Comparison of glyceryl trinitrate-induced with pentaerythrityl tetranitrate-induced in vivo formation of superoxide radicals: effect of vitamin C.

Glyceryl trinitrate (GTN) and pentaerythrityl tetranitrate (PETN) are among the most known organic nitrates that are used in cardiovascular therapy as vasodilators. However, anti-ischemic therapy with organic nitrates is complicated by the induction of nitrate tolerance. When nitrates are metabolized to release nitric oxide (NO), there is considerable coproduction of superoxide radicals in vessels leading to inactivation of NO. However, nitrate-induced increase of superoxide radical formation in vivo has not been reported. In this work, the authors studied the in vivo formation of superoxide radicals induced by treatment with PETN or GTN and determined the antioxidant effect of vitamin C. The formation of superoxide radicals was determined by the oxidation of 1-hydroxy-3-carboxy-pyrrolidine (CP-H) to paramagnetic 3-carboxy-proxyl (CP) using electron spin resonance spectroscopy. CP-H (9 mg/kg intravenous bolus and 0.225 mg/kg per minute continuous intravenous GTN or PETN 130 microg/kg) were infused into anesthetized rabbits. Every 5 min, blood samples were obtained from Arteria carotis to measure the CP formation. Both PETN and GTN showed similar vasodilator effects. Formation of CP in blood after infusions of GTN and PETN were 2.0+/-0.4 microM and 0.98+/-0.23 microM, respectively. Pretreatment with 30 mg/kg vitamin C led to a significant decrease in CP formation: 0.27+/-0.14 microM (vitamin C plus GTN) and 0.34+/-0.15 microM (vitamin C plus PETN). Pretreatment of animals with superoxide dismutase (15,000 units/kg) significantly inhibited nitrate-induced nitroxide formation. Therefore, in vivo infusion of GTN or PETN in rabbits increased the formation of superoxide radicals in the vasculature. PETN provoked a minimal stimulation of superoxide radical formation without simultaneous development of nitrate tolerance. The data suggest that the formation of superoxide radicals induced by organic nitrate correlates with the development of nitrate tolerance. The effect of vitamin C on CP formation leads to the conclusion that vitamin C can be used as an effective antioxidant for protection against nitrate-induced superoxide radical formation in vivo.     

A new approach for extracellular spin trapping of nitroglycerin-induced superoxide radicals both in vitro and in vivo

Anti-ischemic therapy with nitrates is complicated by the induction of tolerance that potentially results from an unwanted coproduction of superoxide radicals. Therefore, we analyzed the localization of in vitro and in vivo, glyceryl trinitrate (GTN)-induced formation of superoxide radicals and the effect of the antioxidant vitamin C and of superoxide dismutase (SOD). Sterically hindered hydroxylamines 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CP-H) and 1-hydroxy-4-phosphonooxy-2,2,6,6-tetramethylpiperidin (PP-H) can be used for in vitro and in vivo quantification of superoxide radical formation. The penetration/incorporation of CP-H or PP-H and of their corresponding nitroxyl radicals was examined by fractionation of the blood and blood cells during a 1-h incubation. For monitoring in vivo, GTN-induced (130 microg/kg) O2*- formation CP-H or PP-H were continuously infused (actual concentration, 800 microM) for 90 to 120 min into rabbits. Formation of superoxide was determined by SOD- or vitamin C-inhibited contents of nitroxide radicals in the blood from A. carotis. The incubation of whole blood with CP-H, PP-H, or corresponding nitroxyl radicals clearly shows that during a 1-h incubation, as much as 8.3% of CP-H but only 0.9% of PP-H is incorporated in cytoplasm. Acute GTN treatment of whole blood and in vivo bolus infusion significantly increased superoxide radical formation as much as 4-fold. Pretreatment with 20 mg/kg vitamin C or 15,000 U/kg superoxide dismutase prevented GTN-induced nitroxide formation. The decrease of trapped radicals after treatment with extracellularly added superoxide dismutase or vitamin C leads to the conclusion that GTN increases the amount of extracellular superoxide radicals both in vitro and in vivo.     

EPR detection of reactive oxygen species in hemolymph of Galleria mellonella and Dendrolimus superans sibiricus (Lepidoptera) larvae.

The formation of reactive oxygen species (ROS) in hemolymph and hemocytes of Galleria mellonella and Dendrolimus superans sibiricus larvae was studied by ESR spectroscopy using spin-trap 1-hydroxy-3-carboxy-pyrrolidine (CP-H). The background level of ROS formation was detected in the intact hemolymph. The addition of dihydroxyphenylalanine (DOPA) into free cells of the hemolymph increased CP-H oxidation about two times for G. mellonella and about four times for D. superans sibiricus. This increase was completely inhibited by a specific inhibitor of phenoloxidase, phenylthiourea. The presence of exogenous superoxide dismutase (SOD) did not change CP-H oxidation in the hemolymph. The data obtained in hemocytes showed only a DOPA-induced increase in CP-H oxidation. Phagocytosis activators did not affect ROS formation in hemocytes of both insect species. SOD decreased DOPA-induced CP-H oxidation 20-30% in suspension of hemocytes of D. superans sibiricus only. Our results are in agreement with the contribution of superoxide radical and DOPA-derived quinones/semiquinones in the immune response of insects.     

Epr analysis reveals three tissues responding to endotoxin by increased formation of reactive oxygen and nitrogen species

The excessive formation of reactive oxygen and nitrogen species (RONS) in tissue has been implicated in the development of various diseases. In this study we adopted ex vivo low temperature EPR spectroscopy combined with spin trapping technique to measure local RONS levels in frozen tissue samples. CP-H (1-hydroxy-3-carboxy-pyrrolidine), a new nontoxic spin probe, was used to analyze RONS in vivo. In addition, nitrosyl complexes of hemoglobin were determined to trace nitric oxide released into blood. By this technique we found that RONS formation in tissue of control animals increased in the following order: liver < heart < brain < cerebellum < lung < muscle < blood < ileum < kidney < duodenum < jejunum. We also found that endotoxin challenge, which represents the most common model of septic shock, increased the formation of RONS in rat liver, heart, lung, and blood, but decreased RONS formation in jejunum. We did not find changes in RONS levels in other parts of gut, brain, skeletal muscles, and kidney. Scavenging of RONS by CP-H was accompanied by an increase in blood pressure, indicating that LPS-induced vasodilatation may be due to RONS, but not due to nitric oxide. Experiments with tissue homogenates incubated in vitro with CP-H showed that ONOO⁻ and O₂^•−, as well as other not identified RONS, are detectable by CP-H in tissue. In summary, low-temperature EPR combined with CP-H infusion allowed detection of local RONS formation in tissues. Increased formation of RONS in response to endotoxin challenge is organ specific.     

A new nitroxyl-probe with high retention in the brain and its application for brain imaging

In order to estimate free radical reactions and image them in the brain of living animals, a nitroxyl spin-probe, carboxy-PROXYL acetoxymethyl ester (CxP-AM) was newly synthesized. CxP-AM was designed to be hydrolyzed by esterase, but not by lipase, so that it would pass through the blood-brain barrier and be retained in the cytosolic phase of parenchymal cells in the brain after intravenous injection. The pharmacokinetics of CxP-AM was compared with those of carboxy-PROXYL (CxP) and its methyl ester (CxP-M). Carboxyl esterase almost completely hydrolyzed CxP-AM within 3 min. After intravenous injection, the brain retained 1.8 times more CxP-AM than CxP-M, and retained it for more than 30 min. Electron spin resonance computed tomographic (ESR-CT) imaging of CxP-AM in the heads of mice produced marked contrast in the encephalon region, while CxP was distributed only in the extracranial region and CxP-M was distributed in both regions, confirming the pharmacokinetics of CxP-AM. The decay rate of CxP-AM determined with time-resolved ESR-CT imaging was different in the two brain regions, suggesting regional differences in the total reducing capability. CxP-AM should become a powerful probe for the investigation and diagnosis of free radical reactions and their imaging in the brain.     

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with ¹¹¹In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of ¹¹¹In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, ¹¹¹In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of ¹¹¹In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.     

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with ¹¹¹In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of ¹¹¹In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, ¹¹¹In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of ¹¹¹In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.     

Redox evaluation in sepsis model mice by the in vivo ESR technique using acyl-protected hydroxylamine

In vivo electron spin resonance (ESR) spectroscopy is a noninvasive technique that measures the oxidative stress in living experimental animals. The rate of decay of the ESR signal right after an injection of nitroxyl radical has been measured to evaluate the oxidative stress in animals, although the probe’s disposition could also affect this rate. Because the amount of probes forming the redox pair of hydroxyl amine and its corresponding nitroxyl radical was shown to be nearly constant in most organs or tissues 10 min after the injection of 1-acetoxy-3-carbamoyl-2,2,5,5-tetramethylpyrrolidine (ACP) in mice, we evaluated the oxidative stress in sepsis model mice induced by lipopolysaccharide (LPS) by intravenously injecting ACP as a precursor of redox probes. The in vivo ESR signal increased up to 7–8 min after the ACP injection and then decreased. Decay of the in vivo signal in LPS-treated mice was significantly slower than that in healthy mice, whereas no significant difference was observed in the rate of change in the total amount of redox probes in the blood and liver between these groups. ESR imaging showed that the in vivo signals observed at the chest and upper abdomen decayed slowly in LPS-treated mice. Suppression of the decay in LPS-treated mice was canceled by the administration of a combination of pegylated superoxide dismutase and catalase, or an inhibitor of nitric oxide synthase, or gadolinium chloride. These results indicate that the LPS-treated mouse is under oxidative stress and that reactive oxygen species, such as superoxide and peroxynitrite, related to macrophages are mainly involved in the oxidative stress.     

Sepsis increases contraction-related generation of reactive oxygen species in the diaphragm.

Recent work indicates that free radicals mediate sepsis-induced diaphragmatic dysfunction. These previous experiments have not, however, established the source of the responsible free radical species. In theory, this phenomenon could be explained if one postulates that sepsis elicits an upregulation of contraction-related free radical formation in muscle. The purpose of the present study was to test this hypothesis by examination of the effect of sepsis on contraction-related free radical generation [i.e. , formation of reactive oxygen species (ROS)] by the diaphragm. Rats were killed 18 h after injection with either saline or endotoxin. In vitro hemidiaphragms were then prepared, and ROS generation during electrically induced contractions (20-Hz trains delivered for 10 min) was assessed by measurement of the conversion of hydroethidine to ethidium. ROS generation was negligible in noncontracting diaphragms from both saline- and endotoxin-treated groups (2.0 +/- 0. 6 and 2.8 +/- 1.0 ng ethidium/mg tissue, respectively), but it was marked in contracting diaphragms from saline-treated animals (19.0 +/- 2.8 ng/mg tissue) and even more pronounced (30.0 +/- 2.8 ng/mg tissue) in diaphragms from septic animals (P < 0.01). This enhanced free radical generation occurred despite the fact that the force-time integral (i.e., the area under the curve of force vs. time) for control diaphragms was higher than that for the septic group. In additional studies, in which we altered the stimulation paradigm in control muscles to achieve a force-time integral similar to that achieved in septic muscles, an even greater difference between control and septic muscle ROS formation was observed. These data indicate that ROS formation during contraction is markedly enhanced in diaphragms from endotoxin-treated septic animals. We speculate that ROS generated in this fashion plays a central role in producing sepsis-related skeletal muscle dysfunction.     

HPLC procedure for the pharmacokinetic study of the spin-trapping agent, alpha-phenyl-N-tert-butyl nitrone (PBN)

Considerable progress has been made in the use of spin-trapping agents for the trapping of free radicals in biological systems. Radicals have been detected in both in vitro and in vivo systems using this methodology. Free radicals have not only been identified by this procedure, but also the intensity of radical generation and the duration of their production has been assessed as well. One of the most widely used spin-trapping agents in biological systems is PBN. This spin trap appears to be relatively nontoxic at the levels required for successful trapping experiments, but there is no information concerning the possible fate of PBN in such biological systems. Metabolism of PBN could alter the concentration of PBN at the site of trapping which may affect the efficiency of radical capture, especially in in vivo systems. In this study, PBN was administered intraperitoneally to rats and the concentration of the spin trap in various organs was determined by high pressure liquid chromatography as a function of time (15 min to 12 h). The concentration of PBN in plasma peaked at 15 min while the maximum in all organs tested occurred at 30 min. The time course of PBN concentrations in all tissues followed similar curves, and declined rather steeply after the 30-min maximum with a biological half-life of 134 min. However, the amount of PBN per gram of tissue was always higher in liver and kidney than in the brain, heart, and lung. PBN was detected in the urine for as long as 24 h after injection of the compound.     

Antrodia camphorata polysaccharide improves inflammatory response in liver injury via the ROS/TLR4/NF‐κB signal

Antrodia Camphorata Polysaccharide (ACP) refers to a kind of polysaccharide extracted from the natural porous fungus Antrodia camphorata. This study investigated the mechanism of action of ACP in protecting the liver. The results showed that ACP suppressed the LPS‐induced KC cell activation, reduced the expression of inflammatory factors, increased the SOD level and suppressed ROS expression. In addition, N‐acetylcysteine (NAC) was adopted for pre‐treatment to suppress ROS. The results indicated that NAC synergistically exerted its effect with ACP, suggesting that ACP played its role through suppressing ROS. Further detection revealed that ACP activated the Nrf2 signal. It was discovered in the mouse model that, ACP effectively improved liver injury in mice, decreased ALT and AST levels, and suppressed the expression of inflammatory factors. This study suggests that ACP can exert its effect against oxidative stress via the Nrf2‐ARE signalling, which further improves the production of ROS and the activation of TLR4‐NF‐κB signalling, and protects the liver against liver injury.     

Serum half-life, distribution, hepatic uptake and biliary excretion of alpha-tocopherol in rats

The serum clearance of alpha-[3H]tocopherol has been studied after intravenous injection of intestinal lymph labeled in vivo with radioactive alpha-tocopherol. The half-life of the injected alpha-[3H]tocopherol was approx. 12 min. Fractionation of plasma by ultracentrifugation 10 min after injection of lymph showed that 91% of the radioactive alpha-tocopherol remaining in plasma was located in chylomicrons (d less than 1.006 g/ml) and 7.8% in high-density lipoproteins (HDL, 1.05 less than d less than 1.21 g/ml). 2 h after administration of alpha-tocopherol, about 35% of the radioactivity recovered in plasma was associated with chylomicrons and approx. 51% with HDLs. alpha-[3H]Tocopherol was initially taken up by the liver, which contained more than 50% of the injected radioactivity after 45-60 min. Separation of parenchymal and nonparenchymal cells demonstrated a preferential uptake of alpha-[3H]tocopherol by the parenchymal liver cells. After 24 h about 11% of the injected dose was recovered in the liver. Considering whole organs the liver, adipose tissue and skeletal muscle had the highest content of radioactivity after 24 h. Furthermore, about 14% of the administered dose was recovered in bile during 24 h draining.     

Adhesion of human neutrophils to fibronectin is inhibited by comaruman,pectin of marsh cinquefoil <Emphasis Type="Italic">Comarum palustre</Emphasis> L., and by its fragments

Earlier, we detected antiinflammatory action of comaruman, pectin of the marsh cinquefoil Comarum palustre L. This effect can be explained by new data concerning inhibition of adhesion of human neutrophils to fibronectin by comaruman and its fragments. The galacturonan backbone fragment of molecular mass >10 kD appears to be the active region of the comaruman macromolecule. Comaruman CP (50-200 microg/ml) was found to decrease adhesion of neutrophils stimulated by phorbol 12-myristate 13-acetate (PMA, 1.625 microM) and by dithiothreitol (DTT, 0.5 mM). The fragments of comaruman CP-H (100 kD), CP-H1 (10-50 kD), and CP-H2 (100 kD) obtained by acidic hydrolysis and representing regions of linear polygalacturonan are shown to inhibit neutrophil adhesion more than the crude pectin. A fragment CP-E (<10 kD) obtained using pectinolysis and representing a branched region of the comaruman macromolecule failed to influence cell adhesion. The parent comaruman CP as well as fragments of its polygalacturonan backbone diminish PMA-initiated generation of oxygen radicals in neutrophils.     

The in vivo incorporation of acetate into different non-saponifiable lipids by neonatal chick tissues

The in vivo incorporation of [l-14C]acetate into non-saponifiable lipids was higher in neonatal chick liver than in intestinal mucosa, brain and kidneys, and proportional to the amount of substrate injected (2-20 mumole). 14CO2 expired in the breath was also proportional to the dose of acetate. Radioactivity from [l-14C]acetate accumulated by liver was maximal 30 min after the injection of acetate and decreased afterwards. Acetate was mainly incorporated into cholesterol by all the tissues assayed, although small percentages of lanosterol and squalene were obtained in liver. In this tissue, distribution of radioactivity was practically independent from the dose of substrate injected while in intestinal mucosa, brain and kidneys the percentage of cholesterol increased with this dose. The time course of the in vivo formation of different non-saponifiable lipids by neonatal chick tissues was also studied. More than 90% of radioactivity in this fraction obtained 15 min after the acetate injection was recovered as cholesterol in liver and kidneys, while in brain and intestinal mucosa this percentage was about 50% at this time, increasing afterwards. A high percentage of lanosterol was found in brain and intestinal mucosa 15 min after the injection of acetate.     

Application of the method of measurement of fluorescence intensity in vivo in biological tissues for pharmacokinetic studies of different chlorin-based photosensitizers

A precise and reproducible method of quantitative determination of the photosensitizer (PS) Photolon in liver samples of laboratory animals by means of a spectrophotometric assay with preliminary extraction has been developed. Conditions of the PS extraction have been optimized and validated for the quantitative determination of the PS Photolon by the spectrophotometric assay and the main analytical characteristics have been investigated. Using the method of quantitative determination of the PS Photolon in liver tissue samples a quantitative estimation of in vivo fluorescence of the liver tissue was performed after PS administration to animals. There was a high correlation (R = 0.99) between results obtained by spectrophotometry ex vivo and spectrofluorimetry in vivo. The method of fluorescence detection in vivo is applicable for studies of the pharmacokinetics of different photosensitizers.     

Evaluation of DEPMPO as a spin trapping agent in biological systems

Cellular toxicity, pharmacokinetics, and the in vitro and in vivo stability of the SO3*- spin adduct of the spin trap, 5-diethoxyphosphoryl-5-methyl-1-pyrroline-n-oxide (DEPMPO), was investigated, and the results were compared with those of the widely used spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Similar to DMPO, DEPMPO was quickly taken up (<15 min) after intraperitoneal injection, and distributed evenly in the liver, heart, and blood of the mice. In the presence of ascorbate the in vitro stability of the adduct DEPMPO/SO3*- was 7 times better than DMPO/SO3*-. Under in vivo conditions, the spin adduct DEPMPO/SO3*- was 2-4 times more stable than DMPO/ SO3*-, depending on the route of administration of the adducts. Using a low frequency EPR spectrometer, we were able to observe the spin trapped SO3*- radical both with DMPO and DEPMPO directly in the intact mouse. DEPMPO had a detectable spin adduct signal at a concentration as low as 1 mM, as compared to 5 mM for DMPO. We conclude that DEPMPO is potentially a good candidate for trapping radicals in functioning biological systems, and represents an improvement over the commonly used trap DMPO.     

The effect of fasting on the activation in vivo of the insulin receptor kinase.

Fasting causes insulin resistance in liver and fat, and increases insulin sensitivity in muscle. We studied the response in vitro and in vivo to insulin of the insulin receptor tyrosine kinase in muscle and liver from 72 h fasted and control rats. Insulin was injected intraperitoneally together with glucose, and blood and tissue samples were obtained 0, 5, 15 and 30 min later. Basal serum glucose and insulin levels were significantly higher in control than in fasting rats. Serum glucose rose to approximately 300 mg/dl at 5 min and then progressively declined without hypoglycaemia. Receptors were prepared from whole tissue by wheat germ lectin affinity chromatography. 125I-insulin binding to purified receptors was increased by fasting in both muscle (18%) and liver (50%). In untreated fasting and control animals, muscle and liver insulin receptor tyrosine kinase activity was stimulated to similar levels by insulin added in vitro. With only insulin treatment in vivo, muscle receptor tyrosine kinase behaved similarly in fasting and control animals with maximal activation at 15 min post injection. In liver, insulin in vivo stimulated receptor tyrosine kinase activity maximally at 5 min post injection in both fasting and control, but in fasting animals the treatment in vivo caused a significantly larger and more prolonged activation of the enzymic activity, possibly due to a decrease in the rate of dephosphorylation and deactivation of the beta subunits.     

Whole-body kinetic image of a redox probe in mice using Overhauser-enhanced MRI

Overhauser-enhanced MRI (OMRI) enables visualization of free radicals in animals based on dynamic nuclear polarization. Real-time data of tissue redox status gathered from kinetic images of redox-sensitive nitroxyl radical probes using OMRI provided both anatomic and physiological information. Phantom experiments demonstrated the linear correlation between the enhancement factor and the concentration of a membrane-impermeable probe, carboxy-PROXYL (3-carboxy-2,2,5,5-tetramethyl- pyrrolidine-1-oxyl). Whole-body OMRI images illustrated the in vivo kinetics of carboxy-PROXYL for 25 min. Initial distribution was observed in lung, heart, liver, and kidney, but not brain, corresponding to its minimal lipophilicity. Based on these images (pixel size, 1.33 × 1.33 mm; slice thickness, 50mm), a time-concentration curve with low coefficient of variance (<0.21) was created to assess pharmacokinetic behaviors. A biexponential curve showed a distribution phase from 1 to 10 min and an elimination phase from 15 to 25 min. The α rate constant was greater than the β rate constant in ROIs, confirming that its pharmacokinetics obeyed a two-compartment model. As a noninvasive technique, combining OMRI imaging with redox probes to monitor tissue redox status may be useful in acquiring valuable information regarding organ function for preclinical and clinical studies of oxidative diseases.     

Simultaneous determination of morphine and monoamine transmitters in a single mouse brain

A simple procedure for the simultaneous determination of morphine and monoamine transmitters was developed. The procedure consisted of (1) n-butanol extraction and (2) separation and quantitative determination by means of high-performance liquid chromatography combined with electrochemical detection. The maximum intracerebral concentration (210 ± 35 ng/g wet tissue) of morphine was detected 30 min after intramuscular injection (10 mg/kg), which agreed with previous research. Noradrenaline was significantly decreased by morphine injection, while dopamine and 5-hydroxytryptamine were unchanged. However, 3-methoxytyramine, a metabolite of dopamine, was increased, suggesting that the drug increased the turnover rate of dopamine. The procedure used revealed a direct correlation between pharmacokinetics (e.g., distribution of morphine) and pharmacodynamics (e.g. changes of monoamine concentrations) of the drug in vivo.     

Hepatic processing and biliary secretion of the cholesteryl esters from beta very-low-density lipoproteins in the rat

beta-Migrating very-low-density lipoproteins (beta-VLDL) are cholesteryl-ester-enriched lipoproteins which accumulate in the serum of cholesterol-fed animals or patients with type III hyperlipoproteinemia. In the rat, beta-VLDL are rapidly cleared by the liver and parenchymal liver cells form the major site for uptake. In this investigation, beta-VLDL were labeled with [3H]cholesteryl esters and the hepatic intracellular transport of these esters was followed. 2 min after injection, the major part of the [3H]cholesteryl esters is already associated with the liver and a significant proportion is recovered in endosomes. Up to 25 min after injection, an increase in radioactivity in the lysosomal compartment is noticed. This radioactivity initially represents cholesteryl esters, while from 25 min onward, radioactivity is mainly present in unesterified cholesterol. Between 45 min and 90 min after beta-VLDL injection, specific transfer of unesterified [3H]cholesterol to the endoplasmic reticulum is observed, while by 3 h the majority is located in this fraction. The appearance of radioactivity in the bile was rather slow as compared to the rapid initial uptake and processing, and up to 5 h after injection only 10% of the injected dose had reached the bile (mainly as bile acids). 72 h after injection, the amount of the injected radioactivity recovered in the bile had increased to 50%. Chloroquine treatment of the rats inhibited the hydrolysis of the cholesteryl esters and the appearance of radioactivity in the bile was retarded. It is concluded that beta-VLDL are rapidly processed by parenchymal liver cells and that the cholesteryl esters from beta-VLDL are hydrolyzed in the lysosomal compartment. Unesterified cholesterol remains associated with the endoplasmic reticulum for a prolonged time, although ultimately the majority will be secreted into the bile as bile acids. The effective operation of this pathway will prevent extrahepatic accumulation of cholesteryl esters from beta-VLDL, while the prolonged residence time of unesterified cholesterol in the endoplasmic reticulum might be important for regulation of low-density lipoprotein (LDL) receptors in liver and thus for LDL levels in the blood.