| 1 Background and objectiveMyocardial infarction(MI), an outcome of coronary artery disease due to persistent acute myocardial ischemia and necrosis caused by hypoxia is currently one of the major disability and cause of deaths in clinical practice among cardiovascular diseases. Ventricular remodeling(VR) after myocardial infarction, refers to the joint action of neurohormonal regulatory mechanisms activated by the inflammatory cytokines and other factors, Remodeling the structure and function of the heart in accordance with a certain pattern causing abnormalities of cardiac morphology, blood flow(hemodynamic), progressive expansion of left ventricle, gradually reduced contractility, eventually leading to heart failure(HF) or death. Hence heart failure is an unfavorable consequence of ventricular remodeling after myocardial infarction. Thereby inhibiting ventricular remodeling become clinically improved quality of life and prognosis of the treatment in myocardial infarction.Ventricular remodeling is processed by developing a variety of coding and non-coding gene regulation, but a lot of gene regulation mechanism is still unclear. micro RNA(mi R) are a class of small RNA with around 22 nucleotides having cell regulatory role. Recent studies have shown that mi RNA are involved in a variety of cardiovascular diseases such as in heart function and myocardial remodeling regulation. Thum reported, mi R-21 is main regulator of ERK-MAP kinase signaling pathway. mi R-21 levels increased selectivity during myocardial infarction by suppressing SPRY1 regulating ERK-MAP kinase signaling pathway, thus involved in the regulation of ventricular remodeling.Low level laser irradiation(LLLI) therapy has been developed over 60 years in the medical profession. Animal studies, clinical practice have fully proved that it is a more mature physical therapy. LLLI therapy is effective and safe which uses low energy output power(milliwatt) in the absence of tissue damage, adjustment of the target tissue, and other biological activation stimulus to promote wound healing, reduce inflammation, enhanced mitochondrial metabolism, accelerate the synthesis of ATP, improve cell proliferation. In recent years, Yang and other studies have shown that LLLI can increase left ventricular wall thickness after myocardial infarction, reduce myocardial collagen tissue generation. Some scholars revealed LLLI after infarction can improve tissue microenvironment, reduce myocardial infarct size.Currently, very few study have been reported about LLLI treatment of myocardial infarction(MI) in rats and its effect on mi R-21 expression and ventricular remodeling. This study aims at the effect of LLLI(635nm diode laser) on mi R-21 expression and the effect on ventricular remodeling 3 weeks after myocardial infarction.2 Maerials and Methods2.1 Materials and groups110 adult female SD rats, weighing 220 g ~ 250 g, were randomly divided into three groups: sham operation group(30), the control group(40), and the treatment group(40). Myocardial infarction model was prepared by ligating the left anterior descending coronary artery(LAD) in the control and treatment groups while simply site threading but without ligating the LAD in the sham operation group.2.2 Screening MI modelAfter three weeks of prepared MI model, the echocardiography screening of the rats heart were performed, the standard model of myocardial infarction were: 1. A Left ventricular ejection fraction(LVEF) <60%; 2. Left ventricular fractional shortening.(LVFS) <30%; 3. Ultrasound practitioner found one or more abnormal appearance of the anterior left ventricular wall motion. At least two of the above screening model is used for selecting the qualified MI model of rats' heart.2.3 Low level laser irradiation treatmentLow energy laser irradiation after 3 weeks of qualified screening results of infarction model: using a laser diode(power 6m W, wavelength 635nm), irradiation of infarcted area about 15 mm away from the diode with the duration of 125 s, laser energy density received was 0.96 J / cm2, 3 group were irradiated, but the sham group and the control group were irradiated without opening power supply.2.4 mi R-21 expressionAt time points 1h, 24 h, 48 h, 72 h, and 7d after the low-energy laser treatment in each group, rats were intra-abdominally anesthetized, intubated, opened the chest and harvested the heart quickly(3 to 6 rats/ time point), heart is placed into physiological saline at 4 ?heart stroke evacuated cavity blood collection box. Central and edge infarct tissue are collected and preserved into-80 ?refrigerator. The relative expression levels of micro RNA-21 in collected tissues are detected by using RT-q PCR.2.5 Cardiac function and tissue slices observedl week after LLLI processing, 2nd time ultrasound testing was performed, evaluation of left ventricular function in control group and treatment group of rats(n = 3 ~ 4 / group). Equipment used during the inspection, indicators and methods of evaluation and the 1st echocardiographic screening evaluations of MI model are the same. 4 weeks after MI model, heart was taken out, each group of 3 to 5 rats, thoroughly rinsed with saline, avoid any blood residues, placed in 10% formaldehyde solution, fixed, HE staining, Masson staining, measuring the collagen fiber content.2.6 Statistical analysisUsing SPSS19.0 software(IBM, USA) for statistical analysis, data were expressed as mean ± standard deviation(x ± s) that the groups were compared using ANOVA, mean pairwise comparisons using LSD test, ? = 0.05 level of significance test.3 Results3.1 Myocardial infarction modelThree weeks after Preparation of myocardial infarction(MI) model, 69 rats(86.3%) were remaining in the control group and the treatment groups, by ultrasound screening, a total of 53 rats(66.3%) were in standard MI model.3.2 Expression of mi R 21-infarct centermi R-21 expression in the central infarct zone after 1h of LLLI treatment: mi R-21 expression was significantly lower in the control group than the sham group(P <0.05), and statistically significant; mi R-21 expression in the treatment group was less than sham group(P <0.05), as well as the control group(P <0.05), both showed a statistically significant difference.mi R-21 expression in Sham group changed little in each time period, while the expression in control group increased slowly from the beginning 1h and approached with the sham group at 7d, the difference was not statistically significant(P> 0.05). The levels of mi R-21 expression in the treatment group was highest at 48 h and decreased slowly and became close to the sham group at 7d, but the difference was still statistically significant(P <0.05).3.3 Expression of mi R 21-infarct border zonemi R-21 expressions in the sham group found a little change in the respective time periods. Expression of mi R-21 at 1h, 24 h, 48 h, 72 h gradually decline in the control group, compared with the sham group, difference was statistically significant(P <0.05), the lowest expression was at 7d, mi R 21-expression at this time with the sham group showed no statistical significance(P> 0.05). The treatment group began to increase expression in 1h, 48 h peak, dropped to the lowest at 7d when, but still higher than the control group(47.20 ± 1.21 VS 42.12 ± 0.55, P <0.05), the difference was statistically significant.3.4 Evaluation of Left Ventricular FunctionThe treatment group; comparison before LLLI processing and one week after LLLI processing: LVEF(%)(39.37 ± 1.35 VS 47.62 ± 2.75, P <0.05), LVFS(%)(19.23 ± 3.12 VS 24.15 ± 2.53, P <0.05) differences were statistically significant; comparing the control group and the treatment group one week after the LLLI processing: LVEF(%)(39.83 ± 1.64 VS 47.62 ± 2.75, P <0.05), LVFS(%)(18.03 ± 1.25 VS 24.15 ± 2.53, P <0.05), the difference was statistically significant.3.5 Section observationLLLI group myocardial infarct size was significantly reduced compared with control group(P <0.05), a statistically significant difference; left ventricular wall thickness comparison, was significantly reduced in LLLI group and the control group than in the sham group(P <0.05), but LLLI group increased significantly compared with control group(P <0.05), a statistically significant difference; compare left ventricular wall collagen fibers, LLLI group and the control group was significantly increased(P <0.05) compared with sham group but significantly reduced in LLLI group than control group(P <0.05), a statistically significant difference; TUNEL staining method for the detection of myocardial apoptosis, apoptosis was significantly higher in LLLI group and the control group than sham group(P <0.05), LLLI apoptosis rate lower than control group(P <0.05), a statistically significant difference.4 ConclusionCardiac remodeling is a key process of cardiovascular diseases which can be associated with atrial fibrillation, heart failure, myocardial infarction and other manifestations. mi R-21 plays an important role in cardiac remodeling which can delay myocardial fibrosis and inhibit apoptosis. LLLI treatment of myocardial infarction and the peri-infarct area is a safe, efficient therapy, play specific role in regulation of mi R-21 expression and provide myocardial protection but the regulatory mechanisms still need further study. |
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