Renato Ribeiro Nogueira Ferraz

Publications (4)10.31 Total impact

• Article: Simplified estimates of ion-activity products of calcium oxalate and calcium phosphate in mouse urine.

  Hans-Göran Tiselius, Renato Ribeiro Nogueira Ferraz, Ita Pfeferman Heilberg
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  ABSTRACT: This study aimed at formulating simplified estimates of ion-activity products of calcium oxalate (AP(CaOx)) and calcium phosphate (AP(CaP)) in mouse urineto find the most important determinants in order to limit the analytical work-up. Literature data on mouse urine composition was used to determine the relative effect of each urine variable on the two ion-activity products. AP(CaOx) and AP(CaP) were calculated by iterative approximation with the EQUIL2 computerized program. The most important determinants for AP(CaOx) were calcium, oxalate and citrate and for AP(CaP) calcium, phosphate, citrate, magnesium and pH. Urine concentrations of the variables were used. A simplified estimate of AP(CaOx) (AP(CaOx)-index(MOUSE)) that numerically approximately corresponded to 10(8) × AP(CaOx) was given the following expression:[Formula: see text]For a series of urine samples with various composition the coefficient of correlation between AP(CaOx)-index(MOUSE) and 10(8) × AP(CaOx) was 0.99 (p = 0.00000). A similar estimate of AP(CaP) (AP(CaP)-index(MOUSE)) was formulated so that it approximately would correspond numerically to 10(14) × AP(CaP) taking the following form:[Formula: see text]For a series of variations in urine composition the coefficient of correlation was 0.95 (p = 0.00000). The two approximate estimates shown in this article are simplified expressions of AP(CaOx) and AP(CaP). The intention of these theoretical calculations was not to get methods for accurate information on the saturation levels in urine, but to have mathematical tools useful for rough conclusions on the outcome of different experimental situations in mice. It needs to be emphasized that the accuracy will be negatively influenced if urine variables not included in the formulas differ very much from basic concentrations.
  Urological Research 12/2011; 40(4):285-91. · 1.23 Impact Factor
• Source

  Available from: Samirah Abreu Gomes

  Article: Preservation of urine samples for metabolic evaluation of stone-forming patients.

  Renato Ribeiro Nogueira Ferraz, Alessandra Calábria Baxmann, Larissa Gorayb Ferreira, José Luiz Nishiura, Priscila Reina Siliano, Samirah Abreu Gomes, Silvia Regina Silva Moreira, Ita Pfeferman Heilberg
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  ABSTRACT: Metabolic evaluation of stone-forming (SF) patients is based on the determination of calcium, oxalate, citrate, uric acid and other parameters in 24-h urine samples under a random diet. A reliable measurement of urinary oxalate requires the collection of urine in a receptacle containing acid preservative. However, urinary uric acid cannot be determined in the same sample under this condition. Therefore, we tested the hypothesis that the addition of preservatives (acid or alkali) after urine collection would not modify the results of those lithogenic parameters. Thirty-four healthy subjects (HS) were submitted to two non-consecutive collections of 24-h urine. The first sample was collected in a receptacle containing hydrochloric acid (HCl 6 N) and the second in a dry plastic container, with HCl being added as soon as the urine sample was received at the laboratory. Additionally, 34 HS and 34 SF patients collected a spot urine sample that was divided into four aliquots, one containing HCl, another containing sodium bicarbonate (NaHCO(3 )5 g/l), and two others in which these two preservative agents were added 24 h later. Urinary oxalate, calcium, magnesium, citrate, creatinine and uric acid were determined. Urinary parameters were also evaluated in the presence of calcium oxalate or uric acid crystals. Mean values of all urinary parameters obtained from previously acidified 24-h urine samples did not differ from those where acid was added after urine collection. The same was true for spot urine samples, with the exception of urinary citrate that presented a slight albeit significant change of 5.9% between samples in HS and 3.1% in SF. Uric acid was also not different between pre- and post-alkalinized spot urine samples. The presence of crystals did not alter these results. We concluded that post-delivery acidification or alkalinization of urine samples does not modify the measured levels of urinary oxalate, calcium, magnesium, creatinine and uric acid, and that the change on citrate was not relevant, hence allowing all parameters to be determined in a single urine sample, thus avoiding the inconvenience and cost of multiple 24-h urine sample collections.
  Urological Research 11/2006; 34(5):329-37. · 1.23 Impact Factor
• Article: Fat malabsorption induced by gastrointestinal lipase inhibitor leads to an increase in urinary oxalate excretion.

  Renato Ribeiro Nogueira Ferraz, Hans-Göran Tiselius, Ita Pfeferman Heilberg, Ita Pfeferman Heiberg
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  ABSTRACT: Unabsorbed fat and bile acids may react with calcium in the intestinal lumen, limiting the amount of free calcium binding with oxalate and thereby raising intestinal oxalate absorption leading to hyperoxaluria. The aim of the present study was to determine whether orlistat (Xenical), a gastrointestinal lipase inhibitor, might increase urinary oxalate in an experimental rat model. Thirty-nine male adult Wistar rats were fed a standard diet alone (controls) or supplemented with either 2% sodium oxalate (NaOx) or 3.2 mL of soy oil, or with both (NaOx + soy oil) for 4 weeks (diet period). Orlistat (16 mg/day) was added to the diet from the 5th to the 8th week (diet + orlistat period). Urinary oxalate (uOx), calcium (uCa), magnesium (uMg), and citrate (uCit) were determined and the ion-activity product of calcium oxalate [AP (CaOx) index(rat)] was estimated. Compared to baseline uOx significantly increased after diet + orlistat in controls (0.64 +/- 0.1 mg/24 hours vs. 0.56 +/-0.1 mg/24 hours), soy oil (0.80 +/- 0.3 mg/24 hours vs. 0.49 +/-0.2 mg/24 hours), and NaOx (2.48 +/- 0.8 mg/24 hours vs. 0.57 +/- 0.2 mg/24 hours), but the most marked increase occurred in NaOx + soy oil (3.87 +/- 0.7 mg/24 hours vs. 0.47 +/- 0.1 mg/24 hours). All groups except controls presented a significant reduction in uCa and uMg. Orlistat induced a significant increase in AP (CaOx) index(rat) compared, respectively, to baseline and to the diet period in NaOx (4.52 +/- 2.34 mg/24 hours vs. 0.94 +/- 0.86 and 1.53 +/- 0.93 mg/24 hours) and NaOx + soy oil (6.49 +/- 4.03 mg/24 hours vs. 0.54 +/- 0.17 and 1.76 +/- 1.32 mg/24 hours). These data suggest that the use of lipase inhibitors, especially under a diet rich in oxalate alone or associated with fat, leads to a significant and marked increase in urinary oxalate and a slight reduction in uCa and uMg that, taken together, resulted in an increase in AP (CaOx) index(rat), elevating the risk of stone formation.
  Kidney International 09/2004; 66(2):676-82. · 6.61 Impact Factor
• Article: An approximate estimate of the ion-activity product of calcium oxalate in rat urine.

  Hans-Göran Tiselius, Renato Ribeiro Nogueira Ferraz, Ita Pfeferman Heilberg
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  ABSTRACT: The objective of this report was to derive a simplified approximate estimate of the ion-activity product of calcium oxalate (AP(CaOx)) in rat urine. The relative effect of each urine variable was assessed by means of iterative computerised approximation with the EQUIL2 program. A basic urine composition was chosen from literature and experimental data. The most pronounced influence on AP(CaOx )was recorded for urinary calcium, oxalate, citrate, magnesium and volume. Based on these calculations, an AP(CaOx) index(RAT) was formulated: [formula; see text]. For a 24-h urine sample, factor A takes the value 4067 and factor F should be set to 0.015. Conclusion. A simplified approximate estimate of AP(CaOx) was derived for rat urine. There was a reasonably good correspondence between AP(CaOx) index(RAT) and AP(CaOx), as derived from EQUIL2 ( r=0.890), provided the other urine variables do not deviate very much from that in the basic composition.
  Urological Research 01/2004; 31(6):410-3. · 1.23 Impact Factor