Genetic susceptibility to Gilbert's syndrome in a valencian population; efficacy of the fasting test

OBJECTIVE

To describe the populational distribution of the UGT1A1*28 variant (genetic variant code rs8175347) located in the promotor of the UGT gene and correlate its genotypes with the results of the fasting test, as well as its relationship with the biochemical disorder of Gilbert's syndrome (GS) in a Valencian population.

PATIENTS AND METHODS

We studied the prevalence of the genotypes (TA)_6/6 (TA)_6/7 and (TA)_7/7 of the deleterious variant rs8175347 in 144 patients with hyperbilirubinemia, 38 of whom had previously undergone the fasting test to diagnose GS, and in 150 control patients. By analysing the genomic region of the TATA box of the UGT1A1 gene promotor using Sanger sequencing, we established the correlation between the rs8175347 genotypes and the fasting test results and with the patients' biochemical disorders.

RESULTS

The rate of heterozygosity of allele (TA)₇ in the control population was 32% and increased to 87.59% among the patients with suspected GS. The rate of genotype TA_7/7 was 81.94% among the patients with hyperbilirubinemia, compared with 11.33% in the control patients. The fasting test showed a 15.79% rate of false negatives and a 5.26% rate of false positives.

CONCLUSIONS

The high frequency of allele (TA)₇ among the Valencian control population, almost double the 5% reported for European control patients, confirms the high rate of GS reported in the Spanish population, without observing significant differences between the geographical ends of the country. The efficacy and reliability of the fasting test for the diagnosis of GS is questionable.

[Regional pilot study to evaluate the laboratory turnaround time according to the client source]

PURPOSE

To show turnaround time to client source in eight laboratories covering eight Health Areas (2,014,475 inhabitants) of the Valencian Community (Spain).

MATERIAL AND METHODS

Internal Laboratory Information System (LIS) registers (test register and verification date and time), and daily LIS registers were used to design the indicators, These indicators showed the percentage of key tests requested (full blood count and serum glucose and thyrotropin) that were validated on the same day the blood was taken (inpatients and Primary Care and/or at 12 a.m. (inpatients). Urgent (stat) tests were also registered as key tests (serum troponin and potassium) and were recorded in minutes. Registers were collected and indicators calculated automatically through a Data Warehouse application and OLAP cube software.

RESULTS

Long turnaround time differences were observed at 12 a.m. in inpatients, and in the day of sample extraction in primary care patients. The variability in turnaround of stat tests is related to hospital size, activity and validation by the laboratory physician.

CONCLUSIONS

The study results show the large turnaround time disparity in eight Health Care Areas of Valencian Community. The various requesting sources covered by the laboratories create the need for continuous mapping processes redesign and benchmarking studies to achieve customer satisfaction.

Long-term response to interferon plus ribavirin in patients with chronic hepatitis C refractory to interferon

OBJECTIVE

A sustained response (SR) to interferon (IFN) is only observed in 15-20% of patients with chronic hepatitis C (CHC). The aim of this study was to determine the long-term effectiveness and safety of the treatment with IFN plus ribavirin (RIB) over two years in CHC patients without SR to IFN.

DESIGN

A prospective and open longitudinal follow-up study was conducted over 3 years.

PATIENTS AND METHODS

A total of 77 CHC patients were included: 63 non-responders (NR) and 14 relapsers (R) to IFN. Patients were treated with IFN (3 MU s.c. three times a week) and RIB (1,000-1,200 mg p.o. daily) for 12 months. Treatment tolerance and viral response (HCV-RNA in serum < 1,000 copies/ml) were assessed after 1, 3, 6 and 12 months of treatment. SR and relapsing rates were subsequently evaluated 6, 12 and 24 months after the end of the treatment, together with those variables capable of predicting SR.

RESULTS

At the end of the treatment, 19/77 patients responded (24.7%), 9/63 (14.3%) were non-responders and 10/14 (71.4%) relapsers, and these same patients exhibited SR after 6 months. The SR rate two years after treatment was 22.1% [8/63 (12.7%) NR and 9/14 (64.3%) R]. The relapse rate after 6 months and two years was respectively 0 and 10.5% (2/77). Independent variables capable of predicting SR were negative viremia conversion within the first month of treatment, maintenance of such negative viremia after 6 months, and R status to IFN. Side effects were recorded in 90.9% of cases (70/77), the most frequent being pseudoinfluenza syndrome. Treatment had to be discontinued in 33.8% of patients (26/77).

CONCLUSIONS

Combined IFN-RIB therapy for 12 months in CHC patients without SR to IFN obtains a long-term SR of 22.1%, this rate being higher in relapsers to prior IFN therapy (64.3% in R versus 12.7% in NR).

Modulation of glutamine synthesis in cultured astrocytes by nitric oxide

1. Previous results suggest that glutamine synthesis in brain could be modulated by nitric oxide. The aim of this work was to assess this possibility. 2. As glutamine synthetase in brain is located mainly in astrocytes, we used primary cultures of astrocytes to assess the effects of increasing or decreasing nitric oxide levels on glutamine synthesis in intact astrocytes. 3. Nitric oxide levels were decreased by adding nitroarginine, an inhibitor of nitric oxide synthase. To increase nitric oxide we used S-nitroso-N-acetylpenicillamine, a nitric oxide generating agent. 4. It is shown that S-nitroso-N-acetylpenicillamine decreases glutamine synthesis in intact astrocytes by approximately 40-50%. Nitroarginine increases glutamine synthesis slightly in intact astrocytes. 5. These results indicate that brain glutamine synthesis may be modulated in vivo by nitric oxide.

Determination of intracellular ATP in primary cultures of neurons

The aim of this work was to develop and characterize a quick and simple procedure to determine the intracellular content of ATP in monolayer primary cultures of neurons. The baseline was to use the minimum amount of cells which still provides reproducible results. The first step consists of releasing intracellular ATP from the cells. This is accomplished by treatment with a detergent solution, the somatic cell releasing reagent from Sigma. This reagent is claimed by the manufacturer to release ATP from a suspension of viable somatic cells. The procedure has been adapted to be used for attached cells (neurons or astrocytes growing in monolayer), thus avoiding the use of alternative time-consuming procedures to release ATP such as boiling buffers or trichloroacetic acid. After its release the free ATP was measured using the firefly luciferase reaction. We have used this protocol to assess the effect of neurotoxic concentrations of glutamate on the intracellular content of ATP in neurons. The same procedure has been used successfully to determine intracellular ATP in primary cultures of astrocytes.

NMDA receptor antagonists prevent acute ammonia toxicity in mice

We proposed that acute ammonia toxicity is mediated by activation of NMDA receptors. To confirm this hypothesis we have tested whether different NMDA receptor antagonists, acting on different sites of NMDA receptors, prevent death of mice induced by injection of 14 mmol/Kg of ammonium acetate, a dose that induces death of 95% of mice. MK-801, phencyclidine and ketamine, which block the ion channel of NMDA receptors, prevent death of at least 75% of mice. CPP, AP-5, CGS 19755, and CGP 40116, competitive antagonists acting on the binding site for NMDA, also prevent death of at least 75% of mice. Butanol, ethanol and methanol which block NMDA receptors, also prevent death of mice. There is an excellent correlation between the EC50 for preventing ammonia-induced death and the IC50 for inhibiting NMDA-induced currents. Acute ammonia toxicity is not prevented by antagonists of kainate/AMPA receptors, of muscarinic or nicotinic acetylcholine receptors or of GABA receptors. Inhibitors of nitric oxide synthase afford partial protection against ammonia toxicity while inhibitors of calcineurin, of glutamine synthetase or antioxidants did not prevent ammonia-induced death of mice. These results strongly support the idea that acute ammonia toxicity is mediated by activation of NMDA receptors.

Glutamate induces a calcineurin-mediated dephosphorylation of Na+,K(+)-ATPase that results in its activation in cerebellar neurons in culture

In primary cultures of cerebellar neurons glutamate neurotoxicity is mainly mediated by activation of the NMDA receptor, which allows the entry of Ca2+ and Na+ into the neuron. To maintain Na+ homeostasis, the excess Na+ entering through the ion channel should be removed by Na+,K(+)-ATPase. It is shown that incubation of primary cultured cerebellar neurons with glutamate resulted in activation of the Na+,K(+)-ATPase. The effect was rapid, peaking between 5 and 15 min (85% activation), and was maintained for at least 2 h. Glutamate-induced activation of Na+,K(+)-ATPase was dose dependent: It was appreciable (37%) at 0.1 microM and peaked (85%) at 100 microM. The increase in Na+,K(+)-ATPase activity by glutamate was prevented by MK-801, indicating that it is mediated by activation of the NMDA receptor. Activation of the ATPase was reversed by phorbol 12-myristate 13-acetate, an activator of protein kinase C, indicating that activation of Na+,K(+)-ATPase is due to decreased phosphorylation by protein kinase C. W-7 or cyclosporin, both inhibitors of calcineurin, prevented the activation of Na+,K(+)-ATPase by glutamate. These results suggest that activation of NMDA receptors leads to activation of calcineurin, which dephosphorylates an amino acid residue of the Na+,K(+)-ATPase that was previously phosphorylated by protein kinase C. This dephosphorylation leads to activation of Na+,K(+)-ATPase.

Ammonia prevents activation of NMDA receptors by glutamate in rat cerebellar neuronal cultures

Acute ammonia toxicity is mediated by activation of NMDA receptors and is prevented by chronic moderate hyperammonaemia. The aim of this work was to assess whether the protective effect of chronic hyperammonaemia is due to impaired activation of the NMDA receptor. It is shown that chronic hyperammonaemia in rats decreases the binding of [3H]MK-801 to synaptosomal membranes from the hippocampus but not the amount of NMDAR1 receptor protein as determined by immunoblotting. In primary cultures of cerebellar neurons, long-term treatment with 1 mM ammonia also decreased significantly the binding of [3H]MK-801. These results suggest that ammonia impairs NMDA receptor activation. To confirm this possibility we tested the effect of long-term treatment of the cultured neurons with 1 mM ammonia on three well known events evoked by activation of the NMDA receptor: neuronal death induced by glutamate, increase in aspartate aminotransferase activity and increase in free intracellular [Ca2+]. Long-term treatment with ammonia prevented noticeably the effects of glutamate or NMDA on all these parameters. These results indicate that long-term treatment of neurons with 1 mM ammonia leads to impaired function of the NMDA receptor, which cannot be activated by glutamate or NMDA. Activation of protein kinase C by a phorbol ester restored the ability of the NMDA receptor to be activated in neurons treated with ammonia. This suggests that ammonia impairs NMDA receptor function by decreasing protein kinase C-dependent phosphorylation.

Lack of correlation between glutamate-induced depletion of ATP and neuronal death in primary cultures of cerebellum

The aim of this work was to identify, using primary cultures of cerebellar neurons, the receptors involved in glutamate-induced depletion of ATP and to assess whether there is a correlation between glutamate-induced ATP depletion and neuronal death. Glutamate induced a rapid depletion of ATP (40% decrease at 5 min). After 60 min incubation with 1 M glutamate ATP content decreased by 60-70%. Similar effects were induced by glutamate, NMDA and kainate while quisqualate, AMPA or trans-ACPD did not affect significantly ATP content. The EC50 were approximately 6, 25 and 30 microM for glutamate, NMDA and kainate, respectively. DNQX and AP-5, competitive antagonists of kainate and NMDA receptors, respectively, prevented in a dose-dependent manner the glutamate-induced depletion of ATP. These results indicate that glutamate-induced depletion of ATP is mediated by activation of kainate and NMDA receptors. Glutamate-induced neuronal death was prevented by MK-801, calphostin C, H7, carnitine, nitroarginine and W7. However, only MK-801 and W7 prevented glutamate-induced depletion of ATP, while calphostin C, H7, carnitine and nitroarginine did not. This indicates that there is not a direct correlation between ATP depletion and neuronal death.

Prenatal exposure of rats to ammonia impairs NMDA receptor function and affords delayed protection against ammonia toxicity and glutamate neurotoxicity

The aim of this work was to assess whether perinatal hyperammonemia impairs the function of NMDA receptors and whether this impairment affords protection against acute ammonia toxicity and glutamate and NMDA neurotoxicity. Rats were exposed to ammonia during the prenatal and lactation periods by feeding the female rats an ammonium-containing diet since day 1 of pregnancy. After weaning (at postnatal day 21), the pups were fed a normal diet with no ammonia added. This treatment resulted in a marked decrease of the growth rate of the animals, which was maintained even 1 month after normalization of ammonia levels. Rats exposed to ammonia were more resistant than controls to acute ammonia toxicity 13 days after feeding a normal diet but not at 3 months. Primary cultures of cerebellar neurons from hyperammonemic rats showed decreased binding of [3H]MK-801 and were remarkably more resistant than controls to glutamate and NMDA toxicities. Also, the increase in aspartate aminotransferase activity induced by low concentrations of NMDA was not produced in such cultures. These results indicate that exposure to ammonia during the prenatal and lactation periods results in long-lasting impairment of NMDA receptor function. This would be the reason for the delayed protection afforded by exposure to low ammonia levels against acute ammonia toxicity in animals and against glutamate and NMDA toxicity in neuronal cultures.

Brain ATP depletion induced by acute ammonia intoxication in rats is mediated by activation of the NMDA receptor and Na+,K(+)-ATPase

Injection of large doses of ammonia into rats leads to depletion of brain ATP. However, the molecular mechanism leading to ATP depletion is not clear. The aim of the present work was to assess whether ammonium-induced depletion of ATP is mediated by activation of the NMDA receptor. It is shown that injection of MK-801, an antagonist of the NMDA receptor, prevented ammonia-induced ATP depletion but did not prevent changes in glutamine, glutamate, glycogen, glucose, and ketone bodies. Ammonia injection increased Na+,K(+)-ATPase activity by 76%. This increase was also prevented by previous injection of MK-801. The molecular mechanism leading to activation of the ATPase was further studied. Na+,K(+)-ATPase activity in samples from ammonia-injected rats was normalized by "in vitro" incubation with phorbol 12-myristate 13-acetate, an activator of protein kinase C. The results obtained suggest that ammonia-induced ATP depletion is mediated by activation of the NMDA receptor, which results in decreased protein kinase C-mediated phosphorylation of Na+,K(+)-ATPase and, therefore, increased activity of the ATPase and increased consumption of ATP.

Molecular mechanism of acute ammonia toxicity and of its prevention by L-carnitine

In summary, we propose that acute ammonia intoxication leads to increased extracellular concentration of glutamate in brain and results in activation of the NMDA receptor. Activation of this receptor mediates ATP depletion and ammonia toxicity since blocking the NMDA receptor with MK-801 prevents both phenomena. Ammonia-induced metabolic alterations (in glycogen, glucose, pyruvate, lactate, glutamine, glutamate, etc) are not prevented by MK-801 and, therefore, it seems that they do not play a direct role in ammonia-induced ATP depletion nor in the molecular mechanism of acute ammonia toxicity. The above results suggest that ammonia-induced ATP depletion is due to activation of Na+/K(+)-ATPase, which, in turn, is a consequence of decreased phosphorylation by protein kinase C. This can be due to decreased activity of PKC or to increased activity of a protein phosphatase. We also show that L-carnitine prevents glutamate toxicity in primary neuronal cultures. The results shown indicate that carnitine increases the affinity of glutamate for the quisqualate type (including metabotropic) of glutamate receptors. Also, blocking the metabotropic receptor with AP-3 prevents the protective effect of L-carnitine, indicating that activation of this receptor mediates the protective effect of carnitine. We suggest that the protective effect of carnitine against acute ammonia toxicity in animals is due to the protection against glutamate neurotoxicity according to the above mechanisms.

Acute ammonia toxicity is mediated by the NMDA type of glutamate receptors

Previous experiments in our laboratory suggested that ammonium toxicity could be mediated by the NMDA type of glutamate receptors. To assess this hypothesis we tested if MK-801, a specific antagonist of the NMDA receptor, is able to prevent ammonium toxicity. Mice and rats were injected i.p. with 12 and 7 mmol/kg of ammonium acetate, respectively. 73% of the mice and 70% of the rats died. However, when the animals were injected i.p. with 2 mg/kg of MK-801, 15 min before ammonium injection, only 5% of the mice and 15% of the rats died. The remarkable protection afforded by MK-801 indicates that ammonia toxicity is mediated by the NMDA receptor.