Circulating neuropeptide Y in plasma from uremic patients consists of multiple peptide fragments

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

Up-regulation of NPY gene expression in hypothalamus of rats with experimental chronic renal failure

Anorexia is possibly one of the most important causes of malnutrition in uremic patients. The cause of this abnormality is still unknown. Considering that: (a) NPY is one of the most important stimulants of food intake; (b) eating is a central nervous system regulated process and (c) NPY is expressed in hypothalamus, we hypothesized that the decrease of NPY gene expression in the hypothalamus could be an important factor contributing to anorexia associated with uremic state. In contrast to the prediction, the results presented in this paper indicate that the NPY gene expression in the hypothalamus of chronic renal failure (CRF) rats was significantly higher than in the hypothalamus of control (pair-fed) rats. Moreover, we found that serum NPY concentration in CRF rats was higher than in control (pair-fed) animals. The increase of plasma NPY concentration in CRF rats may be due to the greater synthesis of the neuropeptide in liver, since higher level of NPY mRNA was found in liver of CRF rats. The results obtained revealed that experimental chronic renal failure is associated with the increase of NPY gene expression in hypothalamus and liver of rats.

Modulator role of neuropeptide Y in human vascular sympathetic neuroeffector junctions

Reverse transcription polymerase chain reaction (RT-PCR) studies identified the mRNA coding for the Y1 and Y2 receptors in human mammary artery/vein and saphenous vein biopsies. Y1 receptors are expressed in vascular smooth muscles and potentiate the contractile action of sympathetic co-transmitters, adenosine triphosphate (ATP) and noradrenaline (NA); BIBP 3226, a competitive Y1 receptor antagonist, blocked the neuropeptide Y (NPY)-induced modulation. The Y2 receptor is expressed in sympathetic nerves terminals and modulates the pool of sympathetic co-transmitters released at the neuroeffector junction. NPY plays a dual role as a modulator of sympathetic co-transmission; it facilitates vascular smooth muscle reactivity and modulates the presynaptic release of ATP and NA. Sympathetic reflexes regulate human vascular resistance, where NPY plays a modulator role of paramount importance following increased sympathetic discharges, such as stress and vascular disease.

Sympathetic co-transmission: the coordinated action of ATP and noradrenaline and their modulation by neuropeptide Y in human vascular neuroeffector junctions

The historical role of noradrenaline as the predominant sympathetic neurotransmitter in vascular neuroeffector junctions has matured to include ATP and the modulator action of neuropeptide Y (NPY). Numerous studies with isolated blood vessels rings demonstrate the presence of key enzymes responsible for the synthesis of ATP, noradrenaline and NPY, their co-storage, and their electrically evoked release from sympathetic perivascular nerve terminals. Functional assays coincide to demonstrate the integral role of these neurochemicals in sympathetic reflexes. In addition, the detection of the diverse receptor populations for ATP, noradrenaline and NPY in blood vessels, either in the smooth muscle, endothelial cells or nerve endings, further contribute to the notion that sympathetic vascular reflexes encompass the orchestrated action of the noradrenaline and ATP, and their modulation by NPY. The future clinical opportunities of sympathetic co-transmission in the control of human cardiovascular diseases will be highlighted.

Neuropeptide Y is released from human mammary and radial vascular biopsies and is a functional modulator of sympathetic cotransmission

The role of neuropeptide Y (NPY) as a modulator of the vasomotor responses mediated by sympathetic cotransmitters was examined by electrically evoking its release from the perivascular nerve terminals of second- to third-order human blood vessel biopsies and by studying the peptide-induced potentiation of the vasomotor responses evoked by exogenous adenosine 5' triphosphate (ATP) and noradrenaline (NA). Electrical depolarization of nerve terminals in mammary vessels and radial artery biopsies elicited a rise in superfusate immunoreactive NPY (ir-NPY), which was chromatographically identical to a standard of human NPY (hNPY); a second peak was identified as oxidized hNPY. The amount released corresponds to 4-6% of the total NPY content in these vessels. Tissue extracts also revealed two peaks; hNPY accounted for 68-85% of the ir-NPY, while oxidized hNPY corresponded to 7-15%. The release process depended on extracellular calcium and on the frequency and duration of the electrical stimuli; guanethidine blocked the release, confirming the peptide's sympathetic origin. Assessment of the functional activity of the oxidized product demonstrated that while it did not change basal tension, the NA-evoked contractions were potentiated to the same extent as with native hNPY. Moreover, NPY potentiated both the vasomotor action of ATP or NA alone and the vasoconstriction elicited by the simultaneous application of both cotransmitters. RT-PCR detected the mRNA coding for the NPY Y(1) receptor. In summary, the release of hNPY or its oxidized species, elicited by nerve terminal depolarization, coupled to the potentiation of the sympathetic cotransmitter vasomotor responses, highlights the modulator role of NPY in both arteries and veins, strongly suggesting its involvement in human vascular sympathetic reflexes.

Release and functional role of neuropeptide Y as a sympathetic modulator in human saphenous vein biopsies

Transmural electrical stimulation of the sympathetic nerve endings of human saphenous vein biopsies released two forms of NPY identified chromatographically as native and oxidized peptide. The release process is dependent on extracellular calcium, the frequency, and the duration of the stimuli. While guanethidine reduced the overflow of ir-NPY, phenoxybenzamine did not augment NPY release, but increased that of noradrenaline. Oxidized NPY, like native NPY, potentiated the noradrenaline and adenosine 5'-triphospahate-induced vasoconstriction, an effect blocked by BIBP 3226 and consonant with the RT-PCR detection of the mRNA encoding the NPY Y1 receptor. These results highlight the functional role of NPY in human vascular sympathetic reflexes.

Elevated plasma concentrations of neuropeptide Y in children and adults with chronic and terminal renal failure

Neuropeptide Y (NPY) is a peptide hormone that is expressed, stored, and released in sympathetic neurones together with noradrenaline. Elevated plasma concentrations of NPY have been reported in patients with neural crest tumors (neuroblastoma, pheochromocytoma) and following exercise. We studied plasma concentrations of NPY in children and adults with chronic and terminal renal failure and compared them with those in healthy controls. Neuropeptide Y was significantly higher in children and adolescents receiving peritoneal dialysis (5.3 +/- 2.8 pmol/L; n = 11 [mean +/- SD]) or hemodialysis (5.4 +/- 2.1 pmol/L; n = 14) than in healthy children (2.3 +/- 0.9 pmol/L; n = 19) or pediatric patients with impaired renal function who are not receiving dialysis (2.7 +/- 0.6 pmol/L; n = 8; mean glomerular filtration rate, 41 mL/min x 1.73 m2). There was a small but insignificant negative correlation between glomerular filtration rate and NPY concentrations in children with impaired renal function (r = 0.49; P = 0.25). In healthy adults, NPY concentration was similar to that in healthy children (1.8 +/- 1.0 pmol/L; n = 13), and it was significantly elevated in adults receiving hemodialysis (5.9 +/- 1.7 pmol/L; n = 16). No significant changes in NPY concentrations were found before and after hemodialysis in pediatric or adult patients. We conclude that plasma concentrations of NPY are elevated in patients with chronic renal failure who are receiving either peritoneal or hemodialysis, but not in patients with moderately impaired renal function. Whether elevated NPY concentration indicates increased sympathetic activity or is caused by reduced NPY clearance remains to be shown.