Transdermal lovastatin enhances fracture repair in rats

Abstract

Statins have been shown to stimulate BMP2 transcription and bone formation. This raises the possibility that they could be useful for enhancing rates of fracture repair. Observational studies in patients treated with oral statins for lipid-lowering have been controversial. The likely reason for their inconsistent effects is that the statin concentration reaching the periphery was too low after oral administration to produce a reproducible biologic effect. Thus, we examined the effects of lovastatin (LV) given transdermally in a well-described preclinical model of fracture repair. Effects on the healing fracture callus were assessed by biomechanical strength, radiographs, and quantitative morphology. LV was administered transdermally (TD) for 5 days after fracture in several doses (0.1-5 mg/kg/d) and compared with vehicle-treated control rats and rats treated with LV by oral gavage (PO) at 5-25 mg/kg/d for 5 days from the day of fracture. Radiological evaluation of bones treated with TD LV showed enhanced fracture repair at 2 and 6 wk. BMD in the callus area at 6 wk was also increased in the TD group compared with vehicle-treated controls (p < 0.05). The force required to break TD-treated bones (0.1 mg/kg/d for 5 days) was 42% greater than vehicle-treated controls (p < 0.02), and there was a 90% increase in stiffness (p < 0.01). PO LV at much higher doses (10 and 25 mg/kg/d) showed increased stiffness but no change in other biomechanical properties. By histological examination, a significant increase was also observed in the size of the callus, surrounding proliferating cell nuclear antigen-positive cells, and osteoblast and osteoclast number in TD-treated rats compared with controls at day 8 after fracture (n = 6). In summary, we found that TD LV in low doses accelerates fracture healing, whereas 10-fold the lipid-lowering dose was required to produce any effect when it was administered orally. These studies provide valuable information on the potential of statins and TD delivery as a new and effective therapeutic modality in fracture repair.

FIG. 1

Radiographic images of fractured femurs (experiments A and B) at 2 and 6 wk after procedure was performed. Two images representative of each group (vehicle and TD LV) are shown (n = 8, experiment A; n = 10, experiment B).

FIG. 2

Radiological score obtained at 2 and 6 wk for experiment B (TD LV groups) using the grading scale presented in the Materials and Methods section (n = 10). Bars represent percentage increase compared with vehicle treated group ± SE.

FIG. 3

BMD of the total callus at the fracture site was obtained for experiment B at 6 wk (n = 6). Bars represent mean ± SE and percentage increase compared with vehicle-treated is shown inside each bar. p < 0.05.

FIG. 4

Representative histological sections comparing vehicle-treated vs. TD LV (2.5 mg/kg/d for 5 days) after 8 days of fracture. Several sections 500 μm proximal and distal to the fracture site were stained for the analysis. Ten regions as described in the Materials and Methods section were analyzed in each section. The table under the images shows the results of the histomorphometric analysis. Osteoclast and osteoblast surface as well as the number of PCNA⁺ cells were counted, and the ratio of PCNA⁺ cells to total cells was calculated and expressed as a percentage.

FIG. 5

Two representative images of transverse sections (at fracture site) 6 wk after fracture. Sections were stained with H&E (n = 6). Fracture can still be observed in the control sections. In the TD LV-treated group, the primary cortex and the new layer of bone have been remodeled and replaced with compact bone underlying the new external periosteal layer.