Maria Rita Sala

Kidney Protein Dynamics and Ammoniagenesis in Humans with Chronic Metabolic Acidosis

To evaluate the effects of chronic metabolic acidosis on protein dynamics and amino acid oxidation in the human kidney, a combination of organ isotopic ((14)C-leucine) and mass-balance techniques in 11 subjects with normal renal function undergoing venous catheterizations was used. Five of 11 studies were performed in the presence of metabolic acidosis. In subjects with normal acid-base balance, kidney protein degradation was 35% to 130% higher than protein synthesis, so net protein leucine balance was markedly negative. In acidemic subjects, kidney protein degradation was no different from protein synthesis and was significantly lower (P < 0.05) than in controls. Kidney leucine oxidation was similar in both groups. Urinary ammonia excretion and total ammonia production were 186% and 110% higher, respectively, and more of the ammonia that was produced was shifted into urine (82% versus 65% in acidemic subjects versus controls). In all studies, protein degradation and net protein balance across the kidney were inversely related to urinary ammonia excretion and to the partition of ammonia into urine, but not to total ammonia production, arterial pH, [HCO(-)(3)], urinary flow, the uptake of glutamine by the kidney, or the ammonia released into the renal veins. The data show that response of the human kidney to metabolic acidosis includes both changes in amino acid uptake and suppression of protein degradation. The latter effect, which is likely induced by the increase in ammonia excretion and partition into the urine, is potentially responsible for kidney hypertrophy.

Effects of a new amino acid supplement on blood AA pools in patients with chronic renal failure

SummaryWe designed a new formula for AA supplement in order to correct blood pools of AA in chronic renal failure (CRF). This supplement was given to 5 patients with CRF and its effectiveness was tested during long term (12–24 weeks) administration. The patients had previously been on a diet providing 0.6 g of protein and 34–36 kcal/kg/day. The diet was then modified to one providing the same caloric content but only 0.3 g/kg high biological value protein per day with the addition of the AA supplement (0.3 g/kg). The new diet corrected most of the abnormalities in blood AA pools. After 1 month of treatment Val, Leu, Thr, Ser and Tyr levels rose and became normal throughout the study. Ratios Tyr/Phe, Ser/Gly and Val/Gly also improved. During the treatment no side effect or toxicity was observed, and serum albumin, transferrin and nutritional anthropometric parameters persisted to be normal. It is concluded that this specially designed AA supplement added to a hypoproteic diet is an acceptable regimen which can quite completely correct the imbalance in blood AA pools in CRF.

Erythropoietin Treatment and Amino Acid Metabolism in Hemodialysis Patients

A previous report suggests that treatment with recombinant human erythropoietin (rH-EPO) significantly improves many abnormalities in circulating amino acids (AA) in hemodialysis patients. We evaluated the effects of a 12-month treatment with rH-EPO (150-250 U/kg/week) on blood AA levels in 10 patients with chronic renal failure under regular dialytic treatment. During treatment, hemoglobin levels increased from 7.0 +/- 0.3 to 10.1 +/- 0.3 g/dl at 3 months remaining steady thereafter. Before the treatment, patients showed reduced levels of essential AA (EAA), mainly valine, leucine and threonine (p < 0.05-0.01); among non-EAA (NEAA), aspartate and serine were reduced, whereas glycine, alanine, proline, citrulline and cyst(e)ine were increased (p < 0.05-0.001). Val/Gly, Ser/Gly and Tyr/Phe ratios were low (p < 0.05-0.01). Total EAA and total NEAA (619 +/- 21 and 1,382 +/- 75 mumol/l, respectively, before the study) were unchanged (639 +/- 22 and 1,410 +/- 89 mumol/l, respectively) at 12 months. Abnormalities in AA levels observed before the treatment persisted throughout the study. Only serine increased at the end of the study (p < 0.05). In conclusion, contrary to what has been reported, treatment with rH-EPO is not associated with an amelioration of AA metabolism in hemodialysis patients.

Reversed-phase high-performance liquid chromatographic analysis of branched-chain keto acid hydrazone derivatives: optimization of techniques and application to branched-chain keto acid balance studies across the forearm.

A sensitive method of quantifying branched-chain keto acids in plasma and whole blood samples is described. It is based on the separation by ion-pair reversed-phase liquid chromatography of 2,4-dinitrophenylhydrazine derivatives with ultraviolet detection. The sample clean-up steps that are usually required for reversed-phase high-performance liquid chromatography are eliminated. A reduction in ketoisocaproate isomer formation is obtained by incubation of derivatives in ice. The method is reproducible (coefficient of variation 2%, n = 5, at the 200-pmol level) and the ultraviolet response is linearly related to branched-chain keto acid concentration. Recoveries are high (greater than 95%). Other keto acids do not co-elute with branched-chain keto acids. Because of its sensitivity and precision, this method can be proposed for whole blood branched-chain keto acid balance studies across organs.

Blood Amino Acid Levels and Erythropoietin Treatment in Hemodialysis Patients

Giacomo Garibotto, MD, Department of Internal Medicine, Nephrology Division, Universita degli Studi di Genova, Viale Benedetto XV, 6, I-16132 Genova (Italy) Dear Sir, Chronic renal failure (CRF) promotes a number of abnormalities in amino acid (AA) metabolism, which are reflected by changes in circulating levels of AA [1]. Changes in blood AA profile, similar to those observed in protein-calorie malnutrition, occur in patients with relatively preserved renal function under high protein and calorie intake and are therefore caused by renal failure per se. Studies carried out to evaluate AA exchange across the organs which pay a major role in AA metabolism show that blood levels of many AA are the consequence of altered kidney or muscle metabolism. At the same time, abnormalities in blood AA may affect AA uptake by the brain and hepatosplanchnic bed [2]. In advanced uremia a low calorie/protein intake can aggravate blood AA profile, since in this condition changes in blood AA profile mimic those observed in CRF patients. Abnormalities persist in hemodialysis patients, even if they are adequately dialyzed and the protein intake is sufficient [3]. Such abnormalities may, in association with the catabolic stress of hemodialysis, increase protein requirements and expose patients to malnutrition. A previous report by Riedel et al. [4] showed that correction of anemia by treatment with rhEpo could significantly improve, over a short-term period, many abnormalities in circulating AA levels in hemodialysis patients. In a second report [5] the same authors compared plasma amino and α-keto acid concentrations in hemodialysis patients with modest (Hb 12.9 ± 1.2 g/dl), or severe (Hb 7.1 ± 2.1 g/dl) anemia; alterations in AA levels were much more marked in severely anemic patients. The authors concluded that ‘severity of anemia influences pattern of AA and α-keto acids in hemodialysis patients’. Unfortunately, both studies did not report data on the nutritional status of patients as well as on their protein and calorie intake. The original report by Riedel et al. [4] prompted us to evaluate the long-term effects of correction of anemia by rhEpo treatment on blood AA in hemodialysis patients [6]. As the blood AA profile in