Development of a digital zebrafish phantom and its application to dedicated small-fish PET

Objective. We are developing a small-fish positron emission tomography (PET) scanner dedicated to small aquatic animals relevant for biomedical and biological research, e.g. zebrafish. We plan to use Monte Carlo simulations to optimize its configuration and the required water-filled imaging chambers. Our objectives were: (1) to create a digital 3D zebrafish phantom using conventional micro-CT, (2) include the phantom into a simulated PET environment based on the framework GATE, and (3) investigate the effects of the water environment on the reconstructed images. Approach. To create the phantom, we performed ex vivo measurements of zebrafish specimen using a tabletop micro-CT and compared three methods to fixate the specimen. From segmented micro-CT images we created digital emission and transmission phantoms which were incorporated in GATE via tessellated volumes. Two chamber sizes were considered. For reference, a simulation with the zebrafish in air was implemented. The simulated data were reconstructed using CASToR. For attenuation correction, we used the exact attenuation information or a uniform distribution (only water). Several realizations of each scenario were performed; the reconstructed images were quantitatively evaluated. Main results. Fixation in formalin led to the best soft-tissue contrast at the cost of some specimen deformation. After attenuation correction, no significant differences were found between the reconstructed images. The PET images reflected well the higher uptake simulated in the brain and heart, despite their small size and surrounding background activity; the swim bladder (no activity) was clearly identified. The simplified attenuation map, consisting only of water, slightly worsened the images. Significance. A conventional micro-CT can provide sufficient image quality to generate numerical phantoms of small fish without contrast media. Such phantoms are useful to evaluate in-silico small aquatic animal imaging concepts and develop imaging protocols. Our results support the feasibility of zebrafish PET with an aqueous environment.

The Molecular Allergen Recognition Profile in China as Basis for Allergen-Specific Immunotherapy

Approximately 30% of the world population suffers from immunoglobulin-E (IgE)-mediated allergy. IgE-mediated allergy affects the respiratory tract, the skin and the gastrointestinal tract and may lead to life-threatening acute systemic manifestations such as anaphylactic shock. The symptoms of allergy are mediated by IgE-recognition of causative allergen molecules from different allergen sources. Today, molecular allergy diagnosis allows determining the disease-causing allergens to develop allergen-specific concepts for prevention and treatment of allergy. Allergen-specific preventive and therapeutic strategies include allergen avoidance, vaccination, and tolerance induction. The implementation of these preventive and therapeutic strategies requires a detailed knowledge of the relevant allergen molecules affecting a given population. China is the world´s most populous country with around 1.4 billion inhabitants and an estimated number of more than 400 million allergic patients. Research in allergy in China has dramatically increased in the last decade. We summarize in this review article what is known about the dominating allergen sources and allergen molecules in China and what further investigations could be performed to draw a molecular map of IgE sensitization for China as a basis for the implementation of systematic and rational allergen-specific preventive and therapeutic strategies to combat allergic diseases in this country.

[177Lu-DOTA(0),Tyr3] octreotate for somatostatin receptor-targeted radionuclide therapy

Receptor-targeted scintigraphy using radiolabeled somatostatin analogs such as octreotate is being used with great success to demonstrate the in vivo presence of somatostatin receptors on various tumors. A new and promising application for these analogs is radionuclide therapy. Radionuclides suitable for this application include the Auger electron-emitter (111)In and the beta-emitters (90)Y (high energy) and (177)Lu (low energy). We investigated [DOTA(0),Tyr(3)]octreotate, labeled with the lanthanide (177)Lu, in biodistribution and radionuclide therapy experiments using male Lewis rats bearing the somatostatin receptor-positive rat CA20948 pancreatic tumor. Biodistribution studies in Lewis rats showed the highest uptake in the rat pancreatic CA20948 tumor and sst(2)-positive organs, which include the adrenals, pituitary and pancreas, of [(177)Lu-DOTA(0),Tyr(3)]octreotate in comparison with (88)Y- and (111)In-labeled analogs. Kidney uptake of [(177)Lu-DOTA(0),Tyr(3)]octreotate could be reduced by approximately 40% by co-injection of 400 mg/kg D-lysine. In radionuclide therapy studies, a 100% cure rate was achieved in the groups of rats bearing small (< or =1 cm(2)) CA20948 tumors after 2 doses of 277.5 MBq or after a single dose of 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate. A cure rate of 75% was achieved after a single administration of 277.5 MBq. In rats bearing larger (> or =1 cm(2)) tumors, 40% and 50% cure rates were achieved in the groups that received 1 or 2 277.5 MBq injections of [(177)Lu-DOTA(0),Tyr(3)]octreotate, respectively. After therapy with [(177)Lu-DOTA(0),Tyr(3)]octreotide in rats bearing small tumors, these data were 40% cure after 1 injection with 277.5 MBq and 60% cure after 2 repeated injections. In conclusion, [(177)Lu-DOTA(0),Tyr(3)]octreotate has demonstrated excellent results in radionuclide therapy studies in rats, especially in animals bearing smaller tumors. This candidate molecule shows great promise for radionuclide therapy in patients with sst(2)-expressing tumors.

Evaluation of a radiolabelled cyclic DTPA-RGD analogue for tumour imaging and radionuclide therapy

Tumours depend on sufficient blood supply for their growth. They are able to promote new blood vessel formation (neoangiogenesis) via angiogenic factors. Inhibition of this process results in tumour involution or necrosis. RGD (Arg-Gly-Asp) peptides are described to antagonise neoangiogenesis, e.g., by binding to alpha(v)beta(3) receptors on blood vessels. In order to visualise neoangiogenesis in tumours in vitro and in vivo, we introduced and tested an RGD analogue [c(Arg-Gly-Asp-D-Tyr-Lys)], coupled to the chelator diethyleletriamepentaacetic acid (DTPA). This analogue can be radiolabelled with both (111)In and (125)I. In autoradiography and immunohistochemistry studies, the (125)I-labelled analogue appeared to bind specifically and with high affinity to alpha(v)beta(3) receptors on neovascular blood vessel sections of different major human cancers, like prostate and breast cancer, which express these receptors. This radioiodinated radiopharmaceutical also bound to and internalised in human carcinoid Bon cells and rat pancreatic CA20948 tumour cells. Internalisation was receptor-specific and appeared to be time and temperature dependent. In vivo in rats, we investigated administration of different peptide amounts (0.1, 0.5, and 100 microg). The best amount of the radiolabelled analogue to be administered to rats appeared to be 0.1 microg/rat, as uptake decreased with increasing peptide amount. We also found receptor-specific accumulation of the (111)In-labelled analogue in the transplantable pancreatic tumour CA20948. The introduction of the DTPA group in this peptide resulted in renal clearance of the radiopharmaceutical, in contrast to the non-DTPA-conjugated compound that is cleared predominantly via the liver. (111)In emits Auger and conversion electrons besides gamma radiation, therefore, this radiopharmaceutical is suitable not only for tumour scintigraphy but also has potential for radionuclide therapy of major human cancers as well. Moreover, after coupling to the chelator DOTA, the analogue could be radiolabelled in a stable way with beta-emitters, e.g., (90)Y and (177)Lu, enlarging its potential. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 186-198 (2000).

Role of cholecystokinin in the control of gastric somatostatin in the rat: in vivo and in vitro studies

Cholecystokinin (CCK) has been shown to be a powerful stimulus for somatostatin release from isolated canine fundic D-cells in short-term culture. The influence of the CCK analogue caerulein on the secretory activity of the D-cell in the intact stomach in vitro and the effect of elevated plasma levels of endogenous CCK on gastric somatostatin stores in vivo were investigated in the rat. Basal somatostatin secretion from the isolated, vascularly perfused rat stomach preparation was not affected by various doses of caerulein. Slight stimulation of somatostatin-like immunoreactivity (SLI) release by epinephrine was significantly inhibited by caerulein, whereas caerulein did not alter half-maximal stimulation of SLI secretion by isoproterenol. Rats with chronically elevated plasma CCK levels induced by experimental exocrine pancreatic insufficiency did not show any change in tissue concentrations of SLI or in D-cell number, both in the antrum and corpus. These data suggest that CCK--in contrast to dogs--is not an important modulator of gastric somatostatin in the rat.

Endocrine pancreatic morphology and function in exocrine insufficiency in rats

Exocrine pancreatic insufficiency was induced in rats by injection of oleic acid into the pancreatic duct. Six weeks after a single injection of 50 microliters oleic acid, the exocrine tissue was reduced by 98%. The islets of Langerhans remained intact and showed no changes in the relative distribution of beta-, alpha-, D-, and PP-cells. In rats fed ad libitum, plasma insulin levels and pancreatic insulin content did not differ between oleic acid-treated animals and controls. The dynamic insulin response was evaluated in the isolated perfused pancreas. The biphasic pattern of insulin release after stimulation by glucose was preserved. The half-maximal (10 mM) glucose-induced insulin release was reduced to 49% after onset of exocrine atrophy. After stimulation of insulin secretion by a maximal glucose load (20 mM), the insulin output from the perfused pancreas was reduced to 56%. A reduction in insulin release to 24% occurred with respect to the arginine (15 + 10 mM glucose)-stimulated secretion. To evaluate the significance of these findings in intact animals, glucose tolerance tests were performed. There were no differences between oleic acid-, saline-, or untreated animals with respect to serum glucose or plasma insulin levels during the oral glucose tolerance test. The insulin response after intravenous glucose in oleic acid-treated rats was not statistically different from controls. Nevertheless, the serum glucose levels in rats with exocrine atrophy were above controls, indicating a slight impairment of glucose tolerance.

Exocrine pancreatic function in oleic acid-induced pancreatic insufficiency in rats

Pancreatic insufficiency was induced in rats by a single injection of 50 microliter oleic acid into the pancreatic duct over a period of 3 min. Exocrine tissue was destroyed within 3-6 days, and after 6 weeks the remaining pancreas equaled 2.7% of the original organ. The rats showed retardation of body weight in spite of normal food intake. After 7 weeks the fecal weight increased by 23%, and the fecal chymotrypsin activity decreased by 90% compared to controls. At this time plasma cholecystokinin (CCK) concentrations were significantly elevated. The amylase content in the remaining pancreas was reduced by 99%, and trypsin content was reduced by 93%. Unstimulated protein discharge from the remnant pancreas in vitro was threefold higher compared to secretion from control tissue. Thus a simple, reproducible model for inducing persistent pancreatic insufficiency was developed. To compensate for the loss of exocrine tissue, the remaining acinar cells adapt by a CCK-mediated increase in protein secretion.