A liquid chromatography-tandem mass spectrometry method for comprehensive determination of metabolites in the purine pathway of rat plasma and its application in anti-gout effects of Lycium ruthenicum Murr.

It has been proved that purine metabolites are implicated in various biological syndromes and disorders. Therefore, the realization of panoramic detection of purine metabolites will be of great significance to the pathogenesis of purine metabolic disorders. In the present study, an ultra-high performance liquid chromatography with tandem mass spectrometry method was developed for the comprehensive quantification of purine metabolites in rat plasma. The 17 purine metabolites were separated and quantified in the short running time of 15 min. The proposed method was strictly validated by applying SeraSub solution as a matrix and proved to be linear (R2 ≥ 0.9944), accurate (the recoveries of all analytes ranged from 85.3% to 103.0%, with relative standard deviation values ≤ 9.3%), and precise (the intra- and inter-day precisions were less than 10.8% and 12.4%, respectively). The method was then successfully applied to the qualification of the endogenous purine metabolites in acute gouty arthritis rats, as well as colchicine and anthocyanin-intervened rats. Results showed that uric acid, xanthine, hypoxanthine, and xanthine were considered the key factors of acute gouty arthritis. The established method and measurement of purines in rat plasma might help the investigation of the action mechanisms between purine disorders and related diseases.

The efficacy and safety of citrate mixture vs sodium bicarbonate on urine alkalization in Chinese primary gout patients with benzbromarone: a prospective, randomized controlled study.

OBJECTIVES: To compare the efficacy and safety of citrate mixture and sodium bicarbonate on urine alkalization in gout patients under benzbromarone treatment. METHODS: A prospective, randomized, parallel controlled trial was conducted among 200 gout patients in the dedicated gout clinic of the Affiliated Hospital of Qingdao University. The participants were randomly divided into two groups (1:1), sodium bicarbonate group (3 g/day) and citrate mixture group (7 g/day). All patients were prescribed with 25 mg/day benzbromarone at initiation and maintained at a dose of 50 mg/day. Clinical and biochemical data were collected at each follow-up time point (baseline, weeks 2, 4, 8 and 12). RESULTS: A total of 182 patients completed the 12-week urine alkalization study. The urine pH value of both groups increased significantly from the baseline to the final follow-up time point (sodium bicarbonate group, 5.50-6.00, P < 0.05; citrate mixture group, 5.53-5.93, P < 0.05). While the comparisons regarding urine pH between treatment groups showed no significant differences for each time point. The estimated glomerular filtration rate (eGFR) dropped significantly after 12 weeks' trial in the sodium bicarbonate group (P < 0.01), while it was comparable between baseline and the last follow-up (P > 0.05) in the citrate mixture group. Results of urine analysis showed that the incident rate of occult blood in the sodium bicarbonate group was higher than that in the citrate mixture group (38 vs 24%, P < 0.05), accompanied by a similar occurrence of kidney stones. After 12-week follow-up, the frequency of twice gout flare in the citrate mixture group was significantly lower than that in sodium bicarbonate group (4 vs 12%, P = 0.037). No treatment-emergent adverse events occurred. CONCLUSION: The efficacy of citrate mixture on urine alkalization is comparable to sodium bicarbonate under benzbromarone treatment without significant adverse events. Citrate mixture is superior to sodium bicarbonate in lowering the incidence of urine occult blood and the frequency of gout attacks. TRIAL REGISTRATION: Registered with ChiCTR (http://www.chictr.org.cn), No. ChiCTR1800018518.

Identification of the urine and serum metabolomics signature of gout.

OBJECTIVE: Gout is the most common inflammatory arthritis and the worldwide incidence is increasing. By revealing the metabolic alterations in serum and urine of gout patients, the first aim of our study was to discover novel molecular biomarkers allowing for early diagnosis. We also aimed to investigate the underlying pathogenic pathways. METHODS: Serum and urine samples from gout patients (n = 30) and age-matched healthy controls (n = 30) were analysed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) to screen the differential metabolites and construct a diagnostic model. Next, the model was verified and optimized in the second validation cohort (n = 100). The pathways were illustrated to understand the underlying pathogenesis of gout. RESULTS: In general, serum metabolomics demonstrated a clearer distinction than urine metabolomics. In the discovery cohort, 40 differential serum metabolites were identified that could distinguish gout patients from healthy controls. Among them, eight serum metabolites were verified in the validation cohort. Through regression analysis, the final model consisted of three serum metabolites-pyroglutamic acid, 2-methylbutyryl carnitine and Phe-Phe-that presented optimal diagnostic power. The three proposed metabolites produced an area under the curve of 0.956 (95% CI 0.911, 1.000). Additionally, the proposed metabolic pathways were primarily involved in purine metabolism, branched-chain amino acids (BCAAs) metabolism, the tricarboxylic acid cycle, synthesis and degradation of ketone bodies, bile secretion and arachidonic acid metabolism. CONCLUSION: The metabolomics signatures could serve as an efficient tool for early diagnosis and provide novel insights into the pathogenesis of gout.

Simultaneous quantification of urinary purines and creatinine by ultra high performance liquid chromatography with ultraviolet spectroscopy and quadrupole time-of-flight mass spectrometry: Method development, validation, and application to gout study.

We present an ultra high performance liquid chromatography with ultraviolet spectroscopy and quadrupole time-of-flight mass spectrometry method for the simultaneous quantification of ten purines (adenine, hypoxanthine, guanine, xanthine, deoxyadenosine, adenosine, inosine, guanosine, xanthosine, and uric acid) and creatinine in human urine. After chromatographic separation on an ACE Excel 2 AQ column, high abundant creatinine and uric acid and the other low abundant purines were sequentially detected by ultraviolet and quadrupole time-of-flight mass spectrometry within a single run. Method validations including specificity (improved by accurate mass measurement), linearity (correlation coefficients ≥0.9944), limit of quantification (0.002-9.756 µg/mL), intra- and interday precision (relative standard deviations ≤9.1 and 14.0%, respectively), accuracy (relative errors ≤13.1%), extraction recovery (between 90.3 and 109.6%), matrix effect (between 85.3 and 110.5%), and stability (relative errors ≤14.3%) were fully evaluated. This approach was applied to characterize the disordered purine metabolism in acute and chronic gout as an example. Quantitative results (normalized by creatinine) showed that an overproduction of urinary purine precursors might be involved in the gout process. The developed method represents a useful tool to investigate the purine disturbances in gout and other relevant diseases.

Urinary Uromodulin/Creatinine Ratio as a Potential Clinical Biomarker for Chronic Kidney Disease Patients with Gout: A Pilot Study.

OBJECTIVE: Recent studies have reported that reduced excretion of urinary uromodulin is associated with renal tubular function and risks of progressive kidney disease. Gouty nephropathy is usually seen in patients with gout. Patients with chronic gouty nephropathy are characterized by the deposition of monosodium urate crystals primarily involving the collecting ducts in the medulla. We postulated that this correlation may be specific to gout and may serve as a useful biomarker for chronic kidney disease (CKD). MATERIALS AND METHODS: A total of 114 Taiwanese patients diagnosed with gout (n = 72), CKD (n = 26), or healthy volunteers (n = 16) were prospectively enrolled for this study from the Rheumatology and Nephrology Outpatient Clinics of our institution. We obtained urine and blood samples on patient visits to the outpatient clinics. Demographic data were obtained from medical records. RESULTS: In patients with gout, the spot urinary uromodulin/creatinine ratio (uUMCR; mg/g) in patients with CKD was significantly lower than that in those without CKD (CKD group: 2.2; non-CKD group: 5.6, p = 0.005). Multivariate analysis revealed that patients with CKD and gout had a lower uUMCR than those with gout alone (p = 0.028). A significant association was not observed in our non-gout cohort. CONCLUSION: The association of decreased uUMCR with CKD status was identified only in patients with gout in the present study. We believe that uUMCR might serve as an indicator of differential CKD in patients with gout.

[Clinical characteristics and renal uric acid excretion in early-onset gout patients].

Objective: To investigate clinical characteristics and renal uric acid excretion in early-onset gout patients. Methods: Consecutive inpatients with primary gout were recruited between 2013 and 2017. The patients with gout onset younger than 30 were defined as early-onset group while the others were enrolled as control group. Clinical characteristics and uric acid (UA) indicators were compared between two groups. Results: Among 202 recruited patients, the early-onset group included 36 patients (17.8%). Compared with control group, the early-onset group presented more patients with obesity [13 patients (36.1%) vs. 22 patients (13.3%), P<0.05], significantly higher serum UA level [(634±124)µmol/L vs.(527±169)µmol/L] and glomerular load of UA[(7.2±2.8)mg·min(-1)·1.73m(-2) vs. (4.4±2.2)mg·min(-1)·1.73m(-2)] and estimated glomerular filtration rate (GFR) [(83±21)ml·min(-1)·1.73m(-2) vs. (67±21)ml·min(-1)·1.73m(-2)] (all P<0.05), lower fractional excretion of UA [4.4% (3.4%,6.1%) vs. 7.2% (5.2%,9.6%),P<0.05], whereas 24h urinary UA excretion was comparable [(2 788±882)µmol/1.73m(2) vs. (2 645±1 140)µmol/1.73m(2), P=0.274]. Subgroup analysis of patients without chronic kidney disease showed significantly lower fractional excretion of UA in the early-onset group [4.5%(3.3%,6.1%) vs. 6.7% (5.1%,8.7%),P<0.05]. Logistic regression analysis showed that obesity (OR=3.25) and fractional excretion of UA less than 7% (OR=9.01, all P<0.05) were risk factors of gout early onset. Conclusion: The gout patients with early-onset younger than 30 present high serum and glomerular load of uric acid which might be due to obesity and relative under-excretion of renal uric acid.

Genome-wide association study of clinically defined gout identifies multiple risk loci and its association with clinical subtypes.

OBJECTIVE: Gout, caused by hyperuricaemia, is a multifactorial disease. Although genome-wide association studies (GWASs) of gout have been reported, they included self-reported gout cases in which clinical information was insufficient. Therefore, the relationship between genetic variation and clinical subtypes of gout remains unclear. Here, we first performed a GWAS of clinically defined gout cases only. METHODS: A GWAS was conducted with 945 patients with clinically defined gout and 1213 controls in a Japanese male population, followed by replication study of 1048 clinically defined cases and 1334 controls. RESULTS: Five gout susceptibility loci were identified at the genome-wide significance level (p<5.0×10(-8)), which contained well-known urate transporter genes (ABCG2 and SLC2A9) and additional genes: rs1260326 (p=1.9×10(-12); OR=1.36) of GCKR (a gene for glucose and lipid metabolism), rs2188380 (p=1.6×10(-23); OR=1.75) of MYL2-CUX2 (genes associated with cholesterol and diabetes mellitus) and rs4073582 (p=6.4×10(-9); OR=1.66) of CNIH-2 (a gene for regulation of glutamate signalling). The latter two are identified as novel gout loci. Furthermore, among the identified single-nucleotide polymorphisms (SNPs), we demonstrated that the SNPs of ABCG2 and SLC2A9 were differentially associated with types of gout and clinical parameters underlying specific subtypes (renal underexcretion type and renal overload type). The effect of the risk allele of each SNP on clinical parameters showed significant linear relationships with the ratio of the case-control ORs for two distinct types of gout (r=0.96 [p=4.8×10(-4)] for urate clearance and r=0.96 [p=5.0×10(-4)] for urinary urate excretion). CONCLUSIONS: Our findings provide clues to better understand the pathogenesis of gout and will be useful for development of companion diagnostics.

Relationship between serum allantoin and urate in healthy subjects and effects of benzbromarone in gout patients.

BACKGROUND: Although hyperuricemia is suggested to increase allantoin production in both pro- and antioxidant manners, it remains undetermined whether it increases the serum concentration of allantoin. In addition, since uric acid has both pro- and antioxidant actions, a decrease in the serum concentration of uric acid may have an effect on the pro-oxidant-antioxidant balance. METHODS: To examine whether serum allantoin is correlated with serum urate, we measured those levels as well as other parameters in 63 healthy subjects. In addition, to determine whether serum allantoin is correlated with reactive oxygen species (ROS) biomarkers, we measured 8-hydroxy deoxyguanosine and 15-F2t-isoprostane, markers of ROS, in urine samples from 30 gout patients before and 1 year after benzbromarone treatment (50 mg/d). RESULTS: The serum concentration of allantoin was correlated with that of urate in healthy subjects (R = 0.27, p < 0.05). Benzbromarone treatment in the patients decreased the concentrations of allantoin and urate in serum by 17% (p < 0.05) and 49% (p < 0.05), respectively, and the benzbromarone-induced change in serum allantoin was correlated with that in serum urate (R = 0.39, p < 0.05). However, benzbromarone treatment did not change the ratios of 8-hydroxydeoxyguanosine/creatinine or 15-F2t-isoprostane/creatinine in urine. CONCLUSIONS: Our findings suggest that hyperuricemia contributes to an increase in serum concentration of allantoin, though they do not indicate that hyperuricemia is a major factor for controlling oxidative stress in vivo.

Urinary UMOD excretion and chronic kidney disease in gout patients: cross-sectional case-control study.

Patients with gout often have concurrent chronic kidney disease (CKD); the relationship between the two conditions is still unclear. Previous studies have identified an association between low level of urinary uromodulin (UMOD) and CKD within the setting of diabetes and lupus. The aim of this study was to examine the association between urinary UMOD excretion and CKD in patients with gout. A total of 53 Taiwanese gout patients with stable disease activity were enrolled. Patients were divided into a CKD group (n = 25) and a non-CKD group (n = 28). Using Pearson correlation analysis, urinary UMOD excretion was positively correlated with estimated glomerular filtration rate (Ha: ρ > 0, p = 0.004). Using multivariate analysis, patients with CKD and gout were associated with lower urinary UMOD excretion than those who have gout alone [odds ratio (95% CI): 0.826 (0.694-0.985), p < 0.001]. Patients with CKD and gout were also more likely to be older (p < 0.001) and have higher uric acid levels (p < 0.001). This study implicates that UMOD might play a role in the relationship between gout and CKD. Further studies with animal models of gout and CKD would be recommended.

[Antihypertensive therapy optimization and endothelial function in patients with gout and chronic urate tubulointerstitial nephritis].

AIM: to characterize the markers of endothelial dysfunction and the effect of antihypertensive drugs on them in patients with chronic urate tubulointestinal nephritis (UTIN) and articular gout. SUBJECTS AND METHODS: The study enrolled 81 patients aged 39 to 59 years with gout and urate nephropathy. All the patients were diagnosed as having grade 1-2 arterial hypertension. A lower glomerular filtration rate (GFR) was noted in 49.9%; microalbuminuria (MAU) and elevated serum endothelin-1 (ET-1) levels were recorded in all the patients. Combination antihypertensive therapy based on the use of angiotensin-converting enzyme (ACE) inhibitors and/or an angiotensin II receptor blocker (ARB) in combination with calcium channel blockers was performed during 12 months. The time course of changes in blood pressure, the parameters of target organ lesion, and the markers of endothelial dysfunction were monitored. RESULTS: Before the study, all the examinees were found to have MAU and increased serum ET-1, which are regarded simultaneously as signs of renal lesion and as markers of endothelial function. A combination of an ACE inhibitor or an ARB could diminish albuminuria and reduce ET-1 concentrations, lower systolic and diastolic blood pressure significantly, and increase GFR. CONCLUSION: The patients with articular gout and chronic UTIN are observed to have signs of endothelial dysfunction eliminated by combination antihypertensive therapy.

Characteristics of the Urinary Microbiome From Patients With Gout: A Prospective Study.

The role of host microbes in the pathogenesis of several diseases has been established, and altered microbiomes have been related to diseases. However, the variability of the urinary microbiome in individuals with gout has not been evaluated to date. Therefore, we conducted the present prospective study to characterize the urinary microbiome and its potential relation to gout. Urine samples from 30 patients with gout and 30 healthy controls were analyzed by Illumina MiSeq sequencing of the 16S rRNA hypervariable regions, and the microbiomes were compared according to alpha-diversity indices, complexity (beta diversity) with principal component analysis, and composition with linear discriminant analysis effect size. The most significantly different taxa at the phylum and genus levels were identified, and their potential as biomarkers for discriminating gout patients was assessed based on receiver operating characteristic (ROC) curve analysis. Compared with the healthy controls, there was a dramatic decrease in microbial richness and diversity in the urine of gout patients. The phylum Firmicutes and its derivatives (Lactobacillus_iners, Family_XI, and Finegoldia), the phylum Actinobacteria and its derivatives (unidentified_Actinobacteria, Corynebacteriales, Corynebacteriale, Corynebacterium_1, and Corynebacterium_tuberculostearicum), and the genera Prevotella and Corynebacterium_1 were significantly enriched in the urine of gout patients. ROC analysis indicated that the top five altered microbial genera could be reliable markers for distinguishing gout patients from healthy individuals. These findings demonstrate that there are specific alterations in the microbial diversity of gout patients. Thus, further studies on the causal relationship between gout and the urinary microbiome will offer new prospects for diagnosing, preventing, and treating gout.

Purine overproduction in man associated with increased phosphoribosylpyrophosphate synthetase activity.

In hemolyzates from red cells of two brothers with purine overproduction and gout, activity of phosphoribosylpyrophosphate synthetase is more than twofold greater than that measured in normal or other gouty individuals. The increased enzyme activity, which is also demonstrable in fibroblasts of the one patient tested, is associated with increased production of 5-phosphoribosyl-1-pyrophosphate by intact cells, an indication that the enzyme abnormality is the basis for the purine overproduction. This genetic abnormality is an example of an increased enzyme activity producing a disease state.

Population-specific factors associated with fractional excretion of uric acid.

BACKGROUND: Reduced renal clearance of uric acid is a major contributor to hyperuricemia. The aim of this study was to examine clinical and genetic variables associated with fractional excretion of uric acid (FEUA). METHODS: Participants (with and without gout) in the Genetics of Gout in Aotearoa study with available genotyping and FEUA data were included (n = 1713). Ten FEUA-associated loci detected within a genome-wide association study for serum urate in a European population were analysed. A polygenic score for FEUA was calculated in each ancestry group to model the cumulative effects of the genetic variants on FEUA. Associations between FEUA and both clinical variables and polygenic score were tested using linear regression models. RESULTS: The mean (SD) FEUA was 5.13 (2.70) % in Eastern Polynesian participants, 4.70 (5.89) % in Western Polynesian participants, and 5.89 (2.73) % in New Zealand European participants. Although association with FEUA was observed for SLC2A9 rs11942223 in New Zealand European participants (P = 2.39 × 10- 8), this association was not observed in Eastern or Western Polynesian participants. The polygenic score was positively associated with FEUA in all ancestry groups. In New Zealand European participants, body mass index, diuretic use, polygenic score, and male sex were associated with FEUA and explained 22% of FEUA variance in the regression model. In Eastern and Western Polynesian participants, the tested variables explained 10% and 4% of FEUA variance respectively. CONCLUSIONS: Both clinical and genetic variables contribute to renal clearance of uric acid. SLC2A9 exerts effects on FEUA variance in people of European ancestry, but not in those of Polynesian ancestry. There is a large unexplained variance in FEUA, particularly in people of Polynesian ancestry.

[Urolithiasis and nephropathy complicated with gout].

Urolithiasis is a clinically important complication of gout. For effective prevention of this complication, it is necessary to comprehend the factors known to be important in its development. Our analysis of stones in gout patients revealed that the incidence of common calcium salt stones was over 60%, while that of uric acid stones was only about 30%. This implies that the disruption of uric acid metabolism promotes not only uric acid stones but also calcium salt stones. Twenty-four per cent of gout patients showed acidic urine throughout the day. Urinary management, which consists of hydration and alkalization of urine, is indispensable along with control of the serum urate level in the treatment of gout.

Urinary Metabolomics Study of Patients with Gout Using Gas Chromatography-Mass Spectrometry.

OBJECTIVES: Gout is a common type of inflammatory arthritis. The aim of this study was to detect urinary metabolic changes in gout patients which may contribute to understanding the pathological mechanism of gout and discovering potential metabolite markers. METHODS: Urine samples from 35 gout patients and 29 healthy volunteers were analyzed by gas chromatography-mass spectrometry (GC-MS). Orthogonal partial least-squares discriminant analysis (OPLS-DA) was performed to screen differential metabolites between two groups, and the variable importance for projection (VIP) values and Student's t-test results were combined to define the significant metabolic changes caused by gout. Further, binary logistic regression analysis was performed to establish a model to distinguish gout patients from healthy people, and receiver operating characteristic (ROC) curve was made to evaluate the potential for diagnosis of gout. RESULT: A total of 30 characteristic metabolites were significantly different between gout patients and controls, mainly including amino acids, carbohydrates, organic acids, and their derivatives, associated with perturbations in purine nucleotide synthesis, amino acid metabolism, purine metabolism, lipid metabolism, carbohydrate metabolism, and tricarboxylic acid cycle. Binary logistic regression and ROC curve analysis showed the combination of urate and isoxanthopterin can effectively discriminate the gout patients from controls with the area under the curve (AUC) of 0.879. CONCLUSION: Thus, the urinary metabolomics study is an efficient tool for a better understanding of the metabolic changes of gout, which may support the clinical diagnosis and pathological mechanism study of gout.

Renal excretion is a cause of decreased serum uric acid during acute gout.

AIMS: To evaluate the fluctuation of serum uric acid (SUA) during acute gout (AG) and explore its potential mechanisms. METHODS: Data such as SUA, urinary uric acid and 24-hour uric acid urinary excretion were collected from 126 patients diagnosed with gout and were analyzed. RESULTS: Serum uric acid was negatively correlated with age in gout patients, and significantly elevated in patients aged ≤50 years. Twenty-four-hour uric acid urinary excretion was affected by SUA, creatinine clearance, age, body mass index and urine volume. In contrast, clearance of uric acid and fractional excretion of uric acid (FEur) were more stable. SUA was significantly downregulated during acute attacks. Of the AG patients, 34.92% had detected SUA <420 µmol/L. Clearance of uric acid and FEur were notably increased in patients during acute attacks, especially in patients with SUA <420 µmol/L. CONCLUSION: This study demonstrated that the level of SUA was remarkably upregulated in young gout patients. Therefore, early onset of gout should be considered of great importance. SUA was downregulated during acute gouty arthritis, which might be associated with increased urinary excretion of uric acid.

Clinical significance of SLC2A9/GLUT9 rs11722228 polymorphisms in gout.

AIM: The main objective of this study is to elucidate the clinical significance of the SLC2A9/GLUT9 rs11722228 polymorphism among male gout patients. METHOD: We consecutively recruited all newly diagnosed male gout patients who were treatment-naive from the rheumatology outpatient clinics of two Malaysian hospitals. Age-matched healthy male adults were employed as controls. All subjects were tested for the SLC2A9/GLUT9 rs11722228 genotypes, serum uric acid (SUA), urine uric acid and creatinine levels. All gout subjects were examined for the presence of tophi and sonographically screened for renal calculi. RESULTS: A total of 73 male gout patients and 73 age-matched healthy male adults were recruited in this study. The genotypic frequencies of SLC2A9/GLUT9 rs1172228 did not differ significantly between the gout cases and the healthy controls. The gout subjects with the CC genotype had significantly higher SUA levels (P = 0.002), family history of gout (P < 0.050) and the occurrence of renal calculi (P = 0.026). The SUA-adjusted odds ratios (OR) of the occurrence of renal calculi in the CC genotype (OR = 1 [reference]) was significantly higher than the CT genotype (OR = 0.338, 95%CI: 0.141-0.813) and the TT genotype (OR = 0.271, 95%CI: 0.086-0.854). CONCLUSIONS: The genotypic distribution of SLC2A9/GLUT9 rs1172228 in male gout patients did not differ significantly from that of healthy male controls. However, the CC genotype in gout had significant associations with higher levels of SUA, renal calculi and a positive family history of gout.

Plasma and urinary amino acids in primary gout, with special reference to glutamine.

Measurement of the plasma free amino acids by column chromatography (AutoAnalyzer) in 32 patients with primary gout showed statistically significant increases or decreases in several components when compared with the spectrum in 18 control subjects, but the absolute amounts involved were small and the mean total plasma amino acid concentrations in both groups were the same. In the urine all major amino acid components, notably glutamine, serine, threonine, and leucine, were lower in our gouty than in our nongouty subjects, as were also the corresponding renal clearance ratios. These deficits could be reproduced by restricting dietary protein, so appear to be due largely to the some-what reduced mean dietary protein intake of our gouty subjects. However, the low renal clearance of glutamine, the most striking and consistent of the deficits in urinary amino acids noted, could not be accounted for by dietary or other relevant factors, and is interpreted as indicating increased tubular reabsorption of glutamine in primary gout. This interpretation was supported by the results of glutamine loading. The possible compensatory relationship of the abnormality in renal handling of glutamine to the deficiency in renal production of ammonia previously reported is discussed.