New Insight into the Effects of Metformin on Diabetic Retinopathy, Aging and Cancer: Nonapoptotic Cell Death, Immunosuppression, and Effects beyond the AMPK Pathway

Under metabolic stress conditions such as hypoxia and glucose deprivation, an increase in the AMP:ATP ratio activates the AMP-activated protein kinase (AMPK) pathway, resulting in the modulation of cellular metabolism. Metformin, which is widely prescribed for type 2 diabetes mellitus (T2DM) patients, regulates blood sugar by inhibiting hepatic gluconeogenesis and promoting insulin sensitivity to facilitate glucose uptake by cells. At the molecular level, the most well-known mechanism of metformin-mediated cytoprotection is AMPK pathway activation, which modulates metabolism and protects cells from degradation or pathogenic changes, such as those related to aging and diabetic retinopathy (DR). Recently, it has been revealed that metformin acts via AMPK- and non-AMPK-mediated pathways to exert effects beyond those related to diabetes treatment that might prevent aging and ameliorate DR. This review focuses on new insights into the anticancer effects of metformin and its potential modulation of several novel types of nonapoptotic cell death, including ferroptosis, pyroptosis, and necroptosis. In addition, the antimetastatic and immunosuppressive effects of metformin and its hypothesized mechanism are also discussed, highlighting promising cancer prevention strategies for the future.

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Identification and characterization of a novel sucrose-non-fermenting protein kinase/AMP-activated protein kinase-related protein kinase, SNARK

Biochemical Journal ◽

10.1042/bj3550297 ◽

2001 ◽

Vol 355 (2) ◽

pp. 297-305 ◽

Cited By ~ 25

Author(s):

Diana L. LEFEBVRE ◽

Yahong BAI ◽

Nazanin SHAHMOLKY ◽

Monika SHARMA ◽

Raymond POON ◽

...

Keyword(s):

Protein Kinase ◽

Cellular Response ◽

Catalytic Domain ◽

Metabolic Stress ◽

Glucose Deprivation ◽

Protein Band ◽

Northern Blotting ◽

Significant Similarity ◽

Amp Activated Protein Kinase

Subtraction hybridization after the exposure of keratinocytes to ultraviolet radiation identified a differentially expressed cDNA that encodes a protein of 630 amino acid residues possessing significant similarity to the catalytic domain of the sucrose-non-fermenting protein kinase (SNF1)/AMP-activated protein kinase (AMPK) family of serine/threonine protein kinases. Northern blotting and reverse-transcriptase-mediated PCR demonstrated that mRNA transcripts for the SNF1/AMPK-related kinase (SNARK) were widely expressed in rodent tissues. The SNARK gene was localized to human chromosome 1q32 by fluorescent in situ hybridization. SNARK was translated in vitro to yield a single protein band of approx. 76kDa; Western analysis of transfected baby hamster kidney (BHK) cells detected two SNARK-immunoreactive bands of approx. 76-80kDa. SNARK was capable of autophosphorylation in vitro; immunoprecipitated SNARK exhibited phosphotransferase activity with the synthetic peptide substrate HMRSAMSGLHLVKRR (SAMS) as a kinase substrate. SNARK activity was significantly increased by AMP and 5-amino-4-imidazolecarboxamide riboside (AICAriboside) in rat keratinocyte cells, implying that SNARK might be activated by an AMPK kinase-dependent pathway. Furthermore, glucose deprivation increased SNARK activity 3-fold in BHK fibroblasts. These findings identify SNARK as a glucose- and AICAriboside-regulated member of the AMPK-related gene family that represents a new candidate mediator of the cellular response to metabolic stress.

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ROS Mediate xCT-Dependent Cell Death in Human Breast Cancer Cells under Glucose Deprivation

Cells ◽

10.3390/cells9071598 ◽

2020 ◽

Vol 9 (7) ◽

pp. 1598 ◽

Cited By ~ 2

Author(s):

Mei-Chun Chen ◽

Li-Lin Hsu ◽

Sheng-Fan Wang ◽

Chih-Yi Hsu ◽

Hsin-Chen Lee ◽

...

Keyword(s):

Breast Cancer ◽

Cell Death ◽

Cancer Cells ◽

Cancer Progression ◽

Breast Cancer Cells ◽

Critical Role ◽

Glucose Deprivation ◽

Glutathione Biosynthesis ◽

Dependent Cell ◽

Amp Activated Protein Kinase

xCT, also known as solute carrier family 7 member 11 (SLC7A11), the light chain of the cystine/glutamate antiporter, is positively correlated with cancer progression due to antioxidant function. During glucose deprivation, the overexpression of xCT does not protect cancer cells but instead promotes cell death. Further understanding the mechanism of glucose deprivation-induced cell death is important for developing anticancer treatments targeting the glucose metabolism. In this study, we found that breast cancer cells with a high expression of xCT demonstrated increased levels of reactive oxygen species (ROS) and were more sensitive to glucose deprivation than the cells with a low expression of xCT. However, AMP-activated protein kinase (AMPK) did not significantly affect glucose-deprivation-induced cell death. The antioxidant N-acetyl-cysteine prevented glucose-deprivation-induced cell death, and the glutathione biosynthesis inhibitor L-buthionine-S, R-sulfoximine enhanced glucose-deprivation-induced cell death. The inhibition of xCT by sulfasalazine or a knockdown of xCT reduced the glucose-deprivation-increased ROS levels and glucose-deprivation-induced cell death. Glucose deprivation reduced the intracellular glutamate, and supplementation with α-ketoglutarate prevented the glucose-deprivation-increased ROS levels and rescued cell death. The knockdown of sirtuin-3 (SIRT3) further enhanced the ROS levels, and promoted xCT-related cell death after glucose deprivation. In conclusion, our results suggested that ROS play a critical role in xCT-dependent cell death in breast cancer cells under glucose deprivation.

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AMP-activated protein kinase: a cellular energy sensor with a key role in metabolic disorders and in cancer

Biochemical Society Transactions ◽

10.1042/bst0390001 ◽

2011 ◽

Vol 39 (1) ◽

pp. 1-13 ◽

Cited By ~ 106

Author(s):

D. Grahame Hardie

Keyword(s):

Protein Kinase ◽

Metabolic Disorders ◽

Adenine Nucleotides ◽

Metabolic Stress ◽

Branch Points ◽

Atp Production ◽

Nucleotide Binding Sites ◽

Anticancer Effects ◽

Energy Sensor ◽

Amp Activated Protein Kinase

It is essential to life that a balance is maintained between processes that produce ATP and those that consume it. An obvious way to do this would be to have systems that monitor the levels of ATP and ADP, although because of the adenylate kinase reaction (2ADP↔ATP+AMP), AMP is actually a more sensitive indicator of energy stress than ADP. Following the discoveries that glycogen phosphorylase and phosphofructokinase were regulated by AMP and ATP, Daniel Atkinson proposed that all enzymes at branch points between biosynthesis and degradation would be regulated by adenine nucleotides. This turned out to be correct, but what Atkinson did not anticipate was that sensing of nucleotides would, in most cases, be performed not by the metabolic enzymes themselves, but by a signalling protein, AMPK (AMP-activated protein kinase). AMPK occurs in essentially all eukaryotes and consists of heterotrimeric complexes comprising catalytic α subunits and regulatory β and γ subunits, of which the latter carries the nucleotide-binding sites. Once activated by a metabolic stress, it phosphorylates numerous targets that alter enzyme activity and gene expression to initiate corrective responses. In lower eukaryotes, it is critically involved in the responses to starvation for a carbon source. Because of its ability to switch cellular metabolism from anabolic to catabolic mode, AMPK has become a key drug target to combat metabolic disorders associated with overnutrition such as Type 2 diabetes, and some existing anti-diabetic drugs (e.g. metformin) and many ‘nutraceuticals’ work by activating AMPK, usually via inhibition of mitochondrial ATP production. AMPK activators also potentially have anticancer effects, and there is already evidence that metformin provides protection against the initiation of cancer. Whether AMPK activators can be used to treat existing cancer is less clear, because many tumour cells appear to have been selected for mutations that inactivate the AMPK system. However, if we can identify the various mechanisms by which this occurs, we may be able to find ways of overcoming it.

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Glucose Deprivation Induces ATF4-Mediated Apoptosis through TRAIL Death Receptors

Molecular and Cellular Biology ◽

10.1128/mcb.00479-16 ◽

2017 ◽

Vol 37 (10) ◽

Cited By ~ 40

Author(s):

Raffaella Iurlaro ◽

Franziska Püschel ◽

Clara Lucía León-Annicchiarico ◽

Hazel O'Connor ◽

Seamus J. Martin ◽

...

Keyword(s):

Cell Death ◽

Stress Response ◽

Er Stress ◽

Death Receptor ◽

Metabolic Stress ◽

Glucose Deprivation ◽

Trail Receptor ◽

Normal Tissues ◽

Trail Receptors ◽

The Unfolded Protein Response

ABSTRACT Metabolic stress occurs frequently in tumors and in normal tissues undergoing transient ischemia. Nutrient deprivation triggers, among many potential cell death-inducing pathways, an endoplasmic reticulum (ER) stress response with the induction of the integrated stress response transcription factor ATF4. However, how this results in cell death remains unknown. Here we show that glucose deprivation triggered ER stress and induced the unfolded protein response transcription factors ATF4 and CHOP. This was associated with the nontranscriptional accumulation of TRAIL receptor 1 (TRAIL-R1) (DR4) and with the ATF4-mediated, CHOP-independent induction of TRAIL-R2 (DR5), suggesting that cell death in this context may involve death receptor signaling. Consistent with this, the ablation of TRAIL-R1, TRAIL-R2, FADD, Bid, and caspase-8 attenuated cell death, although the downregulation of TRAIL did not, suggesting ligand-independent activation of TRAIL receptors. These data indicate that stress triggered by glucose deprivation promotes the ATF4-dependent upregulation of TRAIL-R2/DR5 and TRAIL receptor-mediated cell death.

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Regulation and functional effects of ZNT8 in human pancreatic islets

Journal of Endocrinology ◽

10.1530/joe-12-0071 ◽

2012 ◽

Vol 214 (2) ◽

pp. 225-232 ◽

Cited By ~ 21

Author(s):

Bruno Lefebvre ◽

Brigitte Vandewalle ◽

Anne-Sophie Balavoine ◽

Gurvan Queniat ◽

Ericka Moerman ◽

...

Keyword(s):

Cell Death ◽

Insulin Secretion ◽

Metabolic Stress ◽

Human Islets ◽

Β Cells ◽

Prediabetic State ◽

Zinc Depletion ◽

Packaging Efficiency ◽

Glucose Stimulated Insulin Secretion

Zinc ions are essential for the formation of insulin crystals in pancreatic β cells, thereby contributing to packaging efficiency of stored insulin. Zinc fluxes are regulated through the SLC30A (zinc transporter, ZNT) family. Here, we investigated the effect of metabolic stress associated with the prediabetic state (zinc depletion, glucotoxicity, and lipotoxicity) on ZNT expression and human pancreatic islet function. Both zinc depletion and lipotoxicity (but not glucotoxicity) downregulatedZNT8(SLC30A8) expression and altered the glucose-stimulated insulin secretion index (GSIS).ZNT8overexpression in human islets protected them from the decrease in GSIS induced by tetrakis-(2-pyridylmethyl) ethylenediamine and palmitate but not from cell death. In addition, zinc supplementation decreased palmitate-induced human islet cell death without restoring GSIS. Altogether, we showed thatZNT8expression responds to variation in zinc and lipid levels in human β cells, with repercussions on insulin secretion. Prospects for increasingZNT8expression and/or activity may prove beneficial in type 2 diabetes in humans.

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Regulation of Tumor Progression by Programmed Necrosis

Oxidative Medicine and Cellular Longevity ◽

10.1155/2018/3537471 ◽

2018 ◽

Vol 2018 ◽

pp. 1-28 ◽

Cited By ~ 31

Author(s):

Su Yeon Lee ◽

Min Kyung Ju ◽

Hyun Min Jeon ◽

Eui Kyong Jeong ◽

Yig Ji Lee ◽

...

Keyword(s):

Cell Death ◽

Programmed Cell Death ◽

Tumor Progression ◽

Molecular Mechanisms ◽

Malignant Tumors ◽

Metabolic Stress ◽

High Mobility ◽

Glucose Deprivation ◽

Inflammatory Cells ◽

Programmed Necrosis

Rapidly growing malignant tumors frequently encounter hypoxia and nutrient (e.g., glucose) deprivation, which occurs because of insufficient blood supply. This results in necrotic cell death in the core region of solid tumors. Necrotic cells release their cellular cytoplasmic contents into the extracellular space, such as high mobility group box 1 (HMGB1), which is a nonhistone nuclear protein, but acts as a proinflammatory and tumor-promoting cytokine when released by necrotic cells. These released molecules recruit immune and inflammatory cells, which exert tumor-promoting activity by inducing angiogenesis, proliferation, and invasion. Development of a necrotic core in cancer patients is also associated with poor prognosis. Conventionally, necrosis has been thought of as an unregulated process, unlike programmed cell death processes like apoptosis and autophagy. Recently, necrosis has been recognized as a programmed cell death, encompassing processes such as oncosis, necroptosis, and others. Metabolic stress-induced necrosis and its regulatory mechanisms have been poorly investigated until recently. Snail and Dlx-2, EMT-inducing transcription factors, are responsible for metabolic stress-induced necrosis in tumors. Snail and Dlx-2 contribute to tumor progression by promoting necrosis and inducing EMT and oncogenic metabolism. Oncogenic metabolism has been shown to play a role(s) in initiating necrosis. Here, we discuss the molecular mechanisms underlying metabolic stress-induced programmed necrosis that promote tumor progression and aggressiveness.

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Metformin – its potential anti-cancer and anti-aging effects

Postępy Higieny i Medycyny Doświadczalnej ◽

10.5604/01.3001.0010.3801 ◽

2017 ◽

Vol 71 (1) ◽

pp. 0-0 ◽

Cited By ~ 17

Author(s):

Monika Podhorecka ◽

Blanca Ibanez ◽

Anna Dmoszyńska

Keyword(s):

Metabolic Stress ◽

Glucose Deprivation ◽

Adenosine Monophosphate ◽

Aging Effects ◽

Beneficial Effects ◽

Anti Cancer ◽

Aging Properties ◽

Treatment Of Diabetes ◽

Underlying Mechanisms ◽

Amp Activated Protein Kinase

The generally accepted mechanism of metformin’s effect is stimulation of adenosine monophosphate (AMP)-activated protein kinase (AMPK). AMPK is directly activated by an increase in AMP:ATP ratio in metabolic stress conditions including hypoxia and glucose deprivation. Lately, many novel pathways, besides AMPK induction, have been revealed, which can explain some of metformin’s beneficial effects. It may help to identify new targets for treatment of diabetes and metabolic syndrome. Moreover, metformin is now attracting the attention of researchers in fields other than diabetes, as it has been shown to have anti-cancer, immunoregulatory and anti-aging effects. The aim of this review is to describe the potential anti-cancer and anti-aging properties of metformin and discuss the possible underlying mechanisms.

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AMP-Activated Protein Kinase: Do We Need Activators or Inhibitors to Treat or Prevent Cancer?

International Journal of Molecular Sciences ◽

10.3390/ijms22010186 ◽

2020 ◽

Vol 22 (1) ◽

pp. 186

Author(s):

Fiona M. Russell ◽

David Grahame Hardie

Keyword(s):

Protein Kinase ◽

Genome Stability ◽

Metabolic Disorders ◽

Metabolic Stress ◽

Cellular Energy ◽

Downstream Effector ◽

Wide Range ◽

Cell Growth And Proliferation ◽

Amp Activated Protein Kinase

AMP-activated protein kinase (AMPK) is a key regulator of cellular energy balance. In response to metabolic stress, it acts to redress energy imbalance through promotion of ATP-generating catabolic processes and inhibition of ATP-consuming processes, including cell growth and proliferation. While findings that AMPK was a downstream effector of the tumour suppressor LKB1 indicated that it might act to repress tumourigenesis, more recent evidence suggests that AMPK can either suppress or promote cancer, depending on the context. Prior to tumourigenesis AMPK may indeed restrain aberrant growth, but once a cancer has arisen, AMPK may instead support survival of the cancer cells by adjusting their rate of growth to match their energy supply, as well as promoting genome stability. The two isoforms of the AMPK catalytic subunit may have distinct functions in human cancers, with the AMPK-α1 gene often being amplified, while the AMPK-α2 gene is more often mutated. The prevalence of metabolic disorders, such as obesity and Type 2 diabetes, has led to the development of a wide range of AMPK-activating drugs. While these might be useful as preventative therapeutics in individuals predisposed to cancer, it seems more likely that AMPK inhibitors, whose development has lagged behind that of activators, would be efficacious for the treatment of pre-existing cancers.

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Polymorphisms of the Plasminogen Activator Inhibitor- 1 Gene in Type 1 and Type 2 Diabetes, and in Patients with Diabetic Retinopathy

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642514 ◽

1994 ◽

Vol 71 (06) ◽

pp. 731-736 ◽

Cited By ~ 29

Author(s):

M W Mansfield ◽

M H Stickland ◽

A M Carter ◽

P J Grant

Keyword(s):

Diabetic Retinopathy ◽

Plasminogen Activator Inhibitor ◽

Allelic Frequency ◽

Repeat Sequence ◽

Dinucleotide Repeat ◽

Plasminogen Activator Inhibitor 1 ◽

The Difference ◽

Pai 1

SummaryTo identify whether genotype contributes to the difference in PAI-1 levels in type 1 and type 2 diabetic subjects and whether genotype relates to the development of retinopathy, a Hind III restriction fragment length polymorphism and two dinucleotide repeat polymorphisms were studied. In 519 Caucasian diabetic subjects (192 type 1, 327 type 2) and 123 Caucasian control subjects there were no differences in the frequency of the Hind III restriction alleles (type 1 vs type 2 vs control: allele 1 0.397 vs 0.420 vs 0.448; allele 2 0.603 vs 0.580 vs 0.552) nor in the allelic frequency at either dinucleotide repeat sequence. In 86 subjects with no retinopathy at 15 years or more from diagnosis of diabetes and 190 subjects with diabetic retinopathy there was no difference in the frequency of Hind III restriction alleles (retinopathy present vs retinopathy absent: allele 1 0.400 vs 0.467; allele 2 0.600 vs 0.533) nor in the allelic frequencies at either dinucleotide repeat sequence. The results indicate that there is no or minimal influence of the PAI-1 gene on either PAI-1 levels or the development of diabetic retinopathy in patients with diabetes mellitus.

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