Buformin Suppresses the Expression of Glyceraldehyde 3-Phosphate Dehydrogenase

Abstract

Three biguanides, phenformin, buformin, and metformin, were first used clinically for diabetes mellitus in the 1950s. Since phenformin was found to have a lethal side effect, lactic acidosis, in the late of 1970s, 1) its usage decreased rapidly in many countries and was finally withdrawn. Then use of other biguanides declined gradually because of their own adverse effects. Lactic acidosis, hypoglycemia, and digestive organ dysfunction have been found to be adverse effects of biguanides. Lactic acidosis caused by biguanides results in lethal metabolic acidosis, 2) so their use was stopped. Cohen and Woods 3) proposed a classification for lactic acidosis that consisted of types A, B 1 , B 2 , B 3 , and B 4 , and acidosis caused by biguanides belongs to type B 2 according to this classification. Type B is lactic acidosis occurring when clinical evidence of poor tissue perfusion or oxygenation is absent and type B 2 is due to drugs and toxins.Metformin was recently reported to decrease the risk of diabetes-related endpoints in overweight diabetic patients 4) and, therefore, has begun to be widely used again. The following mechanisms of action of biguanides have been proposed 5) : (i) suppression of glucose release from the liver, (ii) increase of glucose intake in peripheral tissues, (iii) decrease of glucose uptake in an alimentary tract, and (iv) suppression of b-oxidation. Metformin was found to improve resistance to insulin in type II diabetes. Zhou et al. 6) postulated that the suppression of SREBP-1 expression through the activation of AMPactivating protein kinase by metformin eliminated the insulin resistance.The following possible mechanism for the side effect of biguanides has been proposed. 7,8) The biguanide binds to the mitochondrial membrane and causes the disruption of oxidative phosphorylation in the mitochondria. This results in an increase in the NADH level, a decrease in pyruvate dehydrogenase activity, and deactivation of the TCA cycle. Furthermore, gluconeogenesis is suppressed and pyruvic acid accumulates in the liver. This leads to an increase in production of lactic acid. However, the molecular mechanisms of the side effects of biguanides are still unclear.When we researched which gene expressions underwent a change in order to clarify the mechanism of biguanides induced lactic acidosis, we found that the gene expression of glyceraldehyde 3-phosphate dehydrogenase (GAPD) in HepG2 cells decreases significantly by buformin treatment. Since GAPD is involved in the glucolytic pathway, we believe the decrease in GAPD may have caused the lactic acidosis. In this study, we demonstrate that expression of the gene for GAPD in HepG2 cells was suppressed by buformin treatment in a time-dependent manner. We also examined the effect of the biguanide on the protein expression of GAPD and determined the levels of NAD + and ATP in HepG2 cells treated with the biguanide to investigate the mechanism of the lactic acidosis side effect. . Therefore, the reaction equilibrium catalyzed by lactate dehydrogenase le...

Inverse Relationship between Tumor Proliferation Markers and Connexin Expression in a Malignant Cardiac Tumor Originating from Mesenchymal Stem Cell Engineered Tissue in a Rat in vivo Model

“…Since that time a number of papers has shown that in primary tumors or tumor cell lines connexins can be downregulated or even be absent, that oncogenes or cancerogenic drugs often inhibit gap junction channel function or reduce connexin expression (Loewenstein and Kanno, 1966; Trosko et al, 1990; Lampe, 1994; Laird et al, 1999; Mesnil et al, 2005; Salameh and Dhein, 2005; Cronier et al, 2009). However, on the other hand, some researchers found a role of gap junctions promoting invasion, cell extravasation, and migration of tumor cells (Naoi et al, 2007; Saito-Katsuragi et al, 2007; Ezumi et al, 2008), while others do not support this view (Yano et al, 2006; Sato et al, 2008). This lead to the interpretation that connexins might be “differentially regulated during the dissemination of specific tumor types” (Naus and Laird, 2010), and that down-regulation of connexin in early tumors might be linked to invasion, but in later states elevation in connexins can occur facilitating extravasation and formation of secondary tumors (Naus and Laird, 2010).…”

Buformin suppresses proliferation and invasion via AMPK/S6 pathway in cervical cancer and synergizes with paclitaxel

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Regulation of Glyceraldehyde 3-Phosphate Dehydrogenase Expression by Metformin in HepG2 Cells

“…Metformin was reported to raise the intracellular ratio of NADH to NAD ϩ . 9,31) This increase was proposed to result in less lactate being converted to pyruvate by lactate dehydrogenase causing the lactate to accumulate. 32) Since pyruvate is produced not only by glycolysis but also by gluconeogenesis via an intermediate in the citric acid cycle, the reaction equilibrium catalyzed by lactate dehydrogenase appears to shift towards lactate production.…”

“…9) Since GAPD is included in the glycolytic pathway, the decreased expression of GAPD is suggested to cause the accumulation of lactic acid and result in lactic acidosis. GAPD is frequently used as a housekeeping gene for the quantitative measurement of gene expression.…”