Association of urine acidification with visceral obesity and the metabolic syndrome

Clinical characteristics of surgically managed patients with asymptomatic renal stones: Comparison of patients with symptomatic renal stones

PURPOSE

This study aimed to compare the characteristics of asymptomatic and symptomatic nephrolithiasis in patients who underwent surgical treatment for kidney stones.

MATERIALS AND METHODS

Between 2015 and 2019, 245 patients who underwent percutaneous nephrolithotomy or retrograde intrarenal surgery for kidney stones were included. The patients were divided into asymptomatic (n=124) and symptomatic (n=121) groups. All patients underwent blood and urine tests, preoperative non-contrast computed tomography, and postoperative stone composition analysis. We retrospectively analyzed and compared the characteristics of the patients and stones, operation time, stone-free rate, and postoperative complications between the two groups.

RESULTS

In the asymptomatic group, mean body mass index (BMI) was significantly higher (25.7±3.8 kg/m² vs. 24.3±2.8 kg/m², p=0.002) and urine pH was significantly lower (5.6±0.9 vs. 5.9±0.9, p=0.013). The ratio of calcium oxalate dihydrate stones was significantly higher in the symptomatic group (5.3% vs. 15.5%, p=0.023). No significant differences were observed in stone characteristics, postoperative outcomes, or complications. In the multivariate logistic regression analysis for predicting variables for asymptomatic renal stones, BMI (odds ratio [OR], 1.144; 95% confidence interval [CI], 1.038-1.260; p=0.007), and urine pH (OR, 0.608; 95% CI, 0.407-0.910; p=0.016) were independent predictive variables for asymptomatic renal stones.

CONCLUSIONS

This study demonstrated that thorough medical check-ups are needed for the early detection of renal stones in individuals with a high BMI or low urine pH.

Low urine pH predicts new onset of diabetes mellitus during a 10-year period in men: BOREAS-DM1 study

Aims/Introduction

A low level of urine pH (U‐pH) has been reported to be associated with metabolic disorders. However, the relationship between the incidence of diabetes mellitus and U‐pH has not yet been fully addressed.

Materials and Methods

We investigated the relationship between U‐pH and the development of diabetes mellitus during a 10‐year period in a general population of individuals who received annual health examinations in 2006 (n = 28,990). After exclusion of individuals with missing data, and those with diabetes mellitus and/or chronic kidney disease at baseline, a total of 12,476 individuals (men/women: 8,027/4,449) who received health examinations at least once during the period from 2007 to 2016 were recruited. The recruited individuals were divided into four groups according to their U‐pH levels: groups of U‐pH ≤5.0, 5.5, 6.0 and ≥6.5.

Results

During a 10‐year period, 521 men (6.5%) and 132 women (3.0%) had new onset of diabetes mellitus. The cumulative incidence of diabetes mellitus was 7.5% (men/women: 9.3%/4.4%) per 100 person‐years. The hazard ratios (HRs) in the U‐pH ≤5.0 (HR 1.93) and U‐pH 5.5 groups (HR 1.46) were significantly higher than that in the U‐pH ≥6.5 group as a reference for men, but not for women. After adjustment of age, obesity, fasting glucose, smoking and alcohol drinking habits, family history of diabetes mellitus, and use of drugs for hypertension and dyslipidemia, HR in the U‐pH ≤5.0 group (HR 1.39) was significantly higher than that in the U‐pH ≥6.5 group for men, but not for women.

Conclusions

Low U‐pH predicts new onset of diabetes mellitus in a general population of men.

Comprehensive identification of pleiotropic loci for body fat distribution using the NHGRI-EBI Catalog of published genome-wide association studies

We conducted a hypothesis-free cross-trait analysis for waist-to-hip ratio adjusted for body mass index (WHR_adjBMI ) loci derived through genome-wide association studies (GWAS). Summary statistics from published GWAS were used to capture all WHR_adjBMI single-nucleotide polymorphisms (SNPs), and their proxy SNPs were identified. These SNPs were used to extract cross-trait associations between WHR_adjBMI SNPs and other traits through the NHGRI-EBI GWAS Catalog. Pathway analysis was conducted for pleiotropic WHR_adjBMI SNPs. We found 160 WHR_adjBMI SNPs and 3675 proxy SNPs. Cross-trait analysis identified 239 associations, of which 100 were for obesity traits. The remaining 139 associations were filtered down to 101 unique linkage disequilibrium block associations, which were grouped into 13 categories: lipids, red blood cell traits, white blood cell counts, inflammatory markers and autoimmune diseases, type 2 diabetes-related traits, adiponectin, cancers, blood pressure, height, neuropsychiatric disorders, electrocardiography changes, urea measurement, and others. The highest number of cross-trait associations were found for triglycerides (n = 10), high-density lipoprotein cholesterol (n = 9), and reticulocyte counts (n = 8). Pathway analysis for WHR_adjBMI pleiotropic SNPs found immune function pathways as the top canonical pathways. Results from our original methodology indicate a novel genetic association between WHR_adjBMI and reticulocyte counts and highlight the pleiotropy between abdominal obesity, immune pathways, and other traits.

Low urine pH is a risk for non-alcoholic fatty liver disease: A population-based longitudinal study

BACKGROUND

Low urine pH has a close association with insulin resistance. This study was aimed to investigate the association between urine pH and incident non-alcoholic fatty liver disease (NAFLD), which is associated with insulin resistance.

SUBJECTS AND METHODS

In this historical cohort study of 11,012 participants (5503 men and 5509 women), we investigated the effect of urine pH on incident NAFLD. NAFLD was defined as having fatty liver diagnosed by abdominal ultrasonography and excluding the participants consumed ethanol over 60g/day for men and 40g/day for women. We divided the participants into three groups according to urine pH; the lowest group (urine pH≤5.5), the middle group (urine pH=6.0) and the highest group (urine pH≥6.5). Cox proportional hazards models was performed to investigate the effect of urine pH on incident NAFLD, adjusting for age, sex, body mass index, smoking, exercise, alcohol consumption, alanine aminotransferase, triglycerides, systolic blood pressure, uric acid and fasting plasma glucose.

RESULTS

Over the median 6.8-year follow-up duration, 2023 participants developed NAFLD, and the crude proportions were 20.3% (case/N=1104/5447) in the lowest urine pH group, 16.3% (487/2989) in the middle urine pH group and 16.8% (432/2576) in the highest urine pH group. The lowest urine pH group showed a significantly higher risk for incident NAFLD than the highest urine pH group (adjusted hazard ratio 1.48, 95% confidence interval 1.31-1.66, P<0.001).

CONCLUSION

Low urine pH is associated with incident NAFLD. Our findings indicate that urine pH can be an additional data when considering further diagnostic investigation for NAFLD in patients who have other risk factors.

The Proposal of Molecular Mechanisms of Weak Organic Acids Intake-Induced Improvement of Insulin Resistance in Diabetes Mellitus via Elevation of Interstitial Fluid pH

Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35~7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: (1) the carboxyl group (R-COO⁻) but not H⁺ composing weak organic acids in foods is absorbed into the body, and (2) the absorbed the carboxyl group (R-COO⁻) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus; however, the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H⁺ associated with ATP synthesis required for the Na⁺,K⁺-ATPase to extrude the high leveled intracellular Na⁺ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.

Low Urine pH Is Associated with Non-alcoholic Fatty Liver Disease: A Community-based Cross-sectional Study

Objective Low urine pH is associated with several metabolic diseases, such as dyslipidemia, diabetes, and metabolic syndrome. However, the association between low urine pH and non-alcoholic fatty liver disease (NAFLD) remains unknown. Therefore, we conducted a community-based cross-sectional study to investigate this association. Methods Between April 2013 and March 2014, the records of 4,945 Japanese subjects who had undergone annual health checkups were reviewed to identify subjects who met the diagnostic criteria for NAFLD. Patients Based on urine pH, the participants were classified into four groups; a low urine pH was defined as ≤5.5. Of the 3,411 subjects who qualified for enrollment, 1,028 met the diagnostic criteria for NAFLD. Results The prevalence of NAFLD was significantly increased with decreasing urine pH in both men and women (p<0.01 and p=0.02, respectively). A multivariate analysis, including adjustments for age, metabolic markers, and the renal function, showed a significant association between low urine pH and NAFLD in men and women (odds ratio, 1.37; 95% confidence interval, 1.01-1.85, p=0.04 and odds ratio, 1.73; 95% confidence interval, 1.15-2.62, p<0.01, respectively). Conclusion Our study indicates that NAFLD is associated with a low urine pH in both sexes, findings that might help clinicians identify patients at high risk for NAFLD.

Low urine pH affects the development of metabolic syndrome, associative with the increase of dyslipidemia and dysglycemia: Nationwide cross-sectional study (KNHANES 2013-2015) and a single-center retrospective cohort study

INTRODUCTION

Low urine pH (UpH) and high serum uric acid are considered evidence of metabolic disorders. The effect of low UpH on the development of metabolic syndrome (MetS) is less clear than that of high serum uric acid. We investigated the association between low UpH on the development of MetS and its components: central obesity, dyslipidemia, hypertension, and dysglycemia.

METHODS

Two studies were conducted based on 2 datasets. The cross-sectional study included 14,511 subjects aged 19-80 years, based on the Korea National Health and Nutrition Examination Survey in 2013-2015. The retrospective cohort study included 3,453 subjects aged 19-80 years without MetS at the first checkup, who underwent at least 3 health checkups at a single tertiary hospital between 2011 and 2017. UpH was measured using an automatic urine analyzer in the range of 5.0-9.0 at first visit.

RESULTS

In the cross-sectional study, low UpH (= 5.0) was associated with the prevalence of MetS (odds ratio [OR] = 1.480, 95% confidence interval [CI] 1.334-1.643, p<0.001), particularly central obesity, dyslipidemia, and dysglycemia (OR ranges 1.282-1.422, p<0.001, all). In the retrospective cohort study, compared with the highest UpH subgroup, the lowest UpH subgroup (= 5.0) was associated with higher risk of MetS development (hazard ratio = 1.394, 95% CI 1.096-1.772, p = 0.007). The incident risk of MetS increased from the highest to lowest UpH subgroups (p for trend = 0.020), among which dyslipidemia and dysglycemia increased (p for trend <0.01, all).

CONCLUSION

Low UpH can be used as a surrogate marker of MetS and affects the development of MetS, associative with the increase of dyslipidemia and dysglycemia in those without MetS. If UpH is ≤5.0, efforts to prevent metabolic disorders are warranted.

Relationship between urine pH and abnormal glucose tolerance in a community-based study

AIMS/INTRODUCTION

The association between urine pH and abnormal glucose tolerance in men and women is unclear; therefore, we carried out a community-based, cross-sectional study to investigate sex-specific associations between these values, possible indicators of prediabetes and type 2 diabetes.

MATERIALS AND METHODS

We enrolled 4,945 Japanese individuals (2,490 men and 2,455 women), who had undergone annual health checkups. To investigate the relationship between low urine pH and abnormal glucose tolerance, participants were divided into three groups based on their fasting plasma glucose levels (<6.11 mmol/L, 6.11-6.99 mmol/L and ≥6.99 mmol/L), and three groups based on their glycated hemoglobin levels (≤44.3 mmol/mol, 44.3-47.5 mmol/mol and ≥47.5 mmol/mol). To examine the effects of urine pH on abnormal glucose tolerance, participants were categorized into five groups based on their urine pH (5.0, 5.5, 6.0, 6.5 and ≥7.0).

RESULTS

Multivariate analysis adjusted for age, body mass index, systolic blood pressure, triglycerides, high-density lipoprotein cholesterol, uric acid, creatinine and antidiabetic agent use showed significant associations between low urine pH and both high fasting plasma glucose and high glycated hemoglobin levels (P for trend = 0.0260, 0.0075) in men. Furthermore, after the same adjustments, prevalence rates of abnormal glucose tolerance (≥6.11 mmol/L and ≥6.99 mmol/L), increased significantly as urine pH levels decreased (P for trend = 0.0483, 0.0181) in men. In women, a similar trend was observed without a significant difference.

CONCLUSIONS

Low urine pH is significantly associated with abnormal glucose tolerance; therefore, measuring urine pH might prove useful for identifying patients at high risk for diabetes.

Association of urinary citrate excretion, pH, and net gastrointestinal alkali absorption with diet, diuretic use, and blood glucose concentration

Urinary citrate (Ucit) protects against urinary stone formation. Acid base status and diet influence Ucit. However, the effect of demographics, diet, and glucose metabolism on Ucit excretion, urinary pH (U‐pH) and net gastrointestinal alkali absorption (NAA) are not known. Twenty‐four hour urine samples, blood glucose, creatinine, and cystatin C were obtained from non‐Hispanic white sibships in Rochester, MN (n = 446; 64.5 ± 9 years; 58% female). Diet was assessed by a food frequency questionnaire. The impact of blood glucose, demographics and dietary elements on Ucit excretion, U‐pH, and NAA were evaluated in bivariate and multivariable models and interaction models that included age, sex, and weight. NAA significantly associated with Ucit and U‐pH. In multivariate models Ucit increased with age, weight, eGFR_Cys, and blood glucose, but decreased with loop diuretic and thiazide use. U‐pH decreased with serum creatinine, blood glucose, and dietary protein but increased with dietary potassium. NAA was higher in males and increased with age, weight, eGFR_Cys and dietary potassium. Significant interactions were observed for Ucit excretion with age and blood glucose, weight and eGFR_Cys, and sex and thiazide use. Blood glucose had a significant and independent effect on U‐pH and also Ucit. This study provides the first evidence that blood glucose could influence urinary stone risk independent of urinary pH, potentially providing new insight into the association of obesity and urinary stone disease.

Urinary pH is a predictor of diabetes in men; a population based large scale cohort study

AIMS

Previous cross-sectional studies revealed that patients with type 2 diabetes were associated with low urine pH. However, the association between urinary pH and incident type 2 diabetes is still unclear. Thus, we investigated the association between urinary pH and incident type 2 diabetes.

METHODS

This is a 5-year observational study of 3119men. We divided participants into four groups according to quartile of urinary pH. Multivariate logistic regression analysis was performed to calculate adjusted odds ratios (ORs) and 95% CIs for incident type 2 diabetes. We adjusted for age, body mass index, smoking, exercise, alcohol consumption, hypertension, hypertriglyceridemia, low high-density lipoprotein cholesterol levels and impaired fasting glycaemia.

RESULTS

In the follow-up examination, 113men diagnosed as diabetes. The proportion of incident diabetes was 6.9% (case/N=22/318) in the lowest urinary pH group (urinary pH = 5.0), 3.4% (46/1366) in the second lowest group (urinary pH = 5.5), 3.5% (30/856) in the third lowest group (urinary pH = 6.0) and 2.6% (15/579) in the highest group (urinary pH≥6.5). The lowest urinary pH group was associated with the increased risk of incident diabetes compared to the other urinary pH groups (multivariate OR=1.91, 95% CI 1.05-3.36, p=0.033 for the second lowest, multivariate OR=1.99, 95% CI 1.05-3.71, p=0.036 for the third lowest and multivariate OR 2.69, 95% CI 1.30-5.72, p=0.008 for the highest urinary pH groups).

CONCLUSIONS

Low urine pH is an independent predictor of diabetes. We suggest that the urine pH can be an easy practical marker for diabetes.

Influence of a home-based exercise program on the urine pH in elderly female subjects: a secondary analysis of a randomized controlled trial

Background

A low urine pH is a characteristic metabolic feature of metabolic syndrome and type 2 diabetes. The purpose of the current study was to investigate the effects of a 12-week home-based bench step exercise on the urine pH status of elderly female subjects.

Methods

The current study is a secondary analysis of a randomized controlled trial (RCT) in which 59 postmenopausal female subjects were randomized to either the exercise group (n = 29) or the control group (n = 30). The subjects in the exercise group were instructed to perform home-based exercises using a bench step at the anaerobic threshold (AT), with a goal of performing ≥140 min/week at home for 12 weeks. The subjects in the control group were instructed to not change their normal lifestyle. Urine was collected after overnight fasting, and the urine pH was measured using a urinary test strip. The inter-group-differences at baseline and the pre-post changes within groups were assessed using the Mann-Whitney U test and Wilcoxon’s signed-rank test, respectively. Additionally, the difference in the post-intervention urine pH levels of the two groups, adjusted for the pre-intervention values (the estimated effect size) and the precision (95% confidence intervals) were investigated using an analysis of covariance.

Results

The pre-post comparison of the urine pH data using Wilcoxon’s signed-rank test showed a significant increase in the urine pH levels of the exercise group (p < 0.05); there was no significant change in the urine pH levels of the control group. However, the estimated effect size (0.15) was small and the confidence interval straddled 0 (−0.25–0.55).

Conclusions

Based on the results of the current secondary analysis of an RCT, we could not clearly conclude that exercise has a beneficial effect on the urine pH. Further well-designed RCTs should be conducted to determine whether aerobic exercise is truly able to ameliorate urine acidification.

Trial registration

The study was retrospectively registered in the University Hospital Medical Information Network (UMIN) as “Effect of step exercise on aerobic fitness and progression of atherosclerosis in the elderly” under the registration number UMIN 000026743 (the date of registration: March 28, 2017).

Fasting Single-Spot Urine pH Is Associated with Metabolic Syndrome in the Japanese Population

OBJECTIVE

To investigate the relationship between urine pH and metabolic syndrome (MetS) and its components, while controlling for covariates.

SUBJECTS AND METHODS

This cross-sectional study was conducted on 5,430 Japanese subjects (4,691 without MetS; 739 with MetS) undergoing health assessments. Partial correlation analysis and analysis of covariance were used for controlling confounding parameters (age, gender, levels of serum uric acid and high-sensitivity C-reactive protein, estimated glomerular filtration rate, and smoking and drinking status). Using multiple logistic regression analyses, adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for MetS incidence were calculated across urine pH categories. Path analysis was used to determine the relationship between MetS and urine pH.

RESULTS

Subjects with MetS had significantly lower urine pH (5.9 ± 0.7) than those without MetS (6.0 ± 0.7) (p < 0.001). Partial correlation analysis showed that systolic and diastolic blood pressure, and triglyceride and fasting plasma glucose levels were negatively correlated with urine pH, while high-density lipoprotein cholesterol was positively correlated with urine pH. Analysis of covariance indicated that urine pH decreased with an increasing number of metabolic abnormalities. Adjusted ORs (95% CI) for the presence of MetS in subjects with urine pH 5.5-6.0 and pH <5.5 were 1.34 (1.04-1.73) and 1.52 (1.09-2.13), respectively (reference: subjects with a urine pH >6.0).

CONCLUSION

The MetS and its components were independently associated with lower urine pH.

Spot-testing urine pH, a novel dietary biomarker? A randomised cross-over trial

AIM

Spot-tests of urine pH are claimed to be an accessible biomarker of net acid excretion (NAE), and as such, they may be able to determine changes in an individual's intake of acid- or base-forming foods. To test this hypothesis, we aimed to determine if spot-tests of urine pH could index NAE and relay the consumption of a fruit and vegetable (F&V) concentrate whilst determining this concentrate's capacity to modulate NAE.

METHODS

In a double blind, placebo-controlled, cross-over trial, healthy adults (n = 13) were allocated by simple randomisation to receive a F&V concentrate or placebo for three days each, with diet standardised throughout. Measurements of 24-hour NAE, 24-hour urine pH and spot-tests of urine pH were taken throughout the study.

RESULTS

The 24-hour urine pH predicted 24-hour NAE (P = <0.0001). However, spot-tested urine pH displayed prediction intervals too wide to infer 24-hour NAE and inconsistent ability to reflect concentrate ingestion, despite 24-hour NAE and 24-hour urine pH decreasing (-25.8 mEq, 95% CI -44.3 to -7.4, P = 0.01, d = 0.94) and increasing (+0.51, 95% CI 0.25-0.79, P = 0.002, d = 1.3), respectively, following supplementation.

CONCLUSIONS

Spot-tests of urine pH are not a valid dietary biomarker of daily NAE and were unable to reliably track changes, despite a F&V concentrate clearly modulating the daily rate of NAE.

Association between the markers of metabolic acid load and higher all-cause and cardiovascular mortality in a general population with preserved renal function

Although metabolic acid load has been associated with many well-known risk factors for mortality, its clinical implications are not yet clear. To evaluate the association between biomarkers of metabolic acid load, such as serum bicarbonate, serum anion gap and urine pH and mortality, we analyzed the health records of 31,590 adults who underwent a health screening between January 2001 and December 2010 and had an estimated glomerular filtration rate ⩾60 ml min(-1) per 1.73 m2. Urine pH was measured by a dipstick test performed on fast morning urine sample and categorized as acidic (urine pH ⩽5.5), neutral and alkaline (urine pH ⩾8.0). Using the Cox proportional hazard model, the adjusted hazard ratio (aHR) of all-cause mortality of the lowest quartile of serum bicarbonate was 1.460 (95% confidence interval (CI) 1.068-1.995) compared with the highest quartile, after a median follow-up of 93 months. The aHRs of cardiovascular and cancer mortality of the lowest quartile of serum bicarbonate were 2.647 (95% CI 1.148-6.103) and 1.604 (95% CI 1.024-2.513), respectively, compared with the highest quartile. Acidic and neutral urine pH were significantly associated with a higher all-cause mortality (aHR 2.550, 95% CI 1.316-4.935; aHR 2.376 95% CI 1.254-4.501, respectively), compared with an alkaline urine pH. In conclusion, higher metabolic acid load was associated with an increased all-cause and cardiovascular mortality in a healthy population. The association between metabolic acid load and mortality and the causality of the relationship need to be confirmed.

Lower urinary pH is useful for predicting renovascular disorder onset in patients with diabetes

BACKGROUND AND OBJECTIVES

A lower urinary pH (UpH) is closely linked to diabetes. However, its relation to diabetic renovascular damage is unclear. This study aimed to identify the relationship between UpH and the exacerbation of diabetic renovascular disorders.

METHODS

This is a 10-year observational study targeting 400 outpatients with diabetes who registered in 2003. We investigated the relationship between UpH in 2003 and renovascular damage from 2003 to 2013.

RESULTS

A total of 350 participants were eligible for the analysis. During their 10-year outpatient treatment, a decrease was seen in glycated hemoglobin levels, blood pressure, and estimated glomerular filtration rates (eGFRs), and an increase was seen in their urinary albumin-creatinine ratios (ACRs), uric acid (UA) levels, and intima-media thickness (IMT). UpH negatively correlated with urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), body mass index, UA, and ACR, and positively correlated with eGFR. The results of a multiple regression analysis showed that the independent risk factors for UpH were 8-OHdG, UA, eGFR, and ACR. UpH also negatively correlated with the percent change in IMT (%IMT), the percent change in pulse wave velocity (%PWV), and the change in log ACR (Δlog ACR), and positively correlated with the percent change in eGFR. A multiple regression analysis revealed that UpH was an independent risk factor for the %IMT, %PWV and Δlog ACR. Obese patients with low UpH values frequently suffered from sleep apnea syndrome.

CONCLUSIONS

These results suggest that UpH is a useful marker for predicting the onset of renovascular disorder in patients with diabetes.

Importance of pH homeostasis in metabolic health and diseases: crucial role of membrane proton transport

Protons dissociated from organic acids in cells are partly buffered. If not, they are transported to the extracellular fluid through the plasma membrane and buffered in circulation or excreted in urine and expiration gas. Several transporters including monocarboxylate transporters and Na(+)/H(+) exchanger play an important role in uptake and output of protons across plasma membranes in cells of metabolic tissues including skeletal muscle and the liver. They also contribute to maintenance of the physiological pH of body fluid. Therefore, impairment of these transporters causes dysfunction of cells, diseases, and a decrease in physical performance associated with abnormal pH. Additionally, it is known that fluid pH in the interstitial space of metabolic tissues is easily changed due to little pH buffering capacitance in interstitial fluids and a reduction in the interstitial fluid pH may mediate the onset of insulin resistance unlike blood containing pH buffers such as Hb (hemoglobin) and albumin. In contrast, habitual exercise and dietary intervention regulate expression/activity of transporters and maintain body fluid pH, which could partly explain the positive effect of healthy lifestyle on disease prognosis.

Alkalizer administration improves renal function in hyperuricemia associated with obesity

We evaluated the combination effect of the alkalizer citrate with the xanthine oxidase inhibitor allopurinol on renal function and uric acid in patients with hyperuricemia associated with obesity and/or metabolic syndrome (MetS), who were extracted from among the subjects enrolled in a prospective randomized controlled study aimed at assessing the efficacy of such a combination for improving renal function. We also conducted a post hoc analysis to examine influences on lipid profiles.

Patients who consented to participate in the study were randomly allocated to receive either allopurinol alone (monotherapy) or in combination with a citrate preparation (combination therapy). The analysis population consisted of 31 obese patients with a body mass index greater than 25 kg/m² (monotherapy, 15 patients; combination therapy, 16 patients). The creatinine clearance rate (Ccr), serum uric acid levels, and lipid profiles were measured before and at 12 weeks after the start of treatment.

In the combination therapy group, Ccr increased significantly and serum uric acid levels decreased significantly in obese patients, while Ccr tended to increase and serum uric acid levels decreased, though not significantly, in patients with MetS-related clinical parameters. Overall, blood triglyceride levels tended to improve in the combination therapy group as compared with the monotherapy group.

Metabolic syndrome, obesity and kidney stones

OBJECTIVES

To give a comprehensive and focused overview on the current knowledge of the causal relations of metabolic syndrome and/or central obesity with kidney stone formation.

METHODS

Previous reports were reviewed using PubMed, with a strict focus on the keywords (single or combinations thereof): urolithiasis, nephrolithiasis, kidney stones, obesity, metabolic syndrome, bariatric surgery, calcium oxalate stones, hyperoxaluria, insulin resistance, uric acid stones, acid-base metabolism.

RESULTS

Obesity (a body mass index, BMI, of >30 kg/m(2)) affects 10-27% of men and up to 38% of women in European countries. Worldwide, >300 million people are estimated to be obese. Epidemiologically, a greater BMI, greater weight, larger waist circumference and major weight gain are independently associated with an increased risk of renal stone formation, both for calcium oxalate and uric acid stone disease.

CONCLUSIONS

There are two distinct metabolic conditions accounting for kidney stone formation in patients with metabolic syndrome/central obesity. (i) Abdominal obesity predisposes to insulin resistance, which at the renal level causes reduced urinary ammonium excretion and thus a low urinary pH; the consequence is a greater risk of uric acid stone formation. (ii) Bariatric surgery, the only intervention that facilitates significant weight loss in morbidly obese people, carries a greater risk of calcium oxalate nephrolithiasis. The underlying pathophysiological mechanisms are profound enteric hyperoxaluria due to intestinal binding of calcium by malabsorbed fatty acids, and severe hypocitraturia due to soft or watery stools, which lead to chronic bicarbonate losses and intracellular metabolic acidosis.

Uric acid as one of the important factors in multifactorial disorders--facts and controversies

With considering serum concentration of the uric acid in humans we are observing hyperuricemia and possible gout development. Many epidemiological studies have shown the relationship between the uric acid and different disorders such are obesity, metabolic syndrome, hypertension and coronary artery disease. Clinicians and investigators recognized serum uric acid concentration as very important diagnostic and prognostic factor of many multifactorial disorders. This review presented few clinical conditions which are not directly related to uric acid, but the concentrations of uric acid might have a great impact in observing, monitoring, prognosis and therapy of such disorders. Uric acid is recognized as a marker of oxidative stress. Production of the uric acid includes enzyme xanthine oxidase which is involved in producing of radical-oxigen species (ROS). As by-products ROS have a significant role in the increased vascular oxidative stress and might be involved in atherogenesis. Uric acid may inhibit endothelial function by inhibition of nitric oxide-function under conditions of oxidative stress. Down regulation of nitric oxide and induction of endothelial dysfunction might also be involved in pathogenesis of hypertension. The most important and well evidenced is possible predictive role of uric acid in predicting short-term outcome (mortality) in acute myocardial infarction (AMI) patients and stroke. Nephrolithiasis of uric acid origin is significantly more common among patients with the metabolic syndrome and obesity. On contrary to this, uric acid also acts is an “antioxidant”, a free radical scavenger and a chelator of transitional metal ions which are converted to poorly reactive forms.

High serum uric acid level and low urine pH as predictors of metabolic syndrome: a retrospective cohort study in a Japanese urban population

The objective of this study was to evaluate whether hyperuricemia, acidic urine, or their combination predicts metabolic syndrome (MetS). In study 1, 69,094 subjects who received a general health checkup between 1985 and 2005 were included in a cross-sectional study of serum uric acid (SUA) and urine pH in relation to MetS. In study 2, the association of SUA and urine pH with MetS development over a 5-year period was evaluated in 5617 subjects with body mass index less than 25 kg/m(2) at the first examination. In study 1, higher SUA and lower urine pH were both positively correlated to MetS status (P < .001). The combination of high SUA and low urine pH was significantly associated with higher MetS prevalence compared with the combination of low SUA and high urine pH (odds ratio, 3.383; 95% confidence interval [CI], 3.034-3.784 in men; odds ratio, 4.000; 95% CI, 2.992-5.452 in women). In study 2, the top quartile of SUA levels was associated with higher MetS development compared with the bottom quartile during the 5-year period in men (hazard ratio [HR], 1.793; 95% CI, 1.084-2.966; P = .023). In women, the HR was 3.732 (95% CI, 0.391-35.62; P = .252) for the upper vs the lower half of SUA levels. For urine pH, the HR was 1.955 (95% CI, 1.089-3.509; P = .025) for the bottom vs the top quartile in men. A likelihood ratio test confirmed that high SUA and low urine pH act synergistically in the development of MetS. High SUA, low urine pH, and their combination are predictive risk factors for MetS development.

Long-term dietary potential renal acid load during adolescence is prospectively associated with indices of nonalcoholic fatty liver disease in young women

Nonalcoholic fatty liver disease (NAFLD), frequently already present in young subjects, has been linked to reduced growth hormone levels and signaling. Similar hormonal changes occur during metabolic acidosis (MA), which may thus contribute to an increased NAFLD risk. Because subclinical MA can be diet induced, we aimed to examine whether a higher diet-dependent acid load during adolescence is prospectively associated with several currently used NAFLD surrogates in young adulthood. Dietary acidity during adolescence (boys:10-15 y, girls: 9-14 y) was calculated as potential renal acid load (PRAL) from at least three 3-d weighed dietary records according to a published algorithm considering dietary protein and minerals in 145 healthy participants. Routine measurements derived from blood analysis and anthropometric data in participants' young adulthood (18-25 y) were used to determine the NAFLD surrogates alanine-aminotransferase (ALT), hepatic steatosis index (HSI), and fatty liver index (FLI). Sex-stratified linear regression models, adjusted for dietary fiber, saturated fat, protein, and adolescent BMI SD scores, were run with PRAL as the independent variable. Dietary PRAL during puberty was positively associated with ALT (P = 0.02), HSI (P = 0.002), and FLI (P = 0.005) in adult females but not males. Females with an adolescent dietary acid load in the highest tertile had 3.5, 4.4, and 4.5 higher values of ALT, HSI, and FLI as adults, respectively, compared to females with the lowest PRAL. The present findings suggest that higher dietary acidity in adolescence may be prospectively associated with hepatic lipid accumulation in females. Whether this relationship is due to the higher proton load or rather represents an unhealthy dietary pattern requires further investigation.