Histological assessment of cellular half-life in tissues in vivo

The assessment of cellular half-life is of fundamental importance for cell biology and biomedicine. Here, we show that cellular half-life in tissues can be histologically measured under steady state conditions in vivo by analyzing the loss of 5-bromo-2′-deoxyuridine (BrdU)-labeled cells over time after withdrawal of long-term BrdU labeling. To achieve efficient continuous cell labeling, we implanted BrdU-containing subcutaneous slow-release pellets into 12-month-old male Fischer 344 rats, delivering BrdU at a dose of 75 mg/kg per day over 1 (n = 20) or 3 weeks (n = 20). Four to five rats each were killed directly after the labeling or 1, 3, and 7 weeks post-labeling. Cellular half-life after withdrawal of BrdU was analyzed by nonlinear regression analysis of the labeling index, using a model of one-phase exponential decay. We initially validated our technique in the duodenum, where we determined a half-life of 2.4 days for crypt cells. Next, we applied this method to other tissues, and found a half-life of 2.2 weeks for cardiac endothelial cells, and of 5–6 days for pancreatic duct cells. In conclusion, we believe that this novel approach is an important step forward in the histological assessment of cellular half-life.     

Amine promiscuity and toxicology analysis

Drug discovery programs often face challenges to obtain sufficient duration of action of the drug (i.e. seek longer half-lives). If the pharmacodynamic response is driven by free plasma concentration of the drug then extending the plasma drug concentration is a valid approach. Half-life is dependent on the volume of distribution, which in turn can be dependent upon the ionization state of the molecule. Basic compounds tend to have a higher volume of distribution leading to longer half-lives. However, it has been shown that bases may also have higher promiscuity. In this work, we describe an analysis of in vitro pharmacological profiling and toxicology data investigating the role of primary, secondary, and tertiary amines in imparting promiscuity and thus off-target toxicity. Primary amines are found to be less promiscuous in in vitro assays and have improved profiles in in vivo toxicology studies compared to secondary and tertiary amines.     

人体肝癌细胞系(SMMC-7721)糖皮质激素受体的半衰期

用抑制蛋白质合成的方法,测定了人体肝癌细胞系(SMMC-7721)糖皮质激素受体(GCR)的半衰期。结果显示,在蛋白质合成被抑制79.30±3.69%的情况下,GCR的半衰期为3.5±0.3h,降解速度常数为0.200±0.017h~(-1)。如果正常细胞GCR也具有如此短的半衰期,则提示GCR对内外环境的变化可做出迅速的反应,可能在靶细胞对激素反应的调节中起着活跃的作用。     

Dynamics of injected somatostatin in blood of patients with hepatic failure and acromegaly

Plasma somatostatin levels were measured by radioimmunoassay (RIA) at various times after rapid injection into the blood of 4 patients with acromegaly, 4 patients with hepatic failure, and 4 healthy subjects. In contrast to the single peak found in normal and acromegalic individuals, two distinct peaks were observed in each patient with liver failure. The first occurred at about the same time as that observed in the other two groups, but the second occurred about 3 min later. This second peak could not be distinguished immunologically from the intact somatostatin tetradecapeptide. The half-time disappearance of somatostatin in patients with hepatic failure was significantly longer than in the normal subjects. Acromegalic subjects tended to have the shortest half-time disappearance of the injected somatostatin and the highest peak level. The results are consistent with the possibility that altered metabolism and/or binding of somatostatin occurs in hepatic failure and in acromegaly.     

Plasma half-life extension of small recombinant antibodies by fusion to immunoglobulin-binding domains

Many therapeutic proteins possessing a small size are rapidly cleared from circulation. Half-life extension strategies have therefore become increasingly important to improve the pharmacokinetic and pharmacodynamic properties of protein therapeutics. Here, we performed a comparative analysis of the half-life extension properties of various bacterial immunoglobulin-binding domains (IgBDs) derived from Staphylococcus protein A (SpA), Streptococcus protein G (SpG), and Finegoldia (formerly Peptostreptococcus) protein L (PpL). These domains, composed of 50-60 amino acid residues, were fused to the C terminus of a single-chain Fv and a bispecific single-chain diabody, respectively. All fusion proteins were produced in mammalian cells and retained their antigen-binding properties. The half-lives of the antibody molecules were prolonged to varying extents for the different IgBDs. The strongest effects in mice were observed for domain C3 of SpG (SpG(C3)) followed by domains B and D of SpA, suggesting that SpG(C3) is particularly useful to extend the plasma half-life of small proteins.     

Cross-species Binding Analyses of Mouse and Human Neonatal Fc Receptor Show Dramatic Differences in Immunoglobulin G and Albumin Binding

The neonatal Fc receptor (FcRn) regulates the serum half-life of both IgG and albumin through a pH-dependent mechanism that involves salvage from intracellular degradation. Therapeutics and diagnostics built on IgG, Fc, and albumin fusions are frequently evaluated in rodents regarding biodistribution and pharmacokinetics. Thus, it is important to address cross-species ligand reactivity with FcRn, because in vivo testing of such molecules is done in the presence of competing murine ligands, both in wild type (WT) and human FcRn (hFcRn) transgenic mice. Here, binding studies were performed in vitro using enzyme-linked immunosorbent assay and surface plasmon resonance with recombinant soluble forms of human (shFcRn^WT) and mouse (smFcRn^WT) receptors. No binding of albumin from either species was observed at physiological pH to either receptor. At acidic pH, a 100-fold difference in binding affinity was observed. Specifically, smFcRn^WT bound human serum albumin with a K_D of ∼90 μm, whereas shFcRn^WT bound mouse serum albumin with a K_D of 0.8 μm. shFcRn^WT ignored mouse IgG1, and smFcRn^WT bound strongly to human IgG1. The latter pair also interacted at physiological pH with calculated affinity in the micromolar range. In all cases, binding of albumin and IgG from either species to both receptors were additive. Cross-species albumin binding differences could partly be explained by non-conserved amino acids found within the α2-domain of the receptor. Such distinct cross-species FcRn binding differences must be taken into consideration when IgG- and albumin-based therapeutics and diagnostics are evaluated in rodents for their pharmacokinetics.     

Cellular aspects of tolerance. VII. Inheritance of the resistance to tolerance induction

The half-lives of elimination ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) of ¹³¹I-RGG from the body of normal A or Balb/c animals was much longer than the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of SJL mice. At all ages, the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of normal hybrids (A × SJL, SJL × A, Balb/c × SJL) was similar to or longer than that of the A or Balb/c parents. Thus, in terms of the $\text{T}\text{1}\text{2}$ of normal animals, the SJL responsiveness to ¹³¹I-RGG appeared to be a recessive trait. Tolerance could be induced in newborn animals and, in terms of $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, the degree of unresponsiveness at the age of 6 weeks, was the same in A, Balb/c, A × SJL, and Balb/c × SJL animals but was much shorter in SJL mice. Thus, in neonatally induced tolerance, the duration of tolerance was recessive for the SJL type. The average $\text{T}{}_{\mathrm{<mtext>built1</mtext><mtext>2</mtext>}}$ after tolerance induction in 3-week-old hybrids (A × SJL, SJL × A, Balb/c × SJL) was similar to that of the A or Balb/c parent, but by the 8th and 12th week it approached the average $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of the SJL parent. Comparing 8-week-old hybrids, the average $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ was longest in A × SJL hybrids and identical in SJL × A and Balb/c × SJL mice. An examination of $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ distribution in various 8- and 12-week-old crosses and backcrosses revealed a fairly large proportion of individuals with a $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ which was intermediate between SJL and the other parent. There was a tendency for this number to decrease in 12 weeks as compared to 8-week-old mice. In 8-week-old mice, the number of animals with intermediate $\text{T}{}_{\mathrm{<mtext>built1</mtext><mtext>2</mtext>}}$ was smallest when SJL was the maternal animal [(SJL × A); SJL × (A × SJL); SJL × (SJL × A)]. There was no link between $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of tolerant animals and either the immunoglobulin allotype (MuAl/MuA2) or the C5 eniotype (MuB1 positive/MuB1 negative).     

人绒毛膜癌细胞JEG-3中SEPSECS、TRNAU1AP蛋白表达稳定性的分析

目的:通过测定人绒毛膜癌细胞JEG-3中SEPSECS、TRNAU1AP两蛋白的半衰期,分析JEG-3细胞内SEPSECS、TRNAU1AP两蛋白表达的稳定性.方法:采用蛋白合成抑制剂放线茵酮作用于人绒毛膜癌细胞JEG-3,用MTT法确定放线茵酮对细胞的最适作用浓度,之后用最适浓度的放线菌酮处理JEG-3,利用Western b1ot检测10个时间点SEPSECS、TRNAU1AP蛋白表达量,确定SEPSECS、TRNAU1AP蛋白半衰期.结果:CHX作用于细胞的最适浓度为0.1μg/mL,与对照组相比,SEPSECS蛋白表达量在4h、8h有显著性差异(P＜0.01);而TRNAU1AP蛋白表达量在2h、4h有显著性差异(P＜0.01).结论:在JEG-3细胞中SEPSECS蛋白的半衰期可能为4h～8h,而TRNAU1AP蛋白的半衰期可能为2h～4h,前者半衰期明显大于后者,由此,可推测SEPSECS蛋白在JEG3细胞中表达的稳定性要高于TRNAU1AP蛋白,同时也为进一步分析二者在其他肿瘤细胞的表达情况提供依据.     

人组织型纤溶酶原激活剂（t－PA）突变体FrGGI的构建、表达及特性分析

为了获得半衰期延长,特异活性提高及具有ＰＡＬ－１抗性的新型ｔ－ＰＡ溶栓剂,利用基因重组及定位突变技术构建了ｔ－ＰＡ的Ｋ１、Ｋ２区糖基化位点消除,ＰＡＩ－１结合位点缺失,Ｆ与Ｅ区连接序列Ｈｉｓ４４～Ｓｅｒ５０置换为纤粘蛋白Ⅰ型Ｆ区间连接序列ＧｌｕＳｅｒＬｙｓＰｒｏＧｌｕＡｌａＧｌｕＧｌｕ的ｔ－ＰＡ组合突变体ＦｒＧＧＩ,并在中国仓鼠卵巢细胞中获得了高效表达。对表达产物的生物学特性分析表明,ＦｒＧＧＩ在大鼠血浆中的半衰期延长了１５倍,并获得了ＰＡＩ－１抗性,是一株很有希望的新型溶栓剂候选株。     

毕赤酵母高效分泌长效人生长激素的研究

目的:为了延长人生长激素(HGH)在血浆中的半衰期,构建了高效分泌表达人血清白蛋白(HSA)与HGH融合蛋白(HSA-HGH)的工程毕赤酵母菌株。方法:从人胎肝cDNA文库中扩增HSA基因,从HGH工程菌载体中扩增HGH基因,将其克隆至真核表达载体pHIL-D2,载体线性化后采用电击法转化毕赤酵母GS115。通过原位双层膜法筛选高效分泌表达菌株。分别采用SDS-PAGE和Western印迹鉴定融合蛋白。对工程酵母培养条件进行研究,发酵液经离子交换层析、亲和层析和分子筛层析纯化。纯化的蛋白经N端序列测定,分子量测定和等电聚焦电泳进行鉴定。冻干的蛋白制剂经食蟹猴试验进行药代动力学和药效动力学测试。结果:确立了工程酵母的最佳培养工艺,融合蛋白表达量达100mg/L。纯化后蛋白纯度达95%以上,得率达42%。融合蛋白与预期结果一致,经食蟹猴试验,显示有良好的生物活性,与等摩尔剂量的重组人生长激素相比,半衰期延长6.8倍,清除率慢44倍。结论:融合蛋白呈现明显的长效动力学特征,为开发重组长效人生长激素HSA-HGH融合蛋白药物(rHSA-HGH)奠定了基础。