LECT2 functions as a hepatokine that links obesity to skeletal muscle insulin resistance

Recent articles have reported an association between fatty liver disease and systemic insulin resistance in humans, but the causal relationship remains unclear. The liver may contribute to muscle insulin resistance by releasing secretory proteins called hepatokines. Here we demonstrate that leukocyte cell-derived chemotaxin 2 (LECT2), an energy-sensing hepatokine, is a link between obesity and skeletal muscle insulin resistance. Circulating LECT2 positively correlated with the severity of both obesity and insulin resistance in humans. LECT2 expression was negatively regulated by starvation-sensing kinase adenosine monophosphate-activated protein kinase in H4IIEC hepatocytes. Genetic deletion of LECT2 in mice increased insulin sensitivity in the skeletal muscle. Treatment with recombinant LECT2 protein impaired insulin signaling via phosphorylation of Jun NH2-terminal kinase in C2C12 myocytes. These results demonstrate the involvement of LECT2 in glucose metabolism and suggest that LECT2 may be a therapeutic target for obesity-associated insulin resistance.

Quantitative structure-interaction relationship analysis of 1,4-dihydropyridine drugs in concomitant administration with grapefruit juice

Quantitative structure-interaction relationship (QSIR) analyses of 1,4-dihydropyridine drugs were performed on grapefruit juice interaction potentials to characterize the interaction and evaluate drugs not yet tested in clinical research. AUC ratios of drugs with and without grapefruit juice ingestion were estimated as grapefruit juice interaction potentials from clinical studies on dihydropyridine drugs such as amlodipine, azelnidipine, benidipine, cilnidipine, felodipine, manidipine, nicardipine, nifedipine, nimodipine, nisoldipine, and pranidipine. The minimal energy conformation in each dihydropyridine drug was searched for using Merck Molecular Force Field (MMFFaq), and then geometry optimization was performed by density-functional-theory (DFT) calculation (B3LYP/6-31G**). The geometric, electronic, and physicochemical features including molecular size, dipole moment, total energy, HOMO/LUMO energies, and logP values were then obtained. Dragon descriptors were also calculated by optimized 3D-structures. The relation between the potentials and over 1000 of the molecular properties was investigated using statistical techniques including partial least squares analysis with genetic algorithm (GA-PLS) to a variable subset selection. Some PLS regression equations including logP values and dragon descriptors as explanatory variables were constructed in which the maximal contribution coefficient was 94%. These models could be applied to estimate the interaction potentials of other dihydropyridine drugs that have gone unreported in interactions with drugs such as aranidipine, barnidipine, clevidipine, lemildipine, lercanidipine, niguldipine, niludipine, and nilvadipine. In the assessment of major dihydropyridines, amlodipine was found to be the safest drug to avoid interactions among the drugs investigated in the present study.

Effects of clofibric acid on the biliary excretion of benoxaprofen glucuronide and taurine conjugate in rats

Benoxaprofen (BOP) is a 2-methyl propionic acid derivative with anti-inflammatory activity. BOP has an asymmetric carbon, and receives chiral inversion from R to S in vivo. BOP is metabolized to glucuronide (BOP-G) and taurine conjugate (BOP-T). The configuration of BOP-G is mainly S, and that of BOP-T is R. Chiral inversion of R to S of the propionic acid moiety and amino acid conjugation of carboxyl compounds proceed via an acyl CoA intermediate. It is known that fibrates, used in hyperlipidemia, induce acyl CoA synthetase and increase CoA concentration. We administered racemic BOP (10 mg/kg body weight) to rats (CFA+) pre-administered clofibric acid (CFA, 280 mg/kg/day), and studied BOP, BOP-G, and BOP-T enantiomer concentrations in plasma and bile up to 12 h after administration. The findings were compared with those in rats (CFA-) that had not received CFA. Furthermore, we studied the amounts of BOP-G enantiomer produced by glucuronidation in vitro using microsomes pretreated with CFA. The amounts of (S)-BOP-G in CFA+ rats were 2.7-fold larger than that in CFA- rats. Although (R)-BOP-T was excreted in CFA- rats, BOP-T could not be detected in CFA+ rats. Plasma clearance values of racemic BOP and (S)-BOP in CFA+ rats were 5-fold and 6-fold larger than those in CFA- rats, respectively. (S)-BOP-G formation activities were higher than (R)-BOP-G formation activities in both CFA+and CFA- microsomes. These findings suggest that CFA increases biliary excretion of (S)-BOP-G and facilitates plasma elimination of BOP, and further suggests that CFA predominantly induces chiral inversion to S rather than metabolic reaction to (R)-BOP-T, resulting in an increase of (S)-BOP-G.

Construction of a model to estimate the CYP3A inhibitory effect of grapefruit juice

Grapefruit juice (GFJ) is known to affect the pharmacokinetics of a variety of drugs administered concomitantly and this is due to inhibition of intestinal CYP3A, a barrier protein for drug absorption. Some compounds such as furanocoumarin derivatives have been reported as inhibitors of the enzyme. On the other hand, inhibitory potentials of GFJ on CYP3A-oxidation activities differ widely between brands of juices. Information on the percentage contributed by ingredients in GFJ is also limited. Therefore, construction of prediction models for the CYP3A inhibitory potentials of GFJ brands was attempted by using concentrations of ingredients in GFJ. Concentrations of bergaptol, bergamottin, 6', 7'-dihydroxybergamottin, naringin, and naringenin in 23 kinds of GFJ were determined with high-performance liquid chromatography (HPLC). Furthermore, inhibitory effects on CYP3A activity were measured based on the initial rate for testosterone 6beta-hydroxylation in the presence of each GFJ. Results of multi-regression analyses between the ingredients and the enzymatic inhibitory effects revealed that concentrations of bergamottin, 6',7'-dihydroxybergamottin, and naringin were significant variables for CYP3A inhibition of GFJ. According to the standard partial regression coefficient for each explanatory variable, bergamottin and 6',7'-dihydroxybergamottin are the most important factors for inhibition. The multiple correlation coefficient (R) and the multiple correlation coefficient with leave-one-out cross validation (Q) of the model equation were 0.94 and 0.91, respectively. These results suggest that the concentrations of ingredients can explain most variances of inhibitory effects among brands. This model may be a useful method for the prediction of the GFJ interaction potential.

Identification of the UDP-glucuronosyltransferase responsible for bucolome N-glucuronide formation in rats

Bucolome N-glucuronide (BCP-NG), a major metabolite of bucolome (BCP), is the first unique N-glucuronide of barbituric acid derivatives to be reported. The purpose of the present study was to identify the UGT isoform(s) responsible for BCP-NG formation in rats. A pharmacokinetic study of BCP and the biliary excretion of BCP-NG was carried out in Wistar rats pretreated with phenobarbital (PB) (PB-pretreated rats), and the results were compared with those of Wistar rats not pretreated with PB (untreated rats). BCP N-glucuronidation activities were studied using hepatic microsomes prepared from Wistar rats pretreated with PB (primarily induces UGT1A1, 1A6 and 2B1) or with clofibric acid (CF, primarily induces UGT1A1 and 1A6), and from Gunn rats (deficiency of UGT1A family), and the results were compared with those of untreated rat microsomes.The plasma elimination clearance value of BCP in PB-pretreated rats was approximately 1.4 times greater than that of untreated rats. The cumulative amount (20.4 +/- 5.9 % of dose) of BCP-NG excreted in PB-pretreated rat bile was approximately 1.5-fold higher than that (13.4 +/- 2.5% of dose) in untreated rat bile, and BCP-NG (5.9 +/- 3.0%) and BCP (3.0 +/- 2.6%) excreted in PB-pretreated rat urine were approximately 3.0- and 1.8-fold higher than those in untreated rat urine (BCP-NG: 2.0 +/- 1.4%; BCP: 1.7 +/- 1.3%), respectively.BCP N-glucuronidation activities in PB- and CF-pretreated microsomes were approximately 1.5- and 1.6-fold higher than in untreated microsomes, respectively. BCP N-glucuronidation activity in the microsomes of Gunn rats was markedly reduced by approximately 8.5% in untreated rat microsomes. The results suggest that UGT 1A1 is primarily responsible for BCP N-glucuronide formation in rats.

Publication bias on clinical studies of pharmacokinetic interactions between felodipine and grapefruit juice

Plasma concentrations of a variety of drugs are known to be increased by concomitant administration of grapefruit juice (GFJ) when the drugs are administered orally. Dihydropyridine Ca channel blockers, that form one of the major categories of antihypertensive, have been studied for interactions for the longest time in research history. Especially, felodipine has been the most studied dihydropyridine drug. Although a lot of clinical research has been performed on the pharmacokinetic variations of felodipine, there has been no adequate systematic study. Therefore, publications related to felodipine-GFJ interactions were integrated and analyzed with statistical procedures of meta-analysis to characterize these clinical studies. Furthermore, funnel plots were created to validate publication bias in the data. Integration of AUC values on GFJ-administered and control groups in 12 publications revealed that felodipine is apparently affected by interaction. However, publication bias was observed in the funnel plots, and null hypothesis of no bias was rejected by Begg's test. These findings suggest that the pharmacokinetic interactions with GFJ might be overrated in the fundamental trial stage.

Prediction models for feverishness developed during interferon therapy of chronic hepatitis C patients

Pegylated interferon (peginterferon) and ribavirin combination therapy is used extensively for therapy of chronic hepatitis C. Most patients that receive this therapy are known to develop influenza-like symptoms with fever and headache. Therefore, we attempted to construct a multiple-regression model to predict the intensity of feverishness from the profiles of such patients. A retrospective survey of the medical charts of patients with chronic hepatitis C that have been on peginterferon-alpha-2b and ribavirin combination therapy was performed. Body temperatures of patients at 8.5 h after receiving interferon injection on day one of therapy were the objective variables. Patients' profiles such as sex, age, and blood test results before the injection were defined as explanatory variables. Genetic algorism with leave-one-out cross-validation as selection pressure was applied in the selection of variables. The final model for prediction was determined by bootstrap validation. As a result, a significant multiple-regression model including sex, BUN, and leukocyte count as descriptors was constructed. The prediction of patients with severe fever in the model equation is of some help regarding the proper use of antipyretics in interferon therapy.

Quantitative structure-activity relationship (QSAR) analysis of the inhibitory effects of furanocoumarin derivatives on cytochrome P450 3A activities

Furanocoumarin derivatives (FCs) present in grapefruit and other plants cause pharmacokinetic interactions such as increased absorption of various drugs because the constituents have inhibitory effects on drug metabolizing activities of cytochrome P450 (CYP) 3A that is expressed in intestinal mucosal cells. Though it has been 20 years since such an interaction was discovered, little is still known about the relationship between the molecular characters of FCs and their inhibitory effects. Therefore, the chemical and physicochemical characterizations of the biological activities of FCs were examined by quantitative structure-activity relationship (QSAR) analysis using 37 types of FCs. Common logarithmic IC50 values of human liver microsomal testosterone 6beta-hydroxylations were configured as objective variables. A variety of structural, physicochemical, and quantum chemical descriptors were calculated from 2D and optimized 3D structures in the 37 FCs as explanatory variables. Simple and multiple linear regression analyses were used to evaluate these parameters. Constructed regression models were validated with leave-one-out cross validation and applicable regression diagnostic methods. As a result, logP value, molecular volume, molecular weight, molecular surface area, polar surface area, minimal electrostatic potential, formation energy, and homo energy of each FC were significantly related with the logIC50 value. These relationships indicate that molecular characteristics including lipophilicity, molecular size, electrostatic stabilization, and electron-donating ability of FCs can control FC-CYP interactions. These findings could be useful to predict CYP inhibitory effects of other FCs in foods, drinks, and other natural products such as grapefruit juice and herbal drugs.

White and colored grapefruit juice produce similar pharmacokinetic interactions

Colored (pink and red) grapefruit pulp contains lower amounts of the furanocoumarin derivatives that cause pharmacokinetic interactions than white grapefruit pulp. However, few studies have examined interactions with colored juice products. Therefore, we examined the potential interactions of both white and colored grapefruit products by measuring the concentrations of furanocoumarin derivatives and inhibition of the metabolizing cytochrome P450 (CYP) 3A enzymes, the target of the furanocoumarins. We measured concentrations of three major furanocoumarin derivatives, bergaptol, bergamottin, and 6',7'-dihydroxybergamottin, with high-performance liquid chromatography in 21 brands of grapefruit juice sold in Japan, including 14 white and 7 colored brands. The mean difference in bergaptol, bergamottin, and 6',7'-dihydroxybergamottin concentrations in white grapefruit juice samples was 1.59, 0.902, and 1.03 times, respectively, the amounts in colored samples. White samples inhibited CYP3A-mediated testosterone-6beta oxidation in human liver microsomes by 1.04 and 0.922 times (whole juice and furanocoumarin, respectively) the inhibition by colored juice. Thus, colored grapefruit juice may produce drug interactions at the same rate as white grapefruit juice.

Drug interaction potentials among different brands of grapefruit juice

The discrepancy of drug-interaction potential among different brands of grapefruit juice was estimated based on inhibition of CYP3A activity caused by furanocoumarin derivatives in the grapefruit juice. Heat treatment of the grapefruit juice at 95 degrees C for 1 h was utilized to degrade the furanocoumarins. Initial velocity of testosterone 6beta-oxidation using human liver microsomes was determined as an indicator of the CYP3A activities. Changes in the velocities of the reaction mixture were observed when 10% of each brand of untreated grapefruit juice or heat-treated grapefruit juice was added. The differences in the velocities between untreated and heat-treated grapefruit juice were defined as the potentials of furanocoumarin-caused CYP3A-inhibitions.

Determination of bergamottin in human plasma after grapefruit juice ingestion by an UPLC/MS/MS method

Bergamottin was identified as a cause of pharmacokinetic interaction with grapefruit juice intake and as a physiologically active substance involved in lipolysis. However, the quantification method on concentrations of bergamottin in systemic circulation has not been well established. The aim of this study was to develop a simple, sensitive and high-throughput determination system for bergamottin in human plasma using an ultra performance liquid chromatography (UPLC)-MS-MS method. The UPLC system equipped with a UPLC BEH C18 column (2.1 x 50 mm, 1.7 microm) and an ESI prove was appropriate for detection of bergamottin. As a result, a primary product ion (m/z = 203) from precursor ion of bergamottin (m/z = 339) was observed. Plasma from a human volunteer who consumed grapefruit juice one hour before the time of blood sampling, was measured with the UPLC/MS/MS system. The determination of plasma-bergamottin was performed with the highest sensitivity presently available. In conclusion, we succeeded high performance bergamottin-determination in human plasma after grapefruit juice ingestion. The procedure can be usefulto clarify pharmacokinetic and pharmacodynamic characteristics of bergamottin.

Metabolism of bucolome in rats. Stability and biliary excretion of bucolome N-glucuronide

Bucolome (BCP) is a non-steroidal anti-inflammatory drug, which is used in the treatment of chronic articular rheumatism. Bucolome N-glucuronide (BCP-NG), a metabolite of BCP, is the first unique N-glucuronide of barbituric acid derivatives. First, the stability of BCP-NG in various pH aqueous solutions was studied. BCP-NG was quite unstable under neutral and acidic conditions, and is easily hydrolyzed to BCP. Based on these characteristics of BCP-NG, a simple, rapid and highly sensitive method for the simultaneous determination of BCP and BCP-NG with phenylbutazone (I.S.) in biological fluids was developed using high-performance liquid chromatography (HPLC). A reversed-phase ODS column was used for the separation of BCP, BCP-NG and I.S. A pharmacokinetic study for BCP and BCP-NG was carried out in male Wistar/ST rats following i.v. administration of BCP at a dose of 10 mg/kg body weight. The slow plasma elimination of BCP with time was shown. A major metabolite of BCP in bile was N-glucuronide. The cumulative amounts of BCP and BCP-NG in the bile over 8 h were approximately 2.4 +/- 1.4% and 12.6 +/- 2.3% of the dose, respectively. BCP and BCP-NG in the urine were 2.7 +/- 0.7% and 3.2 +/- 0.3% of the dose. Although BCP had a long half-life (over 8.5 h), the preliminary pharmacokinetic parameters (0-8 h) were determined: t 1/2, 8.52 +/- 1.96 h; AUC, 419.9 +/- 45.2 microg x h/ml; MRT, 3.29 +/- 0.11 h; CLtot, 5.93 +/- 0.54 ml/h; and Vdss, 19.5 +/- 1.3 l. These observations are the first pharmacokinetic findings for the N-glucuronide of the barbituric acid derivatives.

Effects of furanocoumarin derivatives in grapefruit juice on nifedipine pharmacokinetics in rats

PURPOSE

It has been reported that grapefruit juice (GJ) causes a pharmacokinetic interaction with many drugs after co-ingestion. It is postulated that the substances in GJ may inhibit the first-pass metabolism during the intestinal absorption process. In recent years, several furanocoumarin derivatives that inhibit P450 activity in intestinal microsomes were isolated from GJ. In this study, we report the effects of the furanocoumarin derivatives in GJ on the nifedipine (NFP) pharmacokinetics in rats.

METHODS

Three furanocoumarin derivatives (bergaptol [BT], bergamottin [BG], and 6',7'-dihydroxybergamottin [DHB]) found in GJ were used in this study. Each furanocoumarin was reconstituted in orange juice at the same concentration as in the GJ. Two milliliters of each sample was administered into the rat duodenum. After 30 min, NFP was intraduodenally administered at a dose of 3 mg/kg body weight. The NFP concentrations in the plasma samples were determined by HPLC.

RESULTS

A significant increase in the AUC of NFP was observed only in the rats administered BG; 1.5 times that of the control group. The result was quite identical with that of the group that was administered GJ. BT and DHB had no significant effects on the NFP pharmacokinetics.

CONCLUSIONS

The results strongly suggested that BG in GJ might be the substance that elevates the NFP plasma concentrations.

[Development of patient-friendly preparations(II): Preparation and characterization of carrageenan gel containing polyethylene (oxide)]

The pharmaceutical utility of the allopurinol gel (APNgel) which consists of allopurinol (APN), carrageenan (kappa-CG or iota-CG) and polyethylene (oxide) (Alkox) was investigated as a possible material for an oral dosage preparation for ease in handling and/or swallowing. The gel formation was studied as a function of a variety of the concentration of Alkox and/or CG added. The APNgel gelled with kappa-CG was not appropriate to the oral dosage form because of its original taste and odor. In contrast, since iota-CG has no odor and/or taste, we added iota-CG as a gel material. From the investigation of the gelation behavior and the handling of the gelled material, the preferred composition of APNgel (Alkox: iota-CG% ratio) seemed to be that of 0.5:2.0, 1.0:2.0 and 2.0:2.0. The gel strength and the in vitro assessment of the adhesiveness of APNgels were evaluated using a creep meter. The gel strength of the APNgel was affected by the amount of the added Alkox. From the in vitro assessment of the adhesiveness of APNgels, the adhesiveness of APNgel increased with an increase in the amount of added Alkox. The release behavior of APN from APNgels was investigated by the paddle bead method, mimicking the chewing action in mouth. The APNgel was sheared by the beads and the release of APN completed within 480 s. From the results of the sensory test, APNgel consisting of 2.0% iota-CG and 1.0% Alkox seemed to be favorite to the jelly-like preparation.

Effects of long-term grapefruit juice ingestion on nifedipine pharmacokinetics: induction of rat hepatic P-450 by grapefruit juice

We studied the effects of short- and long-term ingestion of grapefruit juice (GJ) on nifedipine (NFP) pharmacokinetics in rats. Thirty minutes after intraduodenal (id) administration of 2.0 ml of GJ or saline, NFP was i.v. or id administered at a dose of 3 mg/kg b. wt. No significant differences were observed in pharmacokinetic values between the two groups after i.v. administrations of NFP. By contrast, after id administration, the mean AUC value in the GJ group was approximately 1.62 times that in the control group, and the mean apparent clearance (CL) decreased by approximately 40%. In addition, 2.0 ml of GJ was orally administered twice a day (9:00 AM and 7:00 PM) for 10 consecutive days; on the 11th day the pharmacokinetics of NFP were examined again. Irrespective of route of administration (i.v. or id), NFP CL from plasma in these GJ-treated rats was considerably faster than that in the rats treated with GJ for a short (30-min) period. In microsomes prepared from the intestinal mucosa of animals receiving long-term administration of GJ, NFP oxidation activity (0.21 +/- 0.02 nmol/mg/min) and P-450 content (0.045 +/- 0.009 nmol/mg) were significantly lower than those in untreated rats (0.32 +/- 0.05 nmol/mg/min and 0.060 +/- 0.007 nmol/mg). In hepatic microsomes from the same rats, however, NFP oxidation activity (1.43 +/- 0.17 nmol/mg/min) and P-450 content (0.66 +/- 0.07 nmol/mg) were distinctly greater than those in untreated rats (1.00 +/- 0.06 nmol/mg/min and 0.51 +/- 0.04 nmol/mg). In conclusion, short-term id exposure to GJ resulted in increased NFP bioavailability, whereas long-term administration of GJ resulted in reduced bioavailability and increased CL.

Expression of cofilin isoforms during development of mouse striated muscles

Cofilin (CF) is an actin regulatory protein that plays a critical role in actin filament dynamics in a variety of cells. Two cofilin isoforms. muscle-type (M-CF) and nonmuscle-type (NM-CF) encoded by different genes, exist in mammals; in the adult, the former is predominantly expressed in muscle tissues, while the latter is distributed in various non-muscle tissues (Ono et al., 1994). In this study, we examined cofilin isoform expression during skeletal and cardiac muscle development in mice using cDNA probes and antibodies which distinguish the isoforms. We found that the expression of M-CF was initiated in terminally differentiated myogenic cells in both the myotome and limb buds. In myogenic cell cultures, its expression occurred coupled with myotube formation. NM-CF was expressed in developing skeletal and cardiac muscles but disappeared from skeletal muscle during postnatal development, while its expression persisted in the heart, even in adult mice. A similar situation was observed in the heart of other mammals. Thus, it is likely that the both cofilin isoforms are involved in the regulation of actin assembly during myofibrillogenesis. Only M-CF could be involved in actin dynamics in mature skeletal muscle, while both isoforms could be in the mature heart.

Stereoselective metabolism of benoxaprofen in rats. Biliary excretion of benoxaprofen taurine conjugate and glucuronide

Benoxaprofen (BOP) was administered iv to bile duct-cannulated rats at a dose of 10 mg/kg. BOP and its metabolites in plasma, urine, and bile were quantified using HPLC. A previously unidentified BOP metabolite was found in HPLC chromatograms of rat bile, and the metabolite was isolated chromatographically. Positive-ion fast-atom bombardment (FAB) MS analysis of the compound showed [M+H]+ at m/z 409, i.e. 108 mass units greater than the molecular weight of BOP (301 mass units). In the 1H NMR spectrum of the compound, two signals assigned to two methylene groups appeared at 2.53 ppm and 3. 30 ppm, in addition to BOP signals. Analysis of FAB mass spectra and 1H-1H and 1H-13C correlated NMR spectra of the isolated metabolite suggested that the new metabolite was a BOP taurine conjugate (BOP-T). A BOP-T standard was chemically synthesized, and physicochemical data were compared with those for the isolated metabolite. Identical results, i.e. RF values from TLC, RT values from HPLC, and FAB MS and 1H-13C correlated NMR findings, were obtained, establishing that the new metabolite found in rat bile was BOP-T. In five rats, mean values for per cent excretion of the dose in bile over 12 hr for BOP glucuronide (BOP-G), BOP-T, and unchanged BOP were 13.2 +/- 2.3, 2.54 +/- 0.80, and 0.33 +/- 0.09%, respectively. Furthermore, the optical isomers of BOP and its metabolites in plasma and bile were analyzed using a chiral HPLC column. (R)-BOP showed rapid plasma elimination, whereas the plasma elimination of (S)-BOP was very slow. The amounts of BOP, BOP-G, and BOP-T enantiomers excreted into the bile were as follows: (S)-BOP-G and (R)-BOP-G, 12.5 +/- 1.8 and 2.1 +/- 0.6% of the dose; (R)-BOP-T and (S)-BOP-T, 2.0 +/- 0.6 and 0.3 +/- 0.05% of the dose; (R)-BOP and (S)-BOP, 0.02 +/- 0.03 and 0.2 +/- 0.1% of the dose, respectively. (S)-BOP was metabolized mainly to BOP-G, and BOP-T excreted into the bile was produced mainly from (R)-BOP.

Ion-pair reversed-phase high-performance liquid chromatography of adenine nucleotides and nucleoside using triethylamine as a counterion

An isocratic HPLC method for the simple and selective determination of adenine nucleoside and nucleotides has been developed. The separation is achieved at room temperature by reversed-phase chromatography (Shiseido, Capcell Pak C18). A mixture of 0.1 M triethylamine (TEA) phosphate buffer and methanol (95:5, v/v) is used as a standard eluent. Influence of pH and concentrations of organic modifiers and TEA ion on capacity factors of adenine compounds has been investigated. It has been also found that the TEA ion in the eluent is adsorbed onto the reversed-phase surface. The results clearly demonstrate that ion-pair formation with TEA ion occurs probably both in the mobile phase and on the stationary phase and governs the retention of adenine and nucleotides in the present system. The HPLC system is applied to the analysis of adenine nucleotides formed as intermediates in the synthesis of 3'-phosphoadenosine 5'-phosphosulphate (PAPS) and to the assays of ATPases and 5'-nucleotidase activities in rat liver plasma membrane. This method is a new type of ion-pair reversed-phase HPLC system and is suitable for the separation of highly polar organic anions, especially for adenine nucleotides.

Low molecular-weight G-actin binding proteins involved in the regulation of actin assembly during myofibrillogenesis

We previously demonstrated that small G-actin binding proteins, cofilin, ADF and profilin, are involved in the actin dynamics during myofibrillogenesis (OBINATA, T. (1993). Int. Rev. Cytol., 143: 153-189.). To better understand how they are responsible for the regulation of actin assembly, the amounts of the actin-binding proteins were quantified by means of quantitative immunoblotting and compared with that of G-actin pool. The sum of the amounts of cofilin, ADF and profilin was insufficient at early developmental stages but sufficient at later stages to account for the pool of G-actin in muscle cells. We detected expression of thymosin beta 4 at a considerable level in young embryonic but not in adult skeletal muscles. We, therefore, conclude that the G-actin pool in young embryonic skeletal muscle is mainly due to cofilin, ADF, profilin and thymosin beta 4. Switching from a non-muscle-type (NM-) cofilin to a muscle-type (M-) cofilin was observed during muscle development of mammals. In order to clarify cofilin-dependent regulation of actin assembly in muscle cells, cofilin tagged with fluorescence dyes was introduced into C2 myoblasts by a micro injection method. The exogeneous cofilin, but not ADF, caused quick disassembly of actin filaments and accumulated in furrow region of dividing cells. The analogs of the unphosphorylated form (A3-cofilin) and the phosphorylated form (D3-cofilin) were prepared by converting Ser3, a regulatory phosphorylation site, to Ala or Asp. When A3-cofilin and D3-cofilin were injected into living cells, the former was concentrated at the membrane ruffles and cleavage furrow, while the latter showed only diffuse distribution in the cytoplasm. These results suggest that the subcellular distribution of cofilin as well as its interaction with actin in vivo is regulated by its phosphorylation and dephosphorylation.

Disopyramide concentrations in human plasma and saliva: comparison of disopyramide concentrations in saliva and plasma unbound concentrations

OBJECTIVE

This study was performed to investigate whether it is possible to use saliva instead of blood usually used for therapeutic drug monitoring (TDM) of disopyramide.

METHODS

Six healthy male volunteers ingested 200 mg of disopyramide base, and the disopyramide concentrations in saliva and plasma (total and unbound) were determined by the HPLC.

RESULTS

Disopyramide concentration-time profiles for the saliva were nearly equal to those for the plasma unbound concentrations. A large variation for absorption time of the drug was observed among the subjects. Disopyramide concentrations (Cs) in saliva did not correlated well with plasma total concentrations (Cp), r = 0.799, but did well with unbound concentrations (Cpu), r = 0.969, for the 3-12 h period on the elimination phase. The mean ratio of disopyramide concentrations in the saliva against the plasma unbound concentrations was almost constant (1.02(0.10), CV = 9.7%) for the period. The pharmacokinetic parameters (tmax, t1/2, AUC, AUMC and MRT values) for disopyramide calculated from the saliva data were nearly equal to those from the unbound data.

CONCLUSION

Disopyramide concentrations in saliva correlated well with plasma unbound concentrations on the elimination phase.

Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields

Exposure to extremely low frequency magnetic field (ELFMF) of 50 Hz and 400 mT induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene of human melanoma MeWo cells. The mutant frequency was enhanced both by increasing the exposure period and the induced current intensity. Mutations induced by X-rays were enhanced by ELFMF exposure. No significant increase in mutant frequency occurred when DNA replication was inhibited during ELFMF exposure. DNA replication error is suspected of causing the mutations produced by ELFMF exposure.

Effects of intracoronary infusion of atrial natriuretic peptide on pacing-induced myocardial ischemia in patients with effort angina pectoris

BACKGROUND

Atrial natriuretic peptide (ANP) has been shown to dilate the coronary artery. The aim of this study was to determine whether, in patients with effort angina pectoris, intracoronary infusion of ANP attenuates pacing-induced myocardial ischemia either by dilating the stenotic lesion in a large coronary artery or by dilating collateral vessels.

METHODS

We studied six patients who had total or subtotal occlusion in one coronary artery and well-developed, angiographically visible collateral vessels (group A) and five patients who had a significant stenosis in a large coronary artery with no visible collateral vessels (group B). Their heart rate was increased by atrial pacing both before and after intracoronary infusion of ANP (0.03 microgram/kg/min for 15 min) into the donor artery of collateral vessels in group A or into the stenotic artery in group B.

RESULTS

Before ANP infusion, all patients of both groups developed an ischemic ST-segment depression (> or = 0.1 mV) and angina-like chest pain from pacing tachycardia. After ANP infusion, significant ST-segment depression was induced by rapid pacing in only one out of six patients of group A, whereas it was noted in all patients of group B (P < 0.01). After ANP infusion, chest pain developed in one out of six patients in group A, whereas it appeared in four out of five patients in group B (P < 0.05). ANP significantly dilated the angiographically normal segment of the epicardial coronary artery, but it did not significantly change the severity of the stenotic lesion in either group. ANP did not change the basal arterial pressure or heart rate, nor did it change their response to pacing tachycardia.

CONCLUSION

Infusing ANP into the donor artery of collateral vessels, but not into the artery with culprit stenotic lesion, attenuated pacing-induced myocardial ischemia. Therefore, the beneficial effects of ANP in reducing pacing-induced myocardial ischemia may result from the increase in myocardial perfusion to the ischemic area caused by dilating the collateral vessels.

Simultaneous determination of amfenac sodium and its metabolite (7-benzoyl-2-oxindole) in human plasma by high-performance liquid chromatography

A simple, selective, sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of amfenac sodium (AMF) and its metabolite (7-benzoyl-2-oxindole, S1) in plasma was established. To 100 microliters of plasma, purified water (100 microliters), ammonium sulphate (0.2 g) and ethanol (100 microliters) containing fenbufen (100 micrograms/ml, internal standard) were added. After centrifugation the ethanol layer was directly injected into a reversed-phase ODS column. AMF and S1 were eluted using a gradient buffer system of 20-80% acetonitrile-phosphate buffer (pH 7.0), and detected at 245 nm. The analytical recoveries of AMF at concentrations of 0.5, 2 and 10 micrograms/ml in plasma were ca. 92.1, 95.4 and 94.6%, respectively. The coefficients of variation of the AMF recoveries were below 4.6%. The S1 recoveries at the concentrations of 40, 200 and 400.ng/ml were ca. 93.4, 98.7 and 95.3%, and the coefficients of variation were below 6.0%. The coefficients of variation for intra- and inter-day variation of AMF (5 micrograms/ml) and S1 (100 ng/ml) were 4.5 and 3.6% and 4.2 and 4.2%, respectively. The detection limits of AMF and S1 in plasma were as low as 0.1 microgram/ml and 20 ng/ml, and the coefficients of variation were 4.0 and 4.4%, respectively. The method was applied to determine the plasma concentrations of AMF and S1 after oral administration of AMF capsules (100 mg of AMF) to human volunteers.

Simultaneous determination of nerve-induced adenine nucleotides and nucleosides released from rabbit pulmonary artery

Electrical field stimulation elicits the release of catecholamines, adenine nucleotides, and adenosine from the rabbit pulmonary artery in a frequency dependent manner. To enhance our ability to investigate the release of endogenous adenine nucleotides and adenosine from this and other biological preparations, a new analytical procedure has been developed. This procedure involves the use of an internal standard, 9-beta-D-arabinofuranosyladenine (IS), the derivatization of ATP, ADP, AMP, adenosine (Ado), and IS with chloroacetaldehyde, the isocratic high-performance liquid chromatographic separation of these ethenopurine derivatives on an Ultron N-phenyl HPLC column, and their detection and quantitation by fluorescence spectroscopy. This procedure has enhanced sensitivity and reliability over existing procedures due to the stability of the chromatographic baseline and the use of an internal standard. When this analytical procedure was utilized to measure the adenine nucleotides and Ado that are released from the rabbit pulmonary artery in response to electrical field stimulation, it was observed that the release of endogenous ATP, ADP, AMP, and Ado exceeded that of endogenous norepinephrine. A molar ratio (6-amino purines:catecholamines) of approximately 2000:1 was obtained at a stimulation frequency of 16 Hz. This observation suggests an important extracellular role for adenine nucleotides and nucleosides in the physiology of vascular tissues.

Rectal bioavailability of 6-mercaptopurine in children with acute lymphoblastic leukaemia: partial avoidance of "first-pass" metabolism

Plasma levels and the area under the plasma concentration-time curve (AUC) values of 6-mercaptopurine (6-MP) were determined in a balanced crossover study of oral (powder) and rectal (macrogol suppository) administration to 5 children with acute lymphoblastic leukaemia (ALL). The AUC (538.6 ng.h.ml-1) after the rectal dose of 30 mg/m2 was approximately 1.5-times of that (365.5 ng.h.ml-1) after the oral dose of 87.5 mg/m2. The coefficients of variation of interindividual variability of the AUCs were 21.5% and 32.3%, respectively. The relative bioavailability of the macrogol suppository compared to the powder was approximately 4.39. These findings indicate that rectal administration of 6-MP could avoid the first-pass effect of this drug in the alimentary canal and/or liver, resulting in a large AUC of 6-MP, and so could reduce interindividual variability in plasma 6-MP concentrations. Rectal administration of 6-MP may be more effective than empirical oral dosing for the treatment of children with ALL, especially for patients with nausea and/or vomiting.

Direct injection analysis of melphalan in plasma using column-switching high-performance liquid chromatography

An automated column-switching high-performance liquid chromatographic (HPLC) method with ultraviolet detection is described for a simple and rapid determination of melphalan, an alkylating agent, in human plasma following direct sample injection. The system consists of a pretreatment column and an analytical column connected in series via a switching valve. Plasma samples are loaded onto a pretreatment column with an aqueous mobile phase, with which the sample to be analyzed is retained and the solubilized plasma proteins are flushed to be discarded. The retained compound is eluted from the pretreatment column onto the analytical column by using the chromatographic mobile phase with a higher elution capacity. The column-switching technique can be used to achieve an automated assay. Analytical recovery of the compound was 99.1%, and the coefficients of both intra- and interday variations did not exceed 3.5%. The detection limit was 10 ng/ml for the compound. Recovery of melphalan in plasma was only 2.1% after 4 weeks at 25 degrees C, as compared to 24.5% at 5 degrees C and 100.1% at -20 degrees C.

Determination of 6-mercaptopurine in acute lymphoblastic leukemia patients' plasma by high-performance liquid chromatography

A simple, selective, sensitive, and rapid high-performance liquid chromatography (HPLC) method is described for the quantitation of 6-mercaptopurine (6-MP) in plasma of patients with acute lymphoblastic leukemia (ALL). Pharmacokinetic data are presented for seven children with ALL receiving 6-MP therapy. A sensitivity of greater than or equal to 2 ng/ml in plasma was achieved on a reverse-phase octadecylsilane column using an HPLC system following a cleanup step with a solid-phase extraction cartridge. The chromatogram was monitored at 325 nm. Analytical recovery of 6-MP was 90%. The coefficients of variation for intra- and interday variabilities were 2.51 and 4.23%. This assay method is clinically useful for pharmacokinetic studies of 6-MP in ALL patients.