Worldwide prevalence and burden of gastroparesis-like symptoms as defined by the United European Gastroenterology (UEG) and European Society for Neurogastroenterology and Motility (ESNM) consensus on gastroparesis.

BACKGROUND/OBJECTIVES: The global epidemiology of gastroparesis is unknown. The European UEG and European Society for Neurogastroenterology and motility consensus defines Gastroparesis as a condition characterized by delayed gastric emptying in the absence of mechanical obstruction, with a symptom pattern of nausea and/or vomiting and overlapping postprandial distress syndrome (PDS). Real-world evidence of this gastroparesis-like symptom pattern is a crucial step in understanding the epidemiology of gastroparesis. METHODS: In the Rome Foundation Global Epidemiology Study, 54,127 respondents from 26 countries completed the Rome IV Diagnostic Questionnaire and variables associated with disorders of gut-brain interaction via Internet. We selected subjects with gastroparesis-like symptoms (GPLS) (nausea and/or vomiting ≥1 day/week and simultaneous PDS). Patients reporting organic gastrointestinal disease, or fulfilling criteria for self-induced vomiting, cyclic vomiting or cannabinoid hyperemesis syndrome were excluded. We determined prevalence, associated comorbidities, quality of life (QoL) (PROMIS Global-10), symptoms of anxiety and depression (PHQ-4), somatic symptoms (PHQ-12), and healthcare utilization. RESULTS: The global prevalence of GPLS was 0.9% overall and 1.3% among diabetic individuals. Subjects with GPLS showed frequent overlapping of epigastric pain syndrome and irritable bowel syndrome. Subjects with GPLS had significantly lower body mass index, QoL, more non-gastrointestinal somatic complaints, symptoms of anxiety and depression, higher medication usage and doctor visits in the overall and diabetic population, compared to subjects without these symptoms. CONCLUSIONS: GPLS are common worldwide and more common in diabetic patients. The symptom complex is associated with multiple aspects of illness and an increased healthcare consumption.

Metformin Stimulates Intestinal Glycolysis and Lactate Release: A single-Dose Study of Metformin in Patients With Intrahepatic Portosystemic Stent.

The pharmacodynamic effects of metformin remain elusive, but several lines of evidence suggest a critical role of direct effects in the gastrointestinal (GI) tract. We investigated if metformin stimulates intestinal glucose metabolism and lactate release in the prehepatic circulation. We included eight patients with transjugular intrahepatic portosytemic stent in an open label study. Portal and arterialized peripheral blood was obtained before and 90 minutes after ingestion of 1,000 mg metformin. Metformin increased lactate concentrations by 23% (95% confidence interval (CI): 6-40) after 90 minutes in the portal vein. The plasma concentration of glucose, insulin, and C-peptide was higher in the portal vein compared with arterialized blood (P < 0.05, all) and was lowered at both sampling sites following metformin ingestion (P < 0.01, all). Plasma concentration of GLP-1 was 20% (95% CI: 2-38) higher in the portal vein at baseline and metformin increased the concentration with 11% (1.5 pM, P = 0.05). The median concentration of growth differentiation factor 15 was 10% (95% CI: 1-19) higher in the portal vein compared with arterialized blood. Ninety minutes after metformin administration, the median portal vein concentration increased to around 3,000 ng/mL with a mean portal/arterial ratio of 1.5 (95% CI: 1.2-1.8). Non-targeted metabolomics showed that metformin acutely affected benzoate-hippurate metabolism. A single-dose of metformin directly affects substrate metabolism in the upper GI tract in humans with direct stimulation of nonoxidative glucose metabolism. These data suggest glucose lowering effects of metformin can be intrinsically linked with the GI tract without hepatic uptake of the drug.

Metformin Biodistribution: A Key to Mechanisms of Action?

Metformin has undisputed glucose-lowering effects in diabetes and an impressive safety record. It has also shown promising effects beyond diabetes, and several hundred clinical trials involving metformin are currently planned or active. Metformin targets intracellular effectors, but exactly which remain to be established, and in an era of precision medicine, an incomplete understanding of mechanisms of action may limit the use of metformin. Distribution of metformin depends on specific organic cation transporter proteins that are organ- and species-specific. Therefore, target tissues of metformin can be identified by cellular uptake of the drug, and exploring the biodistribution of the drug in humans becomes an attractive strategy to assist the many investigations into the mechanisms of action of metformin performed in animals. In this review, we combine the emerging evidence from the use of 11C-labeled metformin in humans to discuss metformin action in liver, intestines, and kidney, which are the organs with the most avid uptake of the drug.

Metformin is distributed to tumor tissue in breast cancer patients in vivo: A 11C-metformin PET/CT study.

PURPOSE: Epidemiological studies and randomized clinical trials suggest that the antidiabetic drug, metformin, may have anti-neoplastic effects. The mechanism that mediates these beneficial effects has been suggested to involve direct action on cancer cells, but this will require distribution of metformin in tumor tissue. The present study was designed to investigate metformin distribution in vivo in breast and liver tissue in breast cancer patients. METHODS: Seven patients recently diagnosed with ductal carcinoma were recruited. Using PET/CT, tissue distribution of metformin was determined in vivo for 90 min after injection of a carbon-11-labeled metformin tracer. After surgery, tumor tissue was investigated for gene expression levels of metformin transporter proteins. RESULTS: Tumor tissue displayed a distinct uptake of metformin compared to normal breast tissue AUC0-90 min (75.4 ± 5.5 vs 42.3 ± 6.3) g/ml*min (p = 0.01). Maximal concentration in tumor was at 1 min where it reached approximately 30% of the activity in the liver. The metformin transporter protein with the highest gene expression in tumor tissue was multidrug and toxin extrusion 1 (MATE 1) followed by plasma membrane monoamine transporter (PMAT). CONCLUSION: This study confirms that metformin is transported into tumor tissue in women with breast cancer. This finding support that metformin may have direct anti-neoplastic effects on tumor cells in breast cancer patients. However, distribution of metformin in tumor tissue is markedly lower than in liver, an established metformin target tissue.

Hepatic exposure of metformin in patients with non-alcoholic fatty liver disease.

AIMS: Metformin is first-line treatment of type 2 diabetes mellitus and reduces cardiovascular events in patients with insulin resistance and type 2 diabetes. Target tissue for metformin action is thought to be the liver, where metformin distribution depends on facilitated transport by polyspecific transmembrane organic cation transporters (OCTs). Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the western world with strong associations to insulin resistance and the metabolic syndrome, but whether NAFLD affects metformin biodistribution to the liver is not known. In this study, the primary aim was to investigate in vivo hepatic uptake of metformin dynamically in humans with variable degrees of liver affection. As a secondary aim, we wished to correlate hepatic metformin distribution with OCT gene transcription determined in diagnostic liver biopsies. METHODS: Eighteen patients with biopsy-proven NAFLD were investigated using 11C-metformin PET/CT technique. Gene transcripts of OCTs were determined by real-time polymerase chain reaction (PCR). RESULTS: We observed similar hepatic volume of distribution of metformin between patients with simple steatosis and non-alcoholic steatohepatitis (NASH) (Vd 2.38 ± 0.56 vs. 2.10 ± 0.39, P = 0.3). There was no association between hepatic exposure to metformin and the degree of inflammation or fibrosis, and no clear correlation between metformin distribution and OCT gene transcription. CONCLUSION: Metformin is distributed to the liver in patients with NAFLD and the distribution is not impaired by inflammation or fibrosis. The findings imply that metformin action in liver in patients with NAFLD may be preserved.

Metformin reduces liver glucose production by inhibition of fructose-1-6-bisphosphatase.

Metformin is a first-line drug for the treatment of individuals with type 2 diabetes, yet its precise mechanism of action remains unclear. Metformin exerts its antihyperglycemic action primarily through lowering hepatic glucose production (HGP). This suppression is thought to be mediated through inhibition of mitochondrial respiratory complex I, and thus elevation of 5'-adenosine monophosphate (AMP) levels and the activation of AMP-activated protein kinase (AMPK), though this proposition has been challenged given results in mice lacking hepatic AMPK. Here we report that the AMP-inhibited enzyme fructose-1,6-bisphosphatase-1 (FBP1), a rate-controlling enzyme in gluconeogenesis, functions as a major contributor to the therapeutic action of metformin. We identified a point mutation in FBP1 that renders it insensitive to AMP while sparing regulation by fructose-2,6-bisphosphate (F-2,6-P2), and knock-in (KI) of this mutant in mice significantly reduces their response to metformin treatment. We observe this during a metformin tolerance test and in a metformin-euglycemic clamp that we have developed. The antihyperglycemic effect of metformin in high-fat diet-fed diabetic FBP1-KI mice was also significantly blunted compared to wild-type controls. Collectively, we show a new mechanism of action for metformin and provide further evidence that molecular targeting of FBP1 can have antihyperglycemic effects.

Metformin targets brown adipose tissue in vivo and reduces oxygen consumption in vitro.

AIMS: To test the hypothesis that brown adipose tissue (BAT) is a metformin target tissue by investigating in vivo uptake of [11 C]-metformin tracer in mice and studying in vitro effects of metformin on cultured human brown adipocytes. MATERIALS AND METHODS: Tissue-specific uptake of metformin was assessed in mice by PET/CT imaging after injection of [11 C]-metformin. Human brown adipose tissue was obtained from elective neck surgery and metformin transporter expression levels in human and murine BAT were determined by qPCR. Oxygen consumption in metformin-treated human brown adipocyte cell models was assessed by Seahorse XF technology. RESULTS: Injected [11 C]-metformin showed avid uptake in the murine interscapular BAT depot. Metformin exposure in BAT was similar to hepatic exposure. Non-specific inhibition of the organic cation transporter (OCT) protein by cimetidine administration eliminated BAT exposure to metformin, demonstrating OCT-mediated uptake. Gene expression profiles of OCTs in BAT revealed ample OCT3 expression in both human and mouse BAT. Incubation of a human brown adipocyte cell models with metformin reduced cellular oxygen consumption in a dose-dependent manner. CONCLUSION: These results support BAT as a putative metformin target.

High expression of organic cation transporter 3 in human BAT-like adipocytes. Implications for extraneuronal norepinephrine uptake.

Brown adipose tissue (BAT) is activated by extracellular norepinephrine (NE) released by the sympathetic nervous system. The extracellular concentration of NE is additionally regulated by the disappearance/degradation of NE. Recent studies have introduced the organic cation transporter 3 (OCT3) as a possible contributor in the regulation of NE in adipose tissue. In the present study we set out to investigate the presence of OCT3 in human neck adipose tissue (AT), which is the primary localization of BAT in humans. Moreover, we wanted to assess the possible function and correlation of the transporter with known markers of thermogenic function, e.g. UCP1. When examining neck AT biopsies from 57 individuals we found that OCT3 was expressed at 2.5 ± 0.16 fold higher level in the deep-neck AT compared with subcutaneous AT. UCP1 was found extensively expressed in the deep-neck AT depot and the correlation between UCP1 and OCT3 within the deep-neck AT was found highly significant (r2 = 0.4012, P-value < 0.0001). Lastly, we were able to reduce NE uptake in isolated brown adipocytes in an in vitro culture by adding corticosterone which is a known OCT3-blocker. In conclusion, we found that OCT3 may be a regulator of the concentration of NE in AT and by this mechanism a possible regulator of BAT function and a potential target for pharmacological intervention.

In Vivo Imaging of Human 11C-Metformin in Peripheral Organs: Dosimetry, Biodistribution, and Kinetic Analyses.

Metformin is the most widely prescribed oral antiglycemic drug, with few adverse effects. However, surprisingly little is known about its human biodistribution and target tissue metabolism. In animal experiments, we have shown that metformin can be labeled by 11C and that 11C-metformin PET can be used to measure renal function. Here, we extend these preclinical findings by a first-in-human 11C-metformin PET dosimetry, biodistribution, and tissue kinetics study. METHODS: Nine subjects (3 women and 6 men) participated in 2 studies: in the first study, human radiation dosimetry and biodistribution of 11C-metformin were estimated in 4 subjects (2 women and 2 men) by whole-body PET. In the second study, 11C-metformin tissue kinetics were measured in response to both intravenous and oral radiotracer administration. A dynamic PET scan with a field of view covering target tissues of metformin (liver, kidneys, intestines, and skeletal muscle) was obtained for 90 (intravenous) and 120 (oral) min. RESULTS: Radiation dosimetry was acceptable, with effective doses of 9.5 µSv/MBq (intravenous administration) and 18.1 µSv/MBq (oral administration). Whole-body PET revealed that 11C-metformin was primarily taken up by the kidneys, urinary bladder, and liver but also to a lesser extent in salivary glands, skeletal muscle, and intestines. Reversible 2-tissue-compartment kinetics was observed in the liver, and volume of distribution was calculated to be 2.45 mL/mL (arterial input) or 2.66 mL/mL (portal and arterial input). In the kidneys, compartmental models did not adequately fit the experimental data, and volume of distribution was therefore estimated by a linear approach to be 6.83 mL/mL. Skeletal muscle and intestinal tissue kinetics were best described by 2-tissue-compartment kinetics and showed only discrete tracer uptake. Liver 11C-metformin uptake was pronounced after oral administration of the tracer, with tissue-to-blood ratio double what was observed after intravenous administration. Only slow accumulation of 11C-metformin was observed in muscle. There was no elimination of 11C-metformin through the bile both during the intravenous and during the oral part of the study. CONCLUSION: 11C-metformin is suitable for imaging metformin uptake in target tissues and may prove a valuable tool to assess the impact of metformin treatment in patients with varying metformin transport capacity.

[11C]-Labeled Metformin Distribution in the Liver and Small Intestine Using Dynamic Positron Emission Tomography in Mice Demonstrates Tissue-Specific Transporter Dependency.

Metformin is the most commonly prescribed oral antidiabetic drug, with well-documented beneficial preventive effects on diabetic complications. Despite being in clinical use for almost 60 years, the underlying mechanisms for metformin action remain elusive. Organic cation transporters (OCT), including multidrug and toxin extrusion proteins (MATE), are essential for transport of metformin across membranes, but tissue-specific activity of these transporters in vivo is incompletely understood. Here, we use dynamic positron emission tomography with [(11)C]-labeled metformin ([(11)C]-metformin) in mice to investigate the role of OCT and MATE in a well-established target tissue, the liver, and a putative target of metformin, the small intestine. Ablation of OCT1 and OCT2 significantly reduced the distribution of metformin in the liver and small intestine. In contrast, inhibition of MATE1 with pyrimethamine caused accumulation of metformin in the liver but did not affect distribution in the small intestine. The demonstration of OCT-mediated transport into the small intestine provides evidence of direct effects of metformin in this tissue. OCT and MATE have important but separate roles in uptake and elimination of metformin in the liver, but this is not due to changes in biliary secretion. [(11)C]-Metformin holds great potential as a tool to determine the pharmacokinetic properties of metformin in clinical studies.

Effect of resveratrol on experimental non-alcoholic steatohepatitis.

Non-alcoholic fatty liver disease and non-alcoholic steatohepatitis (NASH) are increasing clinical problems for which effective treatments are required. The polyphenol resveratrol prevents the development of fatty liver disease in a number of experimental studies. We hypothesized that it could revert steatohepatitis, including hepatic inflammation and fibrosis, in an experimental NASH model. To induce hepatic steatohepatitis, a 65% fat, 2% cholesterol and 0.5% cholate (HFC) diet was fed to rats for 1 or 16 weeks, prior to treatment. Subsequently, the diet was supplemented with resveratrol (approx. 100mg/rat/day) to three intervention groups; week 2-4, 2-7 or 17-22. Treated animals were sacrificed at the end of each intervention period with appropriate control and HFC diet controls. Blood and liver were harvested for analysis. When commenced early, resveratrol treatment partially mitigated transaminase elevations, hepatic enlargement and TNFα induced protein-3 protein expression, but generally resveratrol treatment had no effect on elevated hepatic triglyceride levels, histological steatohepatitis or fibrosis. We observed a slight reduction in Collagen1α1 mRNA expression and no reduction in the mRNA expression of other markers of fibrosis, inflammation or steatosis (TGFß, TNFα, α2-MG, or SREBP-1c). Resveratrol metabolites were detected in serum, including trans-resveratrol-3-O-sulphate/trans-resveratrol-4'-O-sulphate (mean concentration 7.9 µg/ml). Contrary to the findings in experimental steatosis, resveratrol treatment had no consistent therapeutic effect in alleviating manifest experimental steatohepatitis.

AMP kinase in exercise adaptation of skeletal muscle.

Regular physical exercise has undisputed health benefits in the prevention and the treatment of many diseases. Understanding the mechanisms that regulate adaptations to exercise training therefore has obvious clinical perspectives. Several lines of evidence suggest that the AMP-activated protein kinase (AMPK) has a central role as a master metabolic regulator in skeletal muscle. Exercise is a potent activator of AMPK, and AMPK signaling can play a key part in regulating protein turnover during and after exercise training.