Vasopressin mediates fructose-induced metabolic syndrome by activating the V1b receptor

A study on the early metabolic effects of salt and fructose consumption: the protective role of water

Increasing serum osmolality has recently been linked with acute stress responses, which over time can lead to increased risk for obesity, hypertension, and other chronic diseases. Salt and fructose are two major stimuli that can induce acute changes in serum osmolality. Here we investigate the early metabolic effects of sodium and fructose consumption and determine whether the effects of sodium or fructose loading can be mitigated by blocking the change in osmolality with hydration. Forty-four healthy subjects without disease and medication were recruited into four groups. After overnight fasting, subjects in Group 1 drank 500 mL of salty soup, while those in Group 2 drank 500 mL of soup without salt for 15 min. Subjects in Group 3 drank 500 mL of 100% apple juice in 5 min, while subjects in Group 4 drank 500 mL of 100% apple juice and 500 mL of water in 5 min. Blood pressure (BP), plasma sodium, and glucose levels were measured every 15 min in the first 2 h. Serum and urine osmolarity, serum uric acid, cortisol, fibroblast growth factor 21 (FGF21), aldosterone, adrenocorticotropic hormone (ACTH) level, and plasma renin activity (PRA) were measured at the baseline and 2 h. Both acute intake of salt or fructose increased serum osmolality (maximum ∼4 mOsm/L peaking at 75 min) associated with a rise in systolic and diastolic BP, PRA, aldosterone, ACTH, cortisol, plasma glucose, uric acid, and FGF21. Salt tended to cause greater activation of the renin-angiotensin-system (RAS), while fructose caused a greater rise in glucose and FGF21. In both cases, hydration could prevent the osmolality and largely block the acute stress response. Acute changes in serum osmolality can induce remarkable activation of the ACTH-cortisol, RAS, glucose metabolism, and uric acid axis that is responsive to hydration. In addition to classic dehydration, salt, and fructose-containing sugars can activate these responses. Staying well hydrated may provide benefits despite exposure to sugar and salt. More studies are needed to investigate whether hydration can block the chronic effects of sugar and salt on disease.

Association between Urine Specific Gravity as a Measure of Hydration Status and Risk of Type 2 Diabetes: The Kailuan Prospective Cohort Study

Diabetes, especially type 2 diabetes (T2D), poses an unprecedented challenge to global public health. Hydration status also plays a fundamental role in human health, especially in people with T2D, which is often overlooked. This study aimed to explore the longitudinal associations between hydration status and the risk of T2D among the Chinese population. This study used data from the large community-based Kailuan cohort, which included adults who attended physical examinations from 2006 to 2007 and were followed until 2020. A total of 71,526 participants who eventually met the standards were divided into five hydration-status groups based on their levels of urine specific gravity (USG). Multivariable and time-dependent Cox proportional hazards models were employed to evaluate the associations of baseline and time-dependent hydration status with T2D incidence. Restricted cubic splines (RCS) analysis was used to examine the dose-response relationship between hydration status and the risk of T2D. Over a median 12.22-year follow-up time, 11,804 of the participants developed T2D. Compared with the optimal hydration-status group, participants with dehydration and severe dehydration had a significantly increased risk of diabetes, with adjusted hazard ratios (95% CI) of 1.30 (1.04-1.63) and 1.38 (1.10-1.74). Time-dependent analyses further confirmed the adverse effects of impending dehydration, dehydration, and severe dehydration on T2D incidence by 16%, 26%, and 33% compared with the reference group. Inadequate hydration is significantly associated with increased risks of T2D among Chinese adults. Our findings provided new epidemiological evidence and highlighted the potential role of adequate hydration status in the early prevention of T2D development.

The fructose survival hypothesis as a mechanism for unifying the various obesity hypotheses

The pathogenesis of obesity remains contested. Although genetics is important, the rapid rise in obesity with Western culture and diet suggests an environmental component. Today, some of the major hypotheses for obesity include the energy balance hypothesis, the carbohydrate-insulin model, the protein-leverage hypothesis, and the seed oil hypothesis. Each hypothesis has its own support, creating controversy over their respective roles in driving obesity. Here we propose that all hypotheses are largely correct and can be unified by another dietary hypothesis, the fructose survival hypothesis. Fructose is unique in resetting ATP levels to a lower level in the cell as a consequence of suppressing mitochondrial function, while blocking the replacement of ATP from fat. The low intracellular ATP levels result in carbohydrate-dependent hunger, impaired satiety (leptin resistance), and metabolic effects that result in the increased intake of energy-dense fats. This hypothesis emphasizes the unique role of carbohydrates in stimulating intake while fat provides the main source of energy. Thus, obesity is a disorder of energy metabolism, in which there is low usable energy (ATP) in the setting of elevated total energy. This leads to metabolic effects independent of excess energy while the excess energy drives weight gain.

The Role of Uric Acid in Human Health: Insights from the Uricase Gene

Uric acid is the final product of purine metabolism and is converted to allantoin in most mammals via the uricase enzyme. The accumulation of loss of function mutations in the uricase gene rendered hominoids (apes and humans) to have higher urate concentrations compared to other mammals. The loss of human uricase activity may have allowed humans to survive environmental stressors, evolution bottlenecks, and life-threatening pathogens. While high urate levels may contribute to developing gout and cardiometabolic disorders such as hypertension and insulin resistance, low urate levels may increase the risk for neurodegenerative diseases. The double-edged sword effect of uric acid has resurrected a growing interest in urate's antioxidant role and the uricase enzyme's role in modulating the risk of obesity. Characterizing both the effect of uric acid levels and the uricase enzyme in different animal models may provide new insights into the potential therapeutic benefits of uric acid and novel uricase-based therapy.

Metabolic effects of vasopressin in pathophysiology of diabetic kidney disease

The diabetic kidney disease (DKD) is the major cause of the chronic kidney disease (CKD). Enhanced plasma vasopressin (VP) levels have been associated with the pathophysiology of DKD and CKD. Stimulation of VP release in DKD is caused by glucose-dependent reset of the osmostat leading to secondary pathophysiologic effects mediated by distinct VP receptor types. VP is a stress hormone exhibiting the antidiuretic action in the kidney along with broad adaptive effects in other organs. Excessive activation of the vasopressin type 2 (V2) receptor in the kidney leads to glomerular hyperfiltration and nephron loss, whereas stimulation of vasopressin V1a or V1b receptors in the liver, pancreas, and adrenal glands promotes catabolic metabolism for energy mobilization, enhancing glucose production and aggravating DKD. Increasing availability of selective VP receptor antagonists opens new therapeutic windows separating the renal and extra-renal VP effects for the concrete applications. Improved understanding of these paradigms is mandatory for further drug design and translational implementation. The present concise review focuses on metabolic effects of VP affecting DKD pathophysiology.

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)'.

Rethinking Vasopressin: New Insights into Vasopressin Signaling and Its Implications

Vasopressin is a highly conserved peptide hormone that has been traditionally associated with water homeostasis. There is accumulating evidence in both humans and animal models that vasopressin is implicated in the regulation of metabolism. This review focuses on the effects that vasopressin exerts on the regulation of glucose and fatty acids with a particular emphasis on the potential repercussions of metabolic dysregulation in kidney disease.

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.

The damaging duo: Obesity and excess dietary salt contribute to hypertension and cardiovascular disease

Hypertension is a primary risk factor for cardiovascular disease. Cardiovascular disease is the leading cause of death among adults worldwide. In this review, we focus on two of the most critical public health challenges that contribute to hypertension-obesity and excess dietary sodium from salt (i.e., sodium chloride). While the independent effects of these factors have been studied extensively, the interplay of obesity and excess salt overconsumption is not well understood. Here, we discuss both the independent and combined effects of excess obesity and dietary salt given their contributions to vascular dysfunction, autonomic cardiovascular dysregulation, kidney dysfunction, and insulin resistance. We discuss the role of ultra-processed foods-accounting for nearly 60% of energy intake in America-as a major contributor to both obesity and salt overconsumption. We highlight the influence of obesity on elevated blood pressure in the presence of a high-salt diet (i.e., salt sensitivity). Throughout the review, we highlight critical gaps in knowledge that should be filled to inform us of the prevention, management, treatment, and mitigation strategies for addressing these public health challenges.

High Fructose Corn Syrup Accelerates Kidney Disease and Mortality in Obese Mice with Metabolic Syndrome

The presence of obesity and metabolic syndrome is strongly linked with chronic kidney disease (CKD), but the mechanisms responsible for the association are poorly understood. Here, we tested the hypothesis that mice with obesity and metabolic syndrome might have increased susceptibility to CKD from liquid high fructose corn syrup (HFCS) by favoring the absorption and utilization of fructose. We evaluated the pound mouse model of metabolic syndrome to determine if it showed baseline differences in fructose transport and metabolism and whether it was more susceptible to chronic kidney disease when administered HFCS. Pound mice have increased expression of fructose transporter (Glut5) and fructokinase (the limiting enzyme driving fructose metabolism) associated with enhanced fructose absorption. Pound mice receiving HFCS rapidly develop CKD with increased mortality rates associated with intrarenal mitochondria loss and oxidative stress. In pound mice lacking fructokinase, the effect of HFCS to cause CKD and early mortality was aborted, associated with reductions in oxidative stress and fewer mitochondria loss. Obesity and metabolic syndrome show increased susceptibility to fructose-containing sugars and increased risk for CKD and mortality. Lowering added sugar intake may be beneficial in reducing the risk for CKD in subjects with metabolic syndrome.

The role of ChREBP in carbohydrate sensing and NAFLD development

Excessive sugar consumption and defective glucose sensing by hepatocytes contribute to the development of metabolic diseases including type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). Hepatic metabolism of carbohydrates into lipids is largely dependent on the carbohydrate-responsive element binding protein (ChREBP), a transcription factor that senses intracellular carbohydrates and activates many different target genes, through the activation of de novo lipogenesis (DNL). This process is crucial for the storage of energy as triglycerides in hepatocytes. Furthermore, ChREBP and its downstream targets represent promising targets for the development of therapies for the treatment of NAFLD and T2DM. Although lipogenic inhibitors (for example, inhibitors of fatty acid synthase, acetyl-CoA carboxylase or ATP citrate lyase) are currently under investigation, targeting lipogenesis remains a topic of discussion for NAFLD treatment. In this Review, we discuss mechanisms that regulate ChREBP activity in a tissue-specific manner and their respective roles in controlling DNL and beyond. We also provide in-depth discussion of the roles of ChREBP in the onset and progression of NAFLD and consider emerging targets for NAFLD therapeutics.

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.

Climate change and nephrology

Climate change should be of special concern for the nephrologist, as the kidney has a critical role in protecting the host from dehydration, but it is also a favorite target of heat stress and dehydration. Here we discuss how rising temperatures and extreme heat events may affect the kidney. The most severe presentation of heat stress is heat stroke, which can result in severe electrolyte disturbance and both acute and chronic kidney disease (CKD). However, lesser levels of heat stress also have multiple effects, including exacerbating kidney disease and precipitating cardiovascular events in subjects with established kidney disease. Heat stress can also increase the risk for kidney stones, cause multiple electrolyte abnormalities and induce both acute and chronic kidney disease. Recently there have been multiple epidemics of CKD of uncertain etiology in various regions of the world, including Mesoamerica, Sri Lanka, India and Thailand. There is increasing evidence that climate change and heat stress may play a contributory role in these conditions, although other causes, including toxins, could also be involved. As climate change worsens, the nephrologist should prepare for an increase in diseases associated with heat stress and dehydration.

Kidney collecting duct cells make vasopressin in response to NaCl-induced hypertonicity

Vasopressin has traditionally been thought to be produced by the neurohypophyseal system and then released into the circulation where it regulates water homeostasis. The questions of whether vasopressin could be produced outside of the brain and if the kidney could be a source of vasopressin are raised by the syndrome of inappropriate antidiuretic hormone secretion (vasopressin). We found that mouse and human kidneys expressed vasopressin mRNA. Using an antibody that detects preprovasopressin, we found that immunoreactive preprovasopressin protein was found in mouse and human kidneys. Moreover, we found that murine collecting duct cells made biologically active vasopressin, which increased in response to NaCl-mediated hypertonicity, and that water restriction increased the abundance of kidney-derived vasopressin mRNA and protein expression in mouse kidneys. Thus, we provide evidence of biologically active production of kidney-derived vasopressin in kidney tubular epithelial cells.

Association between Copeptin and Metabolic Syndrome: A Systematic Review

Background

Copeptin, a reliable marker for vasopressin release, has been associated with cardiometabolic diseases including metabolic syndrome (MetS). This systematic review aims to evaluate the association between copeptin and MetS.

Methods

We searched in Pubmed, Scopus, EMBASE, and Web of Science databases until March 2021 and included observational studies (cohort studies, cross-sectional, and case-control) reporting the risk or prevalence of having MetS in patients with elevated copeptin levels compared to patients without elevated copeptin levels. The risk of bias was evaluated with the Newcastle-Ottawa Scale. Meta-analysis was not performed because of the heterogeneity of the copeptin cut-off values.

Results

A total of 7 studies (5 cross-sectional, 1 case-control, and 1 cohort) were included comprising 11,699 participants. Most of them were performed in the adult general population. Two cross-sectional and one case-control studies found a positive significant association between higher levels of copeptin and MetS. While three cross-sectional and one cohort studies found no association. The case-control study had several methodological limitations, most cross-sectional studies were methodologically adequate and the cohort study had no methodological issues.

Conclusions

The association between copeptin and MetS is inconsistent. However, the arginine-vasopressin system impairment contributes to metabolic disorders, expressing plasma copeptin changes. Thus, more longitudinal studies are required to corroborate the association of copeptin and MetS.

Role of high-salt diet in non-alcoholic fatty liver disease: a mini-review of the evidence

With the rising incidence of both obesity and diabetes, non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. However, lifestyle intervention remains to be an effective approach for NAFLD due to lack of therapeutic medication. Recently, salt, an essential micronutrient free of calories, has raised a global concern owing to its wide-range healthy relevance. Accumulated evidence has suggested that a long-term high-salt diet (HSD) independently increases the risk of NAFLD. In the past decades, a number of studies have been reported regarding the mechanism of much investigation concerning HSD-induced NAFLD. Here, we review the updates in epidemiology and molecular mechanism of HSD-induced NAFLD and provide a novel insight into the role of HSD in the regulation of lipid metabolism.

Fructose Induces Pulmonary Fibrotic Phenotype Through Promoting Epithelial-Mesenchymal Transition Mediated by ROS-Activated Latent TGF-β1

Fructose is a commonly used food additive and has many adverse effects on human health, but it is unclear whether fructose impacts pulmonary fibrosis. TGF-β1, a potent fibrotic inducer, is produced as latent complexes by various cells, including alveolar epithelial cells, macrophages, and fibroblasts, and must be activated by many factors such as reactive oxygen species (ROS). This study explored the impact of fructose on pulmonary fibrotic phenotype and epithelial-mesenchymal transition (EMT) using lung epithelial cells (A549 or BEAS-2B) and the underlying mechanisms. Fructose promoted the cell viability of lung epithelial cells, while N-Acetyl-l-cysteine (NAC) inhibited such. Co-treatment of fructose and latent TGF-β1 could induce the fibrosis phenotype and the epithelial-mesenchymal transition (EMT)-related protein expression, increasing lung epithelial cell migration and invasion. Mechanism analysis shows that fructose dose-dependently promoted the production of total and mitochondrial ROS in A549 cells, while NAC eliminated this promotion. Notably, post-administration with NAC or SB431542 (a potent TGF-β type I receptor inhibitor) inhibited fibrosis phenotype and EMT process of lung epithelial cells co-treated with fructose and latent TGF-β1. Finally, the fibrosis phenotype and EMT-related protein expression of lung epithelial cells were mediated by the ROS-activated latent TGF-β1/Smad3 signal. This study revealed that high fructose promoted the fibrotic phenotype of human lung epithelial cells by up-regulating oxidative stress, which enabled the latent form of TGF-β1 into activated TGF-β1, which provides help and reference for the diet adjustment of healthy people and patients with fibrosis.

THIRSTY FOR FRUCTOSE: Arginine Vasopressin, Fructose, and the Pathogenesis of Metabolic and Renal Disease

We review the pathways by which arginine vasopressin (AVP) and hydration influence the sequelae of the metabolic syndrome induced by high fructose consumption. AVP and inadequate hydration have been shown to worsen the severity of two phenotypes associated with metabolic syndrome induced by high fructose intake-enhanced lipogenesis and insulin resistance. These findings have implications for those who frequently consume sweeteners such as high fructose corn syrup (HFCS). Patients with metabolic syndrome are at higher risk for microalbuminuria and/or chronic kidney disease; however, it is difficult to discriminate the detrimental renal effects of the metabolic syndrome from those of hypertension, impaired glucose metabolism, and obesity. It is not surprising the prevalence of chronic renal insufficiency is growing hand in hand with obesity, insulin resistance, and metabolic syndrome in those who consume large amounts of fructose. Higher AVP levels and low hydration status worsen the renal insufficiency found in patients with metabolic syndrome. This inter-relationship has public health consequences, especially among underserved populations who perform physical labor in environments that place them at risk for dehydration. MesoAmerican endemic nephropathy is a type of chronic kidney disease highly prevalent in hot ambient climates from southwest Mexico through Latin America. There is growing evidence that this public health crisis is being spurred by greater fructose consumption in the face of dehydration and increased dehydration-dependent vasopressin secretion. Work is needed at unraveling the mechanism(s) by which fructose consumption and increased AVP levels can worsen the renal disease associated with components of the metabolic syndrome.

Current Hydration Habits: The Disregarded Factor for the Development of Renal and Cardiometabolic Diseases

Improper hydration habits are commonly disregarded as a risk factor for the development of chronic diseases. Consuming an intake of water below recommendations (underhydration) in addition to the substitution of sugar-sweetened beverages (SSB) for water are habits deeply ingrained in several countries. This behavior is due to voluntary and involuntary dehydration; and because young children are exposed to SSB, the preference for a sweet taste is profoundly implanted in the brain. Underhydration and SSB intake lead to mild hyperosmolarity, which stimulates biologic processes, such as the stimulation of vasopressin and the polyol-fructose pathway, which restore osmolarity to normal but at the expense of the continued activation of these biological systems. Unfortunately, chronic activation of the vasopressin and polyol-fructose pathways has been shown to mediate many diseases, such as obesity, diabetes, metabolic syndrome, chronic kidney disease, and cardiovascular disease. It is therefore urgent that we encourage educational and promotional campaigns that promote the evaluation of personal hydration status, a greater intake of potable water, and a reduction or complete halting of the drinking of SSB.

Sirtuin deficiency and the adverse effects of fructose and uric acid synthesis

Fructose metabolism and hyperuricemia have been shown to drive insulin resistance, metabolic syndrome, hepatic steatosis, hypertension, inflammation, and innate immune reactivity in experimental studies. We suggest that these adverse effects are at least in part the result of suppressed activity of sirtuins, particularly Sirtuin1. Deficiency of sirtuin deacetylations is a consequence of reduced bioavailability of its cofactor nicotinamide adenine dinucleotide (NAD+). Uric acid-induced inflammation and oxidative stress consume NAD+ and activation of the polyol pathway of fructose and uric acid synthesis also reduces the NAD+-to-NADH ratio. Variability in the compensatory regeneration of NAD+ could result in variable recovery of sirtuin activity that may explain the inconsistent benefits of treatments directed to reduce uric acid in clinical trials. Here, we review the pathogenesis of the metabolic dysregulation driven by hyperuricemia and their potential relationship with sirtuin deficiency. In addition, we discuss therapeutic options directed to increase NAD+ and sirtuins activity that may improve the adverse effects resulting from fructose and uric acid synthesis.

The role of sugar-sweetened beverages in the global epidemics of obesity and chronic diseases

Sugar-sweetened beverages (SSBs) are a major source of added sugars in the diet. A robust body of evidence has linked habitual intake of SSBs with weight gain and a higher risk (compared with infrequent SSB consumption) of type 2 diabetes mellitus, cardiovascular diseases and some cancers, which makes these beverages a clear target for policy and regulatory actions. This Review provides an update on the evidence linking SSBs to obesity, cardiometabolic outcomes and related cancers, as well as methods to grade the strength of nutritional research. We discuss potential biological mechanisms by which constituent sugars can contribute to these outcomes. We also consider global trends in intake, alternative beverages (including artificially-sweetened beverages) and policy strategies targeting SSBs that have been implemented in different settings. Strong evidence from cohort studies on clinical outcomes and clinical trials assessing cardiometabolic risk factors supports an aetiological role of SSBs in relation to weight gain and cardiometabolic diseases. Many populations show high levels of SSB consumption and in low-income and middle-income countries, increased consumption patterns are associated with urbanization and economic growth. As such, more intensified policy efforts are needed to reduce intake of SSBs and the global burden of obesity and chronic diseases.

NMR-based Metabolomics and Fatty Acid Profiles to Unravel Biomarkers in Preclinical Animal Models of Compulsive Behavior

Compulsivity is a key manifestation of inhibitory control deficit and a cardinal symptom of psychopathological conditions such as obsessive-compulsive and attention-deficit hyperactivity disorders, in which metabolic alterations have raised attention as putative biomarkers for early identification. The present study assessed the metabolic profile in a preclinical model of a compulsive phenotype of rats. We used the schedule-induced polydipsia (SIP) method to classify male Wistar rats into high drinkers (HDs) or low drinkers (LDs) according to their compulsive drinking rate developed by exposure to a fixed-time 60 s (FT-60) schedule of reinforcement with water available ad libitum during 20 sessions. Before and after SIP, blood samples were collected for subsequent serum analysis by nuclear magnetic resonance spectroscopy coupled to multivariate analysis. Although no differences existed in the pre-SIP set, the compulsive drinking behavior induced remarkable metabolic alterations: HD rats selected by SIP exhibited a hyperlipidemic, hypoglycemic, and hyperglutaminergic profile compared with their low-compulsive counterparts. Interestingly, these alterations were not attributable to the mere exposure to reward pellets because a control experiment did not show differences between HDs and LDs after 20 sessions of pellet consumption without intermittent reinforcement. Our results shed light toward the implication of dietary and metabolic factors underpinning the vulnerability to compulsive behaviors.

Renal Tubular Handling of Glucose and Fructose in Health and Disease

The proximal tubule of the kidney is programmed to reabsorb all filtered glucose and fructose. Glucose is taken up by apical sodium-glucose cotransporters SGLT2 and SGLT1 whereas SGLT5 and potentially SGLT4 and GLUT5 have been implicated in apical fructose uptake. The glucose taken up by the proximal tubule is typically not metabolized but leaves via the basolateral facilitative glucose transporter GLUT2 and is returned to the systemic circulation or used as an energy source by distal tubular segments after basolateral uptake via GLUT1. The proximal tubule generates new glucose in metabolic acidosis and the postabsorptive phase, and fructose serves as an important substrate. In fact, under physiological conditions and intake, fructose taken up by proximal tubules is primarily utilized for gluconeogenesis. In the diabetic kidney, glucose is retained and gluconeogenesis enhanced, the latter in part driven by fructose. This is maladaptive as it sustains hyperglycemia. Moreover, renal glucose retention is coupled to sodium retention through SGLT2 and SGLT1, which induces secondary deleterious effects. SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing independent of kidney function and diabetes. Dietary excess of fructose also induces tubular injury. This can be magnified by kidney formation of fructose under pathological conditions. Fructose metabolism is linked to urate formation, which partially accounts for fructose-induced tubular injury, inflammation, and hemodynamic alterations. Fructose metabolism favors glycolysis over mitochondrial respiration as urate suppresses aconitase in the tricarboxylic acid cycle, and has been linked to potentially detrimental aerobic glycolysis (Warburg effect). © 2022 American Physiological Society. Compr Physiol 12:2995-3044, 2022.

Molecular aspects of fructose metabolism and metabolic disease

Excessive sugar consumption is increasingly considered as a contributor to the emerging epidemics of obesity and the associated cardiometabolic disease. Sugar is added to the diet in the form of sucrose or high-fructose corn syrup, both of which comprise nearly equal amounts of glucose and fructose. The unique aspects of fructose metabolism and properties of fructose-derived metabolites allow for fructose to serve as a physiological signal of normal dietary sugar consumption. However, when fructose is consumed in excess, these unique properties may contribute to the pathogenesis of cardiometabolic disease. Here, we review the biochemistry, genetics, and physiology of fructose metabolism and consider mechanisms by which excessive fructose consumption may contribute to metabolic disease. Lastly, we consider new therapeutic options for the treatment of metabolic disease based upon this knowledge.

Alternative Dietary Patterns for Americans: Low-Carbohydrate Diets

The decades-long dietary experiment embodied in the Dietary Guidelines for Americans (DGA) focused on limiting fat, especially saturated fat, and higher carbohydrate intake has coincided with rapidly escalating epidemics of obesity and type 2 diabetes (T2D) that are contributing to the progression of cardiovascular disease (CVD) and other diet-related chronic diseases. Moreover, the lack of flexibility in the DGA as it pertains to low carbohydrate approaches does not align with the contemporary trend toward precision nutrition. We argue that personalizing the level of dietary carbohydrate should be a high priority based on evidence that Americans have a wide spectrum of metabolic variability in their tolerance to high carbohydrate loads. Obesity, metabolic syndrome, and T2D are conditions strongly associated with insulin resistance, a condition exacerbated by increased dietary carbohydrate and improved by restricting carbohydrate. Low-carbohydrate diets are grounded across the time-span of human evolution, have well-established biochemical principles, and are now supported by multiple clinical trials in humans that demonstrate consistent improvements in multiple established risk factors associated with insulin resistance and cardiovascular disease. The American Diabetes Association (ADA) recently recognized a low carbohydrate eating pattern as an effective approach for patients with diabetes. Despite this evidence base, low-carbohydrate diets are not reflected in the DGA. As the DGA Dietary Patterns have not been demonstrated to be universally effective in addressing the needs of many Americans and recognizing the lack of widely available treatments for obesity, metabolic syndrome, and T2D that are safe, effective, and sustainable, the argument for an alternative, low-carbohydrate Dietary Pattern is all the more compelling.

Peripheral Insulin Resistance Is Associated with Copeptin in Patients with Chronic Kidney Disease

Background

Insulin resistance is associated with cardiovascular disease risk and worsened kidney function. Patients with CKD have higher levels of insulin resistance. Elevated levels of copeptin (a surrogate for vasopressin levels) have been associated with an increased incidence and progression of CKD, and with incident diabetes mellitus. The purpose of our study was to examine the relationship between insulin resistance, copeptin, and CKD.

Methods

We performed a cross-sectional study to investigate if insulin resistance was associated with higher copeptin levels in nondiabetic patients with stage 3-4 CKD versus controls. We measured plasma copeptin levels and used data from 52 patients with stage 3-4 CKD and 85 controls (eGFR ≥60 ml/min per 1.73 m²) enrolled in the Insulin Resistance in Chronic Kidney Disease (IRCKD) study. We then used a multivariable linear-regression model to assess the independent relationship between peripheral or hepatic insulin resistance and copeptin across levels of eGFR.

Results

We found that in patients with CKD (eGFR of 30-60 ml/min per 1.73 m²), but not in controls, peripheral insulin resistance was significantly correlated with higher levels of log copeptin (r=-0.21, P=0.04). In patients with CKD, when adjusted for age, sex, BMI, serum osmolality, log IL6, and log leptin/adiponectin ratio, each 1 SD decrease in insulin sensitivity was associated with a 39% increase in serum copeptin levels. The relationship between hepatic insulin resistance, copeptin, and eGFR is similar between controls and patients with reduced eGFR.

Conclusion

Peripheral insulin resistance is associated with elevated copeptin levels in nondiabetic patients with stage 3-4 CKD. Further research into how the interaction between peripheral insulin resistance and elevated vasopressin affects CKD progression could be of interest.

Neural mechanisms underlying the role of fructose in overfeeding

Fructose consumption has been linked with metabolic syndrome and obesity. Fructose-based sweeteners like high fructose corn syrup taste sweeter, improve food palatability, and are increasingly prevalent in our diet. The increase in fructose consumption precedes the rise in obesity and is a contributing driver to the obesity epidemic worldwide. The role of dietary fructose in obesity can be multifactorial by promoting visceral adiposity, hypertension, and insulin resistance. Interestingly, one emergent finding from human and animal studies is that dietary fructose promotes overfeeding. As the brain is a critical regulator of food intake, we reviewed the evidence that fructose can act in the brain and elucidated the major brain systems underlying fructose-induced overfeeding. We found that fructose acts on multiple interdependent brain systems to increase orexigenic drive and the incentive salience of food while decreasing the latency between food bouts and reducing cognitive control to disinhibit feeding. We concluded that the collective actions of fructose may promote feeding behavior by producing a hunger-like state in the brain.

The Speed of Ingestion of a Sugary Beverage Has an Effect on the Acute Metabolic Response to Fructose

BACKGROUND

The consumption of sweetened beverages is associated with increased risk of metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus.

OBJECTIVE

We hypothesized that the metabolic effects of fructose in sugary beverages might be modulated by the speed of ingestion in addition to the overall amount.

DESIGN

Thirty healthy subjects free of any disease and medication were recruited into two groups. After overnight fasting, subjects in group 1 drank 500 mL of apple juice over an hour by drinking 125 mL every 15 min, while subjects in group 2 drank 500 mL of apple juice over 5 min. Blood samples were collected at time zero and 15, 30, 60, and 120 min after ingestion to be analyzed for serum glucose, insulin, homeostatic model assessment (HOMA-IR) score, fibroblast growth factor 21, copeptin, osmolarity, sodium, blood urea nitrogen (BUN), lactate, uric acid, and phosphate levels.

RESULTS

Serum glucose, insulin, HOMA-IR, fibroblast growth factor 21, copeptin, osmolarity, sodium, BUN, and lactate levels increased following apple juice ingestion. The increases were greater in the fast-drinking group, which were more significant after 15 min and 30 min compared to baseline. The changes in uric acid were not statistically different between the groups. Phosphate levels significantly increased only in the fast-drinking group.

CONCLUSION

Fast ingestion of 100% apple juice causes a significantly greater metabolic response, which may be associated with negative long-term outcomes. Our findings suggest that the rate of ingestion must be considered when evaluating the metabolic impacts of sweetened beverage consumption.