Efficacy of highly bioavailable oral curcumin in asymptomatic or mild COVID-19 patients: a double-blind, randomized, placebo-controlled trial.

INTRODUCTION: Even after the peak of the COVID-19 pandemic, the number of mild cases remains high, requiring continuous control. Curcumin, owing to its anti-inflammatory properties, can suppress vital proliferation and cytokine secretion in animal models. We developed a highly absorbable curcumin, curcuRouge® (cR), which is approximately 100 times more orally bioavailable than conventional curcumin. We evaluated the effect of cR on the inhibition of disease progression in asymptomatic or mildly symptomatic COVID-19 patients. METHODS: This study evaluated the effect of 7-day oral intake of cR (360 mg twice daily). Patients within 5 days of COVID-19 diagnosis were randomly assigned to a placebo or cR group in a double-blind manner. RESULTS: Primary endpoint events [body temperature (BT) ≥ 37.5 °C and saturation of percutaneous oxygen (SpO2) < 96%] were fewer than expected, and the rate of these events was 2.8% in the cR group (2/71) and 6.0% in the placebo group (4/67); hazard ratio (HR) = 0.532, 95% confidence interval (CI) 0.097-2.902. Patients receiving cR tended to take fewer antipyretic medications than those receiving placebo (HR = 0.716, 95% CI 0.374-1.372). Among patients with a normal range of BT at baseline, the BT change rate was significantly (p = 0.014) lower in the cR group (- 0.34%) versus placebo (- 0.01%). CONCLUSION: The relative suppression of event rates and antipyretic medications taken, and significant decrease of subclinical BT support the anti-inflammatory effects of cR in asymptomatic or mildly symptomatic patients with COVID-19. TRIAL REGISTRATION: Japan Registry of Clinical Trials (CRB5200002).

Pharmacologic characterization of TBP1901, a prodrug form of aglycone curcumin, and CRISPR-Cas9 screen for therapeutic targets of aglycone curcumin.

Curcumin (aglycone curcumin) has antitumor properties in a variety of malignancies via the alteration of multiple cancer-related biological pathways; however, its clinical application has been hampered due to its poor bioavailability. To overcome this limitation, we have developed a synthesized curcumin ß-D-glucuronide sodium salt (TBP1901), a prodrug form of aglycone curcumin. In this study, we aimed to clarify the pharmacologic characteristics of TBP1901. In ß-glucuronidase (GUSB)-proficient mice, both curcumin ß-D-glucuronide and its active metabolite, aglycone curcumin, were detected in the blood after TBP1901 injection, whereas only curcumin ß-D-glucuronide was detected in GUSB-impaired mice, suggesting that GUSB plays a pivotal role in the conversion of TBP1901 into aglycone curcumin in vivo. TBP1901 itself had minimal antitumor effects in vitro, whereas it demonstrated significant antitumor effects in vivo. Genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 screen disclosed the genes associated with NF-κB signaling pathway and mitochondria were among the highest hit. In vitro, aglycone curcumin inhibited NF-kappa B signaling pathways whereas it caused production of reactive oxygen species (ROS). ROS scavenger, N-acetyl-L-cysteine, partially reversed antitumor effects of aglycone curcumin. In summary, TBP1901 can exert antitumor effects as a prodrug of aglycone curcumin through GUSB-dependent activation.

Study protocol to determine the effects of highly absorbable oral curcumin on the indicators of cognitive functioning: a double-blind randomised controlled trial.

INTRODUCTION: Mild cognitive impairment (MCI) refers to a state in which cognitive functions, such as memory, have diminished but daily activities are largely unhampered. MCI is often overlooked but carries the risk of leading to development of dementia later. Curcumin is the main component of the natural herbal medicine turmeric. Curcumin is widely used as a health food and is an antioxidant that has anti-inflammatory and anti-amyloid actions. The current trial was designed to determine the effects of curcumin on indicators of cognitive functioning. METHODS AND ANALYSIS: The current trial will be a single-centre randomised placebo-controlled double-blind parallel group trial. The participants will be 60 members of the general public with potential MCI, based on dementia screening using the Japanese version of the Mini Mental State Examination (MMSE-J). The investigational health food used in this trial will be a recently developed preparation for highly absorbable oral curcumin. This trial will determine the effects of the highly absorbable oral curcumin (brand name: curcuRouge) on the indicators of cognitive functioning, including the scores obtained with the MMSE-J, which is an interview-based measure of cognitive functioning, and the blood biomarkers that have been reported to be associated with dementia. ETHICS AND DISSEMINATION: Informed written consent will be obtained from all the participants. The Ethical Review Board of the National Hospital Organization Kyoto Medical Center approved the study protocol. TRIAL REGISTRATION NUMBER: University Hospital Medical Information Network (UMIN000042471).

Intra-Articular Injections of Curcumin Monoglucuronide TBP1901 Suppresses Articular Cartilage Damage and Regulates Subchondral Bone Alteration in an Osteoarthritis Rat Model.

OBJECTIVE: Curcumin monoglucuronide (TBP1901) is highly water soluble and can convert to free form curcumin, which has pharmacological effects, on intravenous administration. This study aimed to investigate the effectiveness of TBP1901 intra-articular injections in an osteoarthritis (OA) rat model. METHODS: Sixty-four male Wistar rats (12 weeks old) who underwent destabilized medial meniscus (DMM) surgery were randomly separated into the TBP1901 injection or saline solution (control) injection group. They were sacrificed at 1, 2, 6, or 10 weeks postoperatively (weeks 1, 2, 6, and 10; n = 8 for each group). TBP1901 (30 mg/mL) or saline solution of 50 µL was injected into the knee joints twice a week during weeks 1 and 2 to investigate the effects in the acute phase of posttraumatic (PT) OA or once a week during weeks 6 and 10 to investigate it in the chronic phase of PTOA. Histology, immunohistochemistry, and micro-computed tomography were performed to evaluate the changes in OA. RESULTS: TBP1901 injections significantly reduced synovial inflammation at weeks 1 and 2, and tumor necrosis factor-α expression in the articular cartilage at week 6. The TBP1901 injections also significantly suppressed articular cartilage damage, subchondral bone (SB) plate thickening, SB plate perforation, and osteophyte formation at week 10. CONCLUSIONS: TBP1901 intra-articular injections suppressed synovial inflammation in the acute phase of PTOA in DMM rats. In the chronic phase, TBP1901 suppresses articular cartilage damage and regulates SB plate changes.

Newly Developed Highly Bioavailable Curcumin Formulation, curcuRougeTM, Reduces Neutrophil/Lymphocyte Ratio in the Elderly: A Double-Blind, Placebo-Controlled Clinical Trial.

Elevated neutrophil/lymphocyte ratio (NLR) has been reported as a sensitive marker for predicting poor prognosis in chronic inflammation-based diseases such as stroke, heart failure, cancers, and diabetes, as well as acute inflammatory diseases such as bacterial and viral infections, including COVID-19. NLR is also known to increase with age and is considered to be an aging marker. We conducted a double-blind, placebo-controlled trial in elderly volunteers to examine the effect of a newly developed, highly bioavailable curcumin formulation (curcuRougeTM) on NLR. Both the white blood cell count and the neutrophil rate decreased significantly, and the lymphocyte rate increased significantly from baseline to after curcuRougeTM administration for 4 wk. curcuRougeTM significantly reduced the NLR (p=0.020). On the other hand, in the placebo group, there were no changes in white blood cell count, neutrophil ratio, lymphocyte ratio, or NLR. The present study demonstrates for the first time, in elderly volunteers, that administration of curcuRougeTM significantly reduces NLR, an indicator of prognosis in cardiovascular diseases, cancer, infectious diseases, and aging. Thus, curcuRougeTM might be expected to improve the prognosis of these diseases as well as exhibit anti-aging effects.

Curcumin ß-D-glucuronide exhibits anti-tumor effects on oxaliplatin-resistant colon cancer with less toxicity in vivo.

The NF-kappa B (NF-κB) pathway plays a pivotal role in tumor progression and chemoresistance, and its inhibition has been shown to suppress tumor growth in a variety of preclinical models. Recently, we succeeded in synthesizing a water-soluble injectable type of curcumin ß-D-glucuronide (CMG), which is converted into a free-form of curcumin by ß-glucuronidase in vivo. Herein, we aimed to clarify the efficacy, safety and pharmacokinetics of CMG in a xenograft mouse model. First, we confirmed that the presence of KRAS/TP53 mutations significantly increased the IC50 of oxaliplatin (L-OHP) and NF-κB activity in HCT116 cells in vitro. Then, we tested the efficacy of CMG in an HCT116 colon cancer xenograft mice model. CMG demonstrated superior anticancer effects compared to L-OHP in an L-OHP-resistant xenograft model. With regard to safety, significant bodyweight loss, severe myelosuppression and AST/ALT elevation were observed in L-OHP-treated mice, whereas none of these toxicity was noted in CMG-treated mice. The combination of CMG and L-OHP exhibited additive effects in these xenograft models without increasing toxicity. Pharmacokinetic analysis revealed that high levels of free-form curcumin were maintained in the tumor tissue after 48 hours following CMG administration, but it was not detected in other major organs, such as the heart, liver and spleen. Immunohistochemistry revealed reduced NF-κB activity in the tumor tissue extracted from CMG-treated mice compared with that from control mice. These results indicated that CMG could be a promising anticancer prodrug for treating colon cancer with minimal toxicity.

Resveratrol improves salivary dysfunction in a non-obese diabetic (NOD) mouse model of Sjögren's syndrome.

Resveratrol is a natural polyphenol produced by plants in response to environmental stress. This compound has been shown to have pharmacological effects against a wide range of diseases including neurological, hepatic, cardiovascular and autoimmune conditions. The non-obese diabetic (NOD) mouse, in which loss of lacrimal and salivary gland function occurs, has been studied as an animal model for Sjögren's syndrome. In this study, we confirmed that administration of resveratrol results in increased secretion of saliva in NOD mice. Although resveratrol enhanced Sirt1 activity, inflammatory cell infiltration was not affected. Moreover, expression of the anti-inflammatory cytokine IL-10 in salivary glands was enhanced in the resveratrol-administered group. Thus, we confirmed a novel therapeutic effect for resveratrol on salivary dysfunction in Sjögren's syndrome.

A pull-down assay for 5' AMP-activated protein kinase activity using the GST-fused protein.

An assay using a specific peptide (SAMS peptide) as a substrate is widely used for determination of AMP-activated protein kinases (AMPK) activity. However, it is not an efficient assay for crude AMPK preparations. In this study, we modified the assay by using the SAMS peptide fused to glutathione-S-transferase (GST-SAMS) instead of the SAMS peptide on its own. Radioactivity incorporated into GST-SAMS can be recovered easily by precipitation with glutathione-agarose. The kinetic parameters of partially purified AMPK for the GST-SAMS were as follows. The Vmax was 0.26 +/- 0.012 nmol/min/mg of total proteins and Km for GST-SAMS was 110 +/- 12 microM. The parameters for ATP were 0.40 +/- 0.016 nmol/min/mg of total proteins (Vmax) and 202 +/- 21 microM (Km). The activity of AMPK in this system was stimulated about threefold by the AMPK activators, AMP or 5-amino-4-imidazolecarboxamide ribotide (ZMP), and inhibited by the AMPK inhibitors, adenine 9-beta-D-arabinofuranoside (ara-A) and iodotubercidin. These values correlate well with those for the SAMS peptide reported previously. Thus, we successfully established a convenient and rapid method to measure AMPK applicable, even for crude enzyme preparations.

Correction of chromosomal mutation and random integration in embryonic stem cells with helper-dependent adenoviral vectors.

For gene therapy of inherited diseases, targeted integration/gene repair through homologous recombination (HR) between exogenous and chromosomal DNA would be an ideal strategy to avoid potentially serious problems of random integration such as cellular transformation and gene silencing. Efficient sequence-specific modification of chromosomes by HR would also advance both biological studies and therapeutic applications of a variety of stem cells. Toward these goals, we developed an improved strategy of adenoviral vector (AdV)-mediated HR and examined its ability to correct an insertional mutation in the hypoxanthine phosphoribosyl transferase (Hprt) locus in male mouse ES cells. The efficiency of HR was compared between four types of AdVs that contained various lengths of homologies at the Hprt locus and with various multiplicities of infections. The frequency of HR with helper-dependent AdVs (HD AdVs) with an 18.6-kb homology reached 0.2% per transduced cell at a multiplicity of infection of 10 genomes per cell. Detection of random integration at DNA levels by PCR revealed extremely high efficiency of 5% per cell. We also isolated and characterized chromosomal sites where HD AdVs integrated in a random manner. In contrast to retroviral, lentiviral, and adeno-associated viral vectors, which tend to integrate into genes, the integration sites of AdV was distributed randomly inside and outside genes. These findings suggest that HR mediated by HD AdVs is efficient and relatively safe and might be a new viable option for ex vivo gene therapy as well as a tool for chromosomal manipulation of a variety of stem cells.

The homeodomain protein PBX participates in JH-related suppressive regulation on the expression of major plasma protein genes in the silkworm, Bombyx mori.

In the silkworm, Bombyx mori, major plasma proteins referred to as 30K proteins are the most abundant proteins in the hemolymph of final (fifth) instar larvae. Surgical extirpation of corpora allata, the source of a juvenile hormone (JH), causes rapid accumulation of 30K proteins in the hemolymph of fourth instar larvae. The 30K protein 6G1 (30K6G1) gene was repressed in primary cultured fat body cells treated with a JH analog (JHA), methoprene. To identify the JH response element present in the promoter region of the 30K6G1 gene, we performed transfection analyses of the 5'-deletion mutants of the 30K6G1 gene using primary cultured fat body cells, gel retardation assays and in vivo footprinting analysis. The results from those analyses revealed that a JH response element exists in the sequence between positions -147 and -140. When the promoter construct mutated at positions -143, -142, and -141 was transfected to fat body primary cultured cells, the suppression effect on the reporter gene expression caused by JHA was reduced. Gel retardation assay using specific antibody revealed that a PBX protein binds to the JH response element. Northern blot analysis revealed that the gene expression of Bombyx PBX is enhanced in the fat body cells by JHA treatment. These results indicate that PBX proteins are involved in the JH signaling pathway and play an important role in suppressing 30K protein gene expression in the fat body of B. mori.

IGF-1 phosphorylates AMPK-alpha subunit in ATM-dependent and LKB1-independent manner.

Serine/threonine protein kinase AMP-activated protein kinase (AMPK) is a key metabolic stress-responsive factor that promotes the adaptation of cells to their microenvironment. Elevated concentrations of intracellular AMP, caused by metabolic stress, are known to activate AMPK by phosphorylation of the catalytic subunit. Recently, the tumor suppressor serine/threonine protein kinase LKB1 was identified as an upstream kinases, AMPKKs. In the current study, we found that stimulation with growth factors also caused AMPK-alpha subunit phosphorylation. Interestingly, even an LKB1-nonexpressing cancer cell line, HeLa, exhibited growth factor-stimulated AMPK-alpha subunit phosphorylation, suggesting the presence of an LKB1-independent pathway for AMPK-alpha subunit phosphorylation. In the human pancreatic cancer cell line PANC-1, AMPK-alpha subunit phosphorylation promoted by IGF-1 was suppressed by antisense ataxia telangiectasia mutated (ATM) expression. We found that IGF-1 also induced AMPK-alpha subunit phosphorylation in the human normal fibroblast TIG103 cell line, but failed to do so in a human fibroblast AT2-KY cell line lacking ATM. Immunoprecipitates of ATM collected from IGF-1-stimulated cells also caused the phosphorylation of the AMPK-alpha subunit in vitro. IGF-1-stimulated ATM phosphorylation at both threonine and tyrosine residues, and our results demonstrated that the phosphorylation of tyrosine in the ATM molecule is important for AMPK-alpha subunit phosphorylation during IGF-1 signaling. These results suggest that IGF-1 induces AMPK-alpha subunit phosphorylation via an ATM-dependent and LKB1-independent pathway.

Regulation of caspase-6 and FLIP by the AMPK family member ARK5.

Colorectal cancer cells are unique in that they escape Fas-mediated cell death in the presence of Fas ligand, and we recently reported that AMP-activated protein kinase-related kinase 5 (ARK5) suppresses cell death signaling mediated by cell death receptor in Akt-dependent manner. In the current study, therefore, we examined whether ARK5 is involved in the escape from Fas-mediated cell death of colorectal cancer cells. Among 10 cell lines, ARK5 mRNA expression was observed in LoVo, SW480, and SW1116 cell lines. Interestingly, SW480 and SW1116 cell lines, but not LoVo cell line, showed expressions of both Fas ligand (FasL) and Fas mRNAs. SW620 cell line also showed FasL mRNA; however, Fas and ARK5 mRNAs were not detected. Furthermore, well-coincided expression among ARK5, FasL, and Fas mRNAs was observed in tumor tissues from patients with colorectal cancer, suggesting the suppression of FasL/Fas system-induced cell death by ARK5 in colorectal cancer cell lines. Intensive cell death, which was dependent on the FasL/Fas system was encountered when ARK5 antisense RNA (ARK5/AS) was introduced into SW480 cells. FLIP was expressed in only ARK5 mRNA-expressing cell lines, and ARK5/AS induced FLIP cleavage in a caspase-6-dependent manner. Amino-acid sequence analysis of caspase-6 revealed two putative sites of phosphorylation by ARK5 at Ser80 and Ser257. Although active caspase-6 overexpression induced cell death in SW480 and DLD-1 cell lines, SW480 cells, but not DLD-1 cells, exhibited strong resistance to procaspase-6 overexpression. Moreover, mutant caspase-6, in which the Ser257 was substituted by Ala (caspase-6/SA), induced cell death and FLIP degradation, even in SW480 cells. Active ARK5 was found to phosphorylate wild-type caspase-6 in vitro, but not caspase-6/SA, and the prevented activation of caspase-6 was promoted due to its phosphorylation by active ARK5 in vitro. On the basis of the results of this study, we propose that ARK5 negatively regulates procaspase-6 by phosphorylation at Ser257, leading to resistance to the FasL/Fas system.

ARK5 is a tumor invasion-associated factor downstream of Akt signaling.

AMP-activated protein kinases (AMPKs) are a class of serine/threonine protein kinases that are activated by an increase in intracellular AMP concentration. They are a sensitive indicator of cellular energy status and have been found to promote tumor cell survival during nutrient starvation. We recently identified a novel AMPK catalytic subunit family member, ARK5, whose activation is directly regulated by Akt, which, in turn, has been reported to be a key player in tumor malignancy. In this study, we attempted to determine whether ARK5 is involved in tumor malignancy under regulation by Akt. Matrigel invasion assays demonstrated that both overexpressed and endogenous ARK5 showed strong activity dependent on Akt. In addition, ARK5 expression induced activation of matrix metalloproteinase 2 (MMP-2) and MMP-9 following new expression of membrane type 1 MMP (MT1-MMP), and the MT1-MMP expression induced by ARK5 was initiated by rapamycin-sensitive signaling. In nude mice, ARK5 expression was associated with a significant increase in tumor growth and significant suppression of necrosis in tumor tissue. Interestingly, only the ARK5-overexpressing PANC-1 cell line (P/ARK) tumor showed invasion and metastasis in nude mice, although Akt was activated in tumors derived from both P/ARK and its parental cell line. We report that a novel AMPK catalytic subunit family member, ARK5, plays a key role in tumor malignancy downstream of Akt.

Induction of cell-cell detachment during glucose starvation through F-actin conversion by SNARK, the fourth member of the AMP-activated protein kinase catalytic subunit family.

SNARK, the fourth member of the AMPK catalytic subunit family, was originally identified in a rat kidney cDNA library, and in this study we isolated its human homologue. A BLAST search analysis using rat SNARK protein yielded a single high homology clone, DKFZp434J037, isolated from human testis, and since its hypothetical protein showed 84% homology to rat SNARK protein, we assumed DKFZp434J037 to be the human SNARK cDNA. The human SNARK cDNA is 3443bp long and encodes a 628 amino acid protein having an estimated molecular weight of 69kDa, and its chromosomal localization had been assigned to 1q32.1. The same as other members of AMPK catalytic subunit family, human SNARK showed AMP-dependent GST-SAMS phosphorylation activity and enhanced HepG2 cell survival during glucose starvation. Human SNARK-overexpressing HepG2 cells (H/SNK) showed acute cell-cell detachment when exposed to glucose-free medium and the cell-cell detachment correlated well with the detection of G-actin. Deletion mutant analysis strongly suggested that the putative catalytic domain of SNARK is necessary for the cell-cell detachment, and Western blotting analysis showed that phosphorylation of FAK and PKC, which were dramatically increased by glucose starvation in HepG2 cells, was markedly suppressed by SNARK.

ARK5 suppresses the cell death induced by nutrient starvation and death receptors via inhibition of caspase 8 activation, but not by chemotherapeutic agents or UV irradiation.

AMPK is a serine/threonine protein kinase family and we recently identified a novel member, ARK5. The activation of ARK5 is triggered by Akt, and ARK5 induces tumor cell survival during nutrient starvation. In the current study, we investigated the mechanisms of induction of cell survival by ARK5. Human hepatoma HepG2 cells undergo necrotic cell death within 24 h after the start of glucose starvation, and the cell death signaling has been found to be mediated by death-receptor-independent activation of caspase 8. When HepG2 cells were transfected with ARK5 expression vector and subjected to several cell death stimuli, ARK5 was found to suppress cell death by glucose starvation, TRAIL, and TNF-alpha, but not by ultraviolet irradiation, camptothecin, or doxorubicin. Western blotting analysis revealed that both TRAIL and glucose starvation induced Bid cleavage and FLIP degradation following caspase 8 activation in a time-dependent manner, and ARK5 overexpression clearly delayed Bid cleavage, FLIP degradation, and caspase 8 activation. On the basis of the results of this study, we report that cell survival induced by ARK5 is, at least in part, due to inhibition of caspase 8 activation.

Identification of a novel protein kinase mediating Akt survival signaling to the ATM protein.

We identified a novel human AMP-activated protein kinase (AMPK) family member, designated ARK5, encoding 661 amino acids with an estimated molecular mass of 74 kDa. The putative amino acid sequence reveals 47, 45.8, 42.4, and 55% homology to AMPK-alpha1, AMPK-alpha2, MELK, and SNARK, respectively, suggesting that it is a new member of the AMPK family. It has a putative Akt phosphorylation motif at amino acids 595-600, and Ser(600) was found to be phosphorylated by active Akt resulting in the activation of kinase activity toward the SAMS peptide, a consensus AMPK substrate. During nutrient starvation, ARK5 supported the survival of cells in an Akt-dependent manner. In addition, we also demonstrated that ARK5, when activated by Akt, phosphorylated the ATM protein that is mutated in the human genetic disorder ataxia-telangiectasia and also induced the phosphorylation of p53. On the basis of our current findings, we propose that a novel AMPK family member, ARK5, is the tumor cell survival factor activated by Akt and acts as an ATM kinase under the conditions of nutrient starvation.

Critical roles of AMP-activated protein kinase in constitutive tolerance of cancer cells to nutrient deprivation and tumor formation.

As tumors grow and invade beyond their homeostatic limits, the tumor cells are subjected to insufficient nutrient and oxygen supplies because of excessive demand for nutrition and oxygen, and insufficient vascularization. We therefore hypothesized that tolerance to nutrient deprivation as well as angiogenesis may be critical in some malignancies, including pancreatic cancers, which are seen to be a hypovascular tumor. In this study, we assessed the effect of AMP-activated protein kinase (AMPK), which plays a major role in protecting cells from metabolic stresses, on tumor biology under nutrient-deprived condition. Whereas hepatic cancer cells had mostly died within 48 h during glucose deprivation, most pancreatic cancer cells survived more than 48 h. The tolerance to glucose deprivation tended to correlate with the cells level of expression of AMPK alpha1 and alpha2. The introduction of AMPK antisense RNA expression vectors into pancreas cancer cell lines, PANC-1 and AsPC-1, significantly diminished their tolerance to glucose deprivation, and the stable transfection of AMPK antisense into PANC-1 cells inhibited tumor growth in nude mice. These findings indicate that AMPK expression contributes to tolerance to nutrient starvation in cancer cells. We propose AMPK as a new target for therapeutic strategies to suppress tumor growth and invasion.

Hypoxia and nitric oxide treatment confer tolerance to glucose starvation in a 5'-AMP-activated protein kinase-dependent manner.

Hypoxia is a critical event for higher organisms, and cells and tissues react by increasing the oxygen supply by vasodilatation, angiogenesis, and erythropoiesis and maintaining cellular energy by increasing glycolysis and inhibiting anabolic pathways. Stimulation of glycolysis has been regarded as the main response that increases energy production during hypoxia; however, there is an obvious conflict during ischemia, because both the oxygen and glucose supply are insufficient. In this study, we found that exposure of HepG2 cells and normal fibroblasts to hypoxia induces cellular tolerance to glucose starvation. The tolerance induced by hypoxia is dependent on several amino acids, indicating a switch from glucose to amino acids as the energy source. When antisense RNA expression vector for 5'-AMP-activated protein kinase or protein kinase B/Akt was transfected into HepG2 cells, the induction of tolerance to glucose was greatly inhibited, indicating that the tolerance was dependent on 5'-AMP-activated protein kinase and protein kinase B/Akt. Similar tolerance was induced by nitric oxide exposure. The tolerance induced was observed in various cells and may represent a previously unknown physiological response related to hypoxia-preconditioning and tumor progression:austerity.

5-amino-4-imidazolecarboxamide riboside confers strong tolerance to glucose starvation in a 5'-AMP-activated protein kinase-dependent fashion.

Acadesine, 5-amino-4-imidazolecarboxamide riboside (AICAR), has been claimed to protect the heart, lung, and small intestine against ischemic damage. The biochemical mechanisms of this effect of AICAR are not yet fully understood. To understand the mechanism, we examined the effect of AICAR on glucose starvation, since cellular responses to ischemia could be regarded as a protective response to an insufficient blood supply, cells might display adaptive reactions not only to oxygen deficiency but to nutrient deficiency. AICAR was found to confer strong tolerance to glucose starvation. By using antisense RNA expression vector for alpha subunit of 5'-AMP-activated protein kinase, the effect of AICAR was found to be dependent on 5'-AMP-activated protein kinase containing the alpha2 subunit. The AICAR effect was also dependent on the presence of amino acids, indicating an energy source switch from glucose to amino acids.