Nephrin strands contribute to a porous slit diaphragm scaffold as revealed by electron tomography

Nephrin is a key functional component of the slit diaphragm, the structurally unresolved molecular filter in renal glomerular capillaries. Abnormal nephrin or its absence results in severe proteinuria and loss of the slit diaphragm. The diaphragm is a thin extracellular membrane spanning the approximately 40-nm-wide filtration slit between podocyte foot processes covering the capillary surface. Using electron tomography, we show that the slit diaphragm comprises a network of winding molecular strands with pores the same size as or smaller than albumin molecules, as demonstrated in humans, rats, and mice. In the network, which is occasionally stratified, immunogold-nephrin antibodies labeled individually detectable globular cross strands, about 35 nm in length, lining the lateral elongated pores. The cross strands, emanating from both sides of the slit, contacted at the slit center but had free distal endings. Shorter strands associated with the cross strands were observed at their base. Immunolabeling of recombinant nephrin molecules on transfected cells and in vitrified solution corroborated the findings in kidney. Nephrin-deficient proteinuric patients with Finnish-type congenital nephrosis and nephrin-knockout mice had only narrow filtration slits that lacked the slit diaphragm network and the 35-nm-long strands but contained shorter molecular structures. The results suggest the direct involvement of nephrin molecules in constituting the macromolecule-retaining slit diaphragm and its pores.     

Vitamin D receptor gene polymorphism as an important modifier of positive family history related breast cancer risk

The association between vitamin D receptor (VDR) gene polymorphisms and diseases such as breast cancer, prostate cancer and osteoporosis has been extensively investigated during recent years. To date, several polymorphisms have been found in the VDR gene. In this Finnish case-control study, comprising 483 breast cancer patients and 482 healthy population controls, we investigated the association between altered breast cancer risk and two polymorphisms in the 3' end of the gene detectable with ApaI and TaqI restriction enzymes. A statistically significant difference was observed in the ApaI genotype distribution between cases and controls. Women with the VDR variant a allele containing genotypes showed a decreased risk for breast cancer [odds ratio (OR) 0.73, 95% confidence interval (CI) 0.54-0.98] compared to women with the AA genotype. This association was especially strong among women with a positive family history of breast cancer (OR 0.14, 95% CI 0.03-0.76). Moreover, there was a trend (P for trend = 0.0007) for decreased risk with increasing number of variant alleles. The lowest risk of breast cancer was seen for the women with the aa genotype (OR 0.03, 95% CI 0.003-0.31) compared to women with the AA genotype. A tendency of decreased risk of breast cancer was also observed for the TaqI T allele containing genotypes (Tt and TT) (OR 0.68, 95% CI 0.41-1.12), but because the distribution of Taql alleles in the controls missed the Hardy-Weinberg equilibrium (P = 0.01), we were unable to properly assess the potential impact of the TaqI polymorphism in breast cancer susceptibility. In conclusion, our results suggest that the VDR ApaI genotype may be an important modifier of individual breast cancer risk among Finnish women, especially if they have a positive family history of breast cancer.     

Effect of extent of motion and type of load on the wear of polyethylene in a biaxial hip simulator

The most commonly used wear test device for prosthetic hip joints is the so-called biaxial rocking motion (BRM) design. The design has been criticized for its excessive sliding distance per cycle. The design was modified so that the extent of motion was reduced from 46 to 23 degrees, and comparative tests were run with the use of 1-kN static load. The present authors have earlier used 1-kN static load with good results. To further confirm this finding, additional, comparative tests were run with double-peak dynamic load and 46 degrees extent of motion. All three tests (46 degrees /static, 23 degrees /static and 46 degrees /dynamic), were done with conventional ultra-high-molecular-weight polyethylene acetabular cups against polished CoCr femoral heads in diluted calf serum lubricant. In all tests, the principal cup wear mechanism was adhesive, manifested as burnishing. With respect to wear particles, those produced in the 46 degrees /dynamic test showed the lowest resemblance to particles isolated from periprosthetic tissues. The 46 degrees /dynamic test produced a mean wear rate 43% higher than 46 degrees /static, whereas the 46 degrees /static and 23 degrees /static tests produced almost identical values. The results indicated that the 46 degrees extent of motion and dynamic load may not always be the optimal combination in BRM tests.     

Effect of cardiac vagal outflow on complexity and fractal correlation properties of heart rate dynamics

1. Cardiac vagal outflow is the major factor determining the magnitude of heart rate (HR) variability analysed by traditional time and frequency domain methods. New analysis techniques, such as fractal and complexity methods, have been developed to probe non-linear features in HR behaviour that may not be detectable by traditional methods. 2. We investigated the effects of vagal blockade (glycopyrrolate i.v. 5 microg kg-1 h-1 for 2 h, n = 8 vs. unmedicated control group, n = 8) and various breathing patterns (n = 12) on two non-linear measures of HR variability--detrended fluctuation analysis (DFA) and approximate entropy (ApEn)--in healthy male volunteers. 3. Glycopyrrolate decreased the mean (+/-SD) ApEn from 1.46 +/- 0.18 to 0.85 +/- 0.24 (P = 0.001 in comparison with the control group), and increased the short-term (alpha 1) and intermediate-term (alpha 2) fractal scaling exponents of DFA, alpha 1 from 0.96 +/- 0.19 to 1.43 +/- 0.29 (P = 0.003) and alpha 2 from 1.13 +/- 0.10 to 1.34 +/- 0.14 (P < 0.001). 4. Decrease in fixed respiration rate from 15 to 6 breaths min-1 increased alpha 1 from 0.83 +/- 0.25 to 1.18 +/- 0.27 (P < 0.001), but decreased alpha 2 from 0.88 +/- 0.09 to 0.45 +/- 0.17 (P < 0.001) and ApEn from 1.26 +/- 0.12 to 1.10 +/- 0.14 (P = 0.028). Rapid breathing (24 min-1) had no influence on these non-linear measures of HR variability. Hyperventilation (15 min-1, tidal volume increased voluntarily by 0.5 l) decreased alpha 1 from 0.83 +/- 0.25 to 0.66 +/- 0.28 (P = 0.002) but did not affect alpha 2 or ApEn. 5. To conclude, vagal blockade alters the fractal scaling properties of R-R intervals (alpha 1, alpha 2) and reduces the complexity (ApEn) of HR behaviour. Both the fractal and complexity measures of HR variability can also be influenced by changes in the breathing pattern.     

Elbow synovectomy on patients with juvenile rheumatoid arthritis

Twenty-four primary elbow synovectomies were done between 1991 and 1998 at the authors' institution on 19 patients (15 females, four males) with juvenile rheumatoid arthritis. Five bilateral and 14 unilateral procedures were done. The mean age of the patients was 29 years (range, 11-64 years) at the time of surgery and the mean disease duration was 19 years (range, 2-51 years). Preoperatively radiographic destruction of Larsen Grade 1 was detected in 21% of elbows, Grade 2 in 54%, and Grade 3 in 4%. In 21% of elbows no radiographic destruction was present (Grade 0). The cumulative survival rate of elbow synovectomy was 84% (95% confidence interval, 68-98) at 5 years. Four resynovectomies and two elbow replacement arthroplasties were done during the followup period. Complete pain relief was documented in 44% of patients and subjective outcome was excellent or good in 72% of patients. No significant improvement was observed in functional ability or range of motion in extension and flexion or pronation and supination. The results of the current study (mean followup, 5 years; range, 2-9 years) are slightly worse compared with the short-term results of elbow synovectomy in patients with adult-onset rheumatoid arthritis.     

Quantifying tumour hypoxia with fluorine-18 fluoroerythronitroimidazole ([<Superscript>18</Superscript>F]FETNIM) and PET using the tumour to plasma ratio

Fluorine-18 fluoroerythronitroimidazole ([(18)F]FETNIM) is a nitroimidazole compound that is potentially useful as a hypoxia marker in positron emission tomography (PET) studies of oncological patients. Our aim was to develop a simple protocol to quantitate uptake of [(18)F]FETNIM in hypoxic tumours. Dynamic imaging data from ten patients with head and neck cancer undergoing [(18)F]FETNIM PET was used in simulations and model fits to assess hypoxia marker uptake under different levels of blood flow. The distribution volume determined from dynamic PET study was compared with simple tumour to plasma and tumour to muscle ratios at 90-120 min. In skeletal muscle having a low but variable blood flow [2-6 ml/(100 gxmin)], differences in hypoxia-specific uptake of [(18)F]FETNIM remain small and may be hard to detect with PET. At higher blood flow [>20 ml/(100 gxmin)], the retention of [(18)F]FETNIM reflects the oxygenation status well and results in satisfactory contrast between hypoxic and well-oxygenated tissue. A good estimate of tissue hypoxia is accomplished by measuring the tissue to plasma [(18)F]FETNIM activity ratio using only a few late time points. The increased hypoxia-specific retention of [(18)F]FETNIM in tissues with high blood flow, such as malignant tumours, may facilitate application of [(18)F]FETNIM as a hypoxia marker in oncological patients. In the assessment of the tumour to non-target uptake ratio, plasma is the preferred reference tissue rather than muscle, which may show a more heterogeneous tracer uptake not easily controlled for.     

Insulin- and exercise-stimulated skeletal muscle blood flow and glucose uptake in obese men

OBJECTIVE: Insulin resistance in obese subjects results in the impaired use of glucose by insulin-sensitive tissues, e.g., skeletal muscle. In the present study, we determined whether insulin resistance in obesity is associated with an impaired ability of exercise to stimulate muscle blood flow, oxygen delivery, or glucose uptake. RESEARCH METHODS AND PROCEDURES: Nine obese (body mass index = 36 +/- 2 kg/m(2)) and 11 age-matched nonobese men (body mass index = 22 +/- 1 kg/m(2)) performed one-legged isometric exercise during hyperinsulinemia. Rates of femoral muscle blood flow, oxygen consumption, and glucose uptake were measured simultaneously in both legs using [(15)O]H(2)O, [(15)O]O(2), [(18)F]fluoro-deoxy-glucose, and positron emission tomography. RESULTS: The obese subjects exhibited resistance to insulin stimulation of glucose uptake in resting muscle, regardless of whether glucose uptake was expressed per kilogram of femoral muscle mass (p = 0.001) or per the total mass of quadriceps femoris muscle. At similar workloads, oxygen consumption, blood flow, and glucose uptake were lower in the obese than the nonobese subjects when expressed per kilogram of muscle, but similar when expressed per quadriceps femoris muscle mass. DISCUSSION: We conclude that obesity is characterized by insulin resistance of glucose uptake in resting skeletal muscle regardless of how glucose uptake is expressed. When compared with nonobese individuals at similar absolute workloads and under identical hyperinsulinemic conditions, the ability of exercise to increase muscle oxygen uptake, blood flow, and glucose uptake per muscle mass is blunted in obese insulin-resistant subjects. However, these defects are compensated for by an increase in muscle mass.