Glomerular sieving of three neutral polysaccharides, polyethylene oxide and bikunin in rat. Effects of molecular size and conformation

AIM: Polysaccharides and many other non-protein polymers generally have a more open, flexible and asymmetrical structure compared with globular proteins. For a given molecular weight (MW), the Stokes-Einstein radius (a(e)) of the following polymers increases in the order: Ficoll < dextran 相似文献   

Glomerular charge selectivity for proteins larger than serum albumin as revealed by lactate dehydrogenase isoforms

It is well known that macromolecules like albumin are markedly restricted in their passage across the glomerular capillary wall. However, the relative importance of solute size, charge and shape is currently debated since much of the previous work is based on dextran in neutral or charge-modified forms. These polymers have certain drawbacks that make them less suitable for analysis of capillary permeability and the notion of a glomerular charge barrier has therefore been questioned. Moreover, macromolecules larger than albumin (mol. wt. 69 000) have been suggested to pass through nonselective 'shunt' pathways. In order to study glomerular permeability, isolated rat kidneys were perfused with albumin solutions containing trace amounts of two differently radiolabelled isoenzymes of lactate dehydrogenase (LDH) at low temperature to inhibit tubular function. The isoenzymes have similar size (mol. wt. 140 000) and shape but differ in charge, one carrying a negative net surface charge (LDH1, ? 19) and the other being slightly cationic (LDH5, + 2). The urine and perfusate samples were subjected to high pressure liquid chromatography (HPLC) gel-filtration to allow for measurements of intact LDH. The fractional clearance was 0.11% ± 0.04% for the anionic LDH1 and 0.56% ± 0.07% for LDH5, whereas that for albumin was 0.21% ± 0.03% at a glomerular filtration rate of 0.11 ± 0.01 mL min^?1 g^?1 kidney wet weight. The results were analysed using a homogenously charged membrane model and are compatible with a charge density of 35 mEq L^?1, with 95% confidence interval of 26–41 mEq L^?1. These findings suggest a significant glomerular charge selectivity for proteins substantially larger than albumin. The charge density is, however, far less than estimated from dextran studies.     

Physiological and morphological effects of perfusing isolated rat kidneys with hyperosmolal mannitol solutions

Recently, we were able to modify the glomerular charge barrier using perfusates with low and normal ionic strengths keeping the osmolality unchanged. The concentration of fixed charges was reversibly reduced from 35 to 12 mEq L^–1 as the solution with low content of NaCl was introduced with no apparent effect on the size selectivity. It can be argued however, that the mannitol used for maintenance of osmolality may induce changes in glomerular permeability per se. To explore this possibility, isolated kidneys were perfused at 8° with hyperosmolal mannitol solutions (560 mOsm) and compared with those perfused with standard albumin solutions (295 mOsm). The vascular resistance (PRU₁₀₀) fell from 0.14 ± 0.01 to 0.11 ± 0.01 mmHg min 100 g mL^–1 as the mannitol solution was introduced (P < 0.001). As the blood pressure should remain unchanged, the flow was increased from 8 to 11 mL min^–1. The glomerular filtration rate (GFR) increased by 50% from 320 ± 40 to 490 ± 20 μL min^?1 g^–1 (P < 0.001). Despite these changes in haemodynamical parameters, there was no significant change in the fractional clearance for albumin. Kidneys perfused with the mannitol solution showed well-preserved histology, while there was a conspicuous collapse of the cortical tissue and signs of tubular epithelial swelling with the standard perfusate. Moreover, all glomeruli were perfused in the mannitol group, as revealed by fluorescence of FITC dextran, while the distribution was uneven in the control kidneys. We conclude that perfusion of isolated kidneys with a hyperosmolal mannitol solution increased GFR by increasing the number of functionally active nephrons with no apparent effect on the glomerular barrier, a pattern differing from alteration of ionic strength.     

Impaired glomerular permselectivity for albumin in chemically medullectomized WKY rats

Chemical renal medullectomy with 2-bromo-ethylamine hydrobromide (BEA) has been used to study the importance of the renal medulla in blood pressure regulation. However, conclusive evidence as to whether BEA treatment affects the glomerular barrier is lacking. In the present study, the effects of BEA upon glomerular permselectivity for albumin were studied using isolated kidneys (IPK) perfused at a low temperature (8 °C) to inhibit tubular reabsorption of proteins. Sixteen WKY rats (W_B) received an i.v. injection of BEA (150 mg kg^-1) while 10 rats served as controls (W_C). Volume balance, urinary osmolality and creatinine clearance (GFR) were measured in metabolic cages. Acute paired experiments (n=9) were performed 5–7 weeks after BEA. The rats were anaesthetized and the total in vivo albumin excretion was recorded. The kidneys were then isolated and perfused for measurements of inulin clearance (GFR) and fractional albumin clearance without tubular reabsorption of protein. The nine BEA treated rats showed polyuria and hypoosmotic urine. In vivo GFR was lower in the BEA treated groups when measured with creatinine clearance (459±22 vs. 213±41 μL min^-1 100 g^-1 body wt, P<0.001), while GFR was not significantly changed in the IPK (W_C=135±27, W_B=92±14 μL min^-1 100 g^-1 body wt, n.s.) when perfused at identical pressures. The fractional albumin clearance was increased three times in the BEA group (W_B=9.6±3.4J, P<0.05). Moreover, albumin excretion in vivo was similar in the two groups despite low GFR in the BEA group. We conclude that BEA treatment affects glomerular permselectivity for albumin.     

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

The classical concept of a negative glomerular charge barrier has recently been questioned, mainly based on the somewhat high clearance for anionic horseradish peroxidase (HRP). The validity of using anionic HRP can be tested by changing the properties of the charge barrier. A rather unequivocal approach is to reduce the ionic composition of the perfusate and hence increase the Debye length. We determined the glomerular clearance for horseradish peroxidase and serum albumin, using isolated rat kidneys perfused at 8 °C to reduce the tubular modification of the primary urine. The perfusate contained trace amounts of the neutral ¹²⁵I-nHRP and the anionic ¹³¹I-aHRP and were otherwise identical except for different ionic strengths, 152 mM and 34 mM , respectively. During control, the fractional clearance was 0.11 ± 0.015 for nHRP and 0.045 ± 0.010 for aHRP, with an average clearance ratio (n/a) of 2.8 ± 0.24. Low ionic strength reduced for aHRP to 0.027 ± 0.006, giving an increased clearance ratio for HRP of 4.2 ± 0.44. The existence of a negative charge barrier is supported by the experiments. The result obtained during normal perfusion is compatible with a charge density (ω) of 34 mEq L^?1, using a model of homogeneously charged membrane. Low ionic strength perfusion reversibly reduced the concentration of fixed charges to 12 mEq L^?1, suggesting an almost threefold increase of the glomerular membrane volume. Thus, the glomerular charge barrier should be regarded to have a dynamic gel structure rather than being a rigid membrane.     

Novel routes of albumin passage across the glomerular filtration barrier

Albuminuria is a hallmark of kidney diseases of various aetiologies and an unambiguous symptom of the compromised integrity of the glomerular filtration barrier. Furthermore, there is increasing evidence that albuminuria per se aggravates the development and progression of chronic kidney disease. This review covers new aspects of the movement of large plasma proteins across the glomerular filtration barrier in health and disease. Specifically, this review focuses on the role of endocytosis and transcytosis of albumin by podocytes, which constitutes a new pathway of plasma proteins across the filtration barrier. Thus, we summarize what is known about the mechanisms of albumin endocytosis by podocytes and address the fate of the endocytosed albumin, which is directed to lysosomal degradation or transcellular movement with subsequent vesicular release into the urinary space. We also address the functional consequences of overt albumin endocytosis by podocytes, such as the formation of pro‐inflammatory cytokines, which might eventually result in a deterioration of podocyte function. Finally, we consider the diagnostic potential of podocyte‐derived albumin‐containing vesicles in the urine as an early marker of a compromised glomerular barrier function. In terms of new technical approaches, the review covers how our knowledge of the movement of albumin across the glomerular filtration barrier has expanded by the use of new intravital imaging techniques.     

Addition of purified orosomucoid preserves the glomerular permeability for albumin in isolated perfused rat kidneys

The serum protein, opsomucoid has been shown to be essential for the maintenance of normal capillary permeability in several different organs, including the kidney. Thus, the clearance of albumin was found to be almost fivefold higher in the absence of orosomucoid in a previous study on isolated rat kidneys, perfused with either of two commercially available human albumin solutions of similar composition, but differing in their content of orosomucoid (0.21 g 1^--¹ vs. < 0.005 g 1^--¹), The following experiments were performed in order to verify the hypothesis that this effect on glomerular permselectivity was due to orosomucoid per se and not to other ingredients in the two solutions. Both kidneys of 12 rats were isolated and perfused with identical albumin solutions without orosomucoid, but with the addition of purified orosomucoid (0.25 g 1^--¹) to one of the kidneys. No significant differences in vascular resistance, urine flow or glomerular filtration rate (GFR), which was found to be 27 ± 2 ml min^-1 100 g^-1, were observed between the two groups of kidneys. The fractional clearance of albumin (θ) was initially similar for both kidneys (0.0022 ± 0.0002). In the absence of orosomucoid, θ gradually increased to 0.0076 ± 0.0013 after 1 h of perfusion compared to 0.0040 ± 0.0006 for the kidneys with orosomucoid added to the perfusate (P < 0.001, n= 12). We conclude that the plasma glycoprotein orosomucoid indeed plays an important role in regulating the dynamic properties of the glomerular capillary wall by reducing the permeability towards macromolecules such as albumin.     

Effects of lactoferrin on rat dermal interstitial fluid pressure (Pif) and in vitro endothelial barrier function

We recently demonstrated that intravenous (i.v.) injection of the iron‐binding protein lactoferrin (Lf) followed by antilactoferrin (aLf) antibodies or iron‐saturated Lf alone increased albumin extravasation in vivo in several tissues including skin. Increased driving pressure for blood‐tissue exchange or direct effects of Lf on the endothelial barrier are possible mechanisms. We therefore, firstly, measured interstitial fluid pressure (P_if) in dermis of rats given 1 mg Lf i.v. followed 30 min later by aLf or saline and circulatory arrest 1 or 5 min thereafter and compared with controls. Secondly, transmonolayer passage of Evans blue labelled albumin (EB‐albumin) was evaluated in porcine pulmonary artery endothelial cells exposed to iron‐free or iron‐saturated Lf (both 100 μg mL^–1) in the absence and presence of 0.5 mM hydrogen peroxide. P_if increased significantly at 11–30 min following Lf to +2.1 ± 0.3 and +1.7 ± 0.2 mmHg at 11–20 and 21–30 min, respectively, compared with +0.1 ± 0.2 mmHg before Lf (P < 0.05, n=25). Endothelial transmonolayer passage of EB‐albumin during 3 h was not affected by iron‐free or iron‐saturated Lf neither in the absence nor presence of hydrogen peroxide that increased passage 3.5 times compared with controls. In conclusion, Lf‐induced increase in albumin extravasation in rat skin is not explained by changes in P_if (because Lf raised P_if significantly) or direct effects of Lf on the endothelial barrier.     

Osmotic barrier properties of the rat peritoneal membrane

In this study the osmotic barrier characteristics of the rat peritoneal membrane were investigated. Fluid movements between the peritoneal cavity and the blood were measured following instillation of isotonic saline (control) and hypertonic solutions of NaCl, glucose, sucrose, raffinose and myoglobin (test solutions). Moreover, 5 and 8% albumin in NaCl were investigated. Osmotic transients were assessed using a simple volume recovery technique. Peritoneal osmotic conductances (i.e. products of peritoneal hydraulic conductances [L_PS] and solute reflection coefficients [s?]) were calculated from the differences in the rates of peritoneal fluid loss and in osmotic pressures between test solutions and the isotonic saline control solution. The osmotic conductance to glucose was estimated to be 1.63/l min^-1 mmHg^-1 m^-2 and that for albumin to be 59.6 μl min^-1 mmHg^-1 m^-2. Assuming an albumin s? of 0.9, the s? of glucose was estimated to be 0.025, in accordance with previous measurements for the cat peritoneal membrane. The osmotic conductances assessed here were compatible with an overal? peritoneal equivalent small pore radius of 47–48 Å, but could also be fitted to a three-pore model of peritoneal permselectivity, including a transcellular (ultra-small pore) pathway and a large pore pathway. The great discrepancy between peritoneal s? for small solutes and that for albumin obtained in this study indicates that small solute reflection coefficients are close to zero while that for albumin is not far from unity. Furthermore, the peritoneal hydraulic conductance (ultrafiltration coefficient) is large enough to allow for a substantial absorption of fluid directly into the plasma when the crystalloid osmotic pressures in blood and peritoneal dialysate are in equilibrium.     

An isolated perfused rat kidney preparation designed for assessment of glomerular permeability characteristics

The aim of the present investigation was to modify the widely used isolated perfused rat kidney preparation to make it more suitable for studies of glomerular permeability to macromolecules. Both kidneys were perfused in situ using separate pumps in two of each other independent systems with Tyrode-solution containing human serum albumin (18.2 g 1^-1). Sodium nitroprusside was administered to induce dilatation and to maintain constant vascular resistance (PRU₁₀₀) during the experiments. The addition of sodium nitroprusside decreased vascular resistance from 0.17 ± 0.05 to 0.09 ± 0.02 mmHg min^-l 100 g^-1 ml^-1 and increased urine flow and glomerular filtration rate. The temperature of the perfusate was reduced from 37°C to 8°C to inhibit tubular reabsorption of protein and fluid, resulting in a urine to plasma concentration ratio of [⁵¹Cr]EDTA of 1.26 ± 0.07. Furosemide reduced the urine to plasma concentration ratio for [⁵¹Cr]EDTA further to 1.15 ± 0.02 and increased glomerular filtration rate. Moreover, by performing the studies at low temperatures (8°C) in the presence of sodium nitroprusside and furosemide it was possible to achieve low and stable albumin fractional clearance values close to those prevailing in vivo. Thus, the described technique, allowing simultaneous perfusions of both kidneys with different solutions, pressures and flows, seem to be well suited for studies of macromolecular transport across glomerular capillaries.     

Human innate immune responses to hexamethylene diisocyanate (HDI) and HDI–albumin conjugates

Background Isocyanates, a leading cause of occupational asthma, are known to induce adaptive immune responses; however, innate immune responses, which generally precede and regulate adaptive immunity, remain largely uncharacterized. Objective The aim of the study was to identify and characterize the cellular, molecular and systemic innate immune responses induced by hexamethylene diisocyanate (HDI). Methods Human peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with HDI–albumin conjugates or control antigen, and changes in phenotype, gene and protein expression were characterized by flow cytometry, microarray, Western blot and ELISA. Cell uptake of isocyanate was visualized microscopically using HDI–albumin conjugates prepared with fluorescently labelled albumin. In vivo, human HDI exposure was performed via a specific inhalation challenge, and subsequent changes in PBMCs and serum proteins were measured by flow cytometry and ELISA. Genotypes were determined by PCR. Results Human monocytes take up HDI–albumin conjugates and undergo marked changes in morphology and gene/protein expression in vitro. The most significant (P‐values 0.007–0.05) changes in mircoarray gene expression were noted in lysosomal genes, especially peptidases and proton pumps involved in antigen processing. Chemokines that regulate monocyte/macrophage trafficking (MIF, MCP‐1) and pattern‐recognition receptors that bind chitin (chitinases) and oxidized low‐density lipoprotein (CD68) were also increased following isocyanate–albumin exposure. In vivo, HDI‐exposed subjects exhibited a drastic increase in the percentage of PBMCs with the same HDI–albumin responsive phenotype characterized in vitro (HLA‐DR⁺/CD11c⁺ with altered light scatter properties). An exposure‐dependent decrease (46±11%; P<0.015) in serum concentrations of chitinase 3‐like‐1 was also observed in individuals who lack the major (type 1) human chitinase (due to genetic polymorphism), but not in individuals possessing at least one functional chitinase‐1 allele. Conclusions Previously unrecognized innate immune responses to HDI and HDI–albumin conjugates could influence the clinical spectrum of exposure reactions.     

Low‐grade albuminuria in children with obstructive sleep apnea

Small urinary protein loss (low‐grade albuminuria or microalbuminuria) may reflect altered permeability of the glomerular filtration barrier. In the present study, it was hypothesized that children with obstructive sleep apnea have an increased risk of microalbuminuria compared with control subjects without sleep‐disordered breathing. Albumin‐to‐creatinine ratio was measured in morning spot urine specimens collected from consecutive children with or without snoring who were referred for polysomnography. Three groups were studied: (i) control subjects (no snoring, apnea–hypopnea index < 1 episode h^?1; n = 31); (ii) mild obstructive sleep apnea (snoring, apnea–hypopnea index = 1–5 episodes h^?1; n = 71); and (iii) moderate‐to‐severe obstructive sleep apnea (snoring, apnea–hypopnea index > 5 episodes?h^?1; n = 27). Indications for polysomnography in control subjects included nightmares, somnambulism and morning headaches. An albumin‐to‐creatinine ratio > median value in the control group (1.85 mg of albumin per g of creatinine) was defined as elevated. Logistic regression analysis revealed that children with moderate‐to‐severe obstructive sleep apnea, but not those with mild obstructive sleep apnea, had increased risk of elevated albumin‐to‐creatinine ratio relative to controls (reference) after adjustment for age, gender and presence of obesity: odds ratio 3.8 (95% confidence interval 1.1–12.6); P = 0.04 and 1.5 (0.6–3.7); P > 0.05, respectively. Oxygen desaturation of hemoglobin and respiratory arousal indices were significant predictors of albumin‐to‐creatinine ratio (r = 0.31, P = 0.01; and r = 0.43, P < 0.01, respectively). In conclusion, children with moderate‐to‐severe obstructive sleep apnea are at significantly higher risk of increased low‐grade excretion of albumin in the morning urine as compared with control subjects without obstructive sleep apnea. These findings may reflect altered permeability of the glomerular filtration barrier related to nocturnal hypoxemia and sympathetic activation which are induced by obstructive sleep apnea.     

Altering the blood-brain barrier in the rat by intracarotid infusion of polycations: a comparison between protamine,poly-L-lysine and poly-L-arginine

To evaluate the role of surface charge for the blood-brain barrier permeability, the albumin content was determined in the cerebrospinal fluid and in the brain 1 h after intracarotid infusion of protamine sulphate, a natural polycationic protein with a high content of arginine (mol. wt 4000–4400), poly-L-arginine (mol. wt 11600) or poly-L-lysine (mol. wt 10200). Five milligrams (4 ± 10^-4 mmol) poly-L-arginine increased the albumin content in the brain IS times more than S mg (5 ± 10^-4 mmol) poly-L-lysine (P < 0.001) and 3.5 times more than 5 mg (1 times 10^-3 mmol) protamine (P < 0.001); the difference between protamine and poly-L-lysine was also significant (P < 0.05). After 0.5 mg (4 ± 10^-4 mmol) poly-L-arginine the albumin extravasation was still higher than after 5 mg protamine (P < 0.01) and 5 mg poly-L-lysine (P < 0.001). Cisternal albumin increased from control values 0.08 mg ml^-1 to 0.30, 0.46 and 1.21 mg ml^-1 in rats given 5 mg poly-L-lysine, protamine and poly-L-arginine, respectively (P < 0.01 for difference between arginine and the other two substances). The higher mol. wt and positive charge of poly-L-arginine may at least in part explain the more pronounced albumin leakage after arginine than after protamine. However, the difference between poly-L-arginine and poly-L-lysine suggests that other factors, possibly related to the guanidino groups, contribute to the blood-brain barrier opening by poly-L-arginine.     

Effects of long‐term inhibition of neuronal nitric oxide synthase on blood pressure and renin release

Nitric oxide (NO) produced by neuronal NO‐synthase (nNOS) in macula densa cells may be involved in the control of renin release. 7‐Nitro indazole (7‐NI) inhibits nNOS, and we investigated the effect of short‐ (4 days) and long‐term (4 weeks) 7‐NI treatment on blood pressure (BP), plasma renin concentration (PRC) and glomerular filtration rate (GFR) in rats on different salt diets. Rats were divided into three groups and given low‐salt (LS), normal (C) and high‐salt (HS) diets. Each diet group was subdivided into two groups treated either with 7‐NI or vehicle. Long‐term 7‐NI‐treated rats (LS and C) showed increased BP compared with controls (LS: 149 ± 4 vs. 133 ± 3; C: 146 ± 4 vs. 127 ± 4 mmHg). Blood pressure in HS rats did not differ from that in controls. Plasma renin concentration was stimulated in LS‐rats (251 ± 64 mGU mL^–1) compared with C and HS rats (42 ± 8 and 39 ± 5 mGU mL^–1, respectively) but was not significantly affected by chronic 7‐NI treatment (350 ± 103, 49 ± 10 and 50 ± 15 mGU mL^–1 in LS, C and HS, respectively). In rats treated with 7‐NI for 4 days, no effect on BP was seen, but PRC was increased in 7‐NI treated LS rats compared with vehicle treated LS rats (107 ± 15 vs. 56 ± 1 mGU mL^–1). Stimulation of PRC in LS rats was further enhanced by 7‐NI after 4 days of treatment, but not affected in rats treated for 4 weeks. This suggests that inhibition of nNOS stimulates renin release but that this stimulatory effect in the long run might be depressed by the increase in blood pressure.     

Importance of molecular charge for the passage of endogenous macromolecules across continuous capillary walls,studied by serum clearance of Lactate Dehydrogenase (LDH) isoenzymes

Electrostatic capillary barrier characteristics was studied in the isolated maximally vasodilated rat hindquarter by use of a modified “tissue uptake” technique (Rippe et al. 1979). The hindquarters were artificially perfused with oxygenated horse serum at isogravimetry. As tracers two isoenzymes of lactate dehydrogenase (LDH) were used, having indentical size (41 Å, M_w? 140000) but with differing molecular charge and labelled with two separable isotopes. LDH-H₄ (¹²⁵I) is negatively charged and LDH-M₄ (¹³¹I) slightly positive, at physiological pH. The negatively charged protein LDH-H₄ was more retarded in its transcapillary passage than LDH-M₄. Net clearance of H₄ was 0.0242±0.0045 ml/min × 100 g and that of M₄ was 0.0748±0.0092 ml/min × 100 g (n= 11, p<0.001). This difference is suggested to be due to an interaction of the polyanionic tracer with a barrier of negative molecular charge, most effective at the small pore equivalent. Clearance data for H₄ and for albumin (Rippe et al. 1979) are compatible with an equivalent large pore radius of 520 Å. Neither vesicular transport (Palade 1953) nor the impact of fibre pore matrix (Michel 1980) is considered to be involved in the transcapillary passage of proteins. Negatively charged proteins probably pass through the large pore equivalent exclusively, while neutral macromolecules also utilize part of the small pore equivalent, for their transcapillary passage.     

Association of incident restless legs syndrome with outcomes in a large cohort of US veterans

Restless legs syndrome is a common sleep disorder, but there is a paucity of large cohort studies examining the association of restless legs syndrome with clinical outcomes, including all‐cause mortality, incident coronary heart disease, stroke and chronic kidney disease. From a nationally representative prospective cohort of over 3 million US veterans [93% male, median follow‐up time of 8.1 years (interquartile range: 7.0–8.5 years)] with baseline estimated glomerular filtration rate ≥60 mL min^?1 1.73 m^?2, a propensity‐matched cohort of 7392 patients was created, and the association between incident restless legs syndrome and the following was examined: (1) all‐cause mortality; (2) incident coronary heart disease; (3) incident strokes; and (4) incident chronic kidney disease defined as estimated glomerular filtration rate <60 mL min^?1 1.73 m^?2. Associations were examined using Cox models. The mean ± SD age of the propensity‐matched cohort at baseline was 59 ± 12 years; 89 and 8% of patients were white and black, respectively; 31% of the patients were diabetic; and the mean baseline estimated glomerular filtration rate was 83.9 ± 15.1 mL min^?1 1.73 m^?2. Propensity matching resulted in a balanced cohort, with the disappearance in baseline differences in comorbidities. Compared with restless legs syndrome‐negative patients, incident restless legs syndrome was associated with 88% higher mortality risk [hazard ratio and 95% confidence interval: 1.88 (1.70–2.08)], and almost four times higher risk of coronary heart disease and stroke [hazard ratio: 3.97 (3.26–4.84) and 3.89 (3.07–4.94), respectively]. The risk of incident chronic kidney disease was also significantly higher in incident restless legs syndrome patients [hazard ratio: 3.17 (2.74–3.66)] compared with restless legs syndrome‐negative counterparts. In this large and contemporary cohort of US veterans, incident restless legs syndrome was associated with higher risk of mortality, incident coronary heart disease, stroke and chronic kidney disease.     

Lowered albumin extravasation rate in heart but not in other organs in β3‐integrin‐deficient mice

Aim: The vascular protein permeability is dependent on the integrity of the vascular wall. The heart capillaries in male mice lacking β3 integrins have an immature phenotype. Previously, we have demonstrated a role for αvβ3 integrins in control of interstitial fluid pressure (Pif) and thereby in the fluid flux during inflammation. We wanted to explore a possible role for αvβ3 integrins in controlling capillary protein permeability during control situation and inflammation. Methods: We performed double‐tracer and microdialysis experiments on β3‐integrin‐deficient mice and wild type control mice. We also measured blood pressure and heart rate in the two mice strains. Results: We found reduced albumin extravasation (during 25 min) in the heart capillaries (0.053 ± 0.003 vs. 0.087 ± 0.009 mL g^?1 dw, P < 0.05), and an increased cardiac mass/body weight (5.3 × 10^?3 ± 0.3 × 10^?3 vs. 3.8 × 10^?3 ± 0.1 × 10^?3, P < 0.01) in the β3‐integrin‐deficient mice (n = 6) compared with the controls (n = 6). Heart rate and blood pressure were the same in mice with and without β3‐integrins. No difference in permeability was found in other tissues studied, or under local inflammation. Conclusion: These results show a function for the αvβ3 integrin in the regulation of protein permeability, selective for the heart capillaries.     

Glomerular albumin filtration through podocyte cell body in puromycin aminonucleoside nephrotic rat

It is an a priori concept that protein molecules including albumin are filtrated through the slit membrane between the foot processes of podocytes. However, foot processes are effaced and the number of slit membranes is reduced in nephrotic syndrome, suggesting another pathway of albumin filtration through the foot process cell body. Thus, we investigated the pathway of gold-and fluorescein isothiocyanate (FITC)-labeled albumin filtration in the puromycin aminonucleoside (PAN) model of nephrotic syndrome in the rat. PAN rats at day 7 with established nephrotic proteinuria were injected with 8-nm gold-labeled albumin and FITC-labeled albumin through the jugular vein followed by kidney fixation at 10 or 30 min. Goldlabeled albumin was accumulated in the paramesangial area and in the endosomes of glomerular endothelial cells of both control and PAN rats by electron microscopy. On the other hand, FITC-labeled albumin was detected between foot processes in the control but more in the podocyte cell body in the PAN rat. In conclusion, albumin will be filtrated through the decreased numbers of slit diaphragms; however, albumin can be also taken up in the podocyte, the mesangium, and the glomerular endothelium, suggesting that there might be other routes of glomerular albumin clearance in nephrotic syndrome.     

Albumin infusion in humans does not model exercise induced hypervolaemia after 24 hours

We rapidly infused 234 ± 3 mL of 5% human serum albumin in eight men while measuring haematocrit, haemoglobin concentration, plasma volume (PV), albumin concentration, total protein concentration, osmolality, sodium concentration, renin activity, aldosterone concentration, and atrial natriuretic peptide concentration to test the hypotheses that plasma volume expansion and plasma albumin content expansion will not persist for 24 h. Plasma volume and albumin content were expanded for the first 6 h after infusion (44.3 ± 1.9–47.2 ± 2.0 mL kg^?1 and 1.9 ± 0.1–2.1 ± 0.1 g kg^?1 at pre-infusion and 1 h, respectively, P < 0.05), but by 24 h plasma volume and albumin content decreased significantly from 1 h post-infusion and were not different from pre-infusion (44.8 ± 1.9 mL kg^?1 and 1.9 ± 0.1 g kg^?1, respectively). Plasma aldosterone concentration showed a significant effect of time over the 24 h after infusion (P < 0.05), and showed a trend to decrease at 2 h after infusion (167.6 ± 32.5^?1 06.2 ± 13.4 pg mL^?1, P = 0.07). These data demonstrate that a 6.8% expansion of plasma volume and 10.5% expansion of plasma albumin content by infusion does not remain in the vascular space for 24 h and suggest a redistribution occurs between the intravascular space and interstitial fluid space.     

Immunomodulation by 8‐week voluntary exercise in mice

This study was designed to evaluate the effects of voluntary exercise on macrophage and lymphocyte functions in mice. Male A/He inbred mice aged 19 weeks were divided into two groups: a group given voluntary exercise and a control group (n = 10 in each group). Exercise consisted of spontaneous running in wheels for 8 weeks (3 days week^–1). Glucose consumption of peritoneal macrophages in the exercise group during incubation up to 72 h was significantly higher than that in the control group (70 and 13%, respectively). Also, activities of acid phosphatase (APH) (10.75 ± 0.37 IU), β‐glucuronidase (GLU) (1.55 ± 0.07 IU) and lactate dehydrogenase (LDH) (43.3 ± 0.7 IU) in the peritoneal macrophages in the exercise group was significantly increased (P < 0.01). Compared with the control group, the exercise group had a significant increase of about twofold in macrophage production of nitric oxide (NO₂^–) stimulated by lipopolysaccharide (LPS) (11.1 ± 0.1 vs. 5.9 ± 0.1 μM mL^–1 in exercise and control groups, respectively; P < 0.01). Stimulation indices both by concanavalin A (Con A) and phytohaemagglutinin were also significantly higher in the exercise group (P < 0.01). A significant increase in the splenocyte production of interleukin‐2 (IL‐2) stimulated by Con A was noticed in the exercise group (354.1 ± 28.8 vs. 218.9 ± 23.5 pg mL^–1 in exercise and control groups, respectively; P < 0.01). These findings suggest that voluntary exercise enhances not only macrophage function but also lymphocyte responsiveness in mice. In the studies of voluntary exercise, evaluation of NO₂^– production, as an indicator of macrophage function, is recommended.