Synergic chemoprevention with dietary carbohydrate restriction and supplementation of AMPK-activating phytochemicals: the role of SIRT1

Natural Phytochemicals as SIRT Activators-Focus on Potential Biochemical Mechanisms

Sirtuins are a family of proteins with enzymatic activity. There are seven mammalian sirtuins (SIRT1-SIRT7) that are found in different cellular compartments. They are a part of crucial cellular pathways and are regulated by many factors, such as chemicals, environmental stress, and phytochemicals. Several in vitro and in vivo studies have presented their involvement in anti-inflammatory, antioxidant, and antiapoptotic processes. Recent findings imply that phytochemicals such as resveratrol, curcumin, quercetin, fisetin, berberine, and kaempferol may regulate the activity of sirtuins. Resveratrol mainly activates SIRT1 and indirectly activates AMPK. Curcumin influences mainly SIRT1 and SIRT3, but its activity is broad, and many pathways in different cells are affected. Quercetin mainly modulates SIRT1, which triggers antioxidant and antiapoptotic responses. Fisetin, through SIRT1 regulation, modifies lipid metabolism and anti-inflammatory processes. Berberine has a wide spectrum of effects and a significant impact on SIRT1 signaling pathways. Finally, kaempferol triggers anti-inflammatory and antioxidant effects through SIRT1 induction. This review aims to summarize recent findings on the properties of phytochemicals in the modulation of sirtuin activity, with a particular focus on biochemical aspects.

Impact of dietary carbohydrate restriction on the pathobiology of Hepatocellular Carcinoma: The gut-liver axis and beyond

Despite decades of fiercely competitive research and colossal financial investments, the majority of patients with advanced solid cancers cannot be treated with curative intent. To improve this situation, conceptually novel treatment approaches are urgently needed. Cancer is increasingly appreciated as a systemic disease and numerous organismal factors are functionally linked to neoplastic growth, e.g. systemic metabolic dysregulation, chronic inflammation, intestinal dysbiosis and disrupted circadian rhythms. It is tempting to hypothesize that interventions targeting these processes could be of significant account for cancer patients. One important driver of tumor-supporting systemic derangements is inordinate consumption of simple and highly processed carbohydrates. This dietary pattern is causally linked to hyperinsulinemia, insulin resistance, chronic inflammation and intestinal dysbiosis, begging the pertinent question whether the adoption of dietary carbohydrate restriction can be beneficial for patients with cancer. This review summarizes the published data on the role of dietary carbohydrate restriction in the pathogenesis of Hepatocellular Carcinoma (HCC), the most frequent type of primary liver cancer. In addition to outlining the functional interplay between diet, the intestinal microbiome and immunity, the review underscores the importance of bile acids as interconnectors between the intestinal microbiota and immune cells.

The role of AMPK in cancer metabolism and its impact on the immunomodulation of the tumor microenvironment

Adenosine monophosphate-activated protein kinase (AMPK) is a key metabolic sensor that is pivotal for the maintenance of cellular energy homeostasis. AMPK contributes to diverse metabolic and physiological effects besides its fundamental role in glucose and lipid metabolism. Aberrancy in AMPK signaling is one of the determining factors which lead to the development of chronic diseases such as obesity, inflammation, diabetes, and cancer. The activation of AMPK and its downstream signaling cascades orchestrate dynamic changes in the tumor cellular bioenergetics. It is well documented that AMPK possesses a suppressor role in the context of tumor development and progression by modulating the inflammatory and metabolic pathways. In addition, AMPK plays a central role in potentiating the phenotypic and functional reprogramming of various classes of immune cells which reside in the tumor microenvironment (TME). Furthermore, AMPK-mediated inflammatory responses facilitate the recruitment of certain types of immune cells to the TME, which impedes the development, progression, and metastasis of cancer. Thus, AMPK appears to play an important role in the regulation of anti-tumor immune response by regulating the metabolic plasticity of various immune cells. AMPK effectuates the metabolic modulation of anti-tumor immunity via nutrient regulation in the TME and by virtue of its molecular crosstalk with major immune checkpoints. Several studies including that from our lab emphasize on the role of AMPK in regulating the anticancer effects of several phytochemicals, which are potential anticancer drug candidates. The scope of this review encompasses the significance of the AMPK signaling in cancer metabolism and its influence on the key drivers of immune responses within the TME, with a special emphasis on the potential use of phytochemicals to target AMPK and combat cancer by modulating the tumor metabolism.

Natural Products for Liver Cancer Treatment: From Traditional Medicine to Modern Drug Discovery

Primary liver cancer was the seventh most diagnosed cancer and the second leading cause of cancer death with about 906,000 cases and 830,000 deaths, respectively, in 2020. Conventional treatment for liver cancer, such as transarterial chemoembolization (TACE) or sorafenib, has limitations in that there is the recurrence of cancer, drug inefficacy, and adverse effects. Traditional medicine and natural products of several regions including Korea, China, Europe, North America, India, and the Middle East have attracted a lot of attention since they have been reported to have anticancer effects with low adverse effects. In this review, several in vivo studies on the effects of natural compounds on liver cancer and clinical trials approving their therapeutic benefits were selected and discussed. As a result of the analysis of these studies, the effects of natural compounds were classified into a few mechanisms: apoptosis, anti-metastasis, and antiangiogenesis. In addition, medications including natural products in clinical trials were observed to exhibit improvements in various liver cancer symptoms and patients’ survival rates. This study presents findings suggestive of the anticancer potential of natural products and their properties in relieving related symptoms.

Regulation of Gene Expression through Food—Curcumin as a Sirtuin Activity Modulator

The sirtuin family comprises NAD⁺-dependent protein lysine deacylases, mammalian sirtuins being either nuclear (SIRT1, SIRT2, SIRT6, and SIRT7), mitochondrial (SIRT3, SIRT4, and SIRT5) or cytosolic enzymes (SIRT2 and SIRT5). They are able to catalyze direct metabolic reactions, thus regulating several physiological functions, such as energy metabolism, stress response, inflammation, cell survival, DNA repair, tissue regeneration, neuronal signaling, and even circadian rhythms. Based on these data, recent research was focused on finding molecules that could regulate sirtuins’ expression and/or activity, natural compounds being among the most promising in the field. Curcumin (1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) can induce, through SIRT, modulation of cancer cell senescence, improve endothelial cells protection against atherosclerotic factors, enhance muscle regeneration in atrophy models, and act as a pro-longevity factor counteracting the neurotoxicity of amyloid-beta. Although a plethora of protective effects was reported (antioxidant, anti-inflammatory, anticancer, etc.), its therapeutical use is limited due to its bioavailability issues. However, all the reported effects may be explained via the bioactivation theory, which postulates that curcumin’s observed actions are modulated via its metabolites and/or degradation products. The present article is focused on bringing together the literature data correlating the ability of curcumin and its metabolites to modulate SIRT activity and its consequent beneficial effects.

Steatosis induced by nonylphenol in HepG2 cells and the intervention effect of curcumin

Non-alcoholic fatty liver disease (NAFLD) has increasingly become a serious public health problem. There is growing evidence that nonylphenol (NP) exposure may cause steatosis, but the underlying mechanism is not fully understood. Curcumin (CUR) improves NAFLD-related lipid metabolism disorders and oxidative stress, but its preventive and therapeutic effects on NP-induced steatosis have not been reported. The objective of this investigation was to determine the capability and potential mechanism of NP to induce steatosis in vitro and the intervention of curcumin. HepG2 cells were treated with 0 μM, 20 μM, 30 μM, 40 μM NP for 24 h. Lipid droplets accumulated significantly in HepG2 cells after NP treatment, and the concentration of triglyceride (TG) and total cholesterol (T-CHO) increased significantly. Simultaneously, lipogenesis gene expression was up-regulated significantly, fatty acid oxidation (FAO) gene expression was significantly down-regulated, and reactive oxygen species (ROS) were overproduced. Meanwhile, the expression of p-AMPK/AMPK in the AMPK/mTOR signaling pathway was significantly down-regulated and the expression of p-mTOR/mTOR was markedly up-regulated. However, blocking ROS production with N-acetyl-L-cysteine (NAC) can reverse these phenomena. In addition, our study found that curcumin effectively ameliorated the effects of NP-induced steatosis. Our study indicates that NP can induce steatosis in HepG2 cells, and may be implicated in inhibiting the ROS-dependent AMPK/mTOR pathway, and that curcumin ameliorates the NAFLD-like changes induced by NP in HepG2 cells.

Curcumin Treatment in Combination with Glucose Restriction Inhibits Intracellular Alkalinization and Tumor Growth in Hepatoma Cells

Dysregulation of cellular energy metabolism is closely linked to cancer development and progression. Calorie or glucose restriction (CR or GR) inhibits energy-dependent pathways, including IGF-1/PI3K/Akt/mTOR, in cancer cells. However, alterations in proton dynamics and reversal of the pH gradient across the cell membrane, which results in intracellular alkalinization and extracellular acidification in cancer tissues, have emerged as important etiopathogenic factors. We measured glucose, lactate, and ATP production after GR, plant-derived CR-mimetic curcumin treatment, and curcumin plus GR in human hepatoma cells. Intracellular pH regulatory effects, in particular, protein-protein interactions within mTOR complex-1 and its structural change, were investigated. Curcumin treatment or GR mildly inhibited Na+/H+ exchanger-1 (NHE1). vATPase, monocarboxylate transporter (MCT)-1, and MCT4 level. Combination treatment with curcumin and GR further enhanced the inhibitory effects on these transporters and proton-extruding enzymes, with intracellular pH reduction. ATP and lactate production decreased according to pH change. Modeling of mTOR protein revealed structural changes upon treatments, and curcumin plus GR decreased binding of Raptor and GβL to mTOR, as well as of Rag A and Rag B to Raptor. Consequently, 4EBP1 phosphorylation was decreased and cell migration and proliferation were inhibited in a pH-dependent manner. Autophagy was increased by curcumin plus GR. In conclusion, curcumin treatment combined with GR may be a useful supportive approach for preventing intracellular alkalinization and cancer progression.

Gut microbiota modulation of chemotherapy efficacy and toxicity

Evidence is growing that the gut microbiota modulates the host response to chemotherapeutic drugs, with three main clinical outcomes: facilitation of drug efficacy; abrogation and compromise of anticancer effects; and mediation of toxicity. The implication is that gut microbiota are critical to the development of personalized cancer treatment strategies and, therefore, a greater insight into prokaryotic co-metabolism of chemotherapeutic drugs is now required. This thinking is based on evidence from human, animal and in vitro studies that gut bacteria are intimately linked to the pharmacological effects of chemotherapies (5-fluorouracil, cyclophosphamide, irinotecan, oxaliplatin, gemcitabine, methotrexate) and novel targeted immunotherapies such as anti-PD-L1 and anti-CLTA-4 therapies. The gut microbiota modulate these agents through key mechanisms, structured as the 'TIMER' mechanistic framework: Translocation, Immunomodulation, Metabolism, Enzymatic degradation, and Reduced diversity and ecological variation. The gut microbiota can now, therefore, be targeted to improve efficacy and reduce the toxicity of current chemotherapy agents. In this Review, we outline the implications of pharmacomicrobiomics in cancer therapeutics and define how the microbiota might be modified in clinical practice to improve efficacy and reduce the toxic burden of these compounds.