119 CHARACTERISATION OF TEMPORAL SUBCHONDRAL BONE CHANGES IN A RAT MODEL OF LOW-DOSE MONOSODIUM IODOACETATE INDUCED OSTEOARTHRITIS: AN IN VIVO MICRO-CT STUDY

Purpose: To determine if advanced glycation endproducts (AGEs) alter the extent of spontaneous osteoarthritis (OA) progression in the male Hartley Guinea Pig (HGP).Some investigators hypothesize that accumulation of AGEs (due to ageing or disease) may play a role in OA pathogenesis by various mechanisms (biochemical, biomechanical).DeGroot et al. (Arth.& Rheum, 2004) reported that a 5-fold increase in AGE content of articular cartilage due to intra-articular injections of PBS containing ribose lead to greater osteoarthritis in a dog ACL injury model of secondary OA.However, that study did not address the possibly more insidious role AGEs may play in primary, idiopathic OA development.Therefore, we determined to study the effect in HGPsthe gold standard model for spontaneous OA.Methods: Fifteen male retired-breeder (~1 year) HGPs received 100 ml intra-articular injections in the right knee [PBS (n = 5), PBS+0.6Mribose (n = 5) or PBS+2.0Mribose (n = 5)] once a week for four weeks.Contralateral (left) knees acted as controls.Femoral cartilage and menisci were harvested for biochemical assays and proximal tibiae were processed for histological grading using Safranin-O staining and histological scoring based on the scheme of Kraus et al (Osteoarthritis & Cartilage, 2010).HPLC was used to quantify pentosidine concentration, an established AGE biomarker, to quantify the extent of AGE accumulation in the cartilage.Subsequently, in a long-term study allowing for significant OA progression in HGP knees, twenty male 3-month old HGPs received intra-articular injections in the right knee [PBS (n = 10), PBS+0.6Mribose (n = 10); left knees were controls] for twenty-four weeks (9 months old).Additionally, four non-injected controls HGPs were euthanized at 3-months and another four at the end of the experiment.The tissues were harvested and prepared as discribed above.Results: In the first study, increased pentosidine content was detected in the menisci of the 0.6M and 2.0M ribose groups compared to the PBS controls.A dose response was confirmed and pentosidine levels reached those of mature human cartilage in the 2.0M treated group (3.5±1.0 mmol pentosidine per mol collagen versus 0.63±0.17mmol pentosidine per mol collagen in control menisci).Histological examination of the tibial plateau confirmed no acute reaction to the injections and did not demonstrate a difference in disease state between the groups (Kraus score ~16±2), likely because the disease had already progressed significantly in the retired breeders by the start of the study.During the 24-week study, the ribose injected group unexpectedly gained less mass, ranging between 6-8% less between weeks 12 and 24.This suggests that the ribose treated group may have experienced greater pain/inflammation.0.6M ribose allows for a slower accumulation of AGEs during the treatment period so that levels remain physiological but reach levels similar to 80-year old human cartilage (approx.8 mmol pentosidine per mol collagen) by 24 weeks.During the period of 3 to 9 months of age, OA typically develops to a moderate level in this model (Kraus score increasing from less than 2 to 12).Conclusions: An in vivo model to test the effect of AGEs on the gradual progression of idiopathic knee osteoarthritis has been established.AGE content reaches levels found in aged cartilage.