Inhibition of ACAT as a Therapeutic Target for Alzheimer's Disease Is Independent of ApoE4 Lipidation

APOE4, encoding apolipoprotein E4 (apoE4), is the greatest genetic risk factor for Alzheimer's disease (AD), compared to the common APOE3. While the mechanism(s) underlying APOE4-induced AD risk remains unclear, increasing the lipidation of apoE4 is an important therapeutic target as apoE4-lipoproteins are poorly lipidated compared to apoE3-lipoproteins. ACAT (acyl-CoA: cholesterol-acyltransferase) catalyzes the formation of intracellular cholesteryl-ester droplets, reducing the intracellular free cholesterol (FC) pool. Thus, inhibiting ACAT increases the FC pool and facilitates lipid secretion to extracellular apoE-containing lipoproteins. Previous studies using commercial ACAT inhibitors, including avasimibe (AVAS), as well as ACAT-knock out (KO) mice, exhibit reduced AD-like pathology and amyloid precursor protein (APP) processing in familial AD (FAD)-transgenic (Tg) mice. However, the effects of AVAS with human apoE4 remain unknown. In vitro, AVAS induced apoE efflux at concentrations of AVAS measured in the brains of treated mice. AVAS treatment of male E4FAD-Tg mice (5xFAD+/-APOE4+/+) at 6-8 months had no effect on plasma cholesterol levels or distribution, the original mechanism for AVAS treatment of CVD. In the CNS, AVAS reduced intracellular lipid droplets, indirectly demonstrating target engagement. Surrogate efficacy was demonstrated by an increase in Morris water maze measures of memory and postsynaptic protein levels. Amyloid-beta peptide (Aβ) solubility/deposition and neuroinflammation were reduced, critical components of APOE4-modulated pathology. However, there was no increase in apoE4 levels or apoE4 lipidation, while amyloidogenic and non-amyloidogenic processing of APP were significantly reduced. This suggests that the AVAS-induced reduction in Aβ via reduced APP processing was sufficient to reduce AD pathology, as apoE4-lipoproteins remained poorly lipidated.

Atorvastatin improves cisplatin sensitivity through modulation of cholesteryl ester homeostasis in breast cancer cells

BACKGROUND

Acquired treatment resistance is a significant problem in breast cancer management, and alterations in lipid metabolism have been proposed to contribute to the development of drug resistance as well as other aspects of tumor progression. The present study aimed to identify the role of cholesterol metabolism in MCF-7 and MDA-MB-231 breast cancer cell response to cisplatin (CDDP) treatment in the acute setting and in a model of CDDP resistance.

METHODS

MCF-7 (luminal A), MDA-MB-231 (triple-negative) and CDDP-resistant MDA-MB-231 (MDACR) cell lines were grown in the presence or absence of CDDP in combination with atorvastatin (ATV), lipid depletion or low-density lipoprotein loading and were analyzed by a variety of biochemical and radiometric techniques.

RESULTS

Co-administration of CDDP and ATV strongly reduced cell proliferation and viability to a greater extent than CDDP alone, especially in MDA-MB-231 cells. These findings were associated with reduced cholesteryl ester synthesis and storage in MDA-MB-231 cells. In MDACR cells, acetyl-CoA acetyltransferase 1 (ACAT-1) was upregulated compared to naïve MDA-MB-231 cells and ATV treatment restored CDDP sensitivity, suggesting that aberrant ACAT-1 expression and associated changes in cholesterol metabolism contribute to CDDP resistance in MDA-MB-231 cells.

CONCLUSION

These findings indicate that the elevated susceptibility of MDA-MB-231 cells to co-administration of CDDP and ATV, is associated with an increased reliance on cholesteryl ester availability. Our data from these cell culture-based studies identifies altered cholesterol homeostasis as an adaptive response to CDDP treatment that contributes to aggressiveness and chemotherapy resistance.

A Dipeptidyl Peptidase-4 Inhibitor Inhibits Foam Cell Formation of Macrophages in Type 1 Diabetes via Suppression of CD36 and ACAT-1 Expression

Dipeptidyl peptidase-4 (DPP-4) inhibitors have been reported to play a protective role against atherosclerosis in both animal models and patients with type 2 diabetes (T2D). However, since T2D is associated with dyslipidemia, hypertension and insulin resistance, part of which are ameliorated by DPP-4 inhibitors, it remains unclear whether DPP-4 inhibitors could have anti-atherosclerotic properties directly by attenuating the harmful effects of hyperglycemia. Therefore, we examined whether a DPP-4 inhibitor, teneligliptin, could suppress oxidized low-density lipoprotein (ox-LDL) uptake, foam cell formation, CD36 and acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) gene expression of macrophages isolated from streptozotocin-induced type 1 diabetes (T1D) mice and T1D patients as well as advanced glycation end product (AGE)-exposed mouse peritoneal macrophages and THP-1 cells. Foam cell formation, CD36 and ACAT-1 gene expression of macrophages derived from T1D mice or patients increased compared with those from non-diabetic controls, all of which were inhibited by 10 nmol/L teneligliptin. AGEs mimicked the effects of T1D; teneligliptin attenuated all the deleterious effects of AGEs in mouse macrophages and THP-1 cells. Our present findings suggest that teneligliptin may inhibit foam cell formation of macrophages in T1D via suppression of CD36 and ACAT-1 gene expression partly by attenuating the harmful effects of AGEs.

Blocking ACAT-1 Activity for Tumor Therapy with Fluorescent Hyperstar Polymer-Encapsulated Avasimible

Targeting the distinct cholesterol metabolism of tumor cells is proposed as a novel way to treat tumors. Blocking acyl-CoA cholesterol acyltransferase-1 (ACAT-1) by the inhibitor avasimible (Ava), which elevates intracellular free cholesterol levels, is shown to effectively induce apoptosis. However, Ava faces disadvantages of poor water solubility, a short half-life, and no capability for fluorescence detection, which have greatly limited its application. Herein, a fluorescent hyperstar polymer (FHSP) is developed to encapsulate Ava to improve its ability to inhibit HeLa cells and K562 cells. The results of this study show that the obtained Ava-FHSP micelles possess a high drug loading capacity of 22.7% and bright green fluorescence. Ava and Ava-FHSP are cytotoxic to both HeLa and K562 cells and cause reductions in cell size, nuclear lysis, and chromatin condensation and hindered proliferation of both cell types by causing S phase cell cycle arrest. Further mechanistic analysis indicates that Ava-FHSP reduces the protein and messenger RNA expression of ACAT-1 and significantly increases intracellular free cholesterol levels, which can increase endoplasmic reticulum stress and finally cause cell apoptosis. All these results suggest that this fluorescent hyperstar polymer represents a potential therapeutic tumor strategy by changing the cholesterol metabolism of tumor cells.

ACAT-1 gene rs1044925 SNP and its relation with different clinical forms of chronic Chagas disease

Chagas disease, caused by the protozoan Trypanosoma cruzi (T. cruzi), although discovered more than a century ago, is still a not very well-elucidated aspect. Individuals in the chronic phase of the disease may present asymptomatic clinical form or symptomatologies related to the cardiac, digestive systems, or both (mixed clinical form). SNPs (single nucleotide polymorphisms) have been identified as important markers because they constitute about 90% of the variation in the human genome. One of them is localized to the ACAT-1 gene (cholesterol acyltransferase 1) (rs1044925) and has been linked to lipid disorders. Some studies have suggested the interaction between T. cruzi and the lipid metabolism of the host. Therefore, the objective of the present study was to evaluate the association between the ACAT-1 gene rs1044925 SNP in relation to clinical manifestations in patients with chronic Chagas disease. A total of 135 individuals with chronic Chagas disease, 86 (63.7%) asymptomatic individuals and 49 (36.3%) symptomatic patients (22 with cardiac clinical form, 18 with digestive form and 9 with mixed form) participated in the study. To evaluate the polymorphism, the PCR-RFLP technique were used. There was a significant difference and a higher frequency of AA and AC genotypes (p = 0.047 and p = 0.016, respectively) of the ACAT-1 gene in asymptomatic chagasic individuals. The result suggests a protective character of the AA and AC genotypes of the rs1044925 SNP in relation to the presence of symptomatic clinical manifestations of the disease in chronic chagasic individuals.

Enhanced chemo-immunotherapy against melanoma by inhibition of cholesterol esterification in CD8+ T cells

Cholesterol facilitated the formation of T cell receptor on cytotoxic CD8⁺ T lymphocytes (CTLs). However, the activation of CD8⁺ T cells always resulted in the upregulation of acetyl-CoA acetyltransferase-1 (ACAT-1) and enhanced the esterification of cholesterol. To relieve the suppression on CD8⁺ T cells, an ACAT-1 inhibitor avasimibe was combined with chemo-immunotherapy. Paclitaxel and immunoadjuvant αGC were co-encapsulated in liposomes modified with pH sensitive TH peptide (PTX/αGC-TH-Lip). After intravenous injections, the combination of avasimibe significantly elevated the free cholesterol level and relieved the inhibition of CD8⁺ T cells caused by PTX/αGC-TH-Lip, leading to enhanced CTL responses and anti-tumor effects of PTX/αGC-TH-Lip in B16F10 melanoma xenograft and lung metastasis models. The adoptive immunotherapy further confirmed the enhanced anti-tumor immune responses of the combined strategy. The combination of avasimibe and PTX/αGC-TH-Lip was proven as a feasible approach to enhance the antitumor effects of chemo-immunotherapy by relieving the inhibition of CD8⁺ T cells.

Effect of valsartan on ACAT-1 and PPAR-γ expression in intima with carotid artery endothelial balloon injury in rabbit

OBJECTIVE

To study the effect of valsartan on ACAT-1 and PPAR-γ expression after vascular endothelial balloon injury in intimal hyperplasia process.

METHODS

24 male New Zealand white rabbits were randomly divided into three groups with 8 in each group.

CONTROL GROUP

rabbits were fed with normal diet; Balloon injury group: rabbits were fed with 0.5% cholesterol, 5% lard rabbit feed; balloon injury + valsartan group, rabbits were fed with 0.5% cholesterol, 5% lard rabbit feed added with 10 mg/(kg.d) valsartan gavage. RT-PCR and Western blotting method were used to detect the carotid ACAT-1, PPAR-γ mRNA and protein expression after 8 weeks of feeding.

RESULTS

In carotid artery balloon injury group, vascular smooth muscle cells (VSMC) proliferation and intimal hyperplasia were significantly higher 14 d after endothelial injury. In 14 days valsartan treatment group VSMC proliferation and intimal hyperplasia were lighter than the surgery group. Compared with the control group, ACAT-1, PPAR-γ mRNA and protein were significantly increased in balloon injury group and valsartan group (P < 0.01 or P < 0.05); the expression of ACAT-1 mRNA and protein were significantly lower in valsartan group and balloon injury group (P < 0.01 or P < 0.05). The expression of PPAR-γ mRNA and protein in valsartan group expression was significantly higher than that in the balloon injury group (P < 0.05). The expression level of ACAT-1 and PPAR-γ mRNA in balloon injury group and valsartan group showed negative correlation (P < 0.05).

CONCLUSION

The expression of ACAT-1, PPAR-γ mRNA and protein content were significantly increased in intimal hyperplasia process after vascular endothelial balloon injury. The effect of valsartan suppressed intimal hyperplasia correlated with the expression of down-regulated ACAT-1 and up-regulated PPAR-γ.

Prophylactic treatment with melatonin before recurrent neonatal seizures: Effects on long-term neurobehavioral changes and the underlying expression of metabolism-related genes in rat hippocampus and cerebral cortex

Although it has been suggested that the protective effect of melatonin against seizure-induced neurotoxicity involves inhibition of neuronal lipid peroxidation, current data concerning the exact molecular mechanism are still limited. This study was undertaken to investigate the changes in neurobehavioral, cognitive and lipid metabolism-related gene expressions in both hippocampus and cerebral cortex of rats subjected to recurrent neonatal seizures, and the effects of melatonin treatment before seizure (55mg/kg, 1mg/ml). 6-day-old (P6) SD rats were randomly divided into four groups of control (CONT, the same below), melatonin treated control (Mel), recurrent neonatal seizure (RS) and melatonin and RS combination treatment (Mel+RS). Neurological behavioral parameters of brain damage (plane righting reflex, negative geotaxis reaction reflex, Cliff avoidance reflex, forelimb suspension reflex) were observed on P31. Morris water maze test was performed during P29-P35. Then the protein levels of ACAT1, Cathepsin-E and Ca(2+)/calmodulin-dependent protein kinase II (CAMK II) in hippocampus and cerebral cortex were detected by western blot method. As expected, RS group showed a significant delay or reduce of the four reflexes, as well as bad performance in the Morris water maze test. Flurothyl-induced neurobehavioral toxicology was blocked by pre-treatment with melatonin. In parallel with these behavioral changes, gene expression by western blot method demonstrated that rats pretreated with melatonin (Mel+RS) showed a significant down-regulated expression of ACAT-1, Cathepsin-E and up-regulated CAMK II in hippocampus and cerebral cortex when compared with RS group. Our findings provide support for ACAT-1/Cathepsin-E as well as CaMK II being potential targets for the treatment of neonatal seizure-induced brain damage by melatonin.

Loss of apoptosis regulator through modulating IAP expression (ARIA) protects blood vessels from atherosclerosis

Atherosclerosis is the primary cause for cardiovascular disease. Here we identified a novel mechanism underlying atherosclerosis, which is provided by ARIA (apoptosis regulator through modulating IAP expression), the transmembrane protein that we recently identified. ARIA is expressed in macrophages present in human atherosclerotic plaque as well as in mouse peritoneal macrophages. When challenged with acetylated LDL, peritoneal macrophages isolated from ARIA-deficient mice showed substantially reduced foam cell formation, whereas the uptake did not differ from that in wild-type macrophages. Mechanistically, loss of ARIA enhanced PI3K/Akt signaling and consequently reduced the expression of acyl coenzyme A:cholesterol acyltransferase-1 (ACAT-1), an enzyme that esterifies cholesterol and promotes its storage, in macrophages. Inhibition of PI3K abolished the reduction in ACAT-1 expression and foam cell formation in ARIA-deficient macrophages. In contrast, overexpression of ARIA reduced Akt activity and enhanced foam cell formation in RAW264.7 macrophages, which was abrogated by treatment with ACAT inhibitor. Of note, genetic deletion of ARIA significantly reduced the atherosclerosis in ApoE-deficient mice. Oil red-O-positive lipid-rich lesion was reduced, which was accompanied by an increase of collagen fiber and decrease of necrotic core lesion in atherosclerotic plaque in ARIA/ApoE double-deficient mice. Analysis of bone marrow chimeric mice revealed that loss of ARIA in bone marrow cells was sufficient to reduce the atherosclerogenesis in ApoE-deficient mice. Together, we identified a unique role of ARIA in the pathogenesis of atherosclerosis at least partly by modulating macrophage foam cell formation. Our results indicate that ARIA could serve as a novel pharmacotherapeutic target for the treatment of atherosclerotic diseases.