Serum Uric Acid, Alzheimer-Related Brain Changes, and Cognitive Impairment

Targeting uric acid: a promising intervention against oxidative stress and neuroinflammation in neurodegenerative diseases

Oxidative stress and neuroinflammation are recognized as key factors in the development of neurodegenerative diseases, yet effective interventions and biomarkers to address oxidative stress and neuroinflammation in these conditions are limited. Uric acid (UA), traditionally associated with gout, is now gaining prominence as a potential target in neurodegenerative diseases. Soluble UA stands out as one of the most vital antioxidant compounds produced by the human body, accounting for up to 55% of the extracellular capacity to neutralize free radicals. While there is increasing evidence supporting the neuroprotective properties of UA in Parkinson's disease and Alzheimer's disease, gaps in knowledge still exist regarding the underlying mechanisms and how to effectively translate these benefits into clinical practice. Moreover, the current UA elevation therapy exhibits unstable antioxidant properties, individual variability, and even adverse effects, limiting its potential clinical applications. This review consolidates recent advancements in understanding how UA exerts neuroprotective effects on neurodegenerative diseases and emphasizes the dual roles of UA in managing oxidative stress and neuroinflammation. Additionally, the review elucidates the mechanisms through which UA confers neuroprotection. Based on this, the review underscores the significance of UA as a potential biomarker and aims to provide a comprehensive understanding of its potential as a therapeutic target, while also addressing possible challenges to clinical implementation.

Oxidative stress and neurodegenerative diseases: a bidirectional Mendelian randomization study

INTRODUCTION

Oxidative stress (OS) has been linked to neurodegenerative diseases in numerous epidemiological studies; however, whether it is a pathogenesis or a downstream factor remains controversial.

METHODS

A two-sample bidirectional Mendelian randomization (MR) analysis was implemented to examine evidence of causality of 15 OS injury markers with 3 major neurodegenerative diseases using available genome-wide association studies statistics. As a main approach, inverse-variance weighted (IVW) analysis was performed. The weighted-median (WM) analysis was used to validate the relationship. In order to investigate the existence of horizontal pleiotropy and correct the IVW estimate, the Radial MR approach was applied. To gauge the consistency and robustness of the findings, several sensitivity and pleiotropy analyses were used. For this analysis, p < 0.05 indicates a nominally causal association; according to the Bonferroni correction test, p < 0.0011 indicates a statistically significant causal association.

RESULTS

Via IVW and WM, in directional MR, it was genetically predicted that zinc was nominally causally correlated with the risk of Parkinson's disease but not after Bonferroni correction test; alpha-tocopherol was nominally causally correlated with the risk of Amyotrophic lateral sclerosis (ALS) but not after Bonferroni correction test; furthermore, in reverse MR, it was genetically predicted that Alzheimer's disease was causally correlated with uric acid but not after Bonferroni correction test. These above findings were stable across sensitivity and pleiotropy analyses.

CONCLUSIONS

Based on the current study, there is no authentic genetic causal association between OS biomarkers and neurodegenerative diseases. The complex relationship is required to be confirmed in future experimental research.

The Association Between Serum Uric Acid Levels and the Risk of Cognitive Dysfunction in Patients With Atrial Fibrillation

Patients with atrial fibrillation (AF) are linked to an increased risk of cognitive dysfunction, and serum uric acid levels play an important factor in cognitive dysfunction. However, the optimal serum uric acid level in patients with AF remains unclear. Therefore, we aimed to explore the relationship between serum uric acid and cognitive dysfunction. 583 patients were conducted in the Affiliated Hospital of Jining Medical University. Cognitive dysfunction was assessed by the Montreal Cognitive Assessment (MoCA). The relationship between serum uric acid levels and the risk of cognitive dysfunction in patients with AF was analyzed using the smoothing spline fitting model and threshold analysis. The average serum uric acid level was (383.26 ± 110.11) μmol/L, and the incidence of cognitive dysfunction was 79.76%. There was a non-linear relationship between serum uric acid levels and the risk of cognitive dysfunction in patients with AF, and the inflection point was 352 μmol/L. At the left of the inflection point, the relationship was significant (OR = 1.02, 95% CI = 1.00-1.04). At the right of the inflection point, there was no statistical difference (p=0.101). When serum uric acid levels are less than 352 μmol/L, the risk of cognitive dysfunction increases by 2% for each unit increase in serum uric acid levels in patients with AF. The study provides evidence for the treatment of serum uric acid levels in patients with AF.

The relationship between uric acid levels, cognition and inflammation in a cohort of elderly subjects

BACKGROUND

Uric acid (UA) is the most powerful antioxidant found among human body fluids. With this effect, UA protects neurons from oxidant effects and ensures the continuation of the structure and functions of neuronal tissue. However, UA has effects on the immune system. This study aims to explain the relationship between UA, cognitive level and inflammation in cases with a wide spectrum of cognitive function.

METHODS

A total of 67 women and 62 men who applied to the psychiatry outpatient clinic to obtain a health report were evaluated. The cognitive states of the individuals were determined with the mini-mental state examination test (MMSE). Additionally, serum uric acid levels and simple inflammatory parameters such as CRP, sedimentation, neutrophil-lymphocyte ratio (NLR), and monocyte-lymphocyte ratio (MLR) were measured. According to the MMSE results, two groups were created. Those with an MMSE score of 24 or above formed the first group, and those with an MMSE score below 24 formed the second group.

RESULTS

While a statistically significant positive strong correlation was found between UA and MMSE in all individuals, negative correlations were found between UA and NLR and MLR in men. UA was found to be significantly lower in the group with MMSE scores below 24 and NLR values were higher in the same group.

CONCLUSION

According to these results, UA seems to have a protective effect on cognitive functions. This situation manifests itself more clearly in men. At physiological concentrations, UA may have an anti-inflammatory effect. It appears that there are complex interactions between UA, cognition, and inflammation. Particularly, men appear to be more susceptible to UA effects.

Development and validation of a predictive model for severe white matter hyperintensity with obesity

Purpose

The purpose of the present study was to identify predictors of severe white matter hyperintensity (WMH) with obesity (SWO), and to build a prediction model for screening obese people with severe WMH without Nuclear Magnetic Resonance Imaging (MRI) examination.

Patients subjects and methods

From September 2020 to October 2021, 650 patients with WMH were recruited consecutively. The subjects were divided into two groups, SWO group and non-SWO group. Univariate and Logistic regression analysis were was applied to explore the potential predictors of SWO. The Youden index method was adopted to determine the best cut-off value in the establishment of the prediction model of SWO. Each parameter had two options, low and high. The score table of the prediction model and nomogram based on the logistic regression were constructed. Of the 650 subjects, 487 subjects (75%) were randomly assigned to the training group and 163 subjects (25%) to the validation group. By resampling the area under the curve (AUC) of the subject's operating characteristics and calibration curves 1,000 times, nomogram performance was verified. A decision curve analysis (DCA) was used to evaluate the nomogram's clinical usefulness. By resampling the area under the curve (AUC) of the subject's operating characteristics and calibration curves 1,000 times, nomogram performance was verified. A decision curve analysis (DCA) was used to evaluate the nomogram's clinical usefulness.

Results

Logistic regression demonstrated that hypertension, uric acid (UA), complement 3 (C3) and Interleukin 8 (IL-8) were independent risk factors for SWO. Hypertension, UA, C3, IL-8, folic acid (FA), fasting C-peptide (FCP) and eosinophil could be used to predict the occurrence of SWO in the prediction models, with a good diagnostic performance, Areas Under Curves (AUC) of Total score was 0.823 (95% CI: 0.760-0.885, p < 0.001), sensitivity of 60.0%, specificity of 91.4%. In the development group, the nomogram's AUC (C statistic) was 0.829 (95% CI: 0.760-0.899), while in the validation group, it was 0.835 (95% CI: 0.696, 0.975). In both the development and validation groups, the calibration curves following 1,000 bootstraps showed a satisfactory fit between the observed and predicted probabilities. DCA showed that the nomogram had great clinical utility.

Conclusion

Hypertension, UA, C3, IL-8, FA, FCP and eosinophil models had the potential to predict the incidence of SWO. When the total score of the model exceeded 9 points, the risk of SWO would increase significantly, and the nomogram enabled visualization of the patient's WMH risk. The application prospect of our models mainly lied in the convenient screening of SWO without MRI examination in order to detect SWO and control the WMH hazards early.

Sex-dependent association of serum uric acid levels with amyloid accumulation among amyloid-positive older adults

We aimed to examine the potential effect of sex on the longitudinal association of baseline serum uric acid levels with brain amyloid accumulation over time among older adults with and without abnormal amyloid. At baseline, the study sample comprised 499 older adults, including 276 men and 223 women. Linear mixed-effects regression models were fitted to estimate the individual slopes of change in brain amyloid accumulation [as measured by AV45 standardized uptake value ratio (SUVR)] over time. At baseline, we did not observe a relationship between serum uric acid levels and brain amyloid deposition in women or men regardless of amyloid status. Among amyloid negative subjects, women and men did not differ in the relationship between baseline serum uric acid and the annual change in amyloid accumulation in subjects with normal amyloid levels. In amyloid positive women, serum uric acid levels were not associated with the annual change in amyloid accumulation (unstandardized β = 0.0005, SE = 0.0006, p value = 0.4179). However, in amyloid positive men, serum uric acid levels were negatively associated with the annual change in amyloid accumulation (unstandardized β = -0.0015, SE = 0.0005, p value = 0.0048). These findings support a potential sex-specific effect on the relationship between serum uric acid levels and amyloid accumulation among amyloid positive older adults.

Investigating metabolic dysregulation in serum of triple transgenic Alzheimer's disease male mice: implications for pathogenesis and potential biomarkers

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease that lacks convenient and accessible peripheral blood diagnostic markers and effective drugs. Metabolic dysfunction is one of AD risk factors, which leaded to alterations of various metabolites in the body. Pathological changes of the brain can be reflected in blood metabolites that are expected to explain the disease mechanisms or be candidate biomarkers. The aim of this study was to investigate the changes of targeted metabolites within peripheral blood of AD mouse model, with the purpose of exploring the disease mechanism and potential biomarkers. Targeted metabolomics was used to quantify 256 metabolites in serum of triple transgenic AD (3 × Tg-AD) male mice. Compared with controls, 49 differential metabolites represented dysregulation in purine, pyrimidine, tryptophan, cysteine and methionine and glycerophospholipid metabolism. Among them, adenosine, serotonin, N-acetyl-5-hydroxytryptamine, and acetylcholine play a key role in regulating neural transmitter network. The alteration of S-adenosine-L-homocysteine, S-adenosine-L-methionine, and trimethylamine-N-oxide in AD mice serum can served as indicator of AD risk. The results revealed the changes of metabolites in serum, suggesting that metabolic dysregulation in periphery in AD mice may be related to the disturbances in neuroinhibition, the serotonergic system, sleep function, the cholinergic system, and the gut microbiota. This study provides novel insights into the dysregulation of several key metabolites and metabolic pathways in AD, presenting potential avenues for future research and the development of peripheral biomarkers.

A review of the flortaucipir literature for positron emission tomography imaging of tau neurofibrillary tangles

Alzheimer's disease is defined by the presence of β-amyloid plaques and neurofibrillary tau tangles potentially preceding clinical symptoms by many years. Previously only detectable post-mortem, these pathological hallmarks are now identifiable using biomarkers, permitting an in vivo definitive diagnosis of Alzheimer's disease. 18F-flortaucipir (previously known as 18F-T807; 18F-AV-1451) was the first tau positron emission tomography tracer to be introduced and is the only Food and Drug Administration-approved tau positron emission tomography tracer (Tauvid™). It has been widely adopted and validated in a number of independent research and clinical settings. In this review, we present an overview of the published literature on flortaucipir for positron emission tomography imaging of neurofibrillary tau tangles. We considered all accessible peer-reviewed literature pertaining to flortaucipir through 30 April 2022. We found 474 relevant peer-reviewed publications, which were organized into the following categories based on their primary focus: typical Alzheimer's disease, mild cognitive impairment and pre-symptomatic populations; atypical Alzheimer's disease; non-Alzheimer's disease neurodegenerative conditions; head-to-head comparisons with other Tau positron emission tomography tracers; and technical considerations. The available flortaucipir literature provides substantial evidence for the use of this positron emission tomography tracer in assessing neurofibrillary tau tangles in Alzheimer's disease and limited support for its use in other neurodegenerative disorders. Visual interpretation and quantitation approaches, although heterogeneous, mostly converge and demonstrate the high diagnostic and prognostic value of flortaucipir in Alzheimer's disease.

Uric acid index is a risk for mild cognitive impairment in type 2 diabetes

BACKGROUND

A new uric acid (UA) index has recently been proposed, while serum uric acid (SUA), fasting triglyceride, and fasting blood glucose levels in the index are shown to affect cognitive function. This study aims to investigate the clinical value of the UA index for assessing mild cognitive impairment (MCI) in type 2 diabetes (T2D) patients.

METHODS

This was an observational cross-sectional study with 616 participants. A generalized additive model was used to determine a linear or curvilinear relationship between cognitive performance and the UA index. Logistic regression and random forest models were both developed. A receiver operating characteristic curve (ROC) was delineated and the area under the curve (AUC) was calculated.

RESULTS

MCI was diagnosed in 313 participants (50.81%). Compared with the T2D-normal cognitive function group, MCI subjects had higher UA indexes, lower cognitive scores, and lower education levels (p < 0.001). Generalized additive models showed the UA index and the Montreal Cognitive Assessment (MoCA) score to be decreased linearly (p < 0.001). The UA index AUC was 0.751 (95% CI = 0.713-0.789, p < 0.001). The optimal cut-off point for the identification of MCI based on the UA index was 11.26 (sensitivity: 62.3%, specificity: 75.9%). Results for females in the cohort yielded an AUC change of + 2.5%, the less-educated population (AUC change of + 4.7%), and the hypertensive population (AUC change of + 1.1%). The AUCs were 0.791 (95% CI = 0.720-0.863) for the random forest model and 0.804 (95% CI = 0.770-0.837) for the logistic regression model, and no statistical significance was found (p = 0.758).

CONCLUSION

This study showed that the increased UA index was independently associated with MCI in patients with T2D, especially among female, less-educated, and hypertensive patients. It could be a potential indicator of MCI in T2D patients.

Moderate elevation of serum uric acid levels improves short-term functional outcomes of ischemic stroke in patients with type 2 diabetes mellitus

BACKGROUND

Serum uric acid (SUA), an end-product of purine catabolism diffused in the blood, is positively associated with the risk of type 2 diabetes mellitus (T2DM). However, in the T2DM population, the association of SUA fluctuation ([Formula: see text]SUA) with the functional outcome of ischemic stroke (IS) is still unclear. Accordingly, this study aimed to assess the correlation between [Formula: see text]SUA and short-term IS functional outcomes in T2DM patients.

METHODS

All T2DM patients diagnosed with IS in the China National Stroke Registry III were included. [Formula: see text]SUA, which was defined as the difference between the SUA levels at baseline and 3 months after symptom onset, was classified into two groups, i.e., elevated [Formula: see text]SUA ([Formula: see text]SUA > 0) and reduced [Formula: see text]SUA ([Formula: see text]SUA [Formula: see text] 0). The outcomes measured using the Modified Rankin Scale (mRS) were scored from 0 to 6, and poor functional outcome was defined as an mRS score of 3-6 at 3 months after IS.

RESULTS

Among the 1255 participants (mean age: 61.6 ± 9.8 years), 64.9% were men. Patients with elevated [Formula: see text]SUA had a lower incidence of poor functional outcomes at 3 months. Compared with reduced [Formula: see text]SUA, elevated [Formula: see text]SUA at 0-50 μmol/L (odds ratio [OR] = 0.46, 95% confidence interval [CI] = 0.28-0.78, p = 0.004) and 50-100 μmol/L (OR = 0.40, 95% CI = 0.21-0.77, p = 0.006) was significantly correlated with a reduced risk of poor functional outcomes at 3 months.

CONCLUSION

This study showed that a moderate increase in [Formula: see text]SUA in the range of 0-100 μmol/L at 3 months after IS might be beneficial in T2DM adults and more studies are warranted to confirm this.

Association of gout with brain reserve and vulnerability to neurodegenerative disease

Studies of neurodegenerative disease risk in gout are contradictory. Relationships with neuroimaging markers of brain structure, which may offer insights, are uncertain. Here we investigated associations between gout, brain structure, and neurodegenerative disease incidence. Gout patients had smaller global and regional brain volumes and markers of higher brain iron, using both observational and genetic approaches. Participants with gout also had higher incidence of all-cause dementia, Parkinson's disease, and probable essential tremor. Risks were strongly time dependent, whereby associations with incident dementia were highest in the first 3 years after gout diagnosis. These findings suggest gout is causally related to several measures of brain structure. Lower brain reserve amongst gout patients may explain their higher vulnerability to multiple neurodegenerative diseases. Motor and cognitive impairments may affect gout patients, particularly in early years after diagnosis.

The Role of Steroidomics in the Diagnosis of Alzheimer's Disease and Type 2 Diabetes Mellitus

Epidemiological studies suggest an association between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). This study aimed to investigate the pathophysiological markers of AD vs. T2DM for each sex separately and propose models that would distinguish control, AD, T2DM, and AD-T2DM comorbidity groups. AD and T2DM differed in levels of some circulating steroids (measured mostly by GC-MS) and in other observed characteristics, such as markers of obesity, glucose metabolism, and liver function tests. Regarding steroid metabolism, AD patients (both sexes) had significantly higher sex hormone binding globulin (SHBG), cortisol, and 17-hydroxy progesterone, and lower estradiol and 5α-androstane-3α,17β-diol, compared to T2DM patients. However, compared to healthy controls, changes in the steroid spectrum (especially increases in levels of steroids from the C21 group, including their 5α/β-reduced forms, androstenedione, etc.) were similar in patients with AD and patients with T2DM, though more expressed in diabetics. It can be assumed that many of these steroids are involved in counter-regulatory protective mechanisms that mitigate the development and progression of AD and T2DM. In conclusion, our results demonstrated the ability to effectively differentiate AD, T2DM, and controls in both men and women, distinguish the two pathologies from each other, and differentiate patients with AD and T2DM comorbidities.

Association of serum uric acid and fasting plasma glucose with cognitive function: a cross-sectional study

BACKGROUND

The combined effect of serum uric acid (SUA) and blood glucose on cognition has not been explored. This study aimed to examine the separate and combined association of SUA and fasting plasma glucose (FPG) or diabetes mellitus (DM) with cognition in a sample of Chinese middle-aged and elderly population.

METHODS

A total of 6,509 participants aged 45 years or older who participated in the China Health and Retirement Longitudinal Study (CHARLS, 2011) were included. The three cognitive domains assessed were episodic memory, mental status, and global cognition (the sum of the first two terms). Higher scores indicated better cognition. SUA and FPG were measured. The participants were grouped based on SUA and FPG quartiles to evaluate their combined associations of cognition with SUA Q1-Q3 only (Low SUA), with FPG Q4 only (High FPG), without low SUA and high FPG levels (Non), and with low SUA and high FPG levels (Both), multivariate linear regression models were used to analyze their association.

RESULTS

Lower SUA quartiles were associated with poorer performance in global cognition and episodic memory compared with the highest quartile. Although no association was found between FPG or DM and cognition, high FPG or DM combined with low SUA levels in women (β_FPG = -0.983, 95% CI: -1.563--0.402; β_DM = -0.800, 95% CI: -1.369--0.232) had poorer cognition than those with low SUA level only (β_FPG = -0.469, 95% CI: -0.926--0.013; β_DM = -0.667, 95% CI: -1.060--0.275).

CONCLUSION

Maintaining an appropriate level of SUA may be important to prevent cognitive impairment in women with high FPG.

The relative and interactive effects of urinary multiple metals exposure on hyperuricemia among urban elderly in China

Objective

Independent and interactive effects of multiple metals levels in urine on the risk of hyperuricemia (HUA) in the elderly were investigated.

Methods

A total of 6,508 individuals from the baseline population of the Shenzhen aging-related disorder cohort were included in this study. We detected urinary concentrations of 24 metals using inductively coupled plasma mass spectrometry, fitted unconditional logistic regression models, and the least absolute shrinkage and selection operator regression models for the selection of metals as well as unconditional stepwise logistic regression models and restricted cubic spline logistic regression models for assessing the associations of urinary metals and HUA risk, and finally applied generalized linear models to determine the interaction with urinary metals on the risk of HUA.

Results

Unconditional stepwise logistic regression models showed the association between urinary vanadium, iron, nickel, zinc, or arsenic and HUA risk (all P < 0.05). We revealed a negative linear dose-response relationship between urinary iron levels and HUA risk (P _overall < 0.001, P _nonliner = 0.682), a positive linear dose-response relationship between urinary zinc levels and HUA risk (P _overall < 0.001, P _nonliner = 0.513), and an additive interaction relationship between urinary low-iron and high-zinc levels and HUA risk (RERI = 0.31, 95% CI: 0.03-0.59; AP = 0.18, 95%CI: 0.02-0.34; S = 1.76, 95%CI: 1.69-3.49).

Conclusion

Urinary vanadium, iron, nickel, zinc, or arsenic levels were associated with HUA risk, and the additive interaction of low-iron (<78.56 μg/L) and high-zinc (≥385.39 μg/L) levels may lead to a higher risk of HUA.

Serum Uric Acid Levels in Neurodegenerative Disorders: A Cross-Sectional Study

Background: Excessive oxidative stress may contribute to neurodegeneration by leading to protein aggregation and mitochondrial dysfunction. Uric acid (UA) is an important endogenous antioxidant that protects against oxidative stress, yet its exact role in neurodegeneration remains unclear. Objective: To explore the performance of serum UA in neurodegenerative disorders. Methods: A total of 839 controls and 840 patients, including Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple system atrophy (MSA), progressive supranuclear palsy (PSP), frontotemporal dementia (FTD), dementia with Lewy bodies (DLB), motor neuron disease (MND), Creutzfeldt-Jakob disease (CJD), and mixed dementia (MixD) were enrolled. Fasting serum UA levels were measured in all participants and compared between patients and controls. Linear regression models were utilized to explore possible relationships of serum UA with cognition, disease duration, age, and age of onset. Results: Compared to controls (355.48 ± 85.38 μmol/L), serum UA was significantly lower in AD (291.29 ± 83.49 μmol/L, p < 0.001), PD (286.95 ± 81.78 μmol/L, p < 0.001), PSP (313.32 ± 88.19 μmol/L, p < 0.001), FTD (313.89 ± 71.18 μmol/L, p = 0.001), and DLB (279.23 ± 65.51 μmol/L, p < 0.001), adjusting for confounding factors including age, gender, education, etc. In addition, serum UA was positively correlated with cognitive levels in all patients (Mini-Mental State Examination: r = 0.136, p = 0.001; and Montreal Cognitive Assessment Scale: r = 0.108, p = 0.009). Conclusion: Decreased levels of serum UA were correlated with AD, PD, PSP, FTD, and DLB, offering significant potential as a promisingly relevant, less-invasive marker of multiple neurodegenerative disorders.

Lower preoperative serum uric acid level may be a risk factor for postoperative delirium in older patients undergoing hip fracture surgery: a matched retrospective case-control study

BACKGROUND

Postoperative delirium (POD) is a common complication after hip fracture surgery that is associated with various short- and long-term outcomes. The mechanism of POD may be associated with the oxidative stress process. Uric acid has been shown to provide a neuroprotective effect in various neurodegenerative diseases through its antioxidant properties. However, it is unclear whether lower preoperative serum uric acid levels are associated with the development of POD after hip fracture surgery. Therefore, this study assessed the association of lower preoperative uric acid levels in patients with POD during hospitalization.

METHODS

This is a matched retrospective case-control study that included 96 older patients (≥65 y) who underwent hip fracture surgery. POD was diagnosed using the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Patients diagnosed with POD (cases) were matched 1:1 with patients without POD (controls) on the basis of age, sex, and anesthesia type. The relationship between preoperative uric acid and POD was analyzed by multivariable analysis.

RESULTS

The POD and non-POD groups each had 48 patients. In the univariate analysis, lower log preoperative serum uric acid value, higher neutrophil-to-lymphocyte ratio, and cerebrovascular disease were more likely in patients with POD than in those with no POD. Multivariable conditional logistic regression analysis showed that lower log preoperative serum uric acid (adjusted odds ratio [aOR], 0.028; confidence interval [CI], 0.001-0.844; p = 0.040), higher neutrophil-to-lymphocyte ratio (aOR, 1.314; 95% CI, 1.053-1.638; p = 0.015), and increased surgery duration (aOR, 1.034; 95% CI, 1.004-1.065; p = 0.024) were associated with increased risk of POD.

CONCLUSIONS

Lower preoperative serum uric acid levels may be an independent risk factor for POD after adjustment for possible confounding factors. However, large prospective studies are needed to confirm this finding.

Moderate increase of serum uric acid within a normal range is associated with improved cognitive function in a non-normotensive population: A nationally representative cohort study

Background

Associations between serum uric acid (SUA) and changes in cognitive function are understudied in non-normotensive populations, and many previous studies only considered the baseline SUA at a single time point. We aimed to examine the effects of baseline SUA and 4-year changes in SUA on cognitive changes in the non-normotensive population.

Materials and methods

In the China Health and Retirement Longitudinal Study (CHARLS), cognitive function was measured based on executive function and episodic memory in four visits (years: 2011, 2013, 2015, and 2018). We identified two study cohorts from CHARLS. The first cohort included 3,905 non-normotensive participants. Group-based single-trajectory and multi-trajectory models were applied to identify 7-year cognitive trajectories. Adjusted ordinal logistics models were performed to assess the association between baseline SUA and 7-year cognitive trajectories, and subgroup analyses were conducted according to the presence of hyperuricemia or SUA levels. The second cohort included 2,077 eligible participants. Multiple linear regression was used to explore the effect of a 4-year change in SUA on cognitive change during the subsequent 3-year follow-up.

Results

Four distinct single-trajectories of global cognitive performance and four multi-trajectories of executive function and episodic memory were identified. Higher baseline SUA levels were significantly associated with more favorable cognitive single-trajectories (OR_{Q4 vs}. _Q1: 0.755; 95% CI: 0.643, 0.900) and multi-trajectories (OR_{Q4 vs}. _Q1: 0.784; 95% CI: 0.659, 0.933). Subgroup analyses revealed that the protective effect of SUA was significant in the non-hyperuricemia groups or the low-level SUA groups. Additionally, changes in SUA could influence future cognitive changes. Compared with non-hyperuricemia participants with elevated SUA, non-hyperuricemia participants with decreased SUA and patients with persistent hyperuricemia had a higher risk for cognitive decline. Furthermore, only the Q3 group of changes in SUA could enhance global cognitive function compared with the Q1 group (β: 0.449; 95% CI: 0.073, 0.826).

Conclusion

Our study indicates that the maintenance of normal SUA levels and a moderate increase of SUA were advantageous in improving cognitive function or trajectories in a non-normotensive population. Conversely, SUA may impair cognitive function in patients with persistent hyperuricemia.

The relationship between uric acid and brain health from observational studies

This study conducts a systematic literature review and meta-analysis regarding the potential influence of serum uric acid levels on cerebral small vessel diseases and the cognitive status in the prodromal stages of dementia. We identified four different cerebral small vessel diseases and three specific domains of cognitive performance to be considered in the literature search. The analysis contained 14 studies (13 cross-sectional design and one longitudinal design) with 11,502 participants measuring the relationship between uric acid and cerebral small vessel disease. In both continuous and categorical analyses, significant associations were found between hyperuricemia and cerebral small vessel diseases (continuous data: pooled OR: 1.00, 95%CI: 1.00-1.01 and categorical data: pooled OR: 1.42, 95%CI: 1.15-1.75). For the relationship between uric acid and cognitive performance, 19 studies with 49,901 participants were considered, including eight cohort studies, and 11 cross-sectional studies. The cross-sectional data showed that a marginal relationship existed between uric acid and global cognition (β: 0.00, 95%CI: -0.01-0.00). The pooled analysis of cohort studies indicated that higher uric acid had a deleterious effect on attention and executive function (continuous data: β: -0.02, 95%CI: -0.04-0.00 and categorical data: β: -0.03, 95%CI: -0.07-0.00). Conclusion: Our study indicated that a higher level of uric acid had an adverse effect on brain health. Furthermore, a high level of uric acid is related to cognitive decline in attention and executive function, which may exist a long time before the diagnosis of dementia.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Purine metabolites and complex diseases: role of genes and nutrients

PURPOSE OF REVIEW

Purines have several important physiological functions as part of nucleic acids and as intracellular and extracellular signaling molecules. Purine metabolites, particularly uric acid, have been implicated in congenital and complex diseases. However, their role in complex diseases is not clear and they have both beneficial and detrimental effects on disease pathogenesis. In addition, the relationship between purines and complex diseases is affected by genetic and nutritional factors. This review presents latest findings about the relationship between purines and complex diseases and the effect of genes and nutrients on this relationship.

RECENT FINDINGS

Evidence from recent studies show strong role of purines in complex diseases. Although they are causal in only few diseases, our knowledge about their role in other diseases is still evolving. Of all the purines, uric acid is the most studied. Uric acid acts as an antioxidant as well as a prooxidant under different conditions, thus, its role in disease also varies. Other purines, adenosine and inosine have been less studied, but they have neuroprotective properties which are valuable in neurodegenerative diseases.

SUMMARY

Purines are molecules with great potential in disease pathogenesis as either metabolic markers or therapeutic targets. More studies need to be conducted to understand their relevance for complex diseases.

The Influence of Serum Uric Acid Level on Alzheimer's Disease: A Narrative Review

As a powerful antioxidant in the human body, uric acid (UA) has been the subject of increasing research that focused on its influence on Alzheimer's disease (AD) in recent years. The latest literature was gathered to describe the influence of serum uric acid (SUA) level on the onset and progression of AD and to analyze the possibility that SUA is a biomarker of Alzheimer's disease. A large number of existing studies suggested that the SUA level was lower or tended to decrease in patients with AD, and increased SUA level may have a protective effect in AD, which could reduce the risk of onset and slowing the course of the disease. However, some Mendelian randomization analyses suggested that genetically determined uric acid was not associated with AD risk. Existing research results are contradictory due to the high inconsistency of the studies, the selection of subjects, and other factors. UA also showed a strong association with cognitive function, and there appeared to be a gender-selective neuroprotective action. Due to its potent antioxidant properties, the low uric acid level may contribute to oxidative stress to accelerate disease progression. But some preclinical data showed a possibility that in some special cases, UA had a prooxidant properties. The possibility was raised in the discussion of the underlying mechanism that both the low uric acid level and the rapidly progressive course of the disease were the consequence of malnutrition. This paper reviews recent advances in the study of SUA and AD which offers the possibility of new biomarker, new prevention, and treatment strategies for Alzheimer's disease.

Effects of baseline serum uric acid and apolipoprotein E4 on longitudinal cognition and cerebral metabolism

Serum uric acid, a natural antioxidant, may have a protective effect on the progression of Alzheimer's disease (AD). To investigate the effect of serum uric acid on longitudinal cognitive and brain metabolic changes, we utilized data on baseline serum uric acid levels, APOE genotyping, and longitudinal cognitive scores from the Alzheimer's Disease Neuroimaging Initiative for 1,343 participants with normal cognition (NC), mild cognitive impairment (MCI), or dementia. In 979 participants, brain metabolism was measured using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) images. Higher serum uric acid levels exhibited a detrimental effect on NC, whereas a protective trend was observed in individuals with cognitive impairment. Interestingly, higher uric acid levels were associated with a slower decline in cognitive scores and brain metabolism in females with MCI, and this effect was found in APOE4 carriers, but not in non-carriers. Longitudinal AD-like patterns of brain metabolism on FDG-PET images also appeared to mediate the effects of baseline uric acid levels on longitudinal cognitive decline. In summary, higher serum uric acid may interact with APOE4 to alleviate longitudinal metabolic changes and cognitive decline in female MCI patients.