Design,synthesis, and ex vivo evaluation of a selective inhibitor for retinaldehyde dehydrogenase enzymes

The retinaldehyde dehydrogenase (RALDH) enzymes, RALDH1, RALDH2, and RALDH3, catalyze the irreversible oxidation of retinaldehyde to all-trans-retinoic acid (ATRA). Despite the importance of the RALDH enzymes in embryonic development, postnatal growth and differentiation, and in several disease states, there are no commercially available inhibitors that specifically target these isozymes. We report here the development and characterization of a small molecule inhibitor dichloro-all-trans-retinone (DAR) (Summers et al., 2017) that is an irreversible inhibitor of RALDH1, 2, and 3 that effectively inhibits RALDH1, 2, and 3 in the nanomolar range but has no inhibitory activity against mitochondrial ALDH2. These results provide support for the development of DAR as a specific ATRA synthesis inhibitor for a variety of experimental and clinical applications.     

Mammalian Carotenoid-oxygenases: Key players for carotenoid function and homeostasis

Humans depend on a dietary intake of lipids to maintain optimal health. Among various classes of dietary lipids, the physiological importance of carotenoids is still controversially discussed. On one hand, it is well established that carotenoids, such as β,β-carotene, are a major source for vitamin A that plays critical roles for vision and many aspects of cell physiology. On the other hand, large clinical trials have failed to show clear health benefits of carotenoids supplementation and even suggest adverse health effects in individuals at risk of disease. In recent years, key molecular players for carotenoid metabolism have been identified, including an evolutionarily well conserved family of carotenoid-oxygenases. Studies in knockout mouse models for these enzymes revealed that carotenoid metabolism is a highly regulated process and that this regulation already takes place at the level of intestinal absorption. These studies also provided evidence that β,β-carotene conversion can influence retinoid-dependent processes in the mouse embryo and in adult tissues. Moreover, these analyses provide an explanation for adverse health effects of carotenoids by showing that a pathological accumulation of these compounds can induce oxidative stress in mitochondria and cell signaling pathways related to disease. Advancing knowledge about carotenoid metabolism will contribute to a better understanding of the biochemical and physiological roles of these important micronutrients in health and disease. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.     

The conserved regulation of mitochondrial uncoupling proteins: From unicellular eukaryotes to mammals

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier protein family and mediate regulated proton leak across the inner mitochondrial membrane. Free fatty acids, aldehydes such as hydroxynonenal, and retinoids activate UCPs. However, there are some controversies about the effective action of retinoids and aldehydes alone; thus, only free fatty acids are commonly accepted positive effectors of UCPs. Purine nucleotides such as GTP inhibit UCP-mediated mitochondrial proton leak. In turn, membranous coenzyme Q may play a role as a redox state-dependent metabolic sensor that modulates the complete activation/inhibition of UCPs. Such regulation has been observed for UCPs in microorganisms, plant and animal UCP1 homologues, and UCP1 in mammalian brown adipose tissue. The origin of UCPs is still under debate, but UCP homologues have been identified in all systematic groups of eukaryotes. Despite the differing levels of amino acid/DNA sequence similarities, functional studies in unicellular and multicellular organisms, from amoebae to mammals, suggest that the mechanistic regulation of UCP activity is evolutionarily well conserved. This review focuses on the regulatory feedback loops of UCPs involving free fatty acids, aldehydes, retinoids, purine nucleotides, and coenzyme Q (particularly its reduction level), which may derive from the early stages of evolution as UCP first emerged.     

Retinoid chemistry: Synthesis and application for metabolic disease

In this review a discussion of the usual procedures used to synthesize retinoids is followed by an overview of the structure-activity relationships of these molecules. The discussion is then focused on the role and impact of retinoids on metabolic disorders with a particular emphasis on obesity, diabetes, and the metabolic syndrome. In these areas, both natural and synthetic retinoids that are being studied are reviewed and areas where likely future research will occur are suggested. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.     

Tissue-specific distribution patterns of retinoids and didehydroretinoids in rainbow trout Oncorhynchus mykiss

Retinoids (vitamin A) are known to be involved in many key biological functions in mammals, such as embryonic development, reproduction or vision. Besides standard vitamin A forms, freshwater fish tissues contain high levels of didehydroretinoids or vitamin A₂ forms. However, the tissue distribution, metabolism and function of both standard and particularly the didehydroretinoids are still poorly known in fish. In this study, we have quantified the levels of retinoids, including retinol, retinaldehyde, retinyl palmitate and their corresponding didehydro forms, as well as the levels of the active polar retinoids all-trans-, 9-cis- and 13-cis-retinoic acid in distinct tissues of juvenile rainbow trout. Our results indicate that the liver is clearly the main retinoid storage tissue in juvenile rainbow trout. Didehydroretinoids were dominant over retinoids in all analyzed tissues with the exception of plasma. Additionally, significant differences among tissues were observed between retinoids and didehydroretinoids, such as differences in the ester profiles and the proportions between free and esterified forms, suggesting that mechanisms that favor the utilization or storage of one of the other groups of compounds might exist in fish. Our data also show the presence of polar retinoids in different tissues of fish at the fmol/g scale. Overall, this study clearly demonstrates the presence of tissue-specific patterns of accumulation of both polar and nonpolar retinoids in fish tissues. The biological relevance of these findings should be the focus of future studies.     

HIV-1 integrase strand transfer inhibitors stabilize an integrase-single blunt-ended DNA complex

Integration of human immunodeficiency virus cDNA ends by integrase (IN) into host chromosomes involves a concerted integration mechanism. IN juxtaposes two DNA blunt ends to form the synaptic complex, which is the intermediate in the concerted integration pathway. The synaptic complex is inactivated by strand transfer inhibitors (STI) with IC₅₀ values of ∼ 20 nM for inhibition of concerted integration. We detected a new nucleoprotein complex on a native agarose gel that was produced in the presence of > 200 nM STI, termed the IN-single DNA (ISD) complex. Two IN dimers appear to bind in a parallel fashion at the DNA terminus, producing an ∼ 32-bp DNase I protective footprint. In the presence of raltegravir (RAL), MK-2048, and L-841,411, IN incorporated ∼ 20-25% of the input blunt-ended DNA substrate into the stabilized ISD complex. Seven other STI also produced the ISD complex (≤ 5% of input DNA). The formation of the ISD complex was not dependent on 3′OH processing, and the DNA was predominantly blunt ended in the complex. The RAL-resistant IN mutant N155H weakly forms the ISD complex in the presence of RAL at ∼ 25% level of wild-type IN. In contrast, MK-2048 and L-841,411 produced ∼ 3-fold to 5-fold more ISD than RAL with N155H IN, which is susceptible to these two inhibitors. The results suggest that STI are slow-binding inhibitors and that the potency to form and stabilize the ISD complex is not always related to inhibition of concerted integration. Rather, the apparent binding and dissociation properties of each STI influenced the production of the ISD complex.     

Maternal-fetal transfer and metabolism of vitamin A and its precursor β-carotene in the developing tissues

The requirement of the developing mammalian embryo for retinoic acid is well established. Retinoic acid, the active form of vitamin A, can be generated from retinol and retinyl ester obtained from food of animal origin, and from carotenoids, mainly β-carotene, from vegetables and fruits. The mammalian embryo relies on retinol, retinyl ester and β-carotene circulating in the maternal bloodstream for its supply of vitamin A. The maternal-fetal transfer of retinoids and carotenoids, as well as the metabolism of these compounds in the developing tissues are still poorly understood. The existing knowledge in this field has been summarized in this review in reference to our basic understanding of the transport and metabolism of retinoids and carotenoids in adult tissues. The need for future research on the metabolism of these essential lipophilic nutrients during development is highlighted. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.     

First report of computational protein–ligand docking to evaluate susceptibility to HIV integrase inhibitors in HIV-infected Iranian patients

BackgroundIran has recently included integrase (INT) inhibitors (INTIs) in the first‐line treatment regimen in human immunodeficiency virus (HIV)-infected patients. However, there is no bioinformatics data to elaborate the impact of resistance-associated mutations (RAMs) and naturally occurring polymorphisms (NOPs) on INTIs treatment outcome in Iranian patients.MethodIn this cross-sectional survey, 850 HIV-1-infected patients enrolled; of them, 78 samples had successful sequencing results for INT gene. Several analyses were performed including docking screening, genotypic resistance, secondary/tertiary structures, post-translational modification (PTM), immune epitopes, etc.ResultThe average docking energy (E value) of different samples with elvitegravir (EVG) and raltegravir (RAL) was more than other INTIs. Phylogenetic tree analysis and Stanford HIV Subtyping program revealed HIV-1 CRF35-AD was the predominant subtype (94.9%) in our cases; in any event, online subtyping tools confirmed A1 as the most frequent subtype. For the first time, CRF-01B and BF were identified as new subtypes in Iran. Decreased CD4 count was associated with several factors: poor or unstable adherence, naïve treatment, and drug user status.ConclusionAs the first bioinformatic report on HIV-integrase from Iran, this study indicates that EVG and RAL are the optimal INTIs in first-line antiretroviral therapy (ART) in Iranian patients. Some conserved motifs and specific amino acids in INT-protein binding sites have characterized that mutation(s) in them may disrupt INT-drugs interaction and cause a significant loss in susceptibility to INTIs. Good adherence, treatment of naïve patients, and monitoring injection drug users are fundamental factors to control HIV infection in Iran effectively.