Nonhepatic glucose production in humans

Intestinal gluconeogenesis: metabolic benefits make sense in the light of evolution

The intestine, like the liver and kidney, in various vertebrates and humans is able to carry out gluconeogenesis and release glucose into the blood. In the fed post-absorptive state, intestinal glucose is sensed by the gastrointestinal nervous system. The latter initiates a signal to the brain regions controlling energy homeostasis and stress-related behaviour. Intestinal gluconeogenesis (IGN) is activated by several complementary mechanisms, in particular nutritional situations (for example, when food is enriched in protein or fermentable fibre and after gastric bypass surgery in obesity). In these situations, IGN has several metabolic and behavioural benefits. As IGN is activated by nutrients capable of fuelling systemic gluconeogenesis, IGN could be a signal to the brain that food previously ingested is suitable for maintaining plasma glucose for a while. This process might account for the benefits observed. Finally, in this Perspective, we discuss how the benefits of IGN in fasting and fed states could explain why IGN emerged and was maintained in vertebrates by natural selection.

Improvement of compliance to the Portland intensive insulin therapy during liver transplantation after introducing an application software: a retrospective single center cohort study

Background

The Portland intensive insulin therapy effectively controls acute hyperglycemic change after graft reperfusion during liver transplantation. However, the time-consuming sophistication acts as a barrier leading to misinterpretation and decreasing compliance to the protocol; thus, we newly introduced an application software “Insulin protocol calculator” which automatically calculates therapeutic bolus/continuous insulin doses based on the Portland protocol.

Methods

Of 144 patients who underwent liver transplantation, 74 patients were treated before the introduction of "Insulin protocol calculator" by using a paper manual, and 70 patients were treated by using the application. Compliance was defined as the proportion of patients treated with exact bolus/continuous insulin dose according to the Portland protocol.

Results

Compliance was significantly greater in app group than in paper group regarding bolus dose (94.5% and 86.9%, P < 0.001), continuous dose (88.9% and 77.3%, P = 0.001), and both doses (86.6% and 73.8%, P < 0.001). Blood glucose concentration was significantly lower in app group at 3 h (125 ± 17 mg/dl vs. 136 ± 19 mg/dl, P = 0.014) and 4 h (135 ± 22 mg/dl vs. 115 ± 15 mg/dl, P = 0.029) after graft reperfusion. Acute hyperglycemic change during 30 min was more prominent in app group while hyperglycemia incidence was 71.4% vs. 54.1% (P = 0.031). However, hyperglycemia risk was comparable at 2 h (31.4% vs. 31.1%, P = 0.964), and even insignificantly lower in app group at 3 h (7.1% vs. 19.5%, P = 0.184).

Conclusions

Compliance to the Portland protocol was significantly improved after introducing the application software; post-reperfusion hyperglycemia was better controlled. “Insulin protocol calculator” is cost-effective and time-saving with potential clinical benefits.

Ins and Outs of the TCA Cycle: The Central Role of Anaplerosis

The reactions of the tricarboxylic acid (TCA) cycle allow the controlled combustion of fat and carbohydrate. In principle, TCA cycle intermediates are regenerated on every turn and can facilitate the oxidation of an infinite number of nutrient molecules. However, TCA cycle intermediates can be lost to cataplerotic pathways that provide precursors for biosynthesis, and they must be replaced by anaplerotic pathways that regenerate these intermediates. Together, anaplerosis and cataplerosis help regulate rates of biosynthesis by dictating precursor supply, and they play underappreciated roles in catabolism and cellular energy status. They facilitate recycling pathways and nitrogen trafficking necessary for catabolism, and they influence redox state and oxidative capacity by altering TCA cycle intermediate concentrations. These functions vary widely by tissue and play emerging roles in disease. This article reviews the roles of anaplerosis and cataplerosis in various tissues and discusses how they alter carbon transitions, and highlights their contribution to mechanisms of disease. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Multitissue 2H/13C flux analysis reveals reciprocal upregulation of renal gluconeogenesis in hepatic PEPCK-C-knockout mice

The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a stable isotope approach to simultaneously quantify gluconeogenic and oxidative metabolic fluxes in the liver and kidney. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; KO). 2H/13C isotopes were infused in fasted KO and WT littermate mice, and fluxes were estimated from isotopic measurements of tissue and plasma metabolites using a multicompartment metabolic model. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by coordinated regulation of gluconeogenic flux through PEPCK-C. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multitissue metabolism in various genetic, pathophysiological, physiological, and pharmacological settings.

Effects of DPP-4 Inhibitors on Blood Glucose Variability in Japanese Patients with Type 2 Diabetes on Maintenance Hemodialysis: A Prospective Observational Exploratory Study

INTRODUCTION

The precise blood glucose (BG) profile of hemodialysis patients is unclear, as is the effectiveness of dipeptidyl peptidase-4 (DPP-4) inhibitors in hemodialysis patients with type 2 diabetes. Here, we used continuous glucose monitoring (CGM) to evaluate BG variability in these patients and to assess the efficacy of DPP-4 inhibitors, particularly during hemodialysis sessions and at nighttime (UMIN000012638).

METHODS

We examined BG profiles using CGM in 31 maintenance hemodialysis patients with type 2 diabetes. Differences between patients with and without DPP-4 inhibitors (n = 15 and 16, respectively) were analyzed using a linear mixed-effects model to assess changes in glucose levels in 5-min intervals.

RESULTS

The model revealed that DPP-4 inhibitor use was significantly associated with suppression of a rapid drop in glucose levels, both with and without adjustment for BG levels at the start of hemodialysis. Moreover, the model revealed that the two groups differed significantly in the pattern of changes in BG levels from 0:00 to 6:55 am. DPP-4 inhibitors suppressed the tendency for subsequent nocturnal hypoglycemia.

CONCLUSIONS

This prospective observational exploratory study showed that DPP-4 inhibitors could suppress BG variability during hemodialysis sessions as well as subsequent nocturnal changes in patients with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, UMIN000012638.

Intestinal gluconeogenesis prevents obesity-linked liver steatosis and non-alcoholic fatty liver disease

OBJECTIVE

Hepatic steatosis accompanying obesity is a major health concern, since it may initiate non-alcoholic fatty liver disease (NAFLD) and associated complications like cirrhosis or cancer. Intestinal gluconeogenesis (IGN) is a recently described function that contributes to the metabolic benefits of specific macronutrients as protein or soluble fibre, via the initiation of a gut-brain nervous signal triggering brain-dependent regulations of peripheral metabolism. Here, we investigate the effects of IGN on liver metabolism, independently of its induction by the aforementioned macronutrients.

DESIGN

To study the specific effects of IGN on hepatic metabolism, we used two transgenic mouse lines: one is knocked down for and the other overexpresses glucose-6-phosphatase, the key enzyme of endogenous glucose production, specifically in the intestine.

RESULTS

We report that mice with a genetic overexpression of IGN are notably protected from the development of hepatic steatosis and the initiation of NAFLD on a hypercaloric diet. The protection relates to a diminution of de novo lipogenesis and lipid import, associated with benefits at the level of inflammation and fibrosis and linked to autonomous nervous system. Conversely, mice with genetic suppression of IGN spontaneously exhibit increased hepatic triglyceride storage associated with activated lipogenesis pathway, in the context of standard starch-enriched diet. The latter is corrected by portal glucose infusion mimicking IGN.

CONCLUSION

We conclude that IGN per se has the capacity of preventing hepatic steatosis and its eventual evolution toward NAFLD.

Intestinal gluconeogenesis and protein diet: future directions

High-protein meals and foods are promoted for their beneficial effects on satiety, weight loss and glucose homeostasis. However, the mechanisms involved and the long-term benefits of such diets are still debated. We here review how the characterisation of intestinal gluconeogenesis (IGN) sheds new light on the mechanisms by which protein diets exert their beneficial effects on health. The small intestine is the third organ (in addition to the liver and kidney) contributing to endogenous glucose production via gluconeogenesis. The particularity of glucose produced by the intestine is that it is detected in the portal vein and initiates a nervous signal to the hypothalamic nuclei regulating energy homeostasis. In this context, we demonstrated that protein diets initiate their satiety effects indirectly via IGN and portal glucose sensing. This induction results in the activation of brain areas involved in the regulation of food intake. The μ-opioid-antagonistic properties of protein digests, exerted in the portal vein, are a key link between IGN induction and protein-enriched diet in the control of satiety. From our results, IGN can be proposed as a mandatory link between nutrient sensing and the regulation of whole-body homeostasis. The use of specific mouse models targeting IGN should allow us to identify several metabolic functions that could be controlled by protein diets. This will lead to the characterisation of the mechanisms by which protein diets improve whole-body homeostasis. These data could be the basis of novel nutritional strategies targeting the serious metabolic consequences of both obesity and diabetes.

Mangosteen Concentrate Drink Supplementation Promotes Antioxidant Status and Lactate Clearance in Rats after Exercise

High-strength or long-duration exercise can lead to significant fatigue, oxidative stress, and muscle damage. The purpose of this study was to examine the effect of mangosteen concentrate drink (MCD) supplementation on antioxidant capacity and lactate clearance in rats after running exercise. Forty rats were divided into five groups: N, non-treatment; C, control; or supplemented with MCD, including M1, M5, and M10 (0.9, 4.5, and 9 mL/day) for 6 weeks. The rats were subjected to 30 min running and exhaustive-running tests using a treadmill. The blood lactate; triglyceride; cholesterol and glucose levels; hepatic and muscular malonaldehyde (MDA) levels; and antioxidant enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT), were analyzed. The results of this study demonstrated that MCD supplementation can increase GPx and CAT activities, alleviate oxidative stress in muscle, and increase lactate clearance, and is thereby beneficial to reduced muscle fatigue after exercise.

Portland Intensive Insulin Therapy During Living Donor Liver Transplantation: Association with Postreperfusion Hyperglycemia and Clinical Outcomes

Many liver transplant recipients experience intraoperative hyperglycemia after graft reperfusion. Accordingly, we introduced the Portland intensive insulin therapy (PoIIT) in our practice to better control blood glucose concentration (BGC). We evaluated the effects of PoIIT by comparing with our conventional insulin therapy (CoIT). Of 128 patients who underwent living donor liver transplantation (LDLT) during the phaseout period of CoIT, 89 were treated with the PoIIT and 39 were treated with CoIT. The primary outcome was hyperglycemia (BGC > 180 mg/dL) during the intraoperative postreperfusion phase. The secondary outcomes were postoperative complications such as infection. The incidence of hyperglycemia (22.5% vs. 53.8%, p = 0.001) and prolonged hyperglycemia for >2 hours (7.9% vs. 30.8%, p = 0.002) was significantly lower in PoIIT group than in CoIT group. A mixed linear model further demonstrated that repeatedly measured BGCs were lower in PoIIT group (p < 0.001). The use of PoIIT was significantly associated with decreases in major infections (OR = 0.23 [0.06-0.85], p = 0.028), prolonged mechanical ventilation (OR = 0.29 [0.09-0.89], p = 0.031), and biliary stricture (OR = 0.23 [0.07-0.78], p = 0.018) after adjustments for age, sex, and diabetes mellitus. In conclusion, the PoIIT is effective for maintaining BGC and preventing hyperglycemia during the intraoperative postreperfusion phase of living donor liver transplantation with potential clinical benefits.

Importance of the gastrointestinal tract in type 2 diabetes. Metabolic surgery is more than just incretin effect

Bariatric and metabolic surgery is creating new concepts about how the intestine assimilates food. Recent studies highlight the role of the gastrointestinal tract in the genesis and evolution of type 2 diabetes. This article has been written to answer frequent questions about metabolic surgery results and the mechanisms of action. For this purpose, a non-systematic search of different databases was carried out, identifying articles published in the last decade referring to the mechanisms of action of metabolic techniques. Understanding these mechanisms will help grasp why some surgeries are more effective than others and why the results can be so disparate among patients undergoing the same surgical approach.

Gut-Brain Glucose Signaling in Energy Homeostasis

Intestinal gluconeogenesis is a recently identified function influencing energy homeostasis. Intestinal gluconeogenesis induced by specific nutrients releases glucose, which is sensed by the nervous system surrounding the portal vein. This initiates a signal positively influencing parameters involved in glucose control and energy management controlled by the brain. This knowledge has extended our vision of the gut-brain axis, classically ascribed to gastrointestinal hormones. Our work raises several questions relating to the conditions under which intestinal gluconeogenesis proceeds and may provide its metabolic benefits. It also leads to questions on the advantage conferred by its conservation through a process of natural selection.

Glycemic responses to intermittent hepatic inflow occlusion in living liver donors

The occurrence of glycemic disturbances has been described for patients undergoing intermittent hepatic inflow occlusion (IHIO) for tumor removal. However, the glycemic responses to IHIO in living liver donors are unknown. This study investigated the glycemic response to IHIO in these patients and examined the association between this procedure and the occurrence of hyperglycemia (blood glucose > 180 mg/dL). The data from 154 living donors were retrospectively reviewed. The decision to perform IHIO was made on the basis of the extent of bleeding that occurred during parenchymal dissection. One round of IHIO consisted of 15 minutes of clamping and 5 minutes of unclamping the hepatic artery and portal vein. Blood glucose concentrations were measured at predetermined time points, including the start and end of IHIO. Repeated hyperglycemic episodes occurred after unclamping. The mean maximum intraoperative blood glucose concentration was greater in donors who underwent ≥3 rounds of IHIO versus those who underwent 1 or 2 rounds (169 ± 30 versus 149 ± 31 mg/dL, P = 0.005). The incidence of intraoperative hyperglycemia was also greater in donors who underwent ≥3 rounds of IHIO versus those who underwent 1 or 2 rounds (38.7% versus 7.7%, odds ratio = 7.1, 95% confidence interval = 2.5-20.4, P < 0.001). Donors who did not undergo IHIO and those who underwent 1 or 2 rounds of IHIO exhibited similar maximum glucose concentrations and similar incidence rates of hyperglycemia. In conclusion, IHIO induced repeated hyperglycemic responses in living donors, and donors who underwent ≥3 rounds of IHIO were more likely to experience intraoperative hyperglycemia. These results provide additional information on the risks and benefits of IHIO in living donors.

A gut-brain neural circuit controlled by intestinal gluconeogenesis is crucial in metabolic health

Objectives

Certain nutrients positively regulate energy homeostasis via intestinal gluconeogenesis (IGN). The objective of this study was to evaluate the impact of a deficient IGN in glucose control independently of nutritional environment.

Methods

We used mice deficient in the intestine glucose-6 phosphatase catalytic unit, the key enzyme of IGN (I-G6pc^−/− mice). We evaluated a number of parameters involved in energy homeostasis, including insulin sensitivity (hyperinsulinemic euglycaemic clamp), the pancreatic function (insulin secretion in vivo and in isolated islets) and the hypothalamic homeostatic function (leptin sensitivity).

Results

Intestinal-G6pc^−/− mice exhibit slight fasting hyperglycaemia and hyperinsulinemia, glucose intolerance, insulin resistance and a deteriorated pancreatic function, despite normal diet with no change in body weight. These defects evoking type 2 diabetes (T2D) derive from the basal activation of the sympathetic nervous system (SNS). They are corrected by treatment with an inhibitor of α-2 adrenergic receptors. Deregulation in a key target of IGN, the homeostatic hypothalamic function (highlighted here through leptin resistance) is a mechanistic link. Hence the leptin resistance and metabolic disorders in I-G6pc^−/− mice are corrected by rescuing IGN by portal glucose infusion. Finally, I-G6pc^−/− mice develop the hyperglycaemia characteristic of T2D more rapidly under high fat/high sucrose diet.

Conclusions

Intestinal gluconeogenesis is a mandatory function for the healthy neural control of glucose homeostasis.

Comprehensive review on lactate metabolism in human health

Metabolic pathways involved in lactate metabolism are important to understand the physiological response to exercise and the pathogenesis of prevalent diseases such as diabetes and cancer. Monocarboxylate transporters are being investigated as potential targets for diagnosis and therapy of these and other disorders. Glucose and alanine produce pyruvate which is reduced to lactate by lactate dehydrogenase in the cytoplasm without oxygen consumption. Lactate removal takes place via its oxidation to pyruvate by lactate dehydrogenase. Pyruvate may be either oxidized to carbon dioxide producing energy or transformed into glucose. Pyruvate oxidation requires oxygen supply and the cooperation of pyruvate dehydrogenase, the tricarboxylic acid cycle, and the mitochondrial respiratory chain. Enzymes of the gluconeogenesis pathway sequentially convert pyruvate into glucose. Congenital or acquired deficiency on gluconeogenesis or pyruvate oxidation, including tissue hypoxia, may induce lactate accumulation. Both obese individuals and patients with diabetes show elevated plasma lactate concentration compared to healthy subjects, but there is no conclusive evidence of hyperlactatemia causing insulin resistance. Available evidence suggests an association between defective mitochondrial oxidative capacity in the pancreatic β-cells and diminished insulin secretion that may trigger the development of diabetes in patients already affected with insulin resistance. Several mutations in the mitochondrial DNA are associated with diabetes mellitus, although the pathogenesis remains unsettled. Mitochondrial DNA mutations have been detected in a number of human cancers. d-lactate is a lactate enantiomer normally formed during glycolysis. Excess d-lactate is generated in diabetes, particularly during diabetic ketoacidosis. d-lactic acidosis is typically associated with small bowel resection.

Microbiota-generated metabolites promote metabolic benefits via gut-brain neural circuits

Soluble dietary fibers promote metabolic benefits on body weight and glucose control, but underlying mechanisms are poorly understood. Recent evidence indicates that intestinal gluconeogenesis (IGN) has beneficial effects on glucose and energy homeostasis. Here, we show that the short-chain fatty acids (SCFAs) propionate and butyrate, which are generated by fermentation of soluble fiber by the gut microbiota, activate IGN via complementary mechanisms. Butyrate activates IGN gene expression through a cAMP-dependent mechanism, while propionate, itself a substrate of IGN, activates IGN gene expression via a gut-brain neural circuit involving the fatty acid receptor FFAR3. The metabolic benefits on body weight and glucose control induced by SCFAs or dietary fiber in normal mice are absent in mice deficient for IGN, despite similar modifications in gut microbiota composition. Thus, the regulation of IGN is necessary for the metabolic benefits associated with SCFAs and soluble fiber.

Nutrient control of energy homeostasis via gut-brain neural circuits

Intestinal gluconeogenesis is a recently described function in intestinal glucose metabolism. In particular, the intestine contributes around 20-25% of total endogenous glucose production during fasting. Intestinal gluconeogenesis appears to regulate energy homeostasis via a neurally mediated mechanism linking the enterohepatic portal system with the brain. The periportal neural system is able to sense glucose produced by intestinal gluconeogenesis in the portal vein walls, which sends a signal to the brain to modulate energy and glucose homeostasis. Dietary proteins mobilize intestinal gluconeogenesis as a mandatory link between the sensing of these proteins in the portal vein and their well-known effect of satiety. Comparably, dietary soluble fibers exert their antiobesity and antidiabetic effects via the induction of intestinal gluconeogenesis. Finally, intestinal gluconeogenesis might be involved in the rapid metabolic improvements in energy homeostasis induced by gastric bypass surgeries of obesity.

Intestinal gluconeogenesis is crucial to maintain a physiological fasting glycemia in the absence of hepatic glucose production in mice

OBJECTIVE

Similar to the liver and kidneys, the intestine has been strongly suggested to be a gluconeogenic organ. However, the precise contribution of the intestine to endogenous glucose production (EGP) remains to be determined. To define the quantitative role of intestinal gluconeogenesis during long-term fasting, we compared changes in blood glucose during prolonged fasting in mice with a liver-deletion of the glucose-6 phosphatase catalytic (G6PC) subunit (LKO) and in mice with a combined deletion of G6PC in both the liver and the intestine (ILKO).

MATERIALS/METHODS

The LKO and ILKO mice were studied after 6h and 40 h of fasting by measuring metabolic and hormonal plasmatic parameters, as well as the expression of gluconeogenic enzymes in the liver, kidneys and intestine.

RESULTS

After a transient hypoglycemic episode (approximately 60 mg/dL) because of their incapacity to mobilize liver glycogen, the LKO mice progressively re-increased their plasma glucose to reach a glycemia comparable to that of wild-type mice (90 mg/dL) from 30 h of fasting. This increase was associated with a rapid induction of renal and intestinal gluconeogenic gene expression, driven by glucagon, glucocorticoids and acidosis. The ILKO mice exhibited a similar induction of renal gluconeogenesis. However, these mice failed to re-increase their glycemia and maintained a plasma glucose level of only 60 mg/dL throughout the 48 h-fasting period.

CONCLUSIONS

These data indicate that intestinal glucose production is essential to maintain glucose homeostasis in the absence of hepatic glucose production during fasting. These data provide a definitive quantitative estimate of the capacity of intestinal gluconeogenesis to sustain EGP during long-term fasting.

Satiety and the role of μ-opioid receptors in the portal vein

Mu-opioid receptors (MORs) are known to influence food intake at the brain level, through their involvement in the food reward system. MOR agonists stimulate food intake. On the other hand, MOR antagonists suppress food intake. MORs are also active in peripheral organs, especially in the small intestine where they control the gut motility. Recently, an indirect role in the control of food intake was ascribed to MORs in the extrinsic gastrointestinal neural system. MORs present in the neurons of the portal vein walls sense blood peptides released from the digestion of dietary protein. These peptides behave as MOR antagonists. Their MOR antagonist action initiates a gut-brain circuitry resulting in the induction of intestinal gluconeogenesis, a function controlling food intake. Thus, periportal MORs are a key mechanistic link in the satiety effect of protein-enriched diets.

Heart surgery stems increased nutritional risk, expressed during the course of stationary rehabilitation

BACKGROUND

Cardiovascular diseases are a vast global health burden. Despite common prevalence, current knowledge and investigations concerning nutritional aspects are limited. Characteristics and dynamics of nutritional risk are not entirely known for most of the entities, disease stages or treatment-induced fluctuations. This study assessed the effects of heart surgery on unintentional weight loss and nutritional risk using the NRS-2002.

METHODS

A noninterventional study that included patients scheduled for rehabilitation 1-6 months after heart surgery was performed. Evaluation included routine cardiovascular diagnostics and review of medical histories. Documented baseline weight was available for >85% of the patients. Nutritional risk screening was performed with the standardized NRS-2002 questionnaire.

RESULTS

A total of 145 patients were involved, with a mean age of 65.3 ± 11.5 years in a range of 23-84 years. The male to female ratio was 121:24 (83.4%:16.6%), respectively. Coronary artery bypass graft surgery (CABG) was performed in 89 patients (61.4%), valvular surgery (VS) in 34 (23.4%) and combined operations (CABG + VS) in 22 (15.2%). Percentage weight loss history was 11.1 ± 3.4% in a range of 0-20.1%, while NRS-2002 was 4.77 ± 1.05 in a range of 1-6. Increased nutritional risk (NRS-2002 ≥3) was found in nearly all patients. Combined ischemic and valvular etiology displayed the highest values of NRS-2002 (5.0 ± 1.2). Patient age and creatinine showed significant correlations with NRS-2002 (Rho = 0.521, p < 0.001 and Rho = 0.335, p < 0.001, respectively).

CONCLUSION

Increased nutritional risk was found to be frequently prevalent in patients scheduled for rehabilitation after heart surgery. Risk was found to be in relation with underlying coronary artery disease as well as with the age of patients and parameters of renal function. Routine application of nutritional risk screening appears to be a valuable clinical tool for detecting this relevant comorbidity, particularly since no connection was found with traditional anthropometrics.

Insulin signalling to the kidney in health and disease

Ninety-one years ago insulin was discovered, which was one of the most important medical discoveries in the past century, transforming the lives of millions of diabetic patients. Initially insulin was considered only important for rapid control of blood glucose by its action on a restricted number of tissues; however, it has now become clear that this hormone controls an array of cellular processes in many different tissues. The present review will focus on the role of insulin in the kidney in health and disease.

Type 2 diabetes mellitus: a possible surgically reversible intestinal dysfunction

Type 2 diabetes mellitus (T2DM) is a global public health problem often associated with obesity. Bariatric surgery is effective for treating serious obesity, and techniques involving intestinal bypass have metabolic benefits, such as complete and early remission of T2DM. We present a literature review of the possible mechanisms of early normalization of glycemic homeostasis after bariatric surgery, including intestinal gluconeogenesis, increased antidiabetogenic signals from L cells located in the distal small intestine, and impaired secretion of diabetogenic signals in the upper part of the small intestine. Adding to these potential mechanisms, unknown factors that regulate insulin sensitivity may be involved and altered by bariatric surgery. This review discusses the various hypotheses about the mechanisms of glycemic control after bariatric surgery involving intestinal bypass. Further research is essential to better understand these mechanisms and to identify potential new mechanisms that might help in developing less invasive and safer alternatives for the treatment of T2DM and reveal novel pharmaceutical targets for glycemic control.

Control of blood glucose in the absence of hepatic glucose production during prolonged fasting in mice: induction of renal and intestinal gluconeogenesis by glucagon

OBJECTIVE

Since the pioneering work of Claude Bernard, the scientific community has considered the liver to be the major source of endogenous glucose production in all postabsorptive situations. Nevertheless, the kidneys and intestine can also produce glucose in blood, particularly during fasting and under protein feeding. The aim of this study was to better define the importance of the three gluconeogenic organs in glucose homeostasis.

RESEARCH DESIGN AND METHODS

We investigated blood glucose regulation during fasting in a mouse model of inducible liver-specific deletion of the glucose-6-phosphatase gene (L-G6pc(-/-) mice), encoding a mandatory enzyme for glucose production. Furthermore, we characterized molecular mechanisms underlying expression changes of gluconeogenic genes (G6pc, Pck1, and glutaminase) in both the kidneys and intestine.

RESULTS

We show that the absence of hepatic glucose release had no major effect on the control of fasting plasma glucose concentration. Instead, compensatory induction of gluconeogenesis occurred in the kidneys and intestine, driven by glucagon, glucocorticoids, and acidosis. Moreover, the extrahepatic action of glucagon took place in wild-type mice.

CONCLUSIONS

Our study provides a definitive quantitative estimate of the capacity of extrahepatic gluconeogenesis to sustain fasting endogenous glucose production under the control of glucagon, regardless of the contribution of the liver. Thus, the current dogma relating to the respective role of the liver and of extrahepatic gluconeogenic organs in glucose homeostasis requires re-examination.

Targeted deletion of liver glucose-6 phosphatase mimics glycogen storage disease type 1a including development of multiple adenomas

BACKGROUND AND AIMS

Glycogen storage disease type 1a (GSD1a) is an inherited disease caused by a deficiency in the catalytic subunit of the glucose-6 phosphatase enzyme (G6Pase). GSD1a is characterized by hypoglycaemia, hyperlipidemia, and lactic acidosis with associated hepatic (including hepatocellular adenomas), renal, and intestinal disorders. A total G6pc (catalytic subunit of G6Pase) knock-out mouse model has been generated that mimics the human pathology. However, these mice rarely live longer than 3 months and long-term liver pathogenesis cannot be evaluated. Herein, we report the long-term characterization of a liver-specific G6pc knock-out mouse model (L-G6pc(-/-)).

METHODS

We generated L-G6pc(-/-) mice using an inducible CRE-lox strategy and followed up the development of hepatic tumours using magnetic resonance imaging.

RESULTS

L-G6pc(-/-) mice are viable and exhibit normoglycemia in the fed state. They develop hyperlipidemia, lactic acidosis, and uricemia during the first month after gene deletion. However, these plasmatic parameters improved after 6 months. L-G6pc(-/-) mice develop hepatomegaly with glycogen accumulation and hepatic steatosis. Using an MRI approach, we could detect hepatic nodules with diameters of less than 1 mm, 9 months after induction of deficiency. Hepatic nodules (1 mm) were detected in 30-40% of L-G6pc(-/-) mice at 12 months. After 18 months, all L-G6pc(-/-) mice developed multiple hepatocellular adenomas of 1-10 mm diameter.

CONCLUSIONS

This is the first report of a viable animal model of the hepatic pathology of GSD1a, including the late development of hepatocellular adenomas.

Perioperative blood glucose management in patients undergoing tumor hepatectomy

STUDY OBJECTIVE

To determine whether our institutional insulin management (modified Atlanta) protocol is efficient and safe in controlling blood glucose levels in the perioperative period in surgical patients undergoing tumor hepatectomy.

DESIGN

Retrospective study.

SETTING

Large community hospital.

PATIENTS

20 consecutive patients undergoing liver resection for hepatocellular carcinoma, liver metastasis, or other hepatobiliary tumors.

INTERVENTIONS AND MEASUREMENTS

All patients continuously received intravenous glucose (5% dextrose in water, one mL/kg/hr); insulin was administered according to a strict algorithm, and dose adjustments were based on measurements of whole-blood glucose intraoperatively at one-hour intervals, and in the intensive care unit (ICU). Lower and upper blood glucose limits were set at 85 mg/dL and 110 mg/dL, respectively, in the operating room (OR). In the ICU, lower and upper limits were 90 mg/dL and 140 mg/dL, respectively.

MAIN RESULTS

Intraoperatively, 51.3% of measurements were within the target range. In the ICU, 75.2% of measurements showed a blood glucose level of 90 - 140 mg/dL. Two of 78 (2.6%) and two of 363 (0.5%) measurements had a blood glucose level < 70 mg/dL in the OR and ICU, respectively. The lowest blood glucose levels were 65 mg/dL (OR) and 66 mg/dL (ICU).

CONCLUSIONS

The modified Atlanta protocol is efficient and safe in controlling blood glucose levels in the perioperative period of hepatic tumor resection. Because of decreased insulin needs in the ICU, the use of a more liberal algorithm successfully reduced the risk of hypoglycemia.

Early hemodynamics and metabolic changes after total abdominal evisceration for experimental multivisceral transplantation

PURPOSE: Multivisceral transplantation (MVTx) has been accepted as standard therapeutic modality for patients with short-bowel syndrome associated with irreversible liver failure. Even nowadays, experimental models of MVTx grounds high incidence of intraoperative or early recipient mortality. Despite the known deleterious effects of hepatosplanchnic exenteration the impact of this procedure on systemic hemodynamics and metabolism remains to be determined. METHODS: Nine dogs (20.1±0.5 kg) were subjected to an en bloc resection of all abdominal organs including, stomach, duodenum, pancreas, liver, spleen, small bowel, and colon. A woven double velour vascular graft was interposed between the suprahepatic and infrahepatic vena cava. Systemic hemodynamic were evaluated through a Swan-Ganz catheter, ultrasonic flowprobes, and arterial lines. Systemic O2-derived variables, glucose, and lactate metabolism were analyzed throughout the experiment. RESULTS: Complete abdominal exenteration was associated with significant reduction in cardiac output, and mean arterial pressure (57% and 14%, respectively). Two hours after reperfusion a significant reduction in arterial pH and glucose were also observed. Oxygen consumption remained unaltered during the first two hours of the experiment, with a significant increase of lactate levels (1.4±0.3 vs. 7.6±0.4, p<0.05). Three animals died before the 3 hours of reperfusion were completed. Total abdominal exenteration for MVTx in dogs is associated with early major hemodynamics, and metabolic changes. CONCLUSION: The deleterious hemodynamic alterations observed are probably related with the association of severe acidosis, hyperlactemia, hypoglycemia, and reduction of total circulating blood volume. Close hemodynamic and metabolic monitoring should be provided during experimental MVTx in order to promote an increase in successful rates of this complex and challenging procedure.

Intestinal gluconeogenesis is a key factor for early metabolic changes after gastric bypass but not after gastric lap-band in mice

Unlike the adjustable gastric banding procedure (AGB), Roux-en-Y gastric bypass surgery (RYGBP) in humans has an intriguing effect: a rapid and substantial control of type 2 diabetes mellitus (T2DM). We performed gastric lap-band (GLB) and entero-gastro anastomosis (EGA) procedures in C57Bl6 mice that were fed a high-fat diet. The EGA procedure specifically reduced food intake and increased insulin sensitivity as measured by endogenous glucose production. Intestinal gluconeogenesis increased after the EGA procedure, but not after gastric banding. All EGA effects were abolished in GLUT-2 knockout mice and in mice with portal vein denervation. We thus provide mechanistic evidence that the beneficial effects of the EGA procedure on food intake and glucose homeostasis involve intestinal gluconeogenesis and its detection via a GLUT-2 and hepatoportal sensor pathway.

Glucose homeostasis in a diabetic patient during liver transplantation: a case report

A 66-year-old woman with type C hepatitis had been treated for hepatocellular carcinoma (HCC) with transcatheter arterial embolization and radiofrequency ablation. Liver function worsened gradually to decompensated liver cirrhosis. She had recurrence of HCC and was later admitted to Juntendo University Hospital for living-donor liver transplantation. Although blood glucose was high, she had never been diagnosed with diabetes mellitus. No diabetes-related complications were detected at that time. We started treatment with multiple insulin injections. There is a unique time called the anhepatic phase during liver transplantation during which the liver does not exist in the body. Recent reports show that it is not necessary to administer glucose for patients with normal glucose tolerance during the anhepatic phase since plasma glucose could be maintained at normoglycemia to hyperglycemia (100-150 mg/dl). In our patient, plasma glucose concentration was rather high during the anhepatic phase without glucose administration. We analyzed the levels of blood glucose, insulin and various other hormones during the anhepatic phase. This could be the first report on glucose homeostasis during the anhepatic phase in a diabetic patient.

Glucose metabolism and catecholamines

Until now, catecholamines were the drugs of choice to treat hypotension during shock states. Catecholamines, however, also have marked metabolic effects, particularly on glucose metabolism, and the degree of this metabolic response is directly related to the beta2-adrenoceptor activity of the individual compound used. Under physiologic conditions, infusing catecholamine is associated with enhanced rates of aerobic glycolysis (resulting in adenosine triphosphate production), glucose release (both from glycogenolysis and gluconeogenesis), and inhibition of insulin-mediated glycogenesis. Consequently, hyperglycemia and hyperlactatemia are the hallmarks of this metabolic response. Under pathophysiologic conditions, the metabolic effects of catecholamines are less predictable because of changes in receptor affinity and density and in drug kinetics and the metabolic capacity of the major gluconeogenic organs, both resulting from the disease per se and the ongoing treatment. It is also well-established that shock states are characterized by a hypermetabolic condition with insulin resistance and increased oxygen demands, which coincide with both compromised tissue microcirculatory perfusion and mitochondrial dysfunction. This, in turn, causes impaired glucose utilization and may lead to inadequate glucose supply and, ultimately, metabolic failure. Based on the landmark studies on intensive insulin use, a crucial role is currently attributed to glucose homeostasis. This article reviews the effects of the various catecholamines on glucose utilization, both under physiologic conditions, as well as during shock states. Because, to date (to our knowledge), no patient data are available, results from relevant animal experiments are discussed. In addition, potential strategies are outlined to influence the catecholamine-induced effects on glucose homeostasis.

In vivo effects of corticotropin-releasing hormone on femoral adipose tissue metabolism in women

OBJECTIVE

To investigate whether i.v. injected corticotropin-releasing hormone (CRH) (1 microg/kg) has a direct effect on adipose tissue metabolism in humans.

DESIGN

Double-blinded, placebo-controlled, crossover study.

SUBJECTS

Twelve healthy normal weight female volunteers (age 20-37 years, body mass index: 22.75+/-1.33 kg/m(2))

MEASUREMENTS

Assessment of local generation of glycerol, and glucose in adipose tissue by microdialysis. Measurement of adipose tissue and skin blood flow by laser Doppler flowmetry.

RESULTS

Injection of CRH acutely increases interstitial concentrations of glycerol (19.0+/-5.4%, P<0.05) and glucose (13.5+/-5.8%, P<0.05) reaching peak levels after 15 min. Plasma glycerol increases in parallel (Delta=16.7+/-5.9% after 15 min (P<0.05)), whereas plasma glucose remains unaffected. Changes in tissue blood flow do not explain interstitial metabolite alterations. Initial CRH effects on adipose tissue metabolism are short lasting and disappear after 15 min.

CONCLUSIONS

The importance of CRH on human energy metabolism is underlined by the present in vivo study demonstrating peptidergic effects on lipolysis and glucose homeostasis in human subcutaneous adipose tissue.

Contribution of intestine and kidney to glucose fluxes in different nutritional states in rat

The liver is considered the main contributor of endogenous glucose production (EGP) in the postabsorptive (PA) state in mammals. However, it has been shown that the kidney, in PA and fasting states, and the intestine, in insulinopenia states, could make significant contributions to EGP. Using glucose tracer dilution combined to a vessel ligaturing approach, we studied the respective role of these organs in glucose turnover under various nutritional conditions in the rat (Rattus norvegicus). Both organs constitute key sites of glucose disposal in all situations in the non-moving rat. The kidney makes a small (12%) contribution to EGP in the PA state (9.6+/-1.3 micromol/kg min, means+/-SEM, n=5), which is dramatically increased (p<0.01) in 24 h-fasting (18.8+/-1.0 micromol/kg min) or streptozotocin diabetes (48+/-3 micromol/kg min). The small intestine contributes to EGP via two ways: a direct glucose contribution that may only take place in fasting and diabetes; an indirect contribution via the supply of alanine and lactate to liver gluconeogenesis that may account for up to 5 micromol/kg min in both PA and fasted states in the rat. These data emphasize the coordinate interactions among the three gluconeogenic organs in glucose homeostasis when nutritional conditions are changing.

Portal sensing of intestinal gluconeogenesis is a mechanistic link in the diminution of food intake induced by diet protein

Protein feeding is known to decrease hunger and subsequent food intake in animals and humans. It has also been suggested that glucose appearance into portal vein, as occurring during meal assimilation, may induce comparable effects. Here, we connect these previous observations by reporting that intestinal gluconeogenesis (i.e., de novo synthesis of glucose) is induced during the postabsorptive time (following food digestion) in rats specifically fed on protein-enriched diet. This results in glucose release into portal blood, counterbalancing the lowering of glycemia resulting from intestinal glucose utilization. Comparable infusions into the portal vein of control postabsorptive rats (fed on starch-enriched diet) decrease food consumption and activate the hypothalamic nuclei regulating food intake. Similar hypothalamic activation occurs on protein feeding. All these effects are absent after denervation of the portal vein. Thus, portal sensing of intestinal gluconeogenesis may be a novel mechanism connecting the macronutrient composition of diet to food intake.

The new functions of the gut in the control of glucose homeostasis

PURPOSE OF REVIEW

It has become clear during the past few years that the intestine is more than a digestive tract. In addition to its role as a subtle endocrine organ, its participation in endogenous glucose production, a property so far believed to be restricted to the liver and kidney, has been emphasized.

RECENT FINDINGS

The role of the gut in the regulation of glucose homeostasis has received further experimental accreditation from both animal and human studies. In relation to the molecular mechanisms of control of glucose production the potential regulatory role of glutaminase and glycerokinase has been suggested from studies of fasting, and the transcription of the glucose-6 phosphatase gene has been specified in an intestinal context. Furthermore, two newly described metabolic pathways accounting for the transepithelial transport of glucose have received further support: from the intestinal lumen to inside the enterocyte, involving a translocation of the glucose transporter Glut2 to the apical membrane, and from inside the enterocyte into the blood, involving glucose 6-phosphatase and independent of Glut2.

SUMMARY

The new knowledge regarding the control of glucose, glutamine, and glycerol metabolisms in the small intestine should be of interest to those who care for diabetic or septic patients, or are involved in nutrition research in humans. They should also be of importance in the knowledge of inherited genetic deficiencies, such as glycogen storage disease type 1 (Von Gierke disease) and the Fanconi-Bickel and glucose-galactose malabsorption syndromes.

Renal Insulin Resistance Syndrome, Adiponectin and Cardiovascular Events in Patients with Kidney Disease: The Mild and Moderate Kidney Disease Study

The relationship among insulin resistance, adiponectin, and cardiovascular (CV) morbidity in patients with mild and moderate kidney disease was investigated. Insulin sensitivity (Homeostasis Model Assessment of Insulin Resistance [HOMA-IR]) and adiponectin plasma levels were assessed in 227 nondiabetic renal patients at different degrees of renal dysfunction and in 76 healthy subjects of similar age and gender distribution and body mass index. In renal patients, association with prevalent CV events was evaluated, and incident CV events were evaluated in a prospective study. HOMA-IR was markedly higher in patients than in healthy subjects (3.59 +/- 3.55 versus 1.39 +/- 0.51; P < 0.01). In renal patients, HOMA-IR was significantly correlated with body mass index (r = 0.477; P < 0.01), triglycerides (r = 0.384; P < 0.01), adiponectin plasma levels (r = -0.253; P < 0.01), and age (r = 0.164; P < 0.05), but not with renal function (GFR by iod-thalamate clearance). Patients with previous CV events were significantly older, had higher HOMA-IR and serum triglycerides, and had lower adiponectin plasma levels (all P < 0.05). Logistic regression analysis revealed age (P < 0.001) and adiponectin (P < 0.002) as independent variables related to prevalent CV events. In the prospective study, median follow-up was 54 mo. Patients who experienced CV events had significantly higher serum glucose and lower adiponectin plasma levels (both P < 0.05). In patients with chronic kidney diseases, a syndrome of insulin resistance is present even in the earliest stage of renal dysfunction, and several components of this syndrome are associated with CV events. Moreover, hypoadiponectinemia is a novel putative CV risk factor in patients with mild and moderate renal failure.

Methods of measuring metabolism during surgery in humans: focus on the liver-brain relationship

PURPOSE OF REVIEW

The purpose of this work is to review recent advances in setting methods and models for measuring metabolism during surgery in humans. Surgery, especially solid organ transplantation, may offer unique experimental models in which it is ethically acceptable to gain information on difficult problems of amino acid and protein metabolism.

RECENT FINDINGS

Two areas are reviewed: the metabolic study of the anhepatic phase during liver transplantation and brain microdialysis during cerebral surgery. The first model offers an innovative approach to understand the relative role of liver and extrahepatic organs in gluconeogenesis, and to evaluate whether other organs can perform functions believed to be exclusively or almost exclusively performed by the liver. The second model offers an insight to intracerebral metabolism that is closely bound to that of the liver.

SUMMARY

The recent advances in metabolic research during surgery provide knowledge immediately useful for perioperative patient management and for a better control of surgical stress. The studies during the anhepatic phase of liver transplantation have showed that gluconeogenesis and glutamine metabolism are very active processes outside the liver. One of the critical organs for extrahepatic glutamine metabolism is the brain. Microdialysis studies helped to prove that in humans there is an intense trafficking of glutamine, glutamate and alanine among neurons and astrocytes. This delicate network is influenced by systemic amino acid metabolism. The metabolic dialogue between the liver and the brain is beginning to be understood in this light in order to explain the metabolic events of brain damage during liver failure.