Acidose metabólica na doença renal crônica: abordagem nutricional

A acidose metabólica é uma das complicações da doença renal crônica e está associada ao aumento do catabolismo protéico, à diminuição da síntese de proteínas e ao balanço nitrogenado negativo. A dieta tem forte influência sobre a geração de ácidos, podendo contribuir, portanto, para determinar a gravidade da acidose no paciente com doença renal crônica. Alguns pesquisadores têm observado que é possível estimar a excreção ácida renal, e que o cálculo dessa carga ácida a partir de alguns componentes da dieta, permitiria uma predição apropriada dos efeitos da dieta na acidose metabólica. Este artigo é uma comunicação sobre as bases fisiológicas, bem como as implicações clínicas da acidose em pacientes com doença renal crônica e a influência da dieta no balanço ácido-básico desses pacientes.

Impact of serum albumin and body-mass index on survival in hemodialysis patients

A low body mass index (BMI) and serum albumin are associated with increased risk of mortality in patients with chronic kidney disease (CKD). The purpose of this study was to evaluate BMI and serum albumin as predictors of all-cause and cardiovascular (CV) mortality in hemodialysed (HD) patients. We describe the results of a five-year retrospective observational study with 187 HD patients (54.9 +/- 15.6 years old, 54% men, and 46% suffering from diabetes) from RenalCor Clinic in Rio de Janeiro, Brazil. The influence of serum albumin levels and BMI (determined every three months) over all-cause mortality was examined using a Cox model, while the influence of the same factors over CV mortality among all-cause mortality was modeled through a logistic regression. During the five years, 26.7% of the patients died, 62% of which due to CV disease (CVD). Analysis by the Cox model showed that low serum albumin and low BMI were significant predictors of mortality. Patients with higher BMI had a lower hazard of death for all-cause mortality (hazard ratio [HR] = 0.92; P ( )= 0.035) and a 1 g/l increase in serum albumin was associated with significantly lower hazard of death (hazard ratio = 0.9679; P < 0.001). The highest BMI value (>30 kg/m(2)) was significantly associated with an increase of odds of CV mortality (odds ratio = 1.22, P = 0.03). We confirm here in a Brazilian cohort of hemodialysis patients that both low BMI (<19 kg/m(2)) and hypoalbuminemia are strong predictors of death.

Zinc levels after iron supplementation in patients with chronic kidney disease

OBJECTIVE

The goal of this study was to evaluate the effects of iron supplementation on zinc distribution in nondialyzed chronic kidney disease (CKD) patients.

DESIGN

Prospective nonrandomized observational study.

SETTING

Outpatients of the Nephrology Division at Federal University of São Paulo.

PATIENTS

Zinc and iron status of 38 nondialyzed patients (63% male; creatinine clearance, 34.5+/-13.3 mL/min/1.73 m2) was evaluated before and after 3 intramuscular injections of 100 mg iron each.

MAIN OUTCOME MEASURES

The following parameters were analyzed: erythrocytes and plasma zinc, zinc protoporphyrin (ZPP), plasma ferritin, transferrin saturation (TFS), and total iron. The patients' diets were analyzed by the Association of Official Analytical Chemists method for macronutrients, and neutron activation analysis was used for iron and zinc concentration determinations.

RESULTS

Ferritin and TFS increased from 86.3+/-67.5 ng/mL to 105.4+/-63.7 ng/mL and from 19.5+/-7.4% to 23.2+/-6.7% (P <.05), respectively, after iron supplementation. Absolute iron deficiency (ferritin <100 microg/L and TFS <20%) was present in 41% of the patients and decreased to 15.7% after iron treatment. In comparison with baseline values (76.4+/-16.7 microg/dL), there were no significant changes in plasma zinc levels, but after supplementation the number of patients with low plasma zinc levels decreased from 46.1% to 23.7% (P =.08). At baseline, erythrocyte zinc was 49.0+/-7.6 microg Zn/gHb, and 76.3% of the patients had high erythrocyte zinc concentration. After iron treatment, erythrocyte zinc decreased to 45.5+/-7.3 microg Zn/gHb (P =.001). No significant change was observed in ZPP concentration. The analysis of the diet showed energy and protein intakes of 26.2+/-7.1 kcal/kg/day and 0.89+/-0.2 g/kg/day, respectively, and a low intake of both iron and zinc.

CONCLUSIONS

This study suggests that iron deficiency may contribute to the inadequate distribution of zinc in patients with CKD and that iron supplementation may decrease the abnormal elevated erythrocyte zinc levels of these patients.

Importância do zinco na nutrição humana

Recentes pesquisas experimentais e clínicas têm reforçado a importância do zinco na saúde humana. O zinco possibilita várias funções bioquímicas, pois é componente de inúmeras enzimas, dentre estas, álcool desidrogenase, superóxido dismutase, anidrase carbônica, fosfatase alcalina e enzimas do sistema nervoso central. Participa na divisão celular, expressão genética, processos fisiológicos como crescimento e desenvolvimento, na transcrição genética, na morte celular, age como estabilizador de estruturas de membranas e componentes celulares, além de participar da função imune e desenvolvimento cognitivo. Sua deficiência pode causar alterações fisiológicas como, hipogonodismo, danos oxidativos, alterações do sistema imune, hipogeusia, danos neuropsicológicos e dermatites. Assim, devido a inúmeras pesquisas referentes a este mineral, este trabalho teve como objetivo mostrar os aspectos atuais sobre a essencialidade do zinco na nutrição humana.

Erythrocyte zinc and carbonic anhydrase levels in nondialyzed chronic kidney disease patients

OBJECTIVE

The aim of the present study was to determine the erythrocyte CAI and CAII concentrations in nondialyzed chronic kidney disease patients, and observe the relationship with acidosis, zinc, anemia, and iron supplementation.

METHODS

Erythrocyte CA concentrations were measured in nondialyzed patients (n = 38) using enzyme-linked immunosorbent assays (ELISA). The zinc concentration was determined by atomic absorption spectrophotometer.

RESULTS AND CONCLUSIONS

The CA levels were observed to be increased in the patients. The mean erythrocyte zinc concentration was also high and the levels of zinc in plasma were baseline values. Correlation was found between CAI and erythrocytes Zn (r = 0.46; P = 0.003), but there was no correlation with ferritin or pH and bicarbonate. The CA levels did not change after iron supplementation, but the zinc erythrocyte levels were reduced. It is concluded that the CA erythrocyte concentration in CKD patients is increased but this cannot be explained by iron deficiency or acidosis.

Iron and zinc status of patients with chronic renal failure who are not on dialysis

OBJECTIVE

The purpose of this study was to assess the zinc and iron status in patients with chronic renal failure (CRF) who were not receiving dialysis.

DESIGN

Cross-sectional study.

SETTING

Outclinic patients of the Nephrology Division at Federal University of São Paulo.

PATIENTS

This study was performed on 29 stable patients with CRF who were not receiving dialysis.

MAIN OUTCOME MEASURE

The parameters for determining iron and zinc status were transferrin saturation, zinc protoporphyrin, serum ferritin, hematocrit, serum iron, total iron binding capacity, erythrocyte, and plasma zinc levels (measured by atomic absorption spectrophotometry).

RESULTS

The serum ferritin level was reduced to 85.5 +/- 67.1 ng/mL and the zinc protoporphyrin level was high (68 +/- 32.9 micromol/mol heme), serum transferrin saturation was 19.9% +/- 7.85%, mean serum iron level was 66.6 +/- 26.3 microg/dL, and mean total iron binding capacity was 336 +/- 45.7 microg/dL. Absolute iron deficiency was found in 34.5% of the patients. Zinc level in erythrocytes was high (50.0 +/- 7.2 microg/g hemoglobin), whereas plasma zinc was at a borderline level (74 +/- 17.7 microg/dL) when compared with normal values. There were significant correlations among plasma zinc and serum iron and transferrin saturation, zinc erythrocyte, and parameters of iron.

CONCLUSION

These results show that absolute iron deficiency can occur in patients who are not receiving dialysis and that there is an abnormal distribution of zinc levels in these patients. Moreover, a possible relationship between iron deficiency and zinc distribution was observed.

Peroxidação lipídica em pacientes com insuficiência renal crônica

Trabalhos demonstram desequilíbrio entre atividade oxidante/antioxidante e um aumento nos níveis de radicais livres em pacientes com insuficiência renal crônica. Várias pesquisas mostram uma maior peroxidação lipídica em eritrócitos e outras células do sangue com implicações importantes na morbidade destes pacientes, principalmente por doenças cardiovasculares. Os níveis de antioxidantes enzimáticos como a glutationa peroxidase, superóxido dismutase e catalase estão reduzidos, bem como os dos elementos traço (Selênio, Zinco). A diminuição das defesas antioxidantes permite o aumento da formação de espécies reativas de oxigênio, o que caracteriza a condição de estresse oxidativo. Em decorrência disto, ocorrem lesões oxidativas que podem alterar a fluidez da membrana dos eritrócitos, contribuindo para a hemólise e piora da anemia, além de causar a oxidação das lipoproteínas de baixa densidade do colesterol, a qual tem um papel importante na patogênese da aterosclerose, que ocorre freqüentemente nos pacientes com insuficiência renal crônica. O objetivo deste trabalho é discutir a relação da peroxidação lipídica e da diminuição das defesas antioxidantes do organismo como fatores importantes na patogênese da insuficiência renal crônica e suas complicações.