The manifold of vitamin B6 dependent enzymes.
Pyridoxal-5'-phosphate (vitamin B6) binding enzymes form a large superfamily that contains at least five different folds. The availability of an increasing number of known three-dimensional structures for members of this superfamily has allowed a detailed structural classification. Most progress has been made with the fold type I or aspartate aminotransferase family. (+info)
Modulation of activity and substrate specificity by modifying the backbone length of the distant interdomain loop of D-amino acid aminotransferase.
The activity and substrate specificity of D-amino acid aminotransferase (D-AAT) (EC 188.8.131.52) can be rationally modulated by replacing the loop core (P119-R120-P121) with glycine chains of different lengths: 1, 3, or 5 glycines. The mutant enzymes were much more active than the wild-type enzyme in the overall reactions between various amino acids and pyruvate. The presteady-state kinetic analyses of half-reactions revealed that the 5-glycine mutant has the highest affinity (Kd) among all mutant enzymes and the wild-type enzyme towards various amino acids except D-aspartate. The 5-glycine mutant was much more efficient as a catalyst than the wild-type enzyme because the mutant enzyme showed the highest value of specificity constant (kmax/Kd) for all amino acids except D-aspartate and D-glutamate. The kmax/Kd values of the three mutants decreased with decrease in glycine chain length for each amino acid examined. Our findings may provide a new approach to rational modulation of enzymes. (+info)
Effects of salts on the conformation and catalytic properties of d-amino acid aminotransferase.
The effects of salts on the biochemical properties of D-amino acid aminotransferase from Bacillus sp. YM-1 have been studied to elucidate both the inhibitory effects of salts on the activity and the protective effects of salts on the substrate-induced inactivation. The results from UV-visible spectroscopy studies on the reaction of the enzyme with D-serine revealed that salt significantly reduced the rate of the formation of the quinonoid intermediate and its accumulation. The kinetic and spectroscopy studies of the reaction with alpha-[(2)H]-DL-serine in different concentrations of NaCl provided evidence that the rate-limiting step was changed from the deprotonation of the external aldimine to another step(s), presumably to the hydrolysis of the ketimine. Gel filtration chromatography data in the presence of NaCl showed that the enzyme volume was reduced sharply with the increasing NaCl concentration, up to 100 mM. An additional increase of the NaCl concentration did not affect the elution volume, which suggests that the enzyme has a limited number of salt-binding groups. These results provide detailed mechanistic evidence for the way salts inhibit the catalytic activity of Damino acid aminotransferase (+info)
Phase I and pharmacokinetic trial of the proapoptotic sulindac analog CP-461 in patients with advanced cancer.
CP-461 is a member of a class of novel proapoptotic drugs that specifically inhibit cyclic GMP phosphodiesterases but not cyclooxygenase-1 or -2. CP-461 inhibits the growth of a broad range of human tumor cell lines in vitro at micromolar concentrations and selectively induces apoptosis in cancer cell lines but not normal cells. Preclinical studies revealed good oral bioavailability and no toxicity in dogs and rats at single doses up to 500 mg/kg. In a Phase I trial, 21 patients with a range of solid tumors and good performance status received CP-461 p.o. twice daily for 28 consecutive days. Cycles were repeated without a treatment-free interval. CP-461 doses ranged from 100 to 800 mg/day. Therapy was well tolerated overall, and a maximum tolerated dose was not reached. Grade 3 asymptomatic aspartate aminotransferase/alanine aminotransferase elevation in 1 patient treated at 800 mg/day was the only dose-limiting toxicity. No hematologic toxicity was noted. Peak plasma concentrations occurred between 1 and 2 h after dosing, and doses above 200 mg/day exceeded the known in vitro EC(50) (1-2 micro M) for apoptosis in cancer cells. No drug was detectable after 24 h of administration, and the terminal half-life was 6.7 h. The area under the plasma concentration-time curve was dose-proportional from 200 to 800 mg/day. Four patients exhibited disease stability after two cycles of treatment. CP-461 is minimally toxic at doses up to 800 mg/day when administered p.o. on a twice-daily schedule. (+info)
Improvement of alanine aminotransferase by administration of suplatast tosilate plus ursodeoxycholic acid in patients with resistance to ursodeoxycholic acid monotherapy on hepatitis C virus-related chronic liver disease.
OBJECTIVE: Inflammatory liver damage and viral persistence after hepatitis C virus (HCV) infection are known to be related in host immunity. Suplatast tosilate is an immunomodulator that selectively inhibits type 2 cytokine production by helper T cells. We investigated the efficacy and safety of the administration of suplatast tosilate for patients with HCV infection by examining the level of serum alanine aminotransferase (ALT) and viremia. PATIENTS AND METHODS: Thirty-eight patients who had shown resistance to ursodeoxycholic acid (UDCA) therapy (600 mg/day tid) over 6 months for HCV-related chronic liver disease were randomized into two groups and received UDCA alone (600 mg/day tid) or UDCA (600 mg/day tid) plus suplatast tosilate (300 mg/day tid) by means of sealed envelopes. RESULTS: After 24 weeks, serum ALT was decreased in the patients receiving UDCA plus suplatast tosilate, with the mean reduction being 40.2% (from 132 to 79 IU/l; p=0.001). In the patients receiving UDCA alone, ALT decreased by 8.3% (from 133 to 122 IU/l; ns). Multiple comparison of individual ALT changes showed that the UDCA plus suplatast tosilate achieved significantly greater improvement (p = 0.001). However, serum HCV RNA was unchanged in both groups. Two patients developed adverse reactions to suplatast tosilate, which resolved promptly after the discontinuation of the therapy. CONCLUSION: These findings suggest that suplatast tosilate promotes biochemical improvement in the patients with chronic hepatitis C. (+info)
Durability of HBeAg seroconversion following antiviral therapy for chronic hepatitis B: relation to type of therapy and pretreatment serum hepatitis B virus DNA and alanine aminotransferase.
BACKGROUND AND AIMS: Interferon (IFN) induced hepatitis B e antigen (HBeAg) seroconversion is durable in 80-90% of chronic hepatitis B patients. Preliminary reports on the durability of HBeAg seroconversion following lamivudine are contradictory. We investigated the durability of response following IFN, lamivudine, or IFN-lamivudine combination therapy in a meta-analysis of individual patient data. PATIENTS AND METHODS: Twenty four centres included 130 patients in total with an HBeAg seroconversion (HBeAg negative, antibodies to hepatitis B e antigen positive) at the end of antiviral therapy: 59 with lamivudine, 49 with interferon, and 22 with combination therapy. Relapse was defined as confirmed reappearance of HBeAg. RESULTS: The three year cumulative HBeAg relapse rate by the Kaplan-Meier method was 54% for lamivudine, 32% for IFN, and 23% for combination therapy (p=0.01). Cox regression analysis identified pretreatment hepatitis B virus (HBV) DNA, alanine aminotransferase (ALT), sex, and therapy as independent predictive factors of post-treatment relapse; Asian race, previous therapy, centre, and type of study were not predictive of relapse. The relative HBeAg relapse risk of lamivudine compared with IFN therapy was 4.6 and that of combination therapy to IFN therapy 0.7 (p(overall)=0.01). CONCLUSIONS: The durability of HBeAg seroconversion following lamivudine treatment was significantly lower than that following IFN or IFN-lamivudine combination therapy. The risk of relapse after HBeAg seroconversion was also related to pretreatment levels of serum ALT and HBV DNA, but independent of Asian race. (+info)
Incidence and predictors of severe liver fibrosis in human immunodeficiency virus-infected patients with chronic hepatitis C: a European collaborative study.
A study was performed in 10 European health care centers in which 914 patients coinfected with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) who had elevated serum alanine aminotransferase (ALT) levels underwent liver biopsy during the period of 1992 through 2002. Overall, the METAVIR liver fibrosis stage was F0 in 10% of patients, F1 in 33%, F2 in 22%, F3 in 22%, and F4 in 13%. Predictors of severe liver fibrosis (METAVIR stage, F3 or F4) in multivariate analysis were age of >35 years (odds ratio [OR], 2.95; 95% confidence interval [CI], 2.08-4.18), alcohol consumption of >50 g/day (OR, 1.61; 95% CI, 1.1-2.35), and CD4+ T cell count of <500 cells/mm3 (OR, 1.43; 95% CI, 1.03-1.98). Forty-six percent of patients aged >40 years had severe liver fibrosis, compared with 15% of subjects aged <30 years. The use of antiretroviral therapy was not associated with the severity of liver fibrosis. In summary, severe liver fibrosis is frequently found in HCV-HIV-coinfected patients with elevated serum ALT levels, and its severity increases significantly with age. The rate of complications due to end-stage liver disease will inevitably increase in this population, for whom anti-HCV therapy should be considered a priority. (+info)
Modest weight loss and physical activity in overweight patients with chronic liver disease results in sustained improvements in alanine aminotransferase, fasting insulin, and quality of life.
BACKGROUND AND AIM: Obesity is a risk factor for progression of fibrosis in chronic liver diseases such as non-alcoholic fatty liver disease and hepatitis C. The aim of this study was to investigate the longer term effect of weight loss on liver biochemistry, serum insulin levels, and quality of life in overweight patients with liver disease and the effect of subsequent weight maintenance or regain. PATIENTS: Thirty one patients completed a 15 month diet and exercise intervention. RESULTS: On completion of the intervention, 21 patients (68%) had achieved and maintained weight loss with a mean reduction of 9.4 (4.0)% body weight. Improvements in serum alanine aminotransferase (ALT) levels were correlated with the amount of weight loss (r = 0.35, p = 0.04). In patients who maintained weight loss, mean ALT levels at 15 months remained significantly lower than values at enrollment (p = 0.004), while in regainers (n = 10), mean ALT levels at 15 months were no different to values at enrollment (p = 0.79). Improvements in fasting serum insulin levels were also correlated with weight loss (r = 0.46, p = 0.04), and subsequent weight maintenance sustained this improvement. Quality of life was significantly improved after weight loss. Weight maintainers sustained recommended levels of physical activity and had higher fasting insulin levels (p = 0.03) at enrollment than weight regainers. CONCLUSION: In summary, these findings demonstrate that maintenance of weight loss and exercise in overweight patients with liver disease results in a sustained improvement in liver enzymes, serum insulin levels, and quality of life. Treatment of overweight patients should form an important component of the management of those with chronic liver disease. (+info)