Simulation for population analysis of Michaelis-Menten elimination kinetics

A simulation study was conducted to compare the cost and performance of various models for population analysis of the steady state pharmacokinetic data arising from a one-compartment model with Michaelis-Menten elimination. The usual Michaelis-Menten model (MM) and its variants provide no estimate of the volume of distribution, and generally give poor estimates of the maximal elimination rate and the Michaelis-Menten constant. The exact solution to the Michaelis-Menten differential equation (TRUE) requires a precise analysis method designed for estimation of population pharmacokinetic parameters (the first-order conditional estimation method) and also considerable computational time to estimate population mean parameters accurately. The one-compartment model with dose-dependent clearance (DDCL), in conjunction with the first-order conditional estimation or Laplacian method, ran approximately 20-fold faster than TRUE and gave accurate population mean parameters for a drug having a long biological half-life relative to the dosing interval. These findings suggest that the well-known MM and its variants should be used carefully for the analysis of blood concentrations of a drug with Michaelis-Menten elimination kinetics, and that TRUE, in conjunction with a precise analysis method, should be considered for estimating population pharmacokinetic parameters. In addition, DDCL is a promising alternative to TRUE with respect to computation time, when the dosing interval is short relative to the biological half-life of a drug. This work was supported in part by the Epilepsy Research Foundation, the Nakatomi Foundation, and a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture of Japan.     

AUGMENTED ENDOGENOUS NITRIC OXIDE PRODUCTION IN PARTIAL PORTAL VEIN-LIGATED RATS

1. Endothelium-derived nitric oxide (NO) is a potent vasodilator. Because the body oxidizes it to nitrate ions, NO₃-, measurement of the serum concentration and the urinary excretion of NO₃- may be an index for endogenous NO. We investigated the role of NO on hyperdynamic circulation in cirrhotic and partial portal vein-ligated rats by measuring NO₃. 2. Liver cirrhosis was induced by administration of thioacetamide. Systemic and splanchnic haemodynamics and splenic-systemic shunting were determined by tracer microspheres. The concentration of NO₃- was measured by using high-performance liquid chromatography with an anion-column. 3. We found that systemic and splanchnic hyperdynamic circulation existed to almost the same extent in cirrhotic and in portal vein-ligated rats as compared to the controls and sham-operated rats, respectively. Splenic-systemic shunting was markedly greater in portal vein-ligated rats than in cirrhotic rats. 4. Serum NO₃- levels and urinary excretion of NO₃- in cirrhotic rats tended to increase as compared to the controls. On the other hand, the levels in portal vein-ligated rats were significantly increased as compared to those of the sham-operated rats, and were significantly and negatively correlated to the splanchnic arterial resistance and total vascular resistance. The amount of urinary excretion of NO₃- significantly correlated to splenic-systemic shunting (r = 0.61, P<0.05) only in portal vein-ligated rats. 5. We suggest that these high levels of NO₃- in portal vein-ligated rats relate to the extensive formation of porto-collateral vasculature or acute changes in systemic and splanchnic haemodynamics due to portal vein-ligation.     

Hemodynamic and volume changes by recombinant human erythropoietin (rHuEPO) in the treatment of anemic hemodialysis patients

Hemodynamic and volume changes induced by recombinant human erythropoietin (rHuEPO) treatment were investigated in 12 chronic hemodialysis patients with refractory anemia. After rHuEPO administration for 49 to 151 days, hematocrit (Ht) significantly improved from 19.4 +/- 2.3 to 30.1 +/- 1.1% (Mean +/- SD). Mean blood pressure (MBP) increased slightly but significantly from 78.8 +/- 13.2 to 88.9 +/- 16.9 mmHg. Hemodynamically, total peripheral resistance index (TPRI) increased significantly from 1,444 +/- 367 to 2,146 +/- 470 dynes.sec.cm-5.m2, while cardiac index (CI) decreased significantly from 4.49 +/- 0.85 to 3.37 +/- 0.60 l/min/m2. Both pulse rate (PR) and stroke volume index (SVI) also decreased significantly, but blood volume (BV) remained unchanged. Plasma renin activity and plasma norepinephrine decreased significantly. There were positive correlations between the change of MBP and that of CI, and between the change in CI and that of BV, respectively (p less than 0.05 or less). In conclusion the improvement of anemia using rHuEPO is hemodynamically associated with an increase in TPRI and a decrease in CI as well. Blood pressure elevation seems to be caused by an inappropriately minor reduction of CI. The contribution of humoral factors is not suggested.     

Differential biologic effects resulting from bimodal binding of recombinant human tumor necrosis factor to myeloid leukemia cells

Human recombinant tumor necrosis factor (rTNF) bound to ML-1 and HL-60 human myeloid leukemia cells in a bimodal manner. Saturable high- affinity binding was maximal at approximately 3 nmol/L rTNF, whereas saturable low-affinity binding reached its maximum at approximately 30 nmol/L. As analyzed by computer program, the observed data fit a two- receptor site model, with p less than .05. High-affinity binding concentrations of rTNF caused the differentiation of both cell lines, whereas low-affinity binding concentrations abolished this effect in a concentration-dependent manner. Thus, the type of biologic response elicited with rTNF in these cells is a function of the concentration at which the factor is applied. If generally applicable, this bimodal effect may require consideration when rTNF is to be used therapeutically.     

Intrahepatic Delivery of Glutathione by Conjugation to Dextran

Glutathione was covalently attached to dextran (T-40) by the CNBr activation method. The compound obtained was a water-soluble powder containing 10 (w/w%) glutathione, which was gradually released from the conjugate in aqueous media. Mice depleted of glutathione by treatment with buthionine sulfoximine, a potent inhibitor of -glutamylcysteine synthetase, exhibited a significant increase in hepatic glutathione level after intravenous injection of the conjugate. In mice given a lethal dose of acetaminophen, the survival rate increased progressively with coadministration of the conjugate, whereas little improvement was found when free glutathione was given. The conjugate maintained the serum transaminase activities at lower level after acetaminophen administration. These findings suggest that the dextran conjugate of glutathione is transported into hepatic cells and is intracellulary hydrolyzed to free form, which protects mice from hepatotoxicity due to acetaminophen.     

Differential diagnosis of adrenal masses by chemical shift and dynamic gadolinium enhanced MR imaging

Chemical shift MRI is widely used for identifying adenomas, but it is not a perfect method. We determined whether combined dynamic MRI methods can lead to improved diagnostic accuracy. Fifty-seven adrenal masses were examined by chemical shift and dynamic MR imaging using 2 MR systems. The masses included 38 adenomas and 19 non-adenomas. In chemical shift MRI studies, the signal intensity index (SI) was calculated, and the lesions classified into 5 types in the dynamic MRI studies. Of the 38 adenomas studied, 37 had an SI greater than 0. In the dynamic MRI, 34 of 38 adenomas showed a benign pattern (type 1). If the SI for the adenomas in the chemical shift MRI was considered to be greater than 0, the positive predictive value was 0.9, and the negative predictive value was 0.94 and kappa = 0.79. If type 1 was considered to indicate adenomas in the dynamic MRI, the corresponding values were 0.94, 0.81 and kappa = 0.77 respectively. The results obtained when the 2 methods were combined were 1, 0.95 and kappa = 0.96 respectively. The chemical shift MRI was found to be useful for identifying adenomas in most cases. If the adrenal mass had a low SI (0 < SI < 5), dynamic MRI was also found to be helpful for making a differential diagnosis.     

A population cytogenetic study of a common fragile site, fra(3)(p14), in a healthy population

A population survey of a common folate-sensitive fragile site, fra(3)(p14), was carried out on PHA-stimulated peripheral lymphocytes of 1,078 healthy subjects. Fra(3)(p14) was expressed more frequently in the younger than in the older, and in males than in females. It also showed some seasonal variation. The age difference of the expression frequency was also observed by aphidicolin treatment. A positive correlation of the expression frequency was found, though not so strongly, between both culture conditions of folate deprivation and aphidicolin treatment, These findings suggest that the inter-individual variation in the expressivity of common fragile sites is not only ascribable to chance, but to some physiological conditions of blood donors such as response rate of lymphocyte to PHA stimulation and blood concentration of folic acid.     

Amino acid residues conferring the nucleotide binding properties of N-acetyl-D-glucosamine 2-epimerase (renin binding protein)

Our recent studies have demonstrated that the middle domain of N-acetyl-D-glucosamine (GlcNAc) 2-epimerase participates in the specificity for and binding of nucleotides. To identify the residue conferring nucleotide binding, amino acid substitutions were introduced in the human and rat GlcNAc 2-epimerases. The mutational analyses indicate that residue 171 of GlcNAc 2-epimerase is critical for the nucleotide binding of GlcNAc 2-epimerase.