N-methyl-2-pyridone-5-carboxamide: a novel uremic toxin?

BACKGROUND: N-methyl-2-pyridone-5-carboxamide (2PY) is one of the end products of nicotinamide-adenine dinucleotide (NAD) degradation. We recently found that serum 2PY concentrations in chronic renal failure (CRF) patients were enhanced to the values, which are potentially toxic. The aim of this study was to determine whether 2PY is an inhibitor of poly(ADP-ribose) polymerase, the nuclear enzyme that is highly involved in variety of physiologic events, including regulation of DNA replication and DNA repair. METHODS: High-performance liquid chromatography (HPLC) was used to determine 2PY and other NAD catabolite concentrations in serum of: nondialyzed patients; patients chronically hemodialyzed; patients after kidney transplantation; and healthy individuals (control group). Moreover, the effect of nicotinamide and 2PY on poly(ADP-ribose) polymerase (PARP-1) in vitro was studied. RESULTS: The serum nicotinamide, 2PY, and 4PY (N-methyl-4-pyridone-3-carboxamide) concentrations are many times elevated in nondialyzed CRF patients when compared with controls. The direct correlations were found between serum 2PY (as well as 4PY and nicotinamide) concentrations and serum creatinine concentration, and negative correlations between serum concentrations of these compounds and creatinine clearance. The concentration of 2PY decreases considerably after hemodialysis (HD) session, but elevates back 48 hours later. It permanently declines after kidney transplantation. Nicotinamide and 2PY significantly inhibit PARP-1 activity in vitro. CONCLUSIONS: Increased serum 2PY concentration, along with a deterioration of kidney function and its toxic properties (significant inhibition of PARP-1 by 2PY), suggest that it could be a novel uremic toxin.     

Cancers of the kidney and urinary tract in patients on dialysis for end-stage renal disease: analysis of data from the United States,Europe, and Australia and New Zealand

Patients on maintenance dialysis have increased risk for cancer, especially in the kidney and urinary tract. In a retrospective cohort of 831,804 patients starting dialysis during 1980 to 1994 in the United States, Europe, or Australia and New Zealand, standardized incidence ratios (SIR) with 95% confidence intervals (CI) were calculated for kidney and bladder cancers. Risks for cancers of the kidney (SIR 3.6; CI 3.5 to 3.8) and bladder (SIR 1.5; CI 1.4 to 1.6) were increased, relatively more in younger than older patients and more in female patients (kidney: SIR 4.6, CI 4.3 to 4.9; bladder: SIR 2.7, CI 2.4 to 2.9) than male patients (kidney: SIR 3.2, CI 3.0 to 3.4; bladder: SIR 1.3, CI 1.2 to 1.3). SIR for kidney cancer were raised in all categories of primary renal disease, and for bladder cancer in all but diabetes and familial, hereditary diseases. Notably high SIR occurred in toxic nephropathies (chiefly analgesic nephropathy) and miscellaneous conditions (a category that includes Balkan nephropathy), the excess of kidney cancer in these conditions being urothelial in origin. SIR for kidney cancer rose significantly, and those for bladder cancer fell (not reaching significance) with time on dialysis. There was no association with type of dialysis. The pattern of increased risk for renal parenchymal cancer in dialysis patients is consistent with causation through acquired renal cystic disease and of urothelial cancers of the kidney and bladder with the carcinogenic effects of certain primary renal diseases.     

Dopamine receptor supersensitivity: an outcome and index of neurotoxicity

The characteristic feature of neurotoxicity is a definable lesion which can account for observed deficits, corresponding to loss of nuclei or axonal fibers normally comprising a specific pathway or tract. However, with ontogenetic lesions, the operative definition fails. In rats lesioned as neonates with 6-hydroxydopamine (6-OHDA), near-total destruction of dopamine- (DA-) containing nerves is produced, and this itself is definable. However, the most prominent feature of rats so-lesioned is the DA receptor supersensitivity (DARSS) that develops and then persists throughout the lifespan. DA D(1) receptors show overt supersensitivity to agonists producing vacuous chewing movements (VCMs), while D(1) receptors associated with locomotor activity have a latent supersensitivity that must be unmasked by repeated D(1) or D(2) agonist treatments - a 'priming' phenomenon. This D(1) DARSS is not usually associated in either a change in D(1) receptor number (B(max)) or affinity (K(d)). In contrast to D(1) DARSS, D(2) receptors are not so predictably supersensitized by a lesion of DA neurons. In reality, the permanently exaggerated response to an agonist by supersensitized receptors is per se a manifestation of neurotoxicity. Despite dramatic behavioral responses mediated by supersensitized receptors, DARSS has not been easy to correlate with enhanced production of second messengers or early response genes. Altered signaling (i.e., neuronal cross-talk) in defined pathways may represent the mechanism that produces so-called receptor supersensitization. Long-lived agonist-induced behavioral abnormality, with or without anatomic evidence of a neuronal lesion, is one of the products of DA D(1) receptor supersensitization -- itself an index of neurotoxicity.     

c-Fos Expression in Ouabain-Treated Vascular Smooth Muscle Cells from rat Aorta: Evidence for an Intracellular-Sodium-Mediated, Calcium-Independent Mechanism

Contractile activity imposed by chronic electrical stimulation of a primary skeletal muscle cell culture grown on microcarriers over several days led to an increase of slow myosin heavy chain I (MHCI) and a decrease of fast MHCII expression at mRNA and protein levels, indicating an ongoing fast-to-slow transformation. Only patterns with periods of continuous stimulation of > 5 min in a 45 min cycle were capable of inducing a fibre type transformation, and this was independent of the applied stimulation frequency over the range 1-10 Hz. We have shown before that the calcineurin-NFATc1 signalling pathway is indispensable in mediating MHCI upregulation during fibre type transformation. Therefore, subcellular localization of NFATc1 was studied immunocytochemically. This revealed that only one stimulation train lasting for > 5 min was sufficient to induce nuclear import of this factor, which was about complete after 20 min of continuous stimulation. For both induction of NFATc1 import and MHCI mRNA upregulation, the minimum stimulation interval of > 5 min was sufficient and stimulation frequency was not crucial between 1 and 10 Hz. Repetition of stimulation cycles, with pauses (< 40 min) shorter than the time required for complete export of NFATc1, led to an accumulation of NFATc1 in the nuclei with each cycle and thus to an amplification of the transformation signal during extended periods of electrostimulation. The temporal behaviour of NFATc import/export appears to determine the effectiveness of various electrostimulation protocols in inducing fast-to-slow fibre transformation.     

The analysis of CFTR mutations in men with azoospermia, oligozoospermia and asthenozoospermia

Mutations in cystic fibrosis transductance regulator gene (CFTR) are known to result in some forms of male infertility. An association between CFTR gene mutations and obstructive azoospermia in cystic fibrosis (CF) and in congenital unilateral and bilateral absence of vas deferens (CUAVD, CBAVD) has been proven. However, the role of CFTR gene mutations in the etiology of non-obstructive azoospermia, as well as in the regulation of spermatogenesis remains unsolved. OBJECTIVES: The aim of the study was to evaluate the frequency of CFTR mutations in patients diagnosed with different forms of spermatogenesis impairment MATERIAL: The molecular analyses were performed in the group of 93 infertile men, diagnosed with either azoospermia, oligospermia or asthenoteratozoospermia. RESULTS: The results of the study revealed the presence of F508del and IVS8-T in 5.4% of analyzed cases. No difference in CFTR gene mutations frequencies among patients with azoospermia, oligospermia and asthenoteratozoospermia has been observed. CONCLUSION: The CFTR gene mutations frequency in men with nonobstructive azoospermia, oligozoospermia and asthenozoospermia is similar to those observed in general population.     

Opioids in neuropathic pain

Opiates lack potent analgesic efficacy in neuropathic pain although it is now generally accepted that the poor effect of these drugs reflects a reduction in their potency. Reduction of morphine antinociceptive potency was postulated to be due to the fact that nerve injury altered the activity of opioid systems or opioid specific signaling. Endogenous opioid systems were found to be represented in the regions involved in the nociception and are implicated in chronic pain. Opioid peptides biosynthesis and opioid receptors density in the nociceptive pathways and their functions change under various conditions associated with neuropathic pain following damage to the spinal cord and injury of peripheral nerves. Identification of a role of opioid systems in neuropathic pain and molecular and cellular mechanisms underlying these processes are of importance to understanding of the opioid action in neuropathic pain that will hopefully facilitate development of therapeutic strategies in which effectiveness of opioids in alleviation neuropathic pain is increased.     

Behavioral alterations in rats prenatally exposed to valproic acid: animal model of autism.

Autism is a severe behavioral disorder characterized by pervasive impairments in social interactions, deficits in verbal and nonverbal communication, and stereotyped, repetitive patterns of behaviors and interests. Recently, a new rodent model of autism was created by exposure of rat fetuses to valproic acid (VPA) on the 12.5th day of gestation (VPA rats). The model has striking anatomical, pathological, and etiological similarities to human data; however, it has not been characterized behaviorally. In order to determine if VPA rats present behavioral aberrations observed in autism, their behavior was extensively evaluated in a battery of tests. The results of the present experiments demonstrate that VPA rats exhibit: (1) lower sensitivity to pain and higher sensitivity to nonpainful stimuli, (2) diminished acoustic prepulse inhibition, (3) locomotor and repetitive/stereotypic-like hyperactivity combined with lower exploratory activity, and (4) decreased number of social behaviors and increased latency to social behaviors. In addition, VPA rats showed delayed maturation, lower body weight, delayed motor development, and attenuated integration of a coordinated series of reflexes, delayed nest-seeking response mediated by olfactory system, and normal negative geotaxis. Interestingly, all behavioral aberrations described in this paper appear before puberty, which could distinguish the VPA rat model of autism from other animal models of neurodevelopmental disorders, especially rodent models of schizophrenia. Our results bring further support to validity of the proposed VPA animal model of autism, suggesting similarities between the observed pattern of behavioral alterations in VPA rats and features of disturbed behavior in autistic patients.