6-[(4-bromo-2,3-dioxobutyl)thio]-6-deaminoadenosine 5'-monophosphate and 5'-diphosphate: new affinity labels for purine nucleotide sites in proteins

Two new adenine nucleotide analogues have been synthesized and characterized: 6-[(4-bromo-2,3-dioxobutyl)thio]-6-deaminoadenosine 5'-monophosphate and 5'-diphosphate. The bromoketo and dioxobutyl moieties have the ability to react with the nucleophilic side chains of several amino acids, as well as with arginine. 6-[(4-Bromo-2,3-dioxobutyl)thio]-6-deaminoadenosine 5'-monophosphate reacts irreversibly with rabbit muscle pyruvate kinase, causing inactivation. Addition of ADP to the reaction mixture (in the presence of Mg2+) markedly decreases the rate of inactivation. Pig heart NAD-dependent isocitrate dehydrogenase is allosterically activated by ADP, which reduces the Km for isocitrate. 6-[(4-Bromo-2,3-dioxobutyl)thio]-6-deaminoadenosine 5'-diphosphate reacts irreversibly with isocitrate dehydrogenase, causing, rapidly, a loss of the ability of ADP to increase the initial velocity of assays conducted at low isocitrate concentrations and, more slowly, inactivation. Addition of ADP to the reaction mixture (in the presence of Mn2+) protects this enzyme against the loss of allosteric activation. It is proposed that the 6-[(4-bromo-2,3-dioxobutyl)thio]-6-deaminoadenine nucleotides react at the active site of pyruvate kinase and at the ADP activating site of isocitrate dehydrogenase and that these compounds may have general applicability as affinity labels of catalytic and regulatory adenine nucleotide sites in proteins.

Creatinine X--potential nonrenal elimination of endogenous creatinine in humans and its clinical significance

From an analysis of the data in the literature for creatinine renal clearance and steady-state serum level and published equations, we estimated a wide range (1.4-76.3 ml/min) of nonrenal clearances of endogenous creatinine. Nonrenal clearance might contribute 0-34% of the total body clearance in patients with normal renal function. This paper discusses the clinical significance of the potential overestimation of renal function by using published nomograms or equations (derived from a direct inverse relationship between the creatinine clearance and steady-state level or the assumption of nonexistence of nonrenal elimination of creatinine) for indirect estimation of creatinine clearances from serum creatinine levels.

Pharmacokinetics of chlorpheniramine after intravenous and oral administration in normal adults

Plasma and urinary levels of chlorpheniramine (CPM) and its 2 demethylated metabolites were measured by HPLC after i.v. and oral dosing. In 5 mg (maleate) i.v. bolus studies in 2 subjects, plasma CPM levels were fitted to triexponential equations with terminal half-lives (t 1/1) of 23 and 22 h and area of 3.6 and 3.21/kg, respectively. Intravenous data predicted hepatic blood extraction ratios for the 2 subjects to be 0.06 and 0,07, respectively. Absolute bioavailability from oral solution (10 mg) was 59 and 34%, and from tablets (8 mg) 44 and 25%, respectively, indicating extensive gut first-pass metabolism. Mean t 1/2 from 7 oral fasting studies in 5 subjects was 28 h (19-43 h). Mean absorption lag time was 0.7 h (0.4-1.3 h), and mean peak time was 2.8 h (2-4 h). In 2 subjects, 6 mg solutions were given every 12 h for 9 doses; good correlation between single and multiple dose kinetics was found. Significant accumulation was demonstrated in simulation studies with frequent daily dosing. Estimated accumulation ratios vary from 4.1 to 9.4 (mean 6.5). The t 1/2 from urinary data (collected for 12 days) was consistent with plasma data. The above results suggest the need to reexamine the current practice of frequent daily dosing and the use of sustained or controlled release dosage forms of this drug. The possible cause of reduced plasma clearance of CPM in renal patients is discussed.

Oral absorption and presystemic first-pass effect of chlorpheniramine in rabbits

The oral absolute bioavailabilities of chloropheniramine (CPM) in four rabbits (New Zealand White, male, mean wt. 3.71 kg), averaged 0.06 +/- 0.03, 0.11 +/- 0.08, and 0.09 +/- 0.01 following a 3, 10.5, and 21 mg/kg dose, respectively. The individual bioavailability data and the AUC of one of the demethylated metabolites, desdimethyl CPM (DDCPM) obtained following different doses suggested the existence of saturable presystemic elimination. Two rabbits received an additional 10.5 mg/kg dose of CPM through portal vein infusion. Based on the oral, intraportal vein and i.v. studies, the mean extraction ratios of gut and the liver calculated for these two rabbits averaged 0.58 and 0.76, respectively. The latter value agreed well with the estimated hepatic extraction ratio from the in vitro liver homogenate study (0.89) or from the i.v. studies (0.83). The existence prehepatic first-pass effect observed in the present study was consistent with similar findings in humans and dogs.

Midpoint back-extrapolation method for the rapid estimation of drugs' volume of distribution and dosage adjustment exhibiting multicompartmental characteristics

A midpoint back-extrapolation method assuming an instantaneous drug input at the midpoint of intravenous infusion based on a linear one-compartment open model is used to estimate the apparent volume of distribution and total body clearance of drugs exhibiting multicompartmental characteristics. Error analyses indicate that the method is clinically satisfactory for drugs not showing a strong multicompartmental property. For drugs exhibiting extensive multicompartmental properties, proper corrections based on the average literature data can be made. This method requires only two to three blood samples for the estimation of clinically useful pharmacokinetic parameters.

Triexponential disposition pharmacokinetics of gentamicin in rabbits

Using a sensitive high-pressure liquid chromatographic method for the determination of gentamicin, plasma-level profiles of gentamicin were found to fit to a triexponential equation in 3 out of 4 rabbits studied after bolus intravenous administration by the application of the Minimum Akaike's Information Criterion Estimation (MAICE) method. This is different from the monoexponential or biexponential decay of gentamicin often reported in humans. Volumes of distribution of central compartment and at the steady-state in rabbits were similar to those reported in humans. Extensive distribution and tissue binding of gentamicin in rabbits were indicated by their high Vdarea, about 3.9 l/kg. It is proposed that rabbits may serve as a useful model for studying the mechanism and prediction of renal toxicity of gentamicin in patients.

Identification of a calcium-binding protein as a calcium-dependent regulator of brain adenylate cyclase

An activating factor of adenylate cyclase (EC 4.6.1.1) HAS BEEN OBTAINED FROM DETERGENT-DISPERSED PREPARATIONS OF PORCINE CEREBRAL CORTEX BY COLUMN CHROMATOGRAPHY ON ECTEOLA-cellulose. The factor was identified by acrylamide gel electrophoresis and by enzyme activation studies as the Ca2+-binding protein that regulates the activity of a brain cyclic nucleotide phosphodiesterase. This Ca2+-binding protein confers a Ca2+-dependent activation upon the adenylate cyclase, which is reversed by the subsequent addition of egta in excess of the free Ca2+. It is proposed that this Ca2+-dependent regulator controls enzymatic activities responsible for the synthesis of adenosine 3':5'-monophosphate and for the hydrolysis of guanosine 3':5'-monophosphate.

Gastric teratoma in infancy: report of a case and review of world literature

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