A pilot study of the modulation of sirtuins on arylamine N-acetyltransferase 1 and 2 enzymatic activity

Expression and significance of SIRT6 in human peritoneal dialysis effluents and peritoneal mesothelial cells

Sirtuin 6 (SIRT6) can inhibit the fibrosis of many organs. However, the relationship between SIRT6 and peritoneal fibrosis (PF) in peritoneal dialysis (PD) remains unclear. We collected 110 PD patients with a duration of PD for more than 3 months and studied the influence of PD duration and history of peritonitis on SIRT6 levels in PD effluents (PDEs). We also analyzed the relationship between SIRT6 levels in PDEs and transforming growth factor beta 1 (TGF-β1), IL-6, PD duration, peritoneal function, PD ultrafiltration (UF), and glucose exposure. We extracted human peritoneal mesothelial cells (HPMCs) from PDEs and measured the protein and gene expression levels of SIRT6, E-cadherin, vimentin, and TGF-β1 in these cells. Based on the clinical results, we used human peritoneal mesothelial cells lines (HMrSV5) to observe the changes in SIRT6 levels and mesothelial-to-mesenchymal transition (MMT) after intervention with PD fluid. By overexpressing and knocking down SIRT6 expression, we investigated the effect of SIRT6 expression on E-cadherin, vimentin, and TGF-β1 expression to elucidate the role of SIRT6 in mesothelial-to-epithelial transition in PMCs. Results: (1) With the extension of PD duration, the influence of infection on SIRT6 levels in PDEs increased. Patients with the PD duration of more than 5 years and a history of peritonitis had the lowest SIRT6 levels. (2) SIRT6 levels in PDEs were negatively correlated with PD duration, total glucose exposure, TGF-β1, IL-6 levels, and the dialysate-to-plasma ratio of creatinine (Cr4hD/P), but positively correlated with UF. This indicates that SIRT6 has a protective effect on the peritoneum. (3) The short-term group (PD ≤ 1 year) had higher SIRT6 and E-cadherin gene and protein levels than the mid-term group (1 year < PD ≤ 5 years) and long-term group (PD > 5 years) in PMCs, while vimentin and TGF-β1 levels were lower in the mid-term group and long-term group. Patients with a history of peritonitis had lower SIRT6 and E-cadherin levels than those without such a history. (4) After 4.25% PD fluid intervention for HPMCs, longer intervention time resulted in lower SIRT6 levels. (5) Overexpressing SIRT6 can lead to increased E-cadherin expression and decreased vimentin and TGF-β1 expression in HPMCs. Knocking down SIRT6 expression resulted in decreased E-cadherin expression and increased vimentin and TGF-β1 expression in HPMCs. This indicates that SIRT6 expression can inhibit MMT in HPMCs, alleviate PF associated with PD, and have a protective effect on the peritoneum.

Function and expression of N-acetyltransferases 1 and 2 are altered in lymphocytes in type 2 diabetes and obesity

The cytosolic enzymes N-Acetyl Transferases 1 and 2 (NATs) transfer an acetyl group from acetyl-CoA to a xenobiotic substrate. NATs are regulated at the genetic and epigenetic levels by deacetylase enzymes such as sirtuins. The enzymatic expression of NAT1, NAT2, and SIRT1 was evaluated by flow cytometry, as well as the enzymatic activity of NATs by cell culture and HPLC analysis. Six SNPs were determined through genotyping. T2D patients (n = 29) and healthy subjects (n = 25) with a median age of 57 and 50, respectively, were recruited. An increased enzyme expression and a diminished NAT2 enzymatic activity were found in cells of T2D patients compared to the control group, while NAT1 was negatively correlated with body fat percentage and BMI. In contrast, Sirtuin inhibition increased NAT2 activity, while Sirtuin agonism decreased its activity in both groups. The analysis of NAT2 SNPs showed a higher frequency of rapid acetylation haplotypes in T2D patients compared to the control group, possibly associated as a risk factor for diabetes. The enzymatic expression of CD3+NAT2+ cells was higher in the rapid acetylators group compared to the slow acetylators group. The levels and activity of NAT1 were associated with total cholesterol and triglycerides. Meanwhile, CD3+NAT2+ cells and NAT2 activity levels were associated with HbA1c and glucose levels. The results indicate that NAT2 could be involved in metabolic processes related to the development of T2D, due to its association with glucose levels, HbA1c, and the altered SIRT-NAT axis. NAT1 may be involved with dyslipidaemias in people who are overweight or obese.

The Arylamine N-Acetyltransferases as Therapeutic Targets in Metabolic Diseases Associated with Mitochondrial Dysfunction

In humans, there are two arylamine N-acetyltransferase genes that encode functional enzymes (NAT1 and NAT2) as well as one pseudogene, all of which are located together on chromosome 8. Although they were first identified by their role in the acetylation of drugs and other xenobiotics, recent studies have shown strong associations for both enzymes in a variety of diseases, including cancer, cardiovascular disease, and diabetes. There is growing evidence that this association may be causal. Consistently, NAT1 and NAT2 are shown to be required for healthy mitochondria. This review discusses the current literature on the role of both NAT1 and NAT2 in mitochondrial bioenergetics. It will attempt to relate our understanding of the evolution of the two genes with biologic function and then present evidence that several major metabolic diseases are influenced by NAT1 and NAT2. Finally, it will discuss current and future approaches to inhibit or enhance NAT1 and NAT2 activity/expression using small-molecule drugs. SIGNIFICANCE STATEMENT: The arylamine N-acetyltransferases (NATs) NAT1 and NAT2 share common features in their associations with mitochondrial bioenergetics. This review discusses mitochondrial function as it relates to health and disease, and the importance of NAT in mitochondrial function and dysfunction. It also compares NAT1 and NAT2 to highlight their functional similarities and differences. Both NAT1 and NAT2 are potential drug targets for diseases where mitochondrial dysfunction is a hallmark of onset and progression.

The role of arylamine N-acetyltransferases in chronic degenerative diseases: Their possible function in the immune system

Since their discovery, arylamine N-acetyltransferases 1 and 2 (NAT1 and NAT2, respectively) have been associated with the metabolism of xenobiotics. NAT2 is the main factor in the therapeutic success of tuberculosis treatment due to its role in the biotransformation of isoniazid. However, researchers have started to investigate the possible participation of NAT1 and NAT2 (NATs) in carcinogenesis, although the mechanisms have not been elucidated fully. NATs enzymatic activity is essential in some types of cancer, such as breast cancer and acute lymphoblastic leukemia. Whether NAT1 and/or NAT2 participate in insulin resistance level in diabetes mellitus or in the immune system remains to be explored. Therefore, it is clear that its role in cell physiology has more implications than just metabolizing compounds.

Arylamine N-Acetyltransferase 1 Activity is Regulated by the Protein Acetylation Status

Arylamine N-acetyltransferase 1 (NAT1) is a drug metabolizing enzyme that influences cancer cell proliferation and survival, especially in breast cancer. Lysine-acetylation is an important Post-Translational Modification (PTM) in the regulation of diverse cellular processes. Histone deacetylases (HDACs) and Sirtuins (SIRT) may have an important role on the NAT1 acetylation status, affecting its catalytic capacity and having an impact on the downstream functions of this protein. The aim of the present work is to investigate the acetylation status of NAT1 in human breast cancer. Breast cancer cell lines MDA-MB-231 (ER-, PR-, HER2-) and ZR-75-1 (estrogen receptor+, PR+, HER2+) were cultured in the presence of HDAC inhibitors (SAHA, TSA) or Sirtuin inhibitors (AGK2, EX527, Sirtinol). Under these conditions, NAT1 protein and gene expression as well as enzymatic activity were quantified. Acetylation of NAT1 protein was evaluated following an immunoprecipitation protocol and acetyl-Lysine quantification. Sirt1 and Sirt2 knockdown were performed and NAT1 protein and NAT1 mRNA expression and catalytic activity were quantified. The treatment of MDA-MB-231 or ZR-75-1 cells with increasing HDAC inhibitors resulted in 2 to 15-fold upregulation in NAT1 message expression. Finally, the catalytic activity of NAT1 in the presence of HDAC inhibition increased 2-fold. Conversely, the inhibition of Sirtuin activity did not cause significant changes in NAT1 message but produced a significant decrease in NAT1 catalytic activity. NAT1 acetylation was higher in the cells treated with HDAC inhibitors, as well as Sirtuin inhibitors. Finally, silencing of Sirt1 and Sirt2 genes by siRNA transient knockdown of each or both genes resulted in reduction of NAT1 protein expression and catalytic activity. The use of HDAC and Sirtuin inhibitors has been demonstrated as a promising powerful therapeutic alternative in various cancers. These inhibitors can significantly attenuate tumor burden by limiting tumor growth and metastasis. These compounds can also induce DNA damage, cell cycle arrest, apoptosis, and autophagy to promote cancer cell death. Several studies have shown that NAT1 is upregulated in cancer cells. The results of the present study show that the acetylation status of NAT1 is an important factor that might have a relevant role in the progression of cancer.

Curcumin attenuates isoniazid-induced hepatotoxicity by the upregulating SIRT1/PGC-1α/NRF1 pathway

As a serious infectious disease, tuberculosis threatens global public health. Isoniazid is the first-line drug not only in active tuberculosis but also in its prevention. Severe hepatotoxicity greatly limits its use. Curcumin, extracted from turmeric, has been found to relieve isoniazid-induced hepatotoxicity. However, the mechanism of isoniazid-induced hepatotoxicity and the protective effects of curcumin are not yet understood completely. We established both cell and animal models about isoniazid-induced hepatotoxicity, and investigated the new mechanism of curcumin against isoniazid-induced liver injury. The experimental data in our study demonstrated that curcumin ameliorated isoniazid-mediated liver oxidative stress. The protective effects of curcumin were demonstrated confirmed to be correlated with upregulating SIRT1/PGC-1α/NRF1 pathway. Western blot revealed that while inhibiting SIRT1 by the siRNA1 (a SIRT1 inhibitor), the expressions of SIRT1, PGC-1α/Ac-PGC-1α, and NRF1 decreased, and the protective effect that curcumin exerted on isoniazid-treated L-02 cells was significantly attenuated. Furthermore, curcumin improved liver functions and reduced necrosis of the isoniazid-treated BALB/c mice, accompanied by downregulating oxidative stress and inflammation in liver. Western blot revealed that curcumin treatment activates the SIRT1/PGC-1α/NRF1 pathway in the isoniazid-treated BALB/c mice. In conclusion, we found one mechanism of isoniazid-induced hepatotoxicity was downregulating the SIRT1/PGC-1α/NRF1 pathway, and curcumin attenuated this hepatotoxicity by activating it. Our study provided a novel approach and mechanism for the treatment of isoniazid-induced hepatotoxicity.

Modulation of Human Arylamine N-Acetyltransferase 1 Activity by Lysine Acetylation: Role of p300/CREB-Binding Protein and Sirtuins 1 and 2

Arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme that also has a role in cancer cell growth and metabolism. Recently, it was reported that NAT1 undergoes lysine acetylation, an important post-translational modification that can regulate protein function. In the current study, we use site-directed mutagenesis to identify K¹⁰⁰ and K¹⁸⁸ as major sites of lysine acetylation in the NAT1 protein. Acetylation of ectopically expressed NAT1 in HeLa cells was decreased by C646, an inhibitor of the protein acetyltransferases p300/CREB-binding protein (CBP). Recombinant p300 directly acetylated NAT1 in vitro. Acetylation of NAT1 was enhanced by the sirtuin (SIRT) inhibitor nicotinamide but not by the histone deacetylase inhibitor trichostatin A. Cotransfection of cells with NAT1 and either SIRT 1 or 2, but not SIRT3, significantly decreased NAT1 acetylation. NAT1 activity was evaluated in cells after nicotinamide treatment to enhance acetylation or cotransfection with SIRT1 to inhibit acetylation. The results indicated that NAT1 acetylation impaired its enzyme kinetics, suggesting decreased acetyl coenzyme A binding. In addition, acetylation attenuated the allosteric effects of ATP on NAT1. Taken together, this study shows that NAT1 is acetylated by p300/CBP in situ and is deacetylated by the sirtuins SIRT1 and 2. It is hypothesized that post-translational modification of NAT1 by acetylation at K¹⁰⁰ and K¹⁸⁸ may modulate NAT1 effects in cells. SIGNIFICANCE STATEMENT: There is growing evidence that arylamine N-acetyltransferase 1 has an important cellular role in addition to xenobiotic metabolism. Here, we show that NAT1 is acetylated at K¹⁰⁰ and K¹⁸⁸ and that changes in protein acetylation equilibrium can modulate its activity in cells.

A Microbiological, Toxicological, and Biochemical Study of the Effects of Fucoxanthin, a Marine Carotenoid, on Mycobacterium tuberculosis and the Enzymes Implicated in Its Cell Wall: A Link Between Mycobacterial Infection and Autoimmune Diseases

This study explored the antitubercular properties of fucoxanthin, a marine carotenoid, against clinical isolates of Mycobacterium tuberculosis (Mtb). Two vital enzymes involved in Mtb cell wall biosynthesis, UDP-galactopyranose mutase (UGM) and arylamine-N-acetyltransferase (TBNAT), were selected as drug targets to reveal the mechanism underlying the antitubercular effect of fucoxanthin. The obtained results showed that fucoxanthin showed a clear bacteriostatic action against the all Mtb strains tested, with minimum inhibitory concentrations (MIC) ranging from 2.8 to 4.1 µM, along with a good degree of selectivity index (ranging from 6.1 to 8.9) based on cellular toxicity evaluation compared with standard drug isoniazid (INH). The potent inhibitory actions of fucoxanthin and standard uridine-5’-diphosphate against UGM were recorded to be 98.2% and 99.2%, respectively. TBNAT was potently inactivated by fucoxanthin (half maximal inhibitory concentration (IC₅₀) = 4.8 µM; 99.1% inhibition) as compared to INH (IC₅₀ = 5.9 µM; 97.4% inhibition). Further, molecular docking approaches were achieved to endorse and rationalize the biological findings along with envisaging structure-activity relationships. Since the clinical evidence of the last decade has confirmed the correlation between bacterial infections and autoimmune diseases, in this study we have discussed the linkage between infection with Mtb and autoimmune diseases based on previous clinical observations and animal studies. In conclusion, we propose that fucoxanthin could demonstrate great therapeutic value for the treatment of tuberculosis by acting on multiple targets through a bacteriostatic effect as well as by inhibiting UGM and TBNAT. Such outcomes may lead to avoiding or decreasing the susceptibility to autoimmune diseases associated with Mtb infection in a genetically susceptible host.

Synergistic antitumor activity of artesunate and HDAC inhibitors through elevating heme synthesis via synergistic upregulation of ALAS1 expression

Artemisinin and its derivatives (ARTs) were reported to display heme-dependent antitumor activity. On the other hand, histone deacetylase inhibitors (HDACi) were known to be able to promote heme synthesis in erythroid cells. Nevertheless, the effect of HDACi on heme homeostasis in non-erythrocytes remains unknown. We envisioned that the combination of HDACi and artesunate (ARS) might have synergistic antitumor activity through modulating heme synthesis. In vitro studies revealed that combination of ARS and HDACi exerted synergistic tumor inhibition by inducing cell death. Moreover, this combination exhibited more effective antitumor activity than either ARS or HDACi monotherapy in xenograft models without apparent toxicity. Importantly, mechanistic studies revealed that HDACi coordinated with ARS to increase 5-aminolevulinate synthase (ALAS1) expression, and subsequent heme production, leading to enhanced cytotoxicity of ARS. Notably, knocking down ALAS1 significantly blunted the synergistic effect of ARS and HDACi on tumor inhibition, indicating a critical role of ALAS1 upregulation in mediating ARS cytotoxicity. Collectively, our study revealed the mechanism of synergistic antitumor action of ARS and HDACi. This finding indicates that modulation of heme synthesis pathway by the combination based on ARTs and other heme synthesis modulators represents a promising therapeutic approach to solid tumors.

The function of histone acetylation in cervical cancer development

Cervical cancer is the fourth most common female cancer in the world. It is well known that cervical cancer is closely related to high-risk human papillomavirus (HPV) infection. However, epigenetics has increasingly been recognized for its role in tumorigenesis. Epigenetics refers to changes in gene expression levels based on non-gene sequence changes, primarily through transcription or translation of genes regulation, thus affecting its function and characteristics. Typical post-translational modifications (PTMs) include acetylation, propionylation, butyrylation, malonylation and succinylation, among which the acetylation modification of lysine sites has been studied more clearly so far. The acetylation modification of lysine residues in proteins is involved in many aspects of cellular life activities, including carbon metabolism, transcriptional regulation, amino acid metabolism and so on. In this review, we summarize the latest discoveries on cervical cancer development arising from the aspect of acetylation, especially histone acetylation.

Expression and genotype-dependent catalytic activity of N-acetyltransferase 2 (NAT2) in human peripheral blood mononuclear cells and its modulation by Sirtuin 1

N-acetyltransferase 2 (NAT2) catalyzes the biotransformation of numerous arylamine and hydrazine drugs and carcinogens. Genetic polymorphisms of NAT2 modify drug efficacy and toxicity and susceptibility to diseases such as cancer and type 2 diabetes. Expression of NAT2 has been documented in the liver and gastrointestinal tract but not in other tissues. Deacetylation of cytosolic proteins by sirtuins is a post-translational modification important in regulatory networks of diverse cellular processes. The aim of the present study was to investigate NAT2 expression in peripheral blood mononuclear cells (PBMC) and the effects of NAT2 genotype and Sirtuin 1 (SIRT1). Both NAT2 and SIRT1 proteins were expressed on PBMC. Their expression was more prevalent on CD3+ compared to CD19+ and CD56+ cell populations. N-acetylation capacity of PBMC exhibited a NAT2 gene-dose response toward the N-acetylation of isoniazid. Subjects with rapid NAT2 genotype showed an apparent V_max of 42.1 ± 2.4; intermediate NAT2 genotypes an apparent V_max of 22.6 ± 2.2; and slow acetylator NAT2 genotypes an apparent V_max of 19.9 ± 1.7 nM acetyl-isoniazid/24 h/million cells. The N-acetylation capacity of NAT2 in the presence of SIRT1 enhancer was significantly decreased (p < 0.001), conversely, the transient silencing of SIRT1 resulted in an increase of N-acetylation capacity (p < 0.001). These findings are the first report of NAT2 genotype-dependent expression on PBMC and post-translational modification by SIRT1. These findings constitute a substantial advance in our understanding of human N-acetyltransferase expression and a new much less invasive method for measurement of human NAT2 expression and phenotype.