Constitutive and 3-methylcholanthrene-induced rat ALDH3A1 expression is mediated by multiple xenobiotic response elements

Fifty Years of Aryl Hydrocarbon Receptor Research as Reflected in the Pages of Drug Metabolism and Disposition

The induction of multiple drug-metabolizing enzymes by halogenated and polycyclic aromatic hydrocarbon toxicants is mediated by the aryl hydrocarbon receptor (AHR). This fascinating receptor also has natural dietary and endogenous ligands, and much is now appreciated about the AHR's developmental and physiologic roles, as well as its importance in cancer and other diseases. The past several years has witnessed increasing emphasis on understanding the multifaceted roles of the AHR in the immune system. Most would agree that the "discovery" of the AHR occurred in 1976, with the report of specific binding of a high affinity radioligand in mouse liver, just three years after the launch of the journal Drug Metabolism and Disposition (DMD) in 1973. Over the ensuing 50 years, the AHR and DMD have led parallel and often intersecting lives. The overall goal of this mini-review is to provide a decade-by-decade overview of major historical landmark discoveries in the AHR field and to highlight the numerous contributions made by publications appearing in the pages of DMD. It is hoped that this historical tour might inspire current and future research in the AHR field. SIGNIFICANCE STATEMENT: With the launch of Drug Metabolism and Disposition (DMD) in 1973 and the discovery of the aryl hydrocarbon receptor (AHR) in 1976, the journal and the receptor have led parallel and often intersecting lives over the past 50 years. Tracing the history of the AHR can reveal how knowledge in the field has evolved to the present and highlight the important contributions made by discoveries reported in DMD. This may inspire additional DMD papers reporting future AHR landmark discoveries.

A Major Intestinal Catabolite of Quercetin Glycosides, 3-Hydroxyphenylacetic Acid, Protects the Hepatocytes from the Acetaldehyde-Induced Cytotoxicity through the Enhancement of the Total Aldehyde Dehydrogenase Activity

Aldehyde dehydrogenases (ALDHs) are the major enzyme superfamily for the aldehyde metabolism. Since the ALDH polymorphism leads to the accumulation of acetaldehyde, we considered that the enhancement of the liver ALDH activity by certain food ingredients could help prevent alcohol-induced chronic diseases. Here, we evaluated the modulating effects of 3-hydroxyphenylacetic acid (OPAC), the major metabolite of quercetin glycosides, on the ALDH activity and acetaldehyde-induced cytotoxicity in the cultured cell models. OPAC significantly enhanced the total ALDH activity not only in mouse hepatoma Hepa1c1c7 cells, but also in human hepatoma HepG2 cells. OPAC significantly increased not only the nuclear level of aryl hydrocarbon receptor (AhR), but also the AhR-dependent reporter gene expression, though not the nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent one. The pretreatment of OPAC at the concentration required for the ALDH upregulation completely inhibited the acetaldehyde-induced cytotoxicity. Silencing AhR impaired the resistant effect of OPAC against acetaldehyde. These results strongly suggested that OPAC protects the cells from the acetaldehyde-induced cytotoxicity, mainly through the AhR-dependent and Nrf2-independent enhancement of the total ALDH activity. Our findings suggest that OPAC has a protective potential in hepatocyte models and could offer a new preventive possibility of quercetin glycosides for targeting alcohol-induced chronic diseases.

Role of Aldehyde Dehydrogenases in Physiopathological Processes

Many different diseases are associated with oxidative stress. One of the main consequences of oxidative stress at the cellular level is lipid peroxidation, from which toxic aldehydes may be generated. Below their toxicity thresholds, some aldehydes are involved in signaling processes, while others are intermediaries in the metabolism of lipids, amino acids, neurotransmitters, and carbohydrates. Some aldehydes ubiquitously distributed in the environment, such as acrolein or formaldehyde, are extremely toxic to the cell. On the other hand, aldehyde dehydrogenases (ALDHs) are able to detoxify a wide variety of aldehydes to their corresponding carboxylic acids, thus helping to protect from oxidative stress. ALDHs are located in different subcellular compartments such as cytosol, mitochondria, nucleus, and endoplasmic reticulum. The aim of this review is to analyze, and highlight, the role of different ALDH isoforms in the detoxification of aldehydes generated in processes that involve high levels of oxidative stress. The ALDH physiological relevance becomes evident by the observation that their expression and activity are enhanced in different pathologies that involve oxidative stress such as neurodegenerative disorders, cardiopathies, atherosclerosis, and cancer as well as inflammatory processes. Furthermore, ALDH mutations bring about several disorders in the cell. Thus, understanding the mechanisms by which these enzymes participate in diverse cellular processes may lead to better contend with the damage caused by toxic aldehydes in different pathologies by designing modulators and/or protocols to modify their activity or expression.

Differentiated demographic histories and local adaptations between Sherpas and Tibetans

BACKGROUND

The genetic relationships reported by recent studies between Sherpas and Tibetans are controversial. To gain insights into the population history and the genetic basis of high-altitude adaptation of the two groups, we analyzed genome-wide data in 111 Sherpas (Tibet and Nepal) and 177 Tibetans (Tibet and Qinghai), together with available data from present-day human populations.

RESULTS

Sherpas and Tibetans show considerable genetic differences and can be distinguished as two distinct groups, even though the divergence between them (~3200-11,300 years ago) is much later than that between Han Chinese and either of the two groups (~6200-16,000 years ago). Sub-population structures exist in both Sherpas and Tibetans, corresponding to geographical or linguistic groups. Differentiation of genetic variants between Sherpas and Tibetans associated with adaptation to either high-altitude or ultraviolet radiation were identified and validated by genotyping additional Sherpa and Tibetan samples.

CONCLUSIONS

Our analyses indicate that both Sherpas and Tibetans are admixed populations, but the findings do not support the previous hypothesis that Tibetans derive their ancestry from Sherpas and Han Chinese. Compared to Tibetans, Sherpas show higher levels of South Asian ancestry, while Tibetans show higher levels of East Asian and Central Asian/Siberian ancestry. We propose a new model to elucidate the differentiated demographic histories and local adaptations of Sherpas and Tibetans.

Aldehyde dehydrogenase 3A1 promotes multi-modality resistance and alters gene expression profile in human breast adenocarcinoma MCF-7 cells

Aldehyde dehydrogenases participate in a variety of cellular homeostatic mechanisms like metabolism, proliferation, differentiation, apoptosis, whereas recently, they have been implicated in normal and cancer cell stemness. We explored roles for ALDH3A1 in conferring resistance to chemotherapeutics/radiation/oxidative stress and whether ectopic overexpression of ALDH3A1 could lead to alterations of gene expression profile associated with cancer stem cell-like phenotype. MCF-7 cells were stably transfected either with an empty vector (mock) or human aldehyde dehydrogenase 3A1 cDNA. The expression of aldehyde dehydrogenase 3A1 in MCF-7 cells was associated with altered cell proliferation rate and enhanced cell resistance against various chemotherapeutic drugs (4-hydroxyperoxycyclophosphamide, doxorubicin, etoposide, and 5-fluorouracil). Aldehyde dehydrogenase 3A1 expression also led to increased tolerance of MCF-7 cells to gamma radiation and hydrogen peroxide-induced stress. Furthermore, aldehyde dehydrogenase 3A1-expressing MCF-7 cells exhibited gene up-regulation of cyclins A, B1, B2, and down-regulation of cyclin D1 as well as transcription factors p21, CXR4, Notch1, SOX2, SOX4, OCT4, and JAG1. When compared to mock cells, no changes were observed in mRNA levels of ABCA2 and ABCB1 protein pumps with only a minor decrease of the ABCG2 pump in the aldehyde dehydrogenase 3A1-expressing cells. Also, the adhesion molecules EpCAM and CD49F were also found to be up-regulated in aldehyde dehydrogenase 3A1expressing cells. Taken together, ALDH3A1 confers a multi-modality resistance phenotype in MCF-7 cells associated with slower growth rate, increased clonogenic capacity, and altered gene expression profile, underlining its significance in cell homeostasis.

Staying alive: PI3K pathway promotes primordial follicle activation and survival in response to 3MC-induced ovotoxicity

3-Methylcholanthrene (3MC) is a potent ovotoxicant capable of causing premature ovarian failure through primordial follicle depletion. Despite 3MCs ovotoxicity having been established for 30 years, relatively little information exists on the mechanisms. In this study, we examined the effects of 3MC exposure on the immature ovarian follicle population. Microarray analysis revealed a complex mechanism of 3MC-induced ovotoxicity involving a number of cellular processes associated with xenobiotic metabolism, ovarian cancer, cell cycle progression, and cell death. 3MC exposure was also found to induce developing follicle atresia and aberrant primordial follicle activation via the stimulation of PI3K/Akt and mammalian target of rapamycin (mTOR) signaling pathways. Inhibition of PI3K/Akt signaling resulted in the severe depletion of the primordial follicle pool, with further analysis identifying increased Akt1-stimulated Bad phosphoinhibition in 3MC-treated primordial follicles. Our results suggest that the primordial follicle pool enters a "prosurvival" state upon 3MC exposure and that its depletion is due to a vicious cycle of primordial follicle activation in an attempt to replace developing follicles undergoing follicular atresia.

Trade-off between toxicity and signal detection orchestrated by frequency- and density-dependent genes

Behaviors in insects are partly highly efficient Bayesian processes that fulfill exploratory tasks ending with the colonization of new ecological niches. The foraging (for) gene in Drosophila encodes a cGMP-dependent protein kinase (PKG). It has been extensively described as a frequency-dependent gene and its transcripts are differentially expressed between individuals, reflecting the population density context. Some for transcripts, when expressed in a population at high density for many generations, concomitantly trigger strong dispersive behavior associated with foraging activity. Moreover, genotype-by-environment interaction (GEI) analysis has highlighted a dormant role of for in energetic metabolism in a food deprivation context. In our current report, we show that alleles of for encoding different cGMP-dependent kinase isoforms influence the oxidation of aldehyde groups of aromatic molecules emitted by plants via Aldh-III and a phosphorylatable adaptor. The enhanced efficiency of oxidation of aldehyde odorants into carboxyl groups by the action of for lessens their action and toxicity, which should facilitate exploration and guidance in a complex odor environment. Our present data provide evidence that optimal foraging performance requires the fast metabolism of volatile compounds emitted by plants to avoid neurosensory saturation and that the frequency-dependent genes that trigger dispersion influence these processes.

Genome-wide computational analysis of dioxin response element location and distribution in the human, mouse, and rat genomes

The aryl hydrocarbon receptor (AhR) mediates responses elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin by binding to dioxin response elements (DRE) containing the core consensus sequence 5'-GCGTG-3'. The human, mouse, and rat genomes were computationally searched for all DRE cores. Each core was then extended by 7 bp upstream and downstream, and matrix similarity (MS) scores for the resulting 19 bp DRE sequences were calculated using a revised position weight matrix constructed from bona fide functional DREs. In total, 72318 human, 70720 mouse, and 88651 rat high-scoring (MS ≥ 0.8437) putative DREs were identified. Gene-encoding intragenic DNA regions had ∼1.6 times more putative DREs than the noncoding intergenic DNA regions. Furthermore, the promoter region spanning ±1.5 kb of a TSS had the highest density of putative DREs within the genome. Chromosomal analysis found that the putative DRE densities of chromosomes X and Y were significantly lower than the mean chromosomal density. Interestingly, the 10 kb upstream promoter region on chromosome X of the genomes were significantly less dense than the chromosomal mean, while the same region in chromosome Y was the most dense. In addition to providing a detailed genomic map of all DRE cores in the human, mouse, and rat genomes, these data will further aid the elucidation of AhR-mediated signal transduction.

Non-P450 aldehyde oxidizing enzymes: the aldehyde dehydrogenase superfamily

BACKGROUND

Aldehydes are highly reactive molecules. While several non-P450 enzyme systems participate in their metabolism, one of the most important is the aldehyde dehydrogenase (ALDH) superfamily, composed of NAD(P)+-dependent enzymes that catalyze aldehyde oxidation.

OBJECTIVE

This article presents a review of what is currently known about each member of the human ALDH superfamily including the pathophysiological significance of these enzymes.

METHODS

Relevant literature involving all members of the human ALDH family was extensively reviewed, with the primary focus on recent and novel findings.

CONCLUSION

To date, 19 ALDH genes have been identified in the human genome and mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria and pyridoxine-dependent seizures. ALDH enzymes also play important roles in embryogenesis and development, neurotransmission, oxidative stress and cancer. Finally, ALDH enzymes display multiple catalytic and non-catalytic functions including ester hydrolysis, antioxidant properties, xenobiotic bioactivation and UV light absorption.