Evaluation of myopathy risk for HMG-CoA reductase inhibitors by urethane infusion method

Evidence of Strong Guest-Host Interactions in Simvastatin Loaded in Mesoporous Silica MCM-41

A rational design of drug delivery systems requires in-depth knowledge not only of the drug itself, in terms of physical state and molecular mobility, but also of how it is distributed among a carrier and its interactions with the host matrix. In this context, this work reports the behavior of simvastatin (SIM) loaded in mesoporous silica MCM-41 matrix (average pore diameter ~3.5 nm) accessed by a set of experimental techniques, evidencing that it exists in an amorphous state (X-ray diffraction, ssNMR, ATR-FTIR, and DSC). The most significant fraction of SIM molecules corresponds to a high thermal resistant population, as shown by thermogravimetry, and which interacts strongly with the MCM silanol groups, as revealed by ATR-FTIR analysis. These findings are supported by Molecular Dynamics (MD) simulations predicting that SIM molecules anchor to the inner pore wall through multiple hydrogen bonds. This anchored molecular fraction lacks a calorimetric and dielectric signature corresponding to a dynamically rigid population. Furthermore, differential scanning calorimetry showed a weak glass transition that is shifted to lower temperatures compared to bulk amorphous SIM. This accelerated molecular population is coherent with an in-pore fraction of molecules distinct from bulklike SIM, as highlighted by MD simulations. MCM-41 loading proved to be a suitable strategy for a long-term stabilization (at least three years) of simvastatin in the amorphous form, whose unanchored population releases at a much higher rate compared to the crystalline drug dissolution. Oppositely, the surface-attached molecules are kept entrapped inside pores even after long-term release assays.

The Anti-hyperlipidemia Effects of Raw Polygonum multiflorum Extract in Vivo

Polygonum multiflorum is widely used in the prevention and treatment of hyperlipidemia in traditional Chinese Medicine. In this study, the effects and relevant mechanisms of lipid-regulation by raw Polygonum multiflorum (RPM) were investigated. The results indicated that the basal plasma lipids, such as low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), and triglycerides (TG), were significantly decreased in RPM treatment groups compared with the model group, especially in the RPM high dose group. The key enzymes involved in lipid metabolism, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) in plasma were generally reduced after oral administration, which was consistent with the transcription levels of their target genes. In addition, the hepatotoxicity of RPM was investigated, and RPM showed slightly less liver injury than that induced by simvastatin. Histological analysis indicated that the fat vacuoles and steatosis in hepatocytes were relieved after oral administration of RPM extract at a high dose of 16.2 g/kg, which was more obvious than that induced by simvastatin. These results revealed that RPM exerted its lipid-lowering effect by regulating the expression of related genes, and performed better than simvastatin in the treatment of hyperlipidemia.

siRNA capsulated brain-targeted nanoparticles specifically knock down OATP2B1 in mice: a mechanism for acute morphine tolerance suppression

Regulating main brain-uptake transporter of morphine may restrict its tolerance generation, then modify its antinociception. In this study, more than 2 fold higher intracellular uptake concentrations for morphine and morphine-6-glucuronide (M6G) were observed in stable expression cells, HEK293-hOATP2B1 than HEK293-MOCK. Specifically, the K_m value of morphine to OATP2B1 (57.58 ± 8.90 μM) is 1.4-time more than that of M6G (80.31 ± 21.75 μM); Cyclosporine A (CsA), an inhibitor of OATP2B1, can inhibit their intracellular accumulations with IC₅₀ = 3.90 ± 0.50 μM for morphine and IC₅₀ = 6.04 ± 0.86 μM for M6G, respectively. To further investigate the role of OATP2B1 in morphine brain transport and tolerance, the novel nanoparticles of DGL-PEG/dermorphin capsulated siRNA (OATP2B1) were applied to deliver siRNA into mouse brain. Along with OATP2B1 depressed, a main reduction was found for each of morphine or M6G in cerebrums or epencephalons of acute morphine tolerance mice. Furthermore, calcium/calmodulin-dependent protein kinase IIα (CaMKIIα) in mouse prefrontal cortex (mPFC) underwent dephosphorylation at Thr286. In conclusion, OATP2B1 downregulation in mouse brain can suppress tolerance via blocking morphine and M6G brain transport. These findings might help to improve the pharmacological effects of morphine.

Myoglobin cast nephropathy in a kidney transplant patient with normal creatine kinase

Delayed graft function in kidney transplant recipients is a known complication associated with increased risk of acute rejection and reduced transplant survival after 1 year. There are multiple risk factors, including prolonged cold ischemia time, donor age, and cause of donor's death. Major causes of delayed graft function are acute kidney injury in the donor, often from prolonged terminal ischemia, reflected by acute tubular injury in the recipient. However, the differential diagnosis of delayed graft function includes acute rejection, recurrence of the primary glomerular diseases, and other less commonly encountered conditions. A transplant kidney biopsy usually is required to elucidate the correct cause and initiate the right treatment, which is crucial for transplant survival. We report a case of a transplant recipient who developed delayed graft function due to an uncommon cause. After correct diagnosis, the patient's transplant function improved.

Statin-induced apoptosis linked with membrane farnesylated Ras small G protein depletion, rather than geranylated Rho protein

Rhabdomyolysis is a severe adverse effect of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins). This myopathy is strongly enhanced by the combination with statins and fibrates, another hypolipidaemic agent. We have evaluated the initial step of statin-induced apoptosis by the detection of membrane flip-flop using flow cytometric analysis. L6 rat myoblasts were treated with various statins (atorvastatin (3 μm), cerivastatin (3 μm), fluvastatin (3 μm), pravastatin (3 mm), or simvastatin (3 μm)) for 2, 4 or 6 h followed by reacting with FITC-conjugated annexin V for the detection of initial apoptosis signal (flip-flop). Various statin-treated myoblasts were significantly stained with FITC-annexin V at 6 h, whereas they were not detected at 2 h. Moreover, immunoblot analysis indicated that when the cells were treated with cerivastatin (3 μm), membrane-associated Ras protein was activated and detached until 6 h, resulting in cell death through the consequent activation of caspase-8. On the other hand, since cytosolic Ras activation did not activate, there is still an unknown mechanism in statin-related Ras depletion. In conclusion, statin-induced apoptosis in muscular tissue was directly initiated by the farnesyl-anchored Ras protein depletion from cell membrane with subsequent apoptosis.

Statin-induced myopathy in the rat: relationship between systemic exposure, muscle exposure and myopathy

Rare instances of myopathy are associated with all statins, but cerivastatin was withdrawn from clinical use due to a greater incidence of myopathy. The mechanism of statin-induced myopathy with respect to tissue disposition was investigated by measuring the systemic, hepatic, and skeletal muscle exposure of cerivastatin, rosuvastatin, and simvastatin in rats before and after muscle damage. The development of myopathy was not associated with the accumulation of statins in skeletal muscle. For each statin exposure was equivalent in muscles irrespective of their fibre-type sensitivity to myopathy. The low amount of each statin in skeletal muscle relative to the liver does not support a significant role for transporters in the disposition of statins in skeletal muscle. Finally, the concentration of cerivastatin necessary to cause necrosis in skeletal muscle was considerably lower than rosuvastatin or simvastatin, supporting the concept cerivastatin is intrinsically more myotoxic than other statins.

FLOW CYTOMETRIC EVALUATION OF SYNERGISTIC PRO-APOPTOTIC EFFECTS OF STATINS AND CLOFIBRATES IN IM-9 HUMAN LYMPHOBLASTS

1. In the present study, we evaluated fibrate-mediated potentiation of statin-induced apoptosis in IM-9 human lymphoblasts. 2. The pro-apoptotic effects of statin and fibrate were measured by flow cytometry with biotin-annexin V, followed by addition of avidin-fluorescein isothiocyanate and propidium iodide. Apoptosis was confirmed using karyopyknotic staining, as well as detection of DNA fragmentation and caspase 3 activation. 3. Incubation of IM-9 cells with both 0.1 micromol/L cerivastatin and 200 micromol/L clofibrate had a synergistic effect compared with 0.1 micromol/L cerivastatin alone or 200 micromol/L clofibrate alone. The magnitude of apoptosis induced by various combinations of statins and clofibrate were as follows: cerivastatin (0.1 micromol/L) + clofibrate (200 micromol/L) > atorvastatin (0.1 micromol/L) + clofibrate (200 micromol/L) > pravastatin (100 micromol/L) + clofibrate (200 micromol/L). Other fibrates (bezafibrate and clinofibrate) did not show any synergistic effect. Furthermore, karyopyknotic staining, caspase 3 activation and DNA fragmentation demonstrated synergistic pro-apoptotic effects of statin and fibrate. 4. The results of the present study suggest that simultaneous treatment with statins and clofibrate could provide improved therapeutic efficacy in leukaemia patients.

Rab-small GTPases are involved in fluvastatin and pravastatin-induced vacuolation in rat skeletal myofibers

Three-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors, known as statins, induce skeletal muscle injury including myalgia, myositis, and rhabdomyolysis. The mechanism of this myotoxicity remains unknown. This study examined the effect of statins on single skeletal myofibers enzymatically isolated from the rat flexor digitorum brevis muscles. Fluvastatin and pravastatin induced the formation of numerous vacuoles in the myofibers after 72 h of treatment. This effect progressed in a time- and concentration-dependent manner and, consequently, cell death occurred after 120 h. Electron micrographs revealed craters along the sarcolemma and swelling of the sarcoplasmic reticula and mitochondria, in addition to intracellular vacuoles. When caffeine was added after 72 h of fluvastatin treatment, contractile shortening of statin-treated myofibers was significantly attenuated and blebs formed on the surface of the myofibers. The coapplication of geranylgeranylpyrophosphate (GGPP) with fluvastatin prevented the morphological changes, while that of farnesylpyrophosphate (FPP) was ineffective. Furthermore, perillyl alcohol, an inhibitor of Rab geranylgeranyl transferase and geranylgeranyl transferase-I (GGTase-I), mimicked the effect of statins, while a specific GGTase-I inhibitor (GGTI-298) or a farnesyl transferase inhibitor (FTI-277) failed to do so. These results suggest that the inactivation of Rab GTPase, which involved in intracellular membrane transport, is a crucial factor in statin-induced-morphological abnormality in skeletal muscle fibers.

Preventive effects of bicarbonate on cerivastatin-induced apoptosis

Although HMG-CoA reductase inhibitors such as statins are the most widely used cholesterol-lowering agents, there is a risk of myopathy or rhabdmyolysis occurring in patients taking these drugs. It has been reported that a number of lipophilic statins cause apoptosis in various cells, but it is still not clear whether intracellular acidification is involved in statin-induced apoptosis. There have been few studies aimed at identifying compounds that suppress statin-induced myotoxicity. In the present study, we examined the relationship between cerivastatin-induced apoptosis and intracellular acidification and the effect of bicarbonate on cerivastatin-induced apoptosis using an RD cell line as a model of in vitro skeletal muscle. Cerivastatin reduced the number of viable cells and caused dramatic morphological changes and DNA fragmentation in a concentration-dependent manner. Moreover, cerivastatin-induced apoptosis was associated with intracellular acidification and caspase-9 and -3/7 activation. On the other hand, bicarbonate suppressed cerivastatin-induced pH alteration, caspase activation, morphological change and reduction of cell viability. Accordingly, bicarbonate suppressed statin-induced apoptosis. The strategy to combine statins with bicarbonate can lead to reduction in the chance of the severe adverse events including myopathy or rhabdmyolysis.

Inhibitory effects of statins on human monocarboxylate transporter 4

Human MCT4 (SLC16A3) is responsible for the efflux of L-lactic acid from skeletal muscle cells and is essential for muscle homeostasis. However, the effects of monocarboxylate drugs, such as statins on the MCT4-mediated transport of L-lactic acid have not been elucidated. Inhibition of L-lactic acid transport mediated by MCT4 might to lead to collapse of muscle homeostasis. The aim of this study was to establish an MCT4 transfected cell line and to clarify the transport mechanism of L-lactic acid and the effects of statins on this transport system. Results of Western blot analyses and immunohistochemistry studies indicated that the expression of CD147 and MCT4-FLAG protein were observed and was displayed clear plasma membrane localization in CD147 and MCT4-FLAG co-transfected cell line (cm cells). Uptake of L-lactic acid in cm cells was significantly greater than that in cells transfected with a vector alone. L-lactic acid uptake was concentration-dependent with a K(m) value of 28.43+/-3.87 mM. The results of a previous study showing a K(m) value of 28.5 mM in hMCT4-expressed oocytes. Lipophilic statins significantly inhibited [(14)C] L-lactic acid uptake in a concentration-dependent manner. In contrast, the inhibitory effects of hydrophilic statins were very weak.

Clofibrate-induced apoptosis is mediated by Ca2+-dependent caspase-12 activation

The mechanism of fibrate-induced myopathy was investigated in this report. When clofibrate (30 to 300 microM) was applied to L6 rat skeletal myoblasts, dose-dependently apoptosis was observed within 24 h. In the apoptotic myoblasts, a caspase-12 cleavage was observed at 2 h and with following caspases-9 and -3-related cascade activation. In contrast, the neutral protease calpain, that is a key enzyme in ER stress-related apoptosis via caspase-12 activation, was significantly decreased during apoptosis. Next, the authors evaluated a role of calcium-dependent signal(s). When clofibrate was added into medium, cytosolic calcium concentration was rapidly and persistently increased. On the other hand, an addition of 10 mM EGTA depressed sustained calcium phase, and concurrent myoblasts apoptosis was completely inhibited. Taken together, our findings indicate that the clofibrate-induced myopathy is triggered by Ca2+ influx, then activated cytosolic caspase-12 through calpain-independent cascade, and consequently caused apoptotic DNA fragmentation.

Functional characterization of SLCO1B1 (OATP-C) variants, SLCO1B1*5, SLCO1B1*15 and SLCO1B1*15+C1007G, by using transient expression systems of HeLa and HEK293 cells

OBJECTIVES

SLCO1B1*5 and SLCO1B1*15 have been reported to reduce the clearance of pravastatin in healthy volunteers. However, there remains controversy in the effects of SLCO1B1*5 on the activity of OATP1B1 in vitro. In addition, the effect of SLCO1B1*15 on the function of OATP1B1 has not been studied using cDNA-expression systems. Object of the present study was to study the influence of SLCO1B1*5, *15 and *15+C1007G, a novel haplotype found in a patient with pravastatin-induced myopathy, on the functional properties of OATP1B1 by transient expression systems of HEK293 and HeLa cells using endogenous conjugates and statins as substrates.

METHODS

Transporting assays for endogenous substrates were performed using tritium labeled estradiol-17beta-D-glucuronide and estrone-3-sulfate. Quantitation of pravastatin, atorvastatin, cerivastatin and simvastatin were carried out using HPLC tandem mass spectrometry.

RESULTS

The transporting activities of cells expressing SLCO1B1*5, *15 and *15+C1007G decreased significantly but those of SLCO1B1*1b, *1a+C1007G and *1b+C1007G were not altered for all of the substrates tested except for simvastatin. Kinetic analysis of pravastatin and atorvastatin showed that Km values were not altered but Vmax values decreased significantly in cells expressing SLCO1B1*5, *15 and *15+C1007G. Immunocytochemical study showed that SLCO1B1*5, *15 and *15+C1007G proteins are localized not only at the plasma membrane but also in the intracellular space.

CONCLUSIONS

These findings suggest that 521T>C, existing commonly in SLCO1B1*5, *15 and *15+C1007G, is the key single nucleotide polymorphism (SNP) that determines the functional properties of SLCO1B1*5, *15 and *15+C1007G allelic proteins and that decreased activities of these variant proteins are mainly caused by a sorting error produced by this SNP.

Evaluation of apoptosis and necrosis induced by statins using fluorescence-enhanced flow cytometry

The purpose of this study was to evaluate the apoptosis and necrosis induced by five kinds of statins in IM-9 human lymphoblasts with fluorescence-enhanced flow cytometry using avidin-biotin complex. IM-9 human lymphoblasts (2 x 10(4) cells/cm2) were seeded into tissue culture plates and incubated with five kinds of statins. Statin-treated cells were first incubated with biotin-annexin V, followed by addition of avidin-FITC and propidium iodide, and then subjected to flow cytometry. The fluorescence intensity was enhanced using an avidin-biotin complex system, resulting in successful separate determination of the statin-induced apoptosis and necrosis by flow cytometry, which enabled us to quantitatively evaluate the statin-induced cell damage. Flow cytometric analysis results in the intensity of statin-induced apoptosis in IM-9 cells as follows: atorvastatin cerivastatin>fluvastatin simvastatin>pravastatin. The intensity of statin-induced necrosis in IM-9 cells was expressed as follows: atorvastatin cerivastatin>fluvastatin simvastatin>pravastatin. The total damage of IM-9 cells induced by five kinds of statins were expressed as the sum of both percentages of apoptosis and necrosis as follows: atorvastatin cerivastatin>fluvastatin simvastatin>pravastatin. Our studies show that fluorescence enhancement with avidin-biotin complex is useful for the identification and quantitation of annexin-positive apoptosis cells and thus, the fluorescence-enhanced flow cytometry was shown to be applicable for screening of statins as new anti-leukemia agents.

Rhabdomyolysis from Simvastatin Triggered by Infection and Muscle Exertion

A 42-year-old woman received a 6-month course of simvastatin (20 mg/d) for hypercholesterolemia. Despite an infection with fever, fatigue, myalgias, and lumbar pain, she continued to perform her regular sports activities. Neurologic examination revealed bilateral ptosis and slight upper limb weakness. Serum creatine kinase was 41,000 U/L. Needle electromyography was nonspecifically abnormal. Discontinuation of simvastatin and reduction of the sports activities was followed by a prompt continual lowering of the elevated muscle enzymes to normal values over a 2-week period. The patient's infection, regular sports activity despite the infection, and a suspected mitochondrial defect were regarded as triggers of rhabdomyolysis.

Eisai hyperbilirubinemic rat (EHBR) as an animal model affording high drug-exposure in toxicity studies on organic anions

The Eisai hyperbilirubinemic rat (EHBR) should be a useful animal model for studies on the toxicity of organic anions which are substrates of multidrug resistance-associated protein 2 (Mrp2), since the systemic exposure to these compounds is expected to be increased in EHBR. In this study, we tested the value of EHBR for this purpose, using pravastatin (PV) and methotrexate (MTX) as model compounds. In the case of a single oral dose of PV (200 mg/kg), C(max) in plasma was 4.0-fold higher and AUC(0-infinity) was 3.6-fold larger than those of normal Sprague-Dawley rats (SDR), respectively. When multiple doses of PV were given to EHBR without co-administration of any other compound, drug-induced skeletal muscle toxicity (myopathy/rhabdomyolysis) and increased creatine phosphokinase (CPK) level were observed, whereas a control experiment using SDR did not show any toxic change. When a single dose of MTX (0.6 mg/kg) was given to EHBR orally, C(max) was 1.7-fold higher and AUC(0-infinity) was 1.6-fold larger than those of SDR, respectively. When multiple doses of MTX were given to EHBR, the changes in bone marrow, spleen and intestines were more severe than those in SDR. These findings support the view that EHBR would be a valuable animal model for toxicity studies on organic anion compounds which are substrates of Mrp2.

Evaluation of the synergistic adverse effects of concomitant therapy with statins and fibrates on rhabdomyolysis

Rhabdomyolysis is a severe adverse effect of hypolipidaemic agents such as statins and fibrates. We evaluated this muscular cytotoxicity with an in-vitro culture system. Cellular apoptosis was determined using phase-contrast and fluorescein microscopic observation with Hoechst 33342 staining. L6 rat myoblasts were treated with various statins and bezafibrate under various conditions. With statins only, skeletal cytotoxicity was ranked as cerivastatin > fluvastatin > simvastatin > atorvastatin > pravastatin in order of decreasing potency. Combined application of fibrates enhanced atorvastatin-induced myopathy, which causes little apoptosis alone. These results suggest that statins and fibrates synergistically aggravate rhabdomyolysis.

Liver-specific distribution of rosuvastatin in rats: comparison with pravastatin and simvastatin

Rosuvastatin is a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. The liver is the target organ for the lipid-regulating effect of rosuvastatin; therefore liver-selective uptake of this drug is a desirable property. The aim of this study was to investigate, and compare with pravastatin and simvastatin, the tissue-specific distribution of rosuvastatin. Bolus intravenous doses (5 mg/kg) of radiolabeled rosuvastatin, pravastatin, and simvastatin were administered to rats, and initial uptake clearance (CL(uptake)) in various tissues was calculated. Hepatic CL(uptake) of rosuvastatin (0.885 ml/min/g tissue) was significantly (p < 0.001) larger than that of pravastatin (0.703 ml/min/g tissue), and rosuvastatin was taken up by the hepatic cells more selectively and efficiently than pravastatin. Hepatic CL(uptake) of simvastatin (1.24 ml/min/g tissue) was significantly larger than that of rosuvastatin (p < 0.01) and pravastatin (p < 0.001). However, adrenal CL(uptake) of simvastatin (1.55 ml/min/g tissue) was larger than hepatic CL(uptake), and simvastatin was distributed to other tissues more easily than rosuvastatin. Microautoradiography of the liver, spleen, and adrenal was undertaken 5 min after administration of the study drugs; distribution was quantified by counting the number of silver grains. After administration of rosuvastatin and pravastatin, silver grains were distributed selectively in the intracellular space of the liver, but more rosuvastatin (3.3 +/- 1.0 x 10(5) particles/mm(2)) than pravastatin (2.0 +/- 0.3 x 10(5) particles/mm(2)) tended to distribute to the liver. Simvastatin was less liver-specific (it also distributed to the spleen and adrenal). The results of this study indicated that rosuvastatin was taken up by hepatic cells more selectively and more efficiently than pravastatin and simvastatin.