Hepatic modeling of metabolite kinetics in sequential and parallel pathways: salicylamide and gentisamide metabolism in perfused rat liver

Previous data on salicylamide (SAM) metabolism in the perfused rat liver had indicated that SAM was metabolized by three parallel (competing) pathways: sulfation, glucuronidation, and hydroxylation, whereas sequential metabolism of the hydroxylated metabolite, gentisamide (GAM), was solely via 5-glucuronidation to form GAM-5G. However, under comparable conditions, preformed GAM formed mainly two monosulfate conjugates at the 2- and 5-positions (GAM-2S and GAM-5S); 5-glucuronidation was a minor pathway. In the present study, the techniques of normal (N) and retrograde (R) rat liver perfusion with SAM and mathematic modeling on SAM and GAM metabolism were used to explore the role of enzymic distributions in determining the dissimilar fates of GAM, as a generated metabolite of SAM or as preformed GAM. Changes in the steady-state extraction ratio of SAM (E) and metabolite formation ratios between N and R perfusions were used as indices of the uneven distribution of enzyme activities. Two SAM concentrations (134 and 295 microM) were used for single-pass perfusion: the lower SAM concentration exceeded the apparent Km for SAM sulfation but was less than those for SAM glucuronidation and hydroxylation; the higher concentration exceeded the apparent Km's for SAM sulfation and glucuronidation but was less than the Km for hydroxylations. Simulation of SAM metabolism data was carried out with various enzyme distribution patterns and extended to include GAM metabolism. At both input concentrations, E was high (0.94 at 134 microM and 0.7 at 295 microM) and unchanged during N and R, with SAM-sulfate (SAM-S) as the major metabolite and GAM-5G as the only detectable metabolite of GAM. Saturation of SAM sulfation occurred at the higher input SAM concentration as shown by a decrease in E and a proportionally less increase in sulfation rates and proportionally more than expected increases in SAM hydroxylation and glucuronidation rates. At both SAM concentrations, the steady-state ratio of metabolite formation rates for SAM-S/SAM-G decreased when flow direction changed from N to R. An insignificant decrease in SAM-S/SAM-OH was observed at the low input SAM concentration, due to the small amount of SAM-OH formed and hence large variation in the ratio among the preparations, whereas at the high input SAM concentration, the decrease in SAM-S/SAM-OH with a change in flow direction from N to R was evident. The metabolite formation ratio, SAM-G/SAM-OH, however, was unchanged at both input concentrations and flow directions.(ABSTRACT TRUNCATED AT 400 WORDS)

Two-dimensional programmable optical neural network

A 2-D hybrid optical neural network using a high resolution video monitor as a programmable associative memory is proposed. Experiments and computer simulations of the system have been conducted. The high resolution and large dynamic range of the video monitor enable us to implement a hybrid neural network with more neurons and more accurate operation. The system operates in a high speed asynchronous mode due to the parallel feedback loop. The programmability of the system permits the use of orthogonal projection and multilevel recognition algorithms to increase the robustness and storage capacity of the network.

First-pass metabolism of salicylamide. Studies in the once-through vascularly perfused rat intestine-liver preparation

Salicylamide (SAM) metabolism was studied in a once-through in situ perfused rat intestine-liver preparation in a manner which mimicked the first-pass effect. SAM (40 or 200 microM) was delivered into the intestine via the superior mesenteric artery at a flow rate of 7.5 ml/min. The intestine venous outflow into the portal vein and the hepatic arterial flow (2.5 ml/min; without drug) served as dual inflows into the liver. The steady state intestinal and hepatic extraction ratios were 0.262 +/- 0.055 and 0.992 +/- 0.014, respectively, at 40 microM, and 0.206 +/- 0.035 and 0.638 +/- 0.117, respectively, at 200 microM. SAM glucuronide was found to be the only metabolite formed by the intestine at both doses. Less than 3% of the dose was secreted into the intestinal lumen, with SAM glucuronide and SAM as the major and minor components, respectively. Hepatic metabolism of SAM, however, revealed SAM sulfation as the predominant pathway, while glucuronidation and hydroxylation were minor metabolic pathways. About 6% of the dose was excreted into bile, mostly as SAM and gentisamide glucuronides. The interrelationship between the intestine and liver clearances was also examined by mass balance considerations and simulation of data. The total rate of elimination of substrate across the two organs is the sum of the rates of metabolism by each organ. However, the overall effective extraction ratio and, hence, the clearance, are less than the sum of the individual extraction ratios and organ clearances, respectively. Our results showed that intestinal metabolism regulated the available substrate for hepatic elimination, and hence modified the contribution of hepatic metabolism in the overall first-pass effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Viability of the vascularly perfused, recirculating rat intestine and intestine-liver preparations

Function and stability of vascularly perfused, recirculating in situ rat intestine (I) and intestine-liver (IL) preparations were evaluated in fasted and nonfasted rats because these techniques may be readily applied in drug metabolism studies. The rat intestine was perfused with blood medium (7.5 ml/min) via the superior mesenteric artery, with the venous outflow draining into the portal vein, which, together with hepatic arterial flow (2.5 ml/min), constituted the total blood flow (10 ml/min) to the liver. Maintenance of intestinal membrane integrity was observed. Rapid [14C]glucose absorption against a concentration gradient and a lack of [3H]-polyethylene glycol 4000 (PEG 4000, less than 4%) and Evans blue absorption by the recirculating I and IL preparations resulted after bolus injections of these markers into the pyloric end of the duodenum. Other indexes that revealed stable intestinal and liver functions were the following: preservation of reservoir perfusate volume, constancy in perfusion pressure, bile flow, and hemoglobin concentrations, evidence of intestinal glucose utilization and liver glucose production, and a lack of significant leakage of serum glutamic oxalic transaminase. The intestine and liver consumed oxygen at relatively constant rates, but the consumption rates for the fasted tissues (I or L) were significantly higher than those for nonfasted tissues. These results indicate that the vascularly perfused I and IL preparations were maintained in a viable and stable state for a 2-h perfusion period.

[The fluorometric method for analysis of some acid drugs]

By using salicylate as a working drug, pyronine was chosen from 31 dyes to form drug-dye complex. In Na2HPO4 solution, salicylate reacts with pyronine to form a complex which is soluble in chloroform. Pyronine fluoresces strongly at lambda ex 542 nm and lambda cm 566 nm and the intensity of pyronine in complex is proportional to the amount of salicylate in the complex with detection limit of 5 ng/ml. By using this method, suberogorgin, flufenamic acid, mechlofenamic acid, mefenamic acid, sodium tauroglycocholate and trichloroacetic acid may be determined with the sensitivity of 10 approximately 50 ng/ml. Salicylate in blood was determined by this method with the sensitivity of 10 ng/ml blood. Good recovery and precision were obtained.

Primary, secondary, and tertiary metabolite kinetics

Because of the propensity of nascently formed metabolites towards sequential metabolism within formation organs, theoretical and experimental treatments that achieve mass conservation must recognize the various sources contributing to primary, secondary, and tertiary metabolite formation. A simple one-compartment open model, with first-order conditions and the liver as the only organ of drug disappearance and metabolite formation, was used to illustrate the metabolism of a drug to its primary, secondary, and tertiary metabolites, encompassing the cascading effects of sequential metabolism. The concentration-time profiles of the drug and metabolites were examined for two routes of drug administration, oral and intravenous. Formation of the primary metabolite from drug in the gut lumen, with or without further absorption, and metabolite formation arising from first-pass metabolism of the drug and the primary metabolite during oral absorption were considered. Mass balance equations, incorporating modifications of the various absorption and conversion rate constants, were integrated to provide the explicit solutions. Simulations, with and without consideration of the sources of metabolite formation other than from its immediate precursor, were used to illustrate the expected differences in circulating metabolite concentrations. However, a simple relationship between the area under the curve of any metabolite, M, or [AUC (m)], its clearance [CL(m)], and route of drug administration was found. The drug dose, route, fraction absorbed into the portal circulation, Fabs, fraction available of drug from the liver, F, availabilities of the metabolites F(m) from formation organs, and CL(m) are determinants of the AUC(m)'s. After iv drug dosing, the area of any intermediary metabolites is determined by the iv drug dose divided by the (CL(m)/F(m] of that metabolite. When a terminal metabolite is not metabolized, its area under the curve becomes the iv dose of drug divided by the clearance of the terminal metabolite since the available fraction for this metabolite is unity. Similarly, after oral drug administration, when loss of drug in the gut lumen does not contribute to the appearance of metabolites systematically, the general solution for AUC(m) is the product of Fabs and oral drug dose divided by [CL(m)/F(m)]. A comparison of the area ratios of any metabolite after po and iv drug dosing, therefore, furnishes Fabs. When this fraction is divided into the overall systemic availability or Fsys, the drug availability from the first-pass organs, F, may be found.(ABSTRACT TRUNCATED AT 400 WORDS)

Preparation and biodistribution of [125I]IBZM: a potential CNS D-2 dopamine receptor imaging agent

A new CNS D-2 dopamine receptor imaging agent [125I]IBZM, (S)-3-[125I]-iodo-N-[(1-ethyl-2-pyrrolidinyl)] methyl-2-hydroxy-6-methoxybenzamide, was prepared by either an exchange reaction or by the chloramine-T method. After an i.v. injection, the agent easily passed through the blood-brain barrier and localized in the rat brain. At 2, 15, 30 and 60 min after the injection, the brain uptake was 2.9, 2.3, 1.8 and 0.7% dose/organ, respectively. Regional uptake ratio of striatum/cerebellum (target to nontarget ratio) increased from 1.4 at 30 s to 10.3 at 2 h after the i.v. injection. Digital autoradiography of rat brain sections showed high regional uptake in the caudate putamen and accumbens nucleus, areas known to have a high concentration of the D-2 dopamine receptor. The specific uptake at the D-2 dopamine receptor site was blocked by pretreatment with spiperone, a selective D-2 antagonist. When labeled with 123I (t1/2 = 13 h, 159 keV), [123I]IBZM may be useful for imaging the CNS D-2 dopamine receptor.

Chromosome sublocalization of a cDNA for human DNA polymerase-beta to 8p11----p12

We have localized a cDNA fragment that codes for human DNA polymerase-beta. Using somatic cell and in situ hybridization techniques, this cDNA was cloned by screening a human KM-3 cell cDNA library in lambda gt 11 for expression of fused beta-galactosidase-human DNA polymerase-beta proteins. We have mapped this human polymerase-beta gene to the short arm of chromosome 8 in the subregion 8p11----p12.

High-performance liquid chromatographic method for the quantitation of salicylamide and its metabolites in biological fluids

A high-performance liquid chromatographic (HPLC) assay is described for the determination of salicylamide (SAM) and its metabolites in biological fluids obtained from an in situ rat liver preparation and rat in vivo. SAM and its six metabolites, salicylamide sulphate, salicylamide glucuronide, gentisamide (GAM), gentisamide 2-sulphate, gentisamide 5-sulphate and gentisamide 5-glucuronide, were separated on a mu Bondapak C18 column with 0.085 M potassium dihydrogenphosphate pH 3.35, as mobile phase and by using a flow gradient. Enriched recovery of SAM and GAM from blood was achieved by extraction followed by a second HPLC procedure with a mobile phase consisting of acetic acid and methanol. Furthermore, the reproducibility and the stability of the samples under assay conditions were investigated.

cDNA sequences of two apolipoproteins from lamprey

The messages for two small but abundant apolipoproteins found in lamprey blood plasma were cloned with the aid of oligonucleotide probes based on amino-terminal sequences. In both cases, numerous clones were identified in a lamprey liver cDNA library, consistent with the great abundance of these proteins in lamprey blood. One of the cDNAs (LAL1) has a coding region of 105 amino acids that corresponds to a 21-residue signal peptide, a putative 8-residue propeptide, and the 76-residue mature protein found in blood. The other cDNA (LAL2) codes for a total of 191 residues, the first 23 of which constitute a signal peptide. The two proteins, which occur in the "high-density lipoprotein fraction" of ultracentrifuged plasma, have amino acid compositions similar to those of apolipoproteins found in mammalian blood; computer analysis indicates that the sequences are largely helix-permissive. When the sequences were searched against an amino acid sequence data base, rat apolipoprotein IV was the best matching candidate in both cases. Although a reasonable alignment can be made with that sequence and LAL1, definitive assignment of the two lamprey proteins to typical mammalian classes cannot be made at this point.