Surface plasmon resonance (SPR) is a phenomenon occuring at metal surfaces (typically gold and silver) when an incident light beam strikes the surface at a particular angle. Depending on the thickness of a molecular layer at the metal surface, the SPR phenomenon results in a graded reduction in intensity of the reflected light. Biomedical applications take advantage of the exquisite sensitivity of SPR to the refractive index of the medium next to the metal surface, which makes it possible to measure accurately the adsorption of molecules on the metal surface and their eventual interactions with specific ligands. The last ten years have seen a tremendous development of SPR use in biomedical applications. The technique is applied not only to the measurement in real-time of the kinetics of ligand–receptor interactions and to the screening of lead compounds in the pharmaceutical industry, but also to the measurement of DNA hybridization, enzyme–substrate interactions, in polyclonal antibody characterization, epitope mapping, protein conformation studies and label-free immunoassays. Conventional SPR is applied in specialized biosensing instruments. These instruments use expensive sensor chips of limited reuse capacity and require complex chemistry for ligand or protein immobilization. Our laboratory has successfully applied SPR with colloidal gold particles in buffered solution. This application offers many advantages over conventional SPR. The support is cheap, easily synthesized, and can be coated with various proteins or protein–ligand complexes by charge adsorption. With colloidal gold, the SPR phenomenon can be monitored in any UV-vis spectrophotometer. For high‒throughput applications, we have adapted the technology in an automated clinical chemistry analyzer. This simple technology finds application in label-free quantitative immunoassay techniques for proteins and small analytes, in conformational studies with proteins as well as in the real-time association-dissociation measurements of receptor–ligand interactions, for high-throughput screening and lead optimization.

Inhibition and working memory deficits, associated with low levels of CBF in the medial frontal gyrus, are related to the difficulty of maintaining short-term abstinence from alcohol.

Recently detoxified non-neurological alcoholic patients appear to be impaired in cognitive tasks measuring inhibitory processes as well as working memory (involving storage and manipulation of information). The aim of this study was to investigate in alcoholic participants the relationship between these two cognitive functions and regional cerebral blood flow (rCBF) studied at rest in regions of interest selected on the basis of recent PET studies which explored inhibitory and working memory in normal subjects. Twenty non-neurological alcoholic patients and 20 normal volunteers were selected for a neuropsychological exploration, including assessment of inhibition processes (by means of the Hayling test) and working memory (by means of the Alpha-span task). rCBF of alcoholics was also evaluated with a semi-quantitative method using a 99mTc-Bicisate single photon emission computed tomography (SPECT) procedure. Alcoholic patients performed worse than controls in the alphabetical condition of the Alpha-span task (involving manipulation and storage of information), and on the Hayling test. Significant correlation emerged between inhibition performance and both the bilateral inferior (left BA 47, r = -0.40; right BA 47, r = -0.599) and median frontal gyrus (left BA 10, r = -0.55; right BA 10, r = -0.59), but not with the region of reference (occipital/cerebellum, r = -0.13). Coordination of storage and manipulation was correlated with bilateral median frontal (left BA 10/46, r = -0.50; right BA 10/46, r = -0.45), but not with bilateral parietal area (left BA 7, r = -0.12, right BA 7, r = -0.18). These results suggest a relationship between inhibition and working memory deficits in alcoholic patients, and regional rCBF measured in frontal areas. Clinical implications of these data related to alcohol relapse are discussed.

We propose a high-throughput screening method which involves colloidal gold nanoparticles sensitized with the binding protein. Upon interaction with a specific ligand (a polypeptide or a small organic molecule), the surface plasmon resonance absorbance peak of the colloidal gold reagent shifts toward longer wavelengths due to the change in refractive index at the particle surface caused by changes in mass. The shift is proportional to the dose of ligand involved for a fixed amount of binding protein and occurs according to the kinetics of interaction. We applied this property to the analysis of association and dissociation of ligand-binding protein interactions in a small random access clinical chemistry analyzer. The instrument measures the changes in A 600 nm over a period of 20 min for each sample. Due to the high degree of automation, the instrument throughput amounts to 144 samples an hour and can be run during 24 h a day in a walk-away mode. When connected to a computer for data handling, a single instrument can consequently handle over 3000 samples a day. Higher throughput instruments are available which can handle as much as ten times more samples. We validated the technique by comparing the affinity constants (range 10 3 210 12 mol 21 ) calculated for 30 pairs of ligand-protein interactions at different ligand doses with those obtained from other methods, including the BIAcore (slope 0.84; coefficient of correlation r = 0.82).

We have shown that orchidectomy in postpubertal 55-day-old rats led beyond 2 months to a decrease in bone growth and loss of weight. At 1 month postorchidectomy, we observed a three-fold increase in bone blood flow, an increase in calcium accretion rate, and an increase in the number of osteoclasts in the metaphysis. In the present experimental study, orchidectomy was performed in 1-year-old rats when bone growth in length was no longer measurable. In the tibia and femur we observed a decrease in bone volume, a still more rapid decrease of bone calcium during the first postoperative month, a thinning of the cortical width, an initial increase in calcium accretion rate (+20% when compared to 31 days controls) followed by a decrease at 120 days (-22% and -11% when compared to controls for tibia and femur respectively), a 29% increase in bone blood flow, and an increase in the number of osteoclasts. We conclude that androgen deprivation in young and old animals leads to a modified bone architecture, independent of the androgen impact on bone growth.

Objective: To assess magnesium enteral absorption from a magnesium-rich mineral water. Design: Experimental study. Setting: Department of Nuclear Medicine, Brugmann Hospital, Brussels, Belgium. Subjects: Ten healthy male volunteers in the age range 25 -42 y. Intervention: Each subject completed two sessions in a random order. At one session, they received an oral load of 300 ml of water (containing 1.2 mmol Mg), traced with 28 Mg, and at the other session they received an intravenous injection of 28 Mg, in order to take into account the metabolism of endogenous magnesium. The dietary consumption was further noted on a weekly diary. Results: The mean bioavailability was 59.1% (s.d. AE 13.6). Magnesium absorption and age were significantly inversely correlated (r ¼ 70.68, P ¼ 0.035). Conclusion: Magnesium-rich mineral water is a reliable source of magnesium. Our observation of decreased magnesium absorption with age deserves further investigations. Sponsorship: The study was sponsored by SEV,

Orchidectomy in postpubertal 55 day old rats, compared to sham-operated controls, led beyond 2 months to a decrease in body weight (87% of controls by 120 d), tibial length (97% of controls) and in tibial calcium content (85% of controls). Bone plasma flow increased three times to reach a peak at 31 days; it was decreased but no significantly at 86 and 120 days. The number of oosteoclasts was maximal at 51 days (X 2.3) and was still elevated at 120 days. The calcium accretion rate increased briefly at 31 days (110% of controls) and was diminished at 86 and 120 days (78% of controls). The initial 'physiological' changes in the tibia occurred before any weight change and might be directly due to the lack of androgens. They can be interpreted as inducing the conditions for enhanced bone resorption. Testosterone replacement therapy, initiated after the initial haemodynamic response, inhibited the negative effect of castration on bone growth. We observed previously an increased bone blood flow in different situations of bone demineralization: paraplegia (Verhas et al. 1980); autoimmune arthritis, deprivation in calcium and/or vitamin D (unpublished data). Saville (1969) reported that castration of prepubertal male rats induced de¬ creases of total body growth and of calcium con¬ tent. Therefore, we investigated whether castra¬ tion, considered by Wink & Felts (1980) to be a model of osteoporosis, would also induce a similar bone haemodynamic response.The growth of castrated vs control animals was appreciated by measuring total body weight, as well as the length and the calcium content of the tibia.Blood flow, calcium accretion rate and number of osteoclasts in the tibial metaphysis was also fol¬ lowed at several intervals for 120 days after castra¬ tion or sham operation. Since indeed transient modifications in bone blood flow were observed within the first 2 months, it was decided to investi¬ gate whether testosterone implanted at 56 days might still reverse the subsequent effects of castra¬ tion on growth. Material and MethodsPostpubertal male Sprague-Dawley rats (55 days old) were castrated or sham-operated. They were divided into 5 groups of 14 animals (7 castrates -7 controls) and sacrificed after 13,31,51, 86, 120 days, respectively.Another experimental group consisted of 18 animals, 12 castrates and 6 sham-operated. After 56 days, 6 castrates received an sc testosterone silastic implant, whereas the other animals were implanted with an empty silastic. Silastic tubing was ID 1.98 mm, OD 3.18 mm and was filled with crystalline testosterone (Sigma) over a length of 2.5 cm. These animals were killed 105 days after operation. Blood was collected by cardiac puncture shortly before death to detemine, by radioimmunoassays, serum levels of FSH (NIA reagents) and testosterone (Bio Merieux kit).All animals were weighed the day of sacrifice. Tibias were separated and cleaned from all remaining tissues. Wet weight of bones was determined and, in the group 120 days, the volume of tibia was calculated by Archimede's princi...

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