Inflammatory cytokines suppress arylamine N-acetyltransferase 1 in cholangiocarcinoma cells

Abstract

B e n j a p o r n B u r a n r a t , A u e m d u a n P r a w a n , V e e r a p o l Kukongviriyapan, Abstract AIM: To evaluate the effect of inflammatory cytokines on arylamine N -acetyltransferase 1 (NAT1), which is a phase-Ⅱ enzyme involved in the biotransformation of aromatic and heterocyclic amines found in food, drugs and the environment. METHODS:Human cholangiocarcinoma KKU-100 cells were treated with a mixture of proinflammatory cytokines (interferon-γ, interleukin-1β, and tumor necrosis factor-α) for 48 h, and the effect on NAT1 activity was assessed by high performance liquid chromatography, while NAT1 expression was determined by reverse-transcription polymerase chain reaction. The oxidative stress on the cells was examined by the formation of nitric oxide, superoxide anion and glutathione (GSH) levels. The cells were also treated with S -nitroso-glutathione (GSNO), a nitric oxide donor, to see if the responses were similar to those obtained with the inflammatory cytokines. RESULTS:Cyt okines suppressed NAT1 activity, reducing the Vmax without affecting the K m. Cytokines also had a significant impact on the induction of nitric oxide production and in reducing the redox ratios of glutathione (GSH) and GSH disulfide. Treatment with GSNO for 2-48 h reduced NAT1 activity without affecting the GSH ratio. Moreover, inflammatory cytokines and GSNO suppressed NAT1 mRNA expression. CONCLUSION:These findings indicate an association between inflammation and suppression of NAT1, which perhaps contributes to chemical-mediated toxicity and carcinogenesis.

Acute murine colitis reduces colonic 5-aminosalicylic acid metabolism by regulation of N-acetyltransferase-2

“…Other work shows that activity of recombinant hNAT1 protein is directly inhibited by reaction of biological oxidants with a cysteine in the enzyme active site (6,15). In contrast, when a mixture of proinflammatory cytokines is added to human cholangiocarcinoma cells for 48 h, hNAT1 activity and mRNA are reduced in parallel (8), an outcome that we did not observe in isolated mouse colonic tissue. We speculate that the observed posttranscriptional regulation of colonic mNAT2 activity may be mediated by increased reactive oxygen species in the inflammatory state.…”

“…Inflammation is known to change activity of many enzymes and transporters that affect therapeutic drugs (8,45,51,62,65); therefore, for drug efficacy, it is important to know if this central feature of IBD is by itself affecting 5-ASA metabolism. Unfortunately, this has only been examined in small studies using IBD patients with diverse clinical status, and results are conflicting.…”

“…Because 5-ASA is a substrate for all mouse and human NAT isoforms (8,22,38) and colonic mucosa expresses at least mNAT1 and mNAT2 (11, 18, 32, 64), we questioned if the basis for altered 5-ASA acetylation during colitis was a change in the contributing mNAT isoform(s). We used substrates shown to be selective for the recombinant mNAT1 (isoniazid) or mNAT2 (p-ABG) (22) and used them as competitive inhibitors of 5-ASA metabolism.…”

Arylamine N-Acetyltransferase 1: A Novel Drug Target in Cancer Development

“…It has been reported that cytokines can cause a decrease in NAT1 activity, possibly by oxidative stress-induced inactivation of the enzyme (Buranrat et al, 2007). However, this study also showed that NAT1 mRNA levels were considerably lower in cytokine-treated cells, suggesting that additional mechanisms may contribute to the loss of NAT1 activity, particularly for longer exposure times.…”

Metabolomics of transformed MDA-MB-231 cell lines expressing different levels of human arylamine N-acetyltransferase 1 (NAT1).

“…Adding to the confusion, NAT1 activity is also modulated by a plethora of post-translational and environmental factors, including direct chemical modification of the active-site cysteine by reactive chemical species [36,37], factors that induce oxidative stress and alter GSH levels [21], cytokines [38], and through inhibition by small molecule inhibitors [39][40][41], heavy metals [42], plant extracts [37], nanoparticles [43], and therapeutic agents [44]. The NAT1 gene copy number can also be increased or decreased when compared to the standard of two, thus causing differences in NAT1 activity.…”