Purine metabolism in patients with gout: the role of lead

Analysis of Metabolite Profiling in Human Endothelial Cells after Plasma Jet Treatment

Cold atmospheric plasma (CAP) is a novel technology, which has been widely applied in biomedicine, especially in wound healing, dermatological treatment, hemostasis, and cancer treatment. In most cases, CAP treatment will interact with innumerable blood capillaries. Therefore, it is important and necessary to understand the effects of CAP treatment on endothelial cell metabolism. In this study, the metabolite profiling of plasma treatment on endothelial cells was measured by gas chromatography tandem time-of-flight mass spectrometry (GC-TOF-MS). We found that 695 signals (metabolites) were detected by GC-TOF-MS and then evaluated using orthogonal projections to latent structures discriminant analysis (OPLS-DA). All the differential metabolites were listed, and proline and xanthosine were the two of the most downregulated metabolites by plasma treatment. By comprehensive metabolic pathway analysis with the KEGG pathway, we showed that alanine, aspartate, glutamate, and purine metabolism pathways were the most significantly suppressed after gas plasma treatment in human endothelial cells. Our finding gives an overall picture of the metabolic pathways affected by plasma treatment in endothelial cells.

Uric acid excretion in healthy subjects: a nomogram to assess the mechanisms underlying purine metabolic disorders

The reference range for urinary uric acid excretion has not been precisely defined. Different urinary variables have been proposed to determine the renal contribution to increased or decreased serum urate concentrations. We examined which urinary variable best indicates uric acid excretion over a wide range of serum urate concentrations. Purine metabolism was studied in 10 healthy male subjects (aged 26-58 years) both at their endogenous normal serum urate levels (normouricemic state) and after the oral administration of allopurinol (300 mg/24 h for 5 days) and ribonucleic acid (4 g/8 h for 4 days) to decrease (hypouricemic state) and increase (hyperuricemic state) serum urate concentrations, respectively. The results from patients with several conditions known to affect uric acid synthesis and/or the renal excretion of uric acid were used to validate a constructed nomogram. Over a wide range of mean serum urate levels (from 2.7 to 9.5 mg/dL) and mean 24-hour urinary uric acid excretion (171 to 1368 mg/[24 h 1.73 m(2)]), the highest correlation coefficient between serum urate and uric acid excretion was obtained for the 24-hour uric acid determination (r = 0.928; P < .001). The constructed nomogram allowed the definition of the mechanism underlying hyperuricemia and hypouricemia in patients with a myriad of diseases known to affect purine metabolism. The urinary variable that best correlates with a wide range of serum urate concentrations is 24-hour urinary uric acid excretion. The constructed nomogram allows the identification of the kidney contribution to a given purine metabolic abnormality.

New and improved strategies for the treatment of gout

The Western world appears to be in the midst of the third great gout epidemic of all time. In this century, gout is increasing in prevalence despite an increased understanding of its risk factors and pathophysiology, and the availability of reasonably effective treatment. The main cultural factors responsible for this appear to be diet, obesity, ethanol use and medications. Excess fructose consumption is a newly recognized modifiable risk factor. The debate has been renewed concerning hyperuricemia as an independent risk factor for renal insufficiency and cardiovascular disease. Prevention is still rooted in lifestyle choices. Existing treatments have proven to be unsatisfactory in many patients with comorbidities. New treatments are available today and on the horizon for tomorrow, which offer a better quality of life for gout sufferers. These include febuxostat, a nonpurine inhibitor of xanthine oxidase with a potentially better combination of efficacy and safety than allopurinol, and investigational inhibitors of URAT-1, an anion exchanger in the proximal tubule that is critical for uric acid homeostasis. New abortive treatments include interleukin-1 antagonists that can cut short the acute attack in 1 to 2 days in persons who cannot take nonsteroidal anti-inflammatory drugs, colchicine or corticosteroids. Lastly, newer formulations of uricase have the ability to dissolve destructive tophi over weeks or months in patients who cannot use currently available hypouricemic agents. Diagnostically, ultrasound and magnetic resonance imaging offer advanced ways to diagnose gout noninvasively, and just as importantly, a way to follow the progress of tophus dissolution. The close association of hyperuricemia with metabolic syndrome, hypertension and renal insufficiency ensures that nephrologists will see increasing numbers of gout-afflicted patients.

Associations among lead dose biomarkers, uric acid, and renal function in Korean lead workers

Recent research suggests that both uric acid and lead may be nephrotoxic at lower levels than previously recognized. We analyzed data from 803 current and former lead workers to determine whether lead biomarkers were associated with uric acid and whether previously reported associations between lead dose and renal outcomes were altered after adjustment for uric acid. Outcomes included uric acid, blood urea nitrogen, serum creatinine, measured and calculated creatinine clearances, and urinary N-acetyl-ss-d-glucosaminidase (NAG) and retinol-binding protein. Mean (+/- SD) uric acid, tibia lead, and blood lead levels were 4.8 +/- 1.2 mg/dL, 37.2 +/- 40.4 microg/g bone mineral, and 32.0 +/- 15.0 microg/dL, respectively. None of the lead measures (tibia, blood, and dimercaptosuccinic-acid-chelatable lead) was associated with uric acid, after adjustment for age, sex, body mass index, and alcohol use. However, when we examined effect modification by age on these relations, both blood and tibia lead were significantly associated (ss = 0.0111, p < 0.01 and ss = 0.0036, p = 0.04, respectively) in participants in the oldest age tertile. These associations decreased after adjustment for blood pressure and renal function, although blood lead remained significantly associated with uric acid (ss = 0.0156, p = 0.01) when the population was restricted to the oldest tertile of workers with serum creatinine greater than the median (0.86 mg/dL). Next, in models of renal function in all workers, uric acid was significantly (p < 0.05) associated with all renal outcomes except NAG. Finally, in the oldest tertile of workers, associations between lead dose and NAG were unchanged, but fewer associations between the lead biomarkers and the clinical renal outcomes remained significant (p less than or equal to 0.05) after adjustment for uric acid. In conclusion, our data suggest that older workers comprise a susceptible population for increased uric acid due to lead. Uric acid may be one, but not the only, mechanism for lead-related nephrotoxicity.

Clinical evidence for the influence of uric acid on hypertension, cardiovascular disease, and kidney disease: A statistical modeling perspective

This article critically evaluates the clinical evidence regarding the influence of uric acid on hypertension, cardiovascular disease, and kidney disease. Data on these relationships are largely observational and exceedingly complex. The complexity is owing to indirect and direct relations, and bidirectional influences, simultaneously operating on multiple outcomes. Limitations of previous analyses include inadequate statistical methods using only bivariate correlations or poorly specified multiple regression models. As a result, great controversy developed as to whether uric acid is an independent predictor of important outcomes. An example of such analytic limitations is including hypertension as an independent variable, together with uric acid, in a multivariate model for predicting cardiovascular disease. Hypertension may predict significant variance in cardiovascular disease, but the contribution of uric acid may not be recognized if uric acid exerts its influence indirectly through hypertension. Path analysis, which can model direct and indirect influences on outcomes simultaneously, would address this substantive question. Studies of uric acid in relation to hypertension, cardiovascular disease, and kidney disease using a path-analytic approach would help specify such conditions as well as optimize design of clinical trials to determine if decreasing uric acid levels improves outcomes.

Phosphoribosylpyrophosphate synthetase overactivity as a cause of uric acid overproduction in a young woman

Overactivity of phosphoribosylpyrophosphate synthetase (PRS) is an X chromosome-linked disorder of purine metabolism that is characterized by gout with uric acid overproduction and, in some families, neurodevelopmental impairment. We present the case of a 24-year-old Spanish woman with renal colic and hyperuricemia, which first manifested at age 11 years. Results of enzymatic and genetic studies supported the view that accelerated purine nucleotide and uric acid production in this woman resulted from defective allosteric regulation of PRS activity, which is, in turn, a consequence of a mutation in one of the patient's PRPS1 genes: an A-to-T substitution at nucleotide 578, encoding leucine for histidine at amino acid residue 192 of the mature PRS1 isoform. A previous example of disordered regulation of PRS1 activity in a family with a different substitution at the same amino acid residue strengthens this proposed mechanism. This is the first reported instance of PRS overactivity in which the propositus and sole affected family member is a woman.

Renal underexcretion of uric acid is present in patients with apparent high urinary uric acid output

OBJECTIVE

To compare renal handling of uric acid in patients with primary gout with that of a control group.

METHODS

A case-control study of 100 patients with primary gout and 72 healthy controls was undertaken. Creatinine clearance, uric acid clearance, 24-hour uric acid urinary excretion, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, urinary uric acid to creatinine ratio, and glomerular uric acid filtered load were calculated using 24-hour urine samples. After treatment with allopurinol to achieve similar glomerular filtered load of uric acid, patients were again compared with controls.

RESULTS

Patients with gout showed lower uric acid clearance, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, and urinary uric acid to creatinine ratio than controls at baseline, when patients showed hyperuricemia. Although the glomerular uric acid filtered load was much higher in patients with gout than controls, 24-hour uric acid excretion was not statistically different. After treatment with allopurinol, and achieving similar uric acid filtered loads, patients still showed lower figures than controls. When patients with 24-hour urinary uric acids levels >700 mg/day were compared with controls, they had lower uric acid clearance and fractional excretion of uric acid than controls, both at baseline and after achieving similar filtered loads with allopurinol therapy.

CONCLUSIONS

Renal underexcretion is the main mechanism for the development of primary hyperuricemia in gout, but even patients showing apparent high 24-hour uric acid output show lower uric acid clearance than controls, indicating that relative, low-grade underexcretion of uric acid is at work.

Environmental lead exposure and urate excretion in the general population

PURPOSE

Chronic occupational exposure to lead is related to low urate excretion and a high incidence of gout in lead workers. However, whether chronic low-level environmental lead exposure influences urate excretion in the general population remains unknown.

SUBJECTS AND METHODS

We studied 111 healthy subjects with normal renal function (serum creatinine level < or =1.4 mg/dL) and no previous lead exposure or systemic diseases. All subjects had their blood lead levels measured, received ethylenediaminetetraacetic acid mobilization tests to assess their body lead burdens, and were investigated for renal function and urate excretion to assess the relation between lead and urate excretion. We studied urate excretion before and after lead chelation therapy in 24 subjects with high-normal body lead burden (>78 mg and <600 mg).

RESULTS

Healthy subjects with gout (n = 27) manifested a higher body lead burden (84 +/- 42 mg vs. 45 +/- 30 mg, P <0.0001) and lower urate clearance (3.7 +/- 1.2 mL/min/1.73 m(2) vs. 6.0 +/- 2.8 mL/min/1.73 m(2), P <0.0001) than did those without gout (n = 84). Blood lead levels and body lead burden of all subjects were within the safe range. In analyses that adjusted for age, sex, body mass index, protein intake, and creatinine clearance, blood lead level was significantly related to serum urate level (beta coefficient [+/- SE] = 0.23 +/- 0.11, P = 0.03), and body lead burdens were related to all indices of urate excretion (serum urate: beta coefficient = 0.023 +/- 0.005, P <0.0001; daily urate excretion: beta coefficient = -1.55 +/- 0.40, P = 0.0002; urate clearance: beta coefficient = -0.030 +/- 0.006, P <0.0001; fractional urate excretion: beta coefficient= -0.034 +/- 0.006, P <0.0001). Following lead chelation therapy, urate clearance increased after body lead burden was reduced (3.4 +/- 1.2 mL/min/1.73 m(2) vs. 4.9 +/- 1.4 mL/min/1.73 m(2), P <0.005).

CONCLUSION

Chronic low-level environmental lead exposure may inhibit urate excretion in the general population, and lead chelation therapy reduces this inhibition. These findings support efforts to reduce sources of environmental lead exposure and suggest alternative approaches to hyperuricemia and gout in the general population.

Lead chelation therapy and urate excretion in patients with chronic renal diseases and gout

BACKGROUND

It is known that chronic renal insufficiency (CRI) patients with gout may have subtle lead poisoning. In addition, gout episodes frequently aggravate progressive renal insufficiency because of the use of nephrotoxic drugs and urate deposition. Our study was arranged to evaluate the causal effect of environmental lead exposure on urate excretion in CRI patients.

METHODS

A cross-section study and a randomized, controlled trial were performed. Initially, 101 patients with CRI and without a history of previous lead exposure received ethylenediaminetetraacetic acid mobilization tests to assess body lead stores (BLS). Then, a clinical trial was performed; 30 CRI patients with gout and high-normal BLS and the changes of urate excretion in these patients were compared before and after lead chelating therapy. The treated group received four-week chelating therapy, and the control group received a placebo therapy.

RESULTS

The BLS of patients with CRI and gout was higher than that of patients with CRI only, and none had subtle lead poisoning. The BLS, not the blood lead level (BLL), significantly correlated to indices of urate excretion in all CRI patients after related factors were adjusted. In addition, after lead chelating therapy, urate clearance markedly improved after a reduction of the BLS of patients with CRI and gout (study group 67.9 +/- 80.0% vs. control group 1.2 +/- 34.0%, P = 0.0056).

CONCLUSION

Our findings suggest that the chronic low-level environmental lead exposure may interfere with urate excretion of CRI patients. Importantly, the inhibition of urate excretion can be markedly improved by lead chelating therapies. These data shed light on additional treatment of CRI patients with gout; however, more studies are needed to confirm our findings.

Purine metabolism in female heterozygotes for hypoxanthine-guanine phosphoribosyltransferase deficiency

BACKGROUND

Female carriers of the X-linked recessive disorder hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency show somatic cell mosaicism, and this may cause an increased synthesis of purines. We have examined whether urinary oxypurines could be useful for carrier diagnosis.

METHODS

Carrier testing was performed in 35 women belonging to 16 unrelated Spanish families with at least one subject affected by the Lesch-Nyhan syndrome (11 families, 14 patients) or the Kelley-Seegmiller syndrome (five families, six patients) by means of HPRT and adenine phosphoribosyltransferase activities in hair follicles and/or molecular studies. Plasma and 24-h urinary concentrations of hypoxanthine, xanthine and uric acid were measured while subjects were on a purine-restricted diet.

RESULTS

Mean plasma urate concentrations and 24-h urinary hypoxanthine, xanthine and uric acid excretion rates were significantly higher in 22 heterozygotes than in 13 non-carriers (P < 0.02). Daily urinary oxypurine excretion rates were also significantly higher in heterozygotes than in 12 normal women (P = 0.0011). Cumulative 5-day radioactivity excretion after [8-14C]-adenine infusion was markedly increased in 10 carrier women compared with five normal women (P = 0.0369). The sensitivity of 24-h urinary hypoxanthine and xanthine excretion rates was 86% and 77%, respectively, and the specificity 100% for both tests.

CONCLUSION

Female heterozygotes for HPRT deficiency show an enhanced purine nucleotide degradation and purine overproduction. An elevated hypoxanthine and/or xanthine excretion rate differentiated most heterozygotes for HPRT deficiency from non-carrier women and thus could be useful for carrier diagnosis.