The Reductive Half-reaction of Xanthine Dehydrogenase from Rhodobacter capsulatus: THE ROLE OF GLU232 IN CATALYSIS*

The kinetic properties of an E232Q variant of the xanthine dehydrogenase from Rhodobacter capsulatus have been examined to ascertain whether Glu²³² in wild-type enzyme is protonated or unprotonated in the course of catalysis at neutral pH. We find that k_red, the limiting rate constant for reduction at high [xanthine], is significantly compromised in the variant, a result that is inconsistent with Glu²³² being neutral in the active site of the wild-type enzyme. A comparison of the pH dependence of both k_red and k_red/K_d from reductive half-reaction experiments between wild-type and enzyme and the E232Q variant suggests that the ionized Glu²³² of wild-type enzyme plays an important role in catalysis by discriminating against the monoanionic form of substrate, effectively increasing the pK_a of substrate by two pH units and ensuring that at physiological pH the neutral form of substrate predominates in the Michaelis complex. A kinetic isotope study of the wild-type R. capsulatus enzyme indicates that, as previously determined for the bovine and chicken enzymes, product release is principally rate-limiting in catalysis. The disparity in rate constants for the chemical step of the reaction and product release, however, is not as great in the bacterial enzyme as compared with the vertebrate forms. The results indicate that the bacterial and bovine enzymes catalyze the chemical step of the reaction to the same degree and that the faster turnover observed with the bacterial enzyme is due to a faster rate constant for product release than is seen with the vertebrate enzyme.     

Monophosphoryl lipid A alleviated radiation-induced testicular injury through TLR4-dependent exosomes

Radiation protection on male testis is an important task for ionizing radiation-related workers or people who receive radiotherapy for tumours near the testicle. In recent years, Toll-like receptors (TLRs), especially TLR4, have been widely studied as a radiation protection target. In this study, we detected that a low-toxicity TLR4 agonist monophosphoryl lipid A (MPLA) produced obvious radiation protection effects on mice testis. We found that MPLA effectively alleviated testis structure damage and cell apoptosis induced by ionizing radiation (IR). However, as the expression abundance differs a lot in distinct cells and tissues, MPLA seemed not to directly activate TLR4 singling pathway in mice testis. Here, we demonstrated a brand new mechanism for MPLA producing radiation protection effects on testis. We observed a significant activation of TLR4 pathway in macrophages after MPLA stimulation and identified significant changes in macrophage-derived exosomes protein expression. We proved that after MPLA treatment, macrophage-derived exosomes played an important role in testis radiation protection, and specially, G-CSF and MIP-2 in exosomes are the core molecules in this protection effect.     

Circulating exosomes repair endothelial cell damage by delivering miR-193a-5p

Circulating exosomes delivering microRNAs are involved in the occurrence and development of cardiovascular diseases. How are the circulating exosomes involved in the repair of endothelial injury in acute myocardial infarction (AMI) convalescence (3-7 days) was still not clear. In this study, circulating exosomes from AMI patients (AMI-Exo) and healthy controls (Normal-Exo) were extracted. In vitro and in vivo, our study showed that circulating exosomes protected endothelial cells (HUVECs) from oxidative stress damage; meanwhile, Normal-Exo showed better protective effects. Through the application of related inhibitors, we found that circulating exosomes shuttled between HUVECs via dynamin. Microarry analysis and qRT-PCR of circulating exosomes showed higher expression of miR-193a-5p in Normal-Exo. Our study showed that miR-193a-5p was the key factor on protecting endothelial cells in vitro and in vivo. Bioinformatics analyses found that activin A receptor type I (ACVR1) was the potential downstream target of miR-193a-5p, which was confirmed by ACVR1 expression and dual-luciferase report. Inhibitor of ACVR1 showed similar protective effects as miR-193a-5p. While overexpression of ACVR1 could attenuate protective effects of miR-193a-5p. To sum up, these findings suggest that circulating exosomes could shuttle between cells through dynamin and deliver miR-193a-5p to protect endothelial cells from oxidative stress damage via ACVR1.     

Q开关激光爆破技术对豚鼠皮肤色素的影响

目的研究Q开关激光爆破术对豚鼠黑素细胞的影响及照射周边组织的变化,为临床治疗皮肤色素病变提供实验依据。方法用Q开关-YAG激光分别照射豚鼠黑色毛区及棕色毛区(波长分别用1064nm和530nm,光斑直径2mm),实验动物20只,随机分四组,分别于照射后间隔7d、10d、14d取材,照射前取材作对照,10%甲醛固定,冰冻切片,分别用HE和DOPA反应显示黑素细胞。结果照射后皮肤黑色素颗粒逐渐减少至消失,照射后30d黑毛区与棕毛区肉眼见照射区皮肤变白,毛也变白,HE染色皮肤、毛囊及毛未见黑色素颗粒,DOPA反应表皮黑色素细胞、毛囊和毛均呈阴性反应,部分豚鼠棕毛区毛及毛囊见黄色色素颗粒。结论波长1064nm和532nm Q-YAG激光对豚鼠皮肤黑色素细胞和黑色素颗粒的破坏效果显著;但对棕色色素清除效果较差。波长1064nm Q-YAG激光对豚鼠皮肤黑色素消减与照射次数有关,与照射间隔时间长短无关。     

TNFα-initiated oxidative/nitrative stress mediates cardiomyocyte apoptosis in traumatic animals

Whole body non-penetrating trauma causes myocardial infarction in humans and mechanical trauma (MT) results in cardiac dysfunction in animals. Our recent study demonstrated that incubation of cardiomyocytes with plasma isolated from MT animals causes significant cardiomyocyte apoptosis that can be blocked by neutralization of TNFα. The present study attempted to obtain direct in vivo evidence to support that overproduction of TNFα plays a causative role in trauma-induced cardiomyocyte apoptosis. Non-lethal MT caused significant TNFα overproduction (2.4-fold at 1.5 h after MT) and increased cardiomyocyte apoptosis (starting 3 h and peaking 12 h after MT). Pharmacological inhibition of TNFα with etanercept or TNFα gene deletion reduced post-trauma myocyte apoptosis (P < 0.01). Expression of iNOS and NADPH oxidase, overproduction of NO and , and excessive protein nitration in the MT heart were all significantly reduced in etanercept-treated or TNFα^−/− mice, suggesting that oxidative/nitrative stress may contribute to TNFα-initiated myocyte apoptosis in MT hearts. Additional experiments demonstrated that inhibiting iNOS (1400W) or NADPH oxidase (apocynin), or scavenging peroxynitrite (FP15) significantly reduced myocyte apoptosis in MT animals (P < 0.01). Collectively, these data demonstrated that non-lethal mechanical trauma caused significant TNFα production that in turn stimulated myocardial apoptosis via oxidative/nitrative stress.