L-amino acid load to enhance PET differentiation between tumor and inflammation: an in vitro study on (18)F-FET uptake.

Labeled amino acids (AA) are tumor tracers for use in nuclear medecine. O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is transported by the L-system, known to function as an exchanger. In vitro utilization of FET, after a preload or prior to an afterload of non radioactive L-amino acids, was evaluated in order to measure the potential effects of AA content on the distinction between tumor and inflammatory lesions. Cellular uptake of FET was studied on rat osteosarcoma cells (ROS 17/2.8) and human leukocytes, initially loaded with nonradioactive L-tyrosine or L-methionine. FET efflux was evaluated from cells loaded with nonradioactive L-phenylalanine after tracer uptake. ROS 17/2.8 showed a higher sensitivity to preload and afterload effects on cellular FET content as compared with the leukocytes. We conclude that preload with L-tyrosine, prior to the administration of FET, may be a potential procedure to improve PET differentiation between tumor and inflammatory lesions.

Protracted systemic changes in bone biology after segmented unloading in the rat.

To investigate whether the decreased bone formation observed in most experimental situations of disuse was caused by an increased inhibition by the bone microenvironment of osteoblast (OB) proliferation, we studied the inhibiting power on ROS 17/2.8 proliferation of the bone marrow extracellular fluid (IPEF) in loaded and unloaded bones of rats submitted to two situations of partial disuse: tail suspension (TS) for 3 days to 2 weeks and around the knee tenectomy (KT) for 2-10 weeks. Histomorphometric parameters and osteoblast precursors dynamics were studied in parallel. Bone volume was lost in the unloaded bones, but not in loaded bones, in both experimental situations. Bone formation was low at early times (7-14 days) in TS rats. However, in KT at later times (4-10 weeks), the osteoblastic index of the unloaded tibia was increased. IPEF was not increased in the unloaded bones 3-7 days after TS. It was decreased later in the course of unloading (after 2 weeks of TS and 2-10 weeks after KT). This decrease was observed in the loaded bones as well. Unexpectedly, we also found that the number of FCFUs was decreased in both loaded and unloaded limbs in TS and KT, and that the yield of cells obtained in primary culture from tibial metaphysis was decreased in both tibiae from KT animals. These data show that an increased IPEF does not play a role in the early inhibition of bone formation responsible for the loss of bone after unloading in the TS model. Its later decrease could be permissive for the increased osteoblastic index observed in the KT model. They also show that, contrary to the usual assumptions, bone biology is changed all over the skeleton after partial unloading, even if the changes result in bone loss in the unloaded bones only. Thus, as yet, unidentified systemic factors probably superimpose on the local factors that control bone volume.

[The nuclear medicine department and the TEP/Biomedical Cyclotron unit]. / Le Service de Médecine Nucléaire et l'Unité TEP/Cyclotron Biomedical.

During the last 25 years, the clinical and experimental activity in nuclear medicine at Erasme hospital has been influenced by the implementation of positron emission tomography (PET) in 1990 as a method of brain functional investigation. The activity of the PET/biomedical cyclotron unit has been dedicated to various subjects in neurology, neurosciences, psychiatry, oncology and cardiology. This has been made possible by developments in radiochemistry. The radiochemistry laboratory has designed and produced original tracers such as 9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)-methyl]guanine (FHPG), a tracer of viral thymidine kinase activity in gene therapy protocols. We have brought new applications of PET, such as its integration into stereotactic neurosurgical and radioneurosurgical techniques in order to improve their diagnostic and therapeutic performance in neurooncology. We have also conducted multiple studies on brain physiology and pathophysiology, in particular with the use of functional and metabolic brain mapping methods and the use of tracers of neurotransmission systems. The Department of nuclear medicine has also performed studies on bone metabolism and investigated in vivo imaging methods of infectious and immune processes.

Selenium deficiency-induced growth retardation is associated with an impaired bone metabolism and osteopenia.

Although the importance of selenium for bone metabolism is unknown, some clinical conditions such as Kashin-Beck osteoarthropathy have been associated with selenium deficiency. Although selenium deficiency induces growth retardation in rats, it has not been established whether this growth inhibition is associated with changes in bone metabolism. We investigated the effect of selenium deficiency on bone metabolism in growing male rats fed a selenium-deficient diet for two generations (Se-). In Se- rats, erythrocyte glutathione peroxidase activity and plasma selenium concentration were strongly reduced compared with pair-fed selenium-adequate rats (Se+). Weight and tail length were reduced by 31% and 13% in the Se- rats, respectively (p < 0.001). The Se- diet was associated with a 68% reduction of pituitary growth hormone (GH; p = 0.01) and a 50% reduction of plasma insulin-like growth factor I (IGF-I; p < 0.001). Plasma calcium was lower and urinary calcium concentration was greater in Se- rats. This group had a 2-fold increase in parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in plasma. Plasma osteocalcin and urinary deoxypyridoline were reduced by 25% and 57% in the Se- rats (p < 0.001). Selenium deficiency resulted in a 23% and 21% reduction in bone mineral density (BMD) of the femur and tibia (p < 0.001) and this effect persisted after adjustment for weight in a linear regression model. A 43% reduction in trabecular bone volume of the femoral metaphysis (p < 0.001) was found in Se- rats. This experimental study shows that growth retardation induced by selenium deficiency is associated with impaired bone metabolism and osteopenia in second-generation selenium-deficient rats.

Age-related inhibitory activity of rat bone marrow supernatant on osteoblast proliferation.

Because histomorphometric indices of bone formation (osteoblastic index, tetracyclin-labeled perimeter) are deeply depressed in aged rats, while in vitro proliferation of trabecular bone cells was found increased, we hypothesized that a signal to proliferate, correctly induced by increased strains on scarce bone, could be opposed in vivo by an inhibitor present in the bone marrow extracellular medium. Thus, we tested the effect of bone marrow extracellular fluid (BM supernatant) of rat femoral diaphysis on cultures of primary osteoblasts and osteoblastic cell lines and found that it inhibited bone cell proliferation. In a group of 69 female rats aged 4, 12, and 15/21 months, there was a stepwise increase in the inhibitory activity of the BM supernatant. The double reciprocal plots relating inhibition power of the medium to BM supernatant dilution suggest that we deal with a simple system and that the kinetics of the phenomenon are the same in older and younger animals. Moreover, proliferation inhibition by BM supernatant and trabecular bone surface measured by histomorphometry in the distal femoral metaphysis were inversely correlated. Because the extracellular fluid of bone marrow is also the medium surrounding the osteoblasts and their precursor cells, our results suggest that the bone marrow negatively regulates osteogenic cells and that this inhibition could contribute to the inability of older animals to supply osteoblasts to bone in proportion to the demand. Preliminary biochemical characterization of the inhibitor suggests it to be a protein of 30-40 kDa with an isoelectric point (pI) of about 6.5.

Trabecular bone cell proliferation ex vivo increases with donor age in the rat: it is correlated with the extent of bone loss and not with histomorphometric indices of bone formation.

Morphometric parameters of bone formation are markedly depressed in senescent, 21-month old rats and even in middle-aged, 12-month-old animals when compared with mature, 4-month old adults. However, osteoblast-like cells obtained from the metaphyseal trabeculae of the distal femur of 21-month-old female and male rats proliferate more rapidly in primary and secondary cultures than cells from 4-month-old donors. In females the increase in proliferation is significant for donor ages from 4 to 12 months and from 12 to 21 months. Ex vivo cell proliferation is inversely correlated with trabecular bone volume and bone surface in females and with bone surface in males. The relationships are being maintained in females (not tested in males) when cells are grown in serum-free medium. We interpret age and bone loss-dependent stimulated cell proliferation as the in vitro response to an in vivo signal to proliferate resulting from higher strains on less trabeculae. The absence of response in vivo could result from the local deficiency of factors brought back to the cells by the serum-enriched culture medium, or from proliferation inhibitors developing with age.

Bone blood flow and in vitro proliferation of bone marrow and trabecular bone osteoblast-like cells in ovariectomized rats.

Ovariectomy in the rat induces a rapid osteopenia associated with an elevated bone turnover. One hundred and twenty-day-old rats were ovariectomized (OVX) or sham-operated (n = 6-8 per group and per time period studied). 45Ca accretion rate and bone blood flow (microspheres trapping technique) in the femurs were determined at 28, 42, 84, and 119 days after ovariectomy. Both parameters were markedly increased by 84 days and subsided thereafter. At the 42nd day, when bone turnover was maximal, bone marrow and trabecular bone cultures were obtained from sham-operated and ovariectomized animals (n = 10/group). Proliferation rate of bone marrow cells and trabecular osteoblast-like cells estimated by fibroblast colony-forming units (FCFU) efficiency and cell counting was markedly increased in primary and secondary cultures in ovariectomy. These data fitted well with the enhanced number of osteoblasts observed in situ in the long bone metaphyses of estrogen-depleted animals. As estrogens were shown in the literature to inhibit proliferation of the red cell line and of other hemopoietic lines, it is possible that estrogens, through a general mechanism, inhibit hemopoietic and stromal lines and also the proliferation of bone marrow-derived trabecular bone cells.

The number of fibroblastic colonies formed from bone marrow is decreased and the in vitro proliferation rate of trabecular bone cells increased in aged rats.

Four- and 21-month old female Sprague-Dawley rats were sacrificed and their tibiae and femurs isolated for histology and initiation of bone marrow and trabecular bone cultures. The bone loss observed in 21-month old rats was associated with a markedly decreased osteoblastic index. The percentages of mineralizing trabecular surfaces were only slightly decreased in aged rats, whereas the percentages of mineralizing endocortical surfaces were strikingly decreased. Diaphyseal femoral marrows from 21-month old rats were less cellular than those from four-month old rats, and developed in culture fewer fibroblast colony forming units (FCFU) and fewer adherent cells with phenotypic characteristics of osteoblast-like cells. Trabecular bone cultures from 21-month old rats produced as many cells as cultures from four-month old rats, whereas the amount of trabeculae put into culture was much less in aged rats. Moreover, the proliferation rate in secondary culture was significantly increased in 21-month old rats. Similar responses to calcitriol were observed in bone marrow and trabecular bone cells from aged and younger mature rats, while cAMP responses to PTH were decreased in cells from aged rats. Our data confirm the age-related decrease in the FCFU efficiency of the bone marrow and show a stimulated proliferation of trabecular bone cultures from 21-month old rats that could be seen either as the result of the inhibition in vivo of the response to a signal to proliferate, or as a rebound response to factors present in the serum-enriched medium and lacking in vivo.

Effects and interactions of 17 beta-estradiol, T3 and 1,25(OH)2D3 on cultured osteoblasts from mature rats.

Osteoporosis being frequently associated with hyperthyroidism and, mostly after menopause, with deficiency in estrogens, we tried to elucidate the interactions of estrogens and triiodothyronine (T3) with calcitriol by using cultured osteoblast-like cells obtained from mature rat bone. The tested parameters included [3H]thymidine incorporation, evaluation of the alkaline phosphatase activity of the cell layer and osteocalcin production in the culture medium. At physiological concentrations, 17 beta-estradiol and T3 stimulated alkaline phosphatase activity, did not enhance osteocalcin production and slightly inhibited [3H]thymidine incorporation. At higher concentrations, 17 beta-estradiol decreased the alkaline phosphatase and osteocalcin response to calcitriol whereas T3, although decreasing alkaline phosphatase activity, markedly increased the osteocalcin secretion elicited by calcitriol. These observations emphasize the complex physiology of osteoblasts and confirm different behaviors of alkaline phosphatase and of osteocalcin as markers of bone turnover.

Tritiated imipramine binding sites in affective disorders and schizophrenia. Influence of circannual variation.

We have investigated platelet [3H]imipramine binding in normal controls and patients with primary endogenous depression (unipolar and bipolar) or schizophrenia. Absolute Bmax values did not differ between subgroups. However, when circannual variation of binding was taken into account by expressing results as percentages of normalised values derived from the multiple linear regression of Bmax values as a function of time of sampling, schizophrenic patients were found to have higher Bmax than normal controls. There was no significant difference between depressed patients and controls, nor between patients exhibiting plasma cortisol suppression and non-suppression after the dexamethasone suppression test. A significant negative correlation was found between relative Bmax values and cerebrospinal 5-HIAA levels in depressed patients.

Seasonal variation of platelet serotonin uptake and 3H-imipramine binding in normal and depressed subjects.

Density of 3H-imipramine binding sites and serotonin (5-HT) uptake in blood platelets were repeatedly recorded in normal controls (n = 9) and depressed patients (n = 7 for the imipramine binding assay and n = 4 for the serotonin uptake) over a 1-year period. The study demonstrated a striking seasonal variation of both parameters in both groups, with lower values in winter and spring than in summer and fall. No difference in the density of 3H-imipramine binding sites was found between the two populations throughout the year, but serotonin uptake was significantly decreased in depressed patients in May and September. These results underscore the importance of studying controls and patients at the same time of the year.

Circannual variations in the density of tritiated imipramine binding sites on blood platelets in man.

We demonstrate a circannual variation in the density of binding sites of 3H-imipramine on human platelets of normal controls and depressed patients. These results imply further reassessment of previously published data on 3H-imipramine binding studies in affective disorders.