Background Marked polyarthritis is induced in male Lewis rats by injection of either heat-killed Mycobacterium tuberculosis in mineral oil (AdA) or lipoidal amine in complete Freund’s adjuvant (LA/CFA). For both models, paw swelling and body weight loss occur in all rats by 10 to 12 days after immunisation.
Objectives Interestingly, however, the present study demonstrates that the morphologic and densitometric changes of AdA and LA/CFA are distinguishable.
Methods We induced AdA or LA/CFA in male Lewis rats (180 g) and evaluated both clinical (body and spleen weight, volume of the tibiotarsal [hock] joints) and morphologic changes (bone mineral density [BMD] by DEXA; histopathologic lesions in the hock and femorotibial [knee] joints). Readings were obtained at the day of onset (as determined by initial paw swelling) as well as 5, 10 and 25 days after onset.
Results Paw swelling, loss of body weight, enhanced spleen weight were identical in AdA and LA/CFA. In contrast, hock inflammation score, hock erosion score and hock cartilage score were lower in LA/CFA, though not statistically significant from AdA. Lesions developed more slowly in LA/CFA than in AdA. However, hock BMD as well as knee inflammation and erosion scores found to be different (shown here at Onset + 5 days):
Conclusion Inflammatory and skeletal changes for AdA and LA/CFA were similar by clinical and histopathologic measures 10 days after onset, while inflammation receded by Onset + 25 days in LA/CFA more than it did in AdA. These data indicate that bone densitometric and morphologic findings can distinguish these two models of adjuvant arthritis despite their similar clinical presentations. This finding may be relevant in screening novel therapeutic candidates as these models may define different potential efficacious effects of a compound.
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