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R Kannan

Publications and source records attributed to R Kannan.

At least 73 records · Page 4Linked to original sources
PubMed1992

Transport of glutathione at blood-brain barrier of the rat: inhibition by glutathione analogs and age-dependence.

We showed previously that glutathione (GSH) may cross the blood-brain barrier intact by a saturable low affinity transport process (Km approximately 6 mM) (Kannan et al., J. Clin. Invest. 85: 2009-2013, 1990). In the present report, breakdown and resynthesis of GSH as the mechanism of apparent GSH uptake were excluded further because > 87% of injected 35S-cysteine taken up at the blood-brain barrier remained unchanged with negligible incorporation into GSH. In an effort to characterize further this GSH transport system, we have studied the influence of a number of potential inhibitors on brain uptake index (BUI) of GSH in rats pretreated with a gamma-glutamyl transpeptidase inhibitor, acivicin. The BUIs of tracer 35S-GSH uptake in the presence or absence of 1 to 20 mM cysteine, glutathione disulfide, gamma-glutamylglutamate, gamma-glutamyl-p-nitroanilide and 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid did not differ significantly from each other. However, S-alkyl glutathiones (hexyl and octyl), sulfobromophthalein-glutathione, glutathione monoethyl ester, probenecid (5 mM) and ophthalmic acid (10 mM) inhibited GSH uptake significantly. Inhibition of GSH uptake by sulfobromophthalein-glutathione and GSH-monoethyl ester was concentration-dependent with apparent Ki approximately 0.016 and 0.083 mM, respectively. There was a decline in GSH-BUI as a function of age in both acivicin and nonacivicin-pretreated rats during the growth and developmental period from 25 to 135 days of age (100-500 g b.wt.). The decrease in BUI with age was specific for GSH; cysteine uptake did not change and no difference in diffusible (H2O) and nondiffusible (sucrose) components was found in this age range.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1991

Isolation and partial characterization of antibody- and globin-enriched complexes from membranes of dense human erythrocytes.

In previous studies we have described a process whereby an erythrocyte in biochemical distress can initiate its own removal by macrophages of the reticuloendothelial system. This process involves the clustering of the integral membrane protein band 3 by denatured haemoglobin and the subsequent recognition of the exofacial poles of clustered band 3 and associated proteins by autologous antibodies. To determine whether this clearance pathway might mediate normal cell turnover, the fraction of normal erythrocytes containing the 0.5% densest cells, which are known to be destined for immediate removal, was isolated and characterized biochemically. This densest fraction was found to contain 6 times more membrane-bound globin (haemichromes) and 10 times more surface-bound autologous IgG than the other fractions containing cells of lower density. To determine whether the autologous IgG was physically associated with the haemichrome-stabilized membrane protein clusters, a procedure was developed for isolation and characterization of the microscopic aggregates. The isolated aggregates were found to contain a disulphide-cross-linked mixture of several membrane proteins, predominantly haemichromes, spectrin and band 3. Although the aggregates constituted only 0.09% of the total membrane protein, they still contained approximately 55% of the total cell-surface IgG. Since in control studies anti-(blood group A) antibodies, which are distributed randomly over the surface of type A cells, could not be recovered in the aggregate, we conclude that the autologous cell-surface IgGs were physically associated with the membrane protein clusters when they were co-isolated with them in our procedure. Thus the 640-fold enrichment of autologous IgG in the aggregates compared with regions of the membrane devoid of tightly clustered protein suggests that sites of integral protein clustering either are non-specifically sticky to IgG or are viewed as foreign or 'non-self' by the immune system and aggressively opsonized with IgG.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1991

Amiodarone toxicity. II. Desethylamiodarone-induced phospholipidosis and ultrastructural changes during repeated administration in rats.

The contribution of desethylamiodarone (DEA), principal metabolite of the antiarrhythmic drug amiodarone, to the major side effects of amiodarone is unclear. The effects of repeated DEA administration to rats on tissue drug accumulation, ultrastructural changes, and phospholipid concentrations were studied. Two groups (n = 8/group) of male Sprague-Dawley rats (250 g body wt) were administered a 5% aqueous solution of DEA (Dose I, 40 mg/kg/day; Dose II, 60 mg/kg/day) intraperitoneally for 21-23 days, while a third group (control, n = 8) received saline. DEA levels were significantly higher with Dose II compared to Dose I in the lung, liver, kidney, spleen, heart, and serum while the tissue to serum ratios were similar with both doses for all tissues except the heart. DEA administration caused a significant elevation in the lipid phosphorus levels of liver, lung, and alveolar macrophages compared to control levels. A strong positive correlation (p less than 0.01) was found between tissue DEA levels and lipid phosphorus for the above tissues. Electron microscopy revealed the presence of lipid inclusion bodies in liver, lung, and alveolar macrophages of DEA-treated rats. A dose-dependent increase in the percentage of vacuolar surface area was found in the lung and alveolar macrophages. The tissue ultrastructural changes after repeated DEA dosing were qualitatively similar to our previous findings with amiodarone. Increased lung and liver phospholipid levels with repeated DEA doses may result from a potent inhibitory action of DEA on tissue phospholipase A as has been observed by others in in vitro studies.

Amiodarone↗
PubMed1990

Reduced suppression of plasma saturated fatty acid mobilization and oxidation by feeding in lymphoma-bearing mice.

Lymphoma-bearing mice have a circulating lipid-mobilizing factor, but increased plasma free fatty acid (FFA) turnover has not been demonstrable in earlier studies using postabsorptive tumor-bearing mice. We hypothesized that FFA mobilization in lymphoma-bearing mice is only elevated in fed mice and may best be observed at night (dark, reversed light cycle). AKR mice with early and advanced tumors (10(6) SL-3 lymphoma cells, i.p.) and controls were fed ad libitum (reversed light cycle, dark) or fasted 4 h (daylight, regular cycle), given injections of [14C]bicarbonate of [1-14C]palmitate-mouse serum albumin, i.v., and plasma [14C]FFA disappearance and/or breath 14CO2 were monitored. Plasma FFA mobilization, estimated by multicompartmental analysis (SAAM) of the oxidation rate was lower in fasted mice with advanced tumors [tumor, 9.5 +/- 6.0% (%SE); controls, 14 +/- 4.4% micrograms-atoms fatty acid-carbon/min/30 g body weight, n = 3 to 6 mice/time point/group]. Feeding reduced these rates 90% in control mice and 53% in mice with early tumors, but only 14% in mice with advanced tumors. Plasma FFA fractional catabolic rates were 2.5 times faster in fed mice with advanced tumors than in controls. Diminished suppression of fatty acid mobilization in fed tumor-bearing mice (at night) probably accounts partially for the body fat loss.

Adipose Tissue↗
PubMed1990

Evidence for carrier-mediated transport of glutathione across the blood-brain barrier in the rat.

Information on the origin of brain glutathione and the possibility of its transport from blood to brain is limited. We found a substantial uptake of 35S-labeled glutathione by the rat brain using the carotid artery injection technique. The brain uptake index of glutathione with and without an irreversible gamma-glutamyl transpeptidase inhibitor, acivicin, was similar. No significant differences in the regional uptake of labeled glutathione were found in rats pretreated with acivicin. The brain uptake index of tracer glutathione was similar to that of cysteine tracer and was lower than that of phenylalanine. The transport of oxidized glutathione (glutathione disfulfide) across the blood-brain barrier was not significantly different from that of sucrose, an impermeable marker. Brain radioactivity 15 s after carotid artery injection of labeled glutathione to rats pretreated with acivicin was predominantly in the form of glutathione. The in vivo glutathione uptake was saturable with an apparent Km of 5.84 mM. Amino acids, amino acid analogues, and other compounds [cysteine, phenylalanine, glutathione disulfide, gamma-glutamylglutamate, gamma-glutamyl p-nitroanilide, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH)] did not affect glutathione transport. Our data suggest that glutathione is transported across the blood-brain barrier by a saturable and specific mechanism.

Animals↗
PubMed1990

Effect of amiodarone on non-deiodinative pathway of thyroid hormone metabolism.

Amiodarone, an iodine containing anti-arrhythmic drug, causes a significant decrease in molar ratio of daily production rates of T3 and T4 from 0.75 in controls to 0.36 in amiodarone-treated rabbits. A model was constructed from the above data which showed that metabolism of T4 via non-deiodinative pathways (e.g. tetraiodothyroacetic acid and/or conjugates) increased from 29% in untreated controls to 66% in amiodarone-treated rabbits. In this study, we have examined the metabolic clearance rate of tetraiodothyroacetic acid in rabbits given amiodarone (20 mg.kg-1.day-1 ip for 3 weeks) or saline (controls). Serum amiodarone and desethylamiodarone levels under the above experimental conditions were 0.20 +/- 0.067 and 0.17 +/- 0.058 mg/l, respectively, which were in the near-therapeutic range observed in humans. Control and amiodarone-treated rabbits were administered [125I]-tetraiodothyroacetic acid (10 muCi/rabbit) iv and blood was collected at 0.5, 1, 2, 4, 6, 10, 32 and 48 h. Serum tetraiodothyroacetic acid radioactivity was determined by trichloroacetic acid precipitation and ethanol extraction and metabolic clearance rates were calculated from the area under the curve of computer fits to tetraiodothyroacetic acid radioactivity data. Amiodarone treatment decreased metabolic clearance rates significantly from 0.107 +/- 0.008 in controls to 0.074 +/- 0.009 l/day in amiodarone-treated rabbits (p less than 0.05). However, when expressed per unit body weight (1.day-1.kg-1), the metabolic clearance rates were not significantly different between the controls and amiodarone-treated rabbits. The terminal serum elimination half-life in the two groups were similar (32.0 +/- 6.7 h in controls vs 49.2 +/- 12.4 h in amiodarone-treated).(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone↗
PubMed1989

Therapeutic tolerance, hemodynamic effects, and oral dose kinetics of dilazep dihydrochloride in hypertensive patients.

The oral dose metabolism of dilazep dihydrochloride [tetrahydro-1H-1,4-diazepine-1,4(5H)-dipropanol 3,4,5-trimethoxybenzoate] was examined in six hypertensive patients receiving a single oral dose of 600 mg of dilazep (3-3.8 mg/kg BW). Blood was collected at 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, and 24 h after administration of the dose and urine was collected for three time intervals of 0-4 h, 4-10 h, and 10-24 h. Dilazep concentrations in blood and urine were determined by high-performance liquid chromatography. Dilazep decayed monoexponentially with a mean elimination rate constant of 0.27 +/- 0.13 h-1 and a mean half-life of 3.04 +/- 1.34 h. The mean tmax of absorption was 1.40 +/- 0.82 h. With maximally tolerated chronic doses, the steady-state concentration measured at 1 week was 25.6 ng/mL in a patient receiving 300 mg daily (100 mg TID) for 3 weeks, and dilazep concentration increased with the dose in others for up to a 600-mg dose daily. Dilazep did not produce any significant changes in heart rate and blood pressure after a single oral dose or during chronic dosing. There was no correlation between blood dilazep levels and the changes in heart rate and blood pressure. In three additional patients, oral dilazep dihydrochloride titrated gradually to maximally tolerated doses (900 mg daily) failed to produce significant effects on biochemical and neurohumoral measurements, and hemodynamic parameters as well as ventricular functional indices measured by radionucleide methods. Oral dilazep administration in maximally tolerated doses is devoid of effects on blood pressure and cardiac hemodynamic function.

Administration, Oral↗
PubMed1989

Tissue drug accumulation and ultrastructural changes during amiodarone administration in rats.

Pulmonary and hepatotoxicity are the two major side effects of chronic amiodarone therapy. We studied the accumulation of amiodarone and its principal metabolite, desethylamiodarone, in lung and liver of rats treated ip for 21 to 23 days with either 40 or 80 mg/kg/day amiodarone. The ultrastructural changes in liver, lung, and alveolar macrophages in saline controls and in rats on the two amiodarone dosage regimens were investigated. There was a dose-dependent increase in amiodarone and desethylamiodarone levels in serum and in tissues. The desethylamiodarone/amiodarone ratios in liver and lung, but not in serum, increased significantly with increasing dose. Serum also contained another metabolite, monodeiodinated desethylamiodarone. Increase in vacuolization and presence of whorled lamellar inclusion bodies in alveolar macrophages occurred with an increase in dose and higher lung amiodarone and desethylamiodarone levels. Electron microscopy of the liver of amiodarone-treated rats revealed the presence of large inclusion bodies partially filled with amorphous material in the cytoplasm. The quantitative relationship of the above changes to organ toxicity and to phospholipidosis that accompanies amiodarone administration remains to be established.

Amiodarone↗
PubMed1989

Electrophysiologic effects of flecainide relative to serum and tissue concentrations in rabbits after chronic drug administration.

The effects of chronic treatment with flecainide on the cellular electrophysiology and the relationship of the electrophysiologic effects to serum and myocardial flecainide concentrations were determined in rabbit ventricular myocardium. Two groups of rabbits were administered flecainide at doses of 7.5 mg/kg body weight (dose I) and 20 mg/kg body weight (dose II) intraperitoneally (i.p.) twice daily for 12-14 days; a third group received saline. Serum and myocardial flecainide concentrations with dose II (0.44 +/- 0.15 micrograms/ml and 3.0 +/- 1.4 micrograms/g, respectively) were significantly (p less than 0.01) higher than with dose I (0.19 +/- 0.11 micrograms/ml and 0.81 +/- 0.15 micrograms/g, respectively). At 1.0-Hz stimulation, only the high dose produced significant changes in transmembrane action potentials of right ventricular myocardial fibers, which showed a 17.6% (n = 6, p less than 0.05) decrease in maximal upstroke velocity (Vmax) of phase 0 and 19.5% (n = 6, p less than 0.05) prolongation of effective refractory period (ERP). Repetitive stimuli led to an exponential decline in Vmax with both dosage regimens. The magnitude of Vmax decrease was frequently dependent and was greater with the higher dose. The rate of decrease of Vmax per action potential (AP) during train of stimuli in rabbits treated with dose II was 0.037 +/- 0.012 (n = 5) at 2.0-Hz stimulation, and the recovery time constant from use-dependent block at 4.0-Hz stimulation increased significantly from 12.6 +/- 3.6% decrease in Vmax with the low dose to 35.6 +/- 7.1% decrease with the high dose. The data show that sodium channel inhibition by chronic flecainide administration is a function of dose, serum, and myocardial flecainide concentrations.

Action Potentials↗
PubMed1988

Isolation and characterization of the hemichrome-stabilized membrane protein aggregates from sickle erythrocytes. Major site of autologous antibody binding.

Because the interaction of denatured hemoglobins (i.e. hemichromes) with the red cell membrane has been associated with several abnormalities commonly observed in hemichrome-containing erythrocytes, we have undertaken to isolate and characterize the hemichrome-rich membrane protein aggregates from sickle cells. The aggregates were isolated by two procedures: one at low ionic strength by centrifugation of detergent-solubilized spectrin-depleted inside-out vesicles, and the other at physiological ionic strength by detergent solubilization of whole cells followed by cytoskeletal disruption and centrifugation. The extensively washed aggregates obtained by both methods yielded similar results. These insoluble complexes were found to be highly cross-linked by predominantly intermolecular disulfide bonds; however, other nonreducible covalent linkages were also observed. Both in the presence and absence of reducing agents, the aggregate disintegrated when the hemichromes were removed by high ionic strength, suggesting that the aggregate depended heavily on the cohesive properties of the hemichromes for stability. Protein assays demonstrated that the aggregates comprised approximately 1.3% of the total membrane protein, roughly two-thirds of which appeared to be globin chains. Other major components identified in the aggregate were band 3, ankyrin, bands 4.1, 4.9, and 5, glycophorins A and B, and autologous IgG. Quantitative analysis of the IgG content demonstrated that three-fourths of the surface-bound IgG on washed sickle cells was clustered at these aggregate sites, representing an enrichment of approximately 250-fold over nonaggregated regions of the membrane. Since clustered cell surface IgG is thought to trigger removal of erythrocytes from circulation, the hemichrome-induced membrane reorganization at these aggregate sites may be an important cause of the greatly shortened life span of sickle cells.

Anemia, Sickle Cell↗
PubMed1988

Electrophysiologic effects of desethylamiodarone, an active metabolite of amiodarone: comparison with amiodarone during chronic administration in rabbits.

During acute superfusion studies by means of the standard microelectrode technique, we previously showed that both amiodarone and its major metabolite, desethylamiodarone, had a modest effect on the lengthening of the action potential duration (APD) at high drug concentrations and produced a rate-dependent block of the sodium channel in cardiac muscle. In this study the comparative electrophysiologic effects of the two compounds in rabbits treated chronically with these compounds were determined with particular reference to repolarization and sinus node automaticity. The changes were correlated with those in serum and tissue drug levels and in thyroid hormone indices. After 1 week neither compound had a significant effect on atrial or sinus nodal potentials; after 3 weeks, amiodarone increased the atrial APD at 90% repolarization time by 10.5% (p less than 0.05) and the effective refractory period (ERP) by 6.7% (p less than 0.05). The corresponding figures for desethylamiodarone were 13% (NS) and 18% (NS). The sinus cycle length was increased 12% (NS) by amiodarone and 27.9% (p less than 0.05) after the metabolite. In animals treated for 6 weeks, amiodarone increased the ventricular APD at 90% repolarization by 58.8% (p less than 0.01) and desethylamiodarone by 42.0% the corresponding figures for the ERP were 63.4% (p less than 0.01 and 47.4% (p less than 0.01), respectively. At the stimulation frequency used, neither compound exerted a significant effect on Vmax. Both amiodarone and desethylamiodarone significantly decreased serum triiodothyronine and increased reverse triiodothyronine levels but had no effect on thyroxine.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Sensitive method for the measurement of amiodarone and desethylamiodarone in serum and tissue and its application to disposition studies.

A high-performance liquid chromatographic (HPLC) method for the measurement of amiodarone (AM) and its metabolite(s) in serum and tissues was developed. The method uses a 5-micron silica column, methanol containing 0.02% perchloric acid at pH 4 as the mobile phase, and ultraviolet detection at 240 nm. The standard curves for AM and desethylamiodarone (DAM) were linear for serum (range 0.025-6.0 microgram/ml) and tissues (range 0.1-0.5 micrograms for 10-25 mg wet weight). There was a significant decrease as a function of time in AM and DAM concentrations in patients' sera left at ambient temperature in the presence of light. This HPLC method was applied to studies on serum AM elimination kinetics in patients and on tissue uptake during chronic AM administration to rabbits. The elimination half-life (5.8 h) of AM after a 5 mg/kg intravenous dose to a patient was similar to that after acute oral doses. AM, being lipophilic, accumulated maximally in the fat tissue (56 micrograms/g wet weight), followed by lung and liver in rabbits injected with AM for six weeks. The latter two tissues also contained nearly equal quantities of DAM. The high concentrations of AM and DAM in the liver and lungs may be related to the hepatic toxicity and pulmonary fibrosis associated with chronic AM therapy. Two new metabolites were found in the lung and bile of AM-treated rabbits, but these have not yet been identified.

Amiodarone↗