Phosphoinositide 3-Kinase Regulates Glycolysis through Mobilization of Aldolase from the Actin Cytoskeleton.

The phosphoinositide 3-kinase (PI3K) pathway regulates multiple steps in glucose metabolism and also cytoskeletal functions, such as cell movement and attachment. Here, we show that PI3K directly coordinates glycolysis with cytoskeletal dynamics in an AKT-independent manner. Growth factors or insulin stimulate the PI3K-dependent activation of Rac, leading to disruption of the actin cytoskeleton, release of filamentous actin-bound aldolase A, and an increase in aldolase activity. Consistently, PI3K inhibitors, but not AKT, SGK, or mTOR inhibitors, cause a significant decrease in glycolysis at the step catalyzed by aldolase, while activating PIK3CA mutations have the opposite effect. These results point toward a master regulatory function of PI3K that integrates an epithelial cell's metabolism and its form, shape, and function, coordinating glycolysis with the energy-intensive dynamics of actin remodeling.

Fructose: A New Variable to Consider in SIADH and the Hyponatremia Associated With Long-Distance Running?

Fructose has recently been proposed to stimulate vasopressin secretion in humans. Fructose-induced vasopressin secretion is not only postulated to result from ingestion of fructose-containing drinks but may also occur from endogenous fructose production via activation of the polyol pathway. This raises the question of whether fructose might be involved in some cases of vasopressin-induced hyponatremia, especially in situations where the cause is not fully known such as in the syndrome of inappropriate secretion of diuretic hormone (SIADH) and exercise-associated hyponatremia, which has been observed in marathon runners. Here we discuss the new science of fructose and vasopressin, and how it may play a role in some of these conditions, as well as in the complications associated with rapid treatment (such as the osmotic demyelination syndrome). Studies to test the role of fructose could provide new pathophysiologic insights as well as novel potential treatment strategies for these common conditions.

The role of thrifty genes in the origin of alcoholism: A narrative review and hypothesis.

In this narrative review, we present the hypothesis that key mutations in two genes, occurring 15 and 10 million years ago (MYA), were individually and then collectively adaptive for ancestral humans during periods of starvation, but are maladaptive in modern civilization (i.e., "thrifty genes"), with the consequence that these genes not only increase our risk today for obesity, but also for alcoholism. Both mutations occurred when ancestral apes were experiencing loss of fruit availability during periods of profound climate change or environmental upheaval. The silencing of uricase (urate oxidase) activity 15 MYA enhanced survival by increasing the ability for fructose present in dwindling fruit to be stored as fat, a consequence of enhanced uric acid production during fructose metabolism that stimulated lipogenesis and blocked fatty acid oxidation. Likewise, a mutation in class IV alcohol dehydrogenase ~10 MYA resulted in a remarkable 40-fold increase in the capacity to oxidize ethanol (EtOH), which allowed our ancestors to ingest fallen, fermenting fruit. In turn, the EtOH ingested could activate aldose reductase that stimulates the conversion of glucose to fructose, while uric acid produced during EtOH metabolism could further enhance fructose production and metabolism. By aiding survival, these mutations would have allowed our ancestors to generate more fat, primarily from fructose, to survive changing habitats due to the Middle Miocene disruption and also during the late-Miocene aridification of East Africa. Unfortunately, the enhanced ability to metabolize and utilize EtOH may now be acting to increase our risk for alcoholism, which may be yet another consequence of once-adaptive thrifty genes.

Recent advances in the pathogenesis of hereditary fructose intolerance: implications for its treatment and the understanding of fructose-induced non-alcoholic fatty liver disease.

Hereditary fructose intolerance (HFI) is a rare inborn disease characterized by a deficiency in aldolase B, which catalyzes the cleavage of fructose 1,6-bisphosphate and fructose 1-phosphate (Fru 1P) to triose molecules. In patients with HFI, ingestion of fructose results in accumulation of Fru 1P and depletion of ATP, which are believed to cause symptoms, such as nausea, vomiting, hypoglycemia, and liver and kidney failure. These sequelae can be prevented by a fructose-restricted diet. Recent studies in aldolase B-deficient mice and HFI patients have provided more insight into the pathogenesis of HFI, in particular the liver phenotype. Both aldolase B-deficient mice (fed a very low fructose diet) and HFI patients (treated with a fructose-restricted diet) displayed greater intrahepatic fat content when compared to controls. The liver phenotype in aldolase B-deficient mice was prevented by reduction in intrahepatic Fru 1P concentrations by crossing these mice with mice deficient for ketohexokinase, the enzyme that catalyzes the synthesis of Fru 1P. These new findings not only provide a potential novel treatment for HFI, but lend insight into the pathogenesis of fructose-induced non-alcoholic fatty liver disease (NAFLD), which has raised to epidemic proportions in Western society. This narrative review summarizes the most recent advances in the pathogenesis of HFI and discusses the implications for the understanding and treatment of fructose-induced NAFLD.

Fructose Production and Metabolism in the Kidney.

Understanding fructose metabolism might provide insights to renal pathophysiology. To support systemic glucose concentration, the proximal tubular cells reabsorb fructose as a substrate for gluconeogenesis. However, in instances when fructose intake is excessive, fructose metabolism is costly, resulting in energy depletion, uric acid generation, inflammation, and fibrosis in the kidney. A recent scientific advance is the discovery that fructose can be endogenously produced from glucose under pathologic conditions, not only in kidney diseases, but also in diabetes, in cardiac hypertrophy, and with dehydration. Why humans have such a deleterious mechanism to produce fructose is unknown, but it may relate to an evolutionary benefit in the past. In this article, we aim to illuminate the roles of fructose as it relates to gluconeogenesis and fructoneogenesis in the kidney.

Osmotic Nephrosis and Acute Kidney Injury Associated With SGLT2 Inhibitor Use: A Case Report.

We report a case of a patient who developed dialysis-requiring acute kidney injury (AKI) after the use of canagliflozin. A 66-year-old man with type 2 diabetes who was recovering from left knee septic arthritis at a rehabilitation facility was admitted with oliguric AKI 5 days after starting treatment with canagliflozin, an inhibitor of sodium/glucose cotransporter 2 (SGLT2). The patient presented with hematuria, non-nephrotic-range proteinuria, and serum creatinine level of 6.8 (baseline, 1.1-1.3) mg/dL. There was no recent use of radiocontrast agents or exposure to other nephrotoxins. The patient subsequently required hemodialysis. Due to recent antibiotic use (ampicillin-sulbactam), acute interstitial nephritis was considered in the differential diagnosis. Kidney biopsy was performed, which showed the presence of osmotic nephropathy. The patient's kidney function returned to baseline after 2 weeks of hemodialysis. This case provides evidence of an association of osmotic nephropathy with the use of canagliflozin and discusses potential mechanisms. We recommend kidney biopsy for cases of severe AKI associated with SGLT2 inhibitors to better understand the relationship of this complication with the use of this class of medications.

Increase of core temperature affected the progression of kidney injury by repeated heat stress exposure.

An epidemic of chronic kidney disease of unknown etiology (Mesoamerican nephropathy) has emerged in hot regions of Central America. We have demonstrated that dehydration associated with recurrent heat exposure causes chronic kidney disease in animal models. However, the independent influence of core body temperature on kidney injury has not been explored. In the present study, we tested the hypothesis that kidney injury could be accelerated by increasing body temperature independent of external temperature. Wild-type mice were exposed to heat (39.5°C, 30 min, 2 times daily) with or without the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) for 10 days. Core temperature, renal function, proteinuria, and renal histological and biochemical analyses were performed. Isolated mitochondria markers of oxidative stress were evaluated from kidney tissue. DNP increased body core temperature in response to heat by 1°C (42 vs. 41°C), which was transient. The mild increase in temperature correlated with worsening albuminuria (R = 0.715, P < 001), renal tubular injury, and interstitial infiltration of monocytes/macrophages. Tubular injury was marked in the outer medulla. This was associated with a reduction in kidney tissue ATP levels (nonheated control: 16.71 ± 1.33 nmol/mg and DNP + heat: 13.08 ± 1.12 nmol/mg, P < 0.01), reduced mitochondria, and evidence for mitochondrial oxidative stress. The results of the present study suggest that kidney injury in heat stress is markedly worsened by increasing core temperature. This is consistent with the hypothesis that clinical and subclinical heat stroke may play a role in Mesoamerican nephropathy.

Climate Change and the Kidney.

The worldwide increase in temperature has resulted in a marked increase in heat waves (heat extremes) that carries a markedly increased risk for morbidity and mortality. The kidney has a unique role not only in protecting the host from heat and dehydration but also is an important site of heat-associated disease. Here we review the potential impact of global warming and heat extremes on kidney diseases. High temperatures can result in increased core temperatures, dehydration, and blood hyperosmolality. Heatstroke (both clinical and subclinical whole-body hyperthermia) may have a major role in causing both acute kidney disease, leading to increased risk of acute kidney injury from rhabdomyolysis, or heat-induced inflammatory injury to the kidney. Recurrent heat and dehydration can result in chronic kidney disease (CKD) in animals and theoretically plays a role in epidemics of CKD developing in hot regions of the world where workers are exposed to extreme heat. Heat stress and dehydration also has a role in kidney stone formation, and poor hydration habits may increase the risk for recurrent urinary tract infections. The resultant social and economic consequences include disability and loss of productivity and employment. Given the rise in world temperatures, there is a major need to better understand how heat stress can induce kidney disease, how best to provide adequate hydration, and ways to reduce the negative effects of chronic heat exposure.

Fructose and sugar: A major mediator of non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome; its rising prevalence parallels the rise in obesity and diabetes. Historically thought to result from overnutrition and a sedentary lifestyle, recent evidence suggests that diets high in sugar (from sucrose and/or high-fructose corn syrup [HFCS]) not only increase the risk of NAFLD, but also non-alcoholic steatohepatitis (NASH). Herein, we review the experimental and clinical evidence that fructose precipitates fat accumulation in the liver, due to both increased lipogenesis and impaired fat oxidation. Recent evidence suggests that the predisposition to fatty liver is linked to the metabolism of fructose by fructokinase C, which results in ATP consumption, nucleotide turnover and uric acid generation that mediate fat accumulation. Alterations to gut permeability, the microbiome, and associated endotoxemia contribute to the risk of NAFLD and NASH. Early clinical studies suggest that reducing sugary beverages and total fructose intake, especially from added sugars, may have a significant benefit on reducing hepatic fat accumulation. We suggest larger, more definitive trials to determine if lowering sugar/HFCS intake, and/or blocking uric acid generation, may help reduce NAFLD and its downstream complications of cirrhosis and chronic liver disease.

Role of fructose and fructokinase in acute dehydration-induced vasopressin gene expression and secretion in mice.

Fructose stimulates vasopressin in humans and can be generated endogenously by activation of the polyol pathway with hyperosmolarity. We hypothesized that fructose metabolism in the hypothalamus might partly control vasopressin responses after acute dehydration. Wild-type and fructokinase-knockout mice were deprived of water for 24 h. The supraoptic nucleus was evaluated for vasopressin and markers of the aldose reductase-fructokinase pathway. The posterior pituitary vasopressin and serum copeptin levels were examined. Hypothalamic explants were evaluated for vasopressin secretion in response to exogenous fructose. Water restriction increased serum and urine osmolality and serum copeptin in both groups of mice, although the increase in copeptin in wild-type mice was larger than that in fructokinase-knockout mice. Water-restricted, wild-type mice showed an increase in vasopressin and aldose reductase mRNA, sorbitol, fructose and uric acid in the supraoptic nucleus. In contrast, fructokinase-knockout mice showed no change in vasopressin or aldose reductase mRNA, and no changes in sorbitol or uric acid, although fructose levels increased. With water restriction, vasopressin in the pituitary of wild-type mice was significantly less than that of fructokinase-knockout mice, indicating that fructokinase-driven vasopressin secretion overrode synthesis. Fructose increased vasopressin release in hypothalamic explants that was not observed in fructokinase-knockout mice. In situ hybridization documented fructokinase mRNA in the supraoptic nucleus, paraventricular nucleus and suprachiasmatic nucleus. Acute dehydration activates the aldose reductase-fructokinase pathway in the hypothalamus and partly drives the vasopressin response. Exogenous fructose increases vasopressin release in hypothalamic explants dependent on fructokinase. Nevertheless, circulating vasopressin is maintained and urinary concentrating is not impaired. NEW & NOTEWORTHY: This study increases our understanding of the mechanisms leading to vasopressin release under conditions of water restriction (acute dehydration). Specifically, these studies suggest that the aldose reductase-fructokinase pathways may be involved in vasopressin synthesis in the hypothalamus and secretion by the pituitary in response to acute dehydration. Nevertheless, mice undergoing water restriction remain capable of maintaining sufficient vasopressin (copeptin) levels to allow normal urinary concentration. Further studies of the aldose reductase-fructokinase system in vasopressin regulation appear indicated.

Enzyme Substrate Specificity Conferred by Distinct Conformational Pathways.

Substrate recognition is one of the hallmarks of enzyme catalysis. Enzyme conformational changes have been linked to selectivity between substrates with little direct evidence. Aldolase, a glycolytic enzyme, must distinguish between two physiologically important substrates, fructose 1-phosphate and fructose 1,6-bisphosphate, and provides an excellent model system for the study of this question. Previous work has shown that isozyme specific residues (ISRs) distant from the active site are responsible for kinetic distinction between these substrates. Notably, most of the ISRs reside in a cluster of five surface α-helices, and the carboxyl-terminal region (CTR), and cooperative interactions among these helices have been demonstrated. To test the hypothesis that conformational changes are at the root of these changes, single surface-cysteine variants were created with the cysteine located on helices of the cluster and CTR. This allowed for site-specific labeling with an environmentally sensitive fluorophore, and subsequent monitoring of conformational changes by fluorescence emission spectrophotometry. These labeled variants revealed different spectra in the presence of saturating amounts of each substrate, which suggested the occurrence of different conformations. Emission spectra collected at various substrate concentrations showed a concentration dependence of the fluorescence spectra, consistent with binding events. Lastly, stopped-flow fluorescence spectrophotometry showed that the rate of these fluorescence changes was on the same time-scale as catalysis, thus suggesting a link between the different fluorescence changes and events during catalysis. On the basis of these results, we propose that different conformational changes may be a common mechanism for dictating substrate specificity in other enzymes with multiple substrates.

Aldolase-B knockout in mice phenocopies hereditary fructose intolerance in humans.

The rise in fructose consumption, and its correlation with symptoms of metabolic syndrome (MBS), has highlighted the need for a better understanding of fructose metabolism. To that end, valid rodent models reflecting the same metabolism as in humans, both biochemically and physiologically, are critical. A key to understanding any type of metabolism comes from study of disease states that affect such metabolism. A serious defect of fructose metabolism is the autosomal recessive condition called hereditary fructose intolerance (HFI), caused by mutations in the human aldolase B gene (Aldob). Those afflicted with HFI experience liver and kidney dysfunction after fructose consumption, which can lead to death, particularly during infancy. With very low levels of fructose exposure, HFI patients develop non-alcoholic fatty acid liver disease and fibrosis, sharing liver pathologies also seen in MBS. A major step toward establishing that fructose metabolism in mice mimics that of humans is reported by investigating the consequences of targeting the mouse aldolase-B gene (Aldo2) for deletion in mice (Aldo2(-/-)). The Aldo2(-/-) homozygous mice show similar pathology following exposure to fructose as humans with HFI such as failure to thrive, liver dysfunction, and potential morbidity. Establishing that this mouse reflects the symptoms of HFI in humans is critical for comparison of rodent studies to the human condition, where this food source is increasing, and increasingly controversial. This animal should provide a valuable resource for answering remaining questions about fructose metabolism in HFI, as well as help investigate the biochemical mechanisms leading to liver pathologies seen in MBS from high fructose diets.

Michaelis-like complex of mouse ketohexokinase isoform C.

Over the past forty years there has been a drastic increase in fructose-related diseases, including obesity, heart disease and diabetes. Ketohexokinase (KHK), the first enzyme in the liver fructolysis pathway, catalyzes the ATP-dependent phosphorylation of fructose to fructose 1-phosphate. Understanding the role of KHK in disease-related processes is crucial for the management and prevention of this growing epidemic. Molecular insight into the structure-function relationship in ligand binding and catalysis by KHK is needed for the design of therapeutic inhibitory ligands. Ketohexokinase has two isoforms: ketohexokinase A (KHK-A) is produced ubiquitously at low levels, whereas ketohexokinase C (KHK-C) is found at much higher levels, specifically in the liver, kidneys and intestines. Structures of the unliganded and liganded human isoforms KHK-A and KHK-C are known, as well as structures of unliganded and inhibitor-bound mouse KHK-C (mKHK-C), which shares 90% sequence identity with human KHK-C. Here, a high-resolution X-ray crystal structure of mKHK-C refined to 1.79 Šresolution is presented. The structure was determined in a complex with both the substrate fructose and the product of catalysis, ADP, providing a view of the Michaelis-like complex of the mouse ortholog. Comparison to unliganded structures suggests that KHK undergoes a conformational change upon binding of substrates that places the enzyme in a catalytically competent form in which the ß-sheet domain from one subunit rotates by 16.2°, acting as a lid for the opposing active site. Similar kinetic parameters were calculated for the mouse and human enzymes and indicate that mice may be a suitable animal model for the study of fructose-related diseases. Knowledge of the similarity between the mouse and human enzymes is important for understanding preclinical efforts towards targeting this enzyme, and this ground-state, Michaelis-like complex suggests that a conformational change plays a role in the catalytic function of KHK-C.

Activation of AMPD2 drives metabolic dysregulation and liver disease in mice with hereditary fructose intolerance.

Hereditary fructose intolerance (HFI) is a painful and potentially lethal genetic disease caused by a mutation in aldolase B resulting in accumulation of fructose-1-phosphate (F1P). No cure exists for HFI and treatment is limited to avoid exposure to fructose and sugar. Using aldolase B deficient mice, here we identify a yet unrecognized metabolic event activated in HFI and associated with the progression of the disease. Besides the accumulation of F1P, here we show that the activation of the purine degradation pathway is a common feature in aldolase B deficient mice exposed to fructose. The purine degradation pathway is a metabolic route initiated by adenosine monophosphate deaminase 2 (AMPD2) that regulates overall energy balance. We demonstrate that very low amounts of fructose are sufficient to activate AMPD2 in these mice via a phosphate trap. While blocking AMPD2 do not impact F1P accumulation and the risk of hypoglycemia, its deletion in hepatocytes markedly improves the metabolic dysregulation induced by fructose and corrects fat and glycogen storage while significantly increasing the voluntary tolerance of these mice to fructose. In summary, we provide evidence for a critical pathway activated in HFI that could be targeted to improve the metabolic consequences associated with fructose consumption.

Hepatic glucokinase regulatory protein and carbohydrate response element binding protein attenuation reduce de novo lipogenesis but do not mitigate intrahepatic triglyceride accumulation in Aldob deficiency.

OBJECTIVE: Stable isotope studies have shown that hepatic de novo lipogenesis (DNL) plays an important role in the pathogenesis of intrahepatic lipid (IHL) deposition. Furthermore, previous research has demonstrated that fructose 1-phosphate (F1P) not only serves as a substrate for DNL, but also acts as a signalling metabolite that stimulates DNL from glucose. The aim of this study was to elucidate the mediators of F1P-stimulated DNL, with special focus on two key regulators of intrahepatic glucose metabolism, i.e., glucokinase regulatory protein (GKRP) and carbohydrate response element binding protein (ChREBP). METHODS: Aldolase B deficient mice (Aldob-/-), characterized by hepatocellular F1P accumulation, enhanced DNL, and hepatic steatosis, were either crossed with GKRP deficient mice (Gckr-/-) or treated with short hairpin RNAs directed against hepatic ChREBP. RESULTS: Aldob-/- mice showed higher rates of de novo palmitate synthesis from glucose when compared to wildtype mice (p < 0.001). Gckr knockout reduced de novo palmitate synthesis in Aldob-/- mice (p = 0.017), without affecting the hepatic mRNA expression of enzymes involved in DNL. In contrast, hepatic ChREBP knockdown normalized the hepatic mRNA expression levels of enzymes involved in DNL and reduced fractional DNL in Aldob-/- mice (p < 0.05). Of interest, despite downregulation of DNL in response to Gckr and ChREBP attenuation, no reduction in intrahepatic triglyceride levels was observed. CONCLUSIONS: Both GKRP and ChREBP mediate F1P-stimulated DNL in aldolase B deficient mice. Further studies are needed to unravel the role of GKRP and hepatic ChREBP in regulating IHL accumulation in aldolase B deficiency.

Targeting of several glycolytic enzymes using RNA interference reveals aldolase affects cancer cell proliferation through a non-glycolytic mechanism.

In cancer, glucose uptake and glycolysis are increased regardless of the oxygen concentration in the cell, a phenomenon known as the Warburg effect. Several (but not all) glycolytic enzymes have been investigated as potential therapeutic targets for cancer treatment using RNAi. Here, four previously untargeted glycolytic enzymes, aldolase A, glyceraldehyde 3-phosphate dehydrogenase, triose phosphate isomerase, and enolase 1, are targeted using RNAi in Ras-transformed NIH-3T3 cells. Of these enzymes, knockdown of aldolase causes the greatest effect, inhibiting cell proliferation by 90%. This defect is rescued by expression of exogenous aldolase. However, aldolase knockdown does not affect glycolytic flux or intracellular ATP concentration, indicating a non-metabolic cause for the cell proliferation defect. Furthermore, this defect could be rescued with an enzymatically dead aldolase variant that retains the known F-actin binding ability of aldolase. One possible model for how aldolase knockdown may inhibit transformed cell proliferation is through its disruption of actin-cytoskeleton dynamics in cell division. Consistent with this hypothesis, aldolase knockdown cells show increased multinucleation. These results are compared with other studies targeting glycolytic enzymes with RNAi in the context of cancer cell proliferation and suggest that aldolase may be a useful target in the treatment of cancer.

Aldolase sequesters WASP and affects WASP/Arp2/3-stimulated actin dynamics.

In addition to its roles in sugar metabolism, fructose-1,6-bisphosphate aldolase (aldolase) has been implicated in cellular functions independent from these roles, termed "moonlighting functions." These moonlighting functions likely involve the known aldolase-actin interaction, as many proteins with which aldolase interacts are involved in actin-dependent processes. Specifically, aldolase interacts both in vitro and in cells with Wiskott-Aldrich Syndrome Protein (WASP), a protein involved in controlling actin dynamics, yet the function of this interaction remains unknown. Here, the effect of aldolase on WASP-dependent processes in vitro and in cells is investigated. Aldolase inhibits WASP/Arp2/3-dependent actin polymerization in vitro. In cells, knockdown of aldolase results in a decreased rate of cell motility and cell spreading, two WASP-dependent processes. Expression of exogenous aldolase rescues these defects. Whether these effects of aldolase on WASP-dependent processes were due to aldolase catalysis or moonlighting functions is tested using aldolase variants defective in either catalytic or actin-binding activity. While the actin-binding deficient aldolase variant is unable to inhibit actin polymerization in vitro and is unable to rescue cell motility defects in cells, the catalytically inactive aldolase is able to perform these functions, providing evidence that aldolase moonlighting plays a role in WASP-mediated processes.

Endogenous Fructose Production and Metabolism Drive Metabolic Dysregulation and Liver Disease in Mice with Hereditary Fructose Intolerance.

Excessive intake of sugar, and particularly fructose, is closely associated with the development and progression of metabolic syndrome in humans and animal models. However, genetic disorders in fructose metabolism have very different consequences. While the deficiency of fructokinase, the first enzyme involved in fructose metabolism, is benign and somewhat desirable, missense mutations in the second enzyme, aldolase B, causes a very dramatic and sometimes lethal condition known as hereditary fructose intolerance (HFI). To date, there is no cure for HFI, and treatment is limited to avoiding fructose and sugar. Because of this, for subjects with HFI, glucose is their sole source of carbohydrates in the diet. However, clinical symptoms still occur, suggesting that either low amounts of fructose are still being consumed or, alternatively, fructose is being produced endogenously in the body. Here, we demonstrate that as a consequence of consuming high glycemic foods, the polyol pathway, a metabolic route in which fructose is produced from glucose, is activated, triggering a deleterious mechanism whereby glucose, sorbitol and alcohol induce severe liver disease and growth retardation in aldolase B knockout mice. We show that generically and pharmacologically blocking this pathway significantly improves metabolic dysfunction and thriving and increases the tolerance of aldolase B knockout mice to dietary triggers of endogenous fructose production.

Could Alzheimer's disease be a maladaptation of an evolutionary survival pathway mediated by intracerebral fructose and uric acid metabolism?

An important aspect of survival is to assure enough food, water, and oxygen. Here, we describe a recently discovered response that favors survival in times of scarcity, and it is initiated by either ingestion or production of fructose. Unlike glucose, which is a source for immediate energy needs, fructose metabolism results in an orchestrated response to encourage food and water intake, reduce resting metabolism, stimulate fat and glycogen accumulation, and induce insulin resistance as a means to reduce metabolism and preserve glucose supply for the brain. How this survival mechanism affects brain metabolism, which in a resting human amounts to 20% of the overall energy demand, is only beginning to be understood. Here, we review and extend a previous hypothesis that this survival mechanism has a major role in the development of Alzheimer's disease and may account for many of the early features, including cerebral glucose hypometabolism, mitochondrial dysfunction, and neuroinflammation. We propose that the pathway can be engaged in multiple ways, including diets high in sugar, high glycemic carbohydrates, and salt. In summary, we propose that Alzheimer's disease may be the consequence of a maladaptation to an evolutionary-based survival pathway and what had served to enhance survival acutely becomes injurious when engaged for extensive periods. Although more studies are needed on the role of fructose metabolism and its metabolite, uric acid, in Alzheimer's disease, we suggest that both dietary and pharmacologic trials to reduce fructose exposure or block fructose metabolism should be performed to determine whether there is potential benefit in the prevention, management, or treatment of this disease.

Fructose might be a clue to the origin of preeclampsia insights from nature and evolution.

Preeclampsia is a hypertensive disorder of pregnancy and is due to abnormal placentation. The pathogenesis remains unclear. Fructose is biologically distinct from glucose and has a critical role in fetal growth in early pregnancy. Many species, including humans, produce fructose in their placenta during the first trimester to assist fetal growth and survival during a time when hypoxia is significant. Fructose is preferred over glucose in hypoxic tissues, and in the developing fetus, fructose has a critical role in stimulating the production of nucleic acids, lipids and glycosaminoglycans. Fructose production normally decreases significantly following the establishment of maternal-fetal circulation following placentation. However, if there is impaired placentation, local hypoxia will continue to drive fructose production. Excessive fructose metabolism drives endothelial dysfunction, oxidative stress, elevated blood pressure, insulin resistance, fatty liver, and a rise in uric acid and vasopressin levels, all of which are features of the preeclamptic state. In addition to fructose production, dietary fructose, for example, from soft drinks, would be additive and has been reported to be a strong independent risk factor for preeclampsia. Uric acid-associated endothelial dysfunction disturbs the invasion of the spiral artery, leading to placental ischemia and further placental hypoxia. Here, we summarize the previous literature regarding the physiological and pathological roles of fructose in pregnancy and propose studies to further investigate the pathogenesis of preeclampsia. Fructose might be a Clue to the Origin of Preeclampsia Insights from Nature and Evolution Preeclampsia is a hypertensive disorder of pregnancy. The pathogenesis remains unclear. Fructose has a critical role in fetal growth in early pregnancy, and might be a key role to developing preeclampsia. Here, we summarize the previous literatures regarding the physiological andpathological roles of fructose in pregnancy to propose studies to further investigate the pathogenesis of preeclampsia.