F.H.M. Corstens

Technetium-99m labelled liposomes to image experimental arthritis

OBJECTIVES Liposomes sterically stabilised with polyethylene glycol (PEG) labelled with technetium-99m were tested for their ability to image adjuvant arthritis in a rat model. METHODS Adjuvant arthritis was induced in the ankle joint of the left hind foot by injection of Mycobacterium butyricum in Freund’s incomplete adjuvant in the foot pad. Seven days later animals received the following radiopharmaceuticals labelled with 99mTc (a) non-PEG-liposomes, (b) PEG-liposomes or (c) non-specific human polyclonal IgG. For each of the radiopharmaceuticals the in vivo distribution of the radiolabel was monitored both scintigraphically as well as by counting the dissected tissues at two, eight, and 24 hours after injection. RESULTS The pharmacokinetics of the radiopharmaceuticals differed considerably (half life in the blood: PEG-liposomes (18 hours) > 99mTc-IgG (3 hours) > non-PEG liposomes (1 hour)). The inflamed focus was visualised with each of the agents. The uptake of each of the radiopharmaceuticals in the inflamed ankle region correlated with their residence time in the blood (inflamed joint uptake: PEG liposomes (1.15% injected dose (ID)/g)>99mTc-IgG (0.35% ID/g)>non-PEG-liposomes (0.05% ID/g)). Quantitative analysis of the images showed that the inflamed ankle to background ratio was highest with the PEG-liposomes (7.5 at 24 hours after injection), while with the other two agents this ratio did not exceed 4. CONCLUSION This study shows that99mTc-labelled PEG-liposomes may be an excellent agent to visualise arthritis. Increased label uptake in the inflamed joint and increased target to background ratios can be obtained with PEG-liposomes because of their long circulating properties. In addition to their use as vehicles for scintigraphic imaging of arthritis PEG-liposomes might also be used for the site specific delivery of antirheumatic drugs.

Radiopharmaceuticals for scintigraphic imaging of infection and inflammation

Abstract: Scintigraphic imaging of infection and inflammation is a powerful diagnostic tool in the management of patients with infectious or inflammatory diseases. Most infectious and inflammatory foci can be visualized accurately with radiolabeled autologous leukocytes. However, preparation of this radiopharmaceutical is laborious and requires the handling of potentially contaminated blood. Nowadays, a few radiopharmaceuticals are available that could replace radiolabeled leukocytes, such as: 67Ga-citrate, 99mTc-IgG and 99mTc-labeled antigranulocyte antibody preparations. Furthermore, various agents labeled with 99mTc are currently developed for this application: chemotactic peptides, cytokines and liposomes. Here, the characteristics and the diagnostic potential of established and experimental radiopharmaceuticals for infection and inflammation imaging are reviewed.

Specific targeting of infectious foci with radioiodinated human recombinant interleukin-1 in an experimental model

In the present study, radioiodinated human recombinant interleukin-1 (IL-1) was investigated for its potential to image infectious foci in vivo in an animal model of infection. Twenty-four hours after induction of aStaphylococcus aureus abscess in the left calf muscle, mice were i.v. injected with both iodine-125 labelled IL-1 and iodine-131 labelled myoglobin, a size-matched control agent. The animals were killed for tissue biodistribution studies at 2, 6, 12, 24 and 48 h p.i. Gamma camera images were obtained at 6, 24 and 48 h after injecting mice with123I-IL-1. Radioiodinated IL-1 rapidly cleared from the body; after 12 h the abscess was the organ with the highest activity. The absolute abscess uptake of125I-IL-1 remained high compared to131I-myo-globin, resulting in significantly higher abscess-to-muscle ratios of125I-IL-1 compared to 1311-myoglobin. The ratios of125I-IL-1 reached the ultimate value of 44.4±10.8 at 48 h p.i., whereas the ratios of131I-myoglobin did not exceed 5.9±0.7. Gamma camera imaging revealed clearly visible abscesses. In conclusion, our results demonstrate specific retention of radioiodinated IL-1 in the abscess, presumably by interaction of IL-1 with its receptor on the inflammatory cells. The high target to-background ratios that were obtained over the course of time indicate that the IL-1 receptor may be a valuable target for the imaging of infectious foci.

Clinical significance of low cobalamin levels in older hospital patients

BACKGROUND It is still a commonly held belief that many of the frequently found low cobalamin (Cbl, vitamin B12) levels in older people do not represent deficiency and are therefore without clinical significance and should not be treated. In this study this notion will be challenged. METHODS In this prospective observational cohort design we studied 28 patients aged 65 years and older with low plasma Cbl (< or =150 pmol/l). A number of haematological (Hb, MCV, five- and six-lobed granulocytes), metabolic (plasma levels of methylmalonic acid and homocysteine), and gastrointestinal (plasma pepsinogen A and C and protein-bound and free Cbl absorption) parameters, and the response to Cbl treatment, were measured. Cbl deficiency was considered to be present when at least one of the following three criteria was fulfilled: (1) haematological or metabolic abnormalities compatible with Cbl deficiency; (2) Cbl malabsorption or atrophic gastritis; (3) a response to Cbl supplementation. RESULTS Haematological or metabolic abnormalities were identified in 27 patients. Atrophic gastritis and Cbl malabsorption were identified in, respectively, 15 and 23 patients. Each treated patient showed a haematological or metabolic response to Cbl supplementation. All patients were considered Cbl deficient: 18 patients (64%) fulfilled three criteria of Cbl deficiency, eight (29%) fulfilled two criteria and two (7%) fulfilled one criterion. CONCLUSIONS According to the generally accepted and a wide variety of criteria, we found that older patients with low Cbl levels were cobalamin deficient. Therefore, these patients should receive Cbl supplementation.

The uptake mechanisms of inflammation- and infection-localizing agents

Over the past 30 years, a wide variety of radiopharmaceuticals have been proposed for the scintigraphic detection of inflammatory and infectious disease. All radiopharmaceuticals yield a functional image of a process placed somewhere in the cascade of reactions in inflammation, this being the common pathway of response to tissue injury. This paper discusses relevant aspects of the biodistribution, in vivo kinetics and mechanisms of uptake of both clinically used and experimental radiopharmaceuticals that have been proposed for the scintigraphic detection of focal inflammation and infection.

Diagnosing infection in febrile granulocytopenic patients with indium-111-labeled human immunoglobulin G.

PURPOSE Delineation of focal infection is a major problem in the management of febrile granulocytopenic patients. The utility of indium-111-labeled human nonspecific immunoglobulin G (In-111-IgG), a newly developed radiopharmaceutical for imaging focal inflammation, was reported in patients with adequate WBC counts. In the present study, we investigated whether In-111-IgG scintigraphy could be used to locate infection in granulocytopenic patients. MATERIALS AND METHODS Granulocytopenic rats with focal infection were imaged after In-111-IgG injection. Thereafter, In-111-IgG scintigraphy was performed in 20 granulocytopenic patients. Images were obtained 4, 24, and 48 hours after injection of 75 mBq In-111-IgG. Scintigraphic findings were compared with clinical, roentgenologic, and ultrasonographic methods and culture results. RESULTS In the animal model high In-111-IgG accumulation was observed in the infectious focus. In the patients, 13 proven pulmonary, abdominal, joint, and soft tissue infections of both bacterial and fungal origin were detected adequately. In-111-IgG uptake not due to verified inflammation was observed in the large bowel of two patients. A thoracic wall infiltrate showing only mild inflammatory activity was not detected. Small toxoplasmosis lesions in heart, liver, and kidneys were obscured by physiologic In-111-IgG activity in these organs. CONCLUSIONS In-111-IgG scintigraphy is a useful technique to delineate focal infection in patients with granulocytopenia. Accumulation of the radiopharmaceutical does not appear to be granulocyte-mediated. In-111-IgG is a safe and convenient radiopharmaceutical that probably contributes to the early diagnosis of focal infection in granulocytopenic patients.

Radioimmunoconjugates in the detection of infection and inflammation

Various nuclear medicine techniques are widely used to image foci of infection and inflammation. Among the relatively new radiopharmaceuticals for this purpose are radioimmunoconjugates such as labeled murine monoclonal antigranulocyte antibodies and labeled human polyclonal nonspecific immunoglobulin G. This article reviews some background information, mechanism of action, side effects, biodistribution, kinetics, results of clinical studies, and dosimetry of several radioimmunoconjugates both of murine monoclonal and human polyclonal origin. The efficacy of these agents has been demonstrated in a variety of clinical conditions. Radiolabeled immunoconjugates may emerge as convenient alternatives to the present technique of choice: in vitro blood cell labeling techniques with their inherent problems and risks.

Technetium-99m labelled hydrazinonicotinamido human non-specific polyclonal immunoglobulin G for detection of infectious foci : a comparison with two other technetium-labelled immunoglobulin preparations

Recently a new linker — hydrazinonicotinate (HYNIC) — was introduced for labelling of proteins and peptides with technetium-99m. HYNIC and other linkers have been used for labelling of human non-specific polyclonal immunoglobulin G (hIgG) with99mTc for the detection of infections. In this study we compared the tissue distribution of three different99mTc-hIgG preparations in groups of five Wistar rats with a focal intramuscular infection withStaphylococcus aureus. We compared99mTc-HYNIC-hIgG with99mTc-hIgG labelled via the so-called Schwarz method (reduction of disulphide bonds) and with the99mTc-labelled commercially available Technescan-HIG. Unlike the HYNIC linker, in the two other labelling methods free sulph-hydryl groups are involved in the binding of99mTc. High-performance liquid chromatography analysis of the labelled preparations and of plasma samples revealed aggregate or polymer formation in all three agents; this was least pronounced in the product labelled by means of the Schwarz method. The tested preparations did not show signs of degradation in vitro. The difference in linker chemistry was reflected in the tissue distribution. Thus the biodistribution of99mTc-HYNIC-hIgG was significantly different from the distribution of the two other preparations: abscess (1.4%±0.2%ID/g), muscle, liver, spleen, plasma, lung, bone marrow, and small intestine concentrations were higher at 24 h p.i.; kidney uptake (1.19%±0.08%ID/g) was significantly lower. The abscess-to-plasma and the abscess-to-muscle ratios (0.5 and 11, respectively), however, were in the same range for the three preparations tested. Quantitative analysis of the scintigraphs revealed that the total body clearance of99mTc-HYNIC-hIgG was significantly slower than for the other agents. The abscess uptake of99mTc-HYNIC-hIgG as a percentage of the remaining body activity was significantly higher. Based on its high abscess uptake, its low uptake in the kidneys and the high percentage of its abscess uptake in relation to the remaining body activity, we conclude that99mTc-HYNIC-hIgG seems superior to the two other preparations tested for the detection of infections.

Free and protein-bound cobalamin absorption in healthy middle-aged and older subjects

OBJECTIVE: To study free‐ and protein‐bound cobalamin absorption and the correlation with atrophic gastritis in healthy middle‐aged and older subjects.

Labelled StealthR liposomes in experimental infection : an alternative to leukocyte scintigraphy?

Indium-111 (111In) and technetium-99m (99Tcm) Stealth liposomes were compared with 111In- and 99Tcm-labelled white blood cells (WBC) in experimental infection in a rabbit model. Preformed polyethylene glycol-coated liposomes and separated WBC were radiolabelled with either 111In-oxine or 99Tcm-hexamethylpropyleneamine oxime (99TcM-HMPAO). After the intravenous administration of one of the four radiopharmaceuticals to rabbits with focal Staphylococcus aureus infection, scintigraphic images were recorded at various time points post-injection and the biodistribution of the radiopharmaceuticals was determined. At 4 h post-injection, uptake of 111In-WBC in the abscess was significantly higher than that of the three other products. AT later time points, 111In-WBC, 111In-liposome and 99Tcm-liposome uptake in the abscess were similar. In contrast, a 20 h post-injection, uptake of 99Tcm-WBC was significantly lower. The abscess-to-background ratios showed a similar pattern to the absolute abscess uptake: initial high values for 111In-WBC, a more gradual increase over time of the liposome preparations to the level of 111In-WBC and persistently low values for 99Tcm-WBC. Clearance from the blood of both labelled WBC preparations was significantly faster and splenic uptake significantly higher compared with those of the labelled liposomes. In conclusion, given the similar in vivo characteristics of labelled liposomes and labelled WBC, labelled liposomes may be an attractive replacement for labelled WBC, providing a continuously available, high-quality, 99Tcm-labelled radiopharmaceutical that can be prepared easily without any need to handle blood.