Renal metabolism of amino acids and ammonia in subjects with normal renal function and in patients with chronic renal insufficiency.

The net renal metabolism of amino acids and ammonia in the post absorptive state was evaluated in subjects with normal renal function and in patients with chronic renal insufficiency by measuring renal uptake and release, and urinary excretion of free amino acids and ammonia. In normal subjects the kidney extracts glutamine, proline, citrulline, and phenylalanine and releases serine, arginine, taurine, threonine, tyrosine, ornithine, lysine, and perhaps alanine. The renal uptake of amino acids from arterial blood occurs by way of plasma only, whereas approximately a half of amino acid release takes place by way of blood cells. Glycine is taken up from arterial plasma, while similar amounts of this amino acid are released by way of blood cells. In the same subjects total renal ammonia production can be largely accounted for by glutamine extracted. In patients with chronic renal insufficiency (a) the renal uptake of phenylalanine and the release of taurine and ornithine disappear; (b) the uptake of glutamine and proline, and the release of serine and threonine are reduced by 80--90%; (c) the uptake of citrulline and the release of alanine, arginine, tyrosine, and lysine are reduced by 60--70%; (d) no exchange of glycine is detectable either by way of plasma or by way of blood cells; (e) exchange of any other amino acid via blood cells disappears, and (f) total renal ammonia production is reduced and not more than 35% of such production can be accounted for by glutamine extracted, so that alternative precursors must be used. A 140% excess of nitrogen release found in the same patients suggests an intrarenal protein and peptide breakdown, which eventually provides free amino acids for ammonia production.

Recognition of donor fibroblast antigens by lymphocytes homing in the human grafted kidney.

A human transplanted kidney, surgically removed because of untreatable chronic rejection, was used as the source of lymphocytes (K-L) of recipient origin that were expanded with interleukin-2 (IL-2), and of kidney fibroblasts (K-F) of donor origin that were maintained as an established line. Cytotoxicity assays were performed using K-L and peripheral blood lymphocytes (PBL) as effectors, and K-F and donor PBL as targets. From the results the following conclusions can be drawn: (1) cytotoxic lymphocytes, presumably involved in the process of chronic graft rejection, home in the kidney (from which they can be recovered) but are not detected in the circulation; (2) cytotoxic lymphocytes can be generated from peripheral lymphocytes by mixed lymphocyte culture (MLC) and further expansion in vitro with IL-2 (MLC-L); and (3) although both K-L and MLC-L are cytotoxic toward K-F, the former are not cytotoxic toward donor PBL. This suggests that although MLC-L recognize antigens shared by K-F and PBL, K-L recognize antigens specific for K-F only. These results, if confirmed, indicate that antigens not present on PBL, and possibly tissue-restricted are important in graft rejection. Thus, while monitoring transplanted patients, a lack of cytotoxicity in the recipient PBL may be misleading because the relevant cytotoxic effector cells may have disappeared from the periphery and the appropriate antigenic target may be absent on donor PBL.

Protein oxidation in hemodialysis and kidney transplantation.

Oxidative damage of plasma proteins determined with the markers carbonyl group (CG) content and thiobarbituric acid-reactive substances (TBARS) was studied in 13 hemodialyzed and eight kidney-transplanted patients. The level of CGs was 38% higher in hemodialysis (HD) patients (1.49 +/- 0.05 nmol/mg protein) than in the healthy subjects (1.08 +/- 0.03 nmol/mg protein); the TBARS level was also higher in HD patients than in the control group (2.64 +/- 0.15 v 1.81 +/- 0.09 nmol/mL, P < .001). These data confirm that in end-stage renal failure, an increased oxidative stress is present and is able to induce protein damage. After transplantation, the CG content in protein was reduced (1.34 +/- 0.08 nmol/mg protein), but it was not significantly different from the level in the HD group. The failure to return to the normal range suggests that an impaired redox status is maintained, resulting in a sustained elevation of CG. Conversely, the level of TBARS in transplanted patients (1.99 +/- 0.22 nmol/mL) was not significantly different from that in the control group (1.81 +/- 0.09), suggesting that lipoperoxidation may be inhibited. These results may be explained by the different turnover rates of the molecules and by the distinct origin of the two markers, resulting from the damage of proteins or lipids. Thus, lipoperoxidation would produce rapidly removable molecules, whereas protein oxidation damage would tend to accumulate. However, the significant correlation found between CGs and TBARS indicates that a common cause (oxidative stress) binds the two markers of damage.

Alterations of erythropoiesis in chronic uremic patients treated with intermittent hemodialysis.

The in vitro growth of the blood burst-forming cells (BFU-E) of 9 chronic uremic patients, treated with intermittent hemodialysis three times a week has been studied at the time of maximum and minimum level of retained nitrogen catabolites. The effect of uremic sera on the vitro growth of normal BFU-E was also studied. The in vitro growth of blood BFU-E was shown to be greatly reduced in all uremic patients and dialysis did not modify their growth. The sera of uremic patients significantly inhibited the in vitro growth of normal blood BFU-E when it was taken at the time of maximum retention of nitrogen catabolites. However, inhibition of normal BFU-E growth was not seen when uremic sera were taken at the time of minimum retention of nitrogen catabolites. These data seem to indicate a long lasting suppression of BFU-E in chronic uremia due to serum inhibitor/s.

T lymphocyte subsets in chronic uremic patients treated with maintenance hemodialysis.

Blood T lymphocyte subsets have been studied using monoclonal antibodies in 10 chronic uremic patients treated with maintenance hemodialysis. Both total T lymphocytes identified by the antibody OKT3, and the helper-inducer T lymphocyte subset identified by the antibody OKT4 were found to be significantly lower than normal. The cytotoxic-suppressor T cell subset was only moderately, even if significantly reduced, so that the T4/T8 ratio in uremic patients was significantly lower than normal. These data provide an additional contribution to the interpretation of immunological and hematological deficiencies observed in chronic uremia.

[Recent findings on the pathogenesis and therapy of anemia in chronic kidney failure]. / Recenti acquisizioni sulla patogenesi e terapia dell'anemia dell'insufficienza renale cronica.

Recent studies showed that the blood BFU-E, when subtracted from the uremic milieu, normally responds to the stimulating factor produced by T lymphocytes. The serum of uremic patients inhibits the in vitro growth of normal BFU-E, however, the inhibition is almost completely reversed by hemodialysis. These data allow to understand why the therapy with erythropoietin relieves the anemia of CRF. Uremic T lymphocytes fail to stimulate the BFU-E growth. Normal T lymphocytes are inhibited by uremic serum and the hemodialysis does not correct the defect. Lymphopenia, decreased number of both T4 and T8 lymphocytes and low T4/T8 ratio were found in 50% of patients. Cimetidine was still able to increase the burst-stimulating activity of uremic T lymphocytes through inhibition of the suppressor T subset. In conclusion, one can say that in CRF T8 lymphocytes are normal and that uremic toxins decrease both number and function of T4 lymphocytes. The deficiency of BPA appears to significantly contribute to the pathogenesis of the anemia of CRF. The experience from our and other Institutions shows the effectiveness of the recombinant human erythropoietin in relieving the anemia of CRF, notwithstanding the hematological milieu is highly modified by uremia.

Five years' experience with Hickman catheters as temporary access for haemodialysis.

Two different types of Hickman catheters were used as central venous access for haemodialysis. The device was implanted in 58 patients with chronic renal failure, already undergoing haemodialysis, because of thrombosis or infection of the previous vascular access, in order to permit immediate treatment and in nine patients with acute renal failure, as a 'first choice' method suitable either for dialysis or for parenteral infusions and nutrition. The catheter was inserted, under local anaesthesia, through the external jugular vein up to the right atrium; the haemodialysis treatment was carried out by single-needle technique 3-4 times weekly and all the catheters were filled daily with heparinised saline and Miconazole solution. The mean duration was 76 +/- 93 days with an overall of 2253 treatments. The flow rate ranged between 150 and 290 ml/min, with acceptable recirculation rate and biochemistry similar to that of standard dialysis. The complication rate was 20%, including thromboses and infections; no operative mortality nor major complications were observed. Based on these data, we believe that the Hickman catheter represents the ideal method of temporary access for haemodialysis.

Effects of metabolic alkalosis, metabolic acidosis and uraemia on whole-body intracellular pH in man.

1. Whole-body intracellular pH (pHi) was measured by the 14C-labelled DMO method in twenty-four control subjects, eighteen normal subjects with induced acute metabolic alkalosis, ten normal subjects with induced acute metabolic acidosis, twelve normal subjects with chronic acidosis and in fifteen patients with chronic renal insufficiency and acidosis. 2. The change in pHi per unit change in extracellular pH is significantly larger in acute metabolic alkalosis than in acute metabolic acidosis. In chronic metabolic acidosis, pHi decreased in proportion to the total amount of ammonium chloride administered; pHi was normal in patients with uraemic acidosis. 3. These observations confirm the role that tissue buffers play in the protection of the cellular environment in some forms of acidosis. When the acid load overwhelms tissue buffer capacity, pHi becomes a function of extracellular pH. 4. Cells seem more protected from acute acidosis than from acute alkalosis.

Effects of chronic renal insufficiency and metabolic acidosis on glutamine metabolism in man.

1. Arterial concentration and arterial-venous differences of glutamine across the kidney, forearm, hepato-splanchnic bed and brain were measured in patients with chronic renal insufficiency and in patients with normally functioning kidneys before and during chronic ammonium chloride acidosis. 2. In chronic renal insufficiency and in chronic metabolic acidosis there is a rise in glutamine release from the muscles and a suppression of glutamine uptake by the hepato-splanchnic bed and the brain. 3. In chronic renal insufficiency arterial glutamine concentrations is significantly increased in comparison with subjects with normal renal function and either normal acid-base balance or chronic metabolic acidosis. 4. In patients with chronic renal insufficiency the kidney extracts negligible amounts of glutamine, which cannot account for the renal ammonia production measured in the same patients.

Effect of cimetidine on peripheral blood lymphocytes from chronic uremic patients: improvement of burst-promoting activity.

We have studied the in vitro effect of cimetidine, an inhibitor of suppressor T lymphocytes, on T lymphocytes of 6 uremic subjects and on normal T lymphocytes preincubated with the serum from the same patients. Cimetidine has been shown to increase the burst-promoting activity (BPA) of uremic T lymphocytes and to partially improve the BPA of normal T lymphocytes preincubated with uremic serum. The present study shows that suppressor T lymphocytes are not affected by uremic inhibitors and that chronic uremia, besides inducing a decrease in the number of helper T lymphocytes, impairs their ability to stimulate the BFU-E in vitro growth.

Effects of hemodialysis on guanidinopropionic acid metabolism.

Blood levels of guanidinopropionic acid (GPA), a putative uremic toxin, have been evaluated in 5 uremic patients before a dialytic session, at the end of it and during the following 68 h. GPA levels are markedly higher in uremic patients than in controls and are significantly reduced at the end of dialysis even if still higher than in controls. The clearance of GPA is similar to those of urea and creatinine, even if at the end of the dialysis session the percent decrease of GPA is significantly lower than that of urea. During the first 8 h after the end of dialysis GPA levels increase steeply; subsequently, the rate of accumulation of GPA in blood declines markedly remaining constant until the 68th hour. In conclusion GPA is markedly increased in blood of uremic patients and is significantly removed by dialysis. The evaluation of GPA increase per hour after the end of dialysis may provide an estimation of GPA production in uremic patients.

Alterations of granulopoiesis in chronic uremic patients treated with intermittent hemodialysis.

Granulocyte-macrophage progenitor cells (CFU-GM), leukocyte colony-stimulating activity (CSA), granuloblast differentiation and proliferation and the effect of uremic serum on the in vitro growth of normal CFU-GM have been studied in 8 chronic uremic patients treated with intermittent hemodialysis three times a week. The studies were performed in the postabsorptive state twice in each patient, that is at the longest and shortest dialytic interval. CFU-GM growth in agar and leukocyte CSA did not differ significantly from the normal level in uremic subjects. The granulocytic and macrophagic differentiation in a liquid culture system was significantly reduced in uremic patients, notwithstanding the appearance of high numbers of undifferentiated blastic cells. The serum of uremic patients had no effect on normal CFU-GM and leukocyte CSA.

Proliferation in autologous mixed lymphocyte reactions, expression of HLA-class II antigen and serum immunomodulatory activity in patients with renal insufficiency on chronic dialysis.

The proliferative and stimulatory capacities in allogeneic and autologous mixed lymphocyte reactions were evaluated in 5 patients affected by renal insufficiency undergoing maintenance hemodialysis. The expression of HLA class II antigens and Interleukin 2 production by PHA-activated T cells were also investigated. Furthermore the immunomodulatory effects of uremic serum and serum fractions on mixed lymphocyte reactions performed with lymphocytes from normal subjects were analyzed. The results show that both responsive and stimulatory capacities in allogeneic and autologous mixed lymphocyte reactions of non-T/T and T/T type are clearly impaired. The expression of HLA class II antigens by PHA-activated T cells was reduced whereas the production of Interleukin 2 was normal. The autologous and allogeneic mixed lymphocyte reactions of normal lymphocytes were inhibited by unfractionated uremic serum and by a wide range of serum fractions with different molecular weights. All the above mentioned immune defects were not corrected by the dialytic treatment. The present study extends previous reports concerning the defective immunocompetence associated with chronic renal insufficiency showing that: a) the autologous mixed lymphocyte reactions of both non-T/T and T/T type are impaired; b) the uremic serum contains several factors inhibiting the autologous mixed lymphocyte reactions of normal lymphocytes; c) the chronic hemodialytic treatment does not correct these defects.

Plasma advanced glycosylation end-products in maintenance haemodialysis patients.

BACKGROUND: Pentosidine is a useful marker of advanced glycation end-products (AGE) which form cross-links between proteins and have been found elevated in plasma and tissues of uraemic and haemodialysed subjects. The origin and fate of these molecules are not clearly understood, but they might play a role in the cardiovascular complications of end stage renal failure. The aim of this study was to evaluate the effect of different types of substitutive therapy on the removal of pentosidine. METHODS: Pentosidine was measured by a two-step HPLC methodology. Its concentration was evaluated in plasma before and after dialysis session, in 24-h urine, and in dialysate of subjects treated with three types of chronic substitutive therapy: bicarbonate haemodialysis, acetate-free biofiltration, and haemofiltration. Pentosidine levels were compared among the three therapy modalities and correlated with clinical and biochemical parameters. RESULTS: Plasma pentosidine level was extremely high (23.7 +/- 2.0 pmol/mg protein) in the patients treated with the different dialysis modalities. The dialysis session had no significant effect on its plasma concentration, but haemofiltration seemed to be the most efficient method (300-2000 nmol of pentosidine removed per session versus 250-700 nmol per session with the two other approaches). An interesting correlation was found between pentosidine and blood urea nitrogen (r = 0.58, P < 0.01) and pentosidine with uric acid (r = 0.48, P < 0.05). CONCLUSIONS: These results suggest that none of the methodology showed a good removal of pentosidine, but among them haemofiltration has the best efficiency. The statistical relationships between pentosidine and urea and uric acid respectively might provide insight into the origin of pentosidine. The accumulation of reactive AGE in uraemic patients may be implicated in the organ and tissue damage observed in uraemia.

Cerebral and hepatic urea synthesis in patients with chronic renal insufficiency.

Urea production by the liver and the brain was evaluated in patients with chronic renal insufficiency and in subjects with normal renal function by measuring the arterial-venous differences of urea across the hepatosplanchnic bed and the brain. In five out of seven patients with chronic renal insufficiency no urea release into the hepatic veins was observed, whereas a high urea output by the brain was measured in 6 out of 8 patients. In the control group urea was released only into the hepatic veins. These data demonstrate a defect in hepatic urea synthesis and a switch to cerebral ureagenesis in chronic renal insufficiency.

Inhibition of BFU-E in vitro growth and of burst-promoting activity of T lymphocytes by serum of chronic uremic patients receiving hemodialysis.

The effects of uremic serum on the in vitro growth of normal BFU-E and on the burst-promoting activity by normal T-lymphocytes were evaluated separately. The effect of hemodialysis on the removal of possible serum inhibitor(s) was also tested. Sera of 12 uremic patients were shown to provoke a 60% inhibition of the in vitro growth of normal BFU-E and almost complete abolition of burst-promoting activity by T lymphocytes. While hemodialysis significantly removed the inhibition of uremic sera on BFU-E growth, it was rather ineffective in removing the inhibitor(s) of T lymphocytes. The different effects of uremic serum on BFU-E and on T lymphocytes are discussed.