Stable incorporation of a lipophilic daunorubicin prodrug into apolipoprotein E-exposing liposomes induces uptake of prodrug via low-density lipoprotein receptor in vivo.
(25/6522)
Many tumors express elevated levels of low-density lipoprotein (LDL) receptors. Therefore, native LDL and synthetic LDL-like particles have been proposed as carriers for antineoplastic drugs. We demonstrated earlier that small apolipoprotein E (apoE)-exposing liposomes were specifically recognized by the LDL receptor. In this study, we incorporated a lipophilic derivative of daunorubicin (LAD) into the apoE liposomes. Up to 11 molecules of LAD could be incorporated per particle without significantly changing the size, lipid composition, and ability to bind apoE of the liposomes. The biological fate of the prodrug was largely determined by its carrier (70% of the initially incorporated LAD was still associated to the liposomes after 4 h of circulation in mice). Compared with free daunorubicin, the circulation half-life of the liposome-associated prodrug was substantially prolonged and undesired tissue disposition was reduced. The role of the LDL receptor in the metabolism of LAD-loaded apoE liposomes was demonstrated in rats with up-regulated hepatic LDL receptors. In these rats, the liver uptake of the prodrug and carrier was increased 5-fold. The addition of apoE was essential for LDL receptor-mediated uptake of the drug-carrier complex. In LDL receptor-deficient mice, the circulation time of both the prodrug and the carrier increased approximately 2-fold compared with wild-type mice. We conclude that LAD-loaded apoE liposomes constitute a stable drug-carrier complex that is well suited for LDL receptor-mediated selective drug delivery to tumors. (+info)
Orexin A but not orexin B rapidly enters brain from blood by simple diffusion.
(26/6522)
We determined the ability of orexin A and orexin B, recently discovered endogenous appetite enhancers, to cross the blood-brain barrier (BBB) of mice. Multiple time-regression analysis showed that an i.v. bolus of 125I-orexin A rapidly entered the brain from the blood, with an influx rate (Ki = 2.5 +/- 0.3 x 10(-4) ml/g.min) many times faster than that of the 99mTc-albumin control. This relatively rapid rate of entry was not reduced by administration of excess orexin A (or leptin) or by fasting for 22 h, even when penetration into only the hypothalamus was measured. Lack of saturability also was shown by perfusion in blood-free buffer. HPLC revealed that most of the injected 125I-orexin A reached the brain as intact peptide. Capillary depletion studies showed that the administered peptide did not remain bound to the endothelial cells comprising the BBB but reached the brain parenchyma. Efflux of 125I-orexin A from the brain occurred at the same rate as 99mTc-albumin. The octanol/buffer partition coefficient of 0.232 showed that orexin A was highly lipophilic, whereas the value for orexin B was only 0.030. Orexin B, moreover, was rapidly degraded in blood, so no 125I-orexin B could be detected in intact form in brain when injected peripherally. Thus, although orexin B is rapidly metabolized in blood and has low lipophilicity, orexin A rapidly crosses the BBB from blood to reach brain tissue by the process of simple diffusion. (+info)
Human endothelin-1 clearance kinetics revealed by a radiotracer technique.
(27/6522)
Levels of endothelin-1 (ET-1) are elevated in many disease states, although its total body kinetics of elimination are poorly understood. Therefore, it remains uncertain whether the presence of elevated levels of ET-1 in the setting of disease are secondary to changes in production or clearance or some combination thereof. Using a 125I-labeled ET-1 infusion technique, the volume of distribution and kinetics of clearance of endothelin were described in five normal volunteers. Heart rate, blood pressure, right atrial pressure, and arterial blood samples for the counting of 125I and the measurement of ET-1 were obtained at multiple time points before and up to 45 h after the start of the infusion. The radiotracer infusion had no effect on heart rate, blood pressure, right atrial pressure, or endogenous ET-1 levels. ET-1 clearance was best described by a three-compartment model, which revealed that ET-1 has a much longer terminal half-life and volume of distribution than was previously reported. This suggests extensive uptake of ET-1 in various organ systems and slow clearance. These new findings have important implications for the understanding of the pathophysiology of ET-1 in disease states as well as for the understanding and development of ET-1 receptor blockers and endothelin-converting enzyme inhibitors. (+info)
Uptake of iodinated human kidney alpha-D-mannosidase by rat liver- Association with membrane elements and stability in vivo and in vitro.
(28/6522)
1. Human kidney alpha-D-mannosidase (form A) was labelled with 125I to a specific radio-activity of approx. 2250muCi/mg of protein, essentially without loss of enzymic activity. The enzymic activity and radioactivity of the iodinated material also co-migrated in gel filtration and gel electrophoresis. 2. The binding of 125I-labelled mannosidase in vitro to particulate material in liver and kidney homogenates was of the other of 2 pg/mg of particulate material in liver and kidney homogenates was of the order of 2pg/mg of particulate protein withing 16h at 37 degrees C, and essentially zero in intervals of up to 60 min. The degradation in vitro of labelled exogenous mannosidase was of the order of 10-20pg/ 16th per mg of protein in postnuclear supernatant, and it was saturated entirely within 1h at 37 degrees C. 3. The binding of labelled mannosidase in vivo to particulate elements of liver homogenates 60 min after intravenous injection was at least 10 times higher in terms of specific radioactivity than the highest value attainable in vitro. Virtually all exogenous enzyme bound to liver particulate material could be recovered in macromolecular form after disruption of membranes by detergents. 4. The radioactive enzyme bound to liver particulate material could be detached almost completely by shearing, repeated freezing and thawing, and exposure to strong detergents under conditions that do not eliminate rough-endoplasmic-membrane structure. It could bot be released, however, by high salt concentration (0.5M-KC1) or by exposure to weak detergents such as Tween 80. The particle-bound enzyme should thus be associated with plasma membranes and lysosome-like elements. 5. Of the rat tissues studied, only liver could approach, within 60 min after the injection, the concentration of exogenous mannosidase found in the blood serum. The activity per g tissue weight fell progressively from liver (60% of serum value) to kidney (16% of serum value), lung (8% of serum vlaue), spleen (6% of serum value) and brain (0.9% of serum value). Most of the radioactive enzyme found in tissues other than liver appeared to be present in a free form, whereas in liver more than 50% of the labelled enzyme was associated with membrane elements. (+info)
Juvenile hypothyroidism among two populations exposed to radioiodine.
(29/6522)
We found an epidemic of juvenile hypothyroidism among a population of self-defined "downwinders" living near the Hanford nuclear facility located in southeast Washington State. The episode followed massive releases of 131I. Self-reported data on 60 cases of juvenile hypothyroidism (<20 years of age) among a group of 801 Hanford downwinders are presented, as well as data concerning the thyroid status of approximately 160,000 children exposed to radioiodine before 10 years of age as a result of the 26 April 1986 Chernobyl explosion in the former Soviet Union. These children were residents of five regions near Chernobyl. They were examined by standardized screening protocols over a period of 5 years from 1991 to 1996. They are a well-defined group of 10 samples. Fifty-six cases of hypothyroidism were found among boys and 92 among girls. Body burdens of 137Cs have been correlated with hypothyroidism prevalence rates. On the other hand, the group of juvenile (<20 years of age) Hanford downwinders is not a representative sample. Most of the 77 cases of juvenile hypothyroidism in the Hanford group were diagnosed from 1945 to 1970. However, the ratio of reported cases to the county population under 20 years of age is roughly correlated with officially estimated mean levels of cumulative thyroid 131I uptake in these counties, providing evidence that juvenile hypothyroidism was associated with radioiodine exposures. Because even subtle hypothyroidism may be of clinical significance in childhood and can be treated, it may be useful to screen for the condition in populations exposed to radioiodine fallout. Although radiation exposure is associated with hypothyroidism, its excess among fallout-exposed children has not been previously quantified. (+info)
Kinetics of thyroglobulin iodination and of hormone synthesis catalysed by thyroid peroxidase. Role of iodide in the coupling reaction.
(30/6522)
The kinetics of tyrosine iodination and of thyroxine synthesis in thyroglobulin, different reactions catalyzed by the same enzyme (thyroid peroxidase), have been compared. Thyroxine synthesis always began after a lag period of 3-5 min. This lag was constant whatever the rate of iodination; this rate of iodination was increased either by increasing the concentration of iodide or enzyme or by decreasing the concentration of thyroglobulin. Increasing the rate of iodination resulted in increasing the number of iodine atoms incorporated during the lag period. Thus the lag observed for thyroxine synthesis was constant and did not depend on the fact that free iodide or non-iodinated tyrosine residues of thyroglobulin were exhausted before thyroxine synthesis occurred. Finally, it appeared that, whatever the explanation of the lag, the enzyme catlyzes thyroid hormone synthesis at a slower rate than iodination. The existence of a lag also allowed us to prepare thyroglobulin samples with different iodine contents but without thyroid hormones. Thus iodination and thyroxine synthesis could be studied independently and the following results were obtained. 1. Iodotyrosine residues which can couple to form thytoxine are made considerably before coupling occurs. 2. H2O2 is required for coupling of these hormonogenic residues; thus the coupling reaction requires enzymic oxidation of the iodotyrosine residues. 3. In addition a strict requirement for iodide was needed for coupling; the requirement was dependent on the concentration of iodide. Thus iodide, a substrate of the iodination reaction, may also have other effects on the activity of thyroid peroxidase. (+info)
67Cu-versus 131I-labeled Lym-1 antibody: comparative pharmacokinetics and dosimetry in patients with non-Hodgkin's lymphoma.
(31/6522)
Antilymphoma mouse monoclonal antibody (MoAb) Lym-1, labeled with 67Cu or 131I, has demonstrated promising results in radioimmunotherapy (RIT) for lymphoma. Although 131I has played a central role in RIT thus far, some properties of 67Cu are preferable. A subset of our patients received both 67Cu- and 131I-labeled Lym-1, allowing a comparative evaluation of the two radiopharmaceuticals administered to a matched population of patients. Four patients with B-lymphocytic non-Hodgkin's lymphoma that had progressed despite standard therapy entered trials of 67Cu- and 131I-labeled Lym-1, which were injected 3-26 days apart. Lym-1 was conjugated to 6-[p-(bromoacetamido)benzyl]-1,4,7,11-tetraazacyclotetradecane-N,N ',N",N'"-tetraacetic acid (BAT) via 2-iminothiolane (2IT) and radiolabeled with 67Cu to prepare 67Cu-2IT-BAT-Lym-1; 131I-Lym-1 was preparred by the chloramine-T reaction. Planar imaging was used to quantitate 67Cu-2IT-BAT-Lym-1 or 131I-Lym-1 in organs and tumors daily for 3 days or longer. 67Cu-2IT-BAT-Lym-1 exhibited higher peak concentration in 92% (12 of 13) of tumors and a longer biological half-time in every tumor than 131I-Lym-1. The mean tumor concentration (%ID/g) of 67Cu-2IT-BAT-Lym-1 was 1.7, 2.2, and 2.8 times that of 131I-Lym-1 at 0, 24, and 48 h after injection, respectively. The mean biological half-times of 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 in tumor were 8.8 and 2.3 days, respectively. Consequently, the mean tumor radiation dose delivered by 67Cu-2IT-BAT-Lym-1 was twice that of 131I-Lym-1, 2.8 (range 0.8-6.7), and 1.4 (range 0.4-35) Gy/GBq, respectively. 67Cu-2IT-BAT-Lym-1 delivered a lower marrow radiation dose than 131I-Lym-1; hence, the tumor:marrow therapeutic indices were 29 and 9.7, respectively. Radiation doses from 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 to normal tissues were similar except for liver, which received a higher dose from 67Cu-2IT-BAT-Lym-1. Images obtained with 67Cu-2IT-BAT-Lym-1 were superior. Radiation dosimetry data for 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 agreed with corresponding data from the larger populations of patients from which the matched population for the current study was drawn. In conclusion, 67Cu-2IT-BAT-Lym-1 given to non-Hodgkin's lymphoma patients in close temporal proximity to 131I-Lym-1 exhibited greater uptake and longer retention in tumor, resulting in higher radiation dose and therapeutic index than 131I-Lym-1. These as well as other factors suggest that 67Cu-2IT-BAT-Lym-1 may be superior to 131I-Lym-1 for RIT. (+info)
Central role of epidermal growth factor (EGF) receptor density in anchorage-independent growth of normal rat kidney cells.
(32/6522)
Epidermal growth factor (EGF) receptor levels are known to play a central role in density dependent growth regulation of normal rat kidney (NRK) fibroblasts. Here we show that EGF receptor expression is strongly decreased when NRK cells are cultured under anchorage independent conditions, and that expression is returned to original levels upon cell readherence. Agents that stimulate anchorage independent growth (AIG) of NRK cells in the presence of EGF are shown to upregulate both EGF receptor promoter activity and (125)I-EGF binding capacity. These data show that two aspects of phenotypic transformation of NRK cells, namely density arrest and AIG, can both directly be correlated to EGF receptor levels. (+info)