Bruno Baggio

Sequential phosphorylation of protein band 3 by Syk and Lyn tyrosine kinases in intact human erythrocytes: identification of primary and secondary phosphorylation sites

Treatment of intact human erythrocytes with pervanadate induces Tyr (Y)-phosphorylation of the transmembrane protein band 3; in parallel, the activity of the immunoprecipitated tyrosine kinases Syk and Lyn is increased. When erythrocytes are incubated with pervanadate together with PP1, a specific inhibitor of Src kinases, including Lyn, the Y-phosphorylation of band 3 is only partially reduced. Indeed, the PP1-resistant phosphorylation of band 3 precedes and is a prerequisite for its coimmunoprecipitation with Lyn, which interacts with the phosphoprotein via the SH2 domain of the enzyme, as proven by binding competition experiments. Upon recruitment to primarily phosphorylated band 3, Lyn catalyzes the secondary phosphorylation of the transmembrane protein. These data are consistent with the view that band 3 is phosphorylated in intact erythrocytes by both PP1-resistant (most likely Syk) and PP1-inhibited (most likely Lyn) tyrosine kinases according to a sequential phosphorylation process. Similar radiolabeled peptide maps are obtained by tryptic digestion of (32)P-band 3 isolated from either pervanadate-treated erythrocytes or red cell membranes incubated with exogenous Syk and Lyn. It has also been demonstrated by means of mass spectrometry that the primary phosphorylation of band 3 occurs at Y8 and Y21, while the secondary phosphorylation affects Y359 and Y904. (Blood. 2000;96:1550-1557)

Effect of alkaline citrate therapy on clearance of residual renal stone fragments after extracorporeal shock wave lithotripsy in sterile calcium and infection nephrolithiasis patients

The natural history of post-extracorporeal shock wave lithotripsy residual stone fragments (clearance, growth and aggregation) is incompletely known, even though they are believed to constitute a risk in terms of new stone formation and persistent infection of the urinary tract. We addressed this issue and the hypothesis that alkaline citrate therapy improves residual stone fragment clearance in a 12-month followup study. There were 40 sterile calcium and 30 struvite stone patients with residual fragments after extracorporeal shock wave lithotripsy (diameter less than 5 mm.) consecutively enrolled and randomly assigned to a citrate therapy (6 to 8 gm. per day) or control (hygienic measures only) group. Infection stone patients also received adequate antibiotic therapy throughout the study. Among the patients in the untreated sterile group 21% and 32% were stone-free at 6 and 12 months, respectively. In the infection group these figures were 27% and 40%, respectively. Among the untreated sterile calcium stone patients in whom clearance was not achieved a high percentage experienced residual fragment growth or reaggregation. Citrate therapy significantly improved the stone clearance rate in the sterile (at 6 and 12 months 65% and 74% were stone-free, respectively) and infection (71% and 86%, respectively) stone patients, and prevented residual fragment growth or reaggregation in subjects in whom clearance was not achieved. The data show that growth and persistence are common in the natural history of residual stone fragments. Citrate ameliorated the outcome of these residual fragments by reducing the growth or agglomeration, and by increasing the clearance rate in calcium oxalate and in infection stone patients.

Increased Urinary Excretion of Renal Enzymes in Idiopathic Calcium Oxalate Nephrolithiasis

Urinary excretion of gamma-glutamyl transpeptidase, angiotensin I converting enzyme, beta-galactosidase and N-acetyl-beta-glucosaminidase was evaluated in 30 patients with idiopathic calcium oxalate urolithiasis. Higher than normal values were observed and the excretory enzyme pattern suggested tubular damage in patients with stones. A parallel study in the rat showed that an oxalate surcharge can promote increased urinary excretion of these enzymes. It is known that urothelium injury may enhance crystal adhesion. If the damage is primary it may be viewed as a promoting factor. If it is secondary it may be considered a factor capable of increasing salt precipitation.

Down-regulation of glomerular matrix metalloproteinase-2 gene in human NIDDM

Summary Regulation of mesangial matrix deposition is a dynamic phenomenon involving synthetic and degradative processes. The latter involve a number of matrix metalloproteinases (MMP) and tissue inhibitors of matrix metalloproteinases (TIMP). Experimental studies suggest that mesangial matrix degradation is inhibited in diabetic nephropathy, and that this phenomenon has a pathogenic role. The expression of genes for MMP2 and TIMP2 in human diabetic nephropathy was investigated. Reverse transcription polymerase chain reaction was carried out in microdissected glomeruli and tubulo-interstitium obtained from kidney biopsies. We studied 16 NIDDM patients, 5 patients with glomerulonephritis or chronic kidney transplant rejection, and 5 normal control subjects. Albumin excretion rate and renal histology for NIDDM patients were available. Contrary to TIMP2 which was expressed both in tubulo-interstitium and glomeruli in almost all renal biopsies, MMP2 gene down-regulation was observed in glomeruli from all NIDDM patients, irrespective of the albumin excretion rate, and of renal histology. In contrast, this gene was expressed in biopsies from other subjects (χ2 = 20.6; p = 0.000). In conclusion, this study demonstrates that: 1) in glomeruli of NIDDM patients the MMP2 gene is down-regulated; 2) in biopsies of NIDDM patients the MMP2/TIMP2 pattern is peculiar for NIDDM; 3) the MMP2 gene down-regulation is observed in all NIDDM patients, irrespective of the level of albuminuria and of renal histology. MMP2 gene down-regulation seems to be a molecular epiphenomenon of diabetes, rather than a marker of diabetic nephropathy. [Diabetologia (1997) 40: 1449–1454]

Fatty acids and cytokine mRNA expression in human osteoblastic cells: a specific effect of arachidonic acid.

Epidemiological, clinical and experimental evidence suggests that fatty acids have a modulatory effect on bone metabolism in animals and humans. To investigate this hypothesis, we evaluated the effects of three different fatty acids, arachidonic acid (AA), eicosapentaenoic acid (EPA) and oleic acid (OA), on the expression of cytokines involved in bone remodelling. Cytokine mRNAs in the human osteoblast-like cell line MG-63 were quantified by reverse transcription-PCR. AA induced increased expression of interleukin-1alpha, interleukin-1beta, tumour necrosis factor-alpha and macrophage colony-stimulating factor mRNAs in a time- and dose-dependent manner. EPA and OA had no stimulatory effects, but instead caused a significant inhibition of AA-induced cytokine mRNA expression. Cell treatment with calphostin C, an inhibitor of protein kinase C (PKC), and cellular PKC down-regulation experiments independently resulted in significant inhibition of AA-induced cytokine expression, suggesting that a PKC-dependent mechanism accounts for the effects of AA on cytokine production. In conclusion, our study demonstrates specific effects of fatty acids on cytokine gene expression in human osteoblast-like cells. The clinical relevance of our findings requires further investigation.

Effects of Cigarette Smoking on Glomerular Structure and Function in Type 2 Diabetic Patients

Prospective studies have established smoking as an independent risk factor for diabetic nephropathy, suggesting an adverse effect of smoking on glomerular structure and function. To test this hypothesis, this study evaluated GFR, metabolic profile, and smoking habits in 96 patients with type 2 diabetes and abnormal albumin excretion rate (AER). All patients underwent percutaneous kidney biopsy: mesangial fractional volume [Vv (mes/glom)] and glomerular basement membrane (GBM) width were estimated by electron microscopic morphometric analysis; interstitial fibrosis was estimated semiquantitatively by light microscopy. Forty-eight patients were smokers. Compared with nonsmokers, smokers had higher values of HbA(1c) (P = 0.002), AER (P = 0.026), GFR (P = 0.004), and GBM width (P = 0.002); moreover, GFR was higher in current smokers than in former smokers (P = 0.001), and GBM width was related to heavy smoking (F = 5.4; P = 0.006). Multiple linear regression analyses revealed that HbA(1c) was associated with fasting blood glucose (beta coef = 0.52; P < 0.001), smoking habit (beta coef = 0.31; P < 0.001), insulin therapy (beta coef = 0.22; P = 0.012), and male gender (beta coef = -0.20; P = 0.020); AER was related to Vv (mes/glom) (beta coef = 0.32; P = 0.003), GBM width (beta coef = 0.28; P = 0.016), and interaction between smoking habit and HbA(1c) (beta coef = 0.24; P = 0.040). GFR was negatively correlated with Vv (mes/glom) (beta coef = -0.57; P < 0.001) and age (beta coef = -0.29; P = 0.001) and positively correlated with GBM width (beta coef = 0.27; P = 0.012), heavy current smoking (beta coef = 0.24; P = 0.028), and HbA(1c) (beta coef = 0.28; P = 0.040); GBM width was explained by Vv (mes/glom) (beta coef = 0.53; P < 0.001), interaction between heavy smoking and HbA(1c) levels (beta coef = 0.25; P = 0.003), and diabetes duration (beta coef = 0.23; P = 0.010). Smoking habit did not affect the index of interstitial fibrosis. In conclusion, cigarette smoking affects glomerular structure and function in type 2 diabetes and may be an important factor for the onset and progression of diabetic nephropathy.

Glycosaminoglycans prevent the functional and morphological peritoneal derangement in an experimental model of peritoneal fibrosis

Chronic peritoneal dialysis results in fibrosis of the peritoneal membrane, which leads to progressive reduction in dialytic efficacy. It was recently shown that the intraperitoneal administration of glycosaminoglycans (GAGs) improves the efficiency of peritoneal dialysis in CAPD patients. To verify whether the favorable effects of GAGs are purely functional or involve a morphological amelioration of the peritoneal membrane structure, a study was carried out in an animal model of plasticizer-induced peritoneal fibrosis. Rats, in which chronic renal failure had been induced by subtotal nephrectomy, received either placebo, plasticizers (i.p.), or GAGs (s.c.), or plasticizers (i.p.) and GAGs (s.c.). Urea dialysate-to-plasma equilibrium, urea and albumin peritoneal clearance, and glucose reabsorption were determined. The peritoneal membrane was evaluated morphometrically and histologically. In plasticizer-treated animals, peritoneal function tests and morphology were dramatically deranged. On the contrary, the subcutaneous administration of GAGs in plasticizer-treated rats maintained the peritoneal physiology and normal structure. The subcutaneous administration of GAGs protects peritoneal functions by affecting the remodeling of the peritoneum, rather than by a purely functional or simple mechanical effect.

RAISED TRANSMEMBRANE OXALATE FLUX IN RED BLOOD CELLS IN IDIOPATHIC CALCIUM OXALATE NEPHROLITHIASIS

Red-blood-cell transmembrane oxalate flux was measured in a group of patients with idiopathic calcium oxalate nephrolithiasis and in normal controls. The mean transmembrane oxalate flux rate was significantly higher in stone-forming patients than in controls (0.93 +/- SD 0.31/min vs 0.29 +/- 0.11/min). 80% of stone-forming patients showed raised (greater than 2SD above the mean in controls) transmembrane oxalate flux. Anomalous cellular oxalate transport may be an important pathogenetic factor in calcium oxalate nephrolithiasis.

Urinary glycosaminoglycans, sialic acid and lysosomal enzymes increase in nonalbuminuric diabetic patients.

Urinary excretion of glycosaminoglycans (GAGS) and sialic acid (SA), as well as the activity of two renal enzymes related to glycoprotein metabolism, N-acetyl-beta-D-glucosaminidase (NAG) and beta-galactosidase (GAL), and two others unrelated to glycosaminoglycans and glycoprotein metabolism, gamma-glutamyltranspeptidase (gamma-Gt) and angiotensin-I-converting enzyme (ACE), were evaluated in 40 insulin-dependent diabetic patients with normal range albuminuria, 21 patients with mesangial glomerulonephritis, and 30 control subjects. Diabetic and glomerulonephritic patients excreted a significantly higher amount of GAGS and SA, and showed greater NAG and GAL activities; gamma-Gt and ACE levels were within normal ranges. No correlation could be demonstrated between diabetes duration and GAGS, SA, NAG and GAL findings. Moreover, no correspondence between degree of metabolic control, as reflected by glycosylated hemoglobin (HbA1a-c) and GAGS, SA, NAG and GAL emerged.

Prevalence of Hyperoxaluria in Idiopathic Calcium Oxalate Kidney Stone Disease

Urinary excretion of oxalate, calcium and urate has been investigated in 88 patients affected by idiopathic calcium oxalate stone disease and in 20 normal subjects. Of these ions, only oxalate was found significantly higher in stone formers. Defining hyperoxaluria as urinary oxalate excretion greater than 2 SD above normal, 50% of stone-forming people were found to be hyperoxaluric. When stone formers were classified in normo- and hyperoxaluric, the prevalence of hypercalciuria, hyperuricuria, family history of stone disease and recurrencies in stone formation was the same in both groups. It is concluded that hyperoxaluria is a frequent finding in finding in idiopathic calcium oxalate renal stone disease.