Abstract
Elderly patients frequently suffer from protein malnutrition leading to major alteration of the somatotropic axis as well as IGF-I local production. IGF-I is a major anabolic agent for cartilage homeostasis. Indeed a decrease of IGF-I induced by protein malnutrition could affect both cartilage and subchondral bone and may contribute to osteoarthritis development. To address this question, 9 months old rats were pair fed a normal or an isocaloric low protein diet (LP) for 2 months (n=6/group). All animals were euthanized and femurs were collected. Micro-computed tomography allows determination of trabecular and cortical subchondral bone (SB) morphometric parameters as well as hyaline and calcified cartilage thickness, and proteoglycan content estimation. Bioindentation with Bioindenter equipment (CSM Instrument, Switzerland) allows determination of cartilage material level properties (indentation depth and Young’s modulus). Systemic IGF-I was decreased in LP group (-18%,p<.001). As expected, in LP group, SB compartment was altered: trabecular SB mass was decreased (-10%,p<.01) as well as SB cortical plate thickness of the medial condyle (-12%,p<.05). Despite no morphologic changes of the cartilage of the medial condyle (thickness tended to decrease by 8% but not significantly), hyaline cartilage biomechanical properties (force, elastic modulus and working energy) were respectively decreased by -47, -58 and -41% (p<.01). We did not observed alterations of proteoglycan. These cartilage degradations are similar to what is observed in early osteoarthritis.We suggest that alteration of the somatotropic axis induced by protein malnutrition could predispose to osteoarthritis. Since protein malnutrition is frequent in elderly this mechanism could be relevant in human.