Stimulation of Hepatic Apolipoprotein A-I Production by Novel Thieno-Triazolodiazepines: Roles of the Classical Benzodiazepine Receptor, PAF Receptor, and Bromodomain Binding

Abstract

Expression and secretion of apolipoprotein A-I (apoA-I) by cultured liver cells can be markedly stimulated by triazolodiazepines (TZDs). It has been shown previously that the thieno-TZD Ro 11-1464 increases plasma levels of apoA-I and in vivomacrophage reverse cholesterol transport in mice. However, these effects were only seen at high doses, at which the compound could act on central benzodiazepine (BZD) receptors or platelet activating factor (PAF) receptors, interfering with its potential utility. In this work, we describe 2 new thieno-TZDs MDCO-3770 and MDCO-3783, both derived from Ro 11-1464. These compounds display the same high efficacy on apoA-I production, metabolic stability, and lack of cytotoxicity in cultured hepatocytes as Ro 11-1464, but they do not bind to the central BZD receptor and PAF receptor. The quinazoline RVX-208 was less efficacious in stimulating apoA-I production and displayed signs of cytotoxicity. Certain TZDs stimulating apoA-I production are now known to be inhibitors of bromodomain (BRD) extra-terminal (BET) proteins BRDT, BRD2, BRD3, and BRD4, and this inhibition was inferred as a main molecular mechanism for their effect on apoA-I expression. We show here that the thieno-TZD (+)-JQ1, a potent BET inhibitor, strongly stimulated apoA-I production in Hep-G2 cells, but that its enantiomer (−)-JQ1, which has no BET inhibitor activity, also showed considerable effect on apoA-I production. MDCO-3770 and MDCO-3783 also inhibited BRD3 and BRD4 in vitro, with potency somewhat below that of (+)-JQ1. We conclude that the effect of thieno-TZDs on apoA-I expression is not due to inhibition of the BZD or PAF receptors and is not completely explained by transcriptional repression by BET proteins.

Link Between ER-Stress, PPAR-Alpha Activation, and BET Inhibition in Relation to Apolipoprotein A-I Transcription in HepG2 Cells

“…Except for JQ1(+), also other BET inhibitors, such as the benzodiazepine GW841819X [Chung et al, ], RVX‐208 [Bailey et al, ], and I‐BET726 (GSK1324726A) [Gosmini et al, ] were found to increase apoA‐I promoter activity in HepG2 cells. Furthermore, the triazolodiazepine Ro 11‐1464 and its derivatives MDCO‐3770 and MDCO‐3783, which were recently also identified as BET inhibitors, increased apoA‐I protein production in human primary hepatocytes [Kempen et al, ]. Benzodiazepine compounds are known modulators of the GABA (γ‐aminobutyric acid) receptor in the central nervous system and are used for treatment of sleeping disorder, muscle spasms and anxiety [Olkkola and Ahonen, ].…”

“…Increased levels of SIRT‐1 are also linked to attenuated ER‐stress [Ghosh et al, ; Jung et al, ], as SIRT‐1 overexpression in LDL knockout mice decreased UPR‐related protein production [Li et al, ]. Furthermore, another BET inhibitor RVX‐208, which is a derivative of the known SIRT‐1 activator resveratrol (3,4',5‐trihydroxy‐transstilbene) [Picaud et al, ; Cote et al, ], increased apoA‐I production in vitro in primary human hepatocytes [Kempen et al, ] and in HepG2 cells, and in vivo in cynomolgus monkeys and humans [Bailey et al, ].…”

Large‐Scale Screening of Natural Products Transactivating Peroxisome Proliferator‐Activated Receptor α Identifies 9S‐Hydroxy‐10E,12Z,15Z‐Octadecatrienoic Acid and Cymarin as Potential Compounds Capable of Increasing Apolipoprotein A‐I Transcription in Human Liver Cells

“…Interestingly, recent studies have demonstrated that besides PPARα activation, inhibition of BRD4 by BET inhibitors increased the production of apoA‐I (Kempen et al, ; McLure et al, ). Data of our group suggest that the effect of BET inhibitor JQ1(+) on apoA‐I transcription is PPARα independent, as PPARα was decreased upon BET inhibition (Krieken et al unpublished data).…”

Search for Natural Compounds That Increase Apolipoprotein A‐I Transcription in HepG2 Cells: Specific Attention for BRD4 Inhibitors

“…For example, in in vitro as well as in in vivo studies, the BET inhibitor RVX208 (or apabetalone) increased apoA‐I transcription and protein production (Gilham et al, ). Additionally, there are many other compounds with BET‐inhibiting function and the capacity to increase apoA‐I synthesis, at least in vitro , such as JQ1(+) (Kempen et al, ), Ro11‐1464 (Zanotti et al, ), GW841819X (Chung et al, ), GSK1210151A or I‐BET151 (Seal et al, ), alaprazolam (Filippakopoulos et al, ), GSK1324762A or I‐BET762 (Mirguet et al, ), and thieno‐ or benzo‐triazolodiazepines (Kempen et al, ) such as U‐34599 and U‐51477 (Princen JMG May 28; Princen and Kooistra, ; Kempen et al, ). In humans, four types of BET proteins have been identified, namely, bromodomain‐containing protein (BRD) 2, BRD3, BRD4, and testes‐specific BRDT.…”