Inhibition of prenyltransferase activity by statins in both liver and muscle cell lines is not causative of cytotoxicity

Using zebrafish embryo bioassays to identify chemicals modulating the regulation of the epigenome: a case study with simvastatin

Contaminants of emerging concern have been increasingly associated with the modulation of the epigenome, leading to potentially inherited and persistent impacts on apical endpoints. Here, we address the performance of the OECD Test No. 236 FET (fish embryo acute toxicity) in the identification of chemicals able to modulate the epigenome. Using zebrafish (Danio rerio) embryos, acute and chronic exposures were performed with the pharmaceutical, simvastatin (SIM), a widely prescribed hypocholesterolemic drug reported to induce inter and transgenerational effects. In the present study, the epigenetic effects of environmentally relevant concentrations of SIM (from 8 ng/L to 2000 ng/L) were addressed following (1) an acute embryo assay based on OECD Test No. 236 FET, (2) a chronic partial life-cycle exposure using adult zebrafish (90 days), and (3) F1 embryos obtained from parental exposed animals. Simvastatin induced significant effects in gene expression of key epigenetic biomarkers (DNA methylation and histone acetylation/deacetylation) in the gonads of exposed adult zebrafish and in 80 hpf zebrafish embryos (acute and chronic parental intergenerational exposure), albeit with distinct effect profiles between biological samples. In the chronic exposure, SIM impacted particularly DNA methyltransferase genes in males and female gonads, whereas in F1 embryos SIM affected mostly genes associated with histone acetylation/deacetylation. In the embryo acute direct exposure, SIM modulated the expression of both genes involved in DNA methylation and histone deacetylase. These findings further support the use of epigenetic biomarkers in zebrafish embryos in a high throughput approach to identify and prioritize epigenome-modulating chemicals.

Protein-enriched extracts from housefly (Musca domestica) maggots alleviates atherosclerosis in apolipoprotein E-deficient mice by promoting bile acid production and consequent cholesterol consumption

Currently, atherosclerosis control is important to prevent future heart attacks or strokes. Protein-enriched extract (PE) from housefly maggots (Musca domestica) can inhibit the development of atherosclerosis partially through its antioxidant effects. Whether PE exerts other anti-atherosclerosis functions remains unclear. Here, PE was found to simultaneously promote cholesterol metabolism effects in apolipoprotein E knockout (ApoE^-/- ) mice. Bile acid synthesis plays a key role in regulating cholesterol homeostasis in atherosclerosis. Whether PE alleviates atherosclerosis by promoting bile acid production and consequent cholesterol consumption was further explored. First, 8-week-old male ApoE^-/- mice were recruited and fed on a cholesterol-enriched diet. After 8 weeks, these mice were divided into three groups and received gavage administration of PE, simvastatin, and saline for another 8 weeks. Atherosclerosis severity was then assessed. Real-time quantitative polymerase chain reaction and western blot were employed to determine the expression of hepatic ATP-binding cassette transporter A1 (ABCA1), liver X receptor α (LXRα), and peroxisome proliferator-activated receptor-γ (PPAR-γ). Serum levels of high-density lipoprotein-cholesterol (HDL), low-density lipoprotein-cholesterol (LDL), and total cholesterol (TC) were determined by enzyme-linked immunoassay. Results revealed that PE reversed the formation of atherosclerotic lesion; increased the expression of PPAR-γ, LXRα, and ABCA1; increased the amount of bile flow and total bile acid; reduced the serum level of LDL and TC; and increased the level of HDL. In conclusion, enhancement on bile acid production and consequent cholesterol consumption may partially contribute to the anti-atherosclerotic effects of PE. The reversal of PPARγ-LXRα-ABCA1 signaling pathway may be involved in this process.

Mechanisms of statin-associated skeletal muscle-associated symptoms

Statins lower the serum low-density lipoprotein cholesterol and prevent cardiovascular events by inhibiting 3-hydroxy-3-methyl-glutaryl-CoA reductase. Although the safety of statins is documented, many patients ingesting statins may suffer from skeletal muscle-associated symptoms (SAMS). Importantly, SAMS are a common reason for stopping the treatment with statins. Statin-associated muscular symptoms include fatigue, weakness and pain, possibly accompanied by elevated serum creatine kinase activity. The most severe muscular adverse reaction is the potentially fatal rhabdomyolysis. The frequency of SAMS is variable but in up to 30% of the patients ingesting statins, depending on the population treated and the statin used. The mechanisms leading to SAMS are currently not completely clarified. Over the last 15 years, several research articles focused on statin-induced mitochondrial dysfunction as a reason for SAMS. Statins can impair the function of the mitochondrial respiratory chain, thereby reducing ATP and increasing ROS production. This can induce mitochondrial membrane permeability transition, release of cytochrome c into the cytosol and induce apoptosis. In parallel, statins inhibit activation of Akt, mainly due to reduced function of mTORC2, which may be related to mitochondrial dysfunction. Mitochondrial dysfunction by statins is also responsible for activation of AMPK, which is associated with impaired activation of mTORC1. Reduced activation of mTORC1 leads to increased skeletal muscle protein degradation, impaired protein synthesis and stimulation of apoptosis. In this paper, we discuss some of the different hypotheses how statins affect skeletal muscle in more detail, focusing particularly on those related to mitochondrial dysfunction and the impairment of the Akt/mTOR pathway.

Statins affect human glioblastoma and other cancers through TGF-β inhibition

The cholesterol-lowering statins have known anti-cancer effects, but the mechanisms and how to utilize statins in oncology have been unclear. We noted in the CellMiner database that statin activity against cancer lines correlated with higher expression of TGF-β target genes such as SERPINE1 and ZYX. This prompted us to assess whether statins affected TGF-β activity in glioblastoma (GBM), a cancer strongly influenced by TGF-β and in dire need of new therapeutic approaches. We noted that statins reduced TGF-β activity, cell viability and invasiveness, Rho/ROCK activity, phosphorylation and activity of the TGF-β mediator Smad3, and expression of TGF-β targets ZYX and SERPINE1 in GBM and GBM-initiating cell (GIC) lines. Statins were most potent against GBM, GIC, and other cancer cells with high TGF-β activity, and exogenous TGF-β further sensitized mesenchymal GICs to statins. Statin toxicity was rescued by addition of exogenous mevalonolactone or geranylgeranyl pyrophosphate, indicating that the observed effects reflected inhibition of HMG CoA-reductase by the statins. Simvastatin significantly inhibited the growth of subcutaneous GIC grafts and prolonged survival in GIC intracranially grafted mice. These results indicate where the statins might best be applied as adjunct therapies in oncology, against GBM and other cancers with high TGF-β activity, and have implications for other statin roles outside of oncology.

Chronic environmentally relevant levels of simvastatin disrupt embryonic development, biochemical and molecular responses in zebrafish (Danio rerio)

Simvastatin (SIM), a hypocholesterolaemic compound, is among the most prescribed pharmaceuticals for cardiovascular disease prevention worldwide. Several studies have shown that acute exposure to SIM causes multiple adverse effects in aquatic organisms. However, uncertainties still remain regarding the chronic effects of SIM in aquatic ecosystems. Therefore, the present study aimed to investigate the effects of SIM in the model freshwater teleost zebrafish (Danio rerio) following a chronic exposure (90 days) to environmentally relevant concentrations ranging from 8 ng/L to 1000 ng/L. This study used a multi-parameter approach integrating distinct ecologically-relevant endpoints, i.e. survival, growth, reproduction and embryonic development, with biochemical markers (cholesterol and triglycerides). Real Time PCR was used to analyse the transcription levels of key genes involved in the mevalonate pathway (hmgcra, cyp51, and dhcr7). Globally, SIM induced several effects that did not follow a dose-response relationship; embryonic development, biochemical and molecular markers, were significantly impacted in the lower concentrations, 8 ng/L, 40 ng/L and/or 200 ng/L, whereas no effects were recorded for the highest tested SIM levels (1000 ng/L). Taken together, these findings expand our understanding of statin effects in teleosts, demonstrating significant impacts at environmentally relevant concentrations and highlight the importance of addressing the effects of chemicals under chronic low-level concentrations.

Geranylgeraniol Prevents Statin-Dependent Myotoxicity in C2C12 Muscle Cells through RAP1 GTPase Prenylation and Cytoprotective Autophagy

The present study investigated the cytotoxic effects of statins (atorvastatin (ATR) and simvastatin (SIM), resp.) and methyl-beta-cyclodextrin (MβCD), at their respective IC₅₀ concentrations, on muscle regeneration in the in vitro model of murine C2C12 myoblasts. Cotreatment with mevalonate (MEV), farnesol (FOH), geranylgeraniol (GGOH), or water-soluble cholesterol (Chol-PEG) was employed to determine whether the statin-dependent myotoxicity resulted from the lower cholesterol levels or the attenuated synthesis of intermediates of mevalonate pathway. Our findings demonstrated that while GGOH fully reverted the statin-mediated cell viability in proliferating myoblasts, Chol-PEG exclusively rescued MβCD-induced toxicity in myocytes. Statins caused loss of prenylated RAP1, whereas the GGOH-dependent positive effect was accompanied by loss of nonprenylated RAP1. Geranylgeranyltransferases are essential for muscle cell survival as inhibition with GGTI-286 could not be reversed by GGOH cotreatment. The increase in cell viability correlated with elevated AKT 1(S463) and GSK-3β(S9) phosphorylations. Slight increase in the levels of autophagy markers (Beclin 1, MAP LC-3IIb) was found in response to GGOH cotreatment. Autophagy rose time-dependently during myogenesis and was inhibited by statins and MβCD. Statins and MβCD also suppressed myogenesis and neither nonsterol isoprenoids nor Chol-PEG could reverse this effect. These results point to GGOH as the principal target of statin-dependent myotoxicity, whereas plasma membrane cholesterol deposit is ultimately essential to restore viability of MβCD-treated myocytes. Overall, this study unveils for the first time a link found between the GGOH- and Chol-PEG-dependent reversal of statin- or MβCD-mediated myotoxicity and cytoprotective autophagy, respectively.

Statin non-adherence and residual cardiovascular risk: There is need for substantial improvement

Although statin therapy has proven to be the cornerstone for prevention and treatment of cardiovascular disease (CVD), there are many patients for whom long-term therapy remains suboptimal. The aims of this article are to review the current complex issues associated with statin use and to explore when novel treatment approaches should be considered. Statin discontinuation as well as adherence to statin therapy remain two of the greatest challenges for lipidologists. Evidence suggests that between 40 and 75% of patients discontinue their statin therapy within one year after initiation. Furthermore, whilst the reasons for persistence with statin therapy are complex, evidence shows that low-adherence to statins negatively impacts clinical outcomes and residual CV risk remains a major concern. Non-adherence or lack of persistence with long-term statin therapy in real-life may be the main cause of inadequate low density lipoprotein cholesterol lowering with statins. There is a large need for the improvement of the use of statins, which have good safety profiles and are inexpensive. On the other hand, in a non-cost-constrained environment, proprotein convertase subtilisin/kexin type 9 inhibitors should arguably be used more often in those patients in whom treatment with statins remains unsatisfactory.

Chamber-specific differences in human cardiac fibroblast proliferation and responsiveness toward simvastatin

Fibroblasts, the most abundant cells in the heart, contribute to cardiac fibrosis, the substrate for the development of arrythmogenesis, and therefore are potential targets for preventing arrhythmic cardiac remodeling. A chamber-specific difference in the responsiveness of fibroblasts from the atria and ventricles toward cytokine and growth factors has been described in animal models, but it is unclear whether similar differences exist in human cardiac fibroblasts (HCFs) and whether drugs affect their proliferation differentially. Using cardiac fibroblasts from humans, differences between atrial and ventricular fibroblasts in serum-induced proliferation, DNA synthesis, cell cycle progression, cyclin gene expression, and their inhibition by simvastatin were determined. The serum-induced proliferation rate of human atrial fibroblasts was more than threefold greater than ventricular fibroblasts with faster DNA synthesis and higher mRNA levels of cyclin genes. Simvastatin predominantly decreased the rate of proliferation of atrial fibroblasts, with inhibition of cell cycle progression and an increase in the G0/G1 phase in atrial fibroblasts with a higher sensitivity toward inhibition compared with ventricular fibroblasts. The DNA synthesis and mRNA levels of cyclin A, D, and E were significantly reduced by simvastatin in atrial but not in ventricular fibroblasts. The inhibitory effect of simvastatin on atrial fibroblasts was abrogated by mevalonic acid (500 μM) that bypasses 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibition. Chamber-specific differences exist in the human heart because atrial fibroblasts have a higher proliferative capacity and are more sensitive to simvastatin-mediated inhibition through HMG-CoA reductase pathway. This mechanism may be useful in selectively preventing excessive atrial fibrosis without inhibiting adaptive ventricular remodeling during cardiac injury.

Synergistic interaction between lipid-loading and doxorubicin exposure in Huh7 hepatoma cells results in enhanced cytotoxicity and cellular oxidative stress: implications for acute and chronic care of obese cancer patients

There has been a dramatic increase in the number of clinically obese individuals in the last twenty years. This has resulted in an increasingly common scenario where obese individuals are treated for other diseases, including cancer. Here, we examine interactions between lipid-induced steatosis and doxorubicin treatment in the human hepatoma cell line Huh7. The response of cells to either doxorubicin, lipid-loading or a combination were examined at the global level by DNA microarray, and for specific endpoints of cytotoxicity, lipid-loading, reactive oxygen species, anti-oxidant response systems, and apoptosis. Both doxorubicin and lipid-loading caused a significant accumulation of lipid within Huh7 cells, with the combination resulting in an additive accumulation. In contrast, cytotoxicity was synergistic for the combination compared to the individual components, suggesting an enhanced sensitivity of lipid-loaded cells to the acute hepatotoxic effects of doxorubicin. We demonstrate that a synergistic increase in reactive oxygen species and deregulation of protective anti-oxidant systems, most notably metallothionein expression, underlies this effect. Transcriptome analysis confirms synergistic changes at the global level, and is consistent with enhanced pro-inflammatory signalling in steatotic cells challenged with doxorubicin. Such effects are consistent with a potentiation of progression along the fatty liver disease spectrum. This suggests that treatment of obese individuals with doxorubicin may increase the risk of both acute (i.e. hepatotoxicity) and chronic (i.e. progress of fatty liver disease) adverse effects. This work highlights the need for more study in the growing therapeutic area to develop risk mitigation strategies.

Activation of the Farnesoid X-receptor in breast cancer cell lines results in cytotoxicity but not increased migration potential

Breast cancer is the commonest form of cancer in women, but successful treatment is confounded by the heterogeneous nature of breast tumours: Effective treatments exist for hormone-sensitive tumours, but triple-negative breast cancer results in poor survival. An area of increasing interest is metabolic reprogramming, whereby drug-induced alterations in the metabolic landscape of a tumour slow tumour growth and/or increase sensitivity to existing therapeutics. Nuclear receptors are transcription factors central to the expression of metabolic and transport proteins, and thus represent potential targets for metabolic reprogramming. We show that activation of the nuclear receptor FXR, either by its endogenous ligand CDCA or the synthetic GW4064, leads to cell death in four breast cancer cell lines with distinct phenotypes: MCF-10A (normal), MCF-7 (receptor positive), MDA-MB-231 and MDA-MB-468 (triple negative). Furthermore, we show that the mechanism of cell death is predominantly through the intrinsic apoptotic pathway. Finally, we demonstrate that FXR agonists do not stimulate migration in breast cancer cell lines, an important potential adverse effect. Together, our data support the continued examination of FXR agonists as a novel class of therapeutics for the treatment of breast cancer.

Lipid-induced Muscle Insulin Resistance Is Mediated by GGPPS via Modulation of the RhoA/Rho Kinase Signaling Pathway

Elevated circulating free fatty acid levels are important contributors to insulin resistance in the muscle and liver, but the underlying mechanisms require further elucidation. Here, we show that geranylgeranyl diphosphate synthase 1 (GGPPS), which is a branch point enzyme in the mevalonic acid pathway, promotes lipid-induced muscle insulin resistance through activation of the RhoA/Rho kinase signaling pathway. We have found that metabolic perturbation would increase GGPPS expression in the skeletal muscles of db/db mice and high fat diet-fed mice. To address the metabolic effects of GGPPS activity in skeletal muscle, we generated mice with specific GGPPS deletions in their skeletal muscle tissue. Heterozygous knock-out of GGPPS in the skeletal muscle improved systemic insulin sensitivity and glucose homeostasis in mice fed both normal chow and high fat diets. These metabolic alterations were accompanied by activated PI3K/Akt signaling and enhanced glucose uptake in the skeletal muscle. Further investigation showed that the free fatty acid-stimulated GGPPS expression in the skeletal muscle was able to enhance the geranylgeranylation of RhoA, which further induced the inhibitory phosphorylation of IRS-1 (Ser-307) by increasing Rho kinase activity. These results implicate a crucial role of the GGPPS/RhoA/Rho kinase/IRS-1 pathway in skeletal muscle, in which it mediates lipid-induced systemic insulin resistance in obese mice. Therefore, skeletal muscle GGPPS may represent a potential pharmacological target for the prevention and treatment of obesity-related type 2 diabetes.