The fructose survival hypothesis for obesity

The fructose survival hypothesis proposes that obesity and metabolic disorders may have developed from over-stimulation of an evolutionary-based biologic response (survival switch) that aims to protect animals in advance of crisis. The response is characterized by hunger, thirst, foraging, weight gain, fat accumulation, insulin resistance, systemic inflammation and increased blood pressure. The process is initiated by the ingestion of fructose or by stimulating endogenous fructose production via the polyol pathway. Unlike other nutrients, fructose reduces the active energy (adenosine triphosphate) in the cell, while blocking its regeneration from fat stores. This is mediated by intracellular uric acid, mitochondrial oxidative stress, the inhibition of AMP kinase and stimulation of vasopressin. Mitochondrial oxidative phosphorylation is suppressed, and glycolysis stimulated. While this response is aimed to be modest and short-lived, the response in humans is exaggerated due to gain of 'thrifty genes' coupled with a western diet rich in foods that contain or generate fructose. We propose excessive fructose metabolism not only explains obesity but the epidemics of diabetes, hypertension, non-alcoholic fatty liver disease, obesity-associated cancers, vascular and Alzheimer's dementia, and even ageing. Moreover, the hypothesis unites current hypotheses on obesity. Reducing activation and/or blocking this pathway and stimulating mitochondrial regeneration may benefit health-span. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

A new ape from Türkiye and the radiation of late Miocene hominines

Fossil apes from the eastern Mediterranean are central to the debate on African ape and human (hominine) origins. Current research places them either as hominines, as hominins (humans and our fossil relatives) or as stem hominids, no more closely related to hominines than to pongines (orangutans and their fossil relatives). Here we show, based on our analysis of a newly identified genus, Anadoluvius, from the 8.7 Ma site of Çorakyerler in central Anatolia, that Mediterranean fossil apes are diverse, and are part of the first known radiation of early members of the hominines. The members of this radiation are currently only identified in Europe and Anatolia; generally accepted hominins are only found in Africa from the late Miocene until the Pleistocene. Hominines may have originated in Eurasia during the late Miocene, or they may have dispersed into Eurasia from an unknown African ancestor. The diversity of hominines in Eurasia suggests an in situ origin but does not exclude a dispersal hypothesis.

Sugar, salt, immunity and the cause of primary hypertension

Despite its discovery more than 150 years ago, the cause of primary hypertension remains unknown. Most studies suggest that hypertension involves genetic, congenital or acquired risk factors that result in a relative inability of the kidney to excrete salt (sodium chloride) in the kidneys. Here we review recent studies that suggest there may be two phases, with an initial phase driven by renal vasoconstriction that causes low-grade ischemia to the kidney, followed by the infiltration of immune cells that leads to a local autoimmune reaction that maintains the renal vasoconstriction. Evidence suggests that multiple mechanisms could trigger the initial renal vasoconstriction, but one way may involve fructose that is provided in the diet (such as from table sugar or high fructose corn syrup) or produced endogenously. The fructose metabolism increases intracellular uric acid, which recruits NADPH oxidase to the mitochondria while inhibiting AMP-activated protein kinase. A drop in intracellular ATP level occurs, triggering a survival response. Leptin levels rise, triggering activation of the sympathetic central nervous system, while vasopressin levels rise, causing vasoconstriction in its own right and stimulating aldosterone production via the vasopressin 1b receptor. Low-grade renal injury and autoimmune-mediated inflammation occur. High-salt diets can amplify this process by raising osmolality and triggering more fructose production. Thus, primary hypertension may result from the overactivation of a survival response triggered by fructose metabolism. Restricting salt and sugar and hydrating with ample water may be helpful in the prevention of primary hypertension.

Evolutionary success of the thrifty genotype depends on both behavioral adaptations and temporal variability in the food environment

Obesity is a result of a long-term energy imbalance due to decisions associated with energy intake and expenditure. Those decisions fit the definition of heuristics: cognitive processes with a rapid and effortless implementation which can be very effective in dealing with scenarios that threaten an organism's viability. We study the implementation and evaluation of heuristics, and their associated actions, using agent-based simulations in environments where the distribution and degree of richness of energetic resources is varied in space and time. Artificial agents utilize foraging strategies, combining movement, active perception, and consumption, while also actively modifying their capacity to store energy-a "thrifty gene" effect-based on three different heuristics. We show that the selective advantage associated with higher energy storage capacity depends on both the agent's foraging strategy and heuristic, as well as being sensitive to the distribution of resources, with the existence and duration of periods of food abundance and scarcity being crucial. We conclude that a "thrifty genotype" is only beneficial in the presence of behavioral adaptations that encourage overconsumption and sedentariness, as well as seasonality and uncertainty in the food distribution.

Smart Bandaid Integrated with Fully Textile OECT for Uric Acid Real-Time Monitoring in Wound Exudate

Hard-to-heal wounds (i.e., severe and/or chronic) are typically associated with particular pathologies or afflictions such as diabetes, immunodeficiencies, compression traumas in bedridden people, skin grafts, or third-degree burns. In this situation, it is critical to constantly monitor the healing stages and the overall wound conditions to allow for better-targeted therapies and faster patient recovery. At the moment, this operation is performed by removing the bandages and visually inspecting the wound, putting the patient at risk of infection and disturbing the healing stages. Recently, new devices have been developed to address these issues by monitoring important biomarkers related to the wound health status, such as pH, moisture, etc. In this contribution, we present a novel textile chemical sensor exploiting an organic electrochemical transistor (OECT) configuration based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) for uric acid (UA)-selective monitoring in wound exudate. The combination of special medical-grade textile materials provides a passive sampling system that enables the real-time and non-invasive analysis of wound fluid: UA was detected as a benchmark analyte to monitor the health status of wounds since it represents a relevant biomarker associated with infections or necrotization processes in human tissues. The sensors proved to reliably and reversibly detect UA concentration in synthetic wound exudate in the biologically relevant range of 220-750 μM, operating in flow conditions for better mimicking the real wound bed. This forerunner device paves the way for smart bandages integrated with real-time monitoring OECT-based sensors for wound-healing evaluation.

The Good, the Bad and the New about Uric Acid in Cancer

Simple Summary

The concentration of uric acid in blood is sex-, age- and diet-dependent and is maintained close to its maximal solubility, indicating that it plays some important role. Indeed, it has been demonstrated that, at physiological concentrations, uric acid is a powerful antioxidant and is a scavenger of singlet oxygen and radicals. At high intracellular concentration, uric acid has been demonstrated to act as a pro-oxidant molecule. Recently, uric acid has been reported to affect the properties of several proteins involved in metabolic regulation and signaling, and the relationship between uric acid and cancer has been extensively investigated. In this review, we present the most recent results on the positive and negative effects played by uric acid in cancer and some new findings and hypotheses about the implication of this metabolite in the pathogenesis of several diseases such as metabolic syndrome, diabetes, and inflammation, thus favoring the development of cancer.

Abstract

Uric acid is the final product of purine catabolism in man and apes. The serum concentration of uric acid is sex-, age- and diet-dependent and is maintained close to its maximal solubility, indicating that it plays some important role. Indeed, it has been demonstrated that, at physiological concentrations, uric acid is a powerful antioxidant, while at high intracellular concentrations, it is a pro-oxidant molecule. In this review, we describe the possible causes of uric acid accumulation or depletion and some of the metabolic and regulatory pathways it may impact. Particular attention has been given to fructose, which, because of the complex correlation between carbohydrate and nucleotide metabolism, causes uric acid accumulation. We also present recent results on the positive and negative effects played by uric acid in cancer and some new findings and hypotheses about the implication of this metabolite in a variety of signaling pathways, which can play a role in the pathogenesis of diseases such as metabolic syndrome, diabetes, and inflammation, thus favoring the development of cancer. The loss of uricase in Homo sapiens and great apes, although exposing these species to the potentially adverse effects of uric acid, appears to be associated with evolutionary advantages.

Do thrifty genes exist? Revisiting uricase

Sixty years ago, the geneticist James Neel proposed that the epidemics of obesity and diabetes today may have evolutionary roots. Specifically, he suggested that our ancestors may have accumulated mutations during periods of famine that provided a survival advantage at that time. However, the presence of this "thrifty genotype" in today's world, where food is plentiful, would predispose us to obesity and diabetes. The "thrifty gene" hypothesis, attractive to some, has been challenged over the years. The authors have previously postulated that the loss of the uricase gene, resulting in a rise in serum and intracellular uric acid levels, satisfies the criteria of a thrifty genotype mutation. This paper reviews and brings up-to-date the evidence supporting the hypothesis and discusses the current arguments that challenge this hypothesis. Although further studies are needed to test the hypothesis, the evidence supporting a loss of uricase as a thrifty gene is substantial and supports a role for evolutionary biology in the pathogenesis of the current obesity and diabetes epidemics.

Multiple types of genomic variation contribute to adaptive traits in the mustelid subfamily Guloninae

Species of the mustelid subfamily Guloninae inhabit diverse habitats on multiple continents, and occupy a variety of ecological niches. They differ in feeding ecologies, reproductive strategies and morphological adaptations. To identify candidate loci associated with adaptations to their respective environments, we generated a de novo assembly of the tayra (Eira barbara), the earliest diverging species in the subfamily, and compared this with the genomes available for the wolverine (Gulo gulo) and the sable (Martes zibellina). Our comparative genomic analyses included searching for signs of positive selection, examining changes in gene family sizes, as well as searching for species-specific structural variants (SVs). Among candidate loci associated with phenotypic traits, we observed many related to diet, body condition and reproduction. For example, for the tayra, which has an atypical gulonine reproductive strategy of aseasonal breeding, we observe species-specific changes in many pregnancy-related genes. For the wolverine, a circumpolar hypercarnivore that must cope with seasonal food scarcity, we observed many changes in genes associated with diet and body condition. All types of genomic variation examined (single nucleotide polymorphisms, gene family expansions, structural variants) contributed substantially to the identification of candidate loci. This strongly argues for consideration of variation other than single nucleotide polymorphisms in comparative genomics studies aiming to identify loci of adaptive significance.

Phylogenetic articulation of uric acid evolution in mammals and how it informs a therapeutic uricase

The role of uric acid during primate evolution has remained elusive ever since it was discovered over 100 years ago that humans have unusually high levels of the small molecule in our serum. It has been difficult to generate a neutral or adaptive explanation in part because the uricase enzyme evolved to become a pseudogene in apes thus masking typical signals of sequence evolution. Adding to the difficulty is a lack of clarity on the functional role of uric acid in apes. One popular hypothesis proposes that uric acid is a potent antioxidant that increased in concentration to compensate for the lack of vitamin C synthesis in primate species ∼65 million years ago (Mya). Here, we have expanded on our previous work with resurrected ancient uricase proteins to better resolve the reshaping of uricase enzymatic activity prior to ape evolution. Our results suggest that the pivotal death-knell to uricase activity occurred between 20-30 Mya despite small sequential modifications to its catalytic efficiency for the tens of millions of years since primates lost their ability to synthesize vitamin C, and thus the two appear uncorrelated. We also use this opportunity to demonstrate how molecular evolution can contribute to biomedicine by presenting ancient uricases to human immune cells that assay for innate reactivity against foreign antigens. A highly stable and highly catalytic ancient uricase is shown to elicit a lower immune response in more human haplotypes than other uricases currently in therapeutic development.

Brief report: The uricase mutation in humans increases our risk for cancer growth

Background

Recent studies suggest that fructose, as well as its metabolite, uric acid, have been associated with increased risk for both cancer incidence and growth. Both substances are known to cause oxidative stress to mitochondria and to reduce adenosine triphosphate (ATP) production by blocking aconitase in the Krebs cycle. The uricase mutation that occurred in the Miocene has been reported to increase serum uric acid and to amplify the effects of fructose to stimulate fat accumulation. Here we tested whether the uricase mutation can also stimulate tumor growth.

Methods

Experiments were performed in mice in which uricase was inactivated by either knocking out the gene or by inhibiting uricase with oxonic acid. We also studied mice transgenic for uricase. These mice were injected with breast cancer cells and followed for 4 weeks.

Results

The inhibition or knockout of uricase was associated with a remarkable increase in tumor growth and metastases. In contrast, transgenic uricase mice showed reduced tumor growth.

Conclusion

A loss of uricase increases the risk for tumor growth. Prior studies have shown that the loss of the mutation facilitated the ability of fructose to increase fat which provided a survival advantage for our ancestors that came close to extinction from starvation in the mid Miocene. Today, however, excessive fructose intake is rampant and increasing our risk not only for obesity and metabolic syndrome, but also cancer. Obesity-associated cancer may be due, in part, to a mutation 15 million years ago that acted as a thrifty gene.

CRISPR-Cas9-mediated reactivation of the uricase pseudogene in human cells prevents acute hyperuricemia

The utility of CRISPR-Cas9 to repair or reverse diseased states that arise from recent genetic mutations in the human genome is now widely appreciated. The use of CRISPR to "design" the outcomes of biology is challenged by both specialized ethicists and the general public. Less of a focus, however, is the ability of CRISPR to provide metabolic supplements or prophylactic molecules that improve long-term human health by overwriting ancient evolutionary events. Here, we use CRISPR to genomically integrate a functional uricase gene that encodes an enzymatically active protein into the human genome. These uricase-producing cells are able to reduce or even eliminate high concentrations of exogenous uric acid despite the enzyme being localized to peroxisomes. Our evolutionary engineered cells represent the first instance of the primate ape lineage expressing a functional uricase encoded in the genome within the last 20 million years. We anticipate that human cells expressing uricase will help prevent hyperuricemia (including gout) as well as hypertension and will help protect against fatty liver disease in the future.

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.

Decrease in Serum Urate Level Is Associated With Loss of Visceral Fat in Male Gout Patients

OBJECTIVE

To clarify the relationship between serum urate (SU) decrease and visceral fat area (VFA) reduction in patients with gout.

METHODS

We retrospectively analyzed 237 male gout patients who had two sets of body composition and metabolic measurements within 6 months. Subjects included had all been treated with urate-lowering therapy (ULT) (febuxostat 20-80 mg/day or benzbromarone 25-50 mg/day, validated by the medical record). All patients were from the specialty gout clinic of The Affiliated Hospital of Qingdao University. The multiple linear regression model evaluated the relationship between change in SU [ΔSU, (baseline SU) - (final visit SU)] and change in VFA [ΔVFA, (baseline VFA) - (final visit VFA)].

RESULTS

ULT resulted in a mean (standard deviation) decrease in SU level (464.22 ± 110.21 μmol/L at baseline, 360.93 ± 91.66 μmol/L at the final visit, p <0.001) accompanied by a decrease in median (interquartile range) VFA [97.30 (81.15-118.55) at baseline, 90.90 (75.85-110.05) at the final visit, p < 0.001]. By multiple regression model, ΔSU was identified to be a significant determinant variable of decrease in VFA (beta, 0.302; p = 0.001).

CONCLUSIONS

The decrease in SU level is positively associated with reduced VFA. This finding provides a rationale for clinical trials to affirm whether ULT promotes loss of visceral fat in patients with gout.

Hyperuricemia in Kidney Disease: A Major Risk Factor for Cardiovascular Events, Vascular Calcification, and Renal Damage

Kidney disease, especially when it is associated with a reduction in estimated glomerular filtration rate, can be associated with an increase in serum urate (uric acid), suggesting that hyperuricemia in subjects with kidney disease may be a strictly secondary phenomenon. Mendelian randomization studies that evaluate genetic scores regulating serum urate also generally have not found evidence that serum urate is a causal risk factor in chronic kidney disease. Nevertheless, this is countered by a large number of epidemiologic, experimental, and clinical studies that have suggested a potentially important role for uric acid in kidney disease and cardiovascular disease. Here, we review the topic in detail. Overall, the studies strongly suggest that hyperuricemia does have an important pathogenic role that likely is driven by intracellular urate levels. An exception may be the role of extracellular uric acid in atherosclerosis and vascular calcification. One of the more striking findings on reviewing the literature is that the primary benefit of lowering serum urate in subjects with CKD is not by slowing the progression of renal disease, but rather by reducing the incidence of cardiovascular events and mortality. We recommend large-scale clinical trials to determine if there is a benefit in lowering serum urate in hyperuricemic subjects in acute and chronic kidney disease and in the reduction of cardiovascular morbidity and mortality in subjects with end-stage chronic kidney disease.

Evolutionary basis for the human diet: consequences for human health

The relationship of evolution with diet and environment can provide insights into modern disease. Fossil evidence shows apes, and early human ancestors were fruit eaters living in environments with strongly seasonal climates. Rapid cooling at the end of the Middle Miocene (15-12 Ma: millions of years ago) increased seasonality in Africa and Europe, and ape survival may be linked with a mutation in uric acid metabolism. Climate stabilized in the later Miocene and Pliocene (12-5 Ma), and fossil apes and early hominins were both adapted for life on ground and in trees. Around 2.5 Ma, early species of Homo introduced more animal products into their diet, and this coincided with developing bipedalism, stone tool technology and increase in brain size. Early species of Homo such as Homo habilis still lived in woodland habitats, and the major habitat shift in human evolution occurred at 1.8 Ma with the origin of Homo erectus. Homo erectus had increased body size, greater hunting skills, a diet rich in meat, control of fire and understanding about cooking food, and moved from woodland to savannah. Group size may also have increased at the same time, facilitating the transmission of knowledge from one generation to the next. The earliest fossils of Homo sapiens appeared about 300 kyr, but they had separated from Neanderthals by 480 kyr or earlier. Their diet shifted towards grain-based foods about 100 kyr ago, and settled agriculture developed about 10 kyr ago. This pattern remains for many populations to this day and provides important insights into current burden of lifestyle diseases.

Fructose metabolism as a common evolutionary pathway of survival associated with climate change, food shortage and droughts

Mass extinctions occur frequently in natural history. While studies of animals that became extinct can be informative, it is the survivors that provide clues for mechanisms of adaptation when conditions are adverse. Here, we describe a survival pathway used by many species as a means for providing adequate fuel and water, while also providing protection from a decrease in oxygen availability. Fructose, whether supplied in the diet (primarily fruits and honey), or endogenously (via activation of the polyol pathway), preferentially shifts the organism towards the storing of fuel (fat, glycogen) that can be used to provide energy and water at a later date. Fructose causes sodium retention and raises blood pressure and likely helped survival in the setting of dehydration or salt deprivation. By shifting energy production from the mitochondria to glycolysis, fructose reduced oxygen demands to aid survival in situations where oxygen availability is low. The actions of fructose are driven in part by vasopressin and the generation of uric acid. Twice in history, mutations occurred during periods of mass extinction that enhanced the activity of fructose to generate fat, with the first being a mutation in vitamin C metabolism during the Cretaceous-Paleogene extinction (65 million years ago) and the second being a mutation in uricase that occurred during the Middle Miocene disruption (12-14 million years ago). Today, the excessive intake of fructose due to the availability of refined sugar and high-fructose corn syrup is driving 'burden of life style' diseases, including obesity, diabetes and high blood pressure.

Asymptomatic hyperuricaemia: a silent activator of the innate immune system

Asymptomatic hyperuricaemia affects ~20% of the general population in the USA, with variable rates in other countries. Historically, asymptomatic hyperuricaemia was considered a benign laboratory finding with little clinical importance in the absence of gout or kidney stones. Yet, increasing evidence suggests that asymptomatic hyperuricaemia can predict the development of hypertension, obesity, diabetes mellitus and chronic kidney disease and might contribute to disease by stimulating inflammation. Although urate has been classically viewed as an antioxidant with beneficial effects, new data suggest that both crystalline and soluble urate activate various pro-inflammatory pathways. This Review summarizes what is known about the role of urate in the inflammatory response. Further research is needed to define the role of asymptomatic hyperuricaemia in these pro-inflammatory pathways.

Earliest evidence of caries lesion in hominids reveal sugar-rich diet for a Middle Miocene dryopithecine from Europe

The formation of dental caries is mainly caused by dietary habits and therefore, may contain information for dietary reconstructions of fossil hominids. This study investigates the caries lesion in the 12.5 Ma old type specimen of Dryopithecus carinthiacus Mottl 1957 (Primates, Hominidae) from St. Stefan (Austria). Potential food sources are identified on associated palynological data, which allow conclusions about food quality, sugar availability and the hominid metabolism during the Middle Miocene. Using micro computed tomography (μCT) and scanning electron microscopy (SEM) we provide a detailed analysis and characterization of the individuals' caries type. Its lesion is compared with a dataset of 311 wild chimpanzees, indicating morphological and etiological differences in caries formation between both species. The affected molar of D. carinthiacus reveals features known from severe dental caries in humans: (1) Cavitation with steep walls and smooth surface; (2) Reparative dentine at the roof of the pulp chamber; (3) Sclerotic dentine below the cavitation; (4) Association with dental calculus and (5) Unilateral usage of the healthy right tooth row. Its advanced primary caries, initiating on the intact enamel surface, indicates a frequent intake of highly cariogenic sugar-rich fruits, which likely exceeds the frugivory of extant chimpanzees. This finding corresponds with the associated palynological record, which infers a habitat with nearly year-round supply (9-10 months/year) of high quality foods (>carbohydrates; < fibers). Our conclusions challenge the model of a step-wise increase in dietary quality during hominid evolution and support the uricase hypothesis, which discusses the hominid autapomorphy of a fructose-based fat accumulation for periods of starvation. This model receives further validation by the identification of soft-tissue preservation, interpreted as fossilized white adipose cells, in the articulated hominid skeleton of Oreopithecus bamboli from Italy.

The sedentary (r)evolution: Have we lost our metabolic flexibility?

During the course of evolution, up until the agricultural revolution, environmental fluctuations forced the human species to develop a flexible metabolism in order to adapt its energy needs to various climate, seasonal and vegetation conditions. Metabolic flexibility safeguarded human survival independent of food availability. In modern times, humans switched their primal lifestyle towards a constant availability of energy-dense, yet often nutrient-deficient, foods, persistent psycho-emotional stressors and a lack of exercise. As a result, humans progressively gain metabolic disorders, such as the metabolic syndrome, type 2 diabetes, non-alcoholic fatty liver disease, certain types of cancer, cardiovascular disease and Alzheimer´s disease, wherever the sedentary lifestyle spreads in the world. For more than 2.5 million years, our capability to store fat for times of food shortage was an outstanding survival advantage. Nowadays, the same survival strategy in a completely altered surrounding is responsible for a constant accumulation of body fat. In this article, we argue that the metabolic disease epidemic is largely based on a deficit in metabolic flexibility. We hypothesize that the modern energetic inflexibility, typically displayed by symptoms of neuroglycopenia, can be reversed by re-cultivating suppressed metabolic programs, which became obsolete in an affluent environment, particularly the ability to easily switch to ketone body and fat oxidation. In a simplified model, the basic metabolic programs of humans' primal hunter-gatherer lifestyle are opposed to the current sedentary lifestyle. Those metabolic programs, which are chronically neglected in modern surroundings, are identified and conclusions for the prevention of chronic metabolic diseases are drawn.

The sedentary (r)evolution: Have we lost our metabolic flexibility?

During the course of evolution, up until the agricultural revolution, environmental fluctuations forced the human species to develop a flexible metabolism in order to adapt its energy needs to various climate, seasonal and vegetation conditions. Metabolic flexibility safeguarded human survival independent of food availability. In modern times, humans switched their primal lifestyle towards a constant availability of energy-dense, yet often nutrient-deficient, foods, persistent psycho-emotional stressors and a lack of exercise. As a result, humans progressively gain metabolic disorders, such as the metabolic syndrome, type 2 diabetes, non-alcoholic fatty liver disease, certain types of cancer, cardiovascular disease and Alzheimer´s disease, wherever the sedentary lifestyle spreads in the world. For more than 2.5 million years, our capability to store fat for times of food shortage was an outstanding survival advantage. Nowadays, the same survival strategy in a completely altered surrounding is responsible for a constant accumulation of body fat. In this article, we argue that the metabolic disease epidemic is largely based on a deficit in metabolic flexibility. We hypothesize that the modern energetic inflexibility, typically displayed by symptoms of neuroglycopenia, can be reversed by re-cultivating suppressed metabolic programs, which became obsolete in an affluent environment, particularly the ability to easily switch to ketone body and fat oxidation. In a simplified model, the basic metabolic programs of humans’ primal hunter-gatherer lifestyle are opposed to the current sedentary lifestyle. Those metabolic programs, which are chronically neglected in modern surroundings, are identified and conclusions for the prevention of chronic metabolic diseases are drawn.

Lowering Uric Acid With Allopurinol Improves Insulin Resistance and Systemic Inflammation in Asymptomatic Hyperuricemia

BACKGROUND

Hyperuricemia is an independent predictor of impaired fasting glucose and type 2 diabetes, but whether it has a causal role in insulin resistance remains controversial. Here we tested the hypothesis that lowering uric acid in hyperuricemic nondiabetic subjects might improve insulin resistance.

METHODS

Subjects with asymptomatic hyperuricemia (n = 73) were prospectively placed on allopurinol (n = 40) or control (n = 33) for 3 months. An additional control group consisted of 48 normouricemic subjects. Serum uric acid, fasting glucose, fasting insulin, HOMA-IR (homeostatic model assessment of insulin resistance), and high-sensitivity C-reactive protein were measured at baseline and at 3 months.

RESULTS

Allopurinol-treated subjects showed a reduction in serum uric acid in association with improvement in fasting blood glucose, fasting insulin, and HOMA-IR index, as well as a reduction in serum high-sensitivity C-reactive protein. The number of subjects with impaired fasting glucose significantly decreased in the allopurinol group at 3 months compared with baseline (n = 8 [20%] vs n = 30 [75%], 3 months vs baseline, P < 0.001). In the hyperuricemic control group, only glucose decreased significantly and, in the normouricemic control, no end point changed.

CONCLUSIONS

Allopurinol lowers uric acid and improves insulin resistance and systemic inflammation in asymptomatic hyperuricemia. Larger clinical trials are recommended to determine if lowering uric acid can help prevent type 2 diabetes.

Catalysis and Structure of Zebrafish Urate Oxidase Provide Insights into the Origin of Hyperuricemia in Hominoids

Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a three-step enzymatic pathway that allows some animals to eliminate purine nitrogen through a water-soluble compound. Inactivation of the pathway in hominoids leads to elevated levels of sparingly soluble urate and puts humans at risk of hyperuricemia and gout. The uricolytic activities lost during evolution can be replaced by enzyme therapy. Here we report on the functional and structural characterization of Uox from zebrafish and the effects on the enzyme of the missense mutation (F216S) that preceded Uox pseudogenization in hominoids. Using a kinetic assay based on the enzymatic suppression of the spectroscopic interference of the Uox reaction product, we found that the F216S mutant has the same turnover number of the wild-type enzyme but a much-reduced affinity for the urate substrate and xanthine inhibitor. Our results indicate that the last functioning Uox in hominoid evolution had an increased Michaelis constant, possibly near to upper end of the normal range of urate in the human serum (~300 μM). Changes in the renal handling of urate during primate evolution can explain the genetic modification of uricolytic activities in the hominoid lineage without the need of assuming fixation of deleterious mutations.

Coevolution of URAT1 and Uricase during Primate Evolution: Implications for Serum Urate Homeostasis and Gout

Uric acid is the highly insoluble end-product of purine metabolism in humans. Serum levels exceeding the solubility threshold can trigger formation of urate crystals resulting in gouty arthritis. Uric acid is primarily excreted through the kidneys with 90% reabsorbed back into the bloodstream through the uric acid transporter URAT1. This reabsorption process is essential for the high serum uric acid levels found in humans. We discovered that URAT1 proteins from humans and baboons have higher affinity for uric acid compared with transporters from rats and mice. This difference in transport kinetics of URAT1 orthologs, along with inability of modern apes to oxidize uric acid due to loss of the uricase enzyme, prompted us to ask whether these events occurred concomitantly during primate evolution. Ancestral URAT1 sequences were computationally inferred and ancient transporters were resurrected and assayed, revealing that affinity for uric acid was increased during the evolution of primates. This molecular fine-tuning occurred between the origins of simians and their diversification into New- and Old-World monkey and ape lineages. Remarkably, it was driven in large-part by only a few amino acid replacements within the transporter. This alteration in primate URAT1 coincided with changes in uricase that greatly diminished the enzymatic activity and took place 27–77 Ma. These results suggest that the modifications to URAT1 transporters were potentially adaptive and that maintaining more constant, high levels of serum uric acid may have provided an advantage to our primate ancestors.

Uric acid in metabolic syndrome: From an innocent bystander to a central player

Uric acid, once viewed as an inert metabolic end-product of purine metabolism, has been recently incriminated in a number of chronic disease states, including hypertension, metabolic syndrome, diabetes, non-alcoholic fatty liver disease, and chronic kidney disease. Several experimental and clinical studies support a role for uric acid as a contributory causal factor in these conditions. Here we discuss some of the major mechanisms linking uric acid to metabolic and cardiovascular diseases. At this time the key to understanding the importance of uric acid in these diseases will be the conduct of large clinical trials in which the effect of lowering uric acid on hard clinical outcomes is assessed. Elevated uric acid may turn out to be one of the more important remediable risk factors for metabolic and cardiovascular diseases.

Sweetening of the global diet, particularly beverages: patterns, trends, and policy responses

Evidence suggests that excessive intake of added sugars has adverse effects on cardiometabolic health, which is consistent with many reviews and consensus reports from WHO and other unbiased sources. 74% of products in the US food supply contain caloric or low-calorie sweeteners, or both. Of all packaged foods and beverages purchased by a nationally representative sample of US households in 2013, 68% (by proportion of calories) contain caloric sweeteners and 2% contain low-calorie sweeteners. We believe that in the absence of intervention, the rest of the world will move towards this pervasiveness of added sugars in the food supply. Our analysis of trends in sales of sugar-sweetened beverages around the world, in terms of calories sold per person per day and volume sold per person per day, shows that the four regions with the highest consumption are North America, Latin America, Australasia, and western Europe. The fastest absolute growth in sales of sugar-sweetened beverages by country in 2009-14 was seen in Chile. We believe that action is needed to tackle the high levels and continuing growth in sales of such beverages worldwide. Many governments have initiated actions to reduce consumption of sugar-sweetened beverages in the past few years, including taxation (eg, in Mexico); reduction of their availability in schools; restrictions on marketing of sugary foods to children; public awareness campaigns; and positive and negative front-of-pack labelling. In our opinion, evidence of the effectiveness of these actions shows that they are moving in the right direction, but governments should view them as a learning process and improve their design over time. A key challenge for policy makers and researchers is the absence of a consensus on the relation of beverages containing low-calorie sweeteners and fruit juices with cardiometabolic outcomes, since decisions about whether these are healthy substitutes for sugar-sweetened beverages are an integral part of policy design.

New insights on the risk for cardiovascular disease in African Americans: the role of added sugars

African Americans are at increased risk for cardiovascular and metabolic diseases, including obesity, high BP, diabetes, CKD, myocardial infarction, and stroke. Here we summarize the current risks and provide an overview of the underlying risk factors that may account for these associations. By reviewing the relationship between cardiovascular and renal diseases and the African-American population during the early 20th century, the historic and recent associations of African heritage with cardiovascular disease, and modern population genetics, it is possible to assemble strong hypotheses for the primary underlying mechanisms driving the increased frequency of disease in African Americans. Our studies suggest that underlying genetic mechanisms may be responsible for the increased frequency of high BP and kidney disease in African Americans, with particular emphasis on the role of APOL1 polymorphisms in causing kidney disease. In contrast, the Western diet, particularly the relatively high intake of fructose-containing sugars and sweetened beverages, appears to be the dominant force driving the increased risk of diabetes, obesity, and downstream complications. Given that intake of added sugars is a remediable risk factor, we recommend clinical trials to examine the reduction of sweetened beverages as a primary means for reducing cardiovascular risk in African Americans.

Why focus on uric acid?

In gouty patients, urate lowering therapies (ULTs) are recommended to bring serum uric acid (SUA) levels below 6.0 mg/dL, with the aim of dissolving urate depositions, thereby reducing disease impact. However, patients with hyperuricemia often present with other conditions associated with cardiovascular (CV) risk, such as high blood pressure, obesity, insulin resistance, fatty liver, and chronic kidney disease. In the last decade, several well grounded pieces of evidence showed that the elevation of uric acid often occurs prior to the development of hypertension or metabolic syndrome, thus suggesting a direct association between elevated SUA and these conditions. This paper will discuss available evidence supporting the key role of serum uric acid in the development of CV and renal disease, with a focus on the molecular mechanisms underlying this causative association. This review is based on a PubMed/Embase database search for articles on hyperuricemia and its impact on cardiovascular and renal function.

PHEX mimetic (SPR4-peptide) corrects and improves HYP and wild type mice energy-metabolism

CONTEXT

PHEX or DMP1 mutations cause hypophosphatemic-rickets and altered energy metabolism. PHEX binds to DMP1-ASARM-motif to form a complex with α5β3 integrin that suppresses FGF23 expression. ASARM-peptides increase FGF23 by disrupting the PHEX-DMP1-Integrin complex. We used a 4.2 kDa peptide (SPR4) that binds to ASARM-peptide/motif to study the DMP1-PHEX interaction and to assess SPR4 for the treatment of energy metabolism defects in HYP and potentially other bone-mineral disorders.

DESIGN

Subcutaneously transplanted osmotic pumps were used to infuse SPR4-peptide or vehicle (VE) into wild-type mice (WT) and HYP-mice (PHEX mutation) for 4 weeks.

RESULTS

SPR4 partially corrected HYP mice hypophosphatemia and increased serum 1.25(OH)2D3. Serum FGF23 remained high and PTH was unaffected. WT-SPR4 mice developed hypophosphatemia and hypercalcemia with increased PTH, FGF23 and 1.25(OH)2D3. SPR4 increased GAPDH HYP-bone expression 60× and corrected HYP-mice hyperglycemia and hypoinsulinemia. HYP-VE serum uric-acid (UA) levels were reduced and SPR4 infusion suppressed UA levels in WT-mice but not HYP-mice. SPR4 altered leptin, adiponectin, and sympathetic-tone and increased the fat mass/weight ratio for HYP and WT mice. Expression of perlipin-2 a gene involved in obesity was reduced in HYP-VE and WT-SPR4 mice but increased in HYP-SPR4 mice. Also, increased expression of two genes that inhibit insulin-signaling, ENPP1 and ESP, occurred with HYP-VE mice. In contrast, SPR4 reduced expression of both ENPP1 and ESP in WT mice and suppressed ENPP1 in HYP mice. Increased expression of FAM20C and sclerostin occurred with HYP-VE mice. SPR4 suppressed expression of FAM20C and sclerostin in HYP and WT mice.

CONCLUSIONS

ASARM peptides and motifs are physiological substrates for PHEX and modulate osteocyte PHEX-DMP1-α5β3-integrin interactions and thereby FGF23 expression. These interactions also provide a nexus that regulates bone and energy metabolism. SPR4 suppression of sclerostin and/or sequestration of ASARM-peptides improves energy metabolism and may have utility for treating familial rickets, osteoporosis, obesity and diabetes.

Uric acid-dependent inhibition of AMP kinase induces hepatic glucose production in diabetes and starvation: evolutionary implications of the uricase loss in hominids

Reduced AMP kinase (AMPK) activity has been shown to play a key deleterious role in increased hepatic gluconeogenesis in diabetes, but the mechanism whereby this occurs remains unclear. In this article, we document that another AMP-dependent enzyme, AMP deaminase (AMPD) is activated in the liver of diabetic mice, which parallels with a significant reduction in AMPK activity and a significant increase in intracellular glucose accumulation in human HepG2 cells. AMPD activation is induced by a reduction in intracellular phosphate levels, which is characteristic of insulin resistance and diabetic states. Increased gluconeogenesis is mediated by reduced TORC2 phosphorylation at Ser171 by AMPK in these cells, as well as by the up-regulation of the rate-limiting enzymes PEPCK and G6Pc. The mechanism whereby AMPD controls AMPK activation depends on the production of a specific AMP downstream metabolite through AMPD, uric acid. In this regard, humans have higher uric acid levels than most mammals due to a mutation in uricase, the enzyme involved in uric acid degradation in most mammals, that developed during a period of famine in Europe 1.5 × 10(7) yr ago. Here, working with resurrected ancestral uricases obtained from early hominids, we show that their expression on HepG2 cells is enough to blunt gluconeogenesis in parallel with an up-regulation of AMPK activity. These studies identify a key role AMPD and uric acid in mediating hepatic gluconeogenesis in the diabetic state, via a mechanism involving AMPK down-regulation and overexpression of PEPCK and G6Pc. The uricase mutation in the Miocene likely provided a survival advantage to help maintain glucose levels under conditions of near starvation, but today likely has a role in the pathogenesis of diabetes.

Evolutionary history and metabolic insights of ancient mammalian uricases

Uricase is an enzyme involved in purine catabolism and is found in all three domains of life. Curiously, uricase is not functional in some organisms despite its role in converting highly insoluble uric acid into 5-hydroxyisourate. Of particular interest is the observation that apes, including humans, cannot oxidize uric acid, and it appears that multiple, independent evolutionary events led to the silencing or pseudogenization of the uricase gene in ancestral apes. Various arguments have been made to suggest why natural selection would allow the accumulation of uric acid despite the physiological consequences of crystallized monosodium urate acutely causing liver/kidney damage or chronically causing gout. We have applied evolutionary models to understand the history of primate uricases by resurrecting ancestral mammalian intermediates before the pseudogenization events of this gene family. Resurrected proteins reveal that ancestral uricases have steadily decreased in activity since the last common ancestor of mammals gave rise to descendent primate lineages. We were also able to determine the 3D distribution of amino acid replacements as they accumulated during evolutionary history by crystallizing a mammalian uricase protein. Further, ancient and modern uricases were stably transfected into HepG2 liver cells to test one hypothesis that uricase pseudogenization allowed ancient frugivorous apes to rapidly convert fructose into fat. Finally, pharmacokinetics of an ancient uricase injected in rodents suggest that our integrated approach provides the foundation for an evolutionarily-engineered enzyme capable of treating gout and preventing tumor lysis syndrome in human patients.

Sugar, uric acid, and the etiology of diabetes and obesity

The intake of added sugars, such as from table sugar (sucrose) and high-fructose corn syrup has increased dramatically in the last hundred years and correlates closely with the rise in obesity, metabolic syndrome, and diabetes. Fructose is a major component of added sugars and is distinct from other sugars in its ability to cause intracellular ATP depletion, nucleotide turnover, and the generation of uric acid. In this article, we revisit the hypothesis that it is this unique aspect of fructose metabolism that accounts for why fructose intake increases the risk for metabolic syndrome. Recent studies show that fructose-induced uric acid generation causes mitochondrial oxidative stress that stimulates fat accumulation independent of excessive caloric intake. These studies challenge the long-standing dogma that "a calorie is just a calorie" and suggest that the metabolic effects of food may matter as much as its energy content. The discovery that fructose-mediated generation of uric acid may have a causal role in diabetes and obesity provides new insights into pathogenesis and therapies for this important disease.

Service learning in a pediatric weight management program to address childhood obesity

This paper describes an inter-professional service learning collaboration and reflects benefits and considerations when incorporating a family-oriented approach in the community-based pediatric weight management program. Because obesity has tremendous consequences on a nation's health and economy, a pediatrician in a community health network has utilized an inter-professional team to implement a pediatric weight management program targeting children between the ages of 8 and 15 years. The team incorporates a culturally sensitive curriculum using a family-oriented approach for obesity prevention and intervention. Physicians, registered dietitians, occupational therapists, nurse practitioners, and mental health professionals assist participants in adopting a healthier lifestyle by addressing physical and psychosocial issues related to obesity, developing a nutrition plan, making healthier food choices, and finding fun ways to be more physically active. Graduate occupational therapy students work closely with the team members to assist delivery of interactive activities and behavior intervention.

Redefining metabolic syndrome as a fat storage condition based on studies of comparative physiology

OBJECTIVE

The metabolic syndrome refers to a constellation of signs including abdominal obesity, elevated serum triglycerides, low HDL-cholesterol, elevated blood pressure, and insulin resistance. Today approximately one third of the adult population has the metabolic syndrome. While there is little doubt that the signs constituting the metabolic syndrome frequently cluster, much controversy exists over the definition, pathogenesis, or clinical utility.

DESIGN AND METHODS

Here we present evidence from the field of comparative physiology that the metabolic syndrome is similar to the biological process that animals engage to store fat in preparation for periods of food shortage.

RESULTS

We propose that the metabolic syndrome be changed to fat storage condition to more clearly align with its etiology. Obesity in humans is likely the consequences of both genetic predisposition (driven in part by thrifty genes) and environment. Recent studies suggest that the loss of the uricase gene may be one factor that predisposes humans to obesity today.

CONCLUSION

Understanding the process animals engage to switch from a lean insulin-sensitive to an obese insulin-resistant state may provide novel insights into the cause of obesity and diabetes in humans, and unique opportunities for reversing their pathology.

Fructokinase, Fructans, Intestinal Permeability, and Metabolic Syndrome: An Equine Connection?

Fructose is a simple sugar present in honey and fruit, but can also exist as a polymer (fructans) in pasture grasses. Mammals are unable to metabolize fructans, but certain gram positive bacteria contain fructanases and can convert fructans to fructose in the gut. Recent studies suggest that fructose generated from bacteria, or directly obtained from the diet, can induce both increased intestinal permeability and features of metabolic syndrome, especially the development of insulin resistance. The development of insulin resistance is driven in part by the metabolism of fructose by fructokinase C in the liver, which results in oxidative stress in the hepatocyte. Similarly, the metabolism of fructose in the small bowel by intestinal fructokinase may lead to increased intestinal permeability and endotoxemia. While speculative, these observations raise the possibility that the mechanism by which fructans induce laminitis could involve intestinal and hepatic fructokinase. Further studies are indicated to determine the role of fructanases, fructose and fructokinase in equine metabolic syndrome and laminitis.

The role of uric acid in the pathogenesis of human cardiovascular disease

Hyperuricaemia is common in subjects with cardiovascular disease, but is not commonly considered a true risk factor. Recent studies suggest that uric acid is biologically active and can stimulate oxidative stress, endothelial dysfunction, inflammation and vasoconstriction. Epidemiological studies have found that uric acid can independently predict the development of hypertension, as well as stroke and heart failure. Experimentally raising uric acid in animals increases blood pressure, and pilot studies suggest that lowering uric acid in humans can reduce blood pressure in hypertensive individuals. Uric acid may also have emerging roles in the pathogenesis of kidney disease, metabolic syndrome and diabetes. More studies need to be performed on the pathophysiology and clinical consequences of hyperuricaemia in cardiovascular disease.

Synergistic effect of uricase blockade plus physiological amounts of fructose-glucose on glomerular hypertension and oxidative stress in rats

Fructose in sweetened beverages (SB) increases the risk for metabolic and cardiorenal disorders, and these effects are in part mediated by a secondary increment in uric acid (UA). Rodents have an active uricase, thus requiring large doses of fructose to increase plasma UA and to induce metabolic syndrome and renal hemodynamic changes. We therefore hypothesized that the effects of fructose in rats might be enhanced in the setting of uricase inhibition. Four groups of male Sprague-Dawley rats (n = 7/group) were studied during 8 wk: water + vehicle (V), water + oxonic acid (OA; 750 mg/k BW), sweetened beverage (SB; 11% fructose-glucose combination) + V, and SB + OA. Systemic blood pressure, plasma UA, triglycerides (TG), glucose and insulin, glomerular hemodynamics, renal structural damage, renal cortex and liver UA, TG, markers of oxidative stress, mitDNA, fructokinase, and fatty liver synthase protein expressions were evaluated at the end of the experiment. Chronic hyperuricemia and SB induced features of the metabolic syndrome, including hypertension, hyperuricemia, hyperglycemia, and systemic and hepatic TG accumulation. OA alone also induced glomerular hypertension, and SB alone induced insulin resistance. SB + OA induced a combined phenotype including metabolic and renal alterations induced by SB or OA alone and in addition also acted synergistically on systemic and glomerular pressure, plasma glucose, hepatic TG, and oxidative stress. These findings explain why high concentrations of fructose are required to induce greater metabolic changes and renal disease in rats whereas humans, who lack uricase, appear to be much more sensitive to the effects of fructose.

Uric acid: a danger signal from the RNA world that may have a role in the epidemic of obesity, metabolic syndrome, and cardiorenal disease: evolutionary considerations

All human beings are uricase knockouts; we lost the uricase gene as a result of a mutation that occurred in the mid-Miocene epoch approximately 15 million years ago. The consequence of being a uricase knockout is that we have higher serum uric acid levels that are less regulatable and can be readily influenced by diet. This increases our risk for gout and kidney stones, but there is also increasing evidence that uric acid increases our risk for hypertension, kidney disease, obesity, and diabetes. This raises the question of why this mutation occurred. In this article we review current hypotheses. We suggest that uric acid is a danger and survival signal carried over from the RNA world. The mutation of uricase that occurred during the food shortage and global cooling that occurred in the Miocene epoch resulted in a survival advantage for early primates, particularly in Europe. Today, the loss of uricase functions as a thrifty gene, increasing our risk for obesity and cardiorenal disease.

Opposing effects of fructokinase C and A isoforms on fructose-induced metabolic syndrome in mice

Fructose intake from added sugars correlates with the epidemic rise in obesity, metabolic syndrome, and nonalcoholic fatty liver disease. Fructose intake also causes features of metabolic syndrome in laboratory animals and humans. The first enzyme in fructose metabolism is fructokinase, which exists as two isoforms, A and C. Here we show that fructose-induced metabolic syndrome is prevented in mice lacking both isoforms but is exacerbated in mice lacking fructokinase A. Fructokinase C is expressed primarily in liver, intestine, and kidney and has high affinity for fructose, resulting in rapid metabolism and marked ATP depletion. In contrast, fructokinase A is widely distributed, has low affinity for fructose, and has less dramatic effects on ATP levels. By reducing the amount of fructose for metabolism in the liver, fructokinase A protects against fructokinase C-mediated metabolic syndrome. These studies provide insights into the mechanisms by which fructose causes obesity and metabolic syndrome.