Uric acid, evolution and primitive cultures

Risk factors for cardio-cerebrovascular events among patients undergoing continuous ambulatory peritoneal dialysis and their association with serum magnesium

Serum magnesium levels exceeding 0.9 mmol/L are associated with increased survival rates in patients with CKD. This retrospective study aimed to identify risk factors for cardio-cerebrovascular events among patients receiving continuous ambulatory peritoneal dialysis (CAPD) and to examine their correlations with serum magnesium levels. Sociodemographic data, clinical physiological and biochemical indexes, and cardio-cerebrovascular event data were collected from 189 patients undergoing CAPD. Risk factors associated with cardio-cerebrovascular events were identified by univariate binary logistic regression analysis. Correlations between the risk factors and serum magnesium levels were determined by correlation analysis. Univariate regression analysis identified age, C-reactive protein (CRP), red cell volume distribution width standard deviation, red cell volume distribution width corpuscular volume, serum albumin, serum potassium, serum sodium, serum chlorine, serum magnesium, and serum uric acid as risk factors for cardio-cerebrovascular events. Among them, serum magnesium ≤0.8 mmol/L had the highest odds ratio (3.996). Multivariate regression analysis revealed that serum magnesium was an independent risk factor, while serum UA (<440 μmol/L) was an independent protective factor for cardio-cerebrovascular events. The incidence of cardio-cerebrovascular events differed significantly among patients with different grades of serum magnesium (χ2 = 12.023, p = 0.002), with the highest incidence observed in patients with a serum magnesium concentration <0.8 mmol/L. High serum magnesium levels were correlated with high levels of serum albumin (r = 0.399, p < 0.001), serum potassium (r = 0.423, p < 0.001), and serum uric acid (r = 0.411, p < 0.001), and low levels of CRP (r = -0.279, p < 0.001). In conclusion, low serum magnesium may predict cardio-cerebrovascular events in patients receiving CAPD.

Single-nucleotide polymorphisms link gout with health-related lifestyle factors in Korean cohorts

Gout-a very painful inflammatory arthritis caused by the deposition of monosodium urate crystals in the joints-is influenced by several factors. We identified the association of single- nucleotide polymorphisms (SNPs) that link gout with health-related lifestyle factors using genomic data from the Korean Genome and Epidemiology Study. We conducted a genome-wide association study (GWAS) on 18,927 samples of 438 Korean patients with gout and 18,489 controls for the discovery stage. For the replication stage, another batch containing samples of 326 patients with gout and 2,737 controls were analyzed. Lastly, a meta-analysis was performed using these two cohorts. We analyzed the effects of health-related lifestyle factors, including eating habits, physical activity, drinking behavior, and smoking behavior, on gout. After identifying the association between GWAS-derived SNPs and health-related lifestyle factors, we confirmed the interaction between the polygenic risk score (PRS) and health-related lifestyle factors. We identified 15 SNPs related to gout, among which rs1481012 of ABCG2 located on chromosome 4 has been newly discovered (P = 2.46e-11). On examining the interaction between SNPs and health-related lifestyles, rs3109823-located in ABCG2-was found to be associated with smoking status. In addition, rs11936395-located in SLC2A9-was significantly associated with the average momentum of exercise per session, whereas rs11066325 located in PTPN11, showed a significant association with the number of exercise sessions per week, smoking status, drinking status, and amount of soju drink per session. rs9421589-located in FAM35A-was significantly associated with the duration of smoking. In addition, we verified that the association between PRS and duration of smoking affects gout. Thus, in this study, we identified novel SNPs that link gout with health-related lifestyle factors in the Korean population.

Mechanisms and rationale for uricase use in patients with gout

Xanthine oxidase inhibitors such as allopurinol and febuxostat have been the mainstay urate-lowering therapy (ULT) for treating hyperuricaemia in patients with gout. However, not all patients receiving oral ULT achieve the target serum urate level, in part because some patients cannot tolerate, or have actual or misconceived contraindications to, their use, mainly due to comorbidities. ULT dosage is also limited by formularies and clinical inertia. This failure to sufficiently lower serum urate levels can lead to difficult-to-treat or uncontrolled gout, usually due to poorly managed and/or under-treated gout. In species other than humans, uricase (urate oxidase) converts urate to allantoin, which is more soluble in urine than uric acid. Exogenic uricases are an exciting therapeutic option for patients with gout. They can be viewed as enzyme replacement therapy. Uricases are being used to treat uncontrolled gout, and can achieve rapid reduction of hyperuricaemia, dramatic resolution of tophi, decreased chronic joint pain and improved quality of life. Availability, cost and uricase immunogenicity have limited their use. Uricases could become a leading choice in severe and difficult-to-treat gout as induction and/or debulking therapy (that is, for lowering of the urate pool) to be followed by chronic oral ULT. This Review summarizes the evidence regarding available uricases and those in the pipeline, their debulking effect and their outcomes related to gout and beyond.

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.

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 widely distributed gene cluster compensates for uricase loss in hominids

Approximately 15% of US adults have circulating levels of uric acid above its solubility limit, which is causally linked to the disease gout. In most mammals, uric acid elimination is facilitated by the enzyme uricase. However, human uricase is a pseudogene, having been inactivated early in hominid evolution. Though it has long been known that uric acid is eliminated in the gut, the role of the gut microbiota in hyperuricemia has not been studied. Here, we identify a widely distributed bacterial gene cluster that encodes a pathway for uric acid degradation. Stable isotope tracing demonstrates that gut bacteria metabolize uric acid to xanthine or short chain fatty acids. Ablation of the microbiota in uricase-deficient mice causes severe hyperuricemia, and anaerobe-targeted antibiotics increase the risk of gout in humans. These data reveal a role for the gut microbiota in uric acid excretion and highlight the potential for microbiome-targeted therapeutics in hyperuricemia.

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.

Evaluation of levels of uric acid and lipid profile in hospitalized patients with diabetes

OBJECTIVE

Diabetes is the most common metabolic disorder that leads to various complications, and among these complications, disruption in the lipid profile and serum uric acid (SUA) is one of the significant cases that can lead to the deterioration of the health status of patients with diabetes. So, we aimed to evaluate the level of SUA and lipid profiles in patients with diabetes. A total of 230 patients with diabetes who were admitted to Razi Hospital, Rasht, Iran, were enrolled in this study. Demographical data and clinical characteristics of the patients include gender, body mass index (BMI), duration of diabetes, history of smoking, FBS, HbA1c, SUA, Creatinine (Cr), Cholesterol (Chol), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides (TG), retinopathy, hypertension, ischemic heart disease (IHD), and microalbuminuria were recorded. All data were analyzed using the SPSS version 21 by a significant level < 0.05.

RESULT

According to our results, 70 were male, and 160 were female, with a mean age of 57.36 ± 8.05 years and a mean BMI of 28.10 ± 4.62. The most frequent comorbidities were hypertension, 67%. The serum level of FBS, HBA1c, SUA, Cr, Chol, LDL, HDL, and TG were 191.47 ± 71.66 mg/dL, 7.94 ± 1.21 mg/dL, 5.65 ± 1.95 mg/dL, 0.94 ± 0.16 mg/dL, 167.28 ± 45.22 mg/dL, 95.91 ± 37.03 mg/dL, 39.78 ± 10.44 mg/dL, and 186.75 ± 76.65 mg/dL, respectively. Only UA had a significant relationship with TG level (P < 0.05).

Implications of serum uric acid for female infertility: results from the national health and nutrition examination survey, 2013-2020

BACKGROUND

There is limited concrete evidence connecting serum uric acid levels to female infertility. Therefore, this study aimed to find out if serum uric acid levels are independently related to female infertility.

METHODS

From the National Health and Nutrition Examination Survey (NHANES) 2013-2020, a total sample of 5872 chosen female participants between the ages of 18 and 49 were identified for this cross-sectional study. The serum uric acid levels (mg/dL) of each participant were tested, and the reproductive health questionnaire was used to evaluate each subject's reproductive status. Both in the analyses of the full sample and each subgroup, logistic regression models were used to evaluate the relationship between the two variables. A stratified multivariate logistic regression model was used to perform the subgroup analysis based on serum uric acid levels.

RESULTS

Infertility was found in 649 (11.1%) of the 5,872 female adults in this study, with greater mean serum uric acid levels (4.7 mg/dL vs. 4.5 mg/dL). Serum uric acid levels were associated with infertility in both the initial and adjusted models. According to multivariate logistic regression, the odds of female infertility were found to be significantly higher with rising serum uric acid levels (Q4 [≥ 5.2 mg/dL] vs. Q1 [≤ 3.6 mg/dL]), adjusted odds ratio [aOR] = 1.59, p = 0.002]. The data suggests that there is a dose-response relationship between the two.

CONCLUSIONS

The results from this nationally representative sample from the United States confirmed the idea that there is a link between increased serum uric acid levels and female infertility. Future research is necessary to evaluate the relationship between serum uric acid levels and female infertility and explicate the underlying mechanisms of this relationship.

Intracellular DAMPs in Neurodegeneration and Their Role in Clinical Therapeutics

Neuroinflammation is the major implication of neurodegeneration. This is a complex process which initiates from the cellular injury triggering the innate immune system which gives rise to damage-associated molecular patterns (DAMPs) which are also recognized as endogenous danger indicators. These originate from various compartments of the cell under pathological stimulus. These are very popular candidates having their origin in the intracellular compartments and organelles of the cell and may have their site of action itself in the intracellular or at the extracellular spaces. Under the influence of the pathological stimuli, they interact with the pattern-recognition receptor to initiate their pro-inflammatory cascade followed by the cytokine release. This provides a good opportunity for diagnostic and therapeutic interventions creating better conditions for repair and reversal. Since the major contributors arise from the intracellular compartment, in this review, we have attempted to focus on the DAMP molecules arising from the intracellular compartments and their specific roles in the neurodegenerative events explaining their downstream mediators and signaling. Moreover, we have tried to cover the latest interventions in terms of DAMPs as clinical biomarkers which can assist in detecting the disease and also target it to reduce the innate-immune activation response which can help in reducing the sterile neuroinflammation having an integral role in the neurodegenerative processes.

Prevalence and related factors of hyperuricaemia in Chinese children and adolescents: a pooled analysis of 11 population-based studies

BACKGROUND AND AIMS

Hyperuricaemia can lead to gout and is associated with an increased risk of cardiometabolic disease. We aimed to investigate the prevalence of hyperuricaemia and its related factors in Chinese children and adolescents.

METHODS

We pooled data from 11 population-based studies comprising 54,580 participants aged 3-19 years. The sex- and age-standardized prevalence of hyperuricaemia was estimated overall and by sex, age, weight status, geographic region and survey year.

RESULTS

Serum uric acid (SUA) increased gradually from 3 to 11 years with no significant sex difference, and then increased dramatically during 11-15 years. The estimated overall prevalence of hyperuricaemia was 23.3% (26.6% in boys and 19.8% in girls, p < .001). The prevalence increased with growing age (3.7, 9.8, 15.8, 35.5 and 31.7% among children aged 3-5, 6-8, 9-11, 12-15 and 16-19 years, respectively, p for trend < .001) and with increasing weight status (18.2, 37.6, 50.6 and 64.5% among children with non-overweight, overweight, obesity and extreme obesity, respectively, p for trend < .001). The prevalence was higher in North than in South (24.2 vs. 19.7%, p < .001), and increased markedly from 16.7% during 2009-2015 to 24.8% during 2016-2019. In multivariable regression analyses, sex, age, obesity, region and survey year were independently associated with odds of hyperuricaemia.

CONCLUSIONS

The prevalence of hyperuricaemia in Chinese children and adolescents is unexpectedly high. The findings suggest an urgent need to implement effective interventions to reduce risk of hyperuricaemia in Chinese youths.KEY MESSAGESQuestion: What is the prevalence of hyperuricaemia in Chinese children and adolescents?Findings: In this large pooled cross-sectional study comprising >50,000 children and adolescents aged 3-19 years, we found that the prevalence of hyperuricaemia was high in overall population and subgroups of sex, age, obesity, region and survey year.Meaning: Our findings indicate that hyperuricaemia is an important health problem in Chinese children and adolescents, and effective intervention strategies are needed to reduce its burden.

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.

A fly GWAS for purine metabolites identifies human FAM214 homolog medusa, which acts in a conserved manner to enhance hyperuricemia-driven pathologies by modulating purine metabolism and the inflammatory response

Elevated serum urate (hyperuricemia) promotes crystalline monosodium urate tissue deposits and gout, with associated inflammation and increased mortality. To identify modifiers of uric acid pathologies, we performed a fly Genome-Wide Association Study (GWAS) on purine metabolites using the Drosophila Genetic Reference Panel strains. We tested the candidate genes using the Drosophila melanogaster model of hyperuricemia and uric acid crystallization ("concretion formation") in the kidney-like Malpighian tubule. Medusa (mda) activity increased urate levels and inflammatory response programming. Conversely, whole-body mda knockdown decreased purine synthesis precursor phosphoribosyl pyrophosphate, uric acid, and guanosine levels; limited formation of aggregated uric acid concretions; and was sufficient to rescue lifespan reduction in the fly hyperuricemia and gout model. Levels of mda homolog FAM214A were elevated in inflammatory M1- and reduced in anti-inflammatory M2-differentiated mouse bone marrow macrophages, and influenced intracellular uric acid levels in human HepG2 transformed hepatocytes. In conclusion, mda/FAM214A acts in a conserved manner to regulate purine metabolism, promotes disease driven by hyperuricemia and associated tissue inflammation, and provides a potential novel target for uric acid-driven pathologies.

Prevalence and risk factors of hyperuricemia and gout: a cross-sectional survey from 31 provinces in mainland China

Background and Objetives

Hyperuricemia (HUA) and gout seriously influence patients’ quality of life. The current study was performed to investigate the prevalence of HUA and gout and the related risk factors in Chinese adults.

Methods

Data were collected from the National Survey of Thyroid Disorders and Diabetes (the Thyroid Disease, Iodine Status, and Diabetes National Epidemiological survey [TIDE]), a cross-sectional investigation conducted during 2015–2017. Using a random, multistage, and stratified sampling strategy, a representative sample (78,130 participants aged 18 years and above) was selected from the general population in 31 provinces of mainland China. The weighted prevalence rates of HUA and gout were calculated, and the related risk factors were analyzed.

Results

The weighted prevalence rates of HUA and gout in Chinese adults were 17.7% and 3.2%, respectively. The prevalence of HUA in males linearly decreased with age, while the prevalence in females showed the opposite trend (both P for trend < 0.01). The prevalence rate of gout exhibited a rising tendency with age in both genders (both P for trend < 0.05). The HUA and gout prevalence rates in males were the highest in Han and Tibetan nationalities, respectively. Logistic regression analysis showed that the morbidities of HUA and gout were differentially associated with age, residence location, nationality, smoking, and other complicating metabolic diseases in the two genders.

Conclusions

There are relatively high prevalence rates of gout and HUA in China, which is currently a developing country. Reducing their burden has become an urgent issue for Chinese people.

The association between uric acid and erectile dysfunction: A systematic review and Meta-analysis

The main purpose of this systematic review and meta-analysis was to explore the association between uric acid (UA) and erectile dysfunction (ED). Databases including PubMed, Cochrane Library and Web of Science were retrieved to identify studies published in English up to 31 June 2021. We preregistered this meta-analysis in the PROSPERO (registration number CRD42021267035). Two independent authors extracted the relevant data from all enrolled articles. We evaluated the quality of enrolled studies using the Newcastle-Ottawa Scale (NOS). The standardized mean difference (SMD), as well as the corresponding 95% confidence intervals (95% CIs), was used to assess the difference between ED patients and healthy subjects. A total of five studies were enrolled for our meta-analysis to explore the association of UA with ED. The pooled SMD of the UA level difference between ED patients and healthy subjects was 0.42 (95% CI:0.09, 0.74, p < 0.001). There were no individual data that significantly influenced the pooled SMDs in the sensitivity analysis. There was no evidence of publication bias. This novel meta-analysis confirmed that UA was an independent risk factor for ED, which suggested that the erectile function of patients with elevated uric acid should be evaluated by clinicians.

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.

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.

Human Evolution and Dietary Ethanol

The "drunken monkey" hypothesis posits that attraction to ethanol derives from an evolutionary linkage among the sugars of ripe fruit, associated alcoholic fermentation by yeast, and ensuing consumption by human ancestors. First proposed in 2000, this concept has received increasing attention from the fields of animal sensory biology, primate foraging behavior, and molecular evolution. We undertook a review of English language citations subsequent to publication of the original paper and assessed research trends and future directions relative to natural dietary ethanol exposure in primates and other animals. Two major empirical themes emerge: attraction to and consumption of fermenting fruits (and nectar) by numerous vertebrates and invertebrates (e.g., Drosophila flies), and genomic evidence for natural selection consistent with sustained exposure to dietary ethanol in diverse taxa (including hominids and the genus Homo) over tens of millions of years. We also describe our current field studies in Uganda of ethanol content within fruits consumed by free-ranging chimpanzees, which suggest chronic low-level exposure to this psychoactive molecule in our closest living relatives.

The biology of urate

Urate is the end-product of the purine metabolism in humans. The dominant source of urate is endogenous purines and the remainder comes through diet. Approximately two thirds of urate is eliminated via the kidney with the rest excreted in the feces. While the transporter BCRP, encoded by ABCG2, has been found to play a role in both the gut and kidney, SLC22A12 and SLC2A9 encoding URAT1 and GLUT9, respectively, are the two transporters best characterized. Only 8-12% of the filtered urate is excreted by the kidney. Renal elimination of urate depends substantially on specific transporters, including URAT1, GLUT9 and BCRP. Studies that have assessed the biologic effects of urate have produced highly variable results. Although there is a suggestion that urate may have anti-oxidant properties in some circumstances, the majority of evidence indicates that urate is pro-inflammatory. Hyperuricemia can result in the formation of monosodium urate (MSU) crystals that may be recognized as danger signals by the immune system. This immune response results in the activation of the NLRP3 inflammasome and ultimately in the production and release of interleukin-1β, and IL-18, that mediate both inflammation, pyroptotic cell death, and necroinflammation. It has also been demonstrated that soluble urate mediates effects on the kidney to induce hypertension and can induce long term epigenetic reprogramming in myeloid cells to induce "trained immunity." Together, these sequelae of urate are thought to mediate most of the physiological effects of hyperuricemia and gout, illustrating this biologically active molecule is more than just an "end-product" of purine metabolism.

Role of Vitamin C in Prophylaxis and Treatment of Gout-A Literature Review

Gout, known as “the disease of the kings”, is the most frequent type of arthritis. It results from sustained hyperuricemia that leads to monosodium urate crystal deposition in joint structures and soft tissue. Environmental factors such as diet affect the incidence of gout; there is a known relationship between the occurrence of an acute attack of gout and the consumption of alcohol and meat; and a low purine diet is a widely recognized nonpharmacological method of supplementing the treatment and preventing recurrence of arthritis. This review aims to summarize the current knowledge about the role of vitamin C in prevention and treatment of gout. A PubMed/Medline database search on the role of vitamin C in purine metabolism was done. Reports from in vitro and animal studies seem to be promising and to allow explanation of the physiological relationship between vitamin C and uric acid. Most epidemiological studies indicate a significant correlation between high vitamin C intake and lower serum uric acid levels. Despite promising observations, there are few observational and interventional studies, and their results do not clearly define the benefits of a high daily intake of vitamin C in preventing the development and recurrence of gout.

Elevated salivary uric acid levels among adolescents with eating disorders

OBJECTIVE

Uric acid (UA) is increasingly recognized as having important physiological roles and associated with several peripheral and central pathophysiological outcomes, and might play a role in eating disorders (ED) pathogenesis. We investigated whether UA levels are altered among adolescents with ED.

METHODS

Morning salivary UA concentrations were compared between adolescents referred to treatment at the Herman Dana Center receiving a DSM-V diagnosis of an ED and matched healthy controls.

RESULTS

Salivary UA was significantly elevated among ED compared with control values (ED mean 3.9 ± 1.2 mg/dl, control mean 2.9 ± 1.9 mg/dl, t = - 3.13 df = 81, p = 0.003).

DISCUSSION

Salivary UA is elevated among adolescents with ED. Further studies are required to replicate and extend this finding and evaluate its generalizability as a state or trait marker as regards ED subtypes, other body fluids (plasma and cerebrospinal fluid), and recovery or premorbid stages, as well as its putative mechanistic relevance to ED.

LEVEL OF EVIDENCE

Level III, case-control analytic study.

The effect of purine content on sensory quality of pork

Although high level of purine in foods is considered a risk factor for hyperuricemia and gout, purine-rich foods continue to be popular for their delicious taste. The main objective of this study was to investigate the effects of purine bases on the sensory quality of pork. A total of 406 longissimus thoracis et lumborum samples were collected from a heterogeneous F6 pig population to determine purine composition and its correlation to sensory quality of pork. The contents of total purine and two major uricogenic bases (adenine and hypoxanthine) were negatively correlated with tenderness, juiciness, oiliness and overall liking (r < -0.2, P < 0.05), but they were not significantly correlated with umami. In contrast, guanine content, which accounts for only about 10% of the total purine content, was positively correlated with umami (r = 0.15, P < 0.05), and had no significant relationships with other sensory indicators. These results imply that purine bases with different uricogenic effects also influence different sensory quality indices of pork.

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.

New insights into purine metabolism in metabolic diseases: role of xanthine oxidoreductase activity

Xanthine oxidoreductase (XOR) consists of two different forms, xanthine dehydrogenase and xanthine oxidase (XO), and is a rate-limiting enzyme of uric acid production from hypoxanthine and xanthine. Uric acid is the end product of purine metabolism in humans and has a powerful antioxidant effect. The lack of ascorbic acid, known as vitamin C, in hominoids has been thought to cause a compensatory increase in uric acid as an antioxidant by unfunctional gene mutation of uricase to a pseudogene. Because XO is involved in an increase in reactive oxygen species (ROS) by generating superoxide and hydrogen peroxide, inadequate activation of XOR promotes oxidative stress-related tissue injury. Plasma XOR activity is associated with obesity, smoking, liver dysfunction, hyperuricemia, dyslipidemia, insulin resistance, and adipokines, indicating a novel biomarker of metabolic disorders. However, XOR activity in adipose tissue is low in humans unlike in rodents, and hypoxanthine is secreted from human adipose tissue. The concentration of hypoxanthine, but not xanthine, is independently associated with obesity in a general population, indicating differential regulation of hypoxanthine and xanthine. Treatment with an XOR inhibitor can decrease uric acid for preventing gout, reduce production of XO-related ROS, and promote reutilization of hypoxanthine and ATP production through the salvage pathway. It has recently been suggested that discontinuation of an XOR inhibitor causes adverse cardiovascular outcomes as XOR inhibitor withdrawal syndrome, possibly due to cardiac disturbance of conduction and contraction by reduced ATP production. New insights into purine metabolism, including the role of XOR activity in the past 5 yr, are mainly discussed in this review.

Cerebral Fructose Metabolism as a Potential Mechanism Driving Alzheimer's Disease

The loss of cognitive function in Alzheimer's disease is pathologically linked with neurofibrillary tangles, amyloid deposition, and loss of neuronal communication. Cerebral insulin resistance and mitochondrial dysfunction have emerged as important contributors to pathogenesis supporting our hypothesis that cerebral fructose metabolism is a key initiating pathway for Alzheimer's disease. Fructose is unique among nutrients because it activates a survival pathway to protect animals from starvation by lowering energy in cells in association with adenosine monophosphate degradation to uric acid. The fall in energy from fructose metabolism stimulates foraging and food intake while reducing energy and oxygen needs by decreasing mitochondrial function, stimulating glycolysis, and inducing insulin resistance. When fructose metabolism is overactivated systemically, such as from excessive fructose intake, this can lead to obesity and diabetes. Herein, we present evidence that Alzheimer's disease may be driven by overactivation of cerebral fructose metabolism, in which the source of fructose is largely from endogenous production in the brain. Thus, the reduction in mitochondrial energy production is hampered by neuronal glycolysis that is inadequate, resulting in progressive loss of cerebral energy levels required for neurons to remain functional and viable. In essence, we propose that Alzheimer's disease is a modern disease driven by changes in dietary lifestyle in which fructose can disrupt cerebral metabolism and neuronal function. Inhibition of intracerebral fructose metabolism could provide a novel way to prevent and treat this disease.

Uric acid is independent and inversely associated to glomerular filtration rate in young adult Brazilian individuals

BACKGROUND AND AIMS

Uric acid, the end-product of human purine metabolism, is associated with hypertension, diabetes and obesity. It has also been independently associated with the onset of chronic kidney disease in several populations. In this study, the association between serum uric acid (SUA) level and estimated glomerular filtration rate (eGFR) was investigated in healthy individuals belonging to two Brazilian birth cohorts.

METHODS AND RESULTS

Data from 3541 to 3482 individuals, aged 30 and 22-years old, respectively, was included. eGFR was calculated using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation based on creatinine measurement. Regression analyses were sex-stratified due to interaction between SUA and sex (p < 0.001) and adjusted for perinatal, cardiometabolic and behavioral variables. We observed an inverse association between eGFR and SUA even after adjustment. In the highest tertile (3rd) of SUA, the eGFR coefficients at 30-years were-0.21 (95%CI -0.24;-0.18) for men and -0.20 (95%CI -0.23; -0.17) for women; at 22-years, were -0.09 (95%CI -0.12;-0.05) for men and -0.13 (95%CI -0.15; -0.10) for women. Higher differences among exponential means (95% CI) of eGFR between the 1st and the 3rd tertile of SUA were seen in older participants, being more pronounced in men. At 22-years, the highest difference was found in women.

CONCLUSIONS

In young healthy individuals from a low-middle income country, SUA level was inversely associated with eGFR. Gender-related differences in eGFR according tertiles of SUA were higher in men at 30-years and in women at 22-years.

Uric Acid and Hypertension: An Update With Recommendations

The association between increased serum urate and hypertension has been a subject of intense controversy. Extracellular uric acid drives uric acid deposition in gout, kidney stones, and possibly vascular calcification. Mendelian randomization studies, however, indicate that serum urate is likely not the causal factor in hypertension although it does increase the risk for sudden cardiac death and diabetic vascular disease. Nevertheless, experimental evidence strongly suggests that an increase in intracellular urate is a key factor in the pathogenesis of primary hypertension. Pilot clinical trials show beneficial effect of lowering serum urate in hyperuricemic individuals who are young, hypertensive, and have preserved kidney function. Some evidence suggest that activation of the renin-angiotensin system (RAS) occurs in hyperuricemia and blocking the RAS may mimic the effects of xanthine oxidase inhibitors. A reduction in intracellular urate may be achieved by lowering serum urate concentration or by suppressing intracellular urate production with dietary measures that include reducing sugar, fructose, and salt intake. We suggest that these elements in the western diet may play a major role in the pathogenesis of primary hypertension. Studies are necessary to better define the interrelation between uric acid concentrations inside and outside the cell. In addition, large-scale clinical trials are needed to determine if extracellular and intracellular urate reduction can provide benefit hypertension and cardiometabolic disease.

Uric acid and cardiometabolic diseases

Hyperuricemia, which has been considered as a cause of gout and nephrolithiasis has recently been suggested to be associated with hypertension, coronary heart disease, heart failure, atrial fibrillation, insulin resistance, and nonalcoholic fatty liver disease. Several clinical and experimental studies have supported uric acid (UA) as an independent risk factor for predicting disease development along with the traditional risk factors. The mechanism by which UA causes cardiometabolic disease has not been fully elucidated to date; however, it has been explained by several hypotheses such as oxidative stress, reduced nitric oxide bioavailability, inflammation, endothelial dysfunction, and so on. Although evidence of the preventive and therapeutic effects of UA lowering therapy on cardiometabolic diseases is still insufficient, it is expected to be considered as a new treatment strategy for such diseases through additional, carefully designed, large-scale clinical studies.

Reactivity of salivary uric acid in response to social evaluative stress in African Americans

High uric acid (UA) is associated with hypertension and cardiovascular disease (CVD), both of which occur disproportionately among African Americans. High UA also predicts greater blood pressure reactivity responses to acute social stress. However, whether UA itself shows reactivity in response to stress is unknown. We evaluated salivary uric acid (sUA) and blood pressure reactivity in response to acute social stress. Healthy African Americans (N = 103; 32 % male; M age = 31.36 years), completed the Trier Social Stress Test. sUA and blood pressure measurements were taken before, during and after the stressor task. sUA showed significant reactivity and recovery, especially among older African Americans. Total sUA activation was also associated with systolic and diastolic blood pressure total activation. Findings illuminate that acute stress may be a way in which UA is implicated in hypertension and CVD, suggesting a critical need to explore UA reactivity as a novel parameter of the acute stress response.

Management of hyperuricemia in asymptomatic patients: A critical appraisal

While there is consensus on starting urate-lowering therapy (ULT) in cases of symptomatic hyperuricemia, the frequent condition of asymptomatic hyperuricemia (AH) remains a challenge due to differences in the findings of studies that have addressed the issue. Uric acid has anti-oxidant properties, but high levels predispose to gout and may play a role in metabolic syndrome. We systematically evaluated randomized controlled trials (RCTs) addressing ULT in patients with AH, to assess the current evidence. We found broad heterogeneity among the studies (13 RCTs), in terms of study design and population, making findings challenging to interpret and generalize; hard end-points were not assessed. Allopurinol is often prescribed for AH despite the fact that its use is not backed by conclusive evidence from prospective RCTs, nor is it recommended by the guidelines. Its potential benefits, in terms of absolute risk reduction, must be weighed against its potential for harm since it can trigger severe adverse hypersensitivity reactions, sometimes even fatal. RCTs with hard end-points are needed to assess the risk/benefit of lowering uric acid in subjects with AH, particularly as secondary prevention for cardiovascular risk and in patients with different degrees of renal disease. To date, particularly after the result from the CARES trial, preventive treatment of asymptomatic and non-severe hyperuricemia is not recommended.

Uric acid and inflammation in kidney disease

Asymptomatic hyperuricemia is frequently observed in patients with kidney disease. Although a substantial number of epidemiologic studies have suggested that an elevated uric acid level plays a causative role in the development and progression of kidney disease, whether hyperuricemia is simply a result of decreased renal excretion of uric acid or is a contributor to kidney disease remains a matter of debate. Over the last two decades, multiple experimental studies have expanded the knowledge of the biological effects of uric acid beyond its role in gout. In particular, uric acid induces immune system activation and alters the characteristics of resident kidney cells, such as tubular epithelial cells, endothelial cells, and vascular smooth muscle cells, toward a proinflammatory and profibrotic state. These findings have led to an increased awareness of uric acid as a potential and modifiable risk factor in kidney disease. Here, we discuss the effects of uric acid on the immune system and subsequently review the effects of uric acid on the kidneys mainly in the context of inflammation.

High-Protein Diet Induces Hyperuricemia in a New Animal Model for Studying Human Gout

Hyperuricemia is a central risk factor for gout and increases the risk for other chronic diseases, including cardiometabolic disease, kidney disease, and hypertension. Overproduction of urate is one of the main reasons for hyperuricemia, and dietary factors including seafoods, meats, and drinking are contributed to the development of it. However, the lack of a suitable animal model for urate metabolism is one of the main reasons for the delay and limitations of hyperuricemia research. Combining evolutionary biological studies and clinical studies, we conclude that chicken is a preferred animal model for hyperuricemia. Thus, we provided chickens a high-protein diet (HPD) to evaluate the changes in the serum urate levels in chickens. In our study, the HPD increased the serum urate level and maintained it at a long-term high level in chickens. Long-term high serum urate levels induced an abnormal chicken claw morphology and the precipitation of monosodium urate (MSU) in joint synovial fluid. In addition, a long-term HPD also decreased the glomerular filtration rate and induced mild renal injury. Most importantly, allopurinol and probenecid displayed the positive effects in decreasing serum urate and then attenuated hyperuricemia in chicken model. These findings provide a novel model for hyperuricemia and a new opportunity to further investigate the effects of long-term hyperuricemia on other metabolic diseases.

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.

The effects of fruit consumption in patients with hyperuricaemia or gout

The consumption of fructose has gained increased attention as a potential cause of hyperuricaemia since fructose metabolism produces urate as a byproduct. In addition to sucrose and high fructose corn syrup, fresh fruits also contain fructose, suggesting that patients with hyperuricaemia or gout might also avoid fresh fruit. However, the effect of fruits is complex. Some studies reported that fruit intake was associated with gout flares while other studies showed that fruits rather lowered the risk for gout. Thus, fruits should not be simply viewed as a source of fructose. The complexity of fruits is accounted for by several nutrients existing in fruits. Vitamin C, epicatechin, flavonols, potassium and fibre are all nutrients in fruits, and these factors could modify fructose and urate effects. In this review, we discuss clinical studies evaluating the effect of fruit and fruit juice intake on hyperuricaemia and gout, and propose potential mechanisms for how fruit may influence urate levels.

Hyperuricemia and Cardiovascular Disease

Purine metabolism in the circulatory system yields uric acid as its final oxidation product, which is believed to be linked to the development of gout and kidney stones. Hyperuricemia is closely correlated with cardiovascular disease, metabolic syndrome, and chronic kidney disease, as attested by the epidemiological and empirical research. In this review, we summarize the recent knowledge about hyperuricemia, with a special focus on its physiology, epidemiology, and correlation with cardiovascular disease. This review also discusses the possible positive effects of treatment to reduce urate levels in patients with cardiovascular disease and hyperuricemia, which may lead to an improved clinical treatment plan.

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.

Association of urinary metal profiles with serum uric acid: a cross-sectional study of traffic policemen in Wuhan, China

OBJECTIVES

Serum uric acid (SUA) is both a strong antioxidant and one of the key risk factors of cardiovascular diseases (CVDs). We aimed to investigate the associations of urinary metal profile with SUA in traffic policemen in Wuhan, China.

DESIGN

A cross-sectional study was carried out in traffic policemen.

SETTING

A seriously polluted Chinese city.

PARTICIPANTS

A total of 186 traffic policemen were recruited in this study. About 56 of them worked in the logistics department and the other 130 maintained traffic order or dealt with traffic accidents on the roads. All these subjects had worked as a policeman for at least 1 year.

MAIN OUTCOME MEASURES

SUA.

RESULTS

The significantly negative association of lead with SUA was consistent between single-metal and multiple-metal models (p=0.004 and p=0.020, respectively). Vanadium, chromium and tin were reversely associated with SUA levels in the single-metal models after false discovery rate (FDR) adjustment (all P_{_FDR} < 0.05). One IQR increase in vanadium, chromium, tin and lead was associated with 26.9 µmol/L (95% CI -44.6 to -9.2; p=0.003), 27.4 µmol/L (95% CI -46.1 to -8.8; p=0.004), 11.2 µmol/L (95% CI -18.9 to -3.4; p=0.005) and 16.4 µmol/L (95% CI -27.6 to -5.2; p=0.004) decrease in SUA, respectively. Significant interaction between smoking and vanadium on decreased SUV was found (p_{for interaction} = 0.007 and p_{_FDR} = 0.028).

CONCLUSIONS

Urinary vanadium, chromium, tin and lead were negatively associated with SUA. Vanadium and cigarette smoking jointly affected SUA levels. Further studies are needed to replicate these findings and to investigate the potential mechanisms.

Reference interval and upper decission limit for serum uric acid – an evidence-based approach on Romanian population using an a posteriori method

Introduction. There is accumulating evidence that high normal serum uric acid (SUA) levels of 6-7 mg/dL are associated with cardiovascular morbidity and metabolic syndrome (MetS), hence the need to redefine its upper limit of normal (ULN). We aimed to derive ULN based on statistics and evidence in a representative sample of the population and to observe its relation to MetS components.

Methods. All SUA measurements form a university rheumatology hospital were extracted between January 5th 2010 and March 21st 2018. SUA levels were measured by a single biochemist a unique type of commercially available kit. Follow-up measurements, patients with diagnoses influencing SUA levels and outlying measurements were excluded. ULNs were studied using least square analysis.

Results. Of the 22503 SUA measurements in the database, only 3318 came from normal individuals: 33.3% men (n=1105), 66.7% women (n = 2213). Least square analysis revealed the following SUA reference intervals (RI): 3.43-6.19 mg/dL for the combined sample; 4.44-7.01 mg/dL for men, 3.28-5.56 mg/dL for women. The values corresponding to the 66th percentile of each group presented lower ULNs: 5.36 mg/dL for all, 6.10 mg/dL for men, 4.90 mg/dL for women. The prevalence of hyperuricemia increased from 13.8% (manufacturer’s gender-specific ULN) to 19.9% (derived ULN). Mean SUA levels significantly increased with the number of MetS components.

Conclusion. We recommend that hyperuricemia should be defined using a statistical approach of ULN selection corresponding to the genderand population-specific 66th percentile of data range.

Distinct Uric Acid Trajectories Are Associated With Different Risks of Incident Hypertension in Middle-Aged Adults

OBJECTIVES

To identify common uric acid (UA) trajectories in middle-aged adults and to examine their association with the risk of hypertension.

PATIENTS AND METHODS

This prospective cohort included 5758 participants who were aged between 30 and 60 years without hypertension on or before June 1, 2011. Latent mixture modeling was used to identify UA trajectories from June 1, 2005, through June 1, 2011, as the predictor. Incident hypertension from June 1, 2011, through June 1, 2017, was used as the outcome.

RESULTS

We detected 5 distinct trajectory groups of UA in both men and women: low-stable (for women, n=720 [24.6%]; for men, n=732 [25.9%]), low-increasing (for women, n=599 [20.4%]; for men, n=696 [24.6%]), moderate-increasing (for women, n=660 [22.5%]; for men, n=634 [22.4%]), high-decreasing (for women, n=314 [10.7%]; for men, n=227 [8.0%]), and high-stable (for women, n=638, 21.8 %; for men, n=538, 19.0%). We observed that 284 women developed hypertension during a median follow-up of 5.9 years (range, 0.8-6.2 years) and 674 men developed hypertension during a median follow-up of 5.9 years (range, 0.7-6.2 years). Compared with the low-stable group, the moderate-increasing group had the highest risk, with adjusted hazard ratios (HRs) of 2.48 (95% CI, 1.64-3.74) in women and 1.84 (95% CI, 1.43-2.35) in men, followed by the high-stable group, with adjusted HRs of 1.97 (95% CI, 1.29-3.01) in women and 1.45 (95% CI, 1.15-1.88) in men. Notably, the low-increasing group with UA in the normal range also exhibited an increased risk, with adjusted HRs of 1.83 (95% CI, 1.20-2.79) in women and 1.42 (95% CI, 1.10-1.83) in men. The high-decreasing group did not exhibit a substantially increased risk. These observed associations between UA trajectories and hypertension were independent of concurrent weight change.

CONCLUSION

Our results suggest that distinct trajectories of UA are differently associated with hypertension risk in middle-aged adults.

Salivary uric acid: Associations with resting and reactive blood pressure response to social evaluative stress in healthy African Americans

High levels of uric acid are associated with greater risk of stress-related cardiovascular illnesses that occur disproportionately among African Americans. Whether hyperuricemia affects biological response to acute stress remains largely unknown, suggesting a need to clarify this potential connection. The current study examined how salivary uric acid (sUA) is associated with resting and reactive blood pressure - two robust predictors of hypertension and related cardiovascular disease and disparity. Healthy African Americans (N = 107; 32% male; M age = 31.74 years), completed the Trier Social Stress Test to induce social-evaluative stress. Systolic and diastolic blood pressure readings were recorded before, during, and after the task to assess resting and reactive change in blood pressure. Participants also provided a saliva sample at baseline that was assayed for sUA. At rest, and controlling for age, sUA was modestly associated with higher systolic (r = .201, p =  .044), but not diastolic (r = .100, p =  .319) blood pressure. In response to the stressor task, and once again controlling for age, sUA was also associated with higher total activation of both systolic (r = .219, p =  .025) and diastolic blood pressure (r = .198, p <  .044). A subsequent moderation analysis showed that associations between sUA and BP measures were significant for females, but not for males. Findings suggest that uric acid may be implicated in hypertension and cardiovascular health disparities through associations with elevated blood pressure responses to acute social stress, and that low levels of uric acid might be protective, particularly for females.

What Is the Biological Function of Uric Acid? An Antioxidant for Neural Protection or a Biomarker for Cell Death

The main aim of the present study was to investigate the biological function of uric acid. The level of uric acid in different organs in normal male rats was determined with uric acid assay kits, and the expression level of genes in the organs was determined by RNA quantitative sequencing. The correlation analysis between uric acid in the organs and gene expression (measured by FPKM value) was made. Serum uric acid (SUA) in patients with breast cancer or with breast benign tumor was assayed when the diagnosis was made, and SUA in patients with breast cancer was also assayed just after chemotherapy. There were 1937 mRNAs whose expression level significantly correlated with the level of uric acid, and most of which were associated with purine or nucleoside metabolism, cellular metabolism, cell cycles, and cell death pathways. Further analysis showed that the level of uric acid was highly correlated with cell death rather than cell viability. The level of SUA in patients with breast cancer was higher than that in patients with breast benign tumor, and the SUA increased after chemotherapy. All the results suggested that uric acid was mainly synthesized from local nucleosides degraded from dead cells, and uric acid could be an important biomarker for cell death rather than an antioxidant for neural protection.

Uric acid enhances longevity and endurance and protects the brain against ischemia

Among mammals, there is a positive correlation between serum uric acid (UA) levels and life span. Humans have high levels of UA because they lack a functional urate oxidase (UOX) enzyme that is present in shorter lived mammals. Here, we show that male and female mice with UOX haploinsufficiency exhibit an age-related elevation of UA levels, and that the life span of female but not male UOX+/- mice is significantly increased compared to wild-type mice. Serum UA levels are elevated in response to treadmill exercise in UOX+/- mice, but not wild-type mice, and the endurance of the UOX+/- mice is significantly greater than wild-type mice. UOX+/- mice exhibit elevated levels of brain-derived neurotrophic factor, reduced brain damage and improved functional outcome in a model of focal ischemic stroke. Levels of oxidative protein nitration and lipid peroxidation are reduced in muscle and brain tissues of UOX+/- mice under conditions of metabolic and oxidative stress (running in the case of muscle and ischemia in the case of the brain), consistent with prior evidence that UA can scavenge peroxynitrite and hydroxyl radical. Our findings reveal roles for UA in life span determination, endurance and adaptive responses to brain injury, and suggest novel approaches for protecting cells against injury and for optimizing physical performance.

Lacking ketohexokinase-A exacerbates renal injury in streptozotocin-induced diabetic mice

OBJECTIVE

Ketohexokinase (KHK), a primary enzyme in fructose metabolism, has two isoforms, namely, KHK-A and KHK-C. Previously, we reported that renal injury was reduced in streptozotocin-induced diabetic mice which lacked both isoforms. Although both isoforms express in kidney, it has not been elucidated whether each isoform plays distinct roles in the development of diabetic kidney disease (DKD). The aim of the study is to elucidate the role of KHK-A for DKD progression.

MATERIALS AND METHODS

Diabetes was induced by five consecutive daily intraperitoneal injections of streptozotocin (50 mg/kg) in C57BL/6J wild-type mice, mice lacking KHK-A alone (KHK-A KO), and mice lacking both KHK-A and KHK-C (KHK-A/C KO). At 35 weeks, renal injury, inflammation, hypoxia, and oxidative stress were examined. Metabolomic analysis including polyol pathway, fructose metabolism, glycolysis, TCA (tricarboxylic acid) cycle, and NAD (nicotinamide adenine dinucleotide) metabolism in kidney and urine was done.

RESULTS

Diabetic KHK-A KO mice developed severe renal injury compared to diabetic wild-type mice, and this was associated with further increases of intrarenal fructose, dihydroxyacetone phosphate (DHAP), TCA cycle intermediate levels, and severe inflammation. In contrast, renal injury was prevented in diabetic KHK-A/C KO mice compared to both wild-type and KHK-A KO diabetic mice. Further, diabetic KHK-A KO mice contained decreased renal NAD⁺ level with the increase of renal hypoxia-inducible factor 1-alpha expression despite having increased renal nicotinamide (NAM) level.

CONCLUSION

These results suggest that KHK-C might play a deleterious role in DKD progression through endogenous fructose metabolism, and that KHK-A plays a unique protective role against the development of DKD.

Hyperuricemia, Acute and Chronic Kidney Disease, Hypertension, and Cardiovascular Disease: Report of a Scientific Workshop Organized by the National Kidney Foundation

Urate is a cause of gout, kidney stones, and acute kidney injury from tumor lysis syndrome, but its relationship to kidney disease, cardiovascular disease, and diabetes remains controversial. A scientific workshop organized by the National Kidney Foundation was held in September 2016 to review current evidence. Cell culture studies and animal models suggest that elevated serum urate concentrations can contribute to kidney disease, hypertension, and metabolic syndrome. Epidemiologic evidence also supports elevated serum urate concentrations as a risk factor for the development of kidney disease, hypertension, and diabetes, but differences in methodologies and inpacts on serum urate concentrations by even subtle changes in kidney function render conclusions uncertain. Mendelian randomization studies generally do not support a causal role of serum urate in kidney disease, hypertension, or diabetes, although interpretation is complicated by nonhomogeneous populations, a failure to consider environmental interactions, and a lack of understanding of how the genetic polymorphisms affect biological mechanisms related to urate. Although several small clinical trials suggest benefits of urate-lowering therapies on kidney function, blood pressure, and insulin resistance, others have been negative, with many trials having design limitations and insufficient power. Thus, whether uric acid has a causal role in kidney and cardiovascular diseases requires further study.

Pre-diagnostic plasma urate and the risk of amyotrophic lateral sclerosis

OBJECTIVE

To prospectively examine for the first time the association between plasma urate levels measured in healthy participants and future amyotrophic lateral sclerosis (ALS) risk.

METHODS

A pooled case-control study nested in five US prospective cohorts comprising 319,617 participants who provided blood, of which 275 had ALS during follow-up. Pre-diagnostic plasma urate was determined for all participants using a clinical colorimetric enzyme assay. Gender-specific multivariable-adjusted rate ratios (RR) of ALS incidence or death estimated by conditional logistic regression and pooled using inverse-variance weighting.

RESULTS

In age- and matching factor-adjusted analyses, a 1 mg/dL increase in urate concentration was associated with RR = 0.88 (95% CI: [0.78, 0.997] p = 0.044). After adjustment for BMI, a strong predictor of ALS and urate levels, and other potential covariates, the RR = 0.89 (95% CI: [0.78, 1.02]; p = 0.08 for 1mg/dL increase in urate).

CONCLUSION

Elevation of plasma urate was modestly inversely associated with the risk of ALS and warrants further study for a potential role in this disease.

Asymptomatic hyperuricemia: is it time to intervene?

Whether to treat hyperuricemia uncomplicated by articular gout, urolithiasis, or uric acid nephropathy is an exercise in clinical judgment and universal agreement is lacking. Patients with coronary artery disease, chronic kidney disease, and early onset hypertension with persistent hyperuricemia are likely to be benefited with urate-lowering therapy. The paradigm of the causative association of hyperuricemia with cardiovascular and chronic kidney diseases seems to have progressed from skepticism to increasing evidence of a true relationship. Although such evidences are mounting, they are not enough to support pharmacotherapy for all patients with asymptomatic hyperuricemia. Further studies are needed to determine which patients are likely to get beneficial effects from pharmacotherapy and the minimum threshold of uric acid level required to experience clinical benefits.