Labeled leukocyte imaging: current status and future directions.

The ability to radiolabel inflammatory cells that migrate to foci of infection was a significant milestone in the evolution of infection imaging. More than 20 years after being approved for clinical use in the United States, labeled leukocyte imaging using cells labeled with [(99m)Tc]exametazime or [(111)In]oxine remains the radionuclide procedure of choice for diagnosing most infections in the immunocompetent population. In the central nervous system, labeled leukocyte imaging is useful for differentiating infection from tumor; in the postoperative setting, this test facilitates the differentiation of infection from normal postoperative changes. Labeled leukocyte imaging accurately diagnoses mycotic aneurysms and infected prosthetic vascular grafts. In patients with fever of unknown origin, a negative study excludes, with a high degree of certainty, infection as the source of fever. Labeled leukocyte imaging accurately diagnoses pedal osteomyelitis and is useful for distinguishing infection from the neuropathic joint in this population. Together with bone marrow imaging, the labeled leukocyte study is the imaging procedure of choice for diagnosing prosthetic joint infection. There are limitations to the test. Most of the leukocytes labeled are neutrophils, and the procedure is most useful for detecting neutrophil-mediated inflammatory processes, i.e., bacterial infections. It is less useful for illnesses in which the predominant cellular response is other than neutrophilic, such as most opportunistic infections and spinal osteomyelitis. The in vitro labeling procedure is time consuming and is not routinely available. Results of in vivo leukocyte labeling methods have been variable; none are available in the United States. Labeled leukocyte imaging suffers from inherently poor quality images. Single photon emission compute tomography/computed tomography improves lesion localization, and will undoubtedly improve the accuracy of the test. Efforts to develop methods of labeling white cells with positron emitting compounds are underway and, if successful, should further strengthen the role of nuclear medicine in infection imaging.

Transplanted hepatocytes engraft, survive, and proliferate in the liver of rats with carbon tetrachloride-induced cirrhosis.

Repopulation of the cirrhotic liver with disease-resistant hepatocytes could offer novel therapies, as well as systems for biological studies. Establishing whether transplanted hepatocytes can engraft, survive, and proliferate in the cirrhotic liver is a critical demonstration. Dipeptidyl peptidase IV-deficient F344 rats were used to localize transplanted hepatocytes isolated from the liver of syngeneic normal F344 rats. Cirrhosis was induced by administration of carbon tetrachloride with phenobarbitone and these drugs were withdrawn prior to cell transplantation. Cirrhotic rats showed characteristic hepatic histology, as well as significant portosystemic shunting. When hepatocytes were transplanted via the spleen, cells were distributed immediately in periportal areas, fibrous septa, and regenerative nodules of the cirrhotic liver. Although some transplanted cells translocated into pulmonary capillaries, this was not deleterious. At 1 week, transplanted cells were fully integrated in the liver parenchyma, along with expression of glucose-6-phosphatase and glycogen as reporters of hepatic function. Transplanted cells proliferated in the liver of cirrhotic animals and survived indefinitely. At 1 year, transplanted hepatocytes formed large clusters containing several-fold more cells than normal control animals, which was in agreement with increased cell turnover in the cirrhotic rat liver. The findings indicate that the cirrhotic liver can be repopulated with functionally intact hepatocytes that are capable of proliferating. Liver repopulation using disease-resistant hepatocytes will be applicable in chronic conditions, such as viral hepatitis or Wilson's disease.

Radionuclide analysis of drug-induced blood-pool changes in liver and other organs.

UNLABELLED: Although it is possible to repopulate the animal liver with transplanted hepatocytes, the success of such transplants depends, in part, on the number of transplanted cells that enter the hepatic sinusoids. Pharmacologic alteration of hepatic vascular tone, and hence blood volume, can increase the number of cells that are successfully transplanted. Although analysis of changes in vascular beds is helpful for developing strategies for cell transplantation, convenient methods to analyze such changes are lacking. The objective of this study was to determine whether 99mTc-labeled red blood cells could be used to reveal pharmacologically induced blood pool changes in various organs. METHODS: F344 rats were injected with syngeneic labeled red blood cells and subjected to blood pool analysis with gamma camera imaging. Animals were treated with phenylephrine, phentolamine, labetalol, and nitroglycerine. To correlate hepatic blood pool changes with structural alterations at the vascular level, microspheres were injected into the portal circulation of these animals. RESULTS: Phenylephrine significantly increased cardiac and pulmonary blood pools, findings in agreement with its alpha-adrenergic effects. Phentolamine increased the hepatic, splenic, and pulmonary blood pools, whereas labetalol increased only the pulmonary blood pool. Nitroglycerine increased both hepatic and splenic blood pools. Prior administration of phentolamine, labetalol, and nitroglycerine prevented the phenylephrine-induced changes. When microspheres were injected into the portal circulation after nitroglycerine administration, they penetrated more distal locations in the liver lobule. CONCLUSION: These data indicate that it is possible, using radionuclide methods, to noninvasively show pharmacologically induced hemodynamic changes. This finding is potentially useful for studying hepatic physiology and may also have applications for cell therapy.

Integration and proliferation of transplanted cells in hepatic parenchyma following D-galactosamine-induced acute injury in F344 rats.

To determine whether liver repopulation with cell transplantation could be of therapeutic value in acute hepatic failure, it is necessary to establish the fate of transplanted hepatocytes. This study used dipeptidyl peptidase IV-deficient F344 rats as recipients to analyse the engraftment and proliferation of transplanted hepatocytes. Syngeneic hepatocytes were transplanted intrasplenically 24-30 h after induction of liver injury by D-galactosamine (GalN). Portosystemic shunting was analysed with 99m-Tc-labelled albumin microspheres. GalN-treated rats showed characteristic hepatic necrosis, inflammation, gamma-glutamyl transpeptidase activation, and regenerative activity, without increased portosystemic shunting (>99% 99m-Tc activity was in the liver in normal and GalN-treated rats). Transplanted cells entered hepatic sinusoids promptly and were observed in liver plates at 48 h. The number of transplanted cells increased in GalN-treated rats by approximately seven-fold (range two- to 12-fold), along with evidence for DNA synthesis between 3 and 14 days after cell transplantation and greater prevalence of larger transplanted cell clusters. These findings indicate that the liver can be safely repopulated in animals with acute liver failure, although the time required for regenesis of plasma membrane structures and proliferation in transplanted hepatocytes will need to be considered in developing therapeutic strategies.

Mechanisms of cell engraftment during liver repopulation with hepatocyte transplantation.

Hepatocyte transplantation has excited much interest among investigators for applications in cell therapy and studies of fundamental mechanisms concerning liver biology. Progress in these areas has been greatly facilitated by the development of novel animal models. An understanding of early events during engraftment of transplanted cells is essential for optimal repopulation of the liver. Insights into how transplanted cells integrate in the parenchyma of the liver with reconstitution of specific plasma membrane structures is critical in devising therapeutic strategies for specific disorders. Moreover, these insights are necessary for understanding mechanisms concerning regulation of cell proliferation and gene expression in transplanted hepatocytes. Finally, analysis of the safety of cell transplantation is necessary for clinical applications of liver repopulation with cell transplantation. This review highlights selected advances in related areas concerning liver repopulation.

Synthesis of aminobenzyltriethylenetetraaminohexaacetic acid: conjugation of the chelator to protein by an alkylamine linkage.

The conjugation of a chelating agent to an antibody as an anchoring site for a radionuclide is the first step in the successful preparation of a radiolabeled antibody for a diagnostic and therapeutic application. The high affinity of the protein bound chelator towards radionuclide ensures a higher selectivity in the delivery of the radionuclide to the targeted tissue. 4-Aminobenzylderivativetriethlenetetraaminohexaacetic acid (TTHA), a hexadentate chelating agent has been now prepared for conjugation with proteins in view of the higher affinity of TTHA metal ions as compared to DTPA. The latent crosslinking potential of alpha-hydroxy aldehydes has been used to conjugate the new chelating agent to proteins through an alkylamine linkage. On incubation of amino benzyl TTHA with glycoladehyde at neutral pH and room temperature, the reagent is converted to oxo ethyl amino benzyl TTHA. On addition of albumin to this reaction mixture, the oxo ethylamino benzyl TTHA generates reversible schiff base adducts with the amino groups of albumin. The reduction of the Schiff base adducts of the chelator with the protein by sodium cyanoborohydride stabilizes the schiff base adducts as stable alkylamine linkages. 4-Thiocyanatobenzyl TTHA has also been prepared and conjugated to albumin through a thiocarbamoyl linkage. Both preparations of TTHA conjugated albumin complexed with 99mTc and 111In, with high affinity and no decomposition of the complex was noticed for at least up to 6 hrs after the preparation. The radiolabels complexed with these TTHA -albumin conjugates could not be 'chased' out by free DTPA. A comparison of the biodistribution of 111In, bound to the TTHA conjugated through an alkylamine and a thiocarbamoyl linkage showed that 111In complexed with alkylamine linked TTHA was retained in blood to a level nearly 17% higher compared to that seen with thicarbamoyl linked TTHA, one hr after the injection into mice. Thus, the alkylamine linkage appears to be more stable under the in vivo conditions. The glycolaldehyde mediated alkylation procedure offers a mild, simple and rapid method for preparation of drug-protein (antibody) conjugates.

Human serum albumin microspheres approximate initial organ-specific biodistributions of transplanted hepatocytes and are effective cell surrogates for safety studies.

Liver repopulation with transplanted hepatocytes will generate novel cell-based therapies, although translocation of transplanted cells into lungs through portasystemic shunts has the potential for embolic complications. To facilitate safety analysis of hepatocyte transplantation, we wished to obtain effective cell surrogates and analyzed biodistributions of similarly sized 99mTc-labeled human serum albumin microspheres and rat hepatocytes. Image analysis with dual 99mTc and 111In labels indicated that cells and microspheres were similarly distributed in the liver when injected into normal rats via the spleen. Also, their distributions were similar when injected via a femoral vein or the superior mesenteric vein with cells and microspheres localizing in lungs or liver, respectively. Upon intraportal injection in rats with portal hypertension, microspheres localized in both liver and lungs, consistent with portasystemic shunting. These data demonstrate that human serum albumin microspheres are effective cell surrogates for approximating the safety of hepatocyte transplantation and should be clinically useful.

Analysis of hepatocyte distribution and survival in vascular beds with cells marked by 99mTC or endogenous dipeptidyl peptidase IV activity.

Knowledge of the kinetics of cell distribution in vascular beds will help optimize engraftment of transplanted hepatocytes. To noninvasively localize transplanted cells in vivo, we developed conditions for labeling rat hepatocytes with 99mTc-pertechnetate. The incorporated o9mTc was bound to intracellular proteins and did not impair cell viability. When 99mTc hepatocytes were intrasplenically injected into normal rats, cells entered liver sinusoids with time-activity curves demonstrating instantaneous cell translocations. 99mTc activity in removed organs was in liver or spleen, and lungs showed little activity. However, when cells were intrasplenically transplanted into rats with portasystemic collaterals, 99mTc appeared in both liver sinusoids and pulmonary alveolar capillaries. To further localize cells, we transplanted DPPIV+ F344 rat hepatocytes into syngeneic DPPIV-recipients. Histochemical staining for DPPIV activity demonstrated engraftment of intrasplenically transplanted cells in liver parenchyma. In contrast, when 99mTc hepatocytes were injected into a peripheral vein, cells were entrapped in pulmonary capillaries but were subsequently broken down with redistribution of 99mTc activity elsewhere. Intact DPPIV+ hepatocytes were identified in lungs, whereas only cell fragments were present in liver, spleen, or kidneys. These findings indicate that although the pulmonary vascular bed offers advantages of easy accessibility and a relatively large capacity, significant early cell destruction is an important limitation.

Efficacy and safety of repeated hepatocyte transplantation for significant liver repopulation in rodents.

BACKGROUND & AIMS: Significant liver repopulation by hepatocyte transplantation will advance clinical applications. The aim of this study was to test the hypothesis that translocation of transplanted cells into liver plates will allow repeated cell transplantation for increasing the transplanted hepatocyte mass. METHODS: Hepatocytes were transplanted via spleen from either F344 rats into syngeneic recipients deficient in dipeptidyl peptidase IV or from transgenic hepatitis B surface antigen-producing G26 mice with hepatitis B virus into nontransgenic congeneic recipients. Portosystemic shunting was shown by radiological methods. RESULTS: Repeated hepatocyte transplantation led to progressively increased liver repopulation. Transplantation of 1.75 x 10(8) hepatocytes in three divided doses repopulated more than an estimated 5% of the host rat liver, with 3.8 x 10(6) +/- 0.1 x 10(6) transplanted cells/cm3 liver. This was a tenfold or threefold mean increase in transplanted cell number compared with recipients of 2.0 x 10(7) or 7.5 x 10(7) cells transplanted in single sessions, respectively (P < 0.001). Repeated hepatocyte transplantation interfered with neither cell integrations in liver parenchyma nor secretory function of transplanted cells. Portal hypertension, portasystemic collaterals, or intrahepatic shunting were not observed in cell recipients. CONCLUSIONS: Repeated transplantation of hepatocytes in large numbers is safe and effective and should advance strategies for liver repopulation.

Studies of liver repopulation using the dipeptidyl peptidase IV-deficient rat and other rodent recipients: cell size and structure relationships regulate capacity for increased transplanted hepatocyte mass in the liver lobule.

The feasibility of liver repopulation with hepatocytes has been shown, although clinical applications demand significant hepatic replacement. To show whether portal vascular bed in large animals could accomodate a greater cell number, we analyzed liver repopulation in syngeneic Fischer 344 rats deficient in dipeptidyl peptidase IV. This system allowed localization of transplanted normal hepatocytes in liver or various ectopic sites, as well as dual studies for analysis of gene expression. Interestingly, the product of a dipeptidyl peptidase IV substrate inactivated bile canalicular adenosine triphosphatase (ATPase) activity in normal but not in dipeptidyl peptidase IV-deficient rats, which allowed localization of dipeptidyl peptidase IV-deficient hepatocytes in normal rat liver for additional reversed transplantation systems. Further studies with genetically marked cells showed that because of the size difference between hepatocytes and portal vein radicles, intrasplenically transplanted cells were distributed in periportal areas (zone 1) in mice, whereas in larger animals (rats or rabbits) cells were also distributed downstream to midlobular (zone 2) or perivenous (zone 3) areas. Transplantation of an escalating number of hepatocytes showed that adult rats tolerated intrasplenic injection of a large cell number in single sessions (up to 1 X 10(8), approximately 10% to 15% of the host hepatocyte mass). Morphometric analysis of recipient livers showed survival of a significantly greater cell number with incorporation in host liver plates. At 4 weeks, transplantation of 2 x 10(7) hepatocytes into adult rats led to a survival of 1.4 +/- 1.0 x 10(6) transplanted cells/cm3 liver, whereas after transplantation of 5 x 10(7) cells or 7.5 x 10(7) cells, the number of surviving transplanted cells in the liver significantly increased to 4.1 +/- 1.4 x 10(6) transplanted cells/cm3 liver (mean, 2.9-fold; P<.003) and 5.5 +/- 1.3 x 10(6) transplanted cells/cm3 liver (mean, 3.9-fold; P<.003), respectively. When cells were injected in greater numbers, transplanted hepatocytes retained normal function and produced more serum albumin or hepatitis B surface antigen in deficient hosts. These data indicate the feasibility in larger animals of significant liver repopulation with hepatocyte transplantation. Use of dipeptidyl peptidase IV-deficient rats should help further analysis of mechanisms in liver repopulation.

111Indium labeling of hepatocytes for analysis of short-term biodistribution of transplanted cells.

Hepatocyte transplantation is useful for ex vivo gene therapy and liver repopulation. Methods for hepatic reconstitution have recently been developed but optimization of hepatocyte transplantation systems is necessary. To develop systems for noninvasive assessment of the biodistribution of transplanted cells, we labeled hepatocytes with 111indium-oxine. Our initial studies showed that hepatocytes incorporated 111indium-oxine with an efficiency of approximately 20%. After labeling, cell viability was unchanged and 111indium was present in hepatocytes after overnight culture, as well as after intrasplenic transplantation. Transplanted cells were successfully localized by means of scintigraphic imaging. The scintigraphic patterns of cell distribution were different when hepatocytes were transplanted by means of either spleen or internal jugular vein, which deposit cells into separate vascular beds. Quantitative analysis of the biodistribution of 111indium-labeled hepatocytes indicated that within 2 hr of intrasplenic transplantation, cells were predominantly localized in liver and spleen, and occasionally in lungs. To determine whether the rate of intrasplenic cell injection influenced translocation of hepatocytes, we transplanted cells in normal rats. Despite intrasplenic cell injection at a variety of rates, organ-specific distribution of 111indium-labeled hepatocytes remained unchanged. Labeling with 111indium did not affect long-term survival of transplanted hepatocytes. These results indicate that 111indium-labeling of hepatocytes should greatly assist noninvasive analysis in the short-term of the biodistribution of transplanted hepatocytes.

Studies on the safety of intrasplenic hepatocyte transplantation: relevance to ex vivo gene therapy and liver repopulation in acute hepatic failure.

Hepatocytes transplanted into the host liver engraft promptly, retain normal function, and survive indefinitely. Although intrasplenic transplantation is effective in delivering hepatocytes to the liver, to define potentially limiting complications, we studied its safety in normal, cirrhotic, and partial portal vein-ligated rats. In normal rats, portal pressures increased severalfold after hepatocyte transplantation but returned to normal within 3 weeks. In contrast, in portal hypertensive rats with partial portal vein ligation or cirrhosis, portal pressures were either unchanged or increased less after hepatocyte transplantation. However, more transplanted cells migrated to the lungs along with a rise in right atrial pressures in portal hypertensive rats. Further quantitative studies using 111Indium-labeled hepatocytes showed that intrasplenic retention of transplanted hepatocytes was similar in all animal groups. Intrahepatic cell translocation was comparable in normal and cirrhotic rats, whereas fewer cells migrated to the liver in partial portal vein-ligated rats. The most remarkable difference, however, was significantly greater intrapulmonary translocation of hepatocytes in portal hypertensive rats, which was presumably related to portosystemic shunting. These results indicate that because intrasplenic hepatocyte transplantation induces only temporary portal hypertension in normal subjects, potential strategies to augment liver repopulation could include repeated cell transplantation. This should be useful for optimizing the results of ex vivo gene therapy, or other hepatocyte-based therapies. However, the hepatic and portal hemodynamic status requires careful evaluation in portal hypertensive or cirrhotic subjects if serious complications are to be avoided.

Permanent engraftment and function of hepatocytes delivered to the liver: implications for gene therapy and liver repopulation.

To examine the distribution of intrasplenically transplanted hepatocytes, we used HBsAg-producing G7 HBV transgenic hepatocytes or cells labeled with 111In. Most hepatocytes translocated to the liver (55% +/- 7%; mean +/- S.D.); the spleen retained a smaller fraction (15% +/- 3%); and some transplanted cells localized in lungs (3%) or pancreas (1%). Transplanted hepatocytes were rapidly assimilated into the liver lobule. Morphometrical quantitation indicated that the numbers of transplanted hepatocytes in the liver at 48 hr and at 9 mo after transplantation were similar. Serum HBsAg was detected in recipients of the G7 HBV hepatocytes during the 1-yr experiment. These results indicate that a large number of hepatocytes can be reproducibly delivered to the liver by transplantation into the spleen. Transplanted hepatocytes engraft rapidly, assimilate into host liver, maintain normal function and survive permanently. Systems for safe delivery and localization of hepatocytes in the liver represent a critical step toward successfully accomplishing hepatocyte-directed gene therapy and repopulation of the acutely devastated liver.

Cellular ions in hypertension, diabetes, and obesity. A nuclear magnetic resonance spectroscopic study.

To investigate the cellular basis linking hypertension, non-insulin-dependent diabetes mellitus (NIDDM), and obesity, we used 31P and 19F nuclear magnetic resonance spectroscopy to measure intracellular pH (pHi), free magnesium (Mgi), and cytosolic free calcium (Cai) in erythrocytes of obese and NIDDM subjects with and without hypertension. Compared with normotensive, nondiabetic controls (Cai, 25.2 +/- 1.4 nM; Mgi, 232 +/- 8 microM), Cai was elevated in both normotensive (36.8 +/- 2.7 nM, sig = 0.005) and hypertensive (43.4 +/- 2.9 nM, sig = 0.001) NIDDM subjects, and Mgi was concomitantly suppressed (normotensive: 206 +/- 11 microM, sig = 0.05; hypertensive: 196 +/- 8 microM, sig = 0.001). Similar but less striking changes were noted in obese subjects. Values of pHi were significantly lower (sig = 0.05) in all hypertensive groups compared with their normotensive controls. Continuous relations were observed for all subjects between Cai and diastolic blood pressure (r = 0.649, p less than 0.001) and body mass index (r = 0.565, p less than 0.001), between Mgi and diastolic blood pressure (r = -0.563, p less than 0.001) and fasting blood glucose (r = -0.580, p less than 0.001), and in diabetics, between pHi and diastolic blood pressure (r = -0.680, p less than 0.001). Thus, the constellation of elevated Cai and suppressed Mgi and pHi levels is characteristic of the hypertensive state. These abnormalities of cellular ion handling in whole or in part common to hypertension, diabetes, and obesity may contribute to the pathophysiology of these syndromes and may help to explain their frequent clinical coexistence.

Antibodies to sperm surface fertilization antigen (FA-1): their specificities and site of interaction with sperm in male genital tract.

The fertilization antigen (FA-1) isolated from murine testes demonstrated its dimeric form of 49,000 +/- 2,000 molecular weight (M.W.) or a monomer of 23,000 M.W. on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The FA-1 was immunogenic in all three female rabbits tested and raised a high-titer antisera [enzyme-linked immunosorbent assay (ELISA) titers; 1:1,024 to 1:4,096]. The rabbit anti-FA-1 antisera predominantly recognized the dimeric form of 49,000 +/- 2,000 M.W. on the Western blot of lithium diiodosalicylate (LIS)-solubilized murine testes. None of the antisera reacted with any somatic tissue, indicating germ-cell specificity of FA-1. To determine the cellular localization of the immunoreactive FA-1, a novel ultrasensitive immunogold-silver staining (IGSS) procedure was developed. The anti-FA-1-IgG showed intense staining in the luminal region of the seminiferous tubules containing spermatids and spermatozoa. No reaction was observed in the peripheral area of the tubules containing Sertoli cells, spermatogonia, leptotene, and zygotene spermatocytes. The biodistribution studies of 125I-labeled anti-FA-1 IgG in mice revealed that the antibodies do not bind to somatic tissues such as blood cell, liver, heart, kidney, muscle, and gastrointestinal tissue and do not transudate into testes and seminal vesicle. However, the antibodies preferentially transudate into epididymis (especially corpus or cauda regions) and vas deferens to bind to sperm cells. In conclusion, our data indicate that FA-1 can induce an immune response that is germ cell-specific, directed against later stages of spermatogenesis. The antibodies to FA-1 interact with sperm after penetration through epididymis (especially corpus and cauda regions) and vas deferens rather than through testes and seminal vesicles.

Technetium-99m labeled p-aminohippuric acid analogues: renal function agents.

A number of p-aminohippuric acid analogues were synthesized in order to develop clinically useful 99mTc-labeled radiopharmaceuticals for evaluation of renal function measurements. Stable 99mTc-labeled complexes were formed at pH 5.7 using a Sn(II) reduction method with all derivatives. The newly synthesized complexes were screened utilizing biodistribution studies in small animals. All complexes were excreted via the GU tract within 60 min post iv administration, with no significant activity in GI tract and liver. The [99mTc]methyl-PAHIDA complex showed optimal biodistribution among these analogues. Further investigation is needed to determine if these derivatives may be used to replace [131I]o-iodohippuric acid for the evaluation of renal function.

Labeling of monoclonal antibodies with radionuclides.

Antibodies, specifically monoclonal antibodies, are potentially very useful and powerful carriers of therapeutic agents to target tissues and diagnostic agents. The loading or charging of antibodies with agents, especially radiotracers, is reviewed here. The choice of radioisotope for immunodetection and/or immunotherapy is based on its availability, half-life, nature of the radiation emitted, and the metabolic pathways of the radionuclide in the body. Most important of all are the derivatization techniques available for labeling the antibody with the given radionuclide. Isotopes of iodine and divalent metal ions are the most commonly used radionuclides. Antibodies labeled with iodine at tyrosine residues are metabolized rapidly in vivo. This leads to the incorporation of metabolized radioactive iodine into various tissues, mainly the thyroid gland and stomach, and to the accumulation of high levels of circulating iodine in the blood, which masks tumor uptake considerably. To overcome these limitations, the use of iodohippurate as an iodine-anchoring molecule to the protein should be considered. When divalent or multivalent metal ions are used as the preferred radionuclide, bifunctional chelating reagents such as ethylenediaminepentaacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) are first coupled to the protein or antibody. These chelating molecules are attached to the protein by formation of an isopeptide linkage between the carboxylate of the chelating reagent and the amino group of the protein. Several procedures are available to generate the isopeptide linkage. When the anchoring of the chelating agent through isopeptide linkage results in the inactivation of the antibody, periodate oxidation of the carbohydrate moiety of the antibody, followed by reductive coupling of chelator, could be considered as an alternative. There is still a need for better, simpler, and more direct methods for labeling antibodies with radionuclides.

N-hydroxysuccinimide-hippuran ester: application for radiolabeling of macro-molecules.

A method for synthesis of N-hydroxysuccinimide ester of radioactive hippuran is developed in order to label human serum albumin in a simple and efficient manner. Organ distribution in mice and rats for the labeled albumin preparation and the commercial radioiodinated serum albumin is similar. Hippuran metabolite released from the labeled preparation into the blood stream results in its rapid urinary clearance. The hippuran labeling method offers a mild and rapid protocol for radioiodine labeling of proteins and antibodies for application in diagnostic nuclear medicine procedures.

Solid phase synthesis of thymosin beta 9.

Thymosin beta 9, a 41 residue thymic polypeptide, has been synthesized by a solid phase method. A modification of the low HF method was used to deprotect and cleave the peptide from the resin. Thymosin beta 9 was then obtained in analytically pure form by a one-step purification procedure in 32% yield. The activity of thymosin beta 9 in the terminal deoxynucleotidyl transferase assay was greater than calf thymus fraction 5, but comparable to thymosin beta 4. In contrast to thymosin alpha 1, neither beta 4 nor beta 9 was active in the rosette inhibition assay.