Role of fibroblast growth factor 19 in the control of glucose homeostasis

The role of bile acid metabolism in bone and muscle: from analytics to mechanisms

Osteoporosis and sarcopenia are both common age-related disorders that are associated with increased morbidity and mortality. Bone and muscle are metabolically very active tissues that require large amounts of energy. Bile acids (BAs), a group of liver-derived steroid compounds, are primarily known as emulsifiers that facilitate the resorption of dietary fat and lipids. In addition, they have pleiotropic metabolic functions in lipoprotein and glucose metabolism, inflammation, and intestinal bacterial growth. Through these effects, they are related to metabolic diseases, such as diabetes, hypertriglyceridemia, atherosclerosis, and nonalcoholic steatohepatitis. BAs mediate their metabolic effects through receptor dependent and receptor-independent mechanisms. Emerging evidence suggests that BAs are also involved in bone and muscle metabolism. Under normal circumstances, BAs support bone health by shifting the delicate equilibrium of bone turnover toward bone formation. In contrast, low or excessive amounts of BAs promote bone resorption. In cholestatic liver disease, BAs accumulate in the liver, reach toxic concentrations in the circulation, and thus may contribute to bone loss and muscle wasting. In addition, the measurement of BAs is in rapid evolution with modern mass spectrometry techniques that allow for the detection of a continuously growing number of BAs. This review provides a comprehensive overview of the biochemistry, physiology and measurement of bile acids. Furthermore, it summarizes the existing literature regarding their role in bone and muscle.

Parenteral nutrition-associated liver injury: clinical relevance and mechanistic insights

Intestinal failure-associated liver disease (IFALD) is a relatively common complication in individuals receiving parenteral nutrition (PN). IFALD can be manifested as different types of liver injury, including steatosis, cholestasis, and fibrosis, and could result in liver failure in some cases. The onset and progression of IFALD are highly dependent on various patient and PN-related risk factors. Despite still being under investigation, several mechanisms have been proposed. Liver injury can originate due to caloric overload, nutrient deficiency, and toxicity, as well as phytosterol content, and omega-6 to omega-3 fatty acids ratio contained in lipid emulsions. Additional mechanisms include immature or defective bile acid metabolism, acute heart failure, infections, and sepsis exerting negative effects via Toll-like receptor 4 and nuclear factor κB inflammatory signaling. Furthermore, lack of enteral feeding, gut dysbiosis, and altered enterohepatic circulation that affect the farnesoid x receptor-fibroblast growth factor 19 axis can also contribute to IFALD. Various best practices can be adopted to minimize the risk of developing IFALD, such as prevention and management of central line infections and sepsis, preservation of intestine's length, a switch to oral and enteral feeding, cyclic PN, avoidance of overfeeding and soybean oil-based lipid formulations, and avoiding hepatotoxic substances. The present review thus provides a comprehensive overview of all relevant aspects inherent to IFALD. Further research focused on clinical observations, translational models, and advanced toxicological knowledge frameworks is needed to gain more insight into the molecular pathogenesis of hepatotoxicity, reduce IFALD incidence, and encourage the safe use of PN.

Profile of the bile acid FXR-FGF15 pathway in the glucolipid metabolism disorder of diabetic mice suffering from chronic stress

Background

Imbalances in bile acid (BA) synthesis and metabolism are involved in the onset of diabetes and depression in humans and rodents. However, the role of BAs and the farnesoid X receptor (FXR)/fibroblast growth factor (FGF) 15 signaling pathway in the development of diabetes and depression is still largely unknown. Therefore, we investigated the potential molecular mechanisms of BAs that may be associated with glucolipid metabolism disorders in diabetic mice subjected to chronic stress.

Methods

The type 2 diabetes mellitus (T2DM) mouse model was induced by feeding mice a high-fat diet and administering an intraperitoneal injection of streptozotocin (STZ). The chronic unpredictable mild stress (CUMS) procedure was performed by introducing a series of mild stressors. Forty mice were randomly divided into the regular chow feeding group and the high-fat diet feeding group. After two weeks of feeding, the mice were randomly divided into four groups: the Control group, CUMS group, T2DM group, and T2DM+CUMS group. The T2DM group and T2DM+CUMS group received an intraperitoneal injection of STZ to induce the T2DM model. The CUMS and T2DM+CUMS groups were exposed to CUMS to induce depressive-like phenotypes. Blood and tissue samples were obtained for pertinent analysis and detection.

Results

Compared with the T2DM mice, T2DM+CUMS mice had higher blood glucose and lipid levels, insulin resistance, inflammation of the liver and pancreas, impaired liver function, and increased total bile acids. These changes were accompanied by attenuated FXR signaling. Chronic stress was found to attenuate FXR expression and its downstream target, FGF15, in the ileum when compared with the T2DM group.

Conclusion

FXR may play a role in the diabetic disorder of glucolipid metabolism when aggravated by chronic stress. FXR and its downstream target, FGF15, may be therapeutic targets for treating comorbid T2DM and depression.

Modulation of foraging-like behaviors by cholesterol-FGF19 axis

BACKGROUND

Foraging for food precedes food consumption and is an important component of the overall metabolic programming that regulates feeding. Foraging is governed by central nervous system neuronal circuits but how it is influenced by diet and hormonal signals is still not well understood.

RESULTS

In this study, we show that dietary cholesterol exerted suppressive effects on locomotor activity and that these effects were partially mediated by the neuropeptide Agouti-related protein (AgRP). High dietary cholesterol stimulated intestinal expression of fibroblast growth factor 15 (Fgf15), an ortholog of the human fibroblast growth factor 19 (FGF19). Intracerebroventricular infusion of FGF19 peptide reduced exploratory activity in the open field test paradigm. On the other hand, the lack of dietary cholesterol enhanced exploratory activity in the open field test, but this effect was abolished by central administration of FGF19.

CONCLUSIONS

Experiments in this study show that dietary cholesterol suppresses locomotor activity and foraging-like behaviors, and this regulation is in part mediated by AgRP neurons. Dietary cholesterol or the central action of FGF19 suppresses exploratory behaviors, and the anxiogenic effects of dietary cholesterol may be mediated by the effect of FGF19 in the mouse brain. This study suggests that dietary cholesterol and intestinal hormone FGF15/19 signal a satiating state to the brain, thereby suppressing foraging-like behaviors.

Lessons on Drug Development: A Literature Review of Challenges Faced in Nonalcoholic Fatty Liver Disease (NAFLD) Clinical Trials

NAFLD is the most common chronic liver disease worldwide, occurring in both obese and lean patients. It can lead to life-threatening liver diseases and nonhepatic complications, such as cirrhosis and cardiovascular diseases, that burden public health and the health care system. Current care is weight loss through diet and exercise, which is a challenging goal to achieve. However, there are no FDA-approved pharmacotherapies for NAFLD. This review thoroughly examines the clinical trial findings from 22 drugs (Phase 2 and above) and evaluates the future direction that trials should take for further drug development. These trialed drugs can broadly be categorized into five groups-hypoglycemic, lipid-lowering, bile-pathway, anti-inflammatory, and others, which include nutraceuticals. The multitude of challenges faced in these yet-to-be-approved NAFLD drug trials provided insight into a few areas of improvement worth considering. These include drug repurposing, combinations, noninvasive outcomes, standardization, adverse event alleviation, and the need for precision medicine with more extensive consideration of NAFLD heterogenicity in drug trials. Understandably, every evolution of the drug development landscape lies with its own set of challenges. However, this paper believes in the importance of always learning from lessons of the past, with each potential improvement pushing clinical trials an additional step forward toward discovering appropriate drugs for effective NAFLD management.

Advances in FGFs for diabetes care applications

BACKGROUND

Diabetes mellitus (DM) is an endocrine and metabolic disease caused by a variety of pathogenic factors, including genetic factors, environmental factors and behavior. In recent decades, the number of cases and the prevalence of diabetes have steadily increased, and it has become one of the most threatening diseases to human health in the world. Currently, insulin is the most effective and direct way to control hyperglycemia for diabetes treatment at a low cost. However, hypoglycemia is often a common complication of insulin treatment. Moreover, with the extension of treatment time, insulin resistance, considered the typical adverse symptom, can appear. Therefore, it is urgent to develop new targets and more effective and safer drugs for diabetes treatment to avoid adverse reactions and the insulin tolerance of traditional hypoglycemic drugs.

SCOPE OF REVIEW

In recent years, it has been found that some fibroblast growth factors (FGFs), including FGF1, FGF19 and FGF21, can safely and effectively reduce hyperglycemia and have the potential to be developed as new drugs for the treatment of diabetes. FGF23 is also closely related to diabetes and its complications, which provides a new approach for regulating blood glucose and solving the problem of insulin tolerance.

MAJOR CONCLUSIONS

This article reviews the research progress on the physiology and pharmacology of fibroblast growth factor in the treatment of diabetes. We focus on the application of FGFs in diabetes care and prevention.

The Saga of Endocrine FGFs

Fibroblast growth factors (FGFs) are cell-signaling proteins with diverse functions in cell development, repair, and metabolism. The human FGF family consists of 22 structurally related members, which can be classified into three separate groups based on their action of mechanisms, namely: intracrine, paracrine/autocrine, and endocrine FGF subfamilies. FGF19, FGF21, and FGF23 belong to the hormone-like/endocrine FGF subfamily. These endocrine FGFs are mainly associated with the regulation of cell metabolic activities such as homeostasis of lipids, glucose, energy, bile acids, and minerals (phosphate/active vitamin D). Endocrine FGFs function through a unique protein family called klotho. Two members of this family, α-klotho, or β-klotho, act as main cofactors which can scaffold to tether FGF19/21/23 to their receptor(s) (FGFRs) to form an active complex. There are ongoing studies pertaining to the structure and mechanism of these individual ternary complexes. These studies aim to provide potential insights into the physiological and pathophysiological roles and therapeutic strategies for metabolic diseases. Herein, we provide a comprehensive review of the history, structure–function relationship(s), downstream signaling, physiological roles, and future perspectives on endocrine FGFs.

The Role of FGF19 and MALRD1 in Enterohepatic Bile Acid Signaling

Bile acids are the catabolic end products of cholesterol metabolism that are best known for their role in the digestion of lipids. In the last two decades, extensive investigation has shown bile acids to be important signaling molecules in metabolic processes throughout the body. Bile acids are ligands that can bind to several receptors, including the nuclear receptor farnesoid X receptor (FXR) in ileal enterocytes. FXR activation induces the expression of fibroblast growth factor (FGF) 15/19, a hormone that can modulate bile acid levels, repress gluconeogenesis and lipogenesis, and promote glycogen synthesis. Recent studies have described a novel intestinal protein, MAM and LDL Receptor Class A Domain containing 1 (MALRD1) that positively affects FGF15/19 levels. This signaling pathway presents an exciting target for treating metabolic disease and bile acid-related disorders.

FGFR4: A promising therapeutic target for breast cancer and other solid tumors

The fibroblast growth factor receptor (FGFR) signaling pathway has long been known to cancer researchers because of its role in cell survival, proliferation, migration, and angiogenesis. Dysregulation of FGFR signaling is frequently reported in cancer studies, but most of these studies focus on FGFR1-3. However, there is growing evidence implicating an important and unique role of FGFR4 in oncogenesis, tumor progression, and resistance to anti-tumor therapy in multiple types of cancer. Importantly, there are several novel FGFR4-specific inhibitors in clinical trials, making FGFR4 an attractive target for further research. In this review, we focus on assessing the role of FGFR4 in cancer, with an emphasis on breast cancer. First, the structure, physiological functions and downstream signaling pathways of FGFR4 are introduced. Next, different mechanisms reported to cause aberrant FGFR4 activation and their functions in cancer are discussed, including FGFR4 overexpression, FGF ligand overexpression, FGFR4 somatic hotspot mutations, and the FGFR4 G388R single nucleotide polymorphism. Finally, ongoing and recently completed clinical trials targeting FGFRs in cancer are reviewed, highlighting the therapeutic potential of FGFR4 inhibition for the treatment of breast cancer.

Development and validation of an ambulatory piglet model for short bowel syndrome with ileo-colonic anastomosis

IMPACT STATEMENT

Short bowel syndrome is associated with significant comorbidities and mortality. This study is important as unlike current systems, it provides a validated piglet model which mirrors anatomical, histological, and serological characteristics observed in human SBS. This model can be used to advance knowledge into mechanistic pathways and therapeutic modalities to improve outcomes for SBS patients. This study is novel in that in addition to significant reduction in the remnant bowel and noted liver disease, we also developed a method to emulate ileocecal valve resection and described gut adaptive responses which has important clinical implications in humans.

Physiological and Epigenetic Features of Yoyo Dieting and Weight Control

Obesity and being overweight have become a worldwide epidemic affecting more than 1.9 billion adults and 340 million children. Efforts to curb this global health burden by developing effective long-term non-surgical weight loss interventions continue to fail due to weight regain after weight loss. Weight cycling, often referred to as Yoyo dieting, is driven by physiological counter-regulatory mechanisms that aim at preserving energy, i.e. decreased energy expenditure, increased energy intake, and impaired brain-periphery communication. Models based on genetically determined set points explained some of the weight control mechanisms, but exact molecular underpinnings remained elusive. Today, gene–environment interactions begin to emerge as likely drivers for the obesogenic memory effect associated with weight cycling. Here, epigenetic mechanisms, including histone modifications and DNA methylation, appear as likely factors that underpin long-lasting deleterious adaptations or an imprinted obesogenic memory to prevent weight loss maintenance. The first part summarizes our current knowledge on the physiology of weight cycling by discussing human and murine studies on the Yoyo-dieting phenomenon and physiological adaptations associated with weight loss and weight re-gain. The second part provides an overview on known associations between obesity and epigenetic modifications. We further interrogate the roles of epigenetic mechanisms in the CNS control of cognitive functions as well as reward and addictive behaviors, and subsequently discuss whether such mechanisms play a role in weight control. The final two parts describe major opportunities and challenges associated with studying epigenetic mechanisms in the CNS with its highly heterogenous cell populations, and provide a summary of recent technological advances that will help to delineate whether an obese memory is based upon epigenetic mechanisms.

Biological Activities of Lactose-Based Prebiotics and Symbiosis with Probiotics on Controlling Osteoporosis, Blood-Lipid and Glucose Levels

Lactose-based prebiotics are synthesized by enzymatic- or microbial- biotransformation of lactose and have unique functional values. In this comprehensive review article, the biochemical mechanisms of controlling osteoporosis, blood-lipid, and glucose levels by lactose-based prebiotics and symbiosis with probiotics are reported along with the results of clinical investigations. Interaction between lactose-based prebiotics and probiotics reduces osteoporosis by (a) transforming insoluble inorganic salts to soluble and increasing their absorption to gut wall; (b) maintaining and protecting mineral absorption surface in the intestine; (c) increasing the expression of calcium-binding proteins in the gut wall; (d) remodeling osteoclasts and osteoblasts formation; (e) releasing bone modulating factors; and (f) degrading mineral complexing phytic acid. Lactose-based prebiotics with probiotics control lipid level in the bloodstream and tissue by (a) suppressing the expressions of lipogenic- genes and enzymes; (b) oxidizing fatty acids in muscle, liver, and adipose tissue; (c) binding cholesterol with cell membrane of probiotics and subsequent assimilation by probiotics; (d) enzymatic-transformations of bile acids; and (e) converting cholesterol to coprostanol and its defecation. Symbiosis of lactose-based prebiotics with probiotics affect plasma glucose level by (a) increasing the synthesis of gut hormones plasma peptide-YY, glucagon-like peptide-1 and glucagon-like peptide-2 from entero-endocrine L-cells; (b) altering glucose assimilation and metabolism; (c) suppressing systematic inflammation; (d) reducing oxidative stress; and (e) producing amino acids. Clinical investigations show that lactose-based prebiotic galacto-oligosaccharide improves mineral absorption and reduces hyperlipidemia. Another lactose-based prebiotic, lactulose, improves mineral absorption, and reduces hyperlipidemia and hyperglycemia. It is expected that this review article will be of benefit to food technologists and medical practitioners.

Pharmacological Applications of Bile Acids and Their Derivatives in the Treatment of Metabolic Syndrome

Apart from well-known functions of bile acids in digestion and solubilization of lipophilic nutrients and drugs in the small intestine, the emerging evidence from the past two decades identified the role of bile acids as signaling, endocrine molecules that regulate the glucose, lipid, and energy metabolism through complex and intertwined pathways that are largely mediated by activation of nuclear receptor farnesoid X receptor (FXR) and cell surface G protein-coupled receptor 1, TGR5 (also known as GPBAR1). Interactions of bile acids with the gut microbiota that result in the altered composition of circulating and intestinal bile acids pool, gut microbiota composition and modified signaling pathways, are further extending the complexity of biological functions of these steroid derivatives. Thus, bile acids signaling pathways have become attractive targets for the treatment of various metabolic diseases and metabolic syndrome opening the new potential avenue in their treatment. In addition, there is a significant effort to unveil some specific properties of bile acids relevant to their intrinsic potency and selectivity for particular receptors and to design novel modulators of these receptors with improved pharmacokinetic and pharmacodynamic profiles. This resulted in synthesis of few semi-synthetic bile acids derivatives such as 6α-ethyl-chenodeoxycholic acid (obeticholic acid, OCA), norursodeoxycholic acid (norUDCA), and 12-monoketocholic acid (12-MKC) that are proven to have positive effect in metabolic and hepato-biliary disorders. This review presents an overview of the current knowledge related to bile acids implications in glucose, lipid and energy metabolism, as well as a potential application of bile acids in metabolic syndrome treatment with future perspectives.

Making way for suppressing the FGF19/FGFR4 axis in cancer

FGF19 is a noncanonical FGF ligand that can control a broad spectrum of physiological responses, which include bile acid homeostasis, liver metabolism and glucose uptake. Many of these responses are mediated by FGF19 binding to its FGFR4/β-klotho receptor complex and controlling activation of an array of intracellular signaling events. Overactivation of the FGF19/FGFR4 axis has been implicated in tumorigenic formation, progression and metastasis, and inhibitors of this axis have recently been developed for single agent use or in combination with other anticancer drugs. Considering the critical role of this receptor complex in cancer, this review focuses on recent developments and applications of FGF19/FGFR4-targeted therapeutics.

Increased Bile Acids and FGF19 After Sleeve Gastrectomy and Roux-en-Y Gastric Bypass Correlate with Improvement in Type 2 Diabetes in a Randomized Trial

BACKGROUND

Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) are both effective bariatric procedures to treat type 2 diabetes (T2DM) and obesity. The contribution of changes in bile acids (BAs) and fibroblast growth factor19 (FGF19) to such metabolic improvements is unclear.

METHODS

We examined associations between changes in BAs, FGF19 (fasting and prandial), with changes in body weight, glycemia, and other metabolic variables in 61 obese patients with T2DM before and 1 year after randomization to SG or RYGB.

RESULTS

Weight loss and diabetes remission (defined by HbA1c < 39 mmol/mol [< 5.7%] in the absence of glucose-lowering therapy) after RYGB and SG was similar (mean weight loss - 29 vs - 31 kg, p = 0.50; diabetes remission proportion 37.5 vs 34%, p = 1.0). Greater increments in fasting and prandial levels of total, secondary, and unconjugated BAs were seen after RYGB than SG. Fasting and prandial increases in total (r = - 0.3, p = 0.01; r = - 0.2, p = 0.04), secondary (r = - 0.3, p = 0.01; r = - 0.4, p = 0.01) and unconjugated BA (r = - 0.3, p = 0.01; r = 0.4, p < 0.01) correlated with decreases in HbA1c, but not weight. Changes in 12α-OH/non 12α-OH were positively associated with prandial glucose increments (r = 0.2, p = 0.03), HbA1c (r = 0.3, p = 0.01), and negatively associated with changes in insulinogenc index (r = - 0.3, p = 0.01). Only changes in prandial FGF19 were negatively associated with HbA1c (r = - 0.4, p < 0.01) and visceral fat (r = - 0.3, p = 0.04).

CONCLUSIONS/INTERPRETATION

The association between increases in secondary, unconjugated BAs and improvements in HBA1c (but not weight) achieved after both RYGB and SG suggest manipulation of BA as a potential strategy for controlling T2DM through weight-independent means.

No Gut No Gain! Enteral Bile Acid Treatment Preserves Gut Growth but Not Parenteral Nutrition-Associated Liver Injury in a Novel Extensive Short Bowel Animal Model

BACKGROUND

Parenteral nutrition (PN) provides nutrition intravenously; however, this life-saving therapy is associated with significant liver disease. Recent evidence indicates improvement in PN-associated injury in animals with intact gut treated with enteral bile acid (BA), chenodeoxycholic acid (CDCA), and a gut farnesoid X receptor (FXR) agonist, which drives the gut-liver cross talk (GLCT). We hypothesized that similar improvement could be translated in animals with short bowel syndrome (SBS).

METHODS

Using piglets, we developed a novel 90% gut-resected SBS model. Fifteen SBS piglets receiving PN were given CDCA or control (vehicle control) for 2 weeks. Tissue and serum were analyzed posteuthanasia.

RESULTS

CDCA increased gut FXR (quantitative polymerase chain reaction; P = .008), but not downstream FXR targets. No difference in gut fibroblast growth factor 19 (FGF19; P = .28) or hepatic FXR (P = .75), FGF19 (P = .86), FGFR4 (P = .53), or Cholesterol 7 α-hydroxylase (P = .61) was noted. PN resulted in cholestasis; however, no improvement was noted with CDCA. Hepatic fibrosis or immunostaining for Ki67, CD3, or Cytokeratin 7 was not different with CDCA. PN resulted in gut atrophy. CDCA preserved (P = .04 vs control) gut mass and villous/crypt ratio. The median (interquartile range) for gut mass for control was 0.28 (0.17-0.34) and for CDCA was 0.33 (0.26-0.46).

CONCLUSIONS

We note that, unlike in animals with intact gut, in an SBS animal model there is inadequate CDCA-induced activation of gut-derived signaling to cause liver improvement. Thus, it appears that activation of GLCT is critically dependent on the presence of adequate gut. This is clinically relevant because it suggests that BA therapy may not be as effective for patients with SBS.

FGF19 Contributes to Tumor Progression in Gastric Cancer by Promoting Migration and Invasion

Gastric cancer is the fourth most common type of cancer and second leading cause of cancer-related death in the world. Since patients are often diagnosed at a late stage, very few effective therapies are left in the arsenal. FGF19, as a hormone, has been reported to promote tumor growth in various types of cancer; however, its function in gastric cancer remains unknown. In the current study, we showed that FGF19 is overexpressed in gastric cancer and is associated with depth of invasion, lymph node metastasis, and TNM stage. In addition, in vitro experiments demonstrated that FGF19 is able to enhance migration and invasion abilities of gastric cancer cells. Given its great potency in gastric cancer progression, FGF19 may be an effective target of treatment for advanced gastric cancer patients.

Metabolic effects of basic fibroblast growth factor in streptozotocin-induced diabetic rats: A 1H NMR-based metabolomics investigation

The fibroblast growth factors (FGFs) family shows a great potential in the treatment of diabetes, but little attention is paid to basic FGF (bFGF). In this study, to explore the metabolic effects of bFGF on diabetes, metabolic changes in serum and feces were analyzed in the normal rats, the streptozocin (STZ)-induced diabetic rats and the bFGF-treated diabetic rats using a ¹H nuclear magnetic resonance (NMR)-based metabolomic approach. Interestingly, bFGF treatment significantly decreased glucose, lipid and low density lipoprotein/very low density lipoprotein (LDL/VLDL) levels in serum of diabetic rats. Moreover, bFGF treatment corrected diabetes-induced reductions in citrate, lactate, choline, glycine, creatine, histidine, phenylalanine, tyrosine and glutamine in serum. Fecal propionate was significantly increased after bFGF treatment. Correlation analysis shows that glucose, lipid and LDL/VLDL were significantly negatively correlated with energy metabolites (citrate, creatine and lactate) and amino acids (alanine, glycine, histidine, phenylalanine, tyrosine and glutamine). In addition, a weak but significant correlation was observed between fecal propionate and serum lipid (R = −0.35, P = 0.046). Based on metabolic correlation and pathway analysis, therefore, we suggest that the glucose and lipid lowering effects of bFGF in the STZ-induced diabetic rats may be achieved by activating microbial metabolism, increasing energy metabolism and correcting amino acid metabolism.

Contribution of the distal small intestine to metabolic improvement after bariatric/metabolic surgery: Lessons from ileal transposition surgery

Roux-en Y gastric bypass is a highly effective bariatric/metabolic surgical procedure that can induce robust weight loss and even remission of type 2 diabetes. One of the characteristic consequences of Roux-en Y gastric bypass is the expedited nutrient delivery to the distal small intestine, where L-cells are abundant and bile acid reabsorption occurs. To examine the role of the distal small intestine in isolation from other components of Roux-en Y gastric bypass, the ileal transposition (IT) surgery has been used in various rat models. IT relocates the distal ileal segment to the upper jejunum distal to the ligament of Treitz without any other alterations in the gastrointestinal anatomy. Therefore, IT exposes the distal ileal tissue to ingested nutrients after a meal faster than the normal condition. Although there is some inconsistency in the effect of IT according to different types of rat models and different types of surgical protocols, IT typically improved glucose tolerance, increased insulin sensitivity and induced weight loss, and the findings were more prominent in obese diabetic rats. Suggested mechanisms for the metabolic improvements after IT include increased L-cell secretion (e.g., glucagon-like peptides and peptide YY), altered bile acid metabolism, altered host-microbial interaction, attenuated metabolic endotoxemia and many others. Based on the effect of IT, we can conclude that the contribution of the distal small intestine to the metabolic benefits of bariatric/metabolic surgery is quite considerable. By unveiling the mechanism of action of IT, we might revolutionize the treatment for obesity and type 2 diabetes.

Mechanisms Linking the Gut Microbiome and Glucose Metabolism

This review details potential mechanisms linking gut dysbiosis to metabolic dysfunction, including lipopolysaccharide, bile acids, short chain fatty acids, gut hormones, and branched-chain amino acids.

Increased Expression of FGF19 Contributes to Tumor Progression and Cell Motility of Human Thyroid Cancer

OBJECTIVE

Numerous reports indicate a role for aberrant expression of fibroblast growth factor 19 (FGF19) in tumor development and progression, and several drugs have been developed to target it. The aim of this study was to investigate the clinical significance of FGF19 and examine whether it plays any roles in progression of thyroid cancer.

STUDY DESIGN

Translation research.

SETTING

Navy General Hospital of Chinese PLA, China.

SUBJECTS AND METHODS

Expression patterns of FGF19 protein in 100 paired formalin-fixed and paraffin-embedded cancerous and adjacent noncancerous tissues from patients with thyroid cancer were detected by immunohistochemistry. Then, in vitro migration and invasion assays of siRNA-targeted FGF19-transfected cells were performed.

RESULTS

Positive immunostaining of FGF19 protein expression was localized in cytoplasm with or without membrane of malignant cells and was observed in 82 (82.0%) of 100 patients with thyroid cancer. Statistically, the expression level of FGF19 protein in thyroid cancer tissues was significantly higher than that in normal tissues. In addition, FGF19 overexpression was significantly associated with the advanced tumor node metastasis staging (P = .008), the presence of extrathyroidal invasion (P = .01), lymph nodes metastasis (P = .01), and distant metastasis (P = .02). Furthermore, knockdown of FGF19 by transfection of siRNA-FGF19 could efficiently suppress the migration and invasion abilities of thyroid cancer cells in vitro.

CONCLUSION

Our data revealed that the increased expression of FGF19 might be involved in the malignant behaviors of thyroid cancer, highlighting its potential as a molecular marker for early diagnosis and as a possible target for therapeutic intervention of this disease.

Is fibroblast growth factor receptor 4 a suitable target of cancer therapy?

Fibroblast growth factors (FGF) and their tyrosine kinase receptors (FGFR) support cell proliferation, survival and migration during embryonic development, organogenesis and tissue maintenance and their deregulation is frequently observed in cancer development and progression. Consequently, increasing efforts are focusing on the development of strategies to target FGF/FGFR signaling for cancer therapy. Among the FGFRs the family member FGFR4 is least well understood and differs from FGFRs1-3 in several aspects. Importantly, FGFR4 deletion does not lead to an embryonic lethal phenotype suggesting the possibility that its inhibition in cancer therapy might not cause grave adverse effects. In addition, the FGFR4 kinase domain differs sufficiently from those of FGFRs1-3 to permit development of highly specific inhibitors. The oncogenic impact of FGFR4, however, is not undisputed, as the FGFR4-mediated hormonal effects of several FGF ligands may also constitute a tissue-protective tumor suppressor activity especially in the liver. Therefore it is the purpose of this review to summarize all relevant aspects of FGFR4 physiology and pathophysiology and discuss the options of targeting this receptor for cancer therapy.

Minireview: Roles of Fibroblast Growth Factors 19 and 21 in Metabolic Regulation and Chronic Diseases

Fibroblast growth factor (FGF)19 and FGF21 are hormones that regulate metabolic processes particularly during feeding or starvation, thus ultimately influencing energy production. FGF19 is secreted by the intestines during feeding and negatively regulates bile acid synthesis and secretion, whereas FGF21 is produced in the liver during fasting and plays a crucial role in regulating glucose and lipid metabolism, as well as maintaining energy homeostasis. FGF19 and FGF21 are regarded as late-acting hormones because their functions are only used after insulin and glucagon have completed their actions. Although FGF19 and FGF21 are activated under different conditions, they show extensively functional overlap in terms of improving glucose tolerance, insulin sensitivity, weight loss, and lipid, and energy metabolism, particularly in pathological conditions such as diabetes, obesity, metabolic syndrome, and cardiovascular and renal diseases. Most patients with these metabolic diseases exhibit reduced serum FGF19 levels, which might contribute to its etiology. In addition, the simultaneous increase in serum FGF21 levels is likely a compensatory response to reduced FGF19 levels, and the 2 proteins concertedly maintain metabolic homeostasis. Here, we review the physiological and pharmacological cross talk between FGF19 and FGF21 in relation to the regulation of endocrine metabolism and various chronic diseases.

The physiology underlying Roux-en-Y gastric bypass: a status report

Obesity and its related comorbidities can be detrimental for the affected individual and challenge public health systems worldwide. Currently, the only available treatment options leading to clinically significant and maintained body weight loss and reduction in obesity-related morbidity and mortality are based on surgical interventions. This review will focus on two main clinical effects of Roux-en-Y gastric bypass (RYGB), namely body weight loss and change in eating behavior. Animal experiments designed to understand the underlying physiological mechanisms of these post-gastric bypass effects will be discussed. Where appropriate, reference will also be made to vertical sleeve gastrectomy. While caloric malabsorption and mechanical restriction seem not to be major factors in this respect, alterations in gut hormone levels are invariably found after RYGB. However, their causal role in RYGB effects on eating and body weight has recently been challenged. Other potential factors contributing to the RYGB effects include increased bile acid concentrations and an altered composition of gut microbiota. RYGB is further associated with remarkable changes in preference for different dietary components, such as a decrease in the preference for high fat or sugar. It needs to be noted, however, that in many cases, the question about the necessity of these alterations for the success of bariatric surgery procedures remains unanswered.

Emerging science of the human microbiome

The human gastrointestinal tract hosts a large number of microbial cells which exceed their mammalian counterparts by approximately 3-fold. The genes expressed by these microorganisms constitute the gut microbiome and may participate in diverse functions that are essential to the host, including digestion, regulation of energy metabolism, and modulation of inflammation and immunity. The gut microbiome can be modulated by dietary changes, antibiotic use, or disease. Different ailments have distinct associated microbiomes in which certain species or genes are present in different relative quantities. Thus, identifying specific disease-associated signatures in the microbiome as well as the factors that alter microbial populations and gene expression will lead to the development of new products such as prebiotics, probiotics, antimicrobials, live biotherapeutic products, or more traditional drugs to treat these disorders. Gained knowledge on the microbiome may result in molecular lab tests that may serve as personalized tools to guide the use of the aforementioned products and monitor interventional progress.

Ostα-/- mice exhibit altered expression of intestinal lipid absorption genes, resistance to age-related weight gain, and modestly improved insulin sensitivity

The organic solute transporter OSTα-OSTβ is a key transporter for the efflux of bile acids across the basolateral membrane of ileocytes and the subsequent return of bile acids to the liver. Ostα(-/-) mice exhibit reduced bile acid pools and impaired lipid absorption. In this study, wild-type and Ostα(-/-) mice were characterized at 5 and 12 mo of age. Ostα(-/-) mice were resistant to age-related weight gain, body fat accumulation, and liver and muscle lipid accumulation, and male Ostα(-/-) mice lived slightly longer than wild-type mice. Caloric intake and activity levels were similar for Ostα(-/-) and wild-type male mice. Fecal lipid excretion was increased in Ostα(-/-) mice, indicating that a defect in lipid absorption contributes to decreased fat accumulation. Analysis of genes involved in intestinal lipid absorption revealed changes consistent with decreased dietary lipid absorption in Ostα(-/-) animals. Hepatic expression of cholesterol synthetic genes was upregulated in Ostα(-/-) mice, showing that increased cholesterol synthesis partially compensated for reduced dietary cholesterol absorption. Glucose tolerance was improved in male Ostα(-/-) mice, and insulin sensitivity was improved in male and female Ostα(-/-) mice. Akt phosphorylation was measured in liver and muscle tissue from mice after acute administration of insulin. Insulin responses were significantly larger in male and female Ostα(-/-) than wild-type mice. These findings indicate that loss of OSTα-OSTβ protects against age-related weight gain and insulin resistance.

Cooperation between brain and islet in glucose homeostasis and diabetes

Although a prominent role for the brain in glucose homeostasis was proposed by scientists in the nineteenth century, research throughout most of the twentieth century focused on evidence that the function of pancreatic islets is both necessary and sufficient to explain glucose homeostasis, and that diabetes results from defects of insulin secretion, action or both. However, insulin-independent mechanisms, referred to as 'glucose effectiveness', account for roughly 50% of overall glucose disposal, and reduced glucose effectiveness also contributes importantly to diabetes pathogenesis. Although mechanisms underlying glucose effectiveness are poorly understood, growing evidence suggests that the brain can dynamically regulate this process in ways that improve or even normalize glycaemia in rodent models of diabetes. Here we present evidence of a brain-centred glucoregulatory system (BCGS) that can lower blood glucose levels via both insulin-dependent and -independent mechanisms, and propose a model in which complex and highly coordinated interactions between the BCGS and pancreatic islets promote normal glucose homeostasis. Because activation of either regulatory system can compensate for failure of the other, defects in both may be required for diabetes to develop. Consequently, therapies that target the BCGS in addition to conventional approaches based on enhancing insulin effects may have the potential to induce diabetes remission, whereas targeting just one typically does not.

Dissociation of intestinal and hepatic activities of FXR and LXRα supports metabolic effects of terminal ileum interposition in rodents

The farnesoid X receptor (FXR) and the liver x receptors (LXRs) are bile acid-activated receptors that are highly expressed in the enterohepatic tissues. The mechanisms that support the beneficial effects of bariatric surgery are only partially defined. We have investigated the effects of ileal interposition (IT), a surgical relocation of the distal ileum into the proximal jejunum, on FXR and LXRs in rats. Seven months after surgery, blood concentrations of total bile acids, taurocholic acid, an FXR ligand, and taurohyocholic acid, an LXRα ligand, were significantly increased by IT (P < 0.05). In contrast, liver and intestinal concentrations of conjugated and nonconjugated bile acids were decreased (P < 0.05). These changes were associated with a robust induction of FXR and FXR-regulated genes in the intestine, including Fgf15, a negative regulator of bile acid synthesis. IT repressed the liver expression of glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase (Pepck), two gluconeogenetic genes, along with the expression of LXRα and its target genes sterol regulatory element-binding protein (Srebp) 1c and fatty acid synthase (Fas) in the liver. Treating IT rats with chenodeoxycholic acid ameliorated insulin signaling in the liver. Whether confirmed in human settings, these results support the association of pharmacological therapies with bariatric surgeries to exploit the selective activation of intestinal nuclear receptors.

Serum fibroblast growth factor 19 levels are decreased in Chinese subjects with impaired fasting glucose and inversely associated with fasting plasma glucose levels

OBJECTIVE

Fibroblast growth factor 19 (FGF19), a hormone secreted from the small intestine, has recently been shown to stimulate glycogen synthesis and inhibit gluconeogenesis through insulin-independent pathways. This study investigated the change of FGF19 in prediabetes and newly diagnosed type 2 diabetes mellitus (T2DM) and explored the association of serum FGF19 levels with parameters of glucose metabolism in Chinese subjects.

RESEARCH DESIGN AND METHODS

Fasting serum FGF19 levels were determined by ELISA in 81 normal glucose tolerance (NGT), 91 impaired fasting glucose (IFG), 93 impaired glucose tolerance (IGT), and 104 newly diagnosed T2DM subjects, and their association with parameters of glucose metabolism was studied. An ordinal logistic regression analysis was performed in subjects with NGT, IFG, and T2DM. Serum FGF19 levels at 2 h after a 75-g oral glucose tolerance test in the different glucose tolerance categories were studied in a subgroup.

RESULTS

Fasting serum FGF19 levels in subjects with IFG (210 pg/mL [142-327]) (median [interquartile range]) and T2DM (196 pg/mL [137-280]) were significantly lower than those in NGT subjects (289 pg/mL [224-393]) (both P < 0.001). However, no significant difference in fasting FGF19 levels was observed between IGT (246 pg/mL [138-379]) and NGT subjects. Fasting serum FGF19 levels were negatively associated with fasting plasma glucose and independently associated with the deterioration of glucometabolic status from NGT to IFG and T2DM.

CONCLUSIONS

Fasting serum FGF19 levels were decreased in Chinese subjects with IFG and inversely associated with fasting glucose levels.

Circulating levels of FGF-21 in obese youth: associations with liver fat content and markers of liver damage

OBJECTIVE

Fibroblast growth factor (FGF)-21 is highly expressed in the liver and regulates glucose and lipid metabolism in rodents. The effects of obesity and fatty liver on circulating FGF-21 levels have been described mainly in adults. Herein, we measured plasma FGF-21 levels in lean and obese adolescents with low and high hepatic fat content (HFF% <5.5% and HFF% ≥ 5.5%, respectively) and explored their relationship with hepatic fat content, measures of hepatic apoptosis, and insulin sensitivity.

METHODS

A total of 217 lean and obese adolescents with both low and high HFF% (lean = 31; obese low HFF% = 107; and obese high HFF% = 79) underwent an oral glucose tolerance test, a fast gradient magnetic resonance imaging to measure the %HFF and abdominal fat distribution. Cytokeratin 18 levels were measured as a biomarker of liver apoptosis. A subset of adolescents underwent a 2-step hyperinsulinemic-euglycemic clamp, and a liver biopsy (N = 14), to assess insulin sensitivity and steatohepatitis, respectively.

RESULTS

Compared to controls, FGF-21 levels were higher in obese youth, especially in those with high HFF (P < .001). FGF-21 significantly correlated with adiposity indexes (P < .001), visceral fat (r² = 0.240, P < .001), hepatic fat content (r² = 0.278, P < .001), cytokeratin 18 (r² = 0.217, P < .001), and alanine aminotransferase (r² = .164, P < .001). In subjects with steatoheaptitis, FGF-21 levels significantly correlated with the nonalcoholic fatty liver disease activity score (r² = 0.27, P = .04). Stepwise regression analysis indicated that these relationships are independent of body mass index, visceral fat, and insulin sensitivity. An inverse correlation was documented with insulin, hepatic resistance indexes, and adipose resistance indexes, which disappeared after adjusting for hepatic fat content.

CONCLUSIONS

Plasma FGF-21 levels are increased in obese adolescents, particularly in those with fatty liver. FGF-21 concentrations significantly and independently correlate with hepatic fat content and markers of hepatic apoptosis in obese youths.

Pleiotropic roles of bile acids in metabolism

Enzymatic oxidation of cholesterol generates numerous distinct bile acids that function both as detergents that facilitate digestion and absorption of dietary lipids, and as hormones that activate four distinct receptors. Activation of these receptors alters gene expression in multiple tissues, leading to changes not only in bile acid metabolism but also in glucose homeostasis, lipid and lipoprotein metabolism, energy expenditure, intestinal motility and bacterial growth, inflammation, liver regeneration, and hepatocarcinogenesis. This review covers the roles of specific bile acids, synthetic agonists, and their cognate receptors in controlling these diverse functions, as well as their current use in treating human diseases.