| Objective:To evaluate the biological distribution properties of the newradioactive molecular probe99mTc-3PRGD2and explore its value in thediagnosis of rheumatoid arthritis (RA) in the experimental study of theanimal model of RA.Methods:15female SD rats (SPF level,6weeks age) were randomly divided into2groups: arthritis model group (12rats) and normal control group (3rats).Model group:0.1ml of complete freund’s adjuvant (CFA) was injectedsubcutaneously to each rat at the base of the tail to induce arthritis;Control group:0.1ml of saline was injected with to each rat in the sameway. During the experiment, the main outcome measures were as follows:general behavior of the rats, joint swelling and hyperplasia, body weight,diameter of the ankle, arthritis index (AI) score (0to4points insequence) according to the degree of joint swelling, histologicalfeatures of joint tissue in HE staining.99mTc-3PRGD2was prepared by using HYNIC-3PRGD2lyophilized kit and99mTcO-4, and the labeling rate measurement of99mTc-3PRGD2was followed.99mTc-3PRGD2was injected to the rats with arthritis via the tail-vein.Planar imaging was performed at30min,1h,2h,4h and6h after theinjection to observe the change of joint uptake of the tracer with thetime, and the value of joint-to-muscle T/NT (target/non-target) wascalculated. The rats were sacrificed at1h. and the joint and normal organs(heart, liver, spleen, lungs, kidneys, stomach, intestine, muscle andblood) were excised, counted on γ-counter and calculated as a percentageactivity of injection dose per gram of tissue (%ID/g) to evaluate the biological distribution characteristics of99mTc-3PRGD2in RA animal model.Immunohistochemical staining was used to test the integrin αvβ3expression in the joint tissue, and correlation analysis between jointuptake (%ID/g) and receptor expression was followed.Results:1. In this study, AIA (adjuvant-induced arthritis) model was successfullydeveloped: the signs of arthritis began to appear at around the19thday after the immunization. From then on, the signs got worse, theweight of the rats decreased during this period. at the same time, jointdiameter, number of diseased limbs and AI scores were graduallyincreased. As a result the symptoms peak appeared after1-2weeks ofthe onset of arthritis. Finally, the incidence of arthritis closelyreached to70%.2. The lesions of the arthritis ankles were shown at30min after theadministration of99mTc-3PRGD2. The kidneys, bladder and liver were seenwith apparently radioactivity accumulation, while the intestinedisplayed with a slight uptake. The arthritis lesions still could befound at6h.3. The joint-to-muscle (T/NT) contrast of AI score from0-4in SPECTimaging was respectively:0.70±0.12,1.10±0.05,1.33±0.12,1.40±0.08and1.82±0.15, with a significant statisticallydifference between each group (F=169.62, P<0.01). There wasstatistically significant difference (P<0.01) among different AIscore except for2and3score group (t=1.44, P>0.05). Thejoint-to-muscle of high score was higher than those of lower score,indicating that T/NT ratio was increased along with the aggravatingarthritis.4. Biodistribution results: The ankle uptake were (0.95±0.10)%ID/g,(1.10±0.07)%ID/g,(1.28±0.05)%ID/g,(1.32±0.02)%ID/g, and(1.73±0.05)%ID/g of AI score from0-4, suggesting that the jointuptake gradually became apparent with AI score increased (F=75.46， P<0.05）. The kidney had a highest uptake (9.16±0.72%ID/g), liverfollowed (5.12±0.43%ID/g) and intestine also had a slightly uptake(3.24±0.20)%ID/g, illustrating that99mTc-3PRGD2was mainly excretedthrough urinary system, partly metabolized by liver.5. Immunohistochemical staining showed positive expression (brown colour)of integrin αvβ3in joint tissue of RA model. The expression rate were:0.47±0.15%(0score),12.36±1.19%(1score),14.51±1.08%(2score),27.62±1.55%(3score),29.79±2.06%(4score), with a statisticallydifference (F=235.21，P<0.01). The integrin αvβ3expression levelson joint tissue followed the trend:4score≈3score>2score≈1score》0score, that is to say, the receptor expression levels of4score and3score were much high than2,1and0score (P<0.05), but the levelsbetween4and3score,2and1score were similar (t=2.12and1.82,P>0.05).6. There was a linear positive correlation (r=0.852, P<0.05) between theankle uptake of99mTc-3PRGD2and the integrin αvβ3expression levels.Conclusion:In this study, we can draw the following conclusions by using the newradioactive molecular probe99mTc-3PRGD2for the first time to explore itsdiagnostic value in rheumatoid arthritis:1.99mTc-3PRGD2can be used in the diagnosis of RA.2. The uptake of the ankle gradually increased with the severity ofarthritis.3. There is a linear positive correlation between the ankle uptake of99mTc-3PRGD2and αvβ3integrin expression levels, providing the basisof the anti-angiogenesis therapy of RA in the future. |
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