Markus Teschner

Folate metabolism in renal failure

In most patients with chronic kidney disease, provision of sufficient human recombinant erythropoietin (rHuEPO) and iron replacement therapy will effectively correct renal anaemia. Folate deficiency has been implicated as a contributory factor in renal anaemia and hyporesponsiveness to rHuEPO treatment. As such, the necessity of regular folate supplementation has been debated over the last decade. Although folate loss through dialysis is greater than by urinary excretion, these losses are easily balanced by a normal mixed diet containing 60 g protein/day. Thus, unless patients show significant folate depletion, additional supplementation of folic acid does not appear to have a beneficial effect on erythropoiesis or on responsiveness to rHuEPO therapy. However, a diagnosis of folate deficiency should be considered in patients with chronic renal insufficiency and significant elevation in mean cell volume or hypersegmented polymorphonuclear leucocytes; in patients with malnutrition or a history of alcohol abuse, or in patients hyporesponsive to rHuEPO treatment, especially when accompanied by macrocytosis. Measurements of serum folate are not necessarily indicative of tissue folate stores and red blood cell (RBC) folate measures provide a more accurate picture. Low RBC folate concentrations in these patients indicate the need for folate supplementation. Folate supplementation can also reduce elevated levels of homocysteine in dialysis patients, which may contribute to the high cardiovascular morbidity prevalent in these individuals. High-dose folate therapy (5-15 mg/day) has been shown to reduce plasma homocysteine levels by 25-30% and appears to be well tolerated provided the patient has adequate vitamin B(12) stores. Although long-term benefits of this intervention for cardiovascular protection and patient survival have yet to be established, folic acid is considered a relatively non-toxic and well-tolerated vitamin.

Prevention of Cardiac Hypertrophy in Experimental Chronic Renal Failure by Long-Term ACE Inhibitor Administration: Potential Role of Lysosomal Proteinases

The pathogenesis of cardiac hypertrophy in chronic uremia is poorly understood. In the present study, the long-term effects of chronic uremia on cardiac morphology and various cysteine proteinases of the heart were investigated in rats with and without antihypertensive therapy by the angiotensin converting enzyme inhibitor enalapril or by the calcium channel blocker verapamil. 16 weeks after subtotal nephrectomy considerable uremia had developed associated with arterial hypertension, rise in heart weight and heart weight/body weight ratio. Morphologically myocardial cells developed marked hypertrophy. Determination of various cysteine proteinases by fluorometry revealed a significant decline of cathepsin B activity while the activities of cathepsin H and L were unchanged. Antihypertensive treatment with enalapril and verapamil normalized the blood pressure and improved renal function significantly. Myocardial cell hypertrophy and the enhanced heart weight/body weight ratio were normalized under treatment with enalapril but not with verapamil. Simultaneously, the impaired cathepsin B activity returned to the normal range after enalapril treatment. It is concluded that the cardiac hypertrophy in uremia is at least partly caused by an activation of the circulating and/or cardiac renin-angiotensin system. Impaired proteinase activity in the uremic state may be involved in the development of cardiac hypertrophy.

Efficiency of 1-Year Treatment with Fluvastatin in Hyperlipidemic Patients with Nephrotic Syndrome

The influence of fluvastatin, a liver-selective, competitive inhibitor of the 3-hydroxymethyl-glutaryl-coenzyme A reductase, on the lipoprotein metabolism was investigated in 9 patients with nephrotic syndrome. All patients had biopsy-proven renal disease as cause of their nephrotic syndrome and exhibited severe hyperlipidemia [baseline: serum cholesterol 358 ± 46 mg/dl (9.3 mmol/l), low-density lipoprotein cholesterol 236 ± 18 mg/dl (6.1 mmol/l), triglyerides 333 ± 28 mg/dl (3.8 mmol/l), and lipoprotein Lp(a) 46 ± 11 mg/dl]. After 1 year of 40 mg of fluvastatin, significant reductions of total cholesterol by 31% to 242 ± 26 mg/dl (6.3 mmol/l) and low-density lipoprotein cholesterol by 29% to 162 ± 12 mg/dl (4.2 mmol/l) were observed. Furthermore, triglyceride values were also lowered significantly by 19% to 268 ± 21 mg/dl (3.1 mmol/l). Lipoprotein Lp(a) and high-density lipoprotein-cholesterol remained unchanged by fluvastatin. These improvements in lipid profile were maintained during the entire follow-up period of 1 year. There were no adverse events, and the slight increase in serum creatinine observed during the study was considered to be due to the primary renal disease. In conclusion, long- term administration of fluvastatin in patients with nephrotic syndrome appears to be an effective and safe treatment of the hyperlipidemia associated with this disorder.

The aging rat kidney displays low glomerular and tubular proteinase activities

The present study was conducted to investigate the relationship of age-related changes in renal function and structure with changes in glomerular and tubular proteinase activities in young (3 weeks), mature (3 months), and older (18 months) male Wistar rats. Glomerular filtration rate, expressed per 100 g body weight, remained unchanged during adolescence, but declined significantly (-44%) in aging animals. In parallel, albuminuria, which was barely detectable in young and mature rats, increased almost 10-fold in the aging animals. In comparison to young animals, the kidney weight in aging rats was 10-fold higher, signifying considerable tubular hypertrophy. The glomerular protein to DNA ratio increased by almost 70%, suggesting deposition of mesangial matrix within the glomerulus. These structural changes were associated with significant reductions in glomerular cysteine and metalloproteinase activities in the adolescent and older animals. Similarly, lower activities of both types of proteinases were observed in isolated proximal tubules. This behavior of proteolytic enzyme activities in the aging rat kidney corresponds well to the 10-fold increase in kidney weight (proximal tubular hypertrophy) and to the enhanced deposition of glomerular matrix. This study suggests a causal involvement of renal cysteine proteinases and metalloproteinases in the protein accumulation of the aging rat kidney.

Evidence for reduced catabolism by the antiglucocorticoid RU 38486 in acutely uremic rats

Previous studies suggested that increased blood levels of, or increased tissue sensitivity to, glucocorticoids may contribute to catabolism in acute uremia. To examine this possibility we determined urea nitrogen (urea-N) appearance, plasma levels of Nt-methylhistidine and the activity of the alkaline myofibrillar proteinase in acutely uremic rats with and without treatment with RU 38486, a selective antiglucocorticoid. Forty-eight hours after bilateral nephrectomy, the rats had markedly elevated serum levels of urea-N, creatinine, potassium and phosphorus. In uremic rats receiving RU 38486, comparable levels of serum creatinine were found, but the serum levels of urea-N (221 +/- 4 vs. 259 +/- 5 mg/dl) and phosphorus (6.5 +/- 0.3 vs. 8.5 +/- 0.4 mmol/l) were significantly decreased as compared to uremic animals without RU 38486. In comparison to sham-operated rats, urea-N appearance (net urea production) was increased by 56% 48 h after bilateral nephrectomy. This increment was almost completely reversed in uremic animals receiving the antiglucocorticoid. In untreated uremic rats, plasma levels of Nt-methylhistidine were 10.3 +/- 0.9 microgram/dl, whereas the administration of RU 38486 caused a significant decline in the levels of this amino acid (7.6 +/- 0.5 microgram/dl). This reduction in Nt-methylhistidine was associated with a concomitant decrease of myofibrillar proteinase activity in muscle tissue homogenates. Compared to sham-operated animals, this proteinase activity was increased by 30% in uremic rats, but was normal in those given RU 38486. Taken together, these data support the view that in acute uremia accelerated ureagenesis occurs, while enhanced muscle protein breakdown, owing to an increment in myofibrillar proteinase activity, provides the necessary amino acid precursors.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppressed Activities of Cathepsins and Metalloproteinases in the Chronic Model of Puromycin Aminonucleoside Nephrosis

Glomerulosclerosis and tubulointerstitial fibrosis are the hallmarks of chronic renal diseases. In the present study, we have investigated the potential involvement of various proteinases in these alterations in the model of puromycin aminonucleoside (PAN) nephrosis. Two groups of male Wistar rats were given either three or seven injections of PAN (2.0 mg/100 g body weight) over a 4– and 12–week period, respectively. The two control groups received saline injections. Activities of cathepsins (B, H and L) were determined in isolated glomeruli and proximal tubules. Moreover, collagenaselike and gelatinaselike activities were analyzed in isolated glomeruli. Three weeks after weekly PAN injection, the rats developed heavy proteinuria (140.8±22.0 vs. 13.5±3.29 mg/day; p<0.001), and at week 11 protein excretion reached 606.6±23.00 vs. 22.8±1.5 mg/day. Renal morphology revealed minimal glomerular mesangial changes at the 4th week after PAN administration. At the 12th week a marked mesangial matrix accumulation as well as severe tubulointerstitial infiltration and fibrosis associated with tubular dilation and atrophy were observed. Glomerular cathepsins B, H, and L and gelatinaselike activities decreased at the 4th week after the first PAN injection and remained at this low level throughout the entire study period. Glomerular collagenaselike activity decreased at the 4th week (p<0.05) and was still mildly lower than that of the control group at the 12th week, but without significance. In the isolated proximal tubules, the activities of cathepsins B, H, and L showed the same pattern of decreases as those found in the glomeruli over the whole experimental period. Taken together, our data in the model of chronic PAN nephrosis suggest that the suppressed activities of cathepsins as well as the decreased gelatinase– and collagenaselike activities participate in the accumulation of extracellular matrix and thereby may contribute to the development of glomerulosclerosis and tubulointerstitial fibrosis.

Chronic ethanol ingestion enhances catabolism and muscle protease activity in acutely uremic rats.

Skeletal muscle wasting in men as well as enhanced urea production in animals due to ethanol consumption has been demonstrated by numerous authors. Furthermore, the outcome of acute renal failure is closely related to the extent of catabolism. The present study was performed to investigate whether chronic ethanol exposition prior to binephrectomy (BN) may represent a predisposing factor for enhanced protein breakdown. Rats underwent BN after exposure to ethanol or isocaloric substrate for 4 weeks. Blood chemistries and muscle samples were obtained 48 h after BN. Animals fed with ethanol revealed significantly higher levels of serum urea nitrogen (SUN) and urea nitrogen appearance (UNA) in comparison to controls. Preconditioning on ethanol-derived calories induced an accelerated fractional degradation rate of myofibrillar protein as demonstrated by a significantly enhanced serum Nt-methylhistidine/creatinine ratio. The increase in serum indicators of enhanced myofibrillar breakdown correlated with the stimulated activities of alkaline myofibrillar protease and cathepsin B. Finally, serum corticosterone levels were enhanced in the experimental group in comparison to controls, indicating an ethanol-related adrenocortical stimulation to be a possible mediating factor of enhanced catabolism in ARF. Thus, chronic ethanol intake prior to the onset of ARF seems to be a risk factor for enhanced catabolism in the course of acute uremia.

Insulin-Like Growth Factor I Induced Reduction in Cysteine Proteinase Activity in Freshly Isolated Proximal Tubule Cells of the Rat

The potential effects of insulin-like growth factor I (IGF-I) on lysosomal cysteine proteinases (cathepsin B, H and L+B activities) were investigated in the freshly isolated proximal tubule cells of rats. IGF-I significantly inhibited these enzyme activities after an incubation time of 80 min. This effect was associated with a dose-dependent increase in cellular protein content. The study suggests that, besides the established enhanced protein synthesis, IGF-I-induced cellular hypertrophy is mediated by a suppression of the proteolytic enzyme activity in proximal tubular cells.

Catabolic Effects of Ethanol in Chronically Uremic Rats

Both ethanol consumption and uremia are considered to be associated with wasting, malnutrition and debilitation. The present study was designed to investigate as to whether ethanol exerts a stimulatory effect on the catabolic state of renal failure. Rats underwent 5/6-nephrectomy and were fed either with or without ethanol. The degree of uremia was comparable in both groups. Ethanol-fed uremic rats, however, displayed higher serum levels of urea (+ 103%) and glucose (+29%), as compared to uremic animals without alcohol. Subsequently, the urea N appearance was enhanced (+60%) in uremic rats with alcohol as compared to uremic animals without alcohol. In sham rats urea N appearance was also increased (+39%) following ethanol administration in comparison to sham-operated rats without alcohol, albeit to a lesser degree. Urinary Nt-methylhistidine excretion, an indicator of myofibrillar protein breakdown, was enhanced throughout the experiment in uremic rats receiving ethanol. Finally, ethanol caused higher urinary excretion rates of corticosterone in uremic animals as compared to uremic rats without ethanol. There was a significant correlation between urinary corticosterone excretion and both urea N appearance and urinary Nt-methylhistidine excretion. We conclude that ethanol consumption further aggravates the catabolic state of uremia and that this is mediated by an increment in glucocorticoid production.

Extrakorporale Therapieverfahren bei akutem Nierenversagen

ZusammenfassungDie Inzidenz des akuten Nierenversagens (ANV) im Bereich der Intensivmedizin hat in den letzten Jahrzehnten deutlich zugenommen. Das Auftreten eines ANV bei Intensivpatienten gilt prognostisch als ungünstig. So liegt die Letalität bei Multiorganversagen mit ANV bei 50 bis 90%.Hinsichtlich der extrakorporalen Nierenersatztherapie haben zahlreiche Verfahren Eingang in die Intensivmedizin gefunden, wobei man im Prinzip mit den allermeisten Techniken bei korrekter Indikationsstellung und sachkundiger Handhabung einen adäquaten Ersatz der exkretorischen Nierenfunktion gewährleisten kann: So bestechend einfach die arteriovenösen Verfahren (CAVH und CAVHD) auch sein mögen, so wurden sie doch in den letzten Jahren wegen ihrer geringen Effektivität zugunsten venovenöser, pumpengestützter Techniken (CVVH und CVVHD) weitgehend verlassen. Dagegen besteht im Schrifttum keine Einigkeit darüber, ob die kontinuierlichen den intermittierenden Nierenersatzverfahren überlegen sind. In praxi werden heute bei Patienten mit Oligurie und Kreislaufinsuffizienz zumeist kontinuierliche Verfahren eingesetzt. Basierend auf der derzeitigen Datenlage wäre es aber durchaus auch vertretbar, mittels täglicher, prolongierter (intermittierender) Hämodialyse zu behandeln. Entscheidend für das Outcome ist höchstwahrscheinlich allein die quantitativ ausreichende Entgiftung (Filtration von 36 bis 48 l/24 h oder tägliche Hämodialyse mit einer Dauer von 3 bis 4 h; Ziel-BUN unter 50 mg/dl), weniger das angewandte Verfahren selbst. Ferner gibt es gute Hinweise dafür, daß die Verwendung von Filtern bzw. Dialysatoren mit biokompatiblen Membranmaterialien (keine Komplement- und Leukozytenaktivierung) anzustreben ist und daß bei großvolumiger Hämofiltration bicarbonathaltige Substitutionslösungen bevorzugt werden sollten.Die extrakorporale Nierenersatztherapie im Rahmen der Intensivmedizin hat sich in den letzten Jahren erheblich fortentwickelt. An dieser Stelle sollte es jedoch nicht versämt werden, auf die eminente Bedeutung der betreuenden Ärzte und des Pflegepersonals hinzuweisen, deren “kontinuierliches” Engagement eine unabdingbare Voraussetzung für eine erfolgreiche extrakorporale Nierenersatztherapie darstellt.AbstractThe most serious forms of acute renal failure (ARF) are nowadays encountered in the intensive care unit (ICU), where up to 25% of new patients are reported to develop ARF. Lethality rates may reach 50 to 90% when the ARF is part of a multiple organ dysfunction syndrome.A multitude of extracorporeal procedures have been introduced into intensive care medicine. Applied with adequate skills and experience, most of these techniques will suffice to replace excretory renal function. However, because of low efficacy arterio-venous procedures (CAVH and CAVHD) have been abandoned for the veno-venous, pump-driven techniques (CVVH and CVVHD). Up to now, there is no consensus whether continuous or intermittent renal replacement therapy is more advantageous. In many cases, oliguric patients with circulatory instability will be treated by CVVH, even though there is no prospective study to show that in terms of outcome continuous treatment is superior to intermittent hemodialysis. It is equally conceivable to treat such patients with daily, prolonged (intermittent) hemodialysis. Apparently, the dose of replacement therapy, be it continuous filtration (36 to 48 l/24 h) or intermittent hemodialysis (daily 3 to 4 h) with a target BUN of less than 50 mg/dl, is more important than the modality of treatment. Moreover, there is good evidence that the use of biocompatible membranes (no complement- or leukocyte activation) is preferable and that with high-volume hemofiltration bicarbonate-containing replacement fluids should be used.However, despite all the technical advances, we firmly believe that the skills and the experience of those physicians and nurses who actually perform renal replacement therapy in the ICU are more important than the modality of treatment applied.