Metformin is the most widely prescribed oral anti-diabetic agent. Recently, we have shown that low metformin concentrations found in the portal vein suppress glucose production in hepatocytes through ...activation of AMPK. Moreover, low concentrations of metformin were found to activate AMPK by increasing the phosphorylation of AMPKα at Thr-172. However, the mechanism underlying the increase in AMPKα phosphorylation at Thr-172 and activation by metformin remains unknown. In the current study, we find that low concentrations of metformin promote the formation of the AMPK αβγ complex, resulting in an increase in net phosphorylation of the AMPK α catalytic subunit at Thr-172 by augmenting phosphorylation by LKB1 and antagonizing dephosphorylation by PP2C.
Background: The mechanism underlying the activation of AMPK by metformin remains unclear.
Results: Metformin promotes the formation of AMPK αβγ heterotrimeric complex.
Conclusion: The formation of the AMPK αβγ heterotrimeric complex augments AMPKα phosphorylation by LKB1 and prevents dephosphorylation by protein phosphatase.
Significance: Metformin-mediated formation of the AMPK αβγ heterotrimeric complex results in AMPK activation by elevating AMPK phosphorylation at Thr-172.
Metformin is a first-line antidiabetic agent taken by 150 million people across the world every year, yet its mechanism remains only partially understood and controversial. It was proposed that ...suppression of glucose production in hepatocytes by metformin is AMPK-independent; however, unachievably high concentrations of metformin were employed in these studies. In the current study, we find that metformin, via an AMP-activated protein kinase (AMPK)-dependent mechanism, suppresses glucose production and gluconeogenic gene expression in primary hepatocytes at concentrations found in the portal vein of animals (60–80 μm). Metformin also inhibits gluconeogenic gene expression in the liver of mice administered orally with metformin. Furthermore, the cAMP-PKA pathway negatively regulates AMPK activity through phosphorylation at Ser-485/497 on the α subunit, which in turn reduces net phosphorylation at Thr-172. Because diabetic patients often have hyperglucagonemia, AMPKα phosphorylation at Ser-485/497 is a therapeutic target to improve metformin efficacy.
Background: Whether suppression of glucose production by metformin is through AMPK-dependent inhibition of gluconeogenic gene expression remains controversial.
Results: Metformin inhibits gluconeogenic gene expression in hepatocytes.
Conclusion: Low metformin concentrations found in the portal vein suppress glucose production via AMPK-dependent mechanism.
Significance: The hyperglucagonemia of diabetes mellitus decreases metformin suppression of glucose production through a PKA-mediated phosphorylation of the AMPK α subunit at Ser-485/497.
Hepatic parenchymal disease, including chronic viral hepatitis, has traditionally been considered a relative contraindication to islet transplantation as the islets are infused into the recipient’s ...liver. We present a case study of a patient with treated chronic hepatitis C infection (HCV) who safely received an autologous islet transplant following total pancreatectomy with excellent clinical outcomes. The patient was a 60-year-old woman diagnosed with debilitating abdominal pain secondary to chronic pancreatitis and with preserved islet function. She had previously been treated >10 years prior to surgical evaluation with interferon monotherapy for 1 year that led to sustained virologic response, including at the time of surgical evaluation for total pancreatectomy and islet autotransplantation (TPIAT). She underwent comprehensive preoperative evaluation of the liver, including liver biopsy, which showed no significant portal inflammation or fibrosis. Following a multidisciplinary meeting and discussion of the potential risks for the patient, the decision was made to proceed with TPIAT. The patient underwent a standard total pancreatectomy, and an autologous islet dose of 6638 islet equivalents/kg body weight was infused into the liver via the portal vein. Portal vein pressure was monitored throughout the infusion with a transient peak pressure of 27 cm H2O (basal pressure of 14 cm H2O) and final pressure of 23 cm H20 at 10 min post-infusion. Aside from a transient transaminitis, liver enzymes were normal at the time of hospital discharge. At greater than 1 year of follow-up, the patient has improved quality of life, with reduction in narcotic analgesia, remains insulin independent (with normal islet function), and has normal liver function. This case illustrates that islet autotransplant into the liver can be safely performed and suggests that carefully selected patients with liver disease may be eligible for TPIAT.
Control of Foxo1 Gene Expression by Co-activator P300 Wondisford, Anne R.; Xiong, Lishou; Chang, Evan ...
Journal of biological chemistry/The Journal of biological chemistry,
02/2014, Volume:
289, Issue:
7
Journal Article
Peer reviewed
Open access
FOXO1 is an important downstream mediator of the insulin signaling pathway. In the fed state, elevated insulin phosphorylates FOXO1 via AKT, leading to its nuclear exclusion and degradation. A ...reduction in nuclear FOXO1 levels then leads to suppression of hepatic glucose production. However, the mechanism leading to expression of Foxo1 gene in the fasted state is less clear. We found that Foxo1 mRNA and FOXO1 protein levels of Foxo1 were increased significantly in the liver of mice after 16 h of fasting. Furthermore, dibutyrl cAMP stimulated the expression of Foxo1 at both mRNA and protein level in hepatocytes. Because cAMP-PKA regulates hepatic glucose production through cAMP-response element-binding protein co-activators, we depleted these co-activators using adenoviral shRNAs. Interestingly, only depletion of co-activator P300 resulted in the decrease of Foxo1 mRNA and FOXO1 protein levels. In addition, inhibition of histone acetyltransferase activity of P300 significantly decreased hepatic Foxo1 mRNA and FOXO1 protein levels in fasted mice, as well as fasting blood glucose levels. By characterization of Foxo1 gene promoter, P300 regulates the Foxo1 gene expression through the binding to tandem cAMP-response element sites in the proximal promoter region of Foxo1 gene.
The mechanism driving hepatic gene expression of Foxo1 in the fasted state remains unclear.
Activation of cAMP-PKA pathway induces Foxo1 gene expression through CREB and co-activator P300.
P300 mediates Foxo1 gene expression by binding to Foxo1 proximal promoter.
Induction of the Foxo1 gene by cAMP-PKA via P300 fully activates the gluconeogenic program during fasting to maintain euglycemia.
Because hepatic glycogenolysis maintains euglycemia during early fasting, proper hepatic glycogen synthesis in the fed/postprandial states is critical. It has been known for decades that ...gluconeogenesis is essential for hepatic glycogen synthesis; however, the molecular mechanism remains unknown. In this report, we show that depletion of hepatic p300 reduces glycogen synthesis, decreases hepatic glycogen storage, and leads to relative hypoglycemia. We previously reported that insulin suppressed gluconeogenesis by phosphorylating cAMP response element binding protein-binding protein (CBP) at S436 and disassembling the cAMP response element-binding protein-CBP complex. However, p300, which is closely related to CBP, lacks the corresponding S436 phosphorylation site found on CBP. In a phosphorylation-competent p300G422S knock-in mouse model, we found that mutant mice exhibited reduced hepatic glycogen content and produced significantly less glycogen in a tracer incorporation assay in the postprandial state. Our study demonstrates the important and unique role of p300 in glycogen synthesis through maintaining basal gluconeogenesis.
Reactive oxygen species (ROS) are elevated in humans with hypertension many of which develop end-stage renal disease (ESRD), and antioxidant capacity is decreased. About one-half of essential ...hypertensives have a salt-sensitive type of hypertension, and the amount of renal damage that occurs in salt-sensitive hypertensives greatly exceeds that of non-salt-sensitive hypertensives. Antioxidant therapy can improve cardiovascular outcomes in humans but only if sufficient doses are used. Salt-sensitive hypertensive animal models, especially Dahl salt-sensitive rats, have been used to investigate the relationship between hypertension, ROS and end-stage renal damage. In experimental salt-sensitive hypertension, ROS increase and significant renal damage occur. In the Dahl salt-sensitive (S) rat on high Na for 3 weeks, renal damage is mild, renal levels of superoxide dismutase are decreased, and treatment with Tempol reduces arterial pressure. In the Dahl S rat on high Na for 5 weeks, renal damage is severe, GFR and renal plasma flow are decreased, and renal superoxide production is high. Treatment with vitamins C and E decreases renal superoxide production and renal damage and prevents the decrease in renal hemodynamics. Antioxidant treatment reduces arterial pressure, aortic superoxide production and renal inflammation in DOCA-salt rats, and decreases blood pressure and aortic superoxide release and increases bioactive nitric oxide in SHR stroke-prone rats. In conclusion, in both human and experimental salt-sensitive hypertension, superoxide production and renal damage are increased, antioxidant capacity is decreased, and antioxidant therapy can be helpful.
Abstract Pheochromocytomas (PCCs) and/or paragangliomas (PGLs) are a challenge to diagnose during pregnancy because of elusive signs and testing difficulties. We report a 25-year-old woman with no ...pertinent medical history who presented to the hospital with hypertension, vision loss, and weakness and was initially diagnosed with preeclampsia. Imaging showed hemangioblastomas in the medulla and thoracic spine, pancreatic cysts, and a renal cyst. The endocrinology service was consulted for possible PCCs associated with von Hippel-Lindau disease (VHL). Serum and urine normetanephrine levels were elevated despite the lack of overt PCCs/PGLs seen on magnetic resonance imaging and magnetic resonance angiography. The patient was medically managed with doxazosin and then labetalol. Despite successful resection of the hemangioblastoma in the medulla, the patient suffered respiratory distress requiring tracheostomy and venous-venous extracorporeal membrane oxygenation (V-V ECMO) and fetal demise. After 3 months, the patient was discharged to rehabilitation. Follow-up genetics were heterozygous for VHL and Lynch syndrome. DOTATATE positron emission tomography/computed tomography scan showed a small hepatic focus of a maximum standard uptake value of 12.1. Altogether, this case illustrates the importance of prompt diagnosis and proper management of PCCs/PGLs during pregnancy and incorporating genetic information during surveillance to lower morbidity and mortality.
Chronic pancreatitis (CP) is a progressive disease that leads to eventual loss of endocrine and exocrine function. Total pancreatectomy and islet autotransplantation (TPIAT) is a treatment option for ...patients with CP; however, predicting postoperative metabolic outcomes remains elusive. In this single-center retrospective study, we report pre-TPIAT characteristics, beta cell function indices, islet yield, and post-TPIAT glucose management data to further understand their relationship. Islet yield, glucose level, and insulin requirement for 72 hours postoperatively were collected for a total of 13 TPIAT recipients between 9-2013 and 9-2018. In addition, their glucose control and basal insulin requirements at 3, 6, and 12 months post-TPIAT were analyzed. All 13 subjects had normal baseline fasting glucose levels. Median islet yield was 4882 IEq/kg (interquartile range 3412 to 8987). Median postoperative total insulin requirement on day 3 was 0.43 units/kg. Pre-TPIAT baseline glucose, insulin, or c-peptide level did not have a significant correlation with the islet yield. Similarly, there was no correlation between islet yield and insulin requirement at 72-hour postoperatively. However, there was an inverse correlation between the absolute islet yield (IEq) and insulin requirement at 6 months and 12 months following post-TPIAT. Further analysis of the relationship between 72-hour post-op insulin requirement and insulin requirement at discharge, 3, 6, and 12 months showed a positive correlation. Despite the finding of inverse correlation of islet yield with long-term basal insulin requirement, this study was not able to detect a correlation between the preoperative parameters to postoperative short-term or long-term outcome as noted in other studies. The 72-hour postoperative insulin requirement is a helpful postoperative predictor of patients needing long-term insulin management following TPIAT. This observation may identify a high-risk group of patients in need of more intensive diabetes education and insulin treatment prior to hospital discharge.
ABSTRACT—The role of oxidative stress in the long-term regulation of arterial pressure, renal hemodynamics, and renal damage was studied in Dahl salt-sensitive rats. Twenty-eight Dahl S/Rapp strain ...rats, equipped with indwelling arterial and venous catheters, were subjected to a 3-week intravenous infusion of either low Na (0.9 mmol/d) or high Na (20.6 mmol/d) or the superoxide dismutase mimetic, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), at 125 μmol · kg · h plus low Na or high Na. After 21 days, mean arterial pressure was 140±3 mm Hg in the high-Na group, 118±1 mm Hg (P <0.05) in the high-Na/Tempol group, and unchanged in the low-Na/Tempol and low-Na groups. Tempol did not change renal blood flow, glomerular filtration rate, or glomerular cross-sectional area in rats subjected to the high-Na intake but did decrease urinary protein excretion, the percentage of sclerotic glomeruli, and the kidney weight to body weight ratio. In 15 additional Dahl S rats subjected to high or low Na intake for 3 weeks, renal cortical and medullary O2 release increased significantly in the high-Na group when compared with the low-Na group. Tempol decreased both renal cortical and medullary O2 release in the high- and low-Na rats, but the decrease in O2 release was greater in high-Na rats. The data suggest that oxidative stress contributes to Dahl salt-sensitive hypertension and the accompanying renal damage.
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