Drying kinetics of deformable and cracking nano-porous gels.

The desiccation of porous materials encompasses a wide range of technological and industrial processes and is acutely sensitive to the hierarchical structure of the porous materials resulting in complex dynamics which are challenging to unravel. Macroscopic observations of the surface and geometry of model colloidal gels during desiccation under controlled air flow highlight the role of crack formation in drying. The density of cracks and their rate of appearance depend on the initial solid fraction of the gels and their adherence to the substrate. While under certain conditions cracking leads to an increase of the drying rate, in other cases cracking allows for its conservation over an extended period of the drying process. Nevertheless, as long as the sample is saturated with water, each piece within the sample shrinks isotropically as if it were an independent drying system. By simulating the airflow around the sample and inside the crack cavities, we show the existence of a perturbation in the air velocity in the vicinity of the crack cavity whose scale depends on the aspect ratio (depth/width) of the latter. On this basis, we propose a simple model which predicts the observed drying rate variations encountered while the sample cracks; and further enables to simulate the desiccation for a designated crack density.

Image formation in CARS and SRS: effect of an inhomogeneous nonresonant background medium.

We investigate the role of a spatially inhomogenous nonresonant background medium on several Raman-based imaging modalities. In particular, we consider a small resonant bead submerged in a spatially heterogeneous nonresonant χ(3) background. Using detailed 3D electrodynamic simulations, we compare coherent anti-Stokes Raman scattering (CARS), frequency-modulated CARS, amplitude-modulated stimulated Raman scattering (SRS), and frequency-modulated SRS. We find that only FM-SRS is background-free.

Image formation in CARS microscopy: effect of the Gouy phase shift.

Image formation in Coherent Anti-Stokes Raman Scattering (CARS) microscopy of sub-wavelength objects is investigated via a combined experimental, numerical and theoretical study. We consider a resonant spherical object in the presence of a nonresonant background, using tightly focused laser pulses. When the object is translated along the laser propagation axis, we find the CARS signal to be asymmetric about the laser focal plane. When the object is located before the focus, there is a distinct shadow within the image, whereas the brightest signal is obtained when the object is behind the focus. This behaviour is caused by interference between resonant and nonresonant signals, and the Gouy phase shift is responsible for the observed asymmetry within the image.

Sympathetic modulation of endothelium-derived relaxing factor.

To determine whether the release of endothelium-derived relaxing factor (EDRF) is sympathetically mediated, we studied the effects of beta-blockade by propranolol, ganglionic blockade with hexamethonium, or mechanical pithing on the blood pressure response to EDRF inhibition in anesthetized rats. We inhibited EDRF with 10 mg/kg of either NG-monomethyl-L-arginine (L-NMMA) or N omega-nitro-L-arginine-methyl ester (L-NAME). In controls, L-NMMA and L-NAME increased blood pressure by 14 +/- 1 (p less than 0.01) and 22 +/- 2 mm Hg (p less than 0.01), respectively. Propranolol lowered blood pressure from 98 +/- 3 to 72 +/- 4 mm Hg without altering the response to L-NAME (delta 26 +/- 3). This response correlated with the resting blood pressure (r = 0.87; p less than 0.001). Hexamethonium (25 mg/kg) lowered blood pressure from 118 +/- 6 to 85 +/- 4 mm Hg but did not change the response to L-NMMA (delta 15 +/- 1). In pithed rats, blood pressure was lowered, but the pressor response to L-NAME was unchanged. When blood pressure was returned to normotensive levels by angiotensin II, norepinephrine, or phenylephrine, L-NAME increased blood pressure by 50 +/- 2, 68 +/- 8, and 109 +/- 7 mm Hg, respectively (p less than 0.001). We conclude that an intact autonomic nervous system is not needed for the pressor response to EDRF inhibition. The enhanced response in pithed rats treated with vasoconstrictors may be due to removal of the buffering effect of the baroreceptors and the absence of EDRF, which would oppose vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a new fluorescent dye method to measure urinary albumin in lieu of urinary total protein.

Urinary total protein (UTP) determinations are notoriously inaccurate, poorly reproducible, and difficult to interpret in early renal disease, causing many investigators to measure urinary albumin instead. In this study, we compare a new nonimmunologic fluorescent dye (AB-dye) for measuring albumin with the more expensive and cumbersome radioimmunoassay. We tested 207 urine specimens from patients with variable protein concentrations and divided the results into five arbitrary ranges (0 to 20, 21 to 50, 51 to 100, 101 to 200, and 201 to 400) for chi-square analysis. There was a high degree of correlation between the two methods (chi-square = 260. 8 with 16 degrees of freedom; P < 0.001). The correlation was also high when analyzed by linear regression (R = 0.86; F < 0.01). Based on our comparison of total protein and albumin concentration in the same urine samples, we hypothesized that patients with mild proteinuria may not necessarily have microalbuminuria. Urine samples with UTP between 150 and 400 microg/mL were tested for albumin by the AB-dye. Of 41 samples in this range, 18 (44%) had normal albumin levels. We conclude that measuring urinary albumin with the AB-dye is comparable in performance to radioimmunoassay and could replace UTP determinations, especially for patients with borderline elevations of UTP, many of whom do not have microalbuminuria.

Suppression of hyperparathyroidism by calcitriol therapy.

We reviewed the charts of 160 patients on hemodialysis and identified 33 with parathyroid hormone (PTH) > 800 pg/ml at any time during the last 3 years to confirm our impression that patients with PTH elevations for short durations of time require significantly smaller doses of calcitriol than those with prolonged PTH elevations. We divided the patients into two groups: 18 with PTH > 800 pg/ml on three or fewer occasions (Group 1, short-term hyperparathyroidism) and 15 with PTH > 800 pg/ml more than three times (Group 2, long-term hyperparathyroidism). Most patients received once weekly intravenous calcitriol, but if this failed to suppress PTH, the dose was increased gradually to three times a week, PTH was measured at mid-week, calcitriol was held if serum calcium rose to >11 mg/dl, and calcitriol was started again when calcium fell to <11 mg/dl. We found that the duration of dialysis was generally shorter in Group 1, as were maximal PTH levels. Calcitriol suppressed PTH levels to <200 pg/ml in both groups. However, the weekly dose of calcitriol needed to suppress PTH was significantly lower in Group 1 (5.4 +/- 1.2 microg in Group 1 and 11.4 +/- 1.8 microg in Group 2; p < 0.001). Further follow-up of seven patients for 1 more year showed continued suppression of PTH, and the dose of calcitriol required to maintain the suppression was lower than the initial dose. Thus patients with longer histories of dialysis and prolonged hyperparathyroidism required higher doses of calcitriol to suppress PTH to the same level as patients who were new on dialysis or with transient hyperparathyroidism. A protocol of three times weekly, high dose calcitriol with strict monitoring of serum calcium will avoid parathyroidectomy in most cases.

An application of EDXRF on the study of barley seedlings growth on sewage sludge.

An energy dispersive X-ray fluorescence method for trace element analysis in plants (leaves and roots) is presented. The method is characterized by the use of a secondary target excitation, thin specimen, and microwave acid digestion. The accuracy is about 10% and the sensitivity is in the range 10-50 ng/cm2. The analysis time (from dry sample to concentration data) is about 4 x 10(3) s. The effects of Cr in sewage sludge on barley seedling growth is presented.

A simple method to detect an albumin permeability factor in the idiopathic nephrotic syndrome.

BACKGROUND: Several investigators have detected an albumin permeability factor in the serum of patients with the idiopathic nephrotic syndrome (INS), that is, minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS), but the methods used have been complex. METHODS: We describe here a simpler method using cultured rat glomerular epithelial cell monolayers grown to confluence on Millicell filters, which allow sampling of apical and basolateral media. 125I-labeled human serum albumin (125I-HSA) was added to the basolateral compartment, and its leakage across the epithelial cell monolayer into the apical compartment was measured. RESULTS: In untreated cells (negative control), the albumin leakage reached 5.3% at 18 hours. Cell monolayers fixed with 95% ethanol (positive control) showed 62% leakage. Sera from three out of four patients with MCD and three out of four with FSGS resulted in considerable albumin leakage, whereas sera from nine patients with other types of nephrotic renal disease and five normal subjects caused no leakage. CONCLUSION: This study shows that the Millicell system provides a simple and useful method to screen for permeability factors in the INS.

Simplified screening for microalbuminuria.

BACKGROUND: Screening for microalbuminuria is increasingly advocated as a way to diagnose early renal involvement in diabetes and other diseases. It usually entails the use of a radioimmunoassay that is expensive and not always readily available. OBJECTIVE: To assess the efficacy of three simple and inexpensive tests for ruling out microalbuminuria. DESIGN: Cross-sectional study. SETTING: Outpatient clinics. PATIENTS: 221 patients from primary care clinics and a diabetes clinic. MEASUREMENTS: Random urine specimens were tested for albumin by using Micral-Test immunoassay strips (Boehringer Mannheim, Mannheim, Germany) and for protein by using sulfosalicylic acid testing and impregnated dipsticks (Chemstrips, Boehringer Mannheim). Radioimmunoassay for albumin was used for all specimens as standard for comparison. RESULTS: When less than 20 mg/L was considered the upper limit of normal for albumin concentration, Micral-Test, sulfosalicylic acid testing, and Chemstrips had negative predictive values of 99%, 95%, and 96%, respectively. Seventy-four specimens tested negative on both sulfosalicylic acid and Chemstrips; the negative predictive value of these two tests combined was 99%. CONCLUSIONS: The combination of sulfosalicylic acid testing and Chemistrips was as good as and less expensive than Micral-Test in ruling out microalbuminuria.

High glucose decreases matrix metalloproteinase-2 activity in rat mesangial cells via transforming growth factor-beta1.

Diabetic nephropathy is characterized by accumulation of mesangial matrix. Glucose-induced inhibition of matrix-degrading enzymes such as collagenases is believed to contribute to matrix accumulation. We have previously demonstrated that 72 kDa type IV collagenase activity is decreased in the rat mesangial cells cultured in high glucose media [Diabetes 1995;44:929-935]. The present studies were designed to investigate if the cytokine transforming growth factor-beta1 (TGF-beta1) mediates this effect of glucose. Type IV collagenases degrade type IV collagen as well as gelatin (denatured collagen) and are thus also called gelatinases. They belong to the family of matrix metalloproteinases (MMPs); MMP activity is controlled by tissue inhibitors of metalloproteinases (TIMPs). The activity of 72 kDa type IV collagenase, also known as matrix metalloproteinase-2 (MMP-2), was assessed using three methods: (1) fluoresceinated gelatin degradation assay to detect free enzyme activity (activity which is present in excess of TIMP-inhibited activity); (2) zymography to measure total (free + TIMP-bound) enzyme activity; (3) ELISA using specific antibodies to measure MMP-2 levels. TGF-beta1 and TIMP-2 levels were also determined by ELISA. Incubation of primary cultures of rat mesangial cells for 5 days in 30 vs. 5 mM glucose resulted in a 3-fold increase in production of total TGF-beta1, a significant decrease in MMP-2 activity and immunoreactive MMP-2 levels, and an increase in TIMP-2 levels. Addition of exogenous TGF-beta1 to mesangial cells incubated in 5 mM glucose replicated the high glucose effect by producing a significant decrease in MMP-2 levels with a concurrent increase in TIMP-2 levels. Furthermore, glucose-induced inhibition of MMP-2 activity was completely blocked by neutralization of TGF-beta1 with anti-TGF-beta1 antibody. We conclude that the decrease in MMP-2 activity induced by glucose loading is mediated via TGF-beta1.

Carbamylated proteins activate glomerular mesangial cells and stimulate collagen deposition.

Carbamylated proteins formed in renal insufficiency from the spontaneous decomposition of urea exert a variety of metabolic effects. Here we examined the effects of carbamylated proteins on glomerular mesangial cells to determine whether urea retention in early renal insufficiency may itself promote glomerular sclerosis and hasten the progression to kidney failure. To this effect we carbamylated fetal bovine serum proteins in vitro and tested their effect on mesangial cell proliferation (by tritiated thymidine uptake), de novo protein synthesis (by tritiated leucine uptake), collagen I and collagen IV accumulation (by avidin-biotin enzyme immunoassay), and gelatinase levels in the medium (by zymography and quantitative fluorescence assay). Carbamylated fetal bovine serum at concentrations present in uremia increased tritiated thymidine incorporation by 50% without altering tritiated leucine incorporation, and it increased collagens I and IV in the monolayer by 150% to 300%. Gelatinase activity was unchanged. We conclude that carbamylated proteins can activate mesangial cells to a profibrogenic phenotype. From a clinical perspective, the carbamylation of proteins by elevated urea levels may accelerate the progression to kidney failure and thus set up a vicious cycle in which the nitrogen retention itself would cause further progression of fibrosis and deterioration of kidney function.

The significance of trace proteinuria.

BACKGROUND: The clinical significance of a trace protein reading on urinalysis is unclear, and such a result is often ignored by the clinician. METHODS: We examined 185 samples of urine with trace proteinuria by both Chemstrips and sulfosalicylic acid testing, and compared the results with those of urinary albumin and total protein concentrations. RESULTS: Taking for the purposes of this study an arbitrary upper limit of normal of 20 mg/l for albumin and 100 mg/l for total protein concentration, we found abnormal albumin excretion in 87% and abnormal total protein excretion in 88% of trace samples. In this study, a negative urinalysis for protein excluded microalbuminuria in 87% and proteinuria in 78% of cases. CONCLUSION: Qualitative testing for protein by urinalysis has a high sensitivity and specificity for diagnosing or ruling out microalbuminuria. Trace proteinuria usually means microalbuminuria; negative proteinuria tends to rule it out.

Changes in collagenases and TGF-beta precede structural alterations in a model of chronic renal fibrosis.

BACKGROUND: To study the role of collagenases and transforming growth factor-beta (TGF-beta) in the genesis of interstitial fibrosis, we used the model of bromoethylamine (BEA)-induced papillary necrosis, which is known to lead over a period of 1 to 12 months to interstitial fibrosis and renal insufficiency. METHODS: Rats were injected with BEA, and urine and kidney tissue (cortex and medulla) were collected after 1, 2, 3, 7, and 30 days. One kidney was perfused and fixed for morphological studies and immunostained for collagen type I, III, and IV. The other kidney was used to prepare cortex and medulla extracts for gelatinases (by fluorometric and zymographic techniques), tissue inhibitors of metalloproteinase-1 (TIMP-1), and TIMP-2 (by enzyme-linked immunosorbent assay, ELISA) and TGF-beta1 (by ELISA). RESULTS: Albuminuria and interstitial fibrosis were present in BEA rats by day 7, which continued until day 30. Immunocytochemical staining for collagen types showed that collagen III and IV increased in the interstitium by day 30, but collagen I remained unchanged. Gelatinase activity in the medulla decreased by 57% compared with control by day 2 and remained low until day 30. In the cortex, gelatinase activity remained unchanged between 0 and 7 days after BEA but decreased by 72% by day 30. TIMP-1 and TIMP-2 were decreased by 80% compared with day 0 in both the medulla (by day 1) and cortex (by day 2) and remained low up to day 30. TGF-beta1 immunoreactivity increased progressively until day 2 in the medulla (16-fold higher than control) and day 3 in the cortex (8-fold higher than control) and returned to control level by day 3 in the medulla and by day 30 in the cortex. Two days after BEA injection, the mRNA for TGF-beta1 was increased eightfold in the cortex and 12-fold in the medulla, and it remained high for up to 30 days. CONCLUSIONS: The fibrosis that follows papillary necrosis is associated with both high TGF-beta1 expression and depressed gelatinolytic activity.