Mechanism of action and biological profile of HMG CoA reductase inhibitors. A new therapeutic alternative

High-throughput functional assay in cystic fibrosis patient-derived organoids allows drug repurposing

Background

Cystic fibrosis (CF) is a rare hereditary disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Recent therapies enable effective restoration of CFTR function of the most common F508del CFTR mutation. This shifts the unmet clinical need towards people with rare CFTR mutations such as nonsense mutations, of which G542X and W1282X are most prevalent. CFTR function measurements in patient-derived cell-based assays played a critical role in preclinical drug development for CF and may play an important role to identify new drugs for people with rare CFTR mutations.

Methods

Here, we miniaturised the previously described forskolin-induced swelling (FIS) assay in intestinal organoids from a 96-well to a 384-well plate screening format. Using this novel assay, we tested CFTR increasing potential of a 1400-compound Food and Drug Administration (FDA)-approved drug library in organoids from donors with W1282X/W1282X CFTR nonsense mutations.

Results

The 384-well FIS assay demonstrated uniformity and robustness based on coefficient of variation and Z'-factor calculations. In the primary screen, CFTR induction was limited overall, yet interestingly, the top five compound combinations that increased CFTR function all contained at least one statin. In the secondary screen, we indeed verified that four out of the five statins (mevastatin, lovastatin, simvastatin and fluvastatin) increased CFTR function when combined with CFTR modulators. Statin-induced CFTR rescue was concentration-dependent and W1282X-specific.

Conclusions

Future studies should focus on elucidating genotype specificity and mode-of-action of statins in more detail. This study exemplifies proof of principle of large-scale compound screening in a functional assay using patient-derived organoids.

Pharmacogenomics of lipid-lowering agents: the impact on efficacy and safety

Hyperlipidemia is a significant risk factor for cardiovascular disease morbidity and mortality. The lipid-lowering drugs are considered the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease. Unfortunately, the lack of efficacy and associated adverse effects, ranging from mild-to-moderate to potentially life-threatening, lead to therapy discontinuation. Numerous reports support the role of gene polymorphisms in drugs' pharmacokinetic parameters and their associated adverse reactions. Therefore, this study aims to understand the pharmacogenomics of lipid-lowering drugs and the impact of genetic variants of key genes on the drugs' efficacy and toxicity. Indeed, genetically guided lipid-lowering therapy enhances overall safety, improves drug adherence and achieves long-term therapy.

The lipid transporter HDLBP promotes hepatocellular carcinoma metastasis through BRAF-dependent epithelial-mesenchymal transition

Tumor metastasis is a major cause of cancer mortality. However, little is known regarding the regulation of abnormal cholesterol metabolism in hepatocellular carcinoma (HCC) metastasis. Here, we show that the expression of high-density lipoprotein binding protein (HDLBP), a lipid transporter, is clinically correlated with tumor metastasis in HCC patients. Moreover, HDLBP was required for cholesterol-induced HCC metastasis. We revealed that knockdown and overexpression of HDLBP significantly inhibited and enhanced, respectively, the metastasis, invasion and epithelial-mesenchymal transition (EMT) of HCC cells in vitro and in vivo. Mechanistically, coimmunoprecipitation and mass spectrometry screening uncovered BRAF as a protein target of HDLBP. HDLBP was found to promote EMT signaling in a BRAF-dependent manner. Furthermore, HDLBP interacts with BRAF and inhibits its ubiquitinated degradation by abrogating BRAF-ITCH interactions. Notably, further studies suggest that dabrafenib exhibited a greater metastasis-suppressive effect in HDLBP knockout HCC than isolated treatment. Overall, our findings imply that cholesterol-induced HDLBP contributes to the metastasis and invasion of HCC through BRAF-dependent EMT signaling and that HDLBP may be applied as a biomarker and therapeutic target for HCC.

Off-Target Effect of Lovastatin Disrupts Dietary Lipid Uptake and Dissemination through Pro-Drug Inhibition of the Mesenteric Lymphatic Smooth Muscle Cell Contractile Apparatus

Previously published, off-target effects of statins on skeletal smooth muscle function have linked structural characteristics within this drug class to myopathic effects. However, the effect of these drugs on lymphatic vascular smooth muscle cell function, and by proxy dietary cholesterol uptake, by the intestinal lymphatic network has not been investigated. Several of the most widely prescribed statins (Atorvastatin, Pravastatin, Lovastatin, and Simvastatin) were tested for their in-situ effects on smooth muscle contractility in rat mesenteric collecting lymphatic vessels. Lovastatin and Simvastatin had a concentration-dependent effect of initially increasing vessel contraction frequency before flatlining the vessel, a phenomenon which was found to be a lactone-ring dependent phenomenon and could be ameliorated through use of Lovastatin- or Simvastatin-hydroxyacid (HA). Simvastatin treatment further resulted in mitochondrial depolymerization within primary-isolated rat lymphatic smooth muscle cells (LMCs) while Lovastatin was found to be acting in a mitochondrial-independent manner, increasing the function of RhoKinase. Lovastatin’s effect on RhoKinase was investigated through pharmacological testing and in vitro analysis of increased MLC and MYPT1 phosphorylation within primary isolated LMCs. Finally, acute in vivo treatment of rats with Lovastatin, but not Lovastatin-HA, resulted in a significantly decreased dietary lipid absorption in vivo through induced disfunction of mesenteric lymph uptake and trafficking.

Comparative Hepatic and Intestinal Efflux Transport of Statins

Previous studies have shown that lipid-lowering statins are transported by various ATP-binding cassette (ABC) transporters. However, because of varying methods, it is difficult to compare the transport profiles of statins. Therefore, we investigated the transport of 10 statins or statin metabolites by six ABC transporters using human embryonic kidney cell-derived membrane vesicles. The transporter protein expression levels in the vesicles were quantified with liquid chromatography-tandem mass spectrometry and used to scale the measured clearances to tissue levels. In our study, apically expressed breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) transported atorvastatin, fluvastatin, pitavastatin, and rosuvastatin. Multidrug resistance-associated protein 3 (MRP3) transported atorvastatin, fluvastatin, pitavastatin, and, to a smaller extent, pravastatin. MRP4 transported fluvastatin and rosuvastatin. The scaled clearances suggest that BCRP contributes to 87%-91% and 84% of the total active efflux of rosuvastatin in the small intestine and the liver, respectively. For atorvastatin, the corresponding values for P-gp-mediated efflux were 43%-79% and 66%, respectively. MRP3, on the other hand, may contribute to 23%-26% and 25%-37% of total active efflux of atorvastatin, fluvastatin, and pitavastatin in jejunal enterocytes and liver hepatocytes, respectively. These data indicate that BCRP may play an important role in limiting the intestinal absorption and facilitating the biliary excretion of rosuvastatin and that P-gp may restrict the intestinal absorption and mediate the biliary excretion of atorvastatin. Moreover, the basolateral MRP3 may enhance the intestinal absorption and sinusoidal hepatic efflux of several statins. Taken together, the data show that statins differ considerably in their efflux transport profiles. SIGNIFICANCE STATEMENT: This study characterized and compared the transport of atorvastatin, fluvastatin, pitavastatin, pravastatin, rosuvastatin, and simvastatin acid and four atorvastatin metabolites by six ABC transporters (BCRP, MRP2, MRP3, MRP4, MRP8, P-gp). Based on in vitro findings and protein abundance data, the study concludes that BCRP, MRP3, and P-gp have a major impact in the efflux of various statins. Together with in vitro metabolism, uptake transport, and clinical data, our findings are applicable for use in comparative systems pharmacology modeling of statins.

Large-scale RNAi screening uncovers therapeutic targets in the parasite Schistosoma mansoni

Schistosome parasites kill 250,000 people every year. Treatment of schistosomiasis relies on the drug praziquantel. Unfortunately, a scarcity of molecular tools has hindered the discovery of new drug targets. Here, we describe a large-scale RNA interference (RNAi) screen in adult Schistosoma mansoni that examined the function of 2216 genes. We identified 261 genes with phenotypes affecting neuromuscular function, tissue integrity, stem cell maintenance, and parasite survival. Leveraging these data, we prioritized compounds with activity against the parasites and uncovered a pair of protein kinases (TAO and STK25) that cooperate to maintain muscle-specific messenger RNA transcription. Loss of either of these kinases results in paralysis and worm death in a mammalian host. These studies may help expedite therapeutic development and invigorate studies of these neglected parasites.

Nanoparticles of Lovastatin: Design, Optimization and in vivo Evaluation

Introduction

The aim of the study was to optimize the processing factors of precipitation–ultrasonication technique to prepare nano-sized particles of Lovastatin (LA) for enhancing its solubility, dissolution rate and in vivo bioavailability.

Methods

LA nanoparticles (LANs) were prepared using precipitation–ultrasonication technique under different processing factors. LANs were characterized in terms of particle size, zeta potential and in vitro release. Stability studies at 4°C, 25°C and 40°C were conducted for optimum formulation. In addition, the in vivo bioavailability of the optimum formula was studied in comparison to a marketed product in white master rats.

Results

The optimized LAN formula (LAN15) had particle size (190±15), polydispersity index (0.626±0.11) and a zeta potential (−25±1.9 mV). The dissolution study of the nanosuspensions showed significant enhancement compared with pure drug. After 50 min, only 20.12±1.85% of LA was dissolved while 99.1±1.09% of LA was released from LAN15. Stability studies verified that nanosuspensions at 4°C and 25°C showed higher stability with no particle growth compared to the samples studied at 40°C. In vivo studies conducted in rats verified that there was 1.45-fold enhancement of C_max of LAN15 as compared to marketed tablets.

Conclusion

Nanoparticle prepared by ultrasonication-assisted precipitation method is a promising formula for enhancing the solubility and hence the bioavailability of Lovastatin.

Simvastatin Inhibits the Malignant Behaviors of Gastric Cancer Cells by Simultaneously Suppressing YAP and β-Catenin Signaling

Background

Statins, which are used to lower blood cholesterol levels by inhibiting HMG-CoA reductase, have shown anticancer effects in many cancer cells. However, the role of statins in gastric cancer remains unclear. This study aims to investigate whether the statins could antagonize progression of gastric cancer cells and tried to find the molecule mechanism.

Methods

Effects of simvastatin on the morphology, proliferation, migration, apoptosis, and invasion of gastric cancer cells were detected and compared. Western blotting, cell viability assay, fluorescence, and transfection were employed to study the molecule mechanism of the effects and the interaction between YAP and β-catenin signaling.

Results

Simvastatin could inhibit proliferation, migration and invasion, and promote the apoptosis in gastric cancer cells. Mechanistic studies showed that simvastatin treatment could inhibit the expression of β-catenin and the activity of YAP and the downstream targets of YAP and β-catenin in gastric cancer cells. Moreover, we found that YAP and β-catenin could form a positive feedback loop in gastric cancer cells. Further investigation revealed that simvastatin mainly acted through by inhibiting the activity of RhoA to inhibit YAP and β-catenin, and the geranylgeranyl pyrophosphate pathway mediated this regulation.

Conclusion

Statins represent a promising therapeutic option for gastric cancer by simultaneously targeting YAP and β-catenin signaling.

The Combined Use of Phenothiazines and Statins Strongly Affects Doxorubicin-Resistance, Apoptosis, and Cox-2 Activity in Colon Cancer Cells

Since none of the multidrug resistance (MDR) modulators tested so far found their way into clinic, a novel approach to overcome the MDR of cancer cells has been proposed. The combined use of two MDR modulators of dissimilar mechanisms of action was suggested to benefit from the synergy between them. The effect of three phenothiazine derivatives that were used as single agents and in combination with simvastatin on cell growth, apoptosis induction, activity, and expression of cyclooxygenase-2 (COX-2) in doxorubicin-resistant colon cancer cells (LoVo/Dx) was investigated. Treatment of LoVo/Dx cells by phenothiazine derivatives combined with simvastatin resulted in an increase of doxorubicin cytotoxicity and its intracellular accumulation as compared to the treatment with phenothiazine derivatives that were used as single agents. Similarly, LoVo/Dx cells treated with two-component mixture of modulators showed the reduced expression of ABCB1 (P-glycoprotein) transporter and COX-2 enzyme, both on mRNA and protein level. Reduced expression of anti-apoptotic Bcl-2 protein and increased expression of pro-apoptotic Bax were also detected. Additionally, COX-2 activity was diminished, and caspase-3 activity was increased to a higher extent by phenothiazine derivative:simvastatin mixtures than by phenothiazine derivatives themselves. Therefore, the introduction of simvastatin strengthened the anti-MDR, anti-inflammatory, and pro-apoptotic properties of phenothiazines in LoVo/Dx cells.

TAZ couples Hippo/Wnt signalling and insulin sensitivity through Irs1 expression

Insulin regulates blood glucose levels by binding its receptor and stimulating downstream proteins through the insulin receptor substrate (IRS). Impaired insulin signalling leads to metabolic syndrome, but the regulation of this process is not well understood. Here, we describe a novel insulin signalling regulatory pathway involving TAZ. TAZ upregulates IRS1 and stimulates Akt- and Glut4-mediated glucose uptake in muscle cells. Muscle-specific TAZ-knockout mice shows significantly decreased Irs1 expression and insulin sensitivity. Furthermore, TAZ is required for Wnt signalling-induced Irs1 expression, as observed by decreased Irs1 expression and insulin sensitivity in muscle-specific APC- and TAZ-double-knockout mice. TAZ physically interacts with c-Jun and Tead4 to induce Irs1 transcription. Finally, statin administration decreases TAZ, IRS1 level and insulin sensitivity. However, in myoblasts, the statin-mediated decrease in insulin sensitivity is counteracted by the expression of a constitutively active TAZ mutant. These results suggest that TAZ is a novel insulin signalling activator that increases insulin sensitivity and couples Hippo/Wnt signalling and insulin sensitivity.

Insulin resistance is associated with development of type 2 diabetes. Here the authors show that TAZ interacts with c-Jun and Tead4, inducing expression of the insulin receptor substrate 1 (IRS1) leading to increased glucose uptake in muscle, and that its activity is counteracted by statin administration.

A systematic review of the protective role of swertiamarin in cardiac and metabolic diseases

BACKGROUND

Swertiamarin, is a secoiridoid glycoside found in genera of Enicostemma Species (Enicostemma littorale and Enicostemma axillare) belonging to the family of gentianaceae, which has been reported to cure many diseases such as diabetes, hypertension, atherosclerosis, arthritis, malaria and abdominal ulcers. However, to the best of our knowledge, till date systematic studies to understand the molecular basis of cardiac and metabolic disease preventing properties of swertiamarin has not been reported.

AIM OF THE REVIEW

The present review aims to compile an up-to-date information on the progress made in the protective role of swertiamarin in cardiac and metabolic diseases with the objective of providing a guide for future research on this bioactive molecule.

MATERIALS AND METHODS

Information on the swertiamarin was collected from major scientific databases (Pubmed, Springer, google scholar, and Web of Science) for publication between1974-2016. In this review, the protective role of swertiamarin on cardiac and metabolic diseases was discussed.

RESULTS

Swertiamarin reported to exhibit a wide range of biological activities such as anti-atherosclerotic, antidiabetic, anti-inflammatory and antioxidant effects. These activities were mainly due to its effect on various signaling pathways associated with cardiac remodeling events such as inhibition of NF-kB expression, LDL oxidation, apoptosis, inflammatory and lipid peroxidation markers and stimulation of antioxidant enzymes.

CONCLUSION

Sweriamarin exhibit a wide range of biological activities. This review presents evidence supporting the point of view that swertiamarin should be considered a potential therapeutic agent against cardiac and metabolic diseases, giving rise to novel applications in their prevention and treatment.

Critical role of toxicologic pathology in a short-term screen for carcinogenicity

Carcinogenic potential of chemicals is currently evaluated using a two year bioassay in rodents. Numerous difficulties are known for this assay, most notably, the lack of information regarding detailed dose response and human relevance of any positive findings. A screen for carcinogenic activity has been proposed based on a 90 day screening assay. Chemicals are first evaluated for proliferative activity in various tissues. If negative, lack of carcinogenic activity can be concluded. If positive, additional evaluation for DNA reactivity, immunosuppression, and estrogenic activity are evaluated. If these are negative, additional efforts are made to determine specific modes of action in the animal model, with a detailed evaluation of the potential relevance to humans. Applications of this approach are presented for liver and urinary bladder. Toxicologic pathology is critical for all of these evaluations, including a detailed histopathologic evaluation of the 90 day assay, immunohistochemical analyses for labeling index, and involvement in a detailed mode of action analysis. Additionally, the toxicologic pathologist needs to be involved with molecular evaluations and evaluations of new molecularly developed animal models. The toxicologic pathologist is uniquely qualified to provide the expertise needed for these evaluations.

The diabetogenic action of statins - mechanisms and clinical implications

Treatment with statins has transformed primary and secondary prevention of cardiovascular disease (CVD), including thrombotic stroke. Evidence-based data demonstrate the benefits and safety of statin therapy and help to guide clinicians in the management of populations at high risk of CVD. Nevertheless, clinical trials, meta-analyses and observational studies highlight a 10-12% increase in new-onset diabetes mellitus (NODM) among patients receiving statins. The risk further increases with intensive therapy and among individuals with known risk factors for NODM. Mechanisms underpinning this effect are not yet fully understood; however, Mendelian randomization studies suggest that they are related to lowered activity of HMG-CoA reductase, the target of statin therapy. In vitro research indicates that statins potentially impair β-cell function and decrease insulin sensitivity but how these findings relate to patients is unknown. In the clinic, statins should be prescribed on the basis of CVD risk and individual patient characteristics. In addition, diet and lifestyle interventions should be emphasized to help mitigate the risk of NODM. Individuals who develop NODM while taking statins do not exhibit increased microvascular disease, which is reassuring. In diabetes mellitus of long duration, the effect of statins on glycaemic control is small and unlikely to be clinically important.

Simvastatin may induce insulin resistance through a novel fatty acid mediated cholesterol independent mechanism

Statins are a class of oral drugs that are widely used for treatment of hypercholesterolemia. Recent clinical data suggest that chronic use of these drugs increases the frequency of new onset diabetes. Studies to define the risks of statin-induced diabetes and its underlying mechanisms are clearly necessary. We explored the possible mechanism of statin induced insulin resistance using a well-established cell based model and simvastatin as a prototype statin. Our data show that simvastatin induces insulin resistance in a cholesterol biosynthesis inhibition independent fashion but does so by a fatty acid mediated effect on insulin signaling pathway. These data may help design strategies for prevention of statin induced insulin resistance and diabetes in patients with hypercholesterolemia.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Cytidine derivatives as IspF inhibitors of Burkolderia pseudomallei

Published biological data suggest that the methyl erythritol phosphate (MEP) pathway, a non-mevalonate isoprenoid biosynthetic pathway, is essential for certain bacteria and other infectious disease organisms. One highly conserved enzyme in the MEP pathway is 2C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (IspF). Fragment-bound complexes of IspF from Burkholderia pseudomallei were used to design and synthesize a series of molecules linking the cytidine moiety to different zinc pocket fragment binders. Testing by surface plasmon resonance (SPR) found one molecule in the series to possess binding affinity equal to that of cytidine diphosphate, despite lacking any metal-coordinating phosphate groups. Close inspection of the SPR data suggest different binding stoichiometries between IspF and test compounds. Crystallographic analysis shows important variations between the binding mode of one synthesized compound and the pose of the bound fragment from which it was designed. The binding modes of these molecules add to our structural knowledge base for IspF and suggest future refinements in this compound series.

Determinants of bone marrow adiposity: the modulation of peroxisome proliferator-activated receptor-γ2 activity as a central mechanism

Although the presence of adipocytes in the bone marrow is a normal physiological phenomenon, the role of these cells in bone homeostasis and during pathological states has not yet been fully delineated. As osteoblasts and adipocytes originate from a common progenitor, with an inverse relationship existing between osteoblastogenesis and adipogenesis, bone marrow adiposity often negatively correlates with osteoblast number and bone mineral density. Bone adiposity can be affected by several physiological and pathophysiological factors, with abnormal, elevated marrow fat resulting in a pathological state. This review focuses on the regulation of bone adiposity by physiological factors, including aging, mechanical loading and growth factor expression, as well as the pathophysiological factors, including diseases such as anorexia nervosa and dyslipidemia, and pharmacological agents such as thiazolidinediones and statins. Although these factors regulate bone marrow adiposity via a plethora of different intracellular signaling pathways, these diverse pathways often converge on the modulation of the expression and/or activity of the pro-adipogenic transcription factor peroxisome proliferator-activated receptor (PPAR)-γ2, suggesting that any factor that affects PPAR-γ2 may have an impact on the fat content of bone.

Biochemistry of the non-mevalonate isoprenoid pathway

The non-mevalonate pathway of isoprenoid (terpenoid) biosynthesis is essential in many eubacteria including the major human pathogen, Mycobacterium tuberculosis, in apicomplexan protozoa including the Plasmodium spp. causing malaria, and in the plastids of plants. The metabolic route is absent in humans and is therefore qualified as a promising target for new anti-infective drugs and herbicides. Biochemical and structural knowledge about all enzymes involved in the pathway established the basis for discovery and development of inhibitors by high-throughput screening of compound libraries and/or structure-based rational design.

Developmental toxicity of the HMG-CoA reductase inhibitor (PPD10558) in rats and rabbits

PPD10558 is an orally active, lipid-lowering 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (statin) being developed as a treatment for hypercholesterolemia in patients who have not been able to tolerate statins because of statin-associated myalgia. We have studied the potential developmental toxicity effects of PPD10558 in pregnant rats and rabbits given daily oral doses during the period of organogenesis. Rats were dosed with 0, 20, 80, or 320 mg/kg/day from Gestation Day (GD) 6 to 17 and rabbits received dose levels of 0, 12.5, 25, or 50 mg/kg/day from GD 6 to 18. Additional groups in both studies served as toxicokinetic animals and received the PPD10558 in the same manner as the main study groups at the same dose levels. Blood samples were collected from toxicokinetic animals at designated time points on GD 6 and 17 in rats and GD 6 and 18 in rabbits. Fetal exposure in rats was assessed on GD 20. Maternal and developmental parameters were evaluated in rats and rabbits on GD 20 and GD 29, respectively. No maternal and developmental toxicity was observed at any of the dose levels used in the rat study. Evidence of fetal exposure was determined in fetal plasma with mean fetal concentrations of PPD10558 and the metabolite (PPD11901) found to be between 1 and 6% of the mean maternal concentrations. In rabbits, marked maternal toxicity including mortality (eight deaths; 1 dose at 25 and 7 at 50 mg/kg/day), abortions (2 at 25 mg/kg/day and 6 at 50 mg/kg/day) and reduction in gestation body weight, gestation body weight changes and decreased food consumption were observed. In addition, fetal body weights of the combined sexes were significantly reduced at 50 mg/kg/day in comparison with the controls. Mean peak exposure (Cmax) and total exposure (AUC(0-24)) of PPD11901 in both rats and rabbits were higher than that of PPD10558 on GD 6 and GD 17 at each of the three dose levels.. Based on the results of these studies, the no observed adverse effect level (NOAEL) for maternal and developmental toxicity in rats was considered to be ≥ 320 mg/kg/day, the highest dose level used in the study. The NOAEL for maternal and developmental toxicity in rabbits was 12.5 mg/kg/day and 25 mg/kg/day, respectively.

Evaluation of Possible Carcinogenic Risk to Humans Based on Liver Tumors in Rodent Assays

The two-year rodent bioassay remains the mainstay for carcinogenicity testing, although numerous difficulties have been identified. Fundamentally, a chemical can increase the risk of cancer (1) by damaging DNA directly (DNA reactive) or (2) indirectly by increasing the number of DNA replications (non–DNA reactive). Mechanistic research has identified numerous precursor lesions in the sequence of key events necessary for neoplasia development. Based on these concepts, the author has proposed a short-term (thirteen-week) assay for screening for carcinogenic potential based on a mode of action analysis and on readily available, identifiable preneoplastic changes. A screening assay that detects all potential rodent hepatocarcinogens has been previously identified ( Toxicol Pathol32 [2004], 393–401) including increased liver weight, hepatocellular necrosis, hypertrophy, and cytomegaly. Labeling index for DNA replication might supply additional support. These markers have high sensitivity but low specificity. However, most chemicals can be appropriately classified as to their mode(s) of action for hepatocarcinogenesis with follow-up mechanistic studies, and a rational evaluation of their relevance to humans can be made. A similar process can be envisioned for other tissues for evaluation for carcinogenic potential.

Changes in cholesterol absorption and cholesterol synthesis caused by ezetimibe and/or simvastatin in men

This study evaluates changes in cholesterol balance in hypercholesterolemic subjects following treatment with an inhibitor of cholesterol absorption or cholesterol synthesis or coadministration of both agents. This was a randomized, double blind, placebo-controlled, four-period crossover study to evaluate the effects of coadministering 10 mg ezetimibe with 20 mg simvastatin (ezetimibe/simvastatin) on cholesterol absorption and synthesis relative to either drug alone or placebo in 41 subjects. Each treatment period lasted 7 weeks. Ezetimibe and ezetimibe/simvastatin decreased fractional cholesterol absorption by 65% and 59%, respectively (P < 0.001 for both relative to placebo). Simvastatin did not significantly affect cholesterol absorption. Ezetimibe and ezetimibe/simvastatin increased fecal sterol excretion (corrected for dietary cholesterol), which also represents net steady state cholesterol synthesis, by 109% and 79%, respectively (P < 0.001). Ezetimibe, simvastatin, and ezetimibe/simvastatin decreased plasma LDL-cholesterol by 20, 38, and 55%, respectively. The coadministered therapy was well tolerated. The decreases in net cholesterol synthesis and increased fecal sterol excretion yielded nearly additive reductions in LDL-cholesterol for the coadministration of ezetimibe and simvastatin.

Lessons learned from statin trials

This article aims to review lessons learned about lipid lowering and statins in the past decade and to consider what developments the future may hold. Results from a series of landmark clinical trials confirm that statins significantly reduce cardiovascular morbidity and mortality in patients with and without previous coronary artery disease. The potential of this drug class has yet to be fully explored. Studies currently under way will answer many of the outstanding questions.

Thyroid hormone beta receptor activation has additive cholesterol lowering activity in combination with atorvastatin in rabbits, dogs and monkeys

BACKGROUND AND PURPOSE

Thyroid hormone receptor (TR) agonists are in clinical trials for the treatment of hypercholesterolaemia. As statins are the standard of clinical care, any new therapies must have adjunctive activity, when given in combination with statins. As already known for the statins, the cholesterol lowering effect of TR activation involves increased expression of the low-density lipoprotein receptor. Using animal models, we tested whether TR activation would have additive cholesterol lowering activity in the presence of effective doses of a statin.

EXPERIMENTAL APPROACH

We evaluated the activity of a liver-targeted prodrug, MB07811, of a novel TH receptor beta agonist, MB07344, as monotherapy and in combination with atorvastatin in rabbits, dogs and monkeys.

KEY RESULTS

In rabbits, MB07344 (i.v.) decreased total plasma cholesterol (TPC) comparable to that achieved with a maximally effective dose of atorvastatin (p.o.). The addition of MB07344 to atorvastatin resulted in a further decrease in TPC. Similarly, the addition of MB07811 (p.o.) to atorvastatin treatment decreased TPC beyond the level achieved with either agent as monotherapy. In dogs and monkeys, atorvastatin and MB07811 were administered as monotherapy or in combination. Consistent with the rabbit studies, the combination treatment caused a greater decrease in TPC than either MB07811 or atorvastatin administered as monotherapy.

CONCLUSIONS AND IMPLICATIONS

We conclude that the effects of MB07811 and atorvastatin in lowering cholesterol are additive in animals. These results would encourage and support the demonstration of similarly improved efficacy of combination versus monotherapy with such agents in the clinic.

Independent inhibition of Alzheimer disease beta- and gamma-secretase cleavage by lowered cholesterol levels

The major molecular risk factor for Alzheimer disease so far identified is the amyloidogenic peptide Abeta(42). In addition, growing evidence suggests a role of cholesterol in Alzheimer disease pathology and Abeta generation. However, the cellular mechanism of lipid-dependent Abeta production remains unclear. Here we describe that the two enzymatic activities responsible for Abeta production, beta-secretase and gamma-secretase, are inhibited in parallel by cholesterol reduction. Importantly, our data indicate that cholesterol depletion within the cellular context inhibits both secretases additively and independently from each other. This is unexpected because the beta-secretase beta-site amyloid precursor protein cleaving enzyme and the presenilin-containing gamma-secretase complex are structurally different from each other, and these enzymes are apparently located in different subcellular compartments. The parallel and additive inhibition has obvious consequences for therapeutic research and may indicate an intrinsic cross-talk between Alzheimer disease-related amyloid precursor protein processing, amyloid precursor protein function, and lipid biology.

Atorvastatin-induced early-onset rhabdomyolysis in a patient with nephrotic syndrome

PURPOSE

A case of early-onset rhabdomyolysis in a patient treated with atorvastatin is described.

SUMMARY

A 17-year-old Indian boy weighing 55 kg was admitted to the hospital after complaining of facial puffiness and pedal edema for four days. His medical history revealed a diagnosis of nephrotic syndrome when he was 2 years old. He had six relapses, the last of which occurred 10 years ago. He was not taking any medications on admission and had not for the past 9 years. His vital signs were normal on admission (day 1), but anasarca was noticed during general examination. Cardiovascular, respiratory, and abdominal examinations were normal. Relapse of nephrotic syndrome was considered, and his 24-hour urine protein value confirmed the diagnosis. Further laboratory tests revealed that the patient had high total and low-density-lipoprotein cholesterol values (597 and 465 mg/dL, respectively), and atorvastatin 10 mg p.o. once daily was initiated on day 2. Prednisolone 60 mg p.o. once daily was initiated on day 3. On day 6, the patient complained of pain in both thighs and had difficulty walking. His creatine kinase (CK) concentration was then measured and found to be elevated (11,821 IU/L). Prednisolone and atorvastatin were then stopped, as statin-induced myopathy was suspected. The patient received i.v. hydration and sodium bicarbonate, and he began to show improvement by day 9. Follow-up three weeks later revealed a normal CK level and no myopathy-related complaints.

CONCLUSION

Early-onset rhabdomyolysis was reported in a patient with nephrotic syndrome who was treated with atorvastatin. Concomitant use of prednisolone and the patient's underlying renal impairment may have predisposed the patient to this adverse reaction.

Perspectives in anti-infective drug design. The late steps in the biosynthesis of the universal terpenoid precursors, isopentenyl diphosphate and dimethylallyl diphosphate

A mevalonate-independent pathway for the biosynthesis of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) that has been elucidated during the last decade is essential in plants, many eubacteria and apicomplexan parasites, but is absent in Archaea and animals. The enzymes of the pathway are potential targets for the development of novel antibiotic, antimalarial and herbicidal agents. This review is focused on the late steps of this pathway. The intermediate 2C-methyl-D-erythritol 2,4-cyclodiphosphate is converted into IPP and DMAPP via 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate by the consecutive action of the iron-sulfur proteins IspG and IspH. IPP and DMAPP can be interconverted by IPP isomerase which is essential in microorganisms using the mevalonate pathway, whereas its presence is optional in microorganisms using the non-mevalonate pathway. A hitherto unknown family of IPP isomerases using FMN as coenzyme has been discovered recently in Archaea and certain eubacteria.

Biosynthesis of isoprenoids: a bifunctional IspDF enzyme from Campylobacter jejuni

In the nonmevalonate pathway of isoprenoid biosynthesis, the conversion of 2C-methyl-d-erythritol 4-phosphate into its cyclic diphosphate proceeds via nucleotidyl intermediates and is catalyzed by the products of the ispD, ispE and ispF genes. An open reading frame of Campylobacter jejuni with similarity to the ispD and ispF genes of Escherichia coli was cloned into an expression vector directing the formation of a 42 kDa protein in a recombinant E. coli strain. The purified protein was shown to catalyze the transformation of 2C-methyl-D-erythritol 4-phosphate into 4-diphosphocytidyl-2C-methyl-D-erythritol and the conversion of 4-diphosphocytidyl-2C-methyl-D-erythritol 2-phosphate into 2C-methyl-D-erythritol 2,4-cyclodiphosphate at catalytic rates of 19 micro mol x mg(-1) x min(-1) and 7 micro mol x mg(-1) x min(-1), respectively. Both enzyme-catalyzed reactions require divalent metal ions. The C. jejuni enzyme does not catalyze the formation of 2C-methyl-D-erythritol 3,4-cyclophosphate from 4-diphosphocytidyl-2C-methyl-D-erythritol, a side reaction catalyzed in vitro by the IspF proteins of E. coli and Plasmodium falciparum. Comparative genomic analysis show that all sequenced alpha- and epsilon-proteobacteria have fused ispDF genes. These bifunctional proteins are potential drug targets in several human pathogens (e.g. Helicobacter pylori, C. jejuni and Treponema pallidum).

Biochemical characterization of Bacillus subtilis type II isopentenyl diphosphate isomerase, and phylogenetic distribution of isoprenoid biosynthesis pathways

An open reading frame (Acc. no. P50740) on the Bacillus subtilis chromosome extending from bp 184,997-186,043 with similarity to the idi-2 gene of Streptomyces sp. CL190 specifying type II isopentenyl diphosphate isomerase was expressed in a recombinant Escherichia coli strain. The recombinant protein with a subunit mass of 39 kDa was purified to apparent homogeneity by column chromatography. The protein was shown to catalyse the conversion of dimethylallyl diphosphate into isopentenyl diphosphate and vice versa at rates of 0.23 and 0.63 micromol.mg(-1).min(-1), respectively, as diagnosed by 1H spectroscopy. FMN and divalent cations are required for catalytic activity; the highest rates were found with Ca2+. NADPH is required under aerobic but not under anaerobic assay conditions. The enzyme is related to a widespread family of (S)-alpha-hydroxyacid oxidizing enzymes including flavocytochrome b2 and L-lactate dehydrogenase and was shown to catalyse the formation of [2,3-13C2]lactate from [2,3-13C2]pyruvate, albeit at a low rate of 1 nmol.mg(-1).min(-1). Putative genes specifying type II isopentenyl diphosphate isomerases were found in the genomes of Archaea and of certain eubacteria but not in the genomes of fungi, animals and plants. The analysis of the occurrence of idi-1 and idi-2 genes in conjunction with the mevalonate and nonmevalonate pathway in 283 completed and unfinished prokaryotic genomes revealed 10 different classes. Type II isomerase is essential in some important human pathogens including Staphylococcus aureus and Enterococcus faecalis where it may represent a novel target for anti-infective therapy.

Treating dyslipidemic patients with lipid-modifying and combination therapies

Updated guidelines from the National Cholesterol Education Program give greater emphasis to lipoproteins other than low-density lipoprotein cholesterol (LDL) than previous guidelines. Although statins remain first-line therapy for most patients to lower LDL, combination therapy is the next logical step in achieving goals in patients with mixed dyslipidemia or elevated LDL despite statin therapy. As the prevalence of diabetes, metabolic syndrome, and atherogenic dyslipidemia rises, the importance of treating the total lipid profile becomes even more crucial. Niacin, fibrates, and bile acid sequestrants are effective in combination with statins in lowering LDL, triglycerides, and total cholesterol levels and increasing high-density lipoprotein cholesterol (HDL). Although combination therapies may increase the risk of myopathy, both fibrate-statin and niacin-statin combinations are considered safe. In addition, niacin-statin therapy reduces atherosclerotic progression and coronary events. New pharmacologic formulations exist that will further affect treatment: a single-tablet combination of lovastatin and extended-release niacin is available, as is ezetimibe, a cholesterol-absorption inhibitor. In all, both HDL and triglyceride levels correlate with cardiovascular risk and should be considered secondary targets of therapy. Combination therapy can be safe and effective and can be constructed to affect all lipoprotein parameters.

Hepatotoxicity of hypolipidemic drugs

Dyslipidemic conditions and their cardiovascular related complications are common. Effective primary and secondary prevention strategies include therapies to lower LDL and total cholesterol and to increase HDL. Further, it seems that there is a need for therapeutic reduction in triglycerides as it emerges as an independent risk factor for CVD. Many clinical trials have been designed to evaluate pharmacologic compounds in the treatment of the dyslipidemias and they seem to have shown a safe profile, both in the experiment phases and in post-marketing observation studies. Nevertheless, sporadic reports of hepatotoxicity with statins and niacin still arise (Table 2). Although routine hepatic biochemical test monitoring is recommended, the cost-effectiveness is questionable because often these reactions are idiosyncratic and may not be identified by this routine screening. The risk/benefit ratio is in favor of using these medications in individuals at risk. There is no evidence to suggest intrinsic hepatotoxic activity as such. Drugs that lower triglycerides such as fibrates, have been observed to improve hepatic biochemical tests, although in small series. This leads to speculation whether treatment with fibrates would be beneficial for non-alcoholic fatty liver disease (NAFLD), a condition that is emerging as one of enormous magnitude.

Cholesterol-modulating agents kill acute myeloid leukemia cells and sensitize them to therapeutics by blocking adaptive cholesterol responses

The mevalonate pathway produces many critical substances in cells, including sterols essential for membrane structure and isoprenoids vital to the function of many membrane proteins. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a rate-limiting enzyme in the mevalonate pathway. Because cholesterol is a product of this pathway, HMG-CoA reductase inhibitors (statins) are used to treat hypercholesterolemia. Statins are also toxic to several malignancies, including acute myeloid leukemia (AML). Although this toxicity has been attributed to the inhibition of Ras/Rho isoprenylation, we have previously shown that statin toxicity in primary AML cells (AMLs) does not correlate with Ras isoprenylation or with activating Ras mutations. In other studies, we have shown that hypoxic and oxidant injuries induce cholesterol increments in renal tubule cells and that statins sensitize these cells to injury by blocking protective cholesterol responses. We now demonstrate that exposing particular AMLs to radiochemotherapy induces much greater cellular cholesterol increments than those seen in similarly treated normal bone marrow. Treatment of these AMLs with mevastatin or zaragozic acid (which inhibits cholesterol synthesis but not isoprenoid synthesis) attenuates the cholesterol increments and sensitizes cells to radiochemotherapy. The extent of toxicity is affected by the availability of extracellular lipoproteins, further suggesting that cellular cholesterol is critical to cell survival in particular AMLs. Because zaragozic acid does not inhibit isoprenoid synthesis, these data suggest that cholesterol modulation is an important mechanism whereby statins exert toxic effects on some AMLs and that cholesterol modulators may improve therapeutic ratios in AML by impacting cholesterol-dependent cytoresistance.

The deoxyxylulose phosphate pathway of isoprenoid biosynthesis: studies on the mechanisms of the reactions catalyzed by IspG and IspH protein

Earlier in vivo studies have shown that the sequential action of the IspG and IspH proteins is essential for the reductive transformation of 2C-methyl-d-erythritol 2,4-cyclodiphosphate into dimethylallyl diphosphate and isopentenyl diphosphate via 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate. A recombinant fusion protein comprising maltose binding protein and IspG protein domains was purified from a recombinant Escherichia coli strain. The purified protein failed to transform 2C-methyl-d-erythritol 2,4-cyclodiphosphate into 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate, but catalytic activity could be restored by the addition of crude cell extract from an ispG-deficient E. coli mutant. This indicates that auxiliary proteins are required, probably as shuttles for redox equivalents. On activation by photoreduced 10-methyl-5-deaza-isoalloxazine, the recombinant protein catalyzed the formation of 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate from 2C-methyl-d-erythritol 2,4-cyclodiphosphate at a rate of 1 nmol x min(-1) x mg(-1). Similarly, activation by photoreduced 10-methyl-5-deaza-isoalloxazine enabled purified IspH protein to catalyze the conversion of 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate into a 6:1 mixture of isopentenyl diphosphate and dimethylallyl diphosphate at a rate of 0.4 micromol x min(-1) x mg(-1). IspH protein could also be activated by a mixture of flavodoxin, flavodoxin reductase, and NADPH at a rate of 3 nmol x min(-1) x mg(-1). The striking similarities of IspG and IspH protein are discussed, and plausible mechanistic schemes are proposed for the two reactions.

Safety and efficacy of simvastatin in hypercholesterolemic patients undergoing chronic renal dialysis

Dyslipidemia is universal but hypercholesterolemia per se is present in around 50% of dialysis patients. Although dietary therapy is of benefit in some, the majority require drug therapy. We compared the efficacy and safety of simvastatin plus an optimized lipid-lowering dialysis diet with placebo plus diet in a randomized, double-blind trial stratified for dialysis modality. Patients treated with hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) for at least 9 months and with serum non-high-density lipoprotein (HDL) cholesterol greater than 135 mg/dL, low-density lipoprotein (LDL) greater than 116 mg/dL, and triglyceride less than 600 mg/dL after a 6-week dietary treatment phase and an 8-week diet plus placebo run-in phase, were enrolled in the 24-week double-blind treatment phase. Fifty-seven patients (16 men, 41 women, median age 63 years, range 22-75 yr) were randomized 2:1 to diet plus 5 mg/day simvastatin (n = 38: 22 HD, 16 CAPD) or diet plus placebo (n = 19: 12 HD, 7 CAPD) for 24 weeks. Dose was doubled bimonthly (maximum 20 mg/day) if non-HDL cholesterol was greater than 135 mg/dL. Forty-two patients (73.7%) completed the trial. Comparing baseline and 24 weeks, simvastatin (median 10 mg/day) was significantly more effective than placebo in reducing serum non-HDL cholesterol concentrations. For HD, the median percentage changes for total cholesterol (TC) (simvastatin versus placebo) were -21.4% and -12.1% (P = 0.011), respectively; for LDL cholesterol, -33.0% and -8.8% (P = 0.023); for non-HDL cholesterol, -25.2% and -14.0% (P = 0.008); and for TC:HDL, -17.65% and -1.67% (P = 0.008). For CAPD, changes for TC were -22.1% and -1.5% (P = 0.003), respectively; for LDL, -36.4% and 0.0% (P = 0.001); for non-HDL cholesterol, -24.9% and -3.6% (P = 0.002); and for TC:HDL ratio, -21.49% and +9.74% (P = 0.045). Changes with CAPD in apolipoprotein (Apo) A1 were -4.7% and +4.0% (P = 0.031); and for ApoB, -19.9% and +2.6%, respectively (P = 0.031). There were no significant changes in ApoA1 or ApoB with HD. Compared with placebo, triglyceride levels fell 10.2% with HD and 6.2% with CAPD. HDL cholesterol was unchanged with HD but rose 8.5% with CAPD. These trends, however, did not reach statistical significance (P > 0.05). There was no effect on Lp (a). The incidence of clinical and laboratory adverse experiences were not increased in the simvastatin-treated patients compared with placebo. Simvastatin appears to be a safe and effective treatment for the reduction of serum non-HDL cholesterol levels in both HD and, particularly, CAPD patients.

Increase in hepatic expression of SREBP-2 by gemfibrozil administration to rats

It is well known that gemfibrozil increases the biliary output of cholesterol and phospholipids, but we have little knowledge about the impact these changes have on liver cholesterol and phospholipid biosynthetic pathways. In the present study, no changes were detected in liver lipids and CTP:phosphocholine cytidylyltransferase after gemfibrozil administration to rats. On the contrary, 3-hydroxy-3-methylglutaryl-CoA reductase mRNA (9.9-fold) and Rd activity (16.7-fold) and phosphatidate phosphohydrolase activity (1.7-fold) increased, while plasma apo B-cholesterol (40%) and triglyceride (43%) levels decreased. As a part of a compensatory homeostatic response, we report for the first time that gemfibrozil administration to rats increased the hepatic sterol regulatory element binding protein-2 (SREBP-2) mRNA (2.9-fold) and mature protein (2.2-fold) levels. An early increase in the transcriptional activity of SREBP-2 elicited by gemfibrozil administration might be responsible for the observed changes in HMG-CoA reductase, phosphatidate phosphohydrolase, and SREBP-2 expression.

Evaluation of pharmacological induction of fatty acid beta-oxidation in X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited neurometabolic disorder associated with elevated levels of saturated unbranched very-long-chain fatty acids (VLCFA; C > 22:0) in plasma and tissues, and reduced VLCFA beta-oxidation in fibroblasts, white blood cells, and amniocytes from X-ALD patients. The X-ALD gene (ABCD1) at Xq28 encodes the adrenoleukodystrophy protein (ALDP) that is related to the peroxisomal ATP-binding cassette (ABCD) transmembrane half-transporter proteins. The function of ALDP is unknown and its role in VLCFA accumulation unresolved. Previously, our laboratory has shown that sodium 4-phenylbutyrate (4PBA) treatment of X-ALD fibroblasts results in increased peroxisomal VLCFA beta-oxidation activity and increased expression of the X-ALD-related protein, ALDRP, encoded by the ABCD2 gene. In this study, the effect of various pharmacological agents on VLCFA beta-oxidation in ALD mouse fibroblasts is tested. 4PBA, styrylacetate and benzyloxyacetate (structurally related to 4PBA), and trichostatin A (functionally related to 4PBA) increase both VLCFA (peroxisomal) and long-chain fatty acid [LCFA (peroxisomal and mitochondrial)] beta-oxidation. Isobutyrate, zaprinast, hydroxyurea, and 5-azacytidine had no effect on VLCFA or LCFA beta-oxidation. Lovastatin had no effect on fatty acid beta-oxidation under normal tissue culture conditions but did result in an increase in both VLCFA and LCFA beta-oxidation when ALD mouse fibroblasts were cultured in the absence of cholesterol. The effect of trichostatin A on peroxisomal VLCFA beta-oxidation is shown to be independent of an increase in ALDRP expression, suggesting that correction of the biochemical abnormality in X-ALD is not dependent on pharmacological induction of a redundant gene (ABCD2). These studies contribute to a better understanding of the role of ALDP in VLCFA accumulation and may lead to the development of more effective pharmacological therapies.

Oxidation of HMG-CoA reductase inhibitors by tert-butoxyl and 1, 1-diphenyl-2-picrylhydrazyl radicals: model reactions for predicting oxidatively sensitive compounds during preformulation

Hydrogen atom abstraction rate constants for the reaction of tert-butoxyl and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical with the HMG-CoA reductase inhibitors lovastatin, simvastatin, and statins I-IV were measured. This series of diene-containing drugs is known to be prone to oxidation. The tert-butoxyl radical was generated by the thermolysis of di-tert-butylperoxyoxalate at 40 degrees C. A competitive kinetic method was used to determine the relative rate of hydrogen atom abstraction by tert-butoxyl radical to beta-scission. The absolute rate constants were calculated using the experimentally determined product ratios of t-butanol to acetone and the known rate of beta-scission of tert-butoxyl radical. The rate constants for the reaction with DPPH radical were measured spectrophotometrically by monitoring the loss of DPPH radical as a function of substrate concentration. The rate constants correlate well with the structure of the molecules studied. These kinetic techniques allow for oxidatively sensitive compounds to be identified early in the drug development cycle. The tert-butoxyl radical, a strong hydrogen atom abstractor, is representative of the hydroxyl (. OH) and alkoxyl (. OR) radicals; in contrast the DPPH radical, a much weaker radical, is a good kinetic model for hydroperoxyl (. OOH) and peroxyl (. OOR) radicals. These kinetic methods can be used to quantitatively assess the lability of drug candidates towards reaction with oxygen-centered radicals at an early stage of development and facilitate the design of inhibiting strategies.

Differences in the effects of HMG-CoA reductase inhibitors on proliferation and viability of smooth muscle cells in culture

We investigated the influence of lovastatin, simvastatin and pravastatin on proliferation and viability of vascular smooth muscle cells (SMC) in vitro and studied the effects of lovastatin on a mouse SMC line transgenic for a temperature-sensitive mutant of SV40 large T antigen (TAg), known to inhibit the function of p53 and pRb family members. We found that lovastatin and simvastatin inhibited cell proliferation by provoking G0/G1 phase arrest with concomitant depression of the proliferation antigen Ki-67/MIB-1. Lovastatin at high concentrations of 20 micromol/l caused cell death in the presence of serum but not under serum starved conditions, which was verified on the basis of increased DNA strand breaks, decreased DNA content and morphological alterations seen by electron microscopy. Cell death was also found for simvastatin, whereas pravastatin did not exhibit antiproliferative or cytotoxic effects. Mouse SMC transgenic for TAg did not show any impaired sensitivity to the antiproliferative and cell death inducing effect of lovastatin, but both effects could be antagonized by the supplementation of mevalonate. The data indicate that antiproliferative and cytotoxic effects of lovastatin are caused by the using up of products of mevalonate metabolism and do not require the presence of p53 or pRb.

Proteomics to display lovastatin-induced protein and pathway regulation in rat liver

Lovastatin is a lipid lowering agent that acts by inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a key regulatory enzyme in cholesterol biosynthesis. In this study the pattern of gene network regulation induced in hepatic proteins as a response to lovastatin treatment was analyzed by proteomics. In livers of male F344 rats treated with 1.6 mg/kg/day lovastatin or 150 mg/kg/day lovastatin for seven days, 36 proteins were found to be significantly altered (p<0.001) in relation to treatment. The changed proteins were classified according to their cellular function and participation in biochemical pathways. The following observations were made: (i) inhibition of HMG-CoA reductase provoked a regulatory response in the cholesterol synthesis pathway including the induction of cytosolic HMG-CoA synthase and of isopentenyl-diphosphate delta-isomerase, (ii) manipulation of the lipid metabolism triggered alterations in key enzymes of the carbohydrate metabolism, and (iii) lovastatin treatment was associated with signs of toxicity as reflected by changes in a heterogeneous set of cellular stress proteins involved in functions such as cytoskeletal structure, calcium homeostasis, protease inhibition, cell signaling or apoptosis. These results present new insights into liver gene network regulations induced by lovastatin and illustrate a yet unexplored application of proteomics to discover new targets by analysis of existing drugs and the pathways that they regulate.

Characterization of peroxisomal 3-hydroxy-3-methylglutaryl coenzyme A reductase in UT2 cells: sterol biosynthesis, phosphorylation, degradation, and statin inhibition

We have previously identified a CHO cell line (UT2 cells) that expresses only one 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase protein which is localized exclusively in peroxisomes [Engfelt, H.W., Shackelford, J.E., Aboushadi, N., Jessani, N., Masuda, K., Paton, V.G., Keller, G.A., and Krisans, S.K. (1997) J. Biol. Chem. 272, 24579-24587]. In this study, we utilized the UT2 cells to determine the properties of the peroxisomal reductase independent of the endoplasmic reticulum (ER) HMG-CoA reductase. We demonstrated major differences between the two proteins. The peroxisomal reductase is not the rate-limiting enzyme for cholesterol biosynthesis in UT2 cells. The peroxisomal reductase protein is not phosphorylated, and its activity is not altered in the presence of inhibitors of cellular phosphatases. Its rate of degradation is not accelerated in response to mevalonate. Finally, the degradation process is not blocked by N-acetyl-Leu-Leu-norleucinal (ALLN). Furthermore, the peroxisomal HMG-CoA reductase is significantly more resistant to inhibition by statins. Taken together, the data support the conclusion that the peroxisomal reductase is functionally and structurally different from the ER HMG-CoA reductase.

Effect of simvastatin on the lipid profile of hemodialysis patients

BACKGROUND

Simvastatin, a 3-hydroxy 3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitor, is used widely for treatment of hypercholesterolemia. Simvastatin may be a suitable treatment for dyslipidemia in hemodialysis (HD) patients. However, investigation of the side-effects and safety of long-term administration of simvastatin to HD patients has been limited. In this study, we investigated the effects and safety of simvastatin and its effects on lipoprotein metabolism in hypercholesterolemic patients on HD.

METHODS

Simvastatin was administered at a dosage of 5 mg/day for 24 weeks to 38 HD patients with high serum total cholesterol (TC) levels (200 mg/dl) or low high-density lipoprotein cholesterol (HDL-C) levels (35 mg/dl). Every four weeks, serum lipids, apolipoprotein, lipoprotein (a) [Lp(a)] and malondialdehyde (MDA) levels were measured. In addition, lipid levels were determined in each lipoprotein fraction separated by ultracentrifugation.

RESULTS

After 24 weeks of simvastatin administration, TC significantly decreased by 25.7%, and low-density lipoprotein cholesterol (LDL-C) was significantly decreased by 33.6%. Triglyceride (TG) and HDL-C showed no significant changes. Apolipoprotein (apo) B significantly decreased by 24.5% and apo E by 30.0%. No significant changes were observed in the other apolipoproteins. MDA was also significantly decreased, whereas Lp(a) was not significantly altered. In the lipoprotein fractions, very LDL cholesterol (VLDL-C), intermediate-density lipoprotein cholesterol (IDL-C), LDL1 cholesterol (LDL1-C), and LDL2 cholesterol (LDL2-C) showed significant decreases. No particular side-effects were observed during the 12 months of simvastatin administration.

CONCLUSIONS

These results suggest that simvastatin appears to be safe and effective in HD patients with hypercholesterolemia.

Enhancement of mdr2 gene transcription mediates the biliary transfer of phosphatidylcholine supplied by an increased biosynthesis in the pravastatin-treated rat

An increase of biliary lipid secretion is known to occur in the rat under sustained administration of statin-type 3-hydroxy-3-methylglutaryl (HMG) coenzyme A (CoA) reductase inhibitors. The present study has addressed critical mechanisms of hepatic lipid synthesis and phosphatidylcholine (PC) biliary transport in the rat fed with a 0.075% pravastatin diet for 3 weeks. After treatment, biliary secretion of PC and cholesterol increased to 233% and 249% of controls, while that of bile salts was unchanged. Activity of cytidylyltransferase (CT), a major regulatory enzyme in the CDP-choline pathway of PC synthesis, was raised in both microsomal and cytosolic fractions (226% and 150% of controls), and there was an increase to 187% in the mass of active enzyme as determined by Western blot of microsomal protein using an antibody specific to CT. Cytosolic activity of choline kinase, another enzyme of the CDP-choline pathway, also increased to 175% of controls. In addition, there was an over eightfold increase in the HMG CoA reductase activity and mRNA. Thus, an increased PC and cholesterol synthetic supply to hepatocytes appeared as a basic mechanism for the biliary hypersecretion of these lipids. Notwithstanding the increased synthesis, hepatic PC content was unchanged, suggesting an enhanced transfer of this lipid into bile. Indeed, there was a sevenfold increase of multidrug resistance gene 2 (mdr2) gene mRNA coding for a main PC canalicular translocase. Thus, hypersecretion of biliary PC in the model studied can be explained by an up-regulation of mdr2 gene transcription and its P-glycoprotein product mediating the biliary transfer of PC supplied by an increased biosynthesis.

Effects of simvastatin on fasting and postprandial triglyceride-rich lipoproteins in patients with type I diabetes mellitus

To assess the effect of simvastatin on fasting and postprandial triglyceride (TG)-rich lipoproteins in subjects with type 1 diabetes and elevated LDL cholesterol levels, eight patients participated in a simvastatin versus placebo, randomized, crossover study. At the end of each drug period fasting and postprandial lipoprotein studies were undertaken. Fasting plasma total and LDL cholesterol and apolipoprotein B (apo B) were significantly lower on simvastatin compared to placebo. Postprandial studies: simvastatin versus placebo consistently decreased the area under the curve (AUC, mean+/-SEM) of TG in plasma (12.52+/-9.07 versus 18.70+/-10.48 mmol x h/L, p = 0.02). Similarly, TG AUC was lower: in the chylomicron subfraction (Sf > 400) 3.24+/-2.71 versus 5.27+/-4.61 mmol x h/L p = 0.03; and in the [chylomicron remnant + VLDL] subfraction (Sf 20-400) 3.98+/-2.51 versus 7.04+/-3.88 mmol x h/L, p = 0.01. This was due to decreased particle n umber rather than size, as shown by a decrease in the AUC of apo B in Sf 20-400 (600+/-360 versus 980+/-600 mg x h/L, p = 0.02) and the lack of change in the ratio of TG/apo B. Intestinal lipoproteins contributed to the simvastatin effect, as shown by the lower AUC of retinyl esters in both subfractions. Chylomicrons: 627.61+/-363.43 versus 948.19+/-568.34 nmol x h/L, p = 0.02 and remnants: 129.23+/-67.12 versus 208.49+/-92.11 nmol x h/L, p = 0.04. Our data suggest an additional mechanism by which simvastatin can decrease the risk of atherosclerosis in patients with type I diabetes: a decrease of the number of circulating intestinal and hepatic postprandial TG-rich lipoprotein particles.