稳定同位素在蛋白质合成率测定中的应用

由于放射性同位素对人体有害,故逐渐被稳定同位素取代,同时随着质谱仪的出现和发展,稳定同位素的应用日趋广泛,目前最常用的稳定同位素测定蛋白质合成率方法有两种:即持续灌注法及冲击法.     

稳定性核素在测定大鼠组织蛋白质合成中的应用

目的:研究应用稳定性核素(L-15N亮氨酸)测定大鼠组织蛋白质合成率的方法. 方法:分别测定静脉注射相同剂量L-15N亮氨酸不同时相的大鼠组织15N丰度及不同剂量L-15N亮氨酸的同一时相大鼠组织15N丰度. 结果:大鼠组织中游离及结合氨基酸同位素丰度在注射后半小时内几乎呈线性上升并达高峰,游离氨基酸15N丰度维持4 h后缓慢下降,结合氨基酸15N丰度在半小时至12 h之内基本维持不变;随着注射剂量的增加,大鼠组织蛋白质分数合成率亦增加.当L-15N亮氨酸剂量＞1.0 mmol/kg,分数合成率并不随施加L-15N Leucine剂量的加大而增加. 结论:在进行大鼠组织蛋白质合成率测定时,一次性静脉注射的测量最佳时限为半小时,剂量为1.0 mmol/kg.     

Variability in Skeletal Muscle Protein Synthesis Rates in Critically Ill Patients

(1) Background: Muscle protein synthesis in critically ill patients is, on average, normal despite dramatic muscle loss, but the variation is much larger than in controls. Here, we evaluate if this variation is due to 1) heterogeneity in synthesis rates, 2) morphological variation or infiltrating cells, or 3) heterogeneity in the synthesis of different protein fractions. (2) Methods: Muscle biopsies were taken from both legs of critically ill patients (n = 17). Mixed and mitochondrial protein synthesis rates and morphologies were evaluated in both legs. Synthesis rates of myosin and actin were determined in combined biopsies and compared with controls. (3) Results: Muscle protein synthesis rates had a large variability in the patients (1.4–10.8%/day). No differences in mixed and mitochondrial protein synthesis rates between both legs were observed. A microscopic examination revealed no morphological differences between the two legs or any infiltrating inflammatory cells. The synthesis rates for myosin were lower and for actin they were higher in the muscles of critically ill patients, compared with the controls. (4) Conclusions: The large variation in muscle protein synthesis rates in critically ill patients is not the result of heterogeneity in synthesis rates, nor due to infiltrating cells. There are differences in the synthesis rates of different proteins, but these do not explain the larger variations.     

应用L-15N亮氨酸测定大鼠骨骼肌蛋白质合成

目的:建立稳定同位素L-15N亮氨酸测定大鼠骨骼肌蛋白质合成率的方法.方法:分别测定静脉注射相同剂量L-15N亮氨酸不同时相的大鼠骨骼肌15N丰度及不同剂量L-15N亮氨酸同一时相的大鼠骨骼肌15N丰度.结果:大鼠骨骼肌游离氨基酸池中15N同位素丰度在注射后30 min内呈线性上升并达高峰,维持4 h后缓慢下降,骨骼肌蛋白质中的15N丰度30 min至12 h基本维持不变;随着注射剂量的增加,大鼠骨骼肌蛋白质分数合成率亦增加,当L-15N亮氨酸剂量＞1.0 mmol/kg,分数合成率并不随施加L-15N亮氨酸剂量的加大而增加.结论:在进行大鼠骨骼肌蛋白质合成率测定时,一次性静脉注射的测量最佳时限为30 min,剂量为1.0 mmol/kg.     

Dietary protein intake affects albumin fractional synthesis rate in younger and older adults equally

Inclusion of dietary protein in meals and beverages affects the hepatic synthesis of the protein albumin. Besides dietary protein, several factors can influence albumin metabolism and affect plasma albumin. The role of aging in albumin synthesis is unclear. Recent research documents that albumin synthesis rate is influenced comparably in younger and older adults by dietary protein ingestion and changes in dietary protein quantity. This emphasizes the importance for all adults to consume an adequate amount of dietary protein.     

L-15N亮氨酸和质谱测定大鼠肝蛋白质合成

目的:建立稳定同位素L-15N亮氨酸测定大鼠肝蛋白质合成率的方法.方法:分别测定静脉注射相同剂量L-15N亮氨酸不同时相的大鼠肝15N丰度及不同剂量L-15N亮氨酸同一时相的大鼠肝15N丰度.结果:大鼠肝游离氨基酸池中15N同位素丰度在注射后30 min内呈线性上升并达高峰,维持4 h后缓慢下降,肝蛋白质中的15N丰度30 min至12 h基本维持不变;随着注射剂量的增加,大鼠肝蛋白质分数合成率亦增加,当L-15N亮氨酸剂量＞1.0 mmol/kg,分数合成率并不随施加L-15N亮氨酸剂量的加大而增加.结论:在进行大鼠肝蛋白质合成率测定时,一次性静脉注射的测量最佳时限为30 min,剂量为1.0 mmol/kg.     

Urea synthesis in patients with chronic pancreatitis: relation to glucagon secretion and dietary protein intake

BACKGROUND & AIMS: Up-regulation of urea synthesis by amino acids and dietary protein intake may be impaired in patients with chronic pancreatitis (CP) due to the reduced glucagon secretion. Conversely, urea synthesis may be increased as a result of the chronic inflammation. The aims of the study were to determine urea synthesis kinetics in CP patients in relation to glucagon secretion (study I) and during an increase in protein intake (study II). METHODS: In study I, urea synthesis rate, calculated as urinary excretion rate corrected for accumulation in total body water and intestinal loss, was measured during infusion of alanine in 7 CP patients and 5 control subjects on spontaneous protein intake. The functional hepatic nitrogen clearance (FHNC), i.e. urea synthesis expressed independent of changes in plasma amino acid concentration, was calculated as the slope of the linear relation between urea synthesis rate and plasma alpha -amino nitrogen concentration. In study II, 6 of the patients of study I had urea synthesis and FHNC determined before and after a period of 14 days of supplementation with a protein-enriched liquid (dietary sequence randomized). RESULTS: Study I: Alanine infusion increased urea synthesis rate by a factor of 10 in the control subjects, and by a factor of 5 in the CP patients (P<0.01). FHNC was 31.9+/-2.4 l/h in the control subjects and 16.5+/-2.0 l/h (P<0.05) in the CP patients. The glucagon response to alanine infusion (AUC) was reduced by 75 % in the CP patients. The reduction in FHNC paralleled the reduced glucagon response (r(2)=0.55, P<0.01). Study II: The spontaneous protein intake was 0.75+/-0.14 g/(kg x day) and increased during the high protein period to 1.77+/-0.12 g/(kg x day). This increased alanine stimulated urea synthesis by a factor of 1.3 (P<0.05), FHNC from 13.5+/-2.6 l/h to 19.4+/-3.1 l/h (P<0.01), and the glucagon response to alanine infusion (AUC) by a factor of 1.8 (P<0.05). CONCLUSIONS: Urea synthesis rate and FHNC are markedly reduced in CP patients. This is associated with, and probably a result of, impaired glucagon secretion, and predicts a lower than normal postprandial hepatic loss of amino nitrogen. An increase in dietary protein intake increases alanine stimulated urea synthesis and FHNC by a mechanism that involves an increase in glucagon. This indicates that the low FHNC during spontaneous protein intake included an adaptation to the low protein intake, effectuated by a further decrease in glucagon secretion.     

外科患者手术后医院感染直接经济损失评价

目的 探讨外科患者手术后医院感染所造成的直接经济损失及特点,为医院感染管理部门决策提供科学依据。方法 选择2016年1月1日-2018年12月31日某三级甲等综合性医院外科手术后发生医院感染的100例患者为病例组,采用1：1配对病例对照研究方法,选择100例手术后未发生医院感染的患者为对照组,采用配对设计的秩和检验方法,比较两组患者直接经济损失及住院日数差异。结果 病例组与对照组比较,住院费用（中位数）增加19 866.3元（Z=-8.338,P<0.01）,住院日数（中位数）增加8.0 d（Z=-6.857,P<0.01）;住院费用增加前三的手术为同种异体肾移植术、神经系统手术及泌尿系统手术,住院日数增加前三的手术为胆囊切除术、椎间盘破坏或切除术、泌尿系统手术,两组比较差异均有统计学意义（均P<0.05）;住院费用增加前三的感染为多部位感染、下呼吸道感染及腹腔内组织感染,住院日数增加前三的感染为多部位感染、深部切口感染及表浅切口感染,两组比较差异均有统计学意义（均P<0.05）。结论 外科患者手术后发生医院感染可导致巨大的直接经济损失,医院感染控制部门应采取有效的防控措施,减少外科多部位感染、下呼吸道感染及手术部位感染等感染的发生,减轻患者经济负担。     

Five preference-based indexes in cataract and heart failure patients were not equally responsive to change

Objective

To compare the responsiveness to clinical change of five widely used preference-based health-related quality-of-life indexes in two longitudinal cohorts.

Study Design and Setting

Five generic instruments were simultaneously administered to 376 adults undergoing cataract surgery and 160 adults in heart failure management programs. Patients were assessed at baseline and reevaluated after 1 and 6 months. The measures were the Short Form (SF)-6D (based on responses scored from SF-36v2), Self-Administered Quality of Well-being Scale (QWB-SA), the EuroQol-5D developed by the EuroQol Group, the Health Utilities Indexes Mark 2 (HUI2) and Mark 3 (HUI3). Cataract patients completed the National Eye Institute Visual Functioning Questionnaire-25, and heart failure patients completed the Minnesota Living with Heart Failure Questionnaire. Responsiveness was estimated by the standardized response mean.

Results

For cataract patients, mean changes between baseline and 1-month follow-up for the generic indices ranged from 0.00 (SF-6D) to 0.052 (HUI3) and were statistically significant for all indexes except the SF-6D. For heart failure patients, only the SF-6D showed significant change from baseline to 1 month, whereas only the QWB-SA change was significant between 1 and 6 months.

Conclusions

Preference-based methods for measuring health outcomes are not equally responsive to change.     

Specific effects of protein deprivation on thymus and spleen; rates of protein synthesis in lymphocytes derived from thymus,spleen and bone marrow

Young adult male rats (body weight 90 g) were fed for 6 days a low protein (3% casein) diet and compared with rats fed a diet optimal in protein (20% casein). To study the dietary effects of protein, but not energy deficiency, intake of energy per unit body weight was kept constant. Wet weights and DNA content of thymus and spleen organs decreased in the low protein diet group. The in vitro incorporation of 14C-leucine into protein by isolated ribosomes was diminished in thymus by 22% and in spleen by 33% per mg of ribosomal RNA, and per mg of DNA by 43% in thymus and 48% in spleen. Lymphocytes were separated by Ficoll gradients. As compared with controls lymphocyte number from thymus decreased by 90%, that of spleen by 43% and of bone marrow by 20%. The rates of protein synthesis were significantly reduced after protein restriction in lymphocytes of the 3 organs. The strongest effects on the rates of protein synthesis were observed in bone marrow. Reduction in lymphocytes recovered was most pronounced in thymus. The results indicate that malnutrition by protein, but not energy deficiency, elicites specific effects on the 3 lymphocyte producing or containing organs studied.     

Effects of non-esterified stanols in a liquid emulsion on cholesterol absorption and synthesis in hypercholesterolemic men

Summary Background Background Numerous studies have shown that dietary plant sterols (phytosterols and phytostanols) and their esters can decrease cholesterol absorption. However, few researchers have examined the effects of plant sterols on cholesterol absorption and synthesis using stable isotope tracers, instead of relying on endogenous pathway precursors. Further, we have worked with non-esterified lecithin-solubilized stanols as opposed to the more frequently studied esterified sterols and stanols. The vehicle was an oil-in-water liquid emulsion rather than the more common spread vehicle typically employed. Aim of the study To determine the effects of relatively low doses of lecithin-solubilized non-esterified stanols in liquid emulsions on cholesterol absorption and synthesis in mildly hypercholesterolemic subjects. Methods In a randomized, double blind crossover design, 12 mildly hypercholesterolemic men received either a free phytostanol supplement (3 g/d in 3 servings) or a control treatment for 3 days. Cholesterol endogenous synthesis rate was determined using the rate of incorporation of deuterium from body water into newly formed cholesterol molecules. Cholesterol absorption at the intestinal level was determined using the dual isotope method using ¹³C cholesterol injected intravenously and ¹⁸O cholesterol given orally. Results Cholesterol absorption was 55.7 ± 6.5 % for the control and 33.5 ± 5.3 % for the phytostanol treatment. This massive reduction of the cholesterol absorption did not induce, on average, a difference in cholesterol endogenous synthesis which was measured at 0.074 ± 0.0015 pool/d for plant sterols and 0.0736 ± 0.0015 pool/d for controls (p > 0.05). Conclusions The results demonstrated that lecithin-solubilized stanols administrated during a short period of time (3 days) in an oil-in-water emulsion can dramatically decrease cholesterol absorption, without a consistent, concomitant increase in synthesis, which is highly suggestive of effective LDL cholesterol lowering. The effects of synthesis should be verified in a longer study with more subjects. Received: 17 September 2001, Accepted: 17 December 2001