Prolonged Half-Life in the Circulation of a Chemical Conjugate Between a Pro-Urokinase Derivative and Human Serum Albumin
Jérôme BretonNieves PezziAgnese MolinariLuisella BonominiJ. LansenGonzalo González de BuitragoIgnacio Priéto
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Pro‐urokinase is a natural plasminogen activator that displays a clot‐lysis activity through a fibrin‐dependent mechanism. It seems to be a promising agent for the treatment of coronary thrombosis. Like tissue‐type plasminogen activator and two‐chain urokinase‐type plasminogen activator, pro‐urokinase has a very short half‐life in circulation. It has been described that conjugation of serum albumin with pro‐urokinase in plasma may occur that could protect this protein from degradation. In this study we describe the insertion of an extra cysteine residue in the N‐terminal end of des‐(C11–K135)‐pro‐urokinase (Δ125‐proUK), a pro‐urokinase deletion mutant lacking amino acids 11–135. We have expressed and purified the new mutein [H5K, S9C, N10T]des‐(C11‐K135)‐pro‐urokinase (Cys‐Δ125‐pro‐urokinase) and chemically conjugated it with serum albumin via the extra cysteine of Cys‐Δ125‐pro‐urokinase. The purified conjugate obtained has a lower specific amidolytic activity (72000 U/mg) than unconjugated Cys‐Δ125‐pro‐urikinase (240000 U/mg) due to its higher molecular mass and has a similar fibrinolytic activity in a clot lysis test to that of Δ125‐pro‐urokinase. We established an ELISA to measure the concentration of the conjugate in plasma and to follow the pharmacokinetics of the conjugate in monkeys after bolus injection. The conjugate displays significant lysis of human plasma clots in vivo and a dramatic increase of the half‐life in the circulation, with respect to pro‐urokinase and Δ125‐pro‐urokinase. Therefore, preliminary biological characterisation of this conjugate indicates that it could be a good candidate to inject as a bolus, compared with the infusion regimen needed with pro‐urokinase.Keywords:
Conjugate
Derivative (finance)
Serum Albumin
Human serum albumin
Circulation (fluid dynamics)
To determine whether there was a difference between pre- and posthemodialysis serum albumin levels and, if so, whether that difference correlated with the amount of fluid removed during treatment.This descriptive study used a comparative data analysis strategy.287 paired measurements of pre- and post-hemodialysis serum albumin levels were collected from 46 patients in a midwestern hemodialysis center.Pre- and posthemodialysis serum albumin levels were obtained using the bromcresol green method.The pretreatment mean for serum albumin levels was 3.875 gm/dL (SD .4) and the posttreatment mean was 4.273 gm/dL (SD .599), significant at p < 0.0001. The amount of fluid removed during treatment was strongly correlated with the difference between pre- and posttreatment albumin levels (R = .6149; p < 0.0001). When data were sub-divided into three groups according to the amount of fluid removed during treatment, the mean differences between pre- and post hemodialysis albumin were significant at p < 0.0001.The strong correlation with fluid removed during hemodialysis suggests that fluid overload may be responsible for the significantly higher posttreatment albumin values in most patients.
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The regulation of albumin synthesis and serum protein secretion was studied in regenerating rat liver by measuring incorporation of 14C-leucine. Albumin was isolated to radiochemical purity, utilizing a method which eliminates the influence of precursor pool changes on protein labeling. Changes in the size of the product pool were measured. The following results were obtained. 1. The time period between intracaval injection of 14Cleucine and the appearance of radioactive protein in the blood (secretion time) decreased from 15 min for normal animals to a minimum of 10 min at 48 hours after removal of 70% of the liver. 2. At 10 min after intracaval injection of 14C-leucine, 3.5% of total protein radioactivity was found in albumin in normal liver, whereas in regenerating liver only 1.4% of the total protein radioactivity was incorporated into albumin. 3. Albumin concentration in the serum decreased from 29.2 mg of albumin per ml of serum for normal rats to a minimum of 17.3 mg of albumin per ml of serum at 4 days after partial hepatectomy. 4. The half-life of albumin was 2.66 days for normal rats and 2.13 days for animals, 48 hours after partial hepatectomy. 5. The intravascular pool of albumin decreased from 100 mg of albumin per 100 g, body wt, in normal rats to 57.8 mg of albumin per 100 g, body wt, in partially hepatectomized animals, 48 hours after operation. The extravascular and the total body pool of albumin also decreased after partial hepatectomy to a minimum at 24 hours after the operation. In contrast to the intravascular pool, the extravascular and the total body pool increased again, reaching a plateau between 2 and 4 days after the operation. 6. During regeneration, the proportion of leucine to other amino acids in total liver protein did not change. Also, this proportion did not differ significantly from that found in serum albumin. 7. The net rate of albumin synthesis changed only slightly from 20.1 mg of albumin per day per g of liver for normal to 23.9 mg albumin per day per g of liver for regenerating liver 48 hours after partial hepatectomy. In contrast, the net rate of synthesis of total liver protein increased from 576 mg protein per day per g of liver in normal rats to 1710 mg of protein per day per g of liver in rats 48 hours after partial hepatectomy.
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Albumin infusion is one of the therapeutic options in hypoalbuminemia patients. Serum albumin can be used to determine the albumininfusion therapy, prognosis and monitoring of liver cirrhosis. The time difference in measurement of serum albumin by bromcresol green(BCG) and bromcresol purple (BCP) methods can give different results. Serum albumin examination was done in 20 sera taken fromcirrhosis patients. Serum albumin was then evaluated before treatment, one (1) hour and 24 hours after the patient received an infusionof albumin and examined by bromcresol green (BCG) and bromcresol purple (BCP) methods. The serum albumin level by BCG methodincreased with a coefficient of 0.12 (p-value=0.022) with BCG method before (1.94±0.32 mg/dL) and after one (1) hour (2.06±0.32mg/dL) receiving intravenous albumin. The coefficient of albumin levels before and after 24 hours (2.12±0.38 mg/dL) was 0.18 (pvalue=0.07), whereas the increased levels of serum albumin after one (1) hour and after 24 hours of intravenous albumin, were notsignificant (p-value=0.467). The BCP method showed that serum albumin before, after one (1) hour and after 24 hours receivingintravenous albumin were 1.68±0.36 mg/dL, 1.87±0.36 mg/dL and 2.12±0.63 mg/dL respectively. The albumin levels showed asignificant increase before and after one (1) hour infusion of albumin (p-value=0.00), both levels shown before and after 24 hours(p-value=0.001), as well as one (1) hour and 24 hours after receiving intravenous albumin (p-value=0.04). The results of this studyshowed that increased serum albumin by BCG method could be detected after 1 (one) hour, whereas by BCP method could only be detectedafter 24 hours receiving intravenous albumin.
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The binding of glycyrrhizin (GLZ) to human serum and human serum albumin (HSA) was examined by an ultrafiltration technique. Specific and nonspecific bindings were observed in both human serum and HSA. The association constants (K) for the specific binddings were very similar : 1.31×105M-1 in human serum and 3.87×105M-1 in HSA. The number of binding sites (n) and the linear binding coefficient (Φ) in HSA were 1.95 and 3.09×103M-1, respectively.When the human serum protein concentration ws assumed to be 4.2% (equal to the measured serum albumin concentration), n in human serum was 3.09, which is similar to the n value in HSA, and Φ in human serum was 0.71×103M-1, which is reasonably close to that for HSA. The binding pattern of GLZ with human serum protein on Sephadex G-200 column chromatography showed that GLZ binds to only the albumin fraction.It was concluded that the GLZ-binding sites in human serum exist mainly on albumin and GLZ binds to specific and nonspecific binding sites at lower and higher concentrations that approximately 2mM, respectively.
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Studies have been made on the molecular weight and amino acid composition of albumin from the blood serum and liver, as well as on its content in liver extracts and in the blood serum of male rabbits at the age of 1, 30, 180, and 720 days. During postnatal life, quantitative changes in the amino acid composition of the proteins investigated take place, which are more significant in liver albumin than in serum albumin. Albumin content of the blood serum and liver extracts decreases at later ontogenetic stages (in 180- and 720-day animals), which is presumably associated with the decrease in synthesis of this protein by the liver. The molecular weight of the albumin remains constant in all age groups being typical for serum albumin of vertebrates.
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The interaction of long-chain fatty acids with cells is important for their uptake and metabolism, as well as their involvement in signalling processes. The majority of long-chain fatty acids circulating in plasma exist as complexes with serum albumin. Thus an understanding of the involvement of serum albumin in these processes is vitally important. The effect of serum albumin on the uptake of long-chain fatty acids was studied in 3T3-L1 adipocytes. Serum albumin had a stimulatory effect on oleate uptake at all ratios of oleate: serum albumin tested. Furthermore, the rate of oleate uptake was saturable with increasing concentrations of serum albumin when the oleate: serum albumin ratio, and therefore the concentration of uncomplexed oleate, remained constant. This was not due to uptake being limited by dissociation of oleate from serum albumin, because oleate did not appear to be limiting. Furthermore, at very high ratios of oleate: serum albumin, when the concentration of uncomplexed oleate was predicted to be large relative to the amount of oleate taken up by cells, the rate of oleate uptake was still dependent on the albumin concentration. Serum albumin, covalently labelled with the photoreactive fatty acid 11-m-diazirinophenoxy[11-3H]undecanoate, bound to cells in a manner exhibiting both saturable (Kd 66.7 microM) and non-saturable processes. These results indicate that the stimulatory effect of serum albumin on the rate of oleate uptake is due to a direct interaction of serum albumin with the cells and point to an involvement of albumin binding sites in the cell surface in the cellular uptake of long-chain fatty acids.
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