Relationship of protein intake to urinary oxalate and glycolate excretion

Secondary oxalate nephropathy and kidney transplantation

PURPOSE OF REVIEW

Secondary hyperoxaluria is associated with poor kidney allograft outcomes after the kidney transplant. Calcium oxalate (CaOx) deposition is common in early allograft biopsies leading to acute tubular necrosis and poor kidney allograft function. Though treatment options for secondary hyperoxaluria are limited, it is crucial to identify patients at increased risk of oxalate nephropathy after the transplant.

RECENT FINDINGS

Recent data suggest that significant changes in renal replacement therapies and dietary modifications in high-risk patients can prevent kidney allograft damage from the calcium oxalate deposition leading to improve allograft outcomes.

SUMMARY

The accurate and timely diagnosis of secondary oxalate nephropathy in kidney transplant recipients is paramount to preserving graft function in the long-term. This review will discuss the incidence, risk factors, prevention, and management of oxalate nephropathy in the kidney allograft.

Oxalate Flux Across the Intestine: Contributions from Membrane Transporters

Epithelial oxalate transport is fundamental to the role occupied by the gastrointestinal (GI) tract in oxalate homeostasis. The absorption of dietary oxalate, together with its secretion into the intestine, and degradation by the gut microbiota, can all influence the excretion of this nonfunctional terminal metabolite in the urine. Knowledge of the transport mechanisms is relevant to understanding the pathophysiology of hyperoxaluria, a risk factor in kidney stone formation, for which the intestine also offers a potential means of treatment. The following discussion presents an expansive review of intestinal oxalate transport. We begin with an overview of the fate of oxalate, focusing on the sources, rates, and locations of absorption and secretion along the GI tract. We then consider the mechanisms and pathways of transport across the epithelial barrier, discussing the transcellular, and paracellular components. There is an emphasis on the membrane-bound anion transporters, in particular, those belonging to the large multifunctional Slc26 gene family, many of which are expressed throughout the GI tract, and we summarize what is currently known about their participation in oxalate transport. In the final section, we examine the physiological stimuli proposed to be involved in regulating some of these pathways, encompassing intestinal adaptations in response to chronic kidney disease, metabolic acid-base disorders, obesity, and following gastric bypass surgery. There is also an update on research into the probiotic, Oxalobacter formigenes, and the basis of its unique interaction with the gut epithelium. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.

Determination of reference interval (RI) of spot urinary oxalate to creatinine ratio in children of pakistani origin under six years of age: A cross-sectional study

Background

The gold standard screening method of hyperoxaluria in children is using 24-hour urine collection. Urine collection may be cumbersome and challenging for children. Reference intervals (RI) of oxalate for the Pakistani population are not readily available. Therefore we aimed to determine the oxalate to creatinine ratio (Ox: Cr) for Pakistani children <6 years of age.

Materials and Methods

A cross-sectional study was conducted at Aga Khan University from June 2018 to October 2019. Random urine samples from apparently healthy children < 6 years were collected and stored at -30°C until analysis after adding 6M HCl. Oxalate was measured on Micro lab 300 using a kit based on oxalate oxidase principle, while creatinine was measured by kinetic Jaffe reaction. Data was analyzed by EP evaluator and SPSS 23. Ox: Cr ratio was calculated and reported with 90% confidence interval (CI) and interquartile range (IQR).

Results

The mean age of study subjects (n=120) was 29 ±22.3 months with an M: F ratio of 1:1. Children of various ethnicities were included from all over Karachi. The majority of the subjects were Urdu speaking (37.5%). Median Ox: Cr was 0.13(0.10). No significant difference was noted in the median Ox: Cr ratio between various ethnicities (p>0.05). It was significantly different in group I to V which was 0.25 (IQR: 0.06), 0.19 (IQR: 0.11), 0.15 (IQR: 0.04), 0.11 (IQR: 0.06) and 0.08 (IQR: 0.04) respectively (pvalue <0.001).

Conclusion

The established RIs of Ox: Cr ratio was 0.05-0.34 (90% CI). Ox: Cr ratio showed a declining trend with age. Large scale reference interval studies are encouraged, taking diet and age into consideration.

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Reference intervals (RI) of oxalate for the Pakistani population are not readily available.

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Established RIs of Ox: Cr ratio was 0.05–0.34 (90% CI) in children under 6 years.

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Ox: Cr ratio showed a declining trend with age.

Which Diet for Calcium Stone Patients: A Real-World Approach to Preventive Care

Kidney stone disease should be viewed as a systemic disorder, associated with or predictive of hypertension, insulin resistance, chronic kidney disease and cardiovascular damage. Dietary and lifestyle changes represent an important strategy for the prevention of kidney stone recurrences and cardiovascular damage. A full screening of risk factors for kidney stones and for cardiovascular damage should be recommended in all cases of calcium kidney stone disease, yet it is rarely performed outside of stone specialist clinics. Many patients have a history of kidney stone disease while lacking a satisfactory metabolic profile. Nonetheless, in a real-world clinical practice a rational management of kidney stone patients is still possible. Different scenarios, with different types of dietary approaches based on diagnosis accuracy level can be envisaged. The aim of this review is to give patient-tailored dietary suggestions whatever the level of clinical and biochemistry evaluation. This can help to deliver a useful recommendation, while avoiding excessive dietary restrictions especially when they are not based on a specific diagnosis, and therefore potentially useless or even harmful. We focused our attention on calcium stones and the different scenarios we may find in the daily clinical practice, including the case of patients who reported renal colic episodes and/or passed stones with no information on stone composition, urinary risk factors or metabolic cardiovascular risk factors; or the case of patients with partial and incomplete information; or the case of patients with full information on stone composition, urinary risk factors and metabolic cardiovascular profile.

Rapid liquid chromatography tandem mass-spectrometry screening method for urinary metabolites of primary hyperoxaluria

Background

The primary hyperoxalurias are inherited disorders of glyoxylate metabolism that lead to overproduction of oxalate, urolithiasis and renal failure. Delays in diagnosis can be costly in terms of preserving renal function. Here we present a rapid liquid chromatography tandem mass-spectrometry screening method for the analysis of metabolites (primary hyperoxaluria metabolites) produced in excess by primary hyperoxaluria patients that include glycolate, glycerate and 2,4-dihydroxyglutarate.

Methods

Assay performance was compared to our existing gas chromatography–mass spectrometry method and clinical utility established by analysis of urine samples from patients with confirmed primary hyperoxalurias (11 PH1, 12 PH2 and 8 PH3) and controls ( n = 12). An additional 67 urine samples from patients with PH3 were used postvalidation to confirm the derived 2,4-dihydroxyglutarate cut-off.

Results

Glycolate, glycerate and 2,4-dihydroxyglutarate showed a mean bias of 3.3, −22.8 and 5.7%, respectively, compared to our previously published gas chromatography–mass spectrometry method. The mean total imprecision for glycolate, glycerate and 2,4-dihydroxyglutarate was shown to be 6.4, 10 and 11%, respectively. Clinical assessment confirmed that mean urinary glycolate, glycerate and 2,4-dihydroxyglutarate excretion were significantly elevated in patients with PH1, PH2 and PH3, respectively. The greatest sensitivity and specificity for PH1, PH2 and PH3 was achieved at cut-offs of 193, 100 and 4.9 μmol/mmol for glycolate, glycerate and 2,4-dihydroxyglutarate, respectively.

Conclusions

A rapid screening method for the identification and differentiation of patients with suspected PH1, PH2 and PH3 is presented that allows focussing of genetic testing, saving time, money and, with earlier treatment, potential preservation of renal function for these patients.

Glycolate oxidase deficiency in a patient with congenital hyperinsulinism and unexplained hyperoxaluria

BACKGROUND

A baby girl was born at 39 weeks gestation to consanguineous Asian parents. From day 1 of life she had severe hypoglycaemia with an inappropriately elevated insulin concentration consistent with congenital hyperinsulinism (CHI), confirmed by the finding of a homozygous mutation in ABCC8 (encoding the sulfonylurea receptor 1).

CASE DIAGNOSIS/TREATMENT

Urine organic acid analysis showed an incidentally elevated excretion of glycolate. Whilst this was unlikely to contribute to the hypoglycaemia, hyperglycolic aciduria is a known feature of primary hyperoxaluria type 1 (PH1); therefore oxalate was also measured in urine and found to be elevated. Sequence analysis of the genes involved in PH1 and also the two other known forms of primary hyperoxaluria revealed no pathological variants. PH1 was definitively excluded by enzyme activity analysis on a liver biopsy, which confirmed normal glyoxylate aminotransferase (AGT) activity and positive AGT immunoreactivity. Glycolate oxidase (GO) deficiency was considered, and thus gene sequencing of HAO1, which encodes GO, was performed. A homozygous change (c.493G>T p.(Gly165Cys)) was found in exon 3 of HAO1, predicted to be deleterious to protein function. Further analysis of the liver biopsy demonstrated absent GO enzyme activity, confirming GO deficiency in this case.

CONCLUSIONS

The results lead to the conclusion that this baby has two unrelated autosomal recessive conditions, CHI and GO deficiency, and also hyperoxaluria of unknown aetiology. Deficiency of GO is a very rare disorder with only two previously published cases. It is considered to be an essentially benign inborn error of metabolism. The present case is unique in that GO deficiency is associated with persistent hyperoxaluria.

Whey protein and albumin effects upon urinary risk factors for stone formation

Protein supplements are consumed for an expected increase in muscle mass and improved exercise performance, but as their impact on lithogenic parameters are unknown, we aimed to evaluate the effects of Whey protein (WP) and Albumin upon the risk factors for nephrolithiasis. WP or Albumin supplements (one scoop/day) were administered for 3 days to 18 healthy volunteers, with 1-week washout period between them. Serum and 24-h urine samples were collected at baseline and after completing each intervention. All participants were asked to replicate their baseline diet during the subsequent urine collection. After WP or albumin, mean protein equivalent of nitrogen appearance (PNA) was significantly higher (p < 0.001), as the result of the consumption of each of the supplements, but mean urinary calcium, phosphorus, sodium, potassium, uric acid, citrate, oxalate, magnesium, creatinine, pH, and urinary saturation indices did not differ from baseline. However, individual increases higher than 50% in urinary calcium were observed in 39% of the individuals and variable decreases in urinary pH in 44 and 67% of them, respectively, after WP or Albumin. Increases higher than 50% in urinary sodium occurred in one-third of them after Albumin. A short-term consumption of WP or albumin by healthy subjects, under controlled diet, did not significantly change the mean lithogenic parameters. Nevertheless, the wide individual variation and relevant increases/decreases observed for urinary calcium, sodium, and pH suggest the need of a closer surveillance of these parameters and adequacy of diet in case of supplementation by stone formers.

Urinary oxalate to creatinine ratios in healthy Turkish schoolchildren

Aim: we aimed to establish reference values for urinary oxalate to creatinine ratios in healthy children aged 6–15 years and to investigate the relationship between their nutritional habits and oxalate excretion.

Materials and methods: Random urine specimens from 953 healthy children aged 6–15 years were obtained and analyzed for oxalate and creatinine. Additionally, a 24-h dietary recall form was prepared and given to them. The ingredient composition of the diet was calculated. The children were divided into three groups according to age: Group I (69 years, n = 353), Group II (10–12 years, n = 335), and Group III (13–15 years, n = 265).

Results: The 95th percentile of the oxalate to creatinine ratio for subjects aged 6–9, 10–12, and 13–15 years were 0.048, 0.042, and 0.042 mg/mg, respectively. The oxalate to creatinine ratio was significantly higher in Group 1 than in Group 2 and Group 3. Urinary oxalate excretion was positively correlated with increased protein intake and negatively correlated with age. A significant positive correlation was determined between urinary oxalate excretion and the proline, serine, protein, and glycine content of diet. Dietary proline intake showed a positive correlation with the urine oxalate to creatinine ratio and was found to be an independent predictor for urinary oxalate.

Conclusions: These data lend support to the idea that every country should have its own normal reference values to determine the underlying metabolic risk factor for kidney stone disease since regional variation in the dietary intake of proteins and other nutrients can affect normal urinary excretion of oxalate.

Characterizing concentrations of diethylene glycol and suspected metabolites in human serum, urine, and cerebrospinal fluid samples from the Panama DEG mass poisoning

CONTEXT

Diethylene glycol (DEG) mass poisoning is a persistent public health problem. Unfortunately, there are no human biological data on DEG and its suspected metabolites in poisoning. If present and associated with poisoning, the evidence for use of traditional therapies such as fomepizole and/or hemodialysis would be much stronger.

OBJECTIVE

To characterize DEG and its metabolites in stored serum, urine, and cerebrospinal fluid (CSF) specimens obtained from human DEG poisoning victims enrolled in a 2006 case-control study.

METHODS

In the 2006 study, biological samples from persons enrolled in a case-control study (42 cases with new-onset, unexplained AKI and 140 age-, sex-, and admission date-matched controls without AKI) were collected and shipped to the Centers for Disease Control and Prevention (CDC) in Atlanta for various analyses and were then frozen in storage. For this study, when sufficient volume of the original specimen remained, the following analytes were quantitatively measured in serum, urine, and CSF: DEG, 2-hydroxyethoxyacetic acid (HEAA), diglycolic acid, ethylene glycol, glycolic acid, and oxalic acid. Analytes were measured using low resolution GC/MS, descriptive statistics calculated and case results compared with controls when appropriate. Specimens were de-identified so previously collected demographic, exposure, and health data were not available. The Wilcoxon Rank Sum test (with exact p-values) and bivariable exact logistic regression were used in SAS v9.2 for data analysis.

RESULTS

The following samples were analyzed: serum, 20 case, and 20 controls; urine, 11 case and 22 controls; and CSF, 11 samples from 10 cases and no controls. Diglycolic acid was detected in all case serum samples (median, 40.7 mcg/mL; range, 22.6-75.2) and no controls, and in all case urine samples (median, 28.7 mcg/mL; range, 14-118.4) and only five (23%) controls (median, < Lower Limit of Quantitation (LLQ); range, < LLQ-43.3 mcg/mL). Significant differences and associations were identified between case status and the following: 1) serum oxalic acid and serum HEAA (both OR = 14.6; 95% C I = 2.8-100.9); 2) serum diglycolic acid and urine diglycolic acid (both OR > 999; exact p < 0.0001); and 3) urinary glycolic acid (OR = 0.057; 95% C I = 0.001-0.55). Two CSF sample results were excluded and two from the same case were averaged, yielding eight samples from eight cases. Diglycolic acid was detected in seven (88%) of case CSF samples (median, 2.03 mcg/mL; range, < LLQ, 7.47).

DISCUSSION

Significantly elevated HEAA (serum) and diglycolic acid (serum and urine) concentrations were identified among cases, which is consistent with animal data. Low urinary glycolic acid concentrations in cases may have been due to concurrent AKI. Although serum glycolic concentrations among cases may have initially increased, further metabolism to oxalic acid may have occurred thereby explaining the similar glycolic acid concentrations in cases and controls. The increased serum oxalic acid concentration results in cases versus controls are consistent with this hypothesis.

CONCLUSION

Diglycolic acid is associated with human DEG poisoning and may be a biomarker for poisoning. These findings add to animal data suggesting a possible role for traditional antidotal therapies. The detection of HEAA and diglycolic acid in the CSF of cases suggests a possible association with signs and symptoms of DEG-associated neurotoxicity. Further work characterizing the pathophysiology of DEG-associated neurotoxicity and the role of traditional toxic alcohol therapies such as fomepizole and hemodialysis is needed.

Optimum nutrition for kidney stone disease

We summarize the data regarding the associations of individual dietary components with kidney stones and the effects on 24-hour urinary profiles. The therapeutic recommendations for stone prevention that result from these studies are applied where possible to stones of specific composition. Idiopathic calcium oxalate stone-formers are advised to reduce ingestion of animal protein, oxalate, and sodium while maintaining intake of 800 to 1200 mg of calcium and increasing consumption of citrate and potassium. There are few data regarding dietary therapy of calcium phosphate stones. Whether the inhibitory effect of citrate sufficiently counteracts increasing urine pH to justify more intake of potassium and citrate is not clear. Reduction of sodium intake to decrease urinary calcium excretion would also be expected to decrease calcium phosphate stone recurrence. Conversely, the most important urine variable in the causation of uric acid stones is low urine pH, linked to insulin resistance as a component of obesity and the metabolic syndrome. The mainstay of therapy is weight loss and urinary alkalinization provided by a more vegetarian diet. Reduction in animal protein intake will reduce purine ingestion and uric acid excretion. For cystine stones, restriction of animal protein is associated with reduction in intake of the cystine precursor methionine as well as cystine. Reduction of urine sodium results in less urine cystine. Ingestion of vegetables high in organic anion content, such as citrate and malate, should be associated with higher urine pH and fewer stones because the amino acid cystine is soluble in more alkaline urine. Because of their infectious origin, diet has no definitive role for struvite stones except for avoiding urinary alkalinization, which may worsen their development.

Response to dietary oxalate after bariatric surgery

BACKGROUND AND OBJECTIVES

Bariatric surgery (BS) may be associated with increased oxalate excretion and a higher risk of nephrolithiasis. This study aimed to investigate urinary abnormalities and responses to an acute oxalate load as an indirect assessment of the intestinal absorption of oxalate in this population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four-hour urine specimens were collected from 61 patients a median of 48 months after BS (post-BS) as well as from 30 morbidly obese (MO) participants; dietary information was obtained through 24-hour food recalls. An oral oxalate load test (OLT), consisting of 2-hour urine samples after overnight fasting and 2, 4, and 6 hours after consuming 375 mg of oxalate (spinach juice), was performed on 21 MO and 22 post-BS patients 12 months after BS. Ten post-BS patients also underwent OLT before surgery (pre-BS).

RESULTS

There was a higher percentage of low urinary volume (<1.5 L/d) in post-BS versus MO (P<0.001). Hypocitraturia and hyperoxaluria (P=0.13 and P=0.36, respectively) were more frequent in BS versus MO patients. The OLT showed intragroup (P<0.001 for all periods versus baseline) and intergroup differences (P<0.001 for post-BS versus MO; P=0.03 for post-BS versus pre-BS). The total mean increment in oxaluria after 6 hours of load, expressed as area under the curve, was higher in both post-BS versus MO and in post-BS versus pre-BS participants (P<0.001 for both).

CONCLUSIONS

The mean oxaluric response to an oxalate load is markedly elevated in post-bariatric surgery patients, suggesting that increased intestinal absorption of dietary oxalate is a predisposing mechanism for enteric hyperoxaluria.

Epidemiology of pediatric urolithiasis

Pediatric urolithiasis has increased globally in the last few decades. There has been a change in the pattern of stone composition with an increase in the frequency of kidney stones and a decrease in bladder stones. The role of familial predisposition and environmental factors in pediatric urolithiasis is now better understood. Metabolic factors are more common in pediatric urolithiasis than in adult stone disease. This review updates on the epidemiology of pediatric urolithiasis with a focus on the changing trends in the stone disease, current spectrum of stone disease encountered in clinical practice, individual predisposition and the role of environmental factors in stone formation.

Effect of oxidative damage due to excessive protein ingestion on pancreas function in mice

The present study was undertaken to evaluate the effect of oxidative damage due to excessive protein diet on pancreas function in mice. For this purpose, thirty male (C57BL/6J) mice were randomly divided into three groups and fed on different diets as follows: group 1 was fed on a normal diet, group 2 was fed on an excessive protein diet and group 3 was fed on an excessive protein diet supplemented with 0.06 g/kg cysteamine. Each group was fed for 2 weeks, and then pancreas samples were collected to examine oxidative and antioxidant parameters and pancreas function. The results showed that ingestion of an excessive protein diet markedly increased contents of malondialdehyde (MDA) and decreased T-AOC and activities of antioxidants SOD and GSH-Px, compared with a normal diet (P < 0.05). Pancreas weight and concentration of protein, DNA and RNA were significantly higher (P < 0.05), digestive enzyme activities were significantly lower and levels of somatostatin and insulin were higher in mice fed with an excessive protein diet than those fed with a normal protein diet. In the group fed with excessive protein diet supplemented with cysteamine, oxidative stress was mitigated and pancreas function was improved. These data demonstrate that excessive protein ingestion could increase oxidative damage of free radicals on pancreas function through destroying the balance of oxidants and antioxidants.

History, epidemiology and regional diversities of urolithiasis

Archeological findings give profound evidence that humans have suffered from kidney and bladder stones for centuries. Bladder stones were more prevalent during older ages, but kidney stones became more prevalent during the past 100 years, at least in the more developed countries. Also, treatment options and conservative measures, as well as 'surgical' interventions have also been known for a long time. Our current preventive measures are definitively comparable to those of our predecessors. Stone removal, first lithotomy for bladder stones, followed by transurethral methods, was definitively painful and had severe side effects. Then, as now, the incidence of urolithiasis in a given population was dependent on the geographic area, racial distribution, socio-economic status and dietary habits. Changes in the latter factors during the past decades have affected the incidence and also the site and chemical composition of calculi, with calcium oxalate stones being now the most prevalent. Major differences in frequency of other constituents, particularly uric acid and struvite, reflect eating habits and infection risk factors specific to certain populations. Extensive epidemiological observations have emphasized the importance of nutritional factors in the pathogenesis of urolithiasis, and specific dietary advice is, nowadays, often the most appropriate for prevention and treatment of urolithiasis.

Glucocorticoids and body fat associated with renal uric acid and oxalate, but not calcium excretion, in healthy children

In patients with hypercortisolism, who are frequently obese, the prevalence of elevated urinary excretion rates of the potential lithogenic factors (calcium, oxalate, and uric acid) is increased. We examined whether the 24-hour urinary excretion rates of calcium, oxalate, and uric acid are already associated with body fat and endogenous glucocorticoids in healthy free-living children, taking relevant nutritional and acid-base factors into account. Urinary analyte excretions were determined in 24-hour urine samples of 300 healthy children aged 4 to 14 years. Potentially bioactive free glucocorticoids were assessed as urinary free cortisol + urinary free cortisone. Associations of glucocorticoids and percentage body fat with the outcome variables were examined in regression models adjusted for sex, height, growth velocity, urinary volume, net acid excretion, and relevant nutritional factors. Percentage body fat and urinary free cortisol + urinary free cortisone explained most of the growth-independent variation of urinary uric acid and also a relevant part of oxalate, but none of calcium. Net acid excretion, an indicator of endogenous acid production, and dietary protein, salt, and fiber intakes were also variably associated with the outcomes urinary calcium, oxalate, and uric acid. In conclusion, body fatness and potentially bioactive free glucocorticoids (even in the physiologic range) appear to affect urinary excretion rates of oxalate and uric acid, whereas urinary calcium output is more strongly related to dietary factors in healthy children. Our data provide the first in vivo-based evidence that the obesity- or hypercortisolism-associated urolithiasis may be a pathophysiologic continuation of the corresponding endocrine metabolic variations in healthy children.

Effect of soda consumption on urinary stone risk parameters

BACKGROUND AND PURPOSE

Fluid consumption has been demonstrated to influence kidney stone formation. Studies have shown that consumption of cola may be a risk factor for stone disease, while fluids containing citric acid may attenuate stone activity. Diet was not always controlled in these investigations, however. We undertook a study to determine the impact of three different fluids on urinary stone risk factors.

SUBJECTS AND METHODS

Six healthy nonstone-forming adults were placed on a standardized metabolic diet and consumed three different types of fluid during three 5-day periods. There was a 2-day washout between each sequence. The three fluids administered during these periods were Le Bleu water, caffeine-free Diet Coke, and Fresca (citrate containing). These two soda preparations were chosen to prevent the known increase in calcium excretion promoted by carbohydrates and caffeine. Twenty-four hour urine specimens were collected on days 4 and 5 of each sequence. The following urinary parameters were measured: Volume, calcium, oxalate, creatinine, uric acid, citrate, sodium, magnesium, phosphorus, sulfate, urea nitrogen, pH, and supersaturation indices. A paired t test was used for statistical analysis.

RESULTS

Urinary volumes were significantly higher and supersaturation of calcium oxalate significantly lower compared with a self-selected dietary regimen. A decrease in uric acid was also seen in the Fresca cohort. There were no statistically significant differences for any of the urinary parameters.

CONCLUSION

There is no increased risk or benefit to consuming Fresca or caffeine-free Diet Coke compared with Le Bleu bottled water with respect to stone formation.

Increased protein intake on controlled oxalate diets does not increase urinary oxalate excretion

High animal protein intake is a risk factor for calcium oxalate stone disease. The effect of dietary protein on the urinary excretion of calcium, acid and citrate is well established. However, its effect on oxalate excretion is unclear, due in part to an inadequate control of dietary oxalate intake in previous studies. This relationship warrants clarification due to the proposed important role of the metabolism of amino acids in endogenous oxalate synthesis. In this study, 11 normal subjects consumed controlled oxalate diets containing 0.6, 1.2 and 1.8 g protein/kg body weight/day. The analysis of 24 h urine collections confirmed that as protein intake increased, urinary calcium and glycolate increased and urinary pH and citrate decreased. The increased glycolate excretion was due in part to an increased hydroxyproline, but not glycolate consumption. Total daily urinary oxalate excretion did not change. When indexed to creatinine there was a small but significant decrease in oxalate excretion. This is most likely due to hyperfiltration. These results indicate that as dietary protein intake increases, the catabolism of diet-derived amino acids is not associated with an increased endogenous oxalate synthesis in normal subjects.

Effect of dietary protein level and origin on the redox status in the digestive tract of mice

The present study was undertaken to evaluate the effects of high protein (soybean protein or casein) on the balance between production of free radicals and antioxidant level in digestive organs of mice. For this purpose, male (C57BL/6J) mice were adapted to experimental diets containing soybean protein or casein with 20% (normal protein diets, NPDs) or 60% (high protein diets, HPDs), and HPDs supplemented with 0.06g/kg cysteamine. After two weeks of feeding, oxidative and antioxidative parameters in duodenum, liver and pancreas were measured. The results show that ingestion of high protein markedly increased contents of superoxide anion and malondialdehyde (MDA), decreased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and Na⁺ K⁺-ATPase, and content of reduced glutathione (GSH) in digestive organs of mice (P<0.05). Levels of oxidative parameters were lower and antioxidant capacity of both enzyme and non-enzyme was higher in mice fed with soybean protein than those fed with casein. In groups fed HPDs supplemented with cysteamine, oxidative stress was mitigated. However, oxidative parameter levels were still higher than those of NPD-fed groups. The present study indicates that ingestion of high protein diets could result in an imbalance between oxidant and antioxidant, and thus induce oxidative stress in digestive organs of mice. The oxidative damage was smaller in mice fed with high level of soy protein in comparison with casein.

Inhalation and epidermal exposure of volunteers to ethylene glycol: kinetics of absorption, urinary excretion, and metabolism to glycolate and oxalate

Ethylene glycol (EG) is a widely used liquid. Limited data are published regarding inhaled EG and no data regarding transdermal EG uptake in humans. In order to gain information on the quantitative fate of EG, four male volunteers inhaled between 1340 and 1610 micromol vaporous 13C-labeled EG (13C2-EG) for 4h. Separately, three of these subjects were epidermally exposed for up to 6h to liquid 13C2-EG (skin area 66 cm2). Plasma concentrations and urinary amounts of 13C2-EG were determined by gas chromatography with mass selective detection. Additionally, plasma was assayed for 13C-labeled glycolic acid 13C2-GA) and urine for 13C2-GA and 13C-labeled oxalic acid (13C2-OA). Both EG metabolites were nephrotoxic in animals and humans and embryotoxic in rodents. 13C-labels enabled to differentiate from also determined endogenous EG, glycolic acid (GA), and oxalic acid (OA). Of 13C2-EG inhaled, 5.5+/-3.0%, 0.77+/-0.15%, and 0.10+/-0.12% were detected in urine as 13C2-EG, 13C2-GA, and 13C2-OA, respectively. The skin permeability constant of liquid EG was 2.7 x 10(-5)+/-0.5 x 10(-5)cm/h. Of the dose taken up transdermally, 8.1+/-3.2% and up to 0.4% were excreted in urine as 13C2-EG and 13C2-GA, respectively. It is calculated that equally long-lasting exposure to 10 ppm vaporous EG or wetting of both hands by liquid EG leads to about the same body burden by EG and metabolites. The amounts of GA and OA excreted daily in urine as a result of exposure (8h/day) to 10 ppm EG are about 15% and 2%, respectively, of those excreted from naturally occurring endogenous GA and OA.

Intestinal and renal handling of oxalate loads in normal individuals and stone formers

The renal handling and intestinal absorption of dietary oxalate are believed to be risk factors for calcium oxalate stone formation. In this study, we have examined the time and dose effects of soluble oxalate loads on the intestinal absorption and renal handling of oxalate in six stone formers (SF) and six normal individuals (N) who consumed diets controlled in oxalate and other nutrients. Urinary and plasma oxalate changes were monitored over 24 h after ingestion of 0, 2, 4, and 8 mmole oxalate loads, containing a mixture of (12)C- and (13)C(2)-oxalate. There were significant time and dose dependent changes in urinary oxalate excretion and secretion after these loads. However, there were no significant differences between SF and N in both the intestinal absorption and the renal handling of oxalate loads, as measured by the urinary excretion of oxalate (P = 0.96) and the ratio of oxalate to creatinine clearance (P = 0.34). (13)C(2)-oxalate absorption studies showed three of the subjects, two SF and one N, had enhanced absorption with the 8 mmole load. A clear difference in absorption was demonstrated in these individuals during the 8-24 h interval, suggesting that in these individuals there was greater oxalate absorption in the large intestine as compared to the other subjects. This enhanced absorption of oxalate warrants further characterization.

Hydroxyproline ingestion and urinary oxalate and glycolate excretion

Endogenous synthesis of oxalate is an important contributor to calcium oxalate stone formation and renal impairment associated with primary hyperoxaluria. Although the principal precursor of oxalate is believed to be glyoxylate, pathways in humans resulting in glyoxylate synthesis are not well defined. Hydroxyproline, a component amino acid of collagen, is a potential glyoxylate precursor. We have investigated the contribution of dietary hydroxyproline derived from gelatin to urinary oxalate and glycolate excretion. Responses to the ingestion of 30 g of gelatin or whey protein were compared on controlled oxalate diets. The time course of metabolism of a 10 g gelatin load was determined as well as the response to varying gelatin loads. Urinary glycolate excretion was 5.3-fold higher on the gelatin diet compared to the whey diet and urinary oxalate excretion was 43% higher. Significant changes in plasma hydroxyproline and urinary oxalate and glycolate were observed with 5 and 10 g gelatin loads, but not 1 and 2 g loads. Extrapolation of these results to daily anticipated collagen turnover and hydroxyproline intake suggests that hydroxyproline metabolism contributes 20-50% of glycolate excreted in urine and 5-20% of urinary oxalate derived from endogenous synthesis. Our results also revealed that the kidney absorbs significant quantities of hydroxyproline and glycolate, and their metabolism to oxalate in this tissue warrants further consideration.

Genetic and dietary factors in urinary citrate excretion

BACKGROUND AND PURPOSE

Hypocitraturia, an important risk factor for calcium oxalate nephrolithiasis, is the result of numerous factors. We studied citrate excretion by patients with and without stones consuming normal and controlled formula diets.

SUBJECTS AND METHODS

Subjects with and without a history of calcium oxalate stones (N = 101 per group) provided two or three 24-hour urine specimens during consumption of self-selected diets. Data also were collected on subsets of subjects consuming formula (Ensure) diets. Citrate was determined using the citrate lyase method of Petrarulo and associates, and values for multiple specimens were averaged. The data were adjusted for creatinine excretion and examined on a per-day basis.

RESULTS

The mean citrate excretion of the non-stone formers was slightly but not significantly higher than that of the stone formers (442 +/- 217 versus 378 +/- 153 mg/g of creatinine). All statistical analyses revealed highly significant differences between, but not within, individuals, a result compatible with a genetic influence. In the normal population, 5% of subjects had a citrate excretion <200 mg/g of creatinine, whereas this result was seen in 34% of the stone-forming subjects. When the subjects consumed a formula diet, women in both groups had much higher citrate excretion than when on a self-selected diet, but little difference was seen in the men. The patterns of citrate recovery suggest low, intermediate, and high excretors. In the normal population, 15% of subjects excreted <340 mg/g of creatinine, whereas this was true of 43% of the stone-forming subjects. Analysis of six families suggested three excretor phenotypes, with a codominant pattern of inheritance.

CONCLUSION

These findings imply a genetic influence on citrate excretion, as has already been demonstrated for calcium excretion. Further studies of genetic influences on calcium oxalate stone formation are warranted.

Energy and nutrient intake of young-old, old-old and very-old elderly in Germany

BACKGROUND

Reliable information about the nutritional status of elderly people in Germany is lacking.

OBJECTIVE

To describe energy and nutrient intake of elderly people living in private households in Germany with special focus on age-related differences in the elderly.

DESIGN

Descriptive nationwide cross-sectional study.

SETTING

Germany, 1998.

SUBJECTS

: A random sample of 4020 elderly men and women living independently in private households stratified in three age groups (65-74, 75-84, 85+ y), of which 1550 participated and 1372 (789 female subjects) provided reliable 3-day estimated dietary records.

RESULTS

The median daily energy intake was 2207 kcal (9.2 MJ) in men and 1994 kcal (8.3 MJ) in women without difference between the age groups. Protein intake amounted to 91 and 81 g/day, respectively, corresponding to 1.2 g/kg body weight per day. The median intake was well above the recommended amount for all nutrients except dietary fibre, calcium, vitamin D and folate, where 38, 35, 75 and 37% did not reach two-thirds of the recommended amount. An age-related decline was observed for calcium intake in male and for dietary fibre, water, calcium, magnesium, iron, vitamins A, E, C and thiamin intake in female participants; however, the overall picture was unaffected by these differences.

CONCLUSIONS

Dietary intake in these independently living elderly, including the very-old, is adequate for most of the evaluated nutrients. Increased intake of foods rich in dietary fibre, calcium, vitamin D and folate as well as regular sunlight exposure is recommended in order to optimize nutrient supply in this population group.

SPONSORSHIP

German Ministry of Health.

Hyperoxaluric calcium nephrolithiasis

Hyperoxaluria leads to increased calcium oxalate supersaturation and calcium oxalate stone formation. Excess oxalate can arise from endogenous overproduction as in primary hyperoxaluria or from dietary sources. In the last 15 years great strides have been made in the diagnosis and treatment of primary hyperoxaluria. However options still seem limited in treating the mild hyperoxaluria found in many stone formers. Inadequate knowledge of food oxalate content, the effect of dietary oxalate precursors on oxalate excretion, and the factors affecting handling of oxalate by the intestine prevent development of rational therapies for treatment of hyperoxaluria. Recent studies of oxalate degrading bacteria and renewed interest in the role of diet calcium in oxalate absorption may lead to better therapeutic strategies for hyperoxaluric calcium nephrolithiasis.

Association of dietary fatty acids with urinary oxalate excretion in calcium oxalate stone-formers in their fourth decade

OBJECTIVE

To examine the influence of the dietary intake of fatty acid on urinary oxalate excretion in calcium oxalate stone-formers in their fourth decade, as previous reports show that animal fat intake is associated with urinary oxalate excretion.

PATIENTS AND METHODS

The dietary intake of 58 idiopathic stone-formers in their fourth decade was recorded using the dietary-record method. The patients collected 24-h urine samples at home and their urinary oxalate excretion was measured in a clinical biochemistry laboratory. The results were used to determine the relationship between the dietary intake of fatty acids and urinary oxalate excretion. Associations between urinary oxalate excretion and dietary contents of animal fat, animal protein and various fatty acids were assessed using Spearman's correlation coefficient and multiple regression.

RESULTS

The dietary content of arachidonic acid was positively correlated with urinary oxalate excretion, as assessed by univariate and multivariate analysis.

CONCLUSION

The association between arachidonic acid and oxalate excretion suggests that arachidonic acid increases the intestinal absorption of oxalate and increases the clearance of oxalate in the kidneys.

Development of amperometric biosensors for the determination of glycolic acid in real samples

The first enzyme-based biosensors capable of determining glycolic acid in various complex matrixes, such as cosmetics, instant coffee, and urine, are presented in this paper. Two separate designs, both based on a three-membrane configuration consisting of an inner cellulose acetate membrane (CA) and an outer polycarbonate membrane (PC), which sandwich a membrane bearing the biomolecule(s), are proposed. Glycolate oxidase was immobilized onto a modified polyethersulfonate membrane by means of chemical bonding, and glycolate oxidase/catalase enzyme mixture was immobilized into a mixed-ester cellulose acetate membrane through physical adsorption. The membrane assemblies were mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3 KCl) or on an oxygen electrode, respectively. Both configurations were optimized with respect to various working parameters. The proposed biosensors are interference-free to common electroactive species and were successfully applied for the determination of glycolic acid in various samples, showing an excellent agreement with a reference photometric method. The validity of the proposed method in samples, in which the reference method was not applicable, was tested with recovery studies. Values of 102 +/- % were obtained. Inherent interference of oxalic acid was manipulated by using a primary amine-containing buffer and the enzyme catalase. Both systems were designed in order to be compatible with the current technology of the most widely used commercial analyzers.

Sensitivity to meat protein intake and hyperoxaluria in idiopathic calcium stone formers

BACKGROUND

High protein intake is an accepted risk factor for renal stone disease. Whether meat protein intake affects oxaluria, however, remains controversial in healthy subjects and in stone formers. This study was designed (1) to test the oxaluric response to a meat protein load in male recurrent idiopathic calcium stone formers (ICSFs) with and without mild metabolic hyperoxaluria (MMH and non-MMH, respectively), as well as in healthy controls, and (2) to seek for possible disturbed vitamin B(6) metabolism in MMH, in analogy with primary hyperoxaluria.

METHODS

Twelve MMH, 8 non-MMH, and 13 healthy males were studied after five days on a high meat protein diet (HPD; 700 g meat/fish daily) following a run-in phase of five days on a moderate protein diet (MPD; 160 g meat/fish daily). In both diets, oxalate-rich nutrients were avoided, as well as sweeteners and vitamin C-containing medicines. Twenty-four-hour urinary excretion of oxalate was measured on the last day of each period, along with 4-pyridoxic acid (U(4PA)) and markers of protein intake, that is, urea, phosphate, uric acid, and sulfate. Serum pyridoxal 5' phosphate (S(P5P)) was measured after protein loading.

RESULTS

Switching from MPD (0.97 +/- 0.18 g protein/kg/day) to HPD (2.26 +/- 0.38 g protein/kg/day) led to the expected rise in the urinary excretion rates of all markers of protein intake in all subjects. Concurrently, the mean urinary excretion of oxalate increased in ICSFs taken as a whole (+73 +/- 134 micromol/24 h, P = 0.024) as well as in the MMH subgroup (+100 +/- 144 micromol/24 h, P = 0.034) but not in controls (-17 +/- 63 micromol/24 h). In seven ICSFs (4 MMH and 3 non-MMH) but in none of the healthy controls (P = 0.016, chi square), an increment in oxaluria was observed and considered as significant based on the intra-assay coefficient of variation at our laboratory (8.5%). There was no difference in S(P5P)nd U(4PA)etween the groups after protein loading.

CONCLUSION

Approximately one third of ICSFs with or without so-called MMH are sensitive to meat protein in terms of oxalate excretion, as opposed to healthy subjects. Mechanisms underlying this sensitivity to meat protein remain to be elucidated and do not seem to involve vitamin B(6) deficiency.

Diets with either beef or plant proteins reduce risk of calcium oxalate precipitation in patients with a history of calcium kidney stones

OBJECTIVE

To determine the effect of substituting equal amounts of dietary protein as animal protein (beef) for plant protein (legumes, seeds, nuts, and grains) on urinary components associated with calcium oxalate precipitability risk.

DESIGN

Randomized crossover trial.

SUBJECTS

Twenty-three normocalciuric patients with a history of calcium kidney stones (8 women and 15 men, mean age 50.7+/-14.6 years) with 24-hour urinary calcium < or =10.3 micromol, 24 hour urinary oxalate excretion between 228 and 963 micromol, and a urinary calcium increase of < or =1.0 micromol in 4 hours after a 25 micromol oral calcium load.

SETTING

Four-day, free-living adaptation period, followed by 2-day metabolic unit study.

INTERVENTION

The study compared consumption of 2 servings of beef (43 g protein for women and 50 g for men) daily with an equal amount of protein from plant foods including legumes, nuts, and grains.

MAIN OUTCOME MEASURES

Tiselius risk index (TRI) for calcium oxalate precipitability calculated from urinary calcium, oxalate, magnesium, citrate, and volume.

STATISTICAL ANALYSES

Paired t tests.

RESULTS

Urinary calcium, oxalate, magnesium, citrate, phosphorus, volume, and TRI did not differ between diets. Urinary sodium and potassium were higher for patients on the plant protein diet. After correcting for variations in urinary sodium and potassium between diets, the difference in urinary calcium remained insignificant. TRI was lower on both beef- and plant-protein diets compared with self-selected prestudy diets for all participants. CONCLUSION/APPLICATIONS: Balanced diets containing moderate amounts of either beef or plant protein are equally effective in reducing calcium oxalate kidney stone risk based on changes in urinary composition.

Contribution of dietary oxalate to urinary oxalate excretion

BACKGROUND

The amount of oxalate excreted in urine has a significant impact on calcium oxalate supersaturation and stone formation. Dietary oxalate is believed to make only a minor (10 to 20%) contribution to the amount of oxalate excreted in urine, but the validity of the experimental observations that support this conclusion can be questioned. An understanding of the actual contribution of dietary oxalate to urinary oxalate excretion is important, as it is potentially modifiable.

METHODS

We varied the amount of dietary oxalate consumed by a group of adult individuals using formula diets and controlled, solid-food diets with a known oxalate content, determined by a recently developed analytical procedure. Controlled solid-food diets were consumed containing 10, 50, and 250 mg of oxalate/2500 kcal, as well as formula diets containing 0 and 180 mg oxalate/2500 kcal. Changes in the content of oxalate and other ions were assessed in 24-hour urine collections.

RESULTS

Urinary oxalate excretion increased as dietary oxalate intake increased. With oxalate-containing diets, the mean contribution of dietary oxalate to urinary oxalate excretion ranged from 24.4 +/- 15.5% on the 10 mg/2500 kcal/day diet to 41.5 +/- 9.1% on the 250 mg/2500 kcal/day diet, much higher than previously estimated. When the calcium content of a diet containing 250 mg of oxalate was reduced from 1002 mg to 391 mg, urinary oxalate excretion increased by a mean of 28.2 +/- 4.8%, and the mean dietary contribution increased to 52.6 +/- 8.6%.

CONCLUSIONS

These results suggest that dietary oxalate makes a much greater contribution to urinary oxalate excretion than previously recognized, that dietary calcium influences the bioavailability of ingested oxalate, and that the absorption of dietary oxalate may be an important factor in calcium oxalate stone formation.

Role of diet in the therapy of urolithiasis

The data reviewed in this paper indicate that there is compelling direct and indirect evidence that certain dietary modifications can limit the risk for stone formation. Fluid therapy should be a front-line approach for all stone formers, because it is safe, cheap, and effective. Restricting sodium and animal-protein consumption produces changes in the urinary environment that should benefit the majority of stone formers, including a decrease in calcium and increase in citrate excretion. Minimizing the intake of processed goods limits sodium gluttony. These dietary modifications also reduce cardiovascular risks. Indiscriminant calcium restriction should be avoided, because it could accelerate stone formation and violate skeletal integrity. Oxalate restriction should be considered for calcium oxalate stone formers, especially those with hyperoxaluria. Specific recommendations for modifying the consumption of other nutrients cannot be made at this time because of the limited available information about the resultant effects. The aforementioned goals can be achieved within the context of a nutritionally balanced diet providing adequate sources of fruits and vegetables. There is a definite need for better designed studies of the nutritional effects on stone disease. This would promote a better understanding of the interplay between the genetic and environmental components of this disorder.

Acute effects of moderate dietary protein restriction in patients with idiopathic hypercalciuria and calcium nephrolithiasis

BACKGROUND

High dietary protein intake is a potential risk factor for nephrolithiasis because of its capacity to increase urinary calcium and to facilitate lithogenesis through many other mechanisms.

OBJECTIVE

Our aim was to verify the effects of moderate protein restriction in hypercalciuric patients.

DESIGN

We studied 18 patients (10 men and 8 women aged 45.6+/-12.3 y) with idiopathic hypercalciuria and renal calculi. Before and after 15 d of a diet with 0.8 g protein x kg(-1) x d(-1) and 955 mg Ca, all patients were evaluated for the main serum and urinary measures of calcium metabolism as well as for urinary uric acid, oxalate, citrate, and prostaglandin E2.

RESULTS

Urinary excretion of urea fell after the diet (P < 0.001). Urinary calcium (P < 0.001), uric acid (P < 0.005), oxalate (P < 0.01), and hydroxyproline (P < 0.01) decreased after protein restriction, whereas urinary citrate increased (P < 0.025). Blood pH increased after the hypoproteic diet (P < 0.05). 1,25-Dihydroxycholecalciferol (calcitriol) concentration fell significantly (P < 0.025) and parathyroid hormone increased (P < 0.001). Creatinine clearance tended to decrease (106.4+/-4.8 compared with 97.5+/-5.7 mL/min) after the diet. The decrease in urinary uric acid after the diet correlated with calcitriol concentration (r = 0.57, P < 0.05) and the decrease in urinary urea correlated positively with that in hydroxyproline excretion (r = 0.58, P < 0.01).

CONCLUSIONS

In hypercalciuric patients, moderate protein restriction decreases calcium excretion, mainly through a reduction in bone resorption and renal calcium loss; both are likely due to a decreased exogenous acid load. Moreover, dietary protein restriction ameliorates the entire lithogenic profile in these patients.

Glyoxylate synthesis, and its modulation and influence on oxalate synthesis

PURPOSE

We define the major pathways of hepatic oxalate synthesis in humans, examine the association with other metabolic pathways and identify ways that oxalate synthesis may be modified. In addition, we suggest what is required for further progress in this area.

MATERIALS AND METHODS

We consolidated relevant data primarily from recently published literature, considered new pharmacological approaches to decrease oxalate synthesis, and formulated an overview of the regulation and modification of oxalate synthesis pathways.

RESULTS

Experiments with animals, including humans, animal cells and in vitro preparations of cellular components, support the existence of a major metabolic pathway linking the amino acids serine, glycine and alanine. Oxalate synthesis is a minor, secondary reaction of a cascade of reactions termed the glyoxylate pathway, which has a prominent role in gluconeogenesis and ureagenesis. The enzymatic steps and effectors which regulate glyoxylate and oxalate synthesis are not well characterized. Pharmacological approaches can reduce oxalate synthesis by diminishing the glyoxylate pool and possibly modifying enzymatic reactions leading to glyoxylate synthesis.

CONCLUSIONS

The individual steps associated with glyoxylate and oxalate synthesis can be identified. The glyoxylate pathway has a significant functional role in intermediary liver metabolism but the way it is regulated is uncertain. Oxalate synthesis can be modified by drugs, indicating that primary and idiopathic hyperoxaluria may respond to pharmacological intervention.

The effects of (L)-2-oxothiazolidine-4-carboxylate on urinary oxalate excretion

PURPOSE

A phase I study was done to evaluate the safety and pharmacokinetics of (L)-2-oxothiazolidine-4-carboxylate (OTZ). An ancillary objective was to compare the effects of treatment with 2 levels of OTZ to placebo on urinary oxalate excretion in healthy male subjects.

MATERIALS AND METHODS

Individuals underwent intravenous infusion of 70 (6) or 100 (6) mg/kg, body weight OTZ, or placebo for 2 hours at 4, 8-hour intervals. Urine was collected during the 12 hours before treatment, and at 0 to 4, 4 to 8, 8 to 24, 24 to 28, 28 to 32 and 32 to 48 hours after the initial infusion. Urine samples were assayed for creatinine, oxalate, citrate, sulfate, urate, phosphate and pH.

RESULTS

Urinary oxalate excretion relative to creatinine decreased significantly in the 100 mg./kg. dose group by 4.1 mg./gm. during the first 24 hours and by 4.6 mg./gm. in 24 to 48 hours compared to baseline values (p < 0.05). Slight decreases of 0.9 and 1.1 mg./gm., respectively, in the 70 mg./kg. dose group, and 1.6 and 2.3 mg./gm., respectively, in the placebo group were observed. Oxalate excretion on day 2 in the 100 mg./kg. dose group was significantly less than that in the placebo group (p = 0.04). Urinary pH decreased and sulfate excretion increased with OTZ therapy.

CONCLUSIONS

Treatment with 100 mg./kg. OTZ every 8 hours decreases urinary oxalate excretion in healthy men.

Urinary alkoxyacetic acids and renal effects of exposure to ethylene glycol ethers

OBJECTIVES

Ethylene glycol ethers and their acetates are widely used in industry, because of their hydrophilic and simultaneously lipophilic properties. Ethylene glycol ethers and their acetates are mainly metabolised to alkoxyacetic acids, but there is also a minor pathway through ethylene glycol to oxalic acid. The main pathway of ethylene glycol ethers is associated with significant clinical or experimental health effects and the minor pathway is also interesting because formation of urinary stones depends principally upon the urinary concentration of oxalate and calcium.

METHODS

Excretion of alkoxyacetic and oxalic acids was examined among silkscreen printers for an entire working week. The aim of the study was to evaluate alkoxyacetic acids as early indicators of exposure to glycol ethers and to evaluate their toxicity to kidneys. The load of alkoxyacetic and oxalic acids was compared with the excretion of calcium, chloride, ammonia, and glycosaminoglycans (GAG). Morning urine was chosen for the main analysis, as the overall metabolite, ethoxyacetic acid (EAA), has a long elimination time from the body.

RESULTS

The excretion of calcium increased according to the urinary alkoxyacetic acid load. The excretion of ammonia and chloride was higher among the exposed workers than among the controls. The highest urinary alkoxyacetic acid load was also associated with increased excretion of GAG, which may reflect the toxicity of metabolites of ethylene glycol ether. The excretion of GAG correlated positively with that of calcium in the printers with highest exposure. The tendency to form urinary stones was 2.4-fold higher among silkscreen printers than among office workers.

CONCLUSION

On the basis of renal effects our study indicates the need for establishing a new biological exposure limit before a workshift that is clearly below 100 mmol ethoxyacetic acids per mol creatinine in morning urine of people occupationally exposed to ethylene glycol ethers.

Glucagon increases urinary oxalate excretion in the guinea pig

Factors that influence hepatic oxalate synthesis are poorly defined. Hormones are important regulators of hepatic metabolism and could potentially be involved. The effects of hyperglucagonemia were examined in guinea pigs injected with either saline or pharmacological doses of glucagon for 4 days. Glucagon treatment increased mean urinary oxalate excretion by 77% in male and 34% in female animals. The levels of hepatic peroxisomal enzymes involved in oxalate synthesis declined with glucagon treatment, but experiments with isolated peroxisomes indicated that oxalate synthesis in vitro was unaffected. Glucagon decreased hepatic alanine levels by 66%, lactate by 69%, and pyruvate by 73%, but glycolate and glyoxylate levels were unaffected. This decrease in alanine would substantially lower the activity of alanine-to-glyoxylate aminotransferase activity in vivo and make more glyoxylate available for oxalate synthesis. The decrease in lactate and pyruvate concentrations would stimulate the enzymatic conversion of glyoxylate to oxalate and may account for the increase in oxalate synthesis without an increase in glyoxylate concentration. These results demonstrate that hepatic oxalate synthesis is influenced by metabolic changes and that alterations in hepatic alanine, lactate, and pyruvate concentrations may be important elements.

Urinary biochemistry in occupational exposure to glycol ethers

Glycol ethers and glycol ether acetates are dehydrogenated to alkoxyacetic acid congeners which may serve as biological indicators of exposure. The ethereal bond may also be cut in an oxidation reaction catalyzed by the mixed function oxidase. In case of ethylene glycol, the eventual endproduct is oxalic acid. Urinary oxalic acid and alkoxyacetic acid excretion together was found to relate to the decrease of the succinate dehydrogenase activity (SDH) as an indicator of renal mitochondrial effects. The excretion of ammonia by exposed workers was doubled as compared to controls. The excretion of chloride was found to be smaller in the exposed than in controls. The excretion of calcium and glycosaminoglycans (GAG) among exposed workers were similar compared to controls.