Differentiation of extrastriatal dopamine D2 receptor density and affinity in the human brain using PET

Dopaminergic neurotransmission in extrastriatal regions may play a crucial role in the pathophysiology and treatment of neuropsychiatric disorders. The high-affinity radioligands [(11)C]FLB 457, [(123)I]epidepride, and [(18)F]fallypride are now used in clinical studies to measure these low-density receptor populations in vivo. However, a single determination of the regional binding potential (BP) does not differentiate receptor density (B(max)) from the apparent affinity (K(D)). In this positron emission tomography (PET) study, we measured extrastriatal dopamine D2 receptor density (B(max)) and apparent affinity (K(D)) in 10 healthy subjects using an in vivo saturation approach. Each subject participated in two to three PET measurements with different specific radioactivity of [(11)C]FLB 457. The commonly used simplified reference tissue model (SRTM) was used in a comparison of BP values with the B(max) values obtained from the saturation analysis. The calculated regional receptor density values were of the same magnitude (0.33-1.68 nM) and showed the same rank order as reported from postmortem studies, that is, in descending order thalamus, lateral temporal cortex, anterior cinguli, and frontal cortex. The affinity ranged from 0.27 to 0.43 nM, that is, approximately 10-20 times the value found in vitro (20 pM). The area under the cerebellar time activity curve (TAC) was slightly lower (11 +/- 8%, mean +/- SD, P = 0.004, n = 10) after injection of low as compared with high specific radioactivity, indicating sensitivity to the minute density of dopamine D2 receptors in the this region. The results of the present study support that dopamine D2 receptor density and affinity can be differentiated in low-density regions using a saturation approach. There was a significant (P < 0.001) correlation between the binding potential calculated with SRTM and the receptor density (B(max)), which supports the use of BP in clinical studies where differentiation of B(max) and K(D) is not required. In such studies, the mass of FLB 457 has to be less than 0.5 microg injected to avoid a mass effect of the radioligand itself.     

Nephrin is specifically located at the slit diaphragm of glomerular podocytes

We describe here the size and location of nephrin, the first protein to be identified at the glomerular podocyte slit diaphragm. In Western blots, nephrin antibodies generated against the two terminal extracellular Ig domains of recombinant human nephrin recognized a 180-kDa protein in lysates of human glomeruli and a 150-kDa protein in transfected COS-7 cell lysates. In immunofluorescence, antibodies to this transmembrane protein revealed reactivity in the glomerular basement membrane region, whereas the podocyte cell bodies remained negative. In immunogold-stained thin sections, nephrin label was found at the slit between podocyte foot processes. The congenital nephrotic syndrome of the Finnish type (NPHS1), a disease in which the nephrin gene is mutated, is characterized by massive proteinuria already in utero and lack of slit diaphragm and foot processes. These features, together with the now demonstrated localization of nephrin to the slit diaphragm area, suggests an essential role for this protein in the normal glomerular filtration barrier. A zipper-like model for nephrin assembly in the slit diaphragm is discussed, based on the present and previous data.     

Bone response to free form-fabricated hydroxyapatite and zirconia scaffolds: a histological study in the human maxilla

Objectives: Synthetic and biological materials are increasingly used to provide temporary or permanent scaffolds for bone regeneration. This study evaluated the effect of material chemistry and microporosity on bone ingrowth and osseointegration of zirconia (ZrO₂) and hydroxyapatite (HA) scaffolds in the human maxilla.
Material and methods: Twelve patients subjected to dental implant placement were enrolled in the study. Scaffolds of ZrO₂ and HA were placed in the maxilla of each subject, using a randomization protocol. After 3 months of healing, biopsies were harvested comprising the scaffolds and surrounding bone tissue. The biopsies were processed for histological evaluation and morphometric analysis (bone ingrowth and bone-to-scaffold contact).
Results: Healing was uneventful in all cases. All scaffolds demonstrated a measurable bone response using light microscopy and scanning electron microscopy. Microporous HA scaffolds revealed four times larger bone ingrowth and seven times larger bone contact as compared with ZrO₂ scaffolds.
Conclusion: The results show that chemistry and microporosity of HA promote bone ingrowth and bone contact of ceramic scaffolds in human maxilla.     

In vivo and in vitro characterization of [18F]-FE-(+)-DTBZ as a tracer for beta-cell mass

IntroductionThe positron emission tomography (PET) tracer 9-[¹⁸F]fluoroethyl-(+)-dihydrotetrabenazine ([¹⁸F]-FE-(+)-DTBZ) is a potential candidate for quantifying beta-cell mass in vivo. The purpose was to investigate in vitro and in vivo utility of this tracer for the assessment of beta-cell mass.MethodsThree pigs were intravenously administered [¹⁸F]-FE-(+)-DTBZ and examined by PET/computed tomography. Binding parameters were estimated by kinetic modeling. In vitro k_D and B_max were determined by saturation binding studies of endocrine and exocrine human tissue homogenates. In vitro pancreatic uptake was determined by tissue autoradiography with pancreases from patients with types 1 (T1DM) and 2 diabetes mellitus (T2DM) and healthy controls.Results[¹⁸F]-FE-(+)-DTBZ had a k_D of 3.5±1.0 nM, a B_max of 382±108 fmol/mg protein and a specificity of 89±1.8% in islet homogenates. The total exocrine uptake was lower and 65% was nondisplaceable. No uptake difference was observed in pancreatic tissue slices from patients with T1DM, T2DM or healthy controls. The in vivo porcine pancreatic uptake reached a peak of standardized uptake value (SUV) of 2.8 with a low distribution volume ratio in all animals. Moderate to high tracer uptake was identified in the bile system and in bone.Conclusions[¹⁸F]-FE-(+)-DTBZ binds to vesicular monoamine transporter 2 (VMAT2) with high specificity in pure islet tissue in vitro. However, there is high nondisplaceable binding to exocrine tissue. In addition, in vivo tracer metabolism and dehalogenation result in severe underestimation of porcine pancreatic VMAT2 expression and BCM. The results do not support [¹⁸F]-FE-(+)-DTBZ as a suitable tracer for in vivo beta-cell imaging.     

The use of biodegradable PGA stents to judge the risk of post-TURP incontinence in patients with combined bladder outlet obstruction and overactive bladder

OBJECTIVE: For patients with the combination of severe bladder outlet obstruction (BOO) and severe overactive bladder (OB), no straightforward and safe treatment exists due to the risk of urge incontinence after TURP. In this study we have used a biodegradable polyglycolic stent to simulate the status after TURP and register the risk for urge incontinence. METHODS: A total of 37 patients with severe OB, combined with moderate to severe BOO, were asked if they wanted to participate. Under cystoscopic vision a polyglycolic biodegradable stent was inserted in the prostatic urethra. RESULTS: Twenty-five of the patients noticed no or only minor leakage and 19 of these have been subjected to TURP with good results. Three patients are on the waiting-list for TURP. Twelve of 37 patients were found to have major leakage after stent insertion. During the stent period, we noted five cases of complications, due to UTI, stent crash and irritation. All of these patients recovered within three weeks. CONCLUSIONS: A biodegradable PGA stent seems to be a new and unique tool to test the risk for post-TURP incontinence in patients with combined BOO and severe OB.     

Neurological signs are common in patients with urodynamically verified "idiopathic" bladder overactivity

Overactive bladder dysfunction is an expression of defective neuromuscular control of the lower urinary tract. The causes and the way to classify this problem are currently under debate. In some patients the overactive bladder is one sign of a neurological disorder, in so called "idiopathic detrusor instability" the cause is less obvious. That an overactive bladder has a neurogenic cause is a reasonable hypothesis. We made a detailed neurological investigation in 45 patients with idiopathic overactive bladder. Cerebrospinal fluid (CSF) was examined and blood tests for vitamin B(12)and folic acid deficiency were checked, too. In 37 of the 45 patients (82%) pathological signs were observed in the neurological tests. The most common finding was central or peripheral paresis of the legs appearing in 24 patients (53%). Of the 45 patients, eight received a neurological diagnosis, definite or possible MS or dorsal column sensation neuropathy. The results of this study give an indication of the importance of the neurological examination and suggest that neuropathy might not be uncommon in patients with so-called idiopathic detrusor instability. This also invites to reconsideration of the current classification. It is possible that a new classification based on a functional view could provide a better fundament in the search of etiologic and pathogenetic factors and also guide in the selection of the treatment most optimal for the individual patient.     

Occupational health in Central America

The 12.4 million economically active population (EAP) of the seven Central American countries includes a large informal sector. Social security covers only 14-60%. No surveillance of occupational safety and health (OSH) hazards or accidents exists. Extrapolating the incidence of occupational accidents among insured Costa Rican workers to the Central American EAP yields two million accidents yearly, still a gross underestimate. Occupational diseases are underreported, misdiagnosed, and not recognized as such. A number of regional OSH programs aim at modernization of the labor administrations and address the formal sector, in particular textile maquila, in connection with free trade agreements. The weak role of the ministries of health is expected to strengthen under the Pan American Health Organization OSH program. Employers largely influence new policies. Workers' influence on OSH policies has been weak, with only about 10% unionization rate and scarce resources and OSH knowledge. Informal workers, however, are getting organized. OSH research is underdeveloped and not linked to policy making. Construction, agriculture, and general un/underemployment are considered priorities for intervention. The informal sector needs to be included in national and regional OSH policies. Regional collaboration and international development support are of strategic importance to achieve sustainable improvement in OSH.     

Influence of preimplant surgical intervention and implant placement on bone wound healing

The aims of the present investigation were to study (1). the influence of preimplant (4 weeks) surgical intervention and (2). the influence of the implant placement per se on bone density and mineralized bone-implant contact (BIC) at implant sites in the rabbit jawbone. The experiment was performed in the edentulous area of the maxillas of 16 adult rabbits. In eight rabbits, the alveolar bone on the left side (test) was surgically exposed and a groove was prepared in the bone crest. Trabecular bone and marrow tissue were removed, and a bioabsorbable barrier membrane was placed to cover the groove. The right side underwent no treatment and served as the control. Four weeks later, a screw-shaped titanium implant was placed transversally through the maxilla, penetrating both the test and the control areas. After another 4 weeks of healing, the animals were killed to obtain ground sections for histomorphometry. Untreated jaws from eight rabbits served as reference specimens. In the rabbits subjected to surgery, the areas (mm2) of both mineralized bone and marrow tissue were similar for test and control (4.9 +/- 1.7 vs. 5.1 +/- 2.2 and 6.3 +/- 5.7 vs. 6.8 +/- 5.7 for bone and marrow, respectively). The BIC (%) for all threads was significantly lower on the test side than on the control side (32.1 +/- 27.7 vs. 47.7 +/- 20.3). The bone density (%) of the total experimental area was similar for test and control (48.5 +/- 12.1 vs. 46.5 +/- 9.3), as was the bone density in the area within the implant thread valleys and their mirror areas (43.0 +/- 13.9 vs. 41.3 +/- 13.5, and 40.2 +/- 11.0 vs. 40.3 +/- 7.2 for thread area and mirror area, respectively). The bone density of the total experimental area in the untreated rabbits was 35.9 +/- 5.2%. This value was significantly lower than the values in the total experimental areas (test and control) of the surgically treated rabbits. Similarly, the density of the reference area in the untreated rabbits was 25.4 +/- 5.3%, which was also significantly lower than the bone density of the periimplant area of the surgically treated rabbits. We conclude that the surgical trauma caused by the placement of implants in the maxilla of rabbits significantly enhanced the bone density of the implant sites. Surgical intervention in the implant sites 4 weeks prior to the implant placements, however, did not further enhance bone density or BIC.