Effects of ribavirin/sofosbuvir treatment and ITPA phenotype on endogenous purines

Ribavirin (RBV), a purine analog, causes hemolytic anemia in some patients. In vitro, anemia appears to result from depletion of endogenous purines, but there are limited data in vivo. Single nucleotide polymorphisms in the gene encoding the inosine triphosphatase (ITPA) enzyme have been associated with protection against RBV-induced anemia and may mediate the effect of RBV treatment on endogenous purines. The purpose of this work was to determine the effect of RBV treatment on endogenous purine concentrations in individuals being treated for chronic hepatitis C virus (HCV) infection. Adenosine triphosphate (ATP), guanosine triphosphate (GTP), inosine triphosphate (ITP) and ribavirin triphosphate (RTP) were measured in whole blood obtained from 47 HCV-infected individuals at day zero (baseline), day three, day 28 and day 84 of RBV/sofosbuvir (SOF) treatment. ATP decreased -35.1% and -38.6% (p < 0.0001) at day 28 and day 84 of treatment, respectively compared to baseline. The decrease in ATP was greater in patients with ≤60% ITPA activity compared to those with 100% ITPA activity (-29.4% vs. -9.6%). GTP did not change during treatment but was 16.5% (p = 0.01) higher per 100 pmol/106 cells RTP in those with 100% ITPA activity. No significant change or effect of RTP or ITPA phenotype was noted for ITP. In summary, only ATP was reduced by RBV/SOF treatment and ITPA variants had larger reductions in ATP suggesting RBV-induced anemia is due to a different mechanism than predicted from in-vitro studies. These data emphasize the importance of characterizing the effect of nucleos(t)ide analog treatment on endogenous purines in-vivo.

[Clinical study of levofloxacin 500 mg qd in the treatment of cervicitis and intrauterine infections caused by Chlamydia trachomatis]

The clinical efficacy and safety of levofloxacin (LVFX) 500mg qd were evaluated in female patients with cervicitis with Chlamydia trachomatis and intrauterine infections. LVFX was administered orally at 500 mg qd for 7 days. Bacteriological efficacy was 94.4% (17/18) and clinical efficacy was 100% (16/16) at 14 to 21 days after the end of treatment in cervicitis. On the other hand, bacteriological efficacy and clinical efficacy at the end of treatment in intrauterine infections were 68.8% (11/16) and 94.7% (18/19), respectively. For safety, adverse drug reactions occurred in 9 of 43 patients (20.9%), i.e., increased y-GTP in 2 patients, glucose urine present in 2, and each of all other adverse reactions occurred in 1. All adverse drug reactions observed were either mild or moderate. Results suggested that LVFX 500 mg qd was effective and safe in the treatment of cervicitis with Chlamydia trachomatis and intrauterine infections.

Multiple strategies of Lake Victoria cichlids to cope with lifelong hypoxia include hemoglobin switching

Many fish species adapt to hypoxia by reducing their metabolic rate and increasing hemoglobin-oxygen (Hb-O(2)) affinity. Pilot studies with young broods of cichlids showed that the young could survive severe hypoxia in contrast with the adults. It was therefore hypothesized that early exposure results in improved oxygen transport. This hypothesis was tested using split brood experiments. Broods of Astatoreochromis alluaudi, Haplochromis ishmaeli, and a tilapia hybrid (Oreochromis) were raised either under normoxia (NR; 80-90% air saturation) or hypoxia (HR; 10% air saturation). The activity of the mitochondrial citrate synthase was not different between NR and HR tilapia, but was significantly decreased in HR A. alluaudi and H. ishmaeli, indicating lowered maximum aerobic capacities. On the other hand, hemoglobin and hematocrit levels were significantly higher in all HR fish of the three species, reflecting a physiological adaptation to safeguard oxygen transport capacity. In HR tilapia, intraerythrocytic GTP levels were decreased, suggesting an adaptive increase of blood-O(2) affinity. Similar changes were not found in HR H. ishmaeli. In this species, however, all HR specimens exhibited a distinctly different iso-Hb pattern compared with their NR siblings, which correlated with a higher intrinsic Hb-O(2) affinity in the former. All HR cichlids thus reveal left-shifted Hb-O(2) equilibrium curves, mediated by either decreased allosteric interaction or, in H. ishmaeli, by the production of new hemoglobins. It is concluded that the adaptation to lifelong hypoxia is mainly due to improved oxygen transport.

Obesity is the only independent factor associated with ultrasound-diagnosed non-alcoholic fatty liver disease: a cross-sectional case-control study

OBJECTIVE

There is increasing interest in ultrasound-diagnosed non-alcoholic fatty liver disease (NAFLD) in the ambulatory care setting. The aim of this study was to determine the clinical and metabolic features of ultrasound-diagnosed NAFLD.

MATERIAL AND METHODS

Fifty ultrasound-diagnosed NAFLD patients who had not consumed alcohol for at least the previous 3 months were matched with 100 controls by age and gender distribution. Clinical, biochemical, and nutritional variables were compared between the ultrasound-diagnosed NAFLD patients and the controls. Conditional logistic regression analyses were used to identify independent factors associated with ultrasound-diagnosed NAFLD.

RESULTS

The ultrasound-diagnosed NAFLD patients had higher values on the anthropometric measurements than those of the controls. Aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT), uric acid, and gamma-glutamyl transpeptidase levels were higher in the ultrasound-diagnosed NAFLD patients than those in the controls (p<0.001). The ASAT/ALAT ratio of the ultrasound-diagnosed NAFLD patients was lower than that of the controls (p<0.001). Total cholesterol, triglycerides, high-density lipoprotein (HDL)-cholesterol, non-HDL-cholesterol, atherogenic index, fasting glucose, systolic blood pressure (BP), diastolic BP, and pulse pressure were higher in the ultrasound-diagnosed NAFLD patients than in the control subjects, while lipoprotein(a) was lower. There were no significant differences in low-density lipoprotein (LDL)-cholesterol levels or nutritional intake between patients and controls. Abnormal ASAT or ALAT, hypertriglyceridemia, lower HDL-cholesterol levels, silent myocardial ischemic pattern on electrocardiogram (ECG), impaired fasting glucose, and obesity were common among the ultrasound-diagnosed NAFLD patients. The only independent factor associated with ultrasound-diagnosed NAFLD was obesity (p<0.001).

CONCLUSIONS

Our data suggest that NAFLD diagnosed by ultrasound is associated with hypertriglyceridemia, impaired fasting glucose, silent myocardial ischemic pattern of ECG, obesity, and abnormal liver tests in adults. Among these factors, obesity was the only independent factor associated with ultrasound-diagnosed NAFLD.

Thiopurine therapies: problems, complexities, and progress with monitoring thioguanine nucleotides

Metabolism of thiopurine drugs--azathioprine, 6-mercaptopurine, and 6-thioguanine--has provided a powerful pharmacogenetic model incorporating polymorphism of the enzyme thiopurine methyltransferase (TPMT) and the primary active metabolite, thioguanine nucleotide (TGN). However, a sense of uncertainty about the usefulness of TGNs and other thiopurine metabolites has appeared. This review critically appraises the basis of thiopurine metabolism and reveals the problems and complexities in TGN research. Erythrocyte TGN is used in transplantation medicine and in chronic inflammatory conditions such as Crohn's disease, as a "surrogate" pharmacokinetic parameter for TGN in the target cells: leukocytes or bone marrow. It is not generally appreciated that erythrocytes do not express the enzyme IMP dehydrogenase and cannot convert mercaptopurine to TGN, which explains some of the confusion in interpretation of erythrocyte TGN measurements. TGN routinely measured in erythrocytes derives from hepatic metabolism. Another concern is that TGN are not generally assayed directly: most methods assay the thiopurine bases. Ion-exchange HPLC and enzymatic conversion of TGNs to nucleosides have been used to overcome this, and may reveal undisclosed roles for an unusual cytotoxic nucleotide, thio-inosine triphosphate, and methylated thiopurines. There appear to be additional interactions between xanthine oxidase and TPMT, and folate and TPMT, that could predict leukopenia. Difficult questions remain to be answered, which may be assisted by technological advances. Prospective TGN studies, long overdue, are at last revealing clearer results.

[Assessment of goserelin treatment in adjuvant therapy for premenopausal patients with breast cancer in Japan-zoladex breast cancer study group trial-B]

OBJECTIVE

Goserelin (GOS) therapy in an adjuvant setting for estrogen receptor(ER)-positive premenopausal patients with breast cancer was assessed in a randomised comparative study.

METHODS

ER positive premenopausal patients with n + or n 0 and T > or = 3 cm received tamoxifen (TAM) 20 mg/day, GOS 3.6 mg/4 weeks or GOS + TAM for 2 years, and the clinical efficacy and safety of these regimens were assessed.

RESULTS

In the data analysis of total 207 patients, hazard ratios of disease free survival (DFS) and overall survival (OS) in the GOS group compared to the TAM group were 0.87 and 2.10,respectively. The incidence of adverse drug reactions was similar (42-55%) in all three groups. Since the number of patients in this study did not reach the target number, the efficacy could not be assessed from a statistical aspect. Therefore,meta-analysis with similar foreign studies(ZIPP) was implemented. The results of meta-analysis showed that the hazard ratios of DFS and OS in the GOS group compared to the non-GOS group were 0.83 and 0.85, respectively.

CONCLUSION

Although the analysis of 207 patients did not show any statistically significant difference between each of the treatment groups, the results of meta-analysis showed a significant prolongation of DFS in the GOS group. Also high tolerability of GOS was suggested. From these results, GOS was considered highly useful in adjuvant therapy for ER-positive premenopausal patients with breast cancer.

Efficacy and effectiveness of liver screening program to detect fatty liver in the periodic health check-ups

To determine whether the current liver screening program for fatty liver has sufficient scientific evidence to justify its continued implementation. The liver screening program to detect fatty liver was performed on 411 Japanese workers utilizing serum aspartate aminotransferase (ALT), alanine aminotransferase (AST), and gammaglutamyl transpeptidase (gamma-GTP). Based on the preceding studies, subjects with viral and alcohol hepatitis were excluded from the evaluation. The diagnosis of fatty liver was based on ultrasound findings. The program was evaluated by efficacy and effectiveness; efficacy was measured according to the receiver operating characteristic (ROC) curves in comparison with the Body Mass Index (BMI). Effectiveness, based on the efficacy determinations, was assessed by means of the positive predictive value (PPV) test performance, the disease characteristics, and the program price. The diagnostic performances of ALT and BMI were nearly acceptable but far from excellent. The areas under the curves of the two indices were 0.69 and 0.63, respectively and these were statistically equivalent. The PPV ranged from 15 to 28% where the prevalence of fatty liver was 12.3%. The price of the program was estimated at US 4 dollars per person based on the medical reimbursement fee rate. The efficacy of the liver screening program was found to be insufficient and BMI monitoring may provide a more suitable and inexpensive alternative. Furthermore, the effectiveness of the program is open to question, considering the generally benign prognosis of the disease in the absence of any accompanying morbid conditions and the high price of the program.

Mycophenolate mofetil treatment following renal transplantation decreases GTP concentrations in mononuclear leucocytes

MMF (mycophenolate mofetil) has been proven to provide an effective immunosuppression by non-competitive selective reversible inhibition of IMPDH (inosine monophosphate dehydrogenase), the enzyme playing a crucial role in GTP biosynthesis. However, the exact metabolic changes induced by inhibition of IMPDH in target cells of the immune system have been the subject of recent debate. The aim of the present study was to evaluate whether MMF treatment produced sustained changes in the guanosine nucleotide pool of MNLs (mononuclear leucocytes) in vivo. Sixty-two renal failure patients were divided into three groups: chronic renal failure patients undergoing haemodialysis (CRF-HD; n=20) and two groups of patients after renal transplantation, the first on AZA (azathioprine; TN-AZA; n=23) and the second treated with MMF (TN-MMF; n=19). In addition, MNLs from 25 healthy subjects were analysed as controls. Anion-exchange HPLC was used to quantify purine and pyrimidine nucleotides in MNLs. We report a significant decrease in GTP and the total MNL guanine nucleotide pool in the TN-MMF group (P<0.05) compared with control, CRF-HD and TN-AZA groups, although no significant differences were found between any of the other groups. Adenine nucleotide concentrations in MNLs were decreased in the TN-AZA group, but not in the TN-MMF group compared with the CRF-HD group and controls. There were no differences in CTP concentrations, but UTP concentrations were decreased in the CRF-HD, TN-AZA and TN-MMF groups compared with controls. MMF caused a significant and sustained decrease in the guanine nucleotide pool in MNLs from renal transplant recipients. This decrease contrasts with the elevation in GTP reported in erythrocytes of MMF-treated patients.

Mycophenolate mofetil, an inhibitor of inosine monophosphate dehydrogenase, causes a paradoxical elevation of GTP in erythrocytes of renal transplant patients

The immunosuppressant MMF (mycophenolate mofetil) has increasingly replaced AZA (azathioprine) in renal transplantation. MMF is a prodrug of MPA (mycophenolic acid), which inhibits lymphocyte IMPDH (inosine monophosphate dehydrogenase), thereby drastically decreasing GTP concentrations essential to lymphocyte proliferation in vitro and in vivo. Erythrocyte GTP concentrations are commonly elevated in severe renal disease, but normalize following successful engraftment. Consequently, elevated GTP in renal transplant recipients might signal impending loss of immunosuppression and graft failure. In the present study, we compared erythrocyte nucleotides and plasma metabolites in two groups of 25 patients after renal transplantation, both receiving prednisolone and cyclosporin A, but one group receiving MMF and the other AZA. No patients had recent allograft biopsy evidence of rejection. Erythrocyte GTP concentrations at MMF commencement were 50.4+/-23.4 micromol/l. An increase occurred during the first 3 months after transplant when MMF was used de novo, stabilizing at 146.7+/-62.9 micromol/l after 4 months. This was significantly higher (P=2.5 x 10(-6)) than erythrocyte GTP (40.4+/-15.9 micromol/l) in the AZA group, which was essentially unchanged from values immediately after successful transplantation. The effect of MMF on erythrocyte GTP levels was reversible, since GTP levels fell when MMF therapy was terminated. The results demonstrate paradoxically high GTP concentrations in erythrocytes of renal transplant patients receiving MMF. MPA may stabilize reticulocyte IMPDH, allowing the protein to persist during erythropoiesis. This behaviour is in marked contrast with the decrease in GTP levels seen in white blood cells of patients on chronic MMF therapy.

A severe variant of childhood ataxia with central hypomyelination/vanishing white matter leukoencephalopathy related to EIF21B5 mutation

Childhood ataxia with central hypomyelination (CACH)/vanishing white matter (VWM) leukoencephalopathy is related to mutations in all five genes of the eukaryotic translation initiation factor (eIF2B). In a fatal infantile leukoencephalopathy, which the authors previously classified as a severe variant of CACH/VWM, a new homozygous missense mutation in the EIF2B5 gene was found. Abnormal decrease in blood uric acid and increase of erythrocyte guanosine 5'-diphosphate sugars found in two siblings may contribute to the explanation of this particularly severe condition.

The aerobic physiology of the air-breathing blue gourami, Trichogaster trichopterus, necessitates behavioural regulation of breath-hold limits during hypoxic stress and predatory challenge

Physiological characteristics of the blood oxygen transport system and muscle metabolism indicate a high dependence on aerobic pathways in the blue gourami, Trichogaster trichopterus. Haemoglobin concentration and haematocrit were modest and the blood oxygen affinity (P50=2.31 kPa at pH 7.4 and 28 degrees C) and its sensitivity to pH (Bohr factor, phi=-0.34) favour oxygen unloading at a relatively high oxygen pressure (PO2). The intracellular buffering capacity (44.0 slykes) and lactate dehydrogenase (LDH) activity (154.3 iu g(-1)) do not support exceptional anaerobic capabilities. Air-breathing frequency in the blue gourami is expected to increase when aquatic oxygen tensions decline. Under threat of predation, however, this behaviour must be modified at a potential cost to aerobic metabolism. We therefore tested the hypothesis that metabolic responses to predatory challenge and aquatic hypoxia are subject to behavioural modulation. Computer-generated visual stimuli consistently reduced air-breathing frequency at 19.95, 6.65 and 3.33 kPa PO2. Bi-directional rates of spontaneous activity were similarly reduced. The metabolic cost of this behaviour was estimated and positively correlated with PO2 but not with visual stimulation thus indicating down-regulation of spontaneous activity rather than breath-holding behaviour. Neither PO2 nor visual stimulation resulted in significant change to muscle lactate and ATP concentrations and confirm that aerobic breath-hold limits were maintained following behavioural modulation of metabolic demands.

Effect of mycophenolate mofetil therapy on inosine monophosphate dehydrogenase induction in red blood cells of heart transplant recipients

BACKGROUND

Mycophenolic acid is reported to provide effective immunosuppression by inhibiting inosine monophosphate dehydrogenase. In an attempt to monitor the biological effects of long-term therapy with mycophenolate mofetil, we measured levels of guanosine 5' triphosphate and adenosine 5' triphosphate in red blood cells (RBCs) of patients after heart transplantations.

METHODS

Fifty-two patients enrolled in the study were randomly assigned to one of two groups. Patients in the control group (n = 27) received cyclosporine A (INN, ciclosporin), azathioprine, and prednisone. Patients in the study group (n = 25) were switched from azathioprine to mycophenolate mofetil 3 months after the heart transplantation. Adenosine 5' triphosphate and guanosine 5' triphosphate levels were determined by means of HPLC. The activities of inosine monophosphate dehydrogenase and hypoxanthine-guanine phosphoribosyltransferase, which are responsible for guanine nucleotide formation, were measured in RBCs by radiochemical methods.

RESULTS

Adenosine 5' triphosphate levels were unchanged in patients treated with mycophenolate mofetil, whereas those of the control group who received azathioprine (from 142 +/- 26 pmol/10(6) RBCs to 165 +/- 25 pmol/10(6) RBCs; P <.001) increased. As the length of mycophenolate mofetil therapy increased, patients in the study group showed significantly elevated guanosine 5' triphosphate levels (15.6 +/- 6.1 pmol/10(6) RBCs versus 6.6 +/- 2.1 pmol/10(6) RBCs; P <.001) and a 5-fold increase in inosine monophosphate dehydrogenase activity (108.6 +/- 13.3 pmol/mg of protein per hour versus 22.5 +/- 1.7 pmol/mg of protein per hour; P <.001) compared with the control group. In addition, a slight but significant enhancement of hypoxanthine-guanine phosphoribosyltransferase activity was seen in the mycophenolate mofetil group.

CONCLUSIONS

Our studies have shown that long-term administration of mycophenolate mofetil is associated with increasing guanosine 5' triphosphate levels in RBCs as the result of an induction of inosine monophosphate dehydrogenase and hypoxanthine-guanine phosphoribosyltransferase activities in erythrocytes.

Exploiting polymerase promiscuity: A simple colorimetric RNA polymerase assay

We developed a convenient colorimetric assay for monitoring RNA synthesis from DNA-dependent RNA polymerases (DdRp) and viral RNA-dependent RNA polymerases (RdRp). ATP and GTP with a p-nitrophenyl moiety attached to the gamma-phosphate were synthesized (PNP-NTPs). These PNP-NTPs can be used for RNA synthesis by several RNA polymerases, including the RdRps from brome mosaic virus and bovine viral diarrhea virus and the DdRps from bacteriophage T7 and SP6. When the polymerase reactions were performed in the presence of alkaline phosphatase, which digests the p-nitrophenylpyrophosphate side-product of phosphoryl transfer to the chromogenic p-nitrophenylate, an increase in absorbence at 405 nm was observed. These nucleotide analogues were used in continuous colorimetric monitoring of polymerase activity. Furthermore, the PNP-NTPs were found to be stable and utilized by RNA polymerases in the presence of human plasma. This simple colorimetric polymerase assay can be performed in a standard laboratory spectrophotometer and will be useful in screens for inhibitors of viral RNA synthesis.

Clustering of beta(2)-integrins on human neutrophils activates dual signaling pathways to PtdIns 3-kinase

The beta(2)-integrins on leukocytes can serve as a signaling unit during cell adhesion and locomotion, and to further clarify this important property we investigated the possible mechanisms of beta(2)-integrin-induced activation of PtdIns 3-kinase. It has previously been demonstrated that clustering of beta(2)-integrins activates p21(ras) by a tyrosine kinase-dependent pathway, and here we show that active p21(ras) interacts with its downstream target, PtdIns 3-kinase. Engagement of beta(2)-integrins also activates the tyrosine kinases p58(c-fgr) and p59/61(hck) and causes them to associate with the p85 subunit of PtdIns 3-kinase. These findings suggest a mechanism whereby p58(c-fgr) and p59/61(hck) are directly involved in the activation of PtdIns 3-kinase. No coupling between p58(c-fgr) and p59/61(hck) could be detected; hence these kinases probably trigger independent but parallel signals to PtdIns 3-kinase. The effect of beta(2)-integrin clustering on PtdIns 3-kinase activity was monitored as the activation of protein kinase B (PKB). Stimulation of PKB by beta(2)-integrins was abolished by genistein and wortmannin but not by using methyl transferase inhibitors to abrogate the influence of p21(ras)-related proteins. Thus, even if PtdIns 3-kinase is not activated by p21(ras), it can maintain full enzyme activity due to the mentioned interaction with p58(c-fgr) or p59/61(hck). These tyrosine kinases apparently activate similar pathways that operate in parallel and therefore have the potential to substitute for each other in mediating adhesion and regulating cell locomotion.

Energy metabolism and lipid peroxidation of human erythrocytes as a function of increased oxidative stress

To study the influence of oxidative stress on energy metabolism and lipid peroxidation in erythrocytes, cells were incubated with increasing concentrations (0.5-10 mM) of hydrogen peroxide for 1 h at 37 degrees C and the main substances of energy metabolism (ATP, AMP, GTP and IMP) and one index of lipid peroxidation (malondialdehyde) were determined by HPLC on cell extracts. Using the same incubation conditions, the activity of AMP-deaminase was also determined. Under nonhaemolysing conditions (at up to 4 mM H2O2), oxidative stress produced, starting from 1 mM H2O2, progressive ATP depletion and a net decrease in the intracellular sum of adenine nucleotides (ATP + ADP + AMP), which were not paralleled by AMP formation. Concomitantly, the IMP level increased by up to 20-fold with respect to the value determined in control erythrocytes, when cells were challenged with the highest nonhaemolysing H2O2 concentration (4 mM). Efflux of inosine, hypoxanthine, xanthine and uric acid towards the extracellular medium was observed. The metabolic imbalance of erythrocytes following oxidative stress was due to a dramatic and unexpected activation of AMP-deaminase (a twofold increase of activity with respect to controls) that was already evident at the lowest dose of H2O2 used; this enzymatic activity increased with increasing H2O2 in the medium, and reached its maximum at 4 mM H2O2-treated erythrocytes (10-fold higher activity than controls). Generation of malondialdehyde was strictly related to the dose of H2O2, being detectable at the lowest H2O2 concentration and increasing without appreciable haemolysis up to 4 mM H2O2. Besides demonstrating a close relationship between lipid peroxidation and haemolysis, these data suggest that glycolytic enzymes are moderately affected by oxygen radical action and strongly indicate, in the change of AMP-deaminase activity, a highly sensitive enzymatic site responsible for a profound modification of erythrocyte energy metabolism during oxidative stress.

Effect of methotrexate on blood purine and pyrimidine levels in patients with rheumatoid arthritis

OBJECTIVE

The mechanism of anti-inflammatory effects of methotrexate (MTX) at low dose may relate to a decrease in availability of the purine precursor or it may depend on accumulation of 5-aminoimidazole-4-carboxamide (AICAR) and the anti-inflammatory nucleoside adenosine. The aim of this study was to evaluate the possible mechanism of action by analysis of changes in blood concentrations of purine and pyrimidine metabolites during MTX treatment.

METHODS

Venous blood samples were collected from rheumatoid arthritis patients before and at different times for up to 7 days after the start of MTX treatment. Whole blood concentrations of adenosine, uridine, hypoxanthine, uric acid and erythrocyte nucleotides were measured by HPLC.

RESULTS

The initial blood adenosine concentration was 0.073 +/- 0.013 microM and no differences were observed during MTX treatment. However, a decrease in uric acid concentration was observed from 205.5+/-13.5 to 160. 9+/-13.5 microM (P<0.05) within 24 h after MTX administration. The hypoxanthine concentration decreased in parallel with uric acid, while the uridine concentration decreased 48 h after MTX administration. No accumulation of AICAR-triphosphate (ZTP) was observed in the erythrocytes.

CONCLUSIONS

MTX decreases circulating purine and pyrimidine concentrations, and their availability for DNA and RNA synthesis, which may affect immune cell proliferation and protein (cytokine) expression. The absence of adenosine concentration changes and lack of ZTP formation is evidence against an AICAR/adenosine mechanism, although localized adenosine concentration changes cannot be excluded.

Rab6 is phosphorylated in thrombin-activated platelets by a protein kinase C-dependent mechanism: effects on GTP/GDP binding and cellular distribution

In platelets and other secretory cells, protein kinase C (PKC) plays a role in exocytosis stimulated by physiological extracellular signals, although its linkage to the secretory machinery is poorly understood. We investigated whether Rab6, a GTP-binding protein that fractionates with platelet alpha-granules, may be involved in linking these processes. We found that Rab6 contains two PKC consensus phosphorylation sites that are evolutionarily conserved. In platelets metabolically labelled with [(32)P]P(i), Rab6 phosphorylation was induced by phorbol esters or by thrombin. This phosphorylation was blocked by a specific PKC inhibitor (Ro-31-8220), but not by a p38 mitogen-activated protein kinase inhibitor (PD-169316). Physiological stimulation of platelets caused a PKC-dependent translocation of Rab6 from platelet particulate fractions, nearly doubling the fraction of Rab6 in the cytosol. A human Rab6 isoform (Rab6C) that is preferentially expressed in human platelet RNA was cloned and its phosphorylation by PKC was characterized. Rab6C incorporated up to 2 mol of [(32)P]P(i) per mol of active protein. Rab6C bound GDP and GTP with K(d) values of 113+/-12 and 119+/-27 nM respectively, and hydrolysed GTP at a rate of 100+/-15 micromol of GTP/mol of Rab6C per min. PKC phosphorylation of Rab6C increased the affinity for GTP by 3-fold, although it had lesser effects on GDP (1.6-fold). Phosphorylation did not alter the GTPase activity. In summary, thrombin activation of platelets leads to PKC-dependent phosphorylation of Rab6 and a translocation of Rab6 to the cytosol. We suggest that PKC phosphorylation may be an important mechanism through which Rab functional interactions in vesicle trafficking and secretion can be altered in response to an external stimulus.

A twenty strain survey and backcross localization of the erythrocytic GTP concentration determining locus Gtpc on mouse chromosome 9

Erythrocyte nucleotide concentrations were surveyed among 20 inbred strains of mice in order to further assess the variability in GTP concentration. There was no significant difference in erythrocytic ATP concentration (Scheffé's test at P = 0.01), 678-1154 nmol/mL packed cells, among the strains surveyed. Two groups were distinguishable with respect to erythrocytic GTP concentration, 8 strains having high GTP, 215 +/- 44 nmole/mL packed cells, and 12 strains having low GTP, 34 +/- 12 nmole/mL packed cells. The erythrocytic GTP concentration determining trait Gtpc was previously shown to be linked to transferrin, Trf, on chromosome 9. Analysis of 232 [(B6 x WB) F1 x B6] backcross individuals for Gtpc and 8 microsatellite markers restricted the localization of Gtpc to a 5.6 +/- 2.1 cM region. The gene order and genetic distances in cM +/- SE are: (D9Mit14) 0.4 +/- 0.4 (D9Mit24) 1.7 +/- 0.8 (Gtpc, D9Mit51, D9Mit116, D9Mit212) 3.9 +/- 1.3 (D9Mit200) 3.0 +/- 1.1 (D9Mit20) 7.8 +/- 1.8 (D9Mit18). The GTP concentration determining trait appears to be a property of erythrocytes as no differences were observed for GTP/ATP ratios of brain, kidney, liver, and tongue from a low GTP strain, C3H/HeHa x Pgk-la and a high GTP strain, C57BL/6J.

Complete hematologic and cytogenetic response to 2-amino-9-beta-D-arabinosyl-6-methoxy-9H-guanine in a patient with chronic myelogenous leukemia in T-cell blastic phase: a case report and review of the literature

BACKGROUND

T-cell lymphoid blastic phase (BP) transformation is rare in chronic myelogenous leukemia (CML). 2-amino-9-beta-D-arabinosyl-6-methoxy-9H-guanine (GW506U78), a prodrug of arabinosylguanine (ara-G), is effective in T-cell leukemias.

METHODS

The authors present a case of a 48-year-old male with Philadelphia chromosome (Ph) positive CML and T-cell lymphoid BP after 17 months in the chronic phase.

RESULTS

Plasma pharmacokinetic studies after an infusion of GW506U78 at a dose of 40 mg/kg showed GW506U78 concentrations of 60 microM, and a peak ara-G concentration of 260 microM in the plasma. Cellular ara-G triphosphate (ara-GTP) concentration in the peripheral blood T-lymphoblasts was 80 microM at the end of GW506U78 infusion and reached a maximum of 150 microM. The patient achieved a complete response that lasted 13 months. Severe neurotoxicity related to GW506U78 was observed.

CONCLUSIONS

GW506U78 showed antileukemic activity against Ph positive T-cell BP CML. Neurotoxicity was dose-limiting in this patient. Treatment with GW506U78 and modulation of ara-GTP concentrations are therapeutic strategies that require further exploration in T-cell malignancies. Investigation of other dosing schedules may limit neurotoxicity.

Pharmacokinetics and pharmacodynamics of oral methotrexate and mercaptopurine in children with lower risk acute lymphoblastic leukemia: a joint children's cancer group and pediatric oncology branch study

We prospectively assessed the pharmacokinetics of methotrexate, mercaptopurine, and erythrocyte thioguanine nucleotide levels in a homogenous population of children with lower risk acute lymphoblastic leukemia and correlated pharmacokinetic parameters with disease outcome. The maintenance therapy regimen included daily oral mercaptopurine (75 mg/m2) and weekly oral methotrexate (20 mg/m2). One hundred ninety-one methotrexate doses and 190 mercaptopurine doses were monitored in 89 patients. Plasma drug concentrations of both agents were highly variable. The area under the plasma concentration-time curve (AUC) of methotrexate ranged from 0.63 to 12 micromol*h/L, and the AUC of mercaptopurine ranged from 0.11 to 8 micromol*h/L. Drug dose, patient age, and duration of therapy did not account for the variability. Methotrexate AUC was significantly higher in girls than boys (P =.007). There was considerable intrapatient variability for both agents. Erythrocyte thioguanine nucleotide levels were also highly variable (range, 0 to 10 pmol/g Hgb) and did not correlate with mercaptopurine dose or AUC. A Cox regression analysis showed that mercaptopurine AUC was a marginally significant (P =.043) predictor of outcome, but a direct comparison of mercaptopurine AUC in the remission and relapsed patient groups failed to show a significant difference. Methotrexate and mercaptopurine plasma concentrations and erythrocyte thioguanine nucleotide levels were highly variable, but measurement of these pharmacokinetic parameters at the start of maintenance will not distinguish patients who are more likely to relapse.

Pharmacological and biochemical strategies to increase the accumulation of arabinofuranosylguanine triphosphatein primary human leukemia cells

Purine nucleoside phosphorylase deficiency leads to a dGTP-mediated T-lymphopenia, suggesting that an analogue of deoxyguanosine would be selectively effective in T-cell disease. 9-beta-D-Arabinofuranosylguanine (ara-G) is relatively resistant to hydrolysis by purine nucleoside phosphorylase and selectively toxic to T cells, but its low solubility has prevented its use in the clinic. 2-Amino-6-methoxy-arabinofuranosylpurine (GW506U) serves as the water-soluble prodrug for ara-G. A Phase I trial in patients with refractory hematological malignancies demonstrated that the clinical responses to this agent were directly related to the peak levels of ara-G 5'-triphosphate (ara-GTP) in target cells. The aim of the present study was to develop and test strategies to increase intracellular accumulation of ara-GTP in primary human leukemia cells of myeloid and B-lymphoid origin. Three strategies were tested. First, incubations with 100 microM ara-G for 4 h produced a linear median accumulation rate of 19 microM/h (range, 2-45 microM/h; n = 15) in lymphoid leukemia cells and 16 microM/h (range, 0.5-41 microM/h; n = 11) in myeloid leukemia cells. Saturation of ara-GTP accumulation was achieved only after 6-8 h exposure in both lymphoid and myeloid leukemia cells, suggesting a rationale for prolonged infusion. Second, a dose-dependent increase in ara-GTP accumulation was observed with incubations of 10-300 microM ara-G for 3 h. Hence, dosing regimens that achieve high plasma levels of ara-G during therapy may increase cellular levels of ara-GTP. Finally, a biochemical modulation approach using in vitro incubation of leukemia cells with 10 microM 9-beta-D-arabinofuranosyl-2-fluoroadenine for 3 h, followed by either 50 or 100 microM ara-G for 4 h, resulted in a statistically significant median 1.3-fold (range, 1.1-9.0-fold; P = 0.034) and 1. 8-fold (range, 0.9-10.6 fold; P = 0.018) increase in ara-GTP compared to cells incubated with ara-G alone. Extension of these studies to ex vivo incubations confirmed our in vitro findings. These strategies will be used in the design of clinical protocols to increase ara-GTP accumulation in leukemia cells during therapy.

Association of Ral GTP-binding protein with human platelet dense granules

GTP-binding proteins of molecular mass of 24-27 kDa were detected in the dense granule fraction of human platelets when nitrocellulose blots containing proteins separated by SDS-polyacrylamide gel electrophoresis were incubated with [alpha-32P]GTP. Further analysis, using isoelectric focusing and two-dimensional polyacrylamide gel electrophoresis, resolved the dense granule 27 kDa and 24 kDa GTP-binding proteins into four distinct forms each. GTP-binding proteins in the total particulate fraction were resolved into seven 27 kDa and four 24 kDa forms. Immunoblotting with antiserum against known platelet low molecular mass GTP-binding proteins demonstrated that rap2 and G25K/CDC42Hs proteins, although present in platelets, were not detected in the dense granule fraction. However, ral was one of the proteins associated with dense granules. Association of specific low molecular mass GTP-binding proteins with dense granules suggests a potential role for these proteins in regulating the release of storage contents from this granule.

Liquid-chromatographic study of purine metabolism abnormalities in purine nucleoside phosphorylase deficiency

Using HPLC methods, we measured the concentrations of nucleosides and nucleotides for a patient with no purine nucleoside phosphorylase (PNP; EC 2.4.2.1) enzymatic activity. Concentrations of inosine and guanosine were abnormally high in urine and plasma, whereas guanosine diphosphate (GDP) and guanosine triphosphate (GTP) concentrations in erythrocytes were depleted. The unusual presence of deoxyribonucleosides (deoxyinosine and deoxyguanosine) and deoxyribonucleotides (dGDP and dGTP) was also notable. Thus, HPLC represents an accurate and useful tool for the study of purine metabolic disorders.

Determination of intracellular levels of 6-mercaptopurine metabolites in erythrocytes utilizing capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis proved to be a useful technique for the analysis of intracellular levels of 6-thioguanosine mono-, di-, and triphosphate with analysis times of 20 min. Conditions required for baseline separation of the thioguanine nucleotides consisted of a 25 mM KH2PO4 (pH 8.0) buffer and a separation voltage of +28 kV. Laser-induced fluorescence detection (lambda ex = 325 nm, lambda em = 410 nm) of the thioguanine nucleotide metabolites of 6-mercaptopurine (6-MP) was possible following oxidation of the thiol functionality. Tedious extraction procedures involving mercury cellulose resins or phenyl mercury adduct formation, which had been required previously for the selective extraction of thiopurines from erythrocytes, were unnecessary due to the overall specificity of the approach. However, the inclusion of 50 mM EDTA in the sample preparation was required to inhibit the anabolic/catabolic enzymatic activity, which was responsible for the degradation of the analytes. The method demonstrated linearity from 5 to 1700 pmol/100 microliters red blood cells for the three analytes (RSDs < or = 8%). The feasibility of the method was demonstrated for the quantitation of 6-thioguanine nucleotides in patients receiving either oral or intravenous 6-MP therapy.

Effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides

The effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides was investigated in 6 athletes. Muscular exercise increased the concentration of inosine monophosphate from 5.9 +/- 1.1 to 7.3 +/- 1.3 nmol/ml in venous erythrocytes and from 5.7 +/- 1.0 to 6.8 +/- 1.4 nmol/ml in arterial erythrocytes, respectively, while it decreased the concentrations of adenosine diphosphate and adenosine monophosphate from 189.3 +/- 42.7 to 141.2 +/- 26.9 and from 26.0 +/- 7.8 to 15.7 +/- 4.3 nmol/ml in venous erythrocytes and also decreased their concentrations from 195.1 +/- 51.0 to 141 +/- 29.2 and from 26.5 +/- 9.6 to 14.8 +/- 3.0 nmol/ml in arterial erythrocytes, respectively. The muscular exercise also increased the concentration of inorganic phosphate in venous plasma from 1.12 +/- 0.12 to 1.46 +/- 0.22 mmol/l, that of NH3 in blood from 41.90 +/- 6.91 to 150.22 +/- 50.80 mumol/l, that of lactic acid in blood from 7.90 +/- 1.71 to 61.03 +/- 18.43 mg/dl and that of hypoxanthine in venous plasma from 1.32 +/- 0.36 to 18.14 +/- 4.87 mumol/l, respectively. Therefore, in vitro study was performed to investigate whether inorganic phosphate, NH4Cl, lactic acid or hypoxanthine affects nucleotides in erythrocytes. After 2 hour-incubation, 2 mM inorganic phosphate increased the erythrocyte concentration of inosine monophosphate 1.6 fold but decreased the erythrocyte concentrations of adenosine monophosphate and adenosine diphosphate 0.72 and 0.89 fold, respectively, in the suspension (pH 7.35), as compared with 1 mM inorganic phosphate. However NH4Cl, lactic acid or hypoxanthine did not affect erythrocyte purine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum hepatocyte growth factor in acute hepatic failure in comparison with acute hepatitis

Serum hepatocyte growth factor (HGF) levels in patients with acute hepatic failure has been reported to increase. However, possible mechanisms responsible for HGF elevation in this syndrome remains to be determined. To explore the possible mechanisms, we measured serum HGF in patients with acute hepatic failure and self-limited acute hepatitis, using an immunoradiometric assay. Serum HGF levels in acute hepatic failure were 36-fold higher compared with those in acute hepatitis. Serum HGF values in acute hepatitis were significantly correlated with serum bilirubin and gamma-GTP levels, whereas those in acute hepatic failure were not. These clinical findings suggest that serum HGF levels in acute hepatic failure may be regulated by different mechanisms from those in self-limited acute hepatitis.

Assignment of a gene that determines erythrocytic guanosine-5'-triphosphate concentration (Gtpc) to mouse chromosome 9

Nine inbred mouse strains surveyed for erythrocytic guanosine-5'-triphosphate (GTP) concentration were found to segregate into two discrete groups. Strains having low GTP levels between 1.4 and 3.4 nmol/10(9) cells were C3H/HeJ, C3H/HeHa, A/J, and WB/ReJ. Strains having high GTP levels between 11.0 and 14.8 nmol/10(9) cells were AKR/J, DBA/2J, CBA/J, C57BL/6J, and C57L/J. Erythrocytic ATP levels did not vary significantly among these groups. Crosses between low and high GTP strains gave F1 progeny having intermediate levels of GTP, and the progeny of F1's backcrossed to parental strains segregated in a 1:1 ratio for GTP concentration. We designated the GTP concentration determining trait, Gtpc. Typing the C57BL/6J x C3H/HeJ (B x H) recombinant inbred strains for GTP levels revealed 0/12 strain distribution pattern differences for loci on both chromosomes 5 and 9. Backcross analysis did not provide evidence for linkage of Gtpc to W (dominant white spotting) on chromosome 5 with 15/45 recombinants. A test for linkage of Gtpc to transferrin (Trf) on chromosome 9 gave evidence of linkage with an observed recombination frequency of 14.6 +/- 5.5 and a 99% confidence interval of 3.9-33.9 cM.

Regulation of the human neutrophil NADPH oxidase by the Rac GTP-binding proteins

Recent progress in our understanding of the regulation of the phagocyte NADPH oxidase by the Rac GTP-binding protein(s) has provided the first detailed glimpse into the mechanisms of leukocyte regulation by a small GTP-binding protein. Studies over the past year have indicated that the activity of the NADPH oxidase can be modulated by regulation of the GTP/GDP state of Rac. Proteins exist in leukocytes that are able to modify GTP-binding protein function in this manner, and their activity may be regulated by signals generated upon phagocyte stimulation.

Determination of guanine and its nucleosides and nucleotides in human erythrocytes by high-performance liquid chromatography with postcolumn fluorescence derivatization using phenylglyoxal reagent

A high-performance liquid chromatographic method with on-line postcolumn fluorescence derivatization is described for the simple and sensitive determination of guanine and its nucleosides and nucleotides in human erythrocytes. After deproteinization of the biospecimen, guanine and its nucleosides and nucleotides were separated on a reversed-phase column (TSKgel ODS-120T) by gradient elution with methanol in the aqueous mobile phase consisting of tetra-n-propylammonium phosphate (pH 6.0) and phosphate buffer (pH 6.0). The compounds were then automatically converted into fluorescent derivatives by reaction with phenylglyoxal. This derivatization was selective for guanine-containing compounds. The present method permitted the reliable quantification of GDP and GTP in human erythrocytes. The detection limits (at a signal-to-noise ratio of 3) for guanine and its nucleosides and nucleotides were 3.2-10.0 pmol in a 20-microliters injection volume. The concentrations of GDP and GTP in human erythrocytes were 17.2 +/- 6.2 and 40.2 +/- 5.8 nmol/ml, respectively.

Activation of respiratory burst oxidase is accompanied by desensitization of p47phox in nucleoside-triphosphate binding along with its translocation to cell membrane

A cytosolic component of human neutrophils, p47phox, potentiates respiratory burst oxidase translocating from cytosol to membrane upon cell stimulation. In this study, the nucleotide-binding ability of p47phox was examined using [32P]GTP dialdehyde (oGTP), [32P]oATP, and [32P]oNADPH. p47phox showed affinities for both oGTP and oATP that were 14 times higher than that for oNADPH, suggesting that it is a nucleoside triphosphate (NTP)-binding protein rather than an NADPH-binding protein. Binding analysis of p47phox using either [32P]oGTP or [32P]oATP revealed an apparent binding constant for each individual NTP analogue and the same maximum binding value, which suggests that both NTPs share a common specific binding site. Stimulation of neutrophils with phorbol myristate acetate (PMA) resulted in enhancement of the oxidase activity to generate O2- anion and was accompanied by substantial translocation of p47phox to membrane. However, p47phox derived from the stimulated cell membrane had lost its NTP-binding ability, unlike that from the resting cytosol. These results suggest that the binding of NTP to p47phox may be involved in the process that activates the oxidase and is desensitized in translocated p47phox.

G protein coupling of human platelet V1 vascular vasopressin receptors

We used several approaches to identify the G protein coupled to V1 vascular arginine vasopressin (AVP) receptors of human platelets. In purified platelet membranes, high-affinity specific binding of [3H]AVP but not that of the V1 vascular antagonist [3H]d(CH2)5Tyr(Me)AVP was modulated by guanosine 5'-O-(3-thiotriphosphate) or sodium fluoride both in the presence and absence of MgCl2. AVP failed to modify the [alpha-32P]GTP labeling pattern or the cytosolic translocation of the 24- to 27-kDa GTP-binding proteins. AVP-stimulated GTPase activity of platelet membranes was blocked by antibodies specific for the COOH-terminal of the Gq alpha protein. AVP increased labeling of a 42-kDa platelet membrane protein by the photoreactive GTP analogue [alpha-32P]azidoanilido GTP. Immunoblotting of platelet proteins with various G protein-specific antibodies revealed that the 42-kDa protein labeled with [alpha-32P]azidoanilido GTP was immunoblotted only by antibodies specific for the alpha-subunit of GQ-11. Thus V1 vascular AVP receptors of human platelets are coupled in a divalent cation-dependent manner to a G protein belonging to the Gq-11 family.

Treatment of patients with chronic hepatitis using ursodeoxycholic acid

We treated 82 patients of chronic hepatitis using 300 mg. of ursodeoxycholic acid (UDCA) daily and observed them for a mean of 10 mo before and 16 mo after UDCA administration. Seven liver function tests (AST, ALT, ALP, LAP, GTP, Ch-E and T-cholest) were assessed monthly. The values were compared before and after the administration of UDCA. The AST, ALT, LAP and GTP improved significantly in the UDCA treated patients, whereas ALP, Ch-E and T-cholest. did not show any change throughout the study. Amongst the liver function tests that improved, the serum--GTP level, in particular decreased markedly and rapidly in patients treated with UDCA. Although UDCA 600-mg daily was administered in patients who showed lack of improvement with 300-mg UDCA treatment, no significant improvement was obtained. Repeated liver biopsies were carried out in six of the 42 patients in whom liver biopsy had been performed before the administration of UDCA. We detected no histological changes during the UDCA treatment. There were no side effects related to therapy with UDCA. In conclusion, we confirmed that UDCA is a safe and effective drug for treating patients with chronic hepatitis and may help in prevention of progression of the disease, particularly in patients with a high serum--GTP level.

Erythrocytic nucleoside triphosphates in marine fish

1. Whole blood purine nucleotides were determined in 19 species of selachians and 27 species of marine teleosts. Concomitant ATP and GTP were revealed inside the erythrocytes of almost all species studied. 2. ATP seems to be the main potential modulator of oxygen affinity in rays, sharks and teleosts, and GTP was not detected in only two teleost species. 3. The mean erythrocytic NTP concentration and the ratio between NTP and intraerythrocytic Hb concentrations in rays were the lowest (2.3 mM and 0.6 respectively), increasing in sharks (3.8 mM and 1.0), and further in teleosts (5.9 mM and 2.1). 4. The intraerythrocytic phosphate contents probably reflect different adaptative strategies associated with the fish habits and habitats, and with the Root effect expression.

Absolute requirement for GTP in activation of human neutrophil NADPH oxidase in a cell-free system: role of ATP in regenerating GTP

Guanine and/or adenine nucleotides appear to be involved in the activation of the superoxide-generating NADPH oxidase of phagocytic cells. Their precise roles, however, are unclear, as much of the evidence for their involvement comes from experiments in which nucleotides have been added to complex systems already rich in both endogenous nucleotides and enzymes capable of interconverting them. To circumvent this problem we have examined the role of nucleotides in neutrophil NADPH oxidase activation by using a cell-free system in which adenine and guanine nucleotide concentrations were carefully controlled and monitored by (i) depletion of endogenous nucleotides by extensive dialysis and charcoal treatment; (ii) reconstitution of the depleted system with reagents analyzed for purity; and (iii) measurement of nucleotide levels in cytosol preparations and in oxidase reaction mixtures by HPLC analysis. In contrast to previous reports that have demonstrated only a several-fold enhancement of oxidase activity by GTP or its analogs, we have shown that oxidase activation was absolutely dependent upon GTP in reactions containing dialyzed cytosol in which the total endogenous nucleotide levels were reduced by greater than 99.5%. Kinetic studies revealed that GTP is required at or before the rate-limiting step in oxidase activation. Two nonhydrolyzable analogs of GTP, guanosine 5'-(gamma-thio)triphosphate and guanylyl imidodiphosphate, were even more active than GTP, suggesting the involvement of one or more GTP-binding proteins. In contrast, ATP was neither necessary nor sufficient for oxidase activation. If reaction mixtures were contaminated with GDP and/or GMP, however, ATP (but not its nonhydrolyzable analog adenylyl imidodiphosphate) could indirectly support oxidase activation by means of endogenous enzymes that catalyze the ATP-dependent conversion of GMP and GDP to GTP.

A case of erythropoietic protoporphyria with severe liver dysfunction suggesting a close relationship between erythrocyte protoporphyrin levels and those of gamma-GTP

A case of erythropoietic protoporphyria (EPP) with severe acute abdominal pain and jaundice was reported. Erythrocyte protoporphyrin (PP) levels were constantly high, and liver histology showed a slight fibrosis with inflammatory infiltration. During the investigation period of 18 months, erythrocyte PP levels closely paralleled those of serum gamma-GTP.

Evidence that the signal-initiating membrane protein CD9 is associated with small GTP-binding proteins

F(ab')2 fragments of anti-CD9 mAb aggregate platelets by a thromboxane-dependent pathway implicating CD9 as signal initiating molecule. We demonstrate that mAbs directed against CD9, but not against GPIIb/IIIa specifically immunoprecipitate, from detergent lysates of human platelets, proteins of 25 and 26 kDa which bind [alpha 32P]GTP on nitrocellulose transfers. The binding is specific since it is blocked by GTP, but not by ATP. The GTP-binding proteins do not belong to a Mg(2+)-sensitive subset since they are unaffected by the addition of 2 microM-20 mM Mg2+. The observations demonstrate that CD9 is associated with selected small G-proteins.

Role of erythrocyte organic phosphates in blood oxygen transport in anemic quail

The effects of two different degrees of experimentally induced anemia and the consequent high percentage of circulating immature erythrocytes on oxygen affinity (pH 7.5 and 41 degrees C), erythrocyte organic phosphates, and Hb fractions have been studied in quail. Blood reticulocytes reached percentages of 24 and 69-87% in the first and second experiments, respectively. Variations in the phosphate levels found during the anemic process were related to the amount of circulating reticulocytes. The erythrocyte [ATP] (brackets indicate concentration) and [ATP]/[Hb] molar ratio increased with the release of reticulocytes and returned to control levels as they matured. The erythrocyte [inositol pentakisphosphate (InsP5)] decreased significantly when circulating reticulocytes showed their highest values, whereas there was hardly any effect on the [InsP5]/[Hb] molar ratio, which changed only slightly. Hb-O2 affinity also exhibited no statistical changes associated with acute anemia. These latter findings indicate that InsP5, at physiological concentrations, is the primary modulator of quail Hb function; the observed rise in [ATP] has no additional influence on Hb-O2 affinity. It is suggested that InsP5 tends to maintain the blood oxygen affinity in both mature erythrocytes and reticulocytes. The main compensatory response at blood level is a rapid bulk reticulocyte release from medulla.

Novel pharmacological strategies in the treatment of life-threatening cytomegalovirus infections. Clinical experience with continuous infusion 9-(1,3-dihydroxy-2-propoxymethyl) guanine

Two novel antiviral pharmacologic strategies were used for therapy of life- and sight-threatening cytomegalovirus (CMV) infection; these were continuous drug infusion by portable pump and individualized patient regimen. 9-(1,3-Dihydroxy-2-propoxymethyl)-guanine (DHPG), an active and recently licensed antiviral drug against cytomegalovirus infection, was administered to five immunocompromised patients with chorioretinitis (all patients), colitis (two), and pneumonitis (three). Through dosage escalation, correlations between plasma levels, toxicity (i.e., myelosuppression), and clinical benefit were ascertained for therapy of acute disease (pneumonitis) as well as long-term therapy (chorioretinitis). Resolution of viremia, pneumonitis, colitis, and chorioretinitis was accomplished with steady-state plasma levels of DHPG approximating the mean ID50 of CMV isolates. The most notable clinical benefit was survival from CMV pneumonia and stabilization of vision. Although no adverse toxicity occurred during the DHPG continuous long-term therapy, survival was limited by the underlying disease.

Metabolic control of the K+ channel of human red cells

The effects of cAMP, ATP and GTP on the Ca2(+)-dependent K+ channel of fresh (1-2 days) or cold-stored (28-36 days) human red cells were studied using atomic absorption flame photometry of Ca2(+)-EGTA loaded ghosts which had been resealed to monovalent cations in dextran solution. When high-K+ ghosts were incubated in an isotonic Na+ medium, the rate constant of Ca2(+)-dependent K+ efflux was reduced by a half on increasing the theophylline concentration to 40 mM. This effect was observed in ghosts from both fresh and stored cells, but only if they were previously loaded with ATP. The inhibition was more marked when Mg2+ was added together with ATP, and it was abolished by raising free Ca2+ to the micromolar level. Like theophylline, isobutyl methylxanthine (10 mM) also affected K+ efflux. cAMP (0.2-0.5 mM), added both internally and externally (as free salt, dibutyryl or bromide derivatives), had no significant effect on K+ loss when the ghost free-Ca2+ level was below 1 microM, but it was slightly inhibitory at higher concentrations. The combined presence of cAMP (0.2 mM) plus either theophylline (10 mM), or isobutyl methylxanthine (0.5 mM), was more effective than cAMP alone. This inhibition showed a strict requirement for ATP plus Mg2+ and it was not overcome by raising internal Ca2+. Ghosts from stored cells seemed more sensitive than those from fresh cells, to the combined action of cAMP and methylxanthines. Loading ATP into ghosts from fresh or stored cells markedly decreased K+ loss. Although this effect was observed in the absence of added Mg2+ (0.5 mM EDTA present), it was potentiated upon adding 2 mM Mg2+. The K+ efflux from ATP-loaded ghosts was not altered by dithio-bis-nitrobenzoic acid (10 mM) or acridine orange (100 microM), while it was increased two- to fourfold by incubating with MgF2 (10 mM), or MgF2 (10 mM) + theophylline (40 mM), respectively. By contrast, a marked efflux reduction was obtained by incorporating 0.5 mM GTP into ATP-containing ghosts. The degree of phosphorylation obtained by incubating membranes with (gamma-32P)ATP under various conditions affecting K+ channel activity, was in direct correspondence to their effect on K+ efflux. The results suggest that the K+ channel of red cells is under complex metabolic control, via cAMP-mediated and nonmediated mechanisms, some which require ATP and presumably, involve phosphorylation of the channel proteins.

Characterization of GTP-gamma-S binding to isolated human platelet plasma membranes and its relationship with the stimulation of a phospholipase C activity

Binding parameters for the interaction of GTP-gamma-[35S] with isolated platelet plasma membranes have been studied. Analysis of the data by a non-linear curve fitting program indicates that the interaction can be satisfactory described by a model with a single, high affinity binding site (Kd = 0.3 +/- 0.07 microM and Bm = 0.4 +/- 0.2 nmoles of GTP-gamma-S/mg of membrane protein). Binding is selectively inhibited by GDP-beta-S and GMP-PNP (1 microM), but not affected by ATP, CTP, ITP, or UTP, even at mM concentration. Optimal conditions for the interaction were 30 degrees C and pH 8.0. Incubation of the isolated membranes with GTP-gamma-S results in a measurable phospholipase C activity (as detected both by a breakdown of phosphoinositides and an increase of inositide phosphates) which under our experimental conditions is only slightly enhanced by addition of cytosolic proteins. Our results indicate that platelet plasma membranes contain all the necessary elements for signal transduction through the diacylglycerol/inositolphosphates pathway.

Nucleotides in lymphocytes of human subjects with zinc deficiency

Cell-mediated immunity in human subjects is affected adversely as a result of zinc deficiency. The mechanism by which a deficiency of zinc may affect lymphocyte proliferation and functions, is not well understood at present. Nucleoside phosphorylase (NPase), a purine catabolic pathway enzyme, is zinc dependent, and a congenital deficiency of this enzyme is known to affect adversely cell-mediated immunity. This effect has been related to an accumulation of toxic nucleotides in lymphocytes as a result of NPase deficiency. Inasmuch as the effect of zinc deficiency on the activity of NPase and the levels of nucleotides in human lymphocytes has not been previously reported, we assayed these parameters in human subjects with zinc deficiency before and after zinc supplementation. A mild deficiency of zinc was diagnosed in those having decreased zinc in two out of three cell lineages (less than 42 micrograms in granulocytes, less than 48 micrograms in lymphocytes, and less than 1.70 microgram in platelets, per 10(10) cells). In comparison with five subjects with sufficient zinc, six subjects with zinc deficiency showed a decrease in the activity of NPase (p = 0.01), an increase in adenosine diphosphate (ADP) level (p = 0.008), a decreased adenosine triphosphate (ATP)-to-ADP ratio (p = 0.0001), and an increase in both guanosine triphosphate (GTP) (p = 0.02) and deoxyadenosine triphosphate (dGTP) (p = 0.04 in the lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

A ras-related protein is phosphorylated and translocated by agonists that increase cAMP levels in human platelets

The antigenicity of platelet proteins was assayed against various monoclonal antibodies (mAbs) that recognize specific epitopes of the ras-encoded p21 protein. mAb M90, which detects the region of p21 protein within amino acids 107-130 and inhibits its GTP-binding activity, strongly reacted with a 22-kDa protein present in the particulate fraction of human platelets. Other mAbs against ras-encoded proteins, including Y13-259, which efficiently detects ras proteins from a variety of organisms, did not recognize the platelet 22-kDa protein. Transfer of the platelet 22-kDa protein to nitrocellulose paper showed that the protein binds [alpha-32P]GTP. Moreover, preincubation of the transferred protein with mAb M90 drastically reduced its GTP-binding activity. Treatment of platelets with iloprost, a prostacyclin analog, caused (i) a time-dependent increase of a 24-kDa protein that is recognized by mAb M90 in particulate and cytosolic fractions and (ii) the gradual decrease of the 22-kDa protein from the particulate fraction. When platelets were labeled with 32P and then treated with iloprost, the 24-kDa protein was found to be phosphorylated. The 32P-labeled 24-kDa protein was specifically immunoprecipitated by mAb M90. These results suggest that appearance of the 24-kDa protein results from phosphorylation of the 22-kDa protein, which shifts its mobility to a higher molecular mass area.

Receptor-regulated formation of GTP[gamma S] with subsequent persistent Gs-protein activation in membranes of human platelets

Preincubation of human platelet membranes with the ATP analog ATP[gamma S] led to persistent adenylate cyclase activation. This stimulation was increased by copreincubation with PGE1 and obliterated by removing endogenous GDP by the NTP-regenerating system, creatine phosphate plus creatine kinase. PGE1 partially reversed the action of the regenerating system. Control formation of GTP[gamma S] from ATP[gamma S] and GDP in platelet membranes was apparently not stimulated by PGE1. In contrast, in the presence of creatine phosphate plus creatine kinase, which prevented formation of GTP[gamma S], PGE1 stimulated formation of this GTP analog, by partially reversing the action of the NTP-regenerating system. The data indicate that GTP[gamma S] can be formed by a membrane-associated nucleoside diphosphokinase from ATP[gamma S] and GDP, resulting in persistent Gs-protein activation, and that this process can be stimulated by an agonist-activated receptor.

"In situ" characterization of guanine nucleotide-binding properties of erythrocyte membranes

Unsealed membranes from human erythrocytes bind GTP and GTP analogs according to first order kinetics, a single rate constant being observed. With [35S]GTP gamma S this is 0.15 +/- 0.2 min-1. Treatment of the membranes with detergents decreases binding considerably. Scatchard plots reveal uncomplicated patterns of ligand association, with Kd values of 10.2 +/- 2.3 nM [35S]GTP gamma S, of 18.2 +/- 4.3 nM [alpha-32P]GTP and of 28.6 +/- 3.5 nM [alpha-32P]GDP, respectively. The stoichiometry with the three ligands is strictly comparable, i.e. 65 +/- 7 picomoles/mg of membrane protein. Binding of each labeled nucleotide is competitively inhibited by the other two unlabeled ligands, the inhibition constants being very close to the corresponding Kd values. Metabolic depletion and subsequent repletion of intact erythrocytes result in membrane preparations still active in guanine nucleotide binding, with unmodified Kd values. However, the stoichiometry falls to 35 picomoles/mg protein with the "depleted" erythrocyte membranes and regains higher values (50 picomoles/mg protein) with the "repleted" cell membranes. Accordingly, the "in situ" characterization of guanine nucleotide-binding properties of erythrocyte membranes seems to represent a new tool for monitoring the metabolic state of intact erythrocytes.