Erythropoietin treatment and plasma levels of corticotropin-releasing hormone, delta sleep-inducing peptide and opioid peptides in hemodialysis patients

Inconsistency of reported uremic toxin concentrations

Discrepancies in reported uremic toxin concentrations were evaluated for 78 retention solutes. For this analysis, 378 publications were screened. Up to eight publications per toxin were retained. The highest and the lowest reported concentrations, as well as the median reported concentration were registered. The ratio between the highest and the lowest (H/L) concentrations and, for some solutes, also the ratio between the highest and the median (H/M) concentrations were calculated. The compounds were arbitrarily subdivided into three groups based on their H/L ratio: group A, H/L < 3 (n = 33); group B, 3 < H/L < 8.5 (n = 20); and group C, H/L > 8.5 (n = 25). Solutes of groups A and B showed a low to intermediate scatter, suggesting a homogeneity of reported data. Group C showed a more substantial scatter. For at least 10 compounds of group C, extremely divergent concentrations were registered (H/M > 5.5) using scatter plot analysis. For all solutes of groups A and B, the highest reported concentration could be used as a reference. For some solutes of group C and for the compounds showing a divergent scatter analysis, however, more refined directives should be followed.

Neuropeptide Y, left ventricular mass and function in patients with end stage renal disease

OBJECTIVE

Neuropeptide Y (NPY) is released during sympathetic stimulation and mediates the central effects of the adipostatic hormone leptin. The plasma concentration of NPY and leptin is increased in patients with end stage renal disease (ESRD), but it is unknown whether these substances are related to biochemical markers of sympathetic activity and to alterations in left ventricular (LV) mass and function in these patients.

DESIGN

We investigated the relationship between NPY, norepinephrine (NE), leptin and echocardiographic measurements in a cross-sectional study in 198 patients with ESRD.

RESULTS

NPY was directly related to plasma NE and heart rate but it was largely independent of arterial pressure and of retention of metabolic waste products. NPY was significantly higher in patients with LV hypertrophy and in those with LV systolic dysfunction than in those without these alterations. Of note, NPY emerged as an independent correlate of LV mass index and of LV ejection fraction (LVEF) (both P <or= 0.002) in multiple linear regression analyses including a series of cardiovascular risk factors. Furthermore in a multiple logistic regression model patients in the top NPY tertile had a risk for LV concentric hypertrophy that was 18.10 (95% confidence interval: 5.87-55.83) times higher than in those in the first tertile (P < 0.001). Leptin was unrelated to NPY as well as to LV mass and to systolic function.

CONCLUSIONS

Elevated NPY is independently associated with LV concentric hypertrophy and systolic dysfunction in ESRD. It remains to be seen whether these links contribute to the high cardiovascular mortality in these patients.

Review on uremic toxins: classification, concentration, and interindividual variability

BACKGROUND

The choice of the correct concentration of potential uremic toxins for in vitro, ex vivo, and in vivo experiments remains a major area of concern; errors at this level might result in incorrect decisions regarding therpeutic correction of uremia and related clinical complications.

METHODS

An encyclopedic list of uremic retention solutes was composed, containing their mean normal concentration (CN), their highest mean/median uremic concentration (CU), their highest concentration ever reported in uremia (CMAX), and their molecular weight. A literature search of 857 publications on uremic toxicity resulted in the selection of data reported in 55 publications on 90 compounds, published between 1968 and 2002.

RESULTS

For all compounds, CU and/or CMAX exceeded CN. Molecular weight was lower than 500 D for 68 compounds; of the remaining 22 middle molecules, 12 exceeded 12,000 D. CU ranged from 32.0 ng/L (methionine-enkephalin) up to 2.3 g/L (urea). CU in the ng/L range was found especially for the middle molecules (10/22; 45.5%), compared with 2/68 (2.9%) for a molecular weight <500 D (P < 0.002). Twenty-five solutes (27.8%) were protein bound. Most of them had a molecular weight <500 D except for leptin and retinol-binding protein. The ratio CU/CN, an index of the concentration range over which toxicity is exerted, exceeded 15 in the case of 20 compounds. The highest values were registered for several guanidines, protein-bound compounds, and middle molecules, to a large extent compounds with known toxicity. A ratio of CMAX/CU <4, pointing to a Gaussian distribution, was found for the majority of the compounds (74/90; 82%). For some compounds, however, this ratio largely exceeded 4 [e.g., for leptin (6.81) or indole-3-acetic acid (10.37)], pointing to other influencing factors than renal function, such as gender, genetic predisposition, proteolytic breakdown, posttranslation modification, general condition, or nutritional status.

CONCLUSION

Concentrations of retention solutes in uremia vary over a broad range, from nanograms per liter to grams per liter. Low concentrations are found especially for the middle molecules. A substantial number of molecules are protein bound and/or middle molecules, and many of these exert toxicity and are characterized by a high range of toxic over normal concentration (CU/CN ratio). Hence, uremic retention is a complex problem that concerns many more solutes than the current markers of urea and creatinine alone. This list provides a basis for systematic analytic approaches to map the relative importance of the enlisted families of toxins.

Beneficial effect of renal transplantation on cognitive brain function

Cognitive brain dysfunction is a common complication of end-stage renal disease. To investigate the cerebral effect of renal transplantation, we studied P300 event-related potentials--an objective marker of cognitive brain function--trailmaking test and Mini-mental state in 15 chronic hemodialysis patients and 45 matched healthy subjects. Before transplantation, patients showed prolonged P300 latency (364 vs. 337 ms, P < 0.01), smaller amplitude (15.2 vs. 19.1 microV) and scored lower (P < 0.05) in trailmaking test and Mini-mental state as compared to healthy subjects. Following renal transplantation (14 months), P300 latency decreased (337 ms, P < 0.01 vs. before) and amplitude increased (17.4 microV, P < 0.05 vs. before), indicating improved cognitive brain function. The trailmaking test and Mini-mental state tended to improve. Following transplantation, P300 findings, trailmaking test and Mini-mental state were not different from healthy subjects. Additional studies following erythropoietin treatment in 6 of the 15 hemodialysis patients revealed decreased (improved) P300 latency (351 vs. 379 ms before, P < 0.05) with further decrease following transplantation (341 ms, P = 0.06). Our findings indicate that cognitive brain dysfunction in hemodialysis patients may be fully reversed by successful renal transplantation.