| Background Despite growing evidences suggesting that stem cell transplantationcan improve cardiac failure in experiment myocardial infarction, the result of recentlypublished clinical trails is controversial. One of the main differences of clinical trailsand animal experiments is that the treatment of antiplatelet drugs was carried out inclinical trails, but not in animal experiments. The treatment of antiplatelet drugs mayinhibit not only aggregation but also release of growth factors contained in platelet.Platelet alpha granules contain a variety of growth factors, such as platelet derivedgrowth factor(VEGF), Platelet Factor 4(PF4), vWF, released into the surroundingenvironment during activation. Meanwhile, a variety of potent angiogenic stimulators,including vascular endothelial growth factor(VEGF), stromal-derived factor-1, basicfibroblast growth factor(bFGF), and transforming growth factor(TGF), are stored inplatelets and released during activation. This property has been used in clinicalmedicine to accelerate the repair process by activating in vitro autologous plateletswith thrombin. We hypothesized that activated platelet may play an important role inthe healing process, which may be blunted in clinical trials. The aim of this researchwas to assess the effect of transplantation of thrombin-activated platelet-rich plasmaon the healing process after acute myocardial infarction.Methods Venous blood from healthy rats was collected. Platelet-rich plasma (PRP)was obtained by centrifugation at 120×g for 5 minutes. The PRP was removed and centrifuged at 1,000×g for 15 minutes. Platelets sedimented on the bottom of the tube,while platelet-poor plasma (PPP) was in the top. Platelet-rich plasma and platelet-poorplasma was stimulated with thrombin (2unit/mL). The platelet suspension then wascentrifuged (2,000×g), and the supematant was stored at -80℃. 8-wk-old Wistar malerats were randomized to PRP group that received activated plateletorich plasmasupernatant (APRPS), operation control group that received activated platelet-poorplasma supematant (APPPS), and sham operation group. Ligation of the left coronaryartery (LCA) was performed. Immediately after ligation of LCA, 100μL APRPS orAPPPS was injected in five different sites at the infarcted border zone. Rats wereanesthetized and sacrificed on the 7th day and 28th day for ex vivo analysis. One partof hearts were stopped with 15% KC1 and removed for determination of leftventricular passive pressure-volume relationship; Another part was stored in at -80℃for making embedded sections. Picrosirius red staining plus circularly polarizedmicroscopy was performed to analyze myocardial infarct thickness, myocardialinfarcted size, index of expansion and collagen remodeling. Immunohistochemicalanalysis plus fluorescence microscope was used for detection of angiogenesis andmyocardial cross-sectional area.Results Compared with control group, PRP group was associated with a leftwardshift of diastolic pressure-volume curve, suggesting reduction in ventricular globalchamber dilation of PRP group on the 28th day. Compared with control group, PRPgroup was associated with a significant increase in myocardial infarct thickness on the7th day (1.93±0.20 vs 1.75±0.12mm, P＜0.01), and a non-significant increase inmyocardial infarct thickness on the 28th day (1.75±0.15 vs 1.59±0.25mm); Comparedwith control group, PRP group was associated with a non-significant decrease inmyocardial infarct size on the 28th day (40.34±4.62 vs 45.60±5.72％); Compared withcontrol group, PRP group was associated with a significant decrease on the 7th(0.41±0.04 vs 0.54±0.06, P＜0.05) and a non-significant decrease on the 28th day (0.64±0.08 vs 0.73±0.09) in index of expansion of left ventricular; 7 days and 28 daysafter MI, the collagen volume fraction of both PRP group and control group had adynamic trend of increase in the infracted region and non-infarcted region. Comparedwith control group, PRP group was associated with a significant increase in collagenvolume fraction in the infracted region on both 7th day and 28th day(42.25±6.72 vs31.93±7.69％, P＜0.01; 0.64±0.08 vs 0.73±0.09％, P＜0.01), and a non-significantdecrease in collagen volume fraction in the non-infarcted region on both 7th day and28th day (7.40±1.06 vs 7.31±1.59％, 8.48±3.89 vs 8.02±1.42％); Green, yellow,orange and red collagen fiber is in order of increasing thickness using picrosirius redstaining in the circularly polarized light. In myocardial scars, compared with controlgroup, PRP group was associated a significant increase in the proportion of greenfibers on 7th day(45.3±2.6 vs 34.6±2.5％, P＜0.01), a significant decrease in theproportion of green fibers on the 28th day(13.7±1.8 vs 24.7±1.5％, P＜0.01), and asignificant increase in the proportion of red fibers on the 28th day(66.9±1.0 vs43.0±1.6％, P＜0.01); Compared with control group, PRP group was associated with asignificant decrease in myocardial cross-sectional areas in the non-infarcted region onboth 7th day and 28th day(419.38±63.65 vs 448.52±79.45μm~2, P＜0.01; 446.05±87.82vs 490.63±83.44μm~2, P＜0.01); Compared with control group, PRP group wasassociated with a significant increase in length density of arterioles in the infarctedregion on both 7th day and 28th day(165.5±32.1 vs 84.2±29.3/mm~2, P＜0.05;116.9±2.4 vs 88.1±5.4/mm~2, P＜0.01)and in length density of arterioles in thenon-infarcted region on both 7th day and 28th day (79.4±8.2 vs 44.1±6.4/mm~2; P＜0.01;63.8±6.0 vs 47.4±4.5/mm~2, P＜0.01); Compared with control group, PRP group wasassociated with a significant increase in capillary density in the infarcted region onboth 7th day and 28th day(82.9±12.5 vs 43.9±11.5 /mm~2, P＜0.01; 67.1±9.8 vs33.4±9.1/mm~2, P＜0.01) and in the non-infarcted region on both 7th day and 28th day(64.8±12.4 vs 36.2±8.7/mm~2; P＜0.01; 54.4±10.0 vs 29.6±8.0/mm~2, P＜0.01). Conclusions Transplantation of activated platelet supernatant could favourablyaffect the recovery of left ventricular function and post-infarction remodeling process.Potential mechanism for enhanced left ventricular function and infarct remodeling liesin improved angiogenesis resulted in accelerated healing process after myocardialinfarction. |
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