Testosterone dose dependently prevents bone and muscle loss in rodents after spinal cord injury

Abstract

Androgen administration protects against musculoskeletal deficits in models of sex-steroid deficiency and injury/disuse. It remains unknown, however, whether testosterone prevents bone loss accompanying spinal cord injury (SCI), a condition that results in a near universal occurrence of osteoporosis. Our primary purpose was to determine whether testosterone-enanthate (TE) attenuates hindlimb bone loss in a rodent moderate/severe contusion SCI model. Forty (n=10/group), 14 week old male Sprague-Dawley rats were randomized to receive: (1) Sham surgery (T9 laminectomy), (2) moderate/severe (250 kdyne) SCI, (3) SCI+Low-dose TE (2.0 mg/week), or (4) SCI+High-dose TE (7.0 mg/week). Twenty-one days post-injury, SCI animals exhibited a 77-85% reduction in hindlimb cancellous bone volume at the distal femur (measured via μCT) and proximal tibia (measured via histomorphometry), characterized by a >70% reduction in trabecular number, 13-27% reduction in trabecular thickness, and increased trabecular separation. A 57% reduction in cancellous volumetric bone mineral density (vBMD) at the distal femur and a 20% reduction in vBMD at the femoral neck were also observed. TE dose dependently prevented hindlimb bone loss after SCI, with high-dose TE fully preserving cancellous bone structural characteristics and vBMD at all skeletal sites examined. Animals receiving SCI also exhibited a 35% reduction in hindlimb weight bearing (triceps surae) muscle mass and a 22% reduction in sublesional non-weight bearing (levator ani/bulbocavernosus [LABC]) muscle mass, and reduced prostate mass. Both TE doses fully preserved LABC mass, while only high-dose TE ameliorated hindlimb muscle losses. TE also dose dependently increased prostate mass. Our findings provide the first evidence indicating that high-dose TE fully prevents hindlimb cancellous bone loss and concomitantly ameliorates muscle loss after SCI, while low-dose TE produces much less profound musculoskeletal benefit. Testosterone-induced prostate enlargement, however, represents a potential barrier to the clinical implementation of high-dose TE as a means of preserving musculoskeletal tissue after SCI.

FIG. 1.

Histologic images of the spinal cord (hematoxylin and eosin stain, 2.5X magnification) from animals subjected to Sham surgery (T9 laminectomy) or moderate/severe (250 kdyne) spinal cord injury (SCI) alone or in combination with a low- (SCI+LowTE) or high-dose (SCI+HighTE) of testosterone-enanthate (TE). Note reduced mass of pink-stained white matter indicative of moderate/severe SCI (B, C, D) versus A (Sham surgery) indicating a qualitatively consistent injury intensity in all groups receiving SCI. Color image is available online at www.liebertpub.com/neu

FIG. 2.

Basso-Beattie-Bresnahan (BBB) scores (A) and body mass change (B) from animals subjected to Sham surgery (T9 laminectomy) or moderate/severe (250 kdyne) spinal cord injury (SCI) alone or in combination with a low- (SCI+LowTE) or high-dose (SCI+HighTE) of testosterone-enanthate (TE). Values are means±standard error of n=8–9/group. Letters a–d indicate differences from respectively labeled groups at p<0.05 or *p<0.01 (a=vs. SHAM, b=vs. SCI, c=vs. SCI+LowTE, d=vs. SCI+HighTE). ^†indicates within-groups difference compared with previous time point and ^‡ indicates within-group difference compared with Day 7 for respectively labeled groups.

FIG. 3.

Histologic images of the proximal tibial metaphysis (von Kossa/tetrachrome stain, 40X) from animals subjected to Sham surgery (T9 laminectomy) or moderate/severe (250 kdyne) spinal cord injury (SCI) alone or in combination with a low- (SCI+LowTE) or high-dose (SCI+HighTE) of testosterone-enanthate (TE). Note reduced mass of black-stained cancellous bone (B) indicative of cancellous osteopenia in SCI animals; high-dose TE (D) fully prevented cancellous bone loss. Values are means±standard error of n=8–9/group. Letters a–d indicate differences from respectively labeled groups at p<0.05 or *p<0.01 (a=vs. SHAM, b=vs. SCI, c=vs. SCI+LowTE, d=vs. SCI+HighTE). Color image is available online at www.liebertpub.com/neu

FIG. 4.

μCT images of cancellous bone at the distal femoral metaphysis and femoral neck of animals subjected to Sham surgery (T9 laminectomy) or moderate/severe (250 kdyne) spinal cord injury (SCI) alone or in combination with a low- (SCI+LowTE) or high-dose (SCI+HighTE) of testosterone-enanthate (TE). Values are means±standard error of n=8–9/group. Letters a–d indicate differences from respectively labeled groups at p<0.05 or *p<0.01 (a=vs. SHAM, b=vs. SCI, c=vs. SCI+LowTE, d=vs. SCI+HighTE). BMD, bone mineral density. Color image is available online at www.liebertpub.com/neu