induced increase in NF-κB expression was suppressed, and the expression of collagen II and TIMP1 genes were upregulated.

Conclusion: cLIUS repaired chondral fissures, and elicited pro-anabolic and anti-catabolic effects, thus demonstrating the potential of cLIUS in improving cartilage repair outcomes.

Keywords: Cartilage; Cytokines; Inflammation; Repair; Ultrasound.

MeSH terms

  • Animals
  • Cartilage, Articular / cytology
  • Cartilage, Articular / injuries*
  • Cartilage, Articular / pathology
  • Cartilage, Articular / radiation effects
  • Cattle
  • Cell Culture Techniques
  • Cell Movement / radiation effects
  • Cell Survival / radiation effects
  • Chondrocytes / metabolism
  • Interleukin-6 / metabolism*
  • Osteochondritis / pathology
  • Osteochondritis / therapy
  • Primary Cell Culture
  • Tumor Necrosis Factor-alpha / metabolism*
  • Ultrasonic Therapy / methods*
  • Wound Healing / radiation effects*


  • Interleukin-6
  • Tumor Necrosis Factor-alpha