Exposure to low‐intensity ultrasound increases aggrecan gene expression in a rat femur fracture model

Abstract

The effects of ultrasound stimulation on various parameters of bone repair after diaphyseal injury were assessed in a standard rat femur fracture model. Bilateral closed femoral fractures were made in 79 skeletally mature male Long-Evans rats. An ultrasound signal consisting of a 200 microsecond burst sine wave of 0.5 MHz repeating at 1 kHz, with an intensity of 50 or 100 mW/cm2 spatial and temporal average, was applied to one fracture in each animal. The contralateral fracture was not exposed to ultrasound and served as a control. Mechanical testing of the healing fracture was performed 3 weeks after injury. In fractures treated with a 50 mW/cm2 ultrasound signal, the average maximum torque (223.5 +/- 50.5 Nmm compared with 172.6 +/- 54.9 Nmm, p = 0.022, paired t test) and average torsional stiffness (13.0 +/- 3.4 Nmm/degree compared with 9.5 +/- 2.9 Nmm/degree, p = 0.017) were significantly greater in treated than in control fractures. In animals treated with a 100 mW/cm2 ultrasound signal, the average maximum torque and torsional stiffness were greater in treated than in control fractures, but this trend did not reach statistical significance. Biochemical analysis of callus in ultrasound-treated and control fractures failed to demonstrate significant differences in cell number, collagen content, or calcium content. Evaluation of gene expression in fractures treated with 50 mW/cm2 ultrasound demonstrated a shift in the expression of genes associated with cartilage formation; aggrecan gene expression was significantly higher on day 7 after fracture and significantly lower on day 21 (p = 0.033 and 0.035, respectively). alpha 1(II) procollagen gene expression was similarly modified, but this trend did not reach statistical significance. Expression of genes coding for bone-related proteins, including alpha 1(I) procollagen, bone gamma-carboxyglutamic acid protein, alkaline phosphatase, and transforming growth factor-beta 1, did not differ between ultrasound-treated and control fractures. These data suggest that ultrasound stimulation increased the mechanical properties of the healing fracture callus by stimulating earlier synthesis of extracellular matrix proteins in cartilage, possibly altering chondrocyte maturation and endochondral bone formation.

Effects of low‐intensity ultrasound (LIUS) stimulation on human cartilage explants

“…Our results are fairly consistent with previous studies in vitro and in animal models (10,12,13,15). However, Zhang et al showed that the expression of aggrecan and collagen type II was induced by LIUS only at a low intensity of 2 mW/cm 2 in chondrocytes from chick embryos (10).…”

“…LIUS was also shown to stimulate the expression of proteoglycan and type II collagen, in a rat fracture model (13) and in a monolayer culture (10,12). Proteoglycan and type II collagen synthesized by chondrocytes are two major components of the extracellular matrix of articular cartilage, and the degradation or decreased synthesis of either protein could lead to significant loss of the cartilage function in patients with arthritic diseases (16,28).…”

“…When applied to a monolayer culture of human chondrocytes, LIUS also increased cellular proliferation and matrix synthesis (10). In animal studies, LIUS stimulation in both bone fractures and cartilage resulted in increased expression of proteoglycan or type II collagen rather than that of bone formation factors such as transforming growth factor-b (TGF-b), osteocalcin, alkaline phosphatase, and a1(I)-procollagen, hence protecting the collagen matrix and preventing the destruction or degradation of cartilage (11)(12)(13). However, the effects of LIUS treatment on chondrocyte proliferation and the expression of matrix proteins such as proteoglycan and collagen type II have not been clearly shown in intact human cartilage.…”

Low-Intensity Pulsed Ultrasound Treatment for Scaphoid Fracture Nonunions in Adolescents

“…The mechanism of action of ultrasound therapy on bone healing is an area of ongoing research. Studies suggest that ultrasound therapy results in a host of changes, ranging from molecular modifications in ion channel permeability 9 and alterations in gene expression [10][11][12] to more mechanical effects such as increased blood flow 4,10,13 and the generation of strain secondary to acoustic perturbations. 14 The impact of these various changes in skeletally immature bone has not been fully elucidated, and the use of ultrasound therapy as an adjunct for treatment of fracture nonunion is off-label in adolescent patients.…”

Tratamentos não farmacológicos na estimulação da osteogênese

“…Yang et al 56 (1996) observaram um aumento significativo da expressão genética de um agregado de proteo-glicanas, composto tanto de sulfato de condroitina quanto de sulfato de queratina, sete dias após a exposição a ultra-som pulsado de baixa intensidade sobre fraturas femorais de ratos. Após 21 dias de exposição ultra-sônica ocorreu uma diminuição significativa desse agregrado.…”